Open versus closed surgical exposure for permanent impacted canines: a systematic review and meta-analyses

Open versus closed surgical exposure for permanent impacted canines: a systematic review and... Summary Background Permanent canines are amongst the teeth most affected by impaction and ectopic eruption. Although impacted canines are often subjected to surgical exposure and alignment with either the open or the closed technique for many decades, their treatment effects have not yet been systematically asssessed. Objectives The aim of this systematic review was to critically assess whether significant differences exist in the outcomes of the open or closed surgical exposure of impacted canines. Search methods An unrestricted electronic search of nine databases from inception to December 2016 was performed. Selection criteria methods Included were randomized or prospective non-randomized studies comparing open versus closed exposure of impacted canines in human patients. Data collection and analysis After duplicate study selection, data extraction, and risk of bias assessment according to the Cochrane guidelines, random-effects meta-analyses of mean differences (MDs) and odds ratios (ORs), including their 95 per cent confidence intervals (CIs) were performed, followed by subgroup and sensitivity analyses. Results A total of eight unique studies and a total of 433 (30.1% male/59.9% female) patients were included, with an average age of 15.2 years and a total of 453 impacted canines (48.6% and 51.4% in the open and closed exposure, respectively). Open exposure of impacted canines was associated with reduced duration of canine alignment (two studies; MD = –2.14 months; 95% CI = –4.23 to –0.05 months; P < 0.05; moderate heterogeneity and moderate quality) and lower odds of tooth ankylosis (one study; OR = 0.15; 95% CI = 0.03–0.83; P < 0.05; low quality) compared to closed exposure; both findings being independent of canine localization. However, initial alignment of palatally impacted canines took overall significantly longer than labially impacted canines (8.87 versus 4.17 months). Conclusions Based on existing evidence, open surgical exposure seems to be superior in treatment duration and ankylosis risk over the closed technique. Due to the limited number of small included trials, further research is needed for robust clinical recommendations. Registration PROSPERO (CRD42016051916). Introduction Rationale The permanent canine is, after the third molars, the tooth with the highest incidence of impaction with prevalence ranging between 0.3 and 2.4 per cent (1, 2). Canine impaction shows a predilection for the palatal over the labial side (3) and has higher prevalence in female patients (2). Canine impaction can be associated with functional or esthetic impairment, while impacted canines might also lead to root resorption of adjacent permanent teeth (4). Therefore, a definitive diagnosis of an impacted canine is often directly followed by an attempt to tackle the impaction, if needed. Common approaches for the management of impacted canines include early interceptive measures (5, 6) or late intervention, including extraction (7), autotransplantation (8), and surgical exposure of the canine’s crown with a subsequent orthodontic alignment of the tooth (9). Given the high aesthetic and functional value of canines, the combined surgical/orthodontic approach to relocate the impacted canine in its proper place in the dental arch is considered often, with two major surgical techniques: the open and the closed technique. The open technique includes the surgical exposure of the crown by either complete removal of bone and soft tissue directly overlying the impacted canine (10) or the use of an apically repositioned gingival flap (11). Afterwards, surgical pack might be used to cover the wound, while the canine can be either left to spontaneously erupt or an orthodontic attachment is directly bonded on the canine in order to directly apply traction. The contemporary closed technique on the other side involves raising a full mucoperiostal flap, exposing the canine crown, and bonding an attachment on it (12). Afterwards, the flap is repositioned and orthodontic traction is applied after initial healing, until the canine erupts in the oral cavity and is subsequently guided to the dental arch. Although, both approaches are versatile, can be adapted to each case (13), and have been used extensively for many years, reports about their comparative performance are mixed. Several studies have evaluated various aspects of their performance, including surgical duration and postoperative recovery time