Bonded versus vacuum-formed retainers: a randomized controlled trial. Part 2: periodontal health outcomes after 12 months

Bonded versus vacuum-formed retainers: a randomized controlled trial. Part 2: periodontal health... Summary Background Retainer have the potential to compromise periodontal health. Objectives Evaluate the periodontal health implications of upper and lower bonded retainers (BRs) versus upper and lower vacuum-formed retainers (VFRs) over 12 months. Trial design Two-arm parallel group multicentre randomized controlled clinical trial. Methods Sixty consecutive patients completing upper and lower fixed appliance therapy and requiring retainers were recruited from three hospital orthodontic departments. They were randomly allocated to either upper and lower labial segment BRs (n = 30) or upper and lower full-arch VFRs (n = 30). Periodontal health was assessed using the plaque and gingival indices of Silness and Loe, and the calculus index of Greene and Vermillion. Data were collected at debond and placement of the retainers (T0), 3 months (T1), 6 months (T2), and 12 months (T3). A random sequence of treatment allocation was computer-generated and implemented by sealing in sequentially numbered opaque sealed envelopes independently prepared in advance. Patients, operators, and outcome could not be blinded due to the nature of the intervention. Results Thirty patients received BRs (median age 16 years, interquartile range [IQR] = 2, 50% female, 50% male) and 30 received VFRs (median age 17 years, IQR = 4, 60% female, 40% male). Gingival inflammation decreased from baseline for both types of retainer. There was significantly less plaque and calculus accumulation and better gingival health with VFRs than BRs over the evaluated 12 months. No serious harm was observed. Limitations It is not known how much the patients chose to wear their removable retainers. The results reported are after 1 year only. Conclusions After 1 year, BRs were associated with greater accumulation of plaque and calculus than VFRs and minimally worse gingival inflammation than VFRs, but this did not appear to produce any clinically significant, adverse periodontal health problems. Trial registration This trial was not registered. Funding There was no funding. Introduction Retainers are commonly fitted at the end of orthodontic treatment to reduce the chances of relapse. The choice of retainers is controversial, with a wide variety of different retainer choices reported across the world (1–5) Whether removable or fixed retainers are used, it is important that they do not compromise the patient’s periodontal health. Due to their continuous presence, mandibular bonded retainers (BRs) have the potential to promote calculus and plaque accumulation and food impaction. It has been suggested that BRs have the potential to adversely affect periodontal health (6). Despite the fact that there is an increasing trend to prescribe BRs in an attempt to seek long-term stability, there is limited high-quality evidence on the periodontal effects of mandibular fixed retention (7). It has therefore been suggested that they should not be used indiscriminately (8). In contrast, though removable retainers rely more on patients’ discipline and long-term compliance, it has been presumed that oral hygiene should not be complicated by their presence. Investigations into the periodontal effects of fixed and removable retainers to date have generally shown them to be compatible with periodontal health. Whilst the presence of a BR (whether bonded to just the canines, or to all teeth in the labial segment) has been shown to be associated with the occasional accumulation of plaque and calculus gingival to the wire, this has not been shown to cause any damage to the hard or soft tissues (7, 9–14). Further, though biochemical and bacteriological analysis has found a statistically significant difference in the characteristics of the gingival crevicular fluid between subjects with and without BRs, this has not been shown to translate to any significant clinical periodontal problems (15). Longer-term retrospective studies of the effects on periodontal health have similarly shown that, although accumulation of dental plaque and calculus tends to be greater in subjects with BRs, this has not led to a significant deterioration in any periodontal or dental health parameter more than 15 years after treatment (16, 17). In the 2016 Cochrane systematic review of orthodontic retention, the authors stressed the need for additional high-quality evidence in the form of well-constructed randomized controlled trials, including investigating the adverse effects on dental and periodontal health of retainers (18). The primary outcome measure of reducing post-treatment changes in irregularity of the labial segment and the secondary outcome measure of retainer survival are reported in paper 1 (19). This paper investigates the secondary outcome of periodontal health. This study tests the null hypothesis that there is no significant difference in periodontal health between patients with BRs and vacuum-formed retainers (VFRs) over a 12-month period. This was assessed in terms of plaque and calculus accumulation, and periodontal health. Subjects and methods Details of the participants, randomisation, and study design have been reported in paper 1 (19). Intervention At the end of active treatment, two calibrated operators placed either: upper and lower BRs, or upper and lower VFRs using standardized procedures and materials. All patients had been seen for supra-gingival debridement prior to removal of the fixed appliances. The BRs were prepared using 0.0195 in (0.45 mm) 3-stranded twistflex stainless steel wire (Wildcat; GAC International, Bohemia, New York, USA). The wire was shaped against the dental casts to lie passively against the lingual surfaces of the upper and lower incisors and canines. The wire was not contoured interproximally. A silicone positioning jig was prepared to aid placement of the retainer. This was molded to engage the wire and rest on the central incisors. The wire was bonded using a low-viscosity light-cured composite (Transbond™ LV; 3M Unitek, Monrovia, California, USA), following the separate application of etchant (37% phosphoric acid), and primer (Transbond™ XT adhesive primer; 3M Unitek). Care was taken not to leave any bonding substance in contact with the gingival tissues. The VFRs (Essix™ C+) were constructed using the same ‘Essix™ machine’ and cooled rapidly with Arctic spray (Ortho-Care). Retainers were trimmed to cover all fully erupted teeth and extend half way across the occlusal surface of the most distal molar. Patients were asked to wear the VFRs only at night. Oral hygiene instructions were given at the time of retainer insertion. All participants were advised to brush their teeth and to visit their dentist every 6 months for routine dental examinations, and to use a daily fluoride mouthrinse. Participants with BRs were instructed how to clean around their retainers with interdental brushes and/or superfloss. Both groups were advised to contact the department as soon as possible if they had any queries, concerns, or problems. Outcome measures Periodontal measurements were taken in the maxilla and mandible by a calibrated operator at removal of the fixed appliances and placement of the retainers, and at the subsequent review appointments. The buccal, lingual, mesial, and distal tooth surfaces of all erupted teeth in both arches were scored for all measured outcomes of this paper. One operator (MS) subsequently calculated the periodontal indices for the whole mouth, the maxilla, the mandible, the intercanine region for both arches, the maxillary intercanine, and the mandibular intercanine regions. These regions were selected to ensure all the areas potentially affected by the two different retainer groups were analysed. Periodontal health was assessed using calculus index (CI), gingival index (GI), and plaque index (PI). Calculus index Calculus was measured according to the Calculus component of the Simplified Oral Health Index (20) (Supplementary Table 1). The coronal extension of supra-gingival calculus and the presence of subgingival calculus was visually estimated and recorded for all erupted teeth in both arches. Gingival index Gingival health was assessed using the GI as described by Löe (21) (Supplementary Table 2). The teeth and gingivae were initially dried lightly and examined visually for signs of gingival inflammation; colour, loss of stippling, oedema, the presence of gingival exudate, and ulceration. As the decisive criterion in the differentiation between the GI scores was the various tendencies of the gingivae to bleed on gentle probing, a blunt Williams periodontal probe was then gently run along the gingival crevice and the gingivae observed for bleeding after 10–15 seconds. Plaque index Plaque accumulations were assessed using the PI (22) (Supplementary Table 3). The tooth was tested by running a probe across the surface at the entrance of the gingival crevice after the tooth has been dried. Disclosing fluid (Plaqsearch, Oraldent Ltd) was used for the recognition of the film of plaque. The solution was gently painted onto all surfaces of the maxillary and mandibular teeth, the patient was instructed to rinse their mouth and then spit out, and then the presence of plaque recorded. Following assessment, the disclosed plaque was demonstrated to the patient as a visual aid. Oral hygiene messages were reinforced and encouragement given as necessary. The teeth were then cleaned thoroughly with prophy polish and a rubber cup. Examination was standardized and started with the upper right second molar, continuing over the midline to the upper left second molar. The distal, buccal, and mesial aspects of the teeth on the right side were then examined followed by the mesial, buccal, and distal surfaces on the left side. When these surfaces had been assessed, the palatal surfaces of the maxillary teeth were assessed starting with the upper right second molar. Examination of the lower jaw started with the lower left second molar and was carried through to the lower right second molar. On the left, the sequence was the distal, buccal, and mesial surface and on those on the right side, mesial, buccal, and distal. All lingual surfaces were scored beginning with the lower left second molar. For each index, four areas of the tooth (buccal, lingual, mesial, and distal) were assessed to give the score for the area. The scores from these four areas were added together and then divided by 4 to calculate the score for the tooth, and then the scores for the teeth were grouped and averaged to designate the score for a group of teeth. All measurements were made at the following time points: T0  Debond T1 3 months post-debond T2 6 months post-debond T3  12 months post-debond Blinding It was not possible to blind the patient or clinician in this study. As the outcome assessor was one of the clinicians, the outcome assessment was also not blinded. Patients leaving the study or refusing treatment To reduce potential assessment bias, as much data as possible were collected from participants who dropped out of the study. If a subject failed to co-operate with the retention regime, the data were still collected and an ‘intention to treat’ analysis was carried out. Therefore, if a patient was allocated to receive VFRs but then subsequently failed to wear them as prescribed, they remained in that intervention group. Statistics Differences in periodontal and dental health indices between the two retainer types were assessed for normality using Shapiro–Wilks tests and Q–Q plots. As several of the measurements were not normally distributed, comparisons were made using Mann–Whitney U-tests, reporting median values and interquartile ranges (IQRs). Repeated-measure analysis of variance (repeated-measure ANOVA) was performed to assess the periodontal data over time, with retainer type and study centre as independent predictors to assess for possible confounding factors. All analyses were conducted at the 5% level of significance. Bland–Altman plots and intra-class correlation coefficients (ICCs) were used to assess intra- and inter-examiner reliability. The SPSS software package was used for data analysis (version 20; SPSS, Chicago, Illinois, USA) and statistical significance was set at the 5% level. Results Participant flow Paper 1 reports the participant flow and includes the CONSORT diagram for the study, as well as reporting the baseline data (19). There were 104 patients initially informed about the study, and 44 were excluded as they either declined to be involved or did not satisfy the inclusion criteria. The CONSORT flow diagram in paper 1 illustrates the passage of the 60 patients through the trial Periodontal indices The median periodontal indices for each retainer at debond, 3, 6, and 12 months are summarized in Table 1 and Supplementary Tables 4–6. Table 1. Medians and IQRs of periodontal measurements by retainer group. 3-3CI, intercanine calculus index; 3-3GI, intercanine gingival index; 3-3PI, intercanine plaque index; FMCI, full mouth calculus index; FMGI, full mouth gingival index; FMPI, full mouth plaque index; Mn3-3CI, mandibular intercanine calculus index; Mn3-3GI, mandibular intercanine gingival index; Mn3-3PI, mandibular intercanine plaque index; MnCI, mandibular calculus index; MnGI, mandibular gingival index; MnPI, mandibular plaque index; Mx3-3CI, maxillary intercanine calculus index; Mx3-3GI, maxillary intercanine gingival index; Mx3-3PI, maxillary intercanine plaque index; MxCI, maxillary calculus index; MxGI, maxillary gingival index; MxPI, maxillary plaque index. P = significance level, given as Asymp. Sig (two tailed) Mann–Whitney U-test. Site Debond 3 Months 6 Months 12 Months BR VFR P BR VFR P BR VFR P BR VFR P Plaque index FMPI 0.50 (0.33) 0.47 (0.33) 0.429 0.33 (0.24) 0.34 (0.37) 0.435 0.38 (0.39) 0.30 (0.35) 0.024* 0.45 (0.36) 0.33 (0.35) 0.044* MxPI 0.48 (0.31) 0.51 (0.31) 0.728 0.29 (0.37) 0.32 (0.29) 0.474 0.37 (0.33) 0.26 (0.38) 0.017* 0.46 (0.33) 0.27 (0.38) 0.048* MnPI 0.50 (0.33) 0.44 (0.34) 0.151 0.44 (0.29) 0.34 (0.37) 0.174 0.42 (0.42) 0.26 (0.32) 0.046* 0.49 (0.38) 0.43 (0.38) 0.056 3-3PI 0.49 (0.26) 0.48 (0.33) 0.953 0.47 (0.33) 0.31 (0.39) 0.032* 0.52 (0.42) 0.24 (0.34) 0.003* 0.54 (0.37) 0.35 (0.27) 0.008* Mx3-3PI 0.48 (0.27) 0.46 (0.26) 0.739 0.42 (0.38) 0.27 (0.37) 0.024* 0.46 (0.43) 0.21 (0.43) 0.005* 0.5 (0.34) 0.33 (0.29) 0.018* Mn3-3PI 0.50 (0.29) 0.42 (0.39) 0.314 0.52 (0.43) 0.29 (0.43) 0.049* 0.54 (0.55) 0.23 (0.32) 0.004* 0.61 (0.47) 0.46 (0.45) 0.026* Gingival index FMGI 0.98 (0.92) 1.22 (0.62) 0.579 0.64 (0.52) 0.64 (0.65) 0.398 0.59 (0.47) 0.40 (0.67) 0.323 0.74 (0.65) 0.42 (0.54) 0.135 MxGI 0.92 (1.14) 1.38 (0.54) 0.487 0.55 (0.56) 0.63 (0.73) 0.457 0.48 (0.43) 0.35 (0.69) 0.602 0.71 (0.77) 0.43 (0.70) 0.253 MnGI 1.00 (0.80) 1.15 (0.60) 0.824 0.62 (0.60) 0.61 (0.59) 0.326 0.65 (0.49) 0.39 (0.54) 0.194 0.78 (0.66) 0.41 (0.42) 0.050* 3-3GI 1.01 (0.83) 1.31 (0.55) 0.647 0.88 (0.83) 0.66 (0.68) 0.076 0.80 (0.86) 0.38 (0.86) 0.124 0.95 (0.89) 0.54 (0.71) 0.054 Mx3-3GI 0.94 (1.00) 1.36 (0.66) 0.359 0.69 (0.75) 0.58 (0.66) 0.030* 0.58 (0.84) 0.36 (1.03) 0.574 0.75 (1.04) 0.42 (0.75) 0.129 Mn3-3GI 1.06 (1.14) 1.13 (0.60) 0.959 0.90 (1.02) 0.67 (0.72) 0.168 0.92 (0.91) 0.46 (0.87) 0.025* 0.92 (0.96) 0.58 (0.71) 0.082 Calculus index FMCI 0.00 (0.04) 0.00 (0.00) 0.112 0.02 (0.05) 0.01 (0.04) 0.472 0.04 (0.06) 0.00 (0.04) 0.015* 0.06 (0.09) 0.02 (0.06) 0.048* MxCI 0.00 (0.00) 0.00 (0.00) 0.981 0.00 (0.00) 0.00 (0.00) 0.280 0.00 (0.00) 0.00 (0.00) 0.571 0.00 (0.00) 0.00 (0.00) 0.470 MnCI 0.00 (0.07) 0.00 (0.00) 0.104 0.04 (0.09) 0.02 (0.07) 0.568 0.05 (0.13) 0.00 (0.09) 0.016* 0.13 (0.19) 0.04 (0.13) 0.051 3-3CI 0.00 (0.08) 0.00 (0.00) 0.104 0.04 (0.10) 0.02 (0.08) 0.549 0.05 (0.15) 0.00 (0.09) 0.014* 0.14 (0.21) 0.04 (0.15) 0.051 Mx3-3CI 0.00 (0.00) 0.00 (0.00) 0.317 0.00 (0.00) 0.00 (0.00) 1.000 0.00 (0.00) 0.00 (0.00) 0.317 0.00 (0.00) 0.00 (0.00) 0.292 Mn3-3CI 0.00 (0.16) 0.00 (0.00) 0.054 0.08 (0.21) 0.04 (0.17) 0.549 0.15 (0.28) 0.00 (0.18) 0.014* 0.23 (0.43) 0.08 (0.29) 0.077 Site Debond 3 Months 6 Months 12 Months BR VFR P BR VFR P BR VFR P BR VFR P Plaque index FMPI 0.50 (0.33) 0.47 (0.33) 0.429 0.33 (0.24) 0.34 (0.37) 0.435 0.38 (0.39) 0.30 (0.35) 0.024* 0.45 (0.36) 0.33 (0.35) 0.044* MxPI 0.48 (0.31) 0.51 (0.31) 0.728 0.29 (0.37) 0.32 (0.29) 0.474 0.37 (0.33) 0.26 (0.38) 0.017* 0.46 (0.33) 0.27 (0.38) 0.048* MnPI 0.50 (0.33) 0.44 (0.34) 0.151 0.44 (0.29) 0.34 (0.37) 0.174 0.42 (0.42) 0.26 (0.32) 0.046* 0.49 (0.38) 0.43 (0.38) 0.056 3-3PI 0.49 (0.26) 0.48 (0.33) 0.953 0.47 (0.33) 0.31 (0.39) 0.032* 0.52 (0.42) 0.24 (0.34) 0.003* 0.54 (0.37) 0.35 (0.27) 0.008* Mx3-3PI 0.48 (0.27) 0.46 (0.26) 0.739 0.42 (0.38) 0.27 (0.37) 0.024* 0.46 (0.43) 0.21 (0.43) 0.005* 0.5 (0.34) 0.33 (0.29) 0.018* Mn3-3PI 0.50 (0.29) 0.42 (0.39) 0.314 0.52 (0.43) 0.29 (0.43) 0.049* 0.54 (0.55) 0.23 (0.32) 0.004* 0.61 (0.47) 0.46 (0.45) 0.026* Gingival index FMGI 0.98 (0.92) 1.22 (0.62) 0.579 0.64 (0.52) 0.64 (0.65) 0.398 0.59 (0.47) 0.40 (0.67) 0.323 0.74 (0.65) 0.42 (0.54) 0.135 MxGI 0.92 (1.14) 1.38 (0.54) 0.487 0.55 (0.56) 0.63 (0.73) 0.457 0.48 (0.43) 0.35 (0.69) 0.602 0.71 (0.77) 0.43 (0.70) 0.253 MnGI 1.00 (0.80) 1.15 (0.60) 0.824 0.62 (0.60) 0.61 (0.59) 0.326 0.65 (0.49) 0.39 (0.54) 0.194 0.78 (0.66) 0.41 (0.42) 0.050* 3-3GI 1.01 (0.83) 1.31 (0.55) 0.647 0.88 (0.83) 0.66 (0.68) 0.076 0.80 (0.86) 0.38 (0.86) 0.124 0.95 (0.89) 0.54 (0.71) 0.054 Mx3-3GI 0.94 (1.00) 1.36 (0.66) 0.359 0.69 (0.75) 0.58 (0.66) 0.030* 0.58 (0.84) 0.36 (1.03) 0.574 0.75 (1.04) 0.42 (0.75) 0.129 Mn3-3GI 1.06 (1.14) 1.13 (0.60) 0.959 0.90 (1.02) 0.67 (0.72) 0.168 0.92 (0.91) 0.46 (0.87) 0.025* 0.92 (0.96) 0.58 (0.71) 0.082 Calculus index FMCI 0.00 (0.04) 0.00 (0.00) 0.112 0.02 (0.05) 0.01 (0.04) 0.472 0.04 (0.06) 0.00 (0.04) 0.015* 0.06 (0.09) 0.02 (0.06) 0.048* MxCI 0.00 (0.00) 0.00 (0.00) 0.981 0.00 (0.00) 0.00 (0.00) 0.280 0.00 (0.00) 0.00 (0.00) 0.571 0.00 (0.00) 0.00 (0.00) 0.470 MnCI 0.00 (0.07) 0.00 (0.00) 0.104 0.04 (0.09) 0.02 (0.07) 0.568 0.05 (0.13) 0.00 (0.09) 0.016* 0.13 (0.19) 0.04 (0.13) 0.051 3-3CI 0.00 (0.08) 0.00 (0.00) 0.104 0.04 (0.10) 0.02 (0.08) 0.549 0.05 (0.15) 0.00 (0.09) 0.014* 0.14 (0.21) 0.04 (0.15) 0.051 Mx3-3CI 0.00 (0.00) 0.00 (0.00) 0.317 0.00 (0.00) 0.00 (0.00) 1.000 0.00 (0.00) 0.00 (0.00) 0.317 0.00 (0.00) 0.00 (0.00) 0.292 Mn3-3CI 0.00 (0.16) 0.00 (0.00) 0.054 0.08 (0.21) 0.04 (0.17) 0.549 0.15 (0.28) 0.00 (0.18) 0.014* 0.23 (0.43) 0.08 (0.29) 0.077 *denotes P < 0.05 View Large Table 1. Medians and IQRs of periodontal measurements by retainer group. 3-3CI, intercanine calculus index; 3-3GI, intercanine gingival index; 3-3PI, intercanine plaque index; FMCI, full mouth calculus index; FMGI, full mouth gingival index; FMPI, full mouth plaque index; Mn3-3CI, mandibular intercanine calculus index; Mn3-3GI, mandibular intercanine gingival index; Mn3-3PI, mandibular intercanine plaque index; MnCI, mandibular calculus index; MnGI, mandibular gingival index; MnPI, mandibular plaque index; Mx3-3CI, maxillary intercanine calculus index; Mx3-3GI, maxillary intercanine gingival index; Mx3-3PI, maxillary intercanine plaque index; MxCI, maxillary calculus index; MxGI, maxillary gingival index; MxPI, maxillary plaque index. P = significance level, given as Asymp. Sig (two tailed) Mann–Whitney U-test. Site Debond 3 Months 6 Months 12 Months BR VFR P BR VFR P BR VFR P BR VFR P Plaque index FMPI 0.50 (0.33) 0.47 (0.33) 0.429 0.33 (0.24) 0.34 (0.37) 0.435 0.38 (0.39) 0.30 (0.35) 0.024* 0.45 (0.36) 0.33 (0.35) 0.044* MxPI 0.48 (0.31) 0.51 (0.31) 0.728 0.29 (0.37) 0.32 (0.29) 0.474 0.37 (0.33) 0.26 (0.38) 0.017* 0.46 (0.33) 0.27 (0.38) 0.048* MnPI 0.50 (0.33) 0.44 (0.34) 0.151 0.44 (0.29) 0.34 (0.37) 0.174 0.42 (0.42) 0.26 (0.32) 0.046* 0.49 (0.38) 0.43 (0.38) 0.056 3-3PI 0.49 (0.26) 0.48 (0.33) 0.953 0.47 (0.33) 0.31 (0.39) 0.032* 0.52 (0.42) 0.24 (0.34) 0.003* 0.54 (0.37) 0.35 (0.27) 0.008* Mx3-3PI 0.48 (0.27) 0.46 (0.26) 0.739 0.42 (0.38) 0.27 (0.37) 0.024* 0.46 (0.43) 0.21 (0.43) 0.005* 0.5 (0.34) 0.33 (0.29) 0.018* Mn3-3PI 0.50 (0.29) 0.42 (0.39) 0.314 0.52 (0.43) 0.29 (0.43) 0.049* 0.54 (0.55) 0.23 (0.32) 0.004* 0.61 (0.47) 0.46 (0.45) 0.026* Gingival index FMGI 0.98 (0.92) 1.22 (0.62) 0.579 0.64 (0.52) 0.64 (0.65) 0.398 0.59 (0.47) 0.40 (0.67) 0.323 0.74 (0.65) 0.42 (0.54) 0.135 MxGI 0.92 (1.14) 1.38 (0.54) 0.487 0.55 (0.56) 0.63 (0.73) 0.457 0.48 (0.43) 0.35 (0.69) 0.602 0.71 (0.77) 0.43 (0.70) 0.253 MnGI 1.00 (0.80) 1.15 (0.60) 0.824 0.62 (0.60) 0.61 (0.59) 0.326 0.65 (0.49) 0.39 (0.54) 0.194 0.78 (0.66) 0.41 (0.42) 0.050* 3-3GI 1.01 (0.83) 1.31 (0.55) 0.647 0.88 (0.83) 0.66 (0.68) 0.076 0.80 (0.86) 0.38 (0.86) 0.124 0.95 (0.89) 0.54 (0.71) 0.054 Mx3-3GI 0.94 (1.00) 1.36 (0.66) 0.359 0.69 (0.75) 0.58 (0.66) 0.030* 0.58 (0.84) 0.36 (1.03) 0.574 0.75 (1.04) 0.42 (0.75) 0.129 Mn3-3GI 1.06 (1.14) 1.13 (0.60) 0.959 0.90 (1.02) 0.67 (0.72) 0.168 0.92 (0.91) 0.46 (0.87) 0.025* 0.92 (0.96) 0.58 (0.71) 0.082 Calculus index FMCI 0.00 (0.04) 0.00 (0.00) 0.112 0.02 (0.05) 0.01 (0.04) 0.472 0.04 (0.06) 0.00 (0.04) 0.015* 0.06 (0.09) 0.02 (0.06) 0.048* MxCI 0.00 (0.00) 0.00 (0.00) 0.981 0.00 (0.00) 0.00 (0.00) 0.280 0.00 (0.00) 0.00 (0.00) 0.571 0.00 (0.00) 0.00 (0.00) 0.470 MnCI 0.00 (0.07) 0.00 (0.00) 0.104 0.04 (0.09) 0.02 (0.07) 0.568 0.05 (0.13) 0.00 (0.09) 0.016* 0.13 (0.19) 0.04 (0.13) 0.051 3-3CI 0.00 (0.08) 0.00 (0.00) 0.104 0.04 (0.10) 0.02 (0.08) 0.549 0.05 (0.15) 0.00 (0.09) 0.014* 0.14 (0.21) 0.04 (0.15) 0.051 Mx3-3CI 0.00 (0.00) 0.00 (0.00) 0.317 0.00 (0.00) 0.00 (0.00) 1.000 0.00 (0.00) 0.00 (0.00) 0.317 0.00 (0.00) 0.00 (0.00) 0.292 Mn3-3CI 0.00 (0.16) 0.00 (0.00) 0.054 0.08 (0.21) 0.04 (0.17) 0.549 0.15 (0.28) 0.00 (0.18) 0.014* 0.23 (0.43) 0.08 (0.29) 0.077 Site Debond 3 Months 6 Months 12 Months BR VFR P BR VFR P BR VFR P BR VFR P Plaque index FMPI 0.50 (0.33) 0.47 (0.33) 0.429 0.33 (0.24) 0.34 (0.37) 0.435 0.38 (0.39) 0.30 (0.35) 0.024* 0.45 (0.36) 0.33 (0.35) 0.044* MxPI 0.48 (0.31) 0.51 (0.31) 0.728 0.29 (0.37) 0.32 (0.29) 0.474 0.37 (0.33) 0.26 (0.38) 0.017* 0.46 (0.33) 0.27 (0.38) 0.048* MnPI 0.50 (0.33) 0.44 (0.34) 0.151 0.44 (0.29) 0.34 (0.37) 0.174 0.42 (0.42) 0.26 (0.32) 0.046* 0.49 (0.38) 0.43 (0.38) 0.056 3-3PI 0.49 (0.26) 0.48 (0.33) 0.953 0.47 (0.33) 0.31 (0.39) 0.032* 0.52 (0.42) 0.24 (0.34) 0.003* 0.54 (0.37) 0.35 (0.27) 0.008* Mx3-3PI 0.48 (0.27) 0.46 (0.26) 0.739 0.42 (0.38) 0.27 (0.37) 0.024* 0.46 (0.43) 0.21 (0.43) 0.005* 0.5 (0.34) 0.33 (0.29) 0.018* Mn3-3PI 0.50 (0.29) 0.42 (0.39) 0.314 0.52 (0.43) 0.29 (0.43) 0.049* 0.54 (0.55) 0.23 (0.32) 0.004* 0.61 (0.47) 0.46 (0.45) 0.026* Gingival index FMGI 0.98 (0.92) 1.22 (0.62) 0.579 0.64 (0.52) 0.64 (0.65) 0.398 0.59 (0.47) 0.40 (0.67) 0.323 0.74 (0.65) 0.42 (0.54) 0.135 MxGI 0.92 (1.14) 1.38 (0.54) 0.487 0.55 (0.56) 0.63 (0.73) 0.457 0.48 (0.43) 0.35 (0.69) 0.602 0.71 (0.77) 0.43 (0.70) 0.253 MnGI 1.00 (0.80) 1.15 (0.60) 0.824 0.62 (0.60) 0.61 (0.59) 0.326 0.65 (0.49) 0.39 (0.54) 0.194 0.78 (0.66) 0.41 (0.42) 0.050* 3-3GI 1.01 (0.83) 1.31 (0.55) 0.647 0.88 (0.83) 0.66 (0.68) 0.076 0.80 (0.86) 0.38 (0.86) 0.124 0.95 (0.89) 0.54 (0.71) 0.054 Mx3-3GI 0.94 (1.00) 1.36 (0.66) 0.359 0.69 (0.75) 0.58 (0.66) 0.030* 0.58 (0.84) 0.36 (1.03) 0.574 0.75 (1.04) 0.42 (0.75) 0.129 Mn3-3GI 1.06 (1.14) 1.13 (0.60) 0.959 0.90 (1.02) 0.67 (0.72) 0.168 0.92 (0.91) 0.46 (0.87) 0.025* 0.92 (0.96) 0.58 (0.71) 0.082 Calculus index FMCI 0.00 (0.04) 0.00 (0.00) 0.112 0.02 (0.05) 0.01 (0.04) 0.472 0.04 (0.06) 0.00 (0.04) 0.015* 0.06 (0.09) 0.02 (0.06) 0.048* MxCI 0.00 (0.00) 0.00 (0.00) 0.981 0.00 (0.00) 0.00 (0.00) 0.280 0.00 (0.00) 0.00 (0.00) 0.571 0.00 (0.00) 0.00 (0.00) 0.470 MnCI 0.00 (0.07) 0.00 (0.00) 0.104 0.04 (0.09) 0.02 (0.07) 0.568 0.05 (0.13) 0.00 (0.09) 0.016* 0.13 (0.19) 0.04 (0.13) 0.051 3-3CI 0.00 (0.08) 0.00 (0.00) 0.104 0.04 (0.10) 0.02 (0.08) 0.549 0.05 (0.15) 0.00 (0.09) 0.014* 0.14 (0.21) 0.04 (0.15) 0.051 Mx3-3CI 0.00 (0.00) 0.00 (0.00) 0.317 0.00 (0.00) 0.00 (0.00) 1.000 0.00 (0.00) 0.00 (0.00) 0.317 0.00 (0.00) 0.00 (0.00) 0.292 Mn3-3CI 0.00 (0.16) 0.00 (0.00) 0.054 0.08 (0.21) 0.04 (0.17) 0.549 0.15 (0.28) 0.00 (0.18) 0.014* 0.23 (0.43) 0.08 (0.29) 0.077 *denotes P < 0.05 View Large Plaque index At baseline (debond), the median PI of both retainer groups ranged from 0.42 to 0.51 with no significant difference between the two groups (P > 0.05; Table 1). At 3 months, 6 months, and 12 months, there was a significantly higher PI in the intercanine region for BRs compared with VFRs. The change in PI with time is shown in Figure 1 and summarized in Supplementary Table 4. Figure 1. View largeDownload slide Changes in plaque index with time. A: full mouth plaque index. B: maxillary plaque index. C: mandibular plaque index. D: intercanine plaque index. E: maxillary intercanine plaque index. F: mandibular intercanine plaque index. Figure 1. View largeDownload slide Changes in plaque index with time. A: full mouth plaque index. B: maxillary plaque index. C: mandibular plaque index. D: intercanine plaque index. E: maxillary intercanine plaque index. F: mandibular intercanine plaque index. After 3 months, the PI showed a tendency to be lower than at baseline for all sites and for both retainer types with the exception of the mandibular intercanine region for BRs which showed an increase from baseline from 0.50 (IQR 0.29) to 0.52 (IQR 0.43; Figure 1 and Supplementary Table 4). The greater intercanine plaque scores with BRs compared to VFRs at 3 months was statistically significant (Supplementary Table 4). After 6 months, there was an increase in median plaque scores at all regions for both retainer types (Figure 1 and Supplementary Table 4). Despite any changes, all scores were in the region of 0.1–1.0 suggestive of scattered deposits of plaque only, so the clinical significance of these changes is questionable (21, 22). Gingival index At baseline, the median GI of both retainer groups ranged from 0.92 to 1.38. There was no statistical significance between the two groups (P > 0.05; Table 1 and Supplementary Table 5). The median GI after wearing the retainers for 3 months was lower than at baseline (debond) for all sites and for both retainer types (Figure 2 and Supplementary Table 5). The gingival health was worse with BRs after 3 months in the maxillary arch and after 6 months in the mandibular arch. Figure 2. View largeDownload slide Changes in gingival index with time. A: full mouth gingival index. B: maxillary gingival index. C: mandibular gingival index. D: intercanine gingival index. E: maxillary intercanine gingival index. F: mandibular intercanine gingival index. Figure 2. View largeDownload slide Changes in gingival index with time. A: full mouth gingival index. B: maxillary gingival index. C: mandibular gingival index. D: intercanine gingival index. E: maxillary intercanine gingival index. F: mandibular intercanine gingival index. At baseline, with the exception of the intercanine (1.01, IQR 0.83) and mandibular intercanine (1.06, IQR 1.14) regions, the median gingival scores for BRs were in the region of 0.1–1.0, suggestive of mild inflammation. At baseline all the median gingival scores for VFRs were in the region of 1.1–2.0 suggestive of moderate inflammation (Supplementary Table 5). However, by 6 months, and continuing until 12 months, all regions for both retainer groups had decreased to less than 1.0 suggestive of mild inflammation only (Supplementary Table 5). This may be clinically significant. Calculus index At baseline (debond), the median CI of both retainer groups was zero with no significant difference between regions between groups (Table 1 and Supplementary Table 6). After 3 months, the CI increased from baseline in the mandible for both retainer types, causing a concomitant increase in the calculus scores for the intercanine region and for the full mouth (Figure 3 and Supplementary Table 6). Calculus scores were higher for BRs than the VFRs at 3 months though the difference was not statistically significant (Supplementary Table 6). The increase in calculus score from baseline to 3 months was statistically significant (P < 0.05) for VFRs (Supplementary Table 6). Figure 3. View largeDownload slide Changes in calculus index with time. A: full mouth calculus index. B: maxillary calculus index. C: mandibular calculus index. D: intercanine calculus index. E: maxillary intercanine calculus index. F: mandibular intercanine calculus index. Figure 3. View largeDownload slide Changes in calculus index with time. A: full mouth calculus index. B: maxillary calculus index. C: mandibular calculus index. D: intercanine calculus index. E: maxillary intercanine calculus index. F: mandibular intercanine calculus index. Between 3 and 6 months, the median CI reverted back to the baseline measurement of zero at all sites for VFRs; however, the median calculus scores for BRs continued to increase in the mandibular intercanine region. (Figure 3 and Supplementary Table 6). Accounting for confounding factors in periodontal indices The differences for the three outcome measures (PI, GI, and CI) between BRs and VFRs with time were re-examined, adjusting for retainer type, study centre, and time to help ensure that any significant differences observed were due to the type of retainer fitted, and not to an identified confounding factor. A 12-month repeated-measure ANOVA for periodontal indices was used. Retainer type The results showed that, other than for the maxillary PI (P = 0.062), there was a statistically significant (P < 0.05) greater plaque accumulation with BRs than VFRs (Table 2). Table 2. Effect of retainer type on plaque, gingival, and calculus indices over 12 months. X, mean difference. P: Adjustment for multiple comparisons: Bonferroni. Index Site Retainer (BR to VFR) X 95% CI P Plaque index FMPI 0.11 0.01, 0.20 0.026* MxPI 0.09 −0.01, 0.01 0.062 MnPI 0.13 0.03, 0.23 0.016* 3-3PI 0.17 0.06, 0.28 0.004* Mx3-3PI 0.17 0.06, 0.28 0.004* Mn3-3PI 0.19 0.06, 0.32 0.006* Gingival index FMGI 0.14 −0.03, 0.31 0.101 MxGI 0.13 −0.04, 0.30 0.126 MnGI 0.15 −0.04, 0.34 0.112 3-3GI 0.25 0.04, 0.45 0.018* Mx3-3GI 0.22 0.03, 0.41 0.027* Mn3-3GI 0.25 0.02, 0.48 0.035* Calculus index FMCI 0.02 −0.004, 0.05 0.095 MxCI 0.003 −0.01, 0.01 0.579 MnCI 0.05 −0.004, 0.09 0.070 3-3 CI 0.05 0.002, 0.102 0.041* Mx3-3CI 0.005 −0.01, 0.02 0.549 Mn3-3CI 0.10 0.003, 0.19 0.043* Index Site Retainer (BR to VFR) X 95% CI P Plaque index FMPI 0.11 0.01, 0.20 0.026* MxPI 0.09 −0.01, 0.01 0.062 MnPI 0.13 0.03, 0.23 0.016* 3-3PI 0.17 0.06, 0.28 0.004* Mx3-3PI 0.17 0.06, 0.28 0.004* Mn3-3PI 0.19 0.06, 0.32 0.006* Gingival index FMGI 0.14 −0.03, 0.31 0.101 MxGI 0.13 −0.04, 0.30 0.126 MnGI 0.15 −0.04, 0.34 0.112 3-3GI 0.25 0.04, 0.45 0.018* Mx3-3GI 0.22 0.03, 0.41 0.027* Mn3-3GI 0.25 0.02, 0.48 0.035* Calculus index FMCI 0.02 −0.004, 0.05 0.095 MxCI 0.003 −0.01, 0.01 0.579 MnCI 0.05 −0.004, 0.09 0.070 3-3 CI 0.05 0.002, 0.102 0.041* Mx3-3CI 0.005 −0.01, 0.02 0.549 Mn3-3CI 0.10 0.003, 0.19 0.043* View Large Table 2. Effect of retainer type on plaque, gingival, and calculus indices over 12 months. X, mean difference. P: Adjustment for multiple comparisons: Bonferroni. Index Site Retainer (BR to VFR) X 95% CI P Plaque index FMPI 0.11 0.01, 0.20 0.026* MxPI 0.09 −0.01, 0.01 0.062 MnPI 0.13 0.03, 0.23 0.016* 3-3PI 0.17 0.06, 0.28 0.004* Mx3-3PI 0.17 0.06, 0.28 0.004* Mn3-3PI 0.19 0.06, 0.32 0.006* Gingival index FMGI 0.14 −0.03, 0.31 0.101 MxGI 0.13 −0.04, 0.30 0.126 MnGI 0.15 −0.04, 0.34 0.112 3-3GI 0.25 0.04, 0.45 0.018* Mx3-3GI 0.22 0.03, 0.41 0.027* Mn3-3GI 0.25 0.02, 0.48 0.035* Calculus index FMCI 0.02 −0.004, 0.05 0.095 MxCI 0.003 −0.01, 0.01 0.579 MnCI 0.05 −0.004, 0.09 0.070 3-3 CI 0.05 0.002, 0.102 0.041* Mx3-3CI 0.005 −0.01, 0.02 0.549 Mn3-3CI 0.10 0.003, 0.19 0.043* Index Site Retainer (BR to VFR) X 95% CI P Plaque index FMPI 0.11 0.01, 0.20 0.026* MxPI 0.09 −0.01, 0.01 0.062 MnPI 0.13 0.03, 0.23 0.016* 3-3PI 0.17 0.06, 0.28 0.004* Mx3-3PI 0.17 0.06, 0.28 0.004* Mn3-3PI 0.19 0.06, 0.32 0.006* Gingival index FMGI 0.14 −0.03, 0.31 0.101 MxGI 0.13 −0.04, 0.30 0.126 MnGI 0.15 −0.04, 0.34 0.112 3-3GI 0.25 0.04, 0.45 0.018* Mx3-3GI 0.22 0.03, 0.41 0.027* Mn3-3GI 0.25 0.02, 0.48 0.035* Calculus index FMCI 0.02 −0.004, 0.05 0.095 MxCI 0.003 −0.01, 0.01 0.579 MnCI 0.05 −0.004, 0.09 0.070 3-3 CI 0.05 0.002, 0.102 0.041* Mx3-3CI 0.005 −0.01, 0.02 0.549 Mn3-3CI 0.10 0.003, 0.19 0.043* View Large However, statistically significant differences in gingival health between the two retainer groups were only detected for the intercanine (P = 0.018), maxillary intercanine (P = 0.027), and mandibular intercanine (P = 0.035) regions, with poorer gingival health associated with BR than VFRs (Table 2). Statistically significant differences in calculus accumulation between BRs and VFRs were only detected in the intercanine (P = 0.041) and mandibular intercanine region (P = 0.043) where more extensive deposits were associated with the presence of BRs (Table 2). Time A statistically significant decrease in plaque accumulation was noted in the first 3 months of retainer placement. The differences noted in gingival health and calculus accumulation were found to be statistically significant from debond and retainer placement to each successive review appointment. However, only the increases in calculus accumulation were found to be statistically significant from 3 months to 1 year (Supplementary Table 7). Study centre The results showed that the study centre the patients were recruited from and assessed at had a statistically significant (P < 0.05) effect on the gingival scores observed, with patients from Bradford having significantly poorer gingival health than those recruited from Leeds. Participants recruited from York had statistically significantly better maxillary plaque scores than those from Leeds (P = 0.036). No significant differences between study centres were observed for calculus accumulation. Reproducibility of the method Intra-examiner reliability for measurement of periodontal indices A random sample of 10 patients was re-assessed to determine intra-examiner reliability. Due to the dynamic nature of the periodontal status, measurements were re-recorded immediately after the first measurements had been made in an attempt to most accurately record the periodontal condition at that time. Each periodontal measurement was tested using a combination of Shapiro–Wilks tests and Q–Q plots. Several of the measurements were not normally distributed and so median values and IQRs were quoted. Intra-examiner reliability was assessed using the ICC and Bland–Altman plots. All of the 18 measurements demonstrated excellent reliability (ICC > 0.9 = excellent, > 0.8 = very good, > 0.7 = good, > 0.6 = fair). Inter-examiner reliability for measurement of periodontal indices A separate random sample of 10 patients was assessed by one operator and then immediately re-assessed by the second operator to determine inter-examiner reliability. Each periodontal measurement was tested using a combination of Shapiro–Wilks tests and Q–Q plots, and, as several of the measurements were not normally distributed, median values and IQRs were quoted. The ICC s demonstrated very good or excellent reliability and systematic errors assessed with Bland–Altman plots included no clinically important discrepancies. This demonstrated that the method of recording the data had a high level of reliability and any method errors were acceptable. Harm No serious harm was observed. Discussion Key findings The presence of BRs appears to increase the levels of plaque, gingival inflammation, and calculus, when compared to patients fitted with VFRs. However, after 12 months, the indices recorded do not suggest clinically significant implications for periodontal health. It is not possible to predict the effects of periodontal health in the long-term from this trial. At the end of fixed appliance treatment, there were generalized but minimal deposits of plaque, minimal calculus deposits in the mandibular intercanine region, and mild-to-moderate gingival inflammation. Any differences in baseline periodontal scores between the BR and VFR groups were small and not significant, and suggest that the oral hygiene at the end of the active orthodontic treatment had been acceptable in both groups. An immediate reduction in plaque accumulation was noted in the first 3 months, with both groups demonstrating a general improvement in OH, with the exception of the mandibular intercanine region in the BR group, which showed greater deposits at 3 months compared to baseline. This improvement, however, was only statistically significant for the VFR group. Whilst this improvement continued in all regions for the VFRs, the plaque scores tended to worsen with BRs. By 12 months, plaque scores had worsened for both groups. This suggests an initial improvement in oral hygiene after removal of the fixed appliances, but, with time, all patients’ periodontal measurements worsened. This highlights the importance of repeated motivation, and reinforcing good oral hygiene instruction at least on a 6-monthly basis to avoid further deterioration in oral hygiene and consequent periodontal problems. Similarly, gingival health significantly improved in both groups following removal of the fixed appliances and placement of retainers. This improvement continued to 6 months, albeit to a lesser extent in the BR group. By 12 months, however, gingival health had deteriorated in the BR group resulting in a statistically significant difference in mandibular intercanine gingival scores between the retainer groups. This is most likely explained as a reaction to the presence of a continuous band of plaque in association with the BR. Deposits of calculus increased in both groups from debond to 3 months. By 6 months, calculus deposits were notably absent in the VFR group but continued to worsen in the BR group. By 12 months, calculus deposits had continued to worsen in the BR group and minimal deposits had reappeared in the VFR group. These findings are after 1 year of retention, so it is not possible to predict whether these increases in plaque and calculus could lead to long-term periodontal problems. Comparison to previous work In contrast to previous studies which limited their data collection to certain teeth or just the lower labial segment (7, 9–15), all erupted teeth were assessed for the various periodontal outcome measures. This is because VFRs usually cover the entire dentition, not just the labial segment, and we did not want to make assumptions that VFRs had no impact on the periodontal health. The findings of this current study are in agreement with the findings of previous studies, as they suggest that placement of BRs promotes plaque and calculus accumulation. Millett et al., reported less gingival bleeding and consequently better gingival health 1 year after removal of the fixed appliances than at baseline for both BRs and VFRs, but with a greater improvement and overall better gingival health with VFRs (13). Rody et al. reported an increase in plaque and gingivitis in patients with fixed retainers compared to removable retainers (14). They also noted an increase in biochemical markers for periodontal disease in the gingival crevicular fluid in patients with BRs (particularly those patients with fixed retainers bonded to all the anterior teeth, like in this study). As in this study, they concluded there was no evidence of severe periodontal disease associated with the BRs, but once again the follow-up was reasonably short (6 months), so the long-term implications are still unknown. Booth et al. also reported that, despite finding statistically significant greater plaque deposits and worse gingival health associated with the BR than the VFR, especially in the intercanine region, at review appointments, there was not a statistically significant difference in calculus accumulation or a demonstrable negative effect on periodontal health between retainer types (16). Similarly, in their cross-sectional study of patients who had been in retention for about 15 years, Cerny et al. found no clinically significant differences in the periodontal health of patients who had worn BRs compared with those fitted with removable retainers. More patients with removable retainers than BRs were reported to have good or very good oral hygiene (80%, compared to 40% of the BR group) and gingival health (95%, compared to 80% of the BR group). There were no ratings of poor periodontal health in either group (17). These results also support the findings of Rody et al. in an earlier study who found no difference in clinical periodontal health, despite slightly increased plaque accumulation, in subjects with BRs compared with night-time wear of removable Hawley, or no retainers (12). Artun et al. found similar results from their series of articles investigating the dental and periodontal health effects of various fixed and removable retainers up to 4 years. Whilst they confirmed the tendency for plaque and calculus to accumulate along the retainer wires, regardless of the type of wire used, and the tendency for these accumulations to increase with time, this did not seem to prevent satisfactory oral hygiene along the gingival margin or impact negatively on periodontal or dental health. Similar to this current study, Artun et al. also reported less gingival bleeding (4 months to 4 years), than at debond, indicative of an improvement in gingival health since removal of the fixed appliances (9–11). This reinforces the observations of Zachrisson et al. of a rapid improvement in gingival health during the first month following removal of fixed appliances despite the presence of retainers (23). Heier et al. also reported a generalized improvement in gingival health in both fixed and removable retainer groups at the review appointments following removal of fixed appliances and consequent improved access for oral hygiene. However, as with this trial, slightly more plaque and calculus was detected lingually with BRs. The authors suggested that, providing motivation and oral hygiene instruction is reinforced every 6 months, periodontal health should not be compromised by the presence of retainers (7). Kaji et al. compared the periodontal status of subjects who had BRs fitted at least 1 month prior to the start of the trial, allowing the gingival inflammation associated with the presence of fixed appliances time to resolve, with that of subjects without retainers over an 8-week period (15). They did, however, find a statistically significant alteration in the characteristics of the gingival crevicular fluid, suggestive of sub-clinical inflammation in the presence of a BR (15). Limitations In this study, it was not possible to blind the operators and patients to the treatment allocations. The assessor was not blinded, as they were one of the clinicians. Although the minimum sample size was achieved, the power calculation was based on the primary outcome measure of the study; the efficacy of each retainer group in minimising the 1 year post-orthodontic treatment change in arch alignment as measured with Little’s Irregularity Index (19). As such, it is possible that the study is underpowered with respect to the outcome measures investigated in this study, increasing the chance of making a Type II error. Furthermore, the effect of individual variation is also more pronounced within a small sample and this may have affected the distribution of certain periodontal variables necessitating non-parametric statistical analyses. A greater variation of statistical tests could have been applied with a larger sample, and more significant intergroup differences may have been found. As a result, the findings at this early stage of the trial indicate some trends, but the statistical weighting should be interpreted with caution. It was not possible to control for any professional cleaning carried out by the patients’ own dentists in-between review appointments. This could potentially lead to lower debris scores independent of the type of retainer used. This study only reports the periodontal health of patients in the first year of retention and further research is required to determine if these findings continue long-term. Generalisability When considering the generalisability of these findings, it is important to note the experience of the operator, the design of the retainer, technique of placement, and materials used in this study. Implications for clinical practice While this study indicates no clinically significant changes in periodontal health, the changes in periodontal indices indicate that BRs have the potential to increase plaque retention, increase gingival inflammation and increased calculus build-up, when compared to VFRs. Clinicians should therefore consider carefully whether patients are able to maintain good oral hygiene and regular dental care before fitting BRs, as they may have the potential to compromise periodontal health more than VFRs. It is important patients fitted with BRs are fully aware of these risks and given clear advice about how to maintain good oral health. Conclusions After 12 months of retention with upper and lower BRs or upper and lower VFRs, BRs were associated with a greater accumulation of plaque and calculus and gingival inflammation compared to VFRs. However, after 1 year this did not appear to adversely affect the overall periodontal health to a clinically significant degree. Supplementary material Supplemental data are available at the European Journal of Orthodontics online. Funding There was no funding to be declared. Conflict of interest None to declare. Acknowledgements We would like to acknowledge and thank Nadia Ahmed for her assistance during the early stages of the trial, and each of the laboratory technicians, reception staff, referring clinicians, and each patient and parent at the three hospitals. References 1. Singh , P. , Grammati , S. and Kirschen , R . ( 2009 ) Orthodontic retention patterns in the United Kingdom . Journal of Orthodontics , 36 , 115 – 121 . Google Scholar CrossRef Search ADS PubMed 2. Meade , M.J. and Millett , D . ( 2013 ) Retention protocols and use of vacuum-formed retainers among specialist orthodontists . Journal of Orthodontics , 40 , 318 – 325 . Google Scholar CrossRef Search ADS PubMed 3. Keim , R.G. , Gottlieb , E.L. , Nelson , A.H. and Vogels , D.S. , III . ( 2002 ) 2002 JCO study of orthodontic diagnosis and treatment procedures. Part 1. Results and trends . Journal of Clinical Orthodontics: JCO , 36 , 553 – 568 . Google Scholar PubMed 4. Valiathan , M. and Hughes , E . ( 2010 ) Results of a survey-based study to identify common retention practices in the United States . American Journal of Orthodontics and Dentofacial Orthopedics , 137 , 170 – 177 ; discussion 177. Google Scholar CrossRef Search ADS PubMed 5. Pratt , M.C. , Kluemper , G.T. , Hartsfield , J.K. , Jr , Fardo , D. and Nash , D.A . ( 2011 ) Evaluation of retention protocols among members of the American Association of Orthodontists in the United States . American Journal of Orthodontics and Dentofacial Orthopedics , 140 , 520 – 526 . Google Scholar CrossRef Search ADS PubMed 6. Pandis , N. , Vlahopoulos , K. , Madianos , P. and Eliades , T . ( 2007 ) Long-term periodontal status of patients with mandibular lingual fixed retention . European Journal of Orthodontics , 29 , 471 – 476 . Google Scholar CrossRef Search ADS PubMed 7. Heier , E.E. , De Smit , A.A. , Wijgaerts , I.A. and Adriaens , P.A . ( 1997 ) Periodontal implications of bonded versus removable retainers . American Journal of Orthodontics and Dentofacial Orthopedics , 112 , 607 – 616 . Google Scholar CrossRef Search ADS PubMed 8. Dahl , E.H. and Zachrisson , B.U . ( 1991 ) Long-term experience with direct-bonded lingual retainers . Journal of Clinical Orthodontics: JCO , 25 , 619 – 630 . Google Scholar PubMed 9. Artun , J . ( 1984 ) Caries and periodontal reactions associated with long-term use of different types of bonded lingual retainers . American Journal of Orthodontics , 86 , 112 – 118 . Google Scholar CrossRef Search ADS PubMed 10. Artun , J. , Spadafora , A.T. , Shapiro , P.A. , McNeill , R.W. and Chapko , M.K . ( 1987 ) Hygiene status associated with different types of bonded, orthodontic canine-to-canine retainers. A clinical trial . Journal of Clinical Periodontology , 14 , 89 – 94 . Google Scholar CrossRef Search ADS PubMed 11. Artun , J. , Spadafora , A.T. and Shapiro , P.A . ( 1997 ) A 3-year follow-up study of various types of orthodontic canine-to-canine retainers . European Journal of Orthodontics , 19 , 501 – 509 . Google Scholar CrossRef Search ADS PubMed 12. Rody , W.J. , Jr , Akhlaghi , H. , Akyalcin , S. , Wiltshire , W.A. , Wijegunasinghe , M. and Filho , G.N . ( 2011 ) Impact of orthodontic retainers on periodontal health status assessed by biomarkers in gingival crevicular fluid . The Angle Orthodontist , 81 , 1083 – 1089 . Google Scholar CrossRef Search ADS PubMed 13. Millett , D. , McDermott , P. , Field , D. , Erfia , I. , Doubleday , B. , Vandenheuvel , A. and Cronin , M . ( 2008 ) Dental and periodontal health with bonded or vacuum-formed retainers . The IADR 86th General Session . Metro Toronto Convention Centre, Toronto . 14. Rody , W.J. , Jr et al. ( 2016 ) Effects of different orthodontic retention protocols on the periodontal health of mandibular incisors . Orthodontics and Craniofacial Research , 19 , 198 – 208 . Google Scholar CrossRef Search ADS PubMed 15. Kaji , A. , Sekino , S. , Ito , H. and Numabe , Y . ( 2013 ) Influence of a mandibular fixed orthodontic retainer on periodontal health . Australian Orthodontic Journal , 29 , 76 – 85 . Google Scholar PubMed 16. Booth , F.A. , Edelman , J.M. and Proffit , W.R . ( 2008 ) Twenty-year follow-up of patients with permanently bonded mandibular canine-to-canine retainers . American Journal of Orthodontics and Dentofacial Orthopedics , 133 , 70 – 76 . Google Scholar CrossRef Search ADS PubMed 17. Cerny , R. , Cockrell , D. and Lloyd , D . ( 2010 ) Long-term results of permanent bonded retention . Journal of Clinical Orthodontics: JCO , 44 , 611 – 622 ; quiz 622. Google Scholar PubMed 18. Littlewood , S.J. , Millett , D.T. , Doubleday , B. , Bearn , D.R. and Worthington , H.V . ( 2016 ). Retention procedures for stabilising tooth position after treatment with orthodontic braces . Cochrane Database of Systematic Reviews , 1 , CD002283 . 10.1002/14651858.CD002283.pub4 19. Forde , K. , Storey , M. , Littlewood , S.J. , Scott , P. , Luther , F. and Kang , J . Bonded versus vacuum-formed retainers over 12 months: A prospective, multi-centre randomised controlled trial. Part 1: Post-Treatment Changes and Retainer Survival Outcomes . Submitted to European Journal of Orthodontics . 20. Greene , J.C. and Vermillion , J.R . ( 1964 ) The simplified oral hygiene index . Journal of the American Dental Association (1939) , 68 , 7 – 13 . Google Scholar CrossRef Search ADS PubMed 21. Löe , H . ( 1967 ) The gingival index, the plaque index and the retention index systems . Journal of Periodontology , 38 , Suppl:610 – Suppl:616 . Google Scholar CrossRef Search ADS 22. Silness , J. and Loe , H . ( 1964 ) Periodontal disease in pregnancy. II. Correlation between oral hygiene and periodontal condition . Acta Odontologica Scandinavica , 22 , 121 – 135 . Google Scholar CrossRef Search ADS PubMed 23. Zachrisson , S. and Zachrisson , B.U . ( 1972 ) Gingival condition associated with orthodontic treatment . The Angle Orthodontist , 42 , 26 – 34 . Google Scholar PubMed © The Author(s) 2017. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oup.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The European Journal of Orthodontics Oxford University Press

Bonded versus vacuum-formed retainers: a randomized controlled trial. Part 2: periodontal health outcomes after 12 months

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Abstract

Summary Background Retainer have the potential to compromise periodontal health. Objectives Evaluate the periodontal health implications of upper and lower bonded retainers (BRs) versus upper and lower vacuum-formed retainers (VFRs) over 12 months. Trial design Two-arm parallel group multicentre randomized controlled clinical trial. Methods Sixty consecutive patients completing upper and lower fixed appliance therapy and requiring retainers were recruited from three hospital orthodontic departments. They were randomly allocated to either upper and lower labial segment BRs (n = 30) or upper and lower full-arch VFRs (n = 30). Periodontal health was assessed using the plaque and gingival indices of Silness and Loe, and the calculus index of Greene and Vermillion. Data were collected at debond and placement of the retainers (T0), 3 months (T1), 6 months (T2), and 12 months (T3). A random sequence of treatment allocation was computer-generated and implemented by sealing in sequentially numbered opaque sealed envelopes independently prepared in advance. Patients, operators, and outcome could not be blinded due to the nature of the intervention. Results Thirty patients received BRs (median age 16 years, interquartile range [IQR] = 2, 50% female, 50% male) and 30 received VFRs (median age 17 years, IQR = 4, 60% female, 40% male). Gingival inflammation decreased from baseline for both types of retainer. There was significantly less plaque and calculus accumulation and better gingival health with VFRs than BRs over the evaluated 12 months. No serious harm was observed. Limitations It is not known how much the patients chose to wear their removable retainers. The results reported are after 1 year only. Conclusions After 1 year, BRs were associated with greater accumulation of plaque and calculus than VFRs and minimally worse gingival inflammation than VFRs, but this did not appear to produce any clinically significant, adverse periodontal health problems. Trial registration This trial was not registered. Funding There was no funding. Introduction Retainers are commonly fitted at the end of orthodontic treatment to reduce the chances of relapse. The choice of retainers is controversial, with a wide variety of different retainer choices reported across the world (1–5) Whether removable or fixed retainers are used, it is important that they do not compromise the patient’s periodontal health. Due to their continuous presence, mandibular bonded retainers (BRs) have the potential to promote calculus and plaque accumulation and food impaction. It has been suggested that BRs have the potential to adversely affect periodontal health (6). Despite the fact that there is an increasing trend to prescribe BRs in an attempt to seek long-term stability, there is limited high-quality evidence on the periodontal effects of mandibular fixed retention (7). It has therefore been suggested that they should not be used indiscriminately (8). In contrast, though removable retainers rely more on patients’ discipline and long-term compliance, it has been presumed that oral hygiene should not be complicated by their presence. Investigations into the periodontal effects of fixed and removable retainers to date have generally shown them to be compatible with periodontal health. Whilst the presence of a BR (whether bonded to just the canines, or to all teeth in the labial segment) has been shown to be associated with the occasional accumulation of plaque and calculus gingival to the wire, this has not been shown to cause any damage to the hard or soft tissues (7, 9–14). Further, though biochemical and bacteriological analysis has found a statistically significant difference in the characteristics of the gingival crevicular fluid between subjects with and without BRs, this has not been shown to translate to any significant clinical periodontal problems (15). Longer-term retrospective studies of the effects on periodontal health have similarly shown that, although accumulation of dental plaque and calculus tends to be greater in subjects with BRs, this has not led to a significant deterioration in any periodontal or dental health parameter more than 15 years after treatment (16, 17). In the 2016 Cochrane systematic review of orthodontic retention, the authors stressed the need for additional high-quality evidence in the form of well-constructed randomized controlled trials, including investigating the adverse effects on dental and periodontal health of retainers (18). The primary outcome measure of reducing post-treatment changes in irregularity of the labial segment and the secondary outcome measure of retainer survival are reported in paper 1 (19). This paper investigates the secondary outcome of periodontal health. This study tests the null hypothesis that there is no significant difference in periodontal health between patients with BRs and vacuum-formed retainers (VFRs) over a 12-month period. This was assessed in terms of plaque and calculus accumulation, and periodontal health. Subjects and methods Details of the participants, randomisation, and study design have been reported in paper 1 (19). Intervention At the end of active treatment, two calibrated operators placed either: upper and lower BRs, or upper and lower VFRs using standardized procedures and materials. All patients had been seen for supra-gingival debridement prior to removal of the fixed appliances. The BRs were prepared using 0.0195 in (0.45 mm) 3-stranded twistflex stainless steel wire (Wildcat; GAC International, Bohemia, New York, USA). The wire was shaped against the dental casts to lie passively against the lingual surfaces of the upper and lower incisors and canines. The wire was not contoured interproximally. A silicone positioning jig was prepared to aid placement of the retainer. This was molded to engage the wire and rest on the central incisors. The wire was bonded using a low-viscosity light-cured composite (Transbond™ LV; 3M Unitek, Monrovia, California, USA), following the separate application of etchant (37% phosphoric acid), and primer (Transbond™ XT adhesive primer; 3M Unitek). Care was taken not to leave any bonding substance in contact with the gingival tissues. The VFRs (Essix™ C+) were constructed using the same ‘Essix™ machine’ and cooled rapidly with Arctic spray (Ortho-Care). Retainers were trimmed to cover all fully erupted teeth and extend half way across the occlusal surface of the most distal molar. Patients were asked to wear the VFRs only at night. Oral hygiene instructions were given at the time of retainer insertion. All participants were advised to brush their teeth and to visit their dentist every 6 months for routine dental examinations, and to use a daily fluoride mouthrinse. Participants with BRs were instructed how to clean around their retainers with interdental brushes and/or superfloss. Both groups were advised to contact the department as soon as possible if they had any queries, concerns, or problems. Outcome measures Periodontal measurements were taken in the maxilla and mandible by a calibrated operator at removal of the fixed appliances and placement of the retainers, and at the subsequent review appointments. The buccal, lingual, mesial, and distal tooth surfaces of all erupted teeth in both arches were scored for all measured outcomes of this paper. One operator (MS) subsequently calculated the periodontal indices for the whole mouth, the maxilla, the mandible, the intercanine region for both arches, the maxillary intercanine, and the mandibular intercanine regions. These regions were selected to ensure all the areas potentially affected by the two different retainer groups were analysed. Periodontal health was assessed using calculus index (CI), gingival index (GI), and plaque index (PI). Calculus index Calculus was measured according to the Calculus component of the Simplified Oral Health Index (20) (Supplementary Table 1). The coronal extension of supra-gingival calculus and the presence of subgingival calculus was visually estimated and recorded for all erupted teeth in both arches. Gingival index Gingival health was assessed using the GI as described by Löe (21) (Supplementary Table 2). The teeth and gingivae were initially dried lightly and examined visually for signs of gingival inflammation; colour, loss of stippling, oedema, the presence of gingival exudate, and ulceration. As the decisive criterion in the differentiation between the GI scores was the various tendencies of the gingivae to bleed on gentle probing, a blunt Williams periodontal probe was then gently run along the gingival crevice and the gingivae observed for bleeding after 10–15 seconds. Plaque index Plaque accumulations were assessed using the PI (22) (Supplementary Table 3). The tooth was tested by running a probe across the surface at the entrance of the gingival crevice after the tooth has been dried. Disclosing fluid (Plaqsearch, Oraldent Ltd) was used for the recognition of the film of plaque. The solution was gently painted onto all surfaces of the maxillary and mandibular teeth, the patient was instructed to rinse their mouth and then spit out, and then the presence of plaque recorded. Following assessment, the disclosed plaque was demonstrated to the patient as a visual aid. Oral hygiene messages were reinforced and encouragement given as necessary. The teeth were then cleaned thoroughly with prophy polish and a rubber cup. Examination was standardized and started with the upper right second molar, continuing over the midline to the upper left second molar. The distal, buccal, and mesial aspects of the teeth on the right side were then examined followed by the mesial, buccal, and distal surfaces on the left side. When these surfaces had been assessed, the palatal surfaces of the maxillary teeth were assessed starting with the upper right second molar. Examination of the lower jaw started with the lower left second molar and was carried through to the lower right second molar. On the left, the sequence was the distal, buccal, and mesial surface and on those on the right side, mesial, buccal, and distal. All lingual surfaces were scored beginning with the lower left second molar. For each index, four areas of the tooth (buccal, lingual, mesial, and distal) were assessed to give the score for the area. The scores from these four areas were added together and then divided by 4 to calculate the score for the tooth, and then the scores for the teeth were grouped and averaged to designate the score for a group of teeth. All measurements were made at the following time points: T0  Debond T1 3 months post-debond T2 6 months post-debond T3  12 months post-debond Blinding It was not possible to blind the patient or clinician in this study. As the outcome assessor was one of the clinicians, the outcome assessment was also not blinded. Patients leaving the study or refusing treatment To reduce potential assessment bias, as much data as possible were collected from participants who dropped out of the study. If a subject failed to co-operate with the retention regime, the data were still collected and an ‘intention to treat’ analysis was carried out. Therefore, if a patient was allocated to receive VFRs but then subsequently failed to wear them as prescribed, they remained in that intervention group. Statistics Differences in periodontal and dental health indices between the two retainer types were assessed for normality using Shapiro–Wilks tests and Q–Q plots. As several of the measurements were not normally distributed, comparisons were made using Mann–Whitney U-tests, reporting median values and interquartile ranges (IQRs). Repeated-measure analysis of variance (repeated-measure ANOVA) was performed to assess the periodontal data over time, with retainer type and study centre as independent predictors to assess for possible confounding factors. All analyses were conducted at the 5% level of significance. Bland–Altman plots and intra-class correlation coefficients (ICCs) were used to assess intra- and inter-examiner reliability. The SPSS software package was used for data analysis (version 20; SPSS, Chicago, Illinois, USA) and statistical significance was set at the 5% level. Results Participant flow Paper 1 reports the participant flow and includes the CONSORT diagram for the study, as well as reporting the baseline data (19). There were 104 patients initially informed about the study, and 44 were excluded as they either declined to be involved or did not satisfy the inclusion criteria. The CONSORT flow diagram in paper 1 illustrates the passage of the 60 patients through the trial Periodontal indices The median periodontal indices for each retainer at debond, 3, 6, and 12 months are summarized in Table 1 and Supplementary Tables 4–6. Table 1. Medians and IQRs of periodontal measurements by retainer group. 3-3CI, intercanine calculus index; 3-3GI, intercanine gingival index; 3-3PI, intercanine plaque index; FMCI, full mouth calculus index; FMGI, full mouth gingival index; FMPI, full mouth plaque index; Mn3-3CI, mandibular intercanine calculus index; Mn3-3GI, mandibular intercanine gingival index; Mn3-3PI, mandibular intercanine plaque index; MnCI, mandibular calculus index; MnGI, mandibular gingival index; MnPI, mandibular plaque index; Mx3-3CI, maxillary intercanine calculus index; Mx3-3GI, maxillary intercanine gingival index; Mx3-3PI, maxillary intercanine plaque index; MxCI, maxillary calculus index; MxGI, maxillary gingival index; MxPI, maxillary plaque index. P = significance level, given as Asymp. Sig (two tailed) Mann–Whitney U-test. Site Debond 3 Months 6 Months 12 Months BR VFR P BR VFR P BR VFR P BR VFR P Plaque index FMPI 0.50 (0.33) 0.47 (0.33) 0.429 0.33 (0.24) 0.34 (0.37) 0.435 0.38 (0.39) 0.30 (0.35) 0.024* 0.45 (0.36) 0.33 (0.35) 0.044* MxPI 0.48 (0.31) 0.51 (0.31) 0.728 0.29 (0.37) 0.32 (0.29) 0.474 0.37 (0.33) 0.26 (0.38) 0.017* 0.46 (0.33) 0.27 (0.38) 0.048* MnPI 0.50 (0.33) 0.44 (0.34) 0.151 0.44 (0.29) 0.34 (0.37) 0.174 0.42 (0.42) 0.26 (0.32) 0.046* 0.49 (0.38) 0.43 (0.38) 0.056 3-3PI 0.49 (0.26) 0.48 (0.33) 0.953 0.47 (0.33) 0.31 (0.39) 0.032* 0.52 (0.42) 0.24 (0.34) 0.003* 0.54 (0.37) 0.35 (0.27) 0.008* Mx3-3PI 0.48 (0.27) 0.46 (0.26) 0.739 0.42 (0.38) 0.27 (0.37) 0.024* 0.46 (0.43) 0.21 (0.43) 0.005* 0.5 (0.34) 0.33 (0.29) 0.018* Mn3-3PI 0.50 (0.29) 0.42 (0.39) 0.314 0.52 (0.43) 0.29 (0.43) 0.049* 0.54 (0.55) 0.23 (0.32) 0.004* 0.61 (0.47) 0.46 (0.45) 0.026* Gingival index FMGI 0.98 (0.92) 1.22 (0.62) 0.579 0.64 (0.52) 0.64 (0.65) 0.398 0.59 (0.47) 0.40 (0.67) 0.323 0.74 (0.65) 0.42 (0.54) 0.135 MxGI 0.92 (1.14) 1.38 (0.54) 0.487 0.55 (0.56) 0.63 (0.73) 0.457 0.48 (0.43) 0.35 (0.69) 0.602 0.71 (0.77) 0.43 (0.70) 0.253 MnGI 1.00 (0.80) 1.15 (0.60) 0.824 0.62 (0.60) 0.61 (0.59) 0.326 0.65 (0.49) 0.39 (0.54) 0.194 0.78 (0.66) 0.41 (0.42) 0.050* 3-3GI 1.01 (0.83) 1.31 (0.55) 0.647 0.88 (0.83) 0.66 (0.68) 0.076 0.80 (0.86) 0.38 (0.86) 0.124 0.95 (0.89) 0.54 (0.71) 0.054 Mx3-3GI 0.94 (1.00) 1.36 (0.66) 0.359 0.69 (0.75) 0.58 (0.66) 0.030* 0.58 (0.84) 0.36 (1.03) 0.574 0.75 (1.04) 0.42 (0.75) 0.129 Mn3-3GI 1.06 (1.14) 1.13 (0.60) 0.959 0.90 (1.02) 0.67 (0.72) 0.168 0.92 (0.91) 0.46 (0.87) 0.025* 0.92 (0.96) 0.58 (0.71) 0.082 Calculus index FMCI 0.00 (0.04) 0.00 (0.00) 0.112 0.02 (0.05) 0.01 (0.04) 0.472 0.04 (0.06) 0.00 (0.04) 0.015* 0.06 (0.09) 0.02 (0.06) 0.048* MxCI 0.00 (0.00) 0.00 (0.00) 0.981 0.00 (0.00) 0.00 (0.00) 0.280 0.00 (0.00) 0.00 (0.00) 0.571 0.00 (0.00) 0.00 (0.00) 0.470 MnCI 0.00 (0.07) 0.00 (0.00) 0.104 0.04 (0.09) 0.02 (0.07) 0.568 0.05 (0.13) 0.00 (0.09) 0.016* 0.13 (0.19) 0.04 (0.13) 0.051 3-3CI 0.00 (0.08) 0.00 (0.00) 0.104 0.04 (0.10) 0.02 (0.08) 0.549 0.05 (0.15) 0.00 (0.09) 0.014* 0.14 (0.21) 0.04 (0.15) 0.051 Mx3-3CI 0.00 (0.00) 0.00 (0.00) 0.317 0.00 (0.00) 0.00 (0.00) 1.000 0.00 (0.00) 0.00 (0.00) 0.317 0.00 (0.00) 0.00 (0.00) 0.292 Mn3-3CI 0.00 (0.16) 0.00 (0.00) 0.054 0.08 (0.21) 0.04 (0.17) 0.549 0.15 (0.28) 0.00 (0.18) 0.014* 0.23 (0.43) 0.08 (0.29) 0.077 Site Debond 3 Months 6 Months 12 Months BR VFR P BR VFR P BR VFR P BR VFR P Plaque index FMPI 0.50 (0.33) 0.47 (0.33) 0.429 0.33 (0.24) 0.34 (0.37) 0.435 0.38 (0.39) 0.30 (0.35) 0.024* 0.45 (0.36) 0.33 (0.35) 0.044* MxPI 0.48 (0.31) 0.51 (0.31) 0.728 0.29 (0.37) 0.32 (0.29) 0.474 0.37 (0.33) 0.26 (0.38) 0.017* 0.46 (0.33) 0.27 (0.38) 0.048* MnPI 0.50 (0.33) 0.44 (0.34) 0.151 0.44 (0.29) 0.34 (0.37) 0.174 0.42 (0.42) 0.26 (0.32) 0.046* 0.49 (0.38) 0.43 (0.38) 0.056 3-3PI 0.49 (0.26) 0.48 (0.33) 0.953 0.47 (0.33) 0.31 (0.39) 0.032* 0.52 (0.42) 0.24 (0.34) 0.003* 0.54 (0.37) 0.35 (0.27) 0.008* Mx3-3PI 0.48 (0.27) 0.46 (0.26) 0.739 0.42 (0.38) 0.27 (0.37) 0.024* 0.46 (0.43) 0.21 (0.43) 0.005* 0.5 (0.34) 0.33 (0.29) 0.018* Mn3-3PI 0.50 (0.29) 0.42 (0.39) 0.314 0.52 (0.43) 0.29 (0.43) 0.049* 0.54 (0.55) 0.23 (0.32) 0.004* 0.61 (0.47) 0.46 (0.45) 0.026* Gingival index FMGI 0.98 (0.92) 1.22 (0.62) 0.579 0.64 (0.52) 0.64 (0.65) 0.398 0.59 (0.47) 0.40 (0.67) 0.323 0.74 (0.65) 0.42 (0.54) 0.135 MxGI 0.92 (1.14) 1.38 (0.54) 0.487 0.55 (0.56) 0.63 (0.73) 0.457 0.48 (0.43) 0.35 (0.69) 0.602 0.71 (0.77) 0.43 (0.70) 0.253 MnGI 1.00 (0.80) 1.15 (0.60) 0.824 0.62 (0.60) 0.61 (0.59) 0.326 0.65 (0.49) 0.39 (0.54) 0.194 0.78 (0.66) 0.41 (0.42) 0.050* 3-3GI 1.01 (0.83) 1.31 (0.55) 0.647 0.88 (0.83) 0.66 (0.68) 0.076 0.80 (0.86) 0.38 (0.86) 0.124 0.95 (0.89) 0.54 (0.71) 0.054 Mx3-3GI 0.94 (1.00) 1.36 (0.66) 0.359 0.69 (0.75) 0.58 (0.66) 0.030* 0.58 (0.84) 0.36 (1.03) 0.574 0.75 (1.04) 0.42 (0.75) 0.129 Mn3-3GI 1.06 (1.14) 1.13 (0.60) 0.959 0.90 (1.02) 0.67 (0.72) 0.168 0.92 (0.91) 0.46 (0.87) 0.025* 0.92 (0.96) 0.58 (0.71) 0.082 Calculus index FMCI 0.00 (0.04) 0.00 (0.00) 0.112 0.02 (0.05) 0.01 (0.04) 0.472 0.04 (0.06) 0.00 (0.04) 0.015* 0.06 (0.09) 0.02 (0.06) 0.048* MxCI 0.00 (0.00) 0.00 (0.00) 0.981 0.00 (0.00) 0.00 (0.00) 0.280 0.00 (0.00) 0.00 (0.00) 0.571 0.00 (0.00) 0.00 (0.00) 0.470 MnCI 0.00 (0.07) 0.00 (0.00) 0.104 0.04 (0.09) 0.02 (0.07) 0.568 0.05 (0.13) 0.00 (0.09) 0.016* 0.13 (0.19) 0.04 (0.13) 0.051 3-3CI 0.00 (0.08) 0.00 (0.00) 0.104 0.04 (0.10) 0.02 (0.08) 0.549 0.05 (0.15) 0.00 (0.09) 0.014* 0.14 (0.21) 0.04 (0.15) 0.051 Mx3-3CI 0.00 (0.00) 0.00 (0.00) 0.317 0.00 (0.00) 0.00 (0.00) 1.000 0.00 (0.00) 0.00 (0.00) 0.317 0.00 (0.00) 0.00 (0.00) 0.292 Mn3-3CI 0.00 (0.16) 0.00 (0.00) 0.054 0.08 (0.21) 0.04 (0.17) 0.549 0.15 (0.28) 0.00 (0.18) 0.014* 0.23 (0.43) 0.08 (0.29) 0.077 *denotes P < 0.05 View Large Table 1. Medians and IQRs of periodontal measurements by retainer group. 3-3CI, intercanine calculus index; 3-3GI, intercanine gingival index; 3-3PI, intercanine plaque index; FMCI, full mouth calculus index; FMGI, full mouth gingival index; FMPI, full mouth plaque index; Mn3-3CI, mandibular intercanine calculus index; Mn3-3GI, mandibular intercanine gingival index; Mn3-3PI, mandibular intercanine plaque index; MnCI, mandibular calculus index; MnGI, mandibular gingival index; MnPI, mandibular plaque index; Mx3-3CI, maxillary intercanine calculus index; Mx3-3GI, maxillary intercanine gingival index; Mx3-3PI, maxillary intercanine plaque index; MxCI, maxillary calculus index; MxGI, maxillary gingival index; MxPI, maxillary plaque index. P = significance level, given as Asymp. Sig (two tailed) Mann–Whitney U-test. Site Debond 3 Months 6 Months 12 Months BR VFR P BR VFR P BR VFR P BR VFR P Plaque index FMPI 0.50 (0.33) 0.47 (0.33) 0.429 0.33 (0.24) 0.34 (0.37) 0.435 0.38 (0.39) 0.30 (0.35) 0.024* 0.45 (0.36) 0.33 (0.35) 0.044* MxPI 0.48 (0.31) 0.51 (0.31) 0.728 0.29 (0.37) 0.32 (0.29) 0.474 0.37 (0.33) 0.26 (0.38) 0.017* 0.46 (0.33) 0.27 (0.38) 0.048* MnPI 0.50 (0.33) 0.44 (0.34) 0.151 0.44 (0.29) 0.34 (0.37) 0.174 0.42 (0.42) 0.26 (0.32) 0.046* 0.49 (0.38) 0.43 (0.38) 0.056 3-3PI 0.49 (0.26) 0.48 (0.33) 0.953 0.47 (0.33) 0.31 (0.39) 0.032* 0.52 (0.42) 0.24 (0.34) 0.003* 0.54 (0.37) 0.35 (0.27) 0.008* Mx3-3PI 0.48 (0.27) 0.46 (0.26) 0.739 0.42 (0.38) 0.27 (0.37) 0.024* 0.46 (0.43) 0.21 (0.43) 0.005* 0.5 (0.34) 0.33 (0.29) 0.018* Mn3-3PI 0.50 (0.29) 0.42 (0.39) 0.314 0.52 (0.43) 0.29 (0.43) 0.049* 0.54 (0.55) 0.23 (0.32) 0.004* 0.61 (0.47) 0.46 (0.45) 0.026* Gingival index FMGI 0.98 (0.92) 1.22 (0.62) 0.579 0.64 (0.52) 0.64 (0.65) 0.398 0.59 (0.47) 0.40 (0.67) 0.323 0.74 (0.65) 0.42 (0.54) 0.135 MxGI 0.92 (1.14) 1.38 (0.54) 0.487 0.55 (0.56) 0.63 (0.73) 0.457 0.48 (0.43) 0.35 (0.69) 0.602 0.71 (0.77) 0.43 (0.70) 0.253 MnGI 1.00 (0.80) 1.15 (0.60) 0.824 0.62 (0.60) 0.61 (0.59) 0.326 0.65 (0.49) 0.39 (0.54) 0.194 0.78 (0.66) 0.41 (0.42) 0.050* 3-3GI 1.01 (0.83) 1.31 (0.55) 0.647 0.88 (0.83) 0.66 (0.68) 0.076 0.80 (0.86) 0.38 (0.86) 0.124 0.95 (0.89) 0.54 (0.71) 0.054 Mx3-3GI 0.94 (1.00) 1.36 (0.66) 0.359 0.69 (0.75) 0.58 (0.66) 0.030* 0.58 (0.84) 0.36 (1.03) 0.574 0.75 (1.04) 0.42 (0.75) 0.129 Mn3-3GI 1.06 (1.14) 1.13 (0.60) 0.959 0.90 (1.02) 0.67 (0.72) 0.168 0.92 (0.91) 0.46 (0.87) 0.025* 0.92 (0.96) 0.58 (0.71) 0.082 Calculus index FMCI 0.00 (0.04) 0.00 (0.00) 0.112 0.02 (0.05) 0.01 (0.04) 0.472 0.04 (0.06) 0.00 (0.04) 0.015* 0.06 (0.09) 0.02 (0.06) 0.048* MxCI 0.00 (0.00) 0.00 (0.00) 0.981 0.00 (0.00) 0.00 (0.00) 0.280 0.00 (0.00) 0.00 (0.00) 0.571 0.00 (0.00) 0.00 (0.00) 0.470 MnCI 0.00 (0.07) 0.00 (0.00) 0.104 0.04 (0.09) 0.02 (0.07) 0.568 0.05 (0.13) 0.00 (0.09) 0.016* 0.13 (0.19) 0.04 (0.13) 0.051 3-3CI 0.00 (0.08) 0.00 (0.00) 0.104 0.04 (0.10) 0.02 (0.08) 0.549 0.05 (0.15) 0.00 (0.09) 0.014* 0.14 (0.21) 0.04 (0.15) 0.051 Mx3-3CI 0.00 (0.00) 0.00 (0.00) 0.317 0.00 (0.00) 0.00 (0.00) 1.000 0.00 (0.00) 0.00 (0.00) 0.317 0.00 (0.00) 0.00 (0.00) 0.292 Mn3-3CI 0.00 (0.16) 0.00 (0.00) 0.054 0.08 (0.21) 0.04 (0.17) 0.549 0.15 (0.28) 0.00 (0.18) 0.014* 0.23 (0.43) 0.08 (0.29) 0.077 Site Debond 3 Months 6 Months 12 Months BR VFR P BR VFR P BR VFR P BR VFR P Plaque index FMPI 0.50 (0.33) 0.47 (0.33) 0.429 0.33 (0.24) 0.34 (0.37) 0.435 0.38 (0.39) 0.30 (0.35) 0.024* 0.45 (0.36) 0.33 (0.35) 0.044* MxPI 0.48 (0.31) 0.51 (0.31) 0.728 0.29 (0.37) 0.32 (0.29) 0.474 0.37 (0.33) 0.26 (0.38) 0.017* 0.46 (0.33) 0.27 (0.38) 0.048* MnPI 0.50 (0.33) 0.44 (0.34) 0.151 0.44 (0.29) 0.34 (0.37) 0.174 0.42 (0.42) 0.26 (0.32) 0.046* 0.49 (0.38) 0.43 (0.38) 0.056 3-3PI 0.49 (0.26) 0.48 (0.33) 0.953 0.47 (0.33) 0.31 (0.39) 0.032* 0.52 (0.42) 0.24 (0.34) 0.003* 0.54 (0.37) 0.35 (0.27) 0.008* Mx3-3PI 0.48 (0.27) 0.46 (0.26) 0.739 0.42 (0.38) 0.27 (0.37) 0.024* 0.46 (0.43) 0.21 (0.43) 0.005* 0.5 (0.34) 0.33 (0.29) 0.018* Mn3-3PI 0.50 (0.29) 0.42 (0.39) 0.314 0.52 (0.43) 0.29 (0.43) 0.049* 0.54 (0.55) 0.23 (0.32) 0.004* 0.61 (0.47) 0.46 (0.45) 0.026* Gingival index FMGI 0.98 (0.92) 1.22 (0.62) 0.579 0.64 (0.52) 0.64 (0.65) 0.398 0.59 (0.47) 0.40 (0.67) 0.323 0.74 (0.65) 0.42 (0.54) 0.135 MxGI 0.92 (1.14) 1.38 (0.54) 0.487 0.55 (0.56) 0.63 (0.73) 0.457 0.48 (0.43) 0.35 (0.69) 0.602 0.71 (0.77) 0.43 (0.70) 0.253 MnGI 1.00 (0.80) 1.15 (0.60) 0.824 0.62 (0.60) 0.61 (0.59) 0.326 0.65 (0.49) 0.39 (0.54) 0.194 0.78 (0.66) 0.41 (0.42) 0.050* 3-3GI 1.01 (0.83) 1.31 (0.55) 0.647 0.88 (0.83) 0.66 (0.68) 0.076 0.80 (0.86) 0.38 (0.86) 0.124 0.95 (0.89) 0.54 (0.71) 0.054 Mx3-3GI 0.94 (1.00) 1.36 (0.66) 0.359 0.69 (0.75) 0.58 (0.66) 0.030* 0.58 (0.84) 0.36 (1.03) 0.574 0.75 (1.04) 0.42 (0.75) 0.129 Mn3-3GI 1.06 (1.14) 1.13 (0.60) 0.959 0.90 (1.02) 0.67 (0.72) 0.168 0.92 (0.91) 0.46 (0.87) 0.025* 0.92 (0.96) 0.58 (0.71) 0.082 Calculus index FMCI 0.00 (0.04) 0.00 (0.00) 0.112 0.02 (0.05) 0.01 (0.04) 0.472 0.04 (0.06) 0.00 (0.04) 0.015* 0.06 (0.09) 0.02 (0.06) 0.048* MxCI 0.00 (0.00) 0.00 (0.00) 0.981 0.00 (0.00) 0.00 (0.00) 0.280 0.00 (0.00) 0.00 (0.00) 0.571 0.00 (0.00) 0.00 (0.00) 0.470 MnCI 0.00 (0.07) 0.00 (0.00) 0.104 0.04 (0.09) 0.02 (0.07) 0.568 0.05 (0.13) 0.00 (0.09) 0.016* 0.13 (0.19) 0.04 (0.13) 0.051 3-3CI 0.00 (0.08) 0.00 (0.00) 0.104 0.04 (0.10) 0.02 (0.08) 0.549 0.05 (0.15) 0.00 (0.09) 0.014* 0.14 (0.21) 0.04 (0.15) 0.051 Mx3-3CI 0.00 (0.00) 0.00 (0.00) 0.317 0.00 (0.00) 0.00 (0.00) 1.000 0.00 (0.00) 0.00 (0.00) 0.317 0.00 (0.00) 0.00 (0.00) 0.292 Mn3-3CI 0.00 (0.16) 0.00 (0.00) 0.054 0.08 (0.21) 0.04 (0.17) 0.549 0.15 (0.28) 0.00 (0.18) 0.014* 0.23 (0.43) 0.08 (0.29) 0.077 *denotes P < 0.05 View Large Plaque index At baseline (debond), the median PI of both retainer groups ranged from 0.42 to 0.51 with no significant difference between the two groups (P > 0.05; Table 1). At 3 months, 6 months, and 12 months, there was a significantly higher PI in the intercanine region for BRs compared with VFRs. The change in PI with time is shown in Figure 1 and summarized in Supplementary Table 4. Figure 1. View largeDownload slide Changes in plaque index with time. A: full mouth plaque index. B: maxillary plaque index. C: mandibular plaque index. D: intercanine plaque index. E: maxillary intercanine plaque index. F: mandibular intercanine plaque index. Figure 1. View largeDownload slide Changes in plaque index with time. A: full mouth plaque index. B: maxillary plaque index. C: mandibular plaque index. D: intercanine plaque index. E: maxillary intercanine plaque index. F: mandibular intercanine plaque index. After 3 months, the PI showed a tendency to be lower than at baseline for all sites and for both retainer types with the exception of the mandibular intercanine region for BRs which showed an increase from baseline from 0.50 (IQR 0.29) to 0.52 (IQR 0.43; Figure 1 and Supplementary Table 4). The greater intercanine plaque scores with BRs compared to VFRs at 3 months was statistically significant (Supplementary Table 4). After 6 months, there was an increase in median plaque scores at all regions for both retainer types (Figure 1 and Supplementary Table 4). Despite any changes, all scores were in the region of 0.1–1.0 suggestive of scattered deposits of plaque only, so the clinical significance of these changes is questionable (21, 22). Gingival index At baseline, the median GI of both retainer groups ranged from 0.92 to 1.38. There was no statistical significance between the two groups (P > 0.05; Table 1 and Supplementary Table 5). The median GI after wearing the retainers for 3 months was lower than at baseline (debond) for all sites and for both retainer types (Figure 2 and Supplementary Table 5). The gingival health was worse with BRs after 3 months in the maxillary arch and after 6 months in the mandibular arch. Figure 2. View largeDownload slide Changes in gingival index with time. A: full mouth gingival index. B: maxillary gingival index. C: mandibular gingival index. D: intercanine gingival index. E: maxillary intercanine gingival index. F: mandibular intercanine gingival index. Figure 2. View largeDownload slide Changes in gingival index with time. A: full mouth gingival index. B: maxillary gingival index. C: mandibular gingival index. D: intercanine gingival index. E: maxillary intercanine gingival index. F: mandibular intercanine gingival index. At baseline, with the exception of the intercanine (1.01, IQR 0.83) and mandibular intercanine (1.06, IQR 1.14) regions, the median gingival scores for BRs were in the region of 0.1–1.0, suggestive of mild inflammation. At baseline all the median gingival scores for VFRs were in the region of 1.1–2.0 suggestive of moderate inflammation (Supplementary Table 5). However, by 6 months, and continuing until 12 months, all regions for both retainer groups had decreased to less than 1.0 suggestive of mild inflammation only (Supplementary Table 5). This may be clinically significant. Calculus index At baseline (debond), the median CI of both retainer groups was zero with no significant difference between regions between groups (Table 1 and Supplementary Table 6). After 3 months, the CI increased from baseline in the mandible for both retainer types, causing a concomitant increase in the calculus scores for the intercanine region and for the full mouth (Figure 3 and Supplementary Table 6). Calculus scores were higher for BRs than the VFRs at 3 months though the difference was not statistically significant (Supplementary Table 6). The increase in calculus score from baseline to 3 months was statistically significant (P < 0.05) for VFRs (Supplementary Table 6). Figure 3. View largeDownload slide Changes in calculus index with time. A: full mouth calculus index. B: maxillary calculus index. C: mandibular calculus index. D: intercanine calculus index. E: maxillary intercanine calculus index. F: mandibular intercanine calculus index. Figure 3. View largeDownload slide Changes in calculus index with time. A: full mouth calculus index. B: maxillary calculus index. C: mandibular calculus index. D: intercanine calculus index. E: maxillary intercanine calculus index. F: mandibular intercanine calculus index. Between 3 and 6 months, the median CI reverted back to the baseline measurement of zero at all sites for VFRs; however, the median calculus scores for BRs continued to increase in the mandibular intercanine region. (Figure 3 and Supplementary Table 6). Accounting for confounding factors in periodontal indices The differences for the three outcome measures (PI, GI, and CI) between BRs and VFRs with time were re-examined, adjusting for retainer type, study centre, and time to help ensure that any significant differences observed were due to the type of retainer fitted, and not to an identified confounding factor. A 12-month repeated-measure ANOVA for periodontal indices was used. Retainer type The results showed that, other than for the maxillary PI (P = 0.062), there was a statistically significant (P < 0.05) greater plaque accumulation with BRs than VFRs (Table 2). Table 2. Effect of retainer type on plaque, gingival, and calculus indices over 12 months. X, mean difference. P: Adjustment for multiple comparisons: Bonferroni. Index Site Retainer (BR to VFR) X 95% CI P Plaque index FMPI 0.11 0.01, 0.20 0.026* MxPI 0.09 −0.01, 0.01 0.062 MnPI 0.13 0.03, 0.23 0.016* 3-3PI 0.17 0.06, 0.28 0.004* Mx3-3PI 0.17 0.06, 0.28 0.004* Mn3-3PI 0.19 0.06, 0.32 0.006* Gingival index FMGI 0.14 −0.03, 0.31 0.101 MxGI 0.13 −0.04, 0.30 0.126 MnGI 0.15 −0.04, 0.34 0.112 3-3GI 0.25 0.04, 0.45 0.018* Mx3-3GI 0.22 0.03, 0.41 0.027* Mn3-3GI 0.25 0.02, 0.48 0.035* Calculus index FMCI 0.02 −0.004, 0.05 0.095 MxCI 0.003 −0.01, 0.01 0.579 MnCI 0.05 −0.004, 0.09 0.070 3-3 CI 0.05 0.002, 0.102 0.041* Mx3-3CI 0.005 −0.01, 0.02 0.549 Mn3-3CI 0.10 0.003, 0.19 0.043* Index Site Retainer (BR to VFR) X 95% CI P Plaque index FMPI 0.11 0.01, 0.20 0.026* MxPI 0.09 −0.01, 0.01 0.062 MnPI 0.13 0.03, 0.23 0.016* 3-3PI 0.17 0.06, 0.28 0.004* Mx3-3PI 0.17 0.06, 0.28 0.004* Mn3-3PI 0.19 0.06, 0.32 0.006* Gingival index FMGI 0.14 −0.03, 0.31 0.101 MxGI 0.13 −0.04, 0.30 0.126 MnGI 0.15 −0.04, 0.34 0.112 3-3GI 0.25 0.04, 0.45 0.018* Mx3-3GI 0.22 0.03, 0.41 0.027* Mn3-3GI 0.25 0.02, 0.48 0.035* Calculus index FMCI 0.02 −0.004, 0.05 0.095 MxCI 0.003 −0.01, 0.01 0.579 MnCI 0.05 −0.004, 0.09 0.070 3-3 CI 0.05 0.002, 0.102 0.041* Mx3-3CI 0.005 −0.01, 0.02 0.549 Mn3-3CI 0.10 0.003, 0.19 0.043* View Large Table 2. Effect of retainer type on plaque, gingival, and calculus indices over 12 months. X, mean difference. P: Adjustment for multiple comparisons: Bonferroni. Index Site Retainer (BR to VFR) X 95% CI P Plaque index FMPI 0.11 0.01, 0.20 0.026* MxPI 0.09 −0.01, 0.01 0.062 MnPI 0.13 0.03, 0.23 0.016* 3-3PI 0.17 0.06, 0.28 0.004* Mx3-3PI 0.17 0.06, 0.28 0.004* Mn3-3PI 0.19 0.06, 0.32 0.006* Gingival index FMGI 0.14 −0.03, 0.31 0.101 MxGI 0.13 −0.04, 0.30 0.126 MnGI 0.15 −0.04, 0.34 0.112 3-3GI 0.25 0.04, 0.45 0.018* Mx3-3GI 0.22 0.03, 0.41 0.027* Mn3-3GI 0.25 0.02, 0.48 0.035* Calculus index FMCI 0.02 −0.004, 0.05 0.095 MxCI 0.003 −0.01, 0.01 0.579 MnCI 0.05 −0.004, 0.09 0.070 3-3 CI 0.05 0.002, 0.102 0.041* Mx3-3CI 0.005 −0.01, 0.02 0.549 Mn3-3CI 0.10 0.003, 0.19 0.043* Index Site Retainer (BR to VFR) X 95% CI P Plaque index FMPI 0.11 0.01, 0.20 0.026* MxPI 0.09 −0.01, 0.01 0.062 MnPI 0.13 0.03, 0.23 0.016* 3-3PI 0.17 0.06, 0.28 0.004* Mx3-3PI 0.17 0.06, 0.28 0.004* Mn3-3PI 0.19 0.06, 0.32 0.006* Gingival index FMGI 0.14 −0.03, 0.31 0.101 MxGI 0.13 −0.04, 0.30 0.126 MnGI 0.15 −0.04, 0.34 0.112 3-3GI 0.25 0.04, 0.45 0.018* Mx3-3GI 0.22 0.03, 0.41 0.027* Mn3-3GI 0.25 0.02, 0.48 0.035* Calculus index FMCI 0.02 −0.004, 0.05 0.095 MxCI 0.003 −0.01, 0.01 0.579 MnCI 0.05 −0.004, 0.09 0.070 3-3 CI 0.05 0.002, 0.102 0.041* Mx3-3CI 0.005 −0.01, 0.02 0.549 Mn3-3CI 0.10 0.003, 0.19 0.043* View Large However, statistically significant differences in gingival health between the two retainer groups were only detected for the intercanine (P = 0.018), maxillary intercanine (P = 0.027), and mandibular intercanine (P = 0.035) regions, with poorer gingival health associated with BR than VFRs (Table 2). Statistically significant differences in calculus accumulation between BRs and VFRs were only detected in the intercanine (P = 0.041) and mandibular intercanine region (P = 0.043) where more extensive deposits were associated with the presence of BRs (Table 2). Time A statistically significant decrease in plaque accumulation was noted in the first 3 months of retainer placement. The differences noted in gingival health and calculus accumulation were found to be statistically significant from debond and retainer placement to each successive review appointment. However, only the increases in calculus accumulation were found to be statistically significant from 3 months to 1 year (Supplementary Table 7). Study centre The results showed that the study centre the patients were recruited from and assessed at had a statistically significant (P < 0.05) effect on the gingival scores observed, with patients from Bradford having significantly poorer gingival health than those recruited from Leeds. Participants recruited from York had statistically significantly better maxillary plaque scores than those from Leeds (P = 0.036). No significant differences between study centres were observed for calculus accumulation. Reproducibility of the method Intra-examiner reliability for measurement of periodontal indices A random sample of 10 patients was re-assessed to determine intra-examiner reliability. Due to the dynamic nature of the periodontal status, measurements were re-recorded immediately after the first measurements had been made in an attempt to most accurately record the periodontal condition at that time. Each periodontal measurement was tested using a combination of Shapiro–Wilks tests and Q–Q plots. Several of the measurements were not normally distributed and so median values and IQRs were quoted. Intra-examiner reliability was assessed using the ICC and Bland–Altman plots. All of the 18 measurements demonstrated excellent reliability (ICC > 0.9 = excellent, > 0.8 = very good, > 0.7 = good, > 0.6 = fair). Inter-examiner reliability for measurement of periodontal indices A separate random sample of 10 patients was assessed by one operator and then immediately re-assessed by the second operator to determine inter-examiner reliability. Each periodontal measurement was tested using a combination of Shapiro–Wilks tests and Q–Q plots, and, as several of the measurements were not normally distributed, median values and IQRs were quoted. The ICC s demonstrated very good or excellent reliability and systematic errors assessed with Bland–Altman plots included no clinically important discrepancies. This demonstrated that the method of recording the data had a high level of reliability and any method errors were acceptable. Harm No serious harm was observed. Discussion Key findings The presence of BRs appears to increase the levels of plaque, gingival inflammation, and calculus, when compared to patients fitted with VFRs. However, after 12 months, the indices recorded do not suggest clinically significant implications for periodontal health. It is not possible to predict the effects of periodontal health in the long-term from this trial. At the end of fixed appliance treatment, there were generalized but minimal deposits of plaque, minimal calculus deposits in the mandibular intercanine region, and mild-to-moderate gingival inflammation. Any differences in baseline periodontal scores between the BR and VFR groups were small and not significant, and suggest that the oral hygiene at the end of the active orthodontic treatment had been acceptable in both groups. An immediate reduction in plaque accumulation was noted in the first 3 months, with both groups demonstrating a general improvement in OH, with the exception of the mandibular intercanine region in the BR group, which showed greater deposits at 3 months compared to baseline. This improvement, however, was only statistically significant for the VFR group. Whilst this improvement continued in all regions for the VFRs, the plaque scores tended to worsen with BRs. By 12 months, plaque scores had worsened for both groups. This suggests an initial improvement in oral hygiene after removal of the fixed appliances, but, with time, all patients’ periodontal measurements worsened. This highlights the importance of repeated motivation, and reinforcing good oral hygiene instruction at least on a 6-monthly basis to avoid further deterioration in oral hygiene and consequent periodontal problems. Similarly, gingival health significantly improved in both groups following removal of the fixed appliances and placement of retainers. This improvement continued to 6 months, albeit to a lesser extent in the BR group. By 12 months, however, gingival health had deteriorated in the BR group resulting in a statistically significant difference in mandibular intercanine gingival scores between the retainer groups. This is most likely explained as a reaction to the presence of a continuous band of plaque in association with the BR. Deposits of calculus increased in both groups from debond to 3 months. By 6 months, calculus deposits were notably absent in the VFR group but continued to worsen in the BR group. By 12 months, calculus deposits had continued to worsen in the BR group and minimal deposits had reappeared in the VFR group. These findings are after 1 year of retention, so it is not possible to predict whether these increases in plaque and calculus could lead to long-term periodontal problems. Comparison to previous work In contrast to previous studies which limited their data collection to certain teeth or just the lower labial segment (7, 9–15), all erupted teeth were assessed for the various periodontal outcome measures. This is because VFRs usually cover the entire dentition, not just the labial segment, and we did not want to make assumptions that VFRs had no impact on the periodontal health. The findings of this current study are in agreement with the findings of previous studies, as they suggest that placement of BRs promotes plaque and calculus accumulation. Millett et al., reported less gingival bleeding and consequently better gingival health 1 year after removal of the fixed appliances than at baseline for both BRs and VFRs, but with a greater improvement and overall better gingival health with VFRs (13). Rody et al. reported an increase in plaque and gingivitis in patients with fixed retainers compared to removable retainers (14). They also noted an increase in biochemical markers for periodontal disease in the gingival crevicular fluid in patients with BRs (particularly those patients with fixed retainers bonded to all the anterior teeth, like in this study). As in this study, they concluded there was no evidence of severe periodontal disease associated with the BRs, but once again the follow-up was reasonably short (6 months), so the long-term implications are still unknown. Booth et al. also reported that, despite finding statistically significant greater plaque deposits and worse gingival health associated with the BR than the VFR, especially in the intercanine region, at review appointments, there was not a statistically significant difference in calculus accumulation or a demonstrable negative effect on periodontal health between retainer types (16). Similarly, in their cross-sectional study of patients who had been in retention for about 15 years, Cerny et al. found no clinically significant differences in the periodontal health of patients who had worn BRs compared with those fitted with removable retainers. More patients with removable retainers than BRs were reported to have good or very good oral hygiene (80%, compared to 40% of the BR group) and gingival health (95%, compared to 80% of the BR group). There were no ratings of poor periodontal health in either group (17). These results also support the findings of Rody et al. in an earlier study who found no difference in clinical periodontal health, despite slightly increased plaque accumulation, in subjects with BRs compared with night-time wear of removable Hawley, or no retainers (12). Artun et al. found similar results from their series of articles investigating the dental and periodontal health effects of various fixed and removable retainers up to 4 years. Whilst they confirmed the tendency for plaque and calculus to accumulate along the retainer wires, regardless of the type of wire used, and the tendency for these accumulations to increase with time, this did not seem to prevent satisfactory oral hygiene along the gingival margin or impact negatively on periodontal or dental health. Similar to this current study, Artun et al. also reported less gingival bleeding (4 months to 4 years), than at debond, indicative of an improvement in gingival health since removal of the fixed appliances (9–11). This reinforces the observations of Zachrisson et al. of a rapid improvement in gingival health during the first month following removal of fixed appliances despite the presence of retainers (23). Heier et al. also reported a generalized improvement in gingival health in both fixed and removable retainer groups at the review appointments following removal of fixed appliances and consequent improved access for oral hygiene. However, as with this trial, slightly more plaque and calculus was detected lingually with BRs. The authors suggested that, providing motivation and oral hygiene instruction is reinforced every 6 months, periodontal health should not be compromised by the presence of retainers (7). Kaji et al. compared the periodontal status of subjects who had BRs fitted at least 1 month prior to the start of the trial, allowing the gingival inflammation associated with the presence of fixed appliances time to resolve, with that of subjects without retainers over an 8-week period (15). They did, however, find a statistically significant alteration in the characteristics of the gingival crevicular fluid, suggestive of sub-clinical inflammation in the presence of a BR (15). Limitations In this study, it was not possible to blind the operators and patients to the treatment allocations. The assessor was not blinded, as they were one of the clinicians. Although the minimum sample size was achieved, the power calculation was based on the primary outcome measure of the study; the efficacy of each retainer group in minimising the 1 year post-orthodontic treatment change in arch alignment as measured with Little’s Irregularity Index (19). As such, it is possible that the study is underpowered with respect to the outcome measures investigated in this study, increasing the chance of making a Type II error. Furthermore, the effect of individual variation is also more pronounced within a small sample and this may have affected the distribution of certain periodontal variables necessitating non-parametric statistical analyses. A greater variation of statistical tests could have been applied with a larger sample, and more significant intergroup differences may have been found. As a result, the findings at this early stage of the trial indicate some trends, but the statistical weighting should be interpreted with caution. It was not possible to control for any professional cleaning carried out by the patients’ own dentists in-between review appointments. This could potentially lead to lower debris scores independent of the type of retainer used. This study only reports the periodontal health of patients in the first year of retention and further research is required to determine if these findings continue long-term. Generalisability When considering the generalisability of these findings, it is important to note the experience of the operator, the design of the retainer, technique of placement, and materials used in this study. Implications for clinical practice While this study indicates no clinically significant changes in periodontal health, the changes in periodontal indices indicate that BRs have the potential to increase plaque retention, increase gingival inflammation and increased calculus build-up, when compared to VFRs. Clinicians should therefore consider carefully whether patients are able to maintain good oral hygiene and regular dental care before fitting BRs, as they may have the potential to compromise periodontal health more than VFRs. It is important patients fitted with BRs are fully aware of these risks and given clear advice about how to maintain good oral health. Conclusions After 12 months of retention with upper and lower BRs or upper and lower VFRs, BRs were associated with a greater accumulation of plaque and calculus and gingival inflammation compared to VFRs. However, after 1 year this did not appear to adversely affect the overall periodontal health to a clinically significant degree. Supplementary material Supplemental data are available at the European Journal of Orthodontics online. Funding There was no funding to be declared. Conflict of interest None to declare. Acknowledgements We would like to acknowledge and thank Nadia Ahmed for her assistance during the early stages of the trial, and each of the laboratory technicians, reception staff, referring clinicians, and each patient and parent at the three hospitals. References 1. Singh , P. , Grammati , S. and Kirschen , R . 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For permissions, please email: journals.permissions@oup.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

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The European Journal of OrthodonticsOxford University Press

Published: Aug 1, 2018

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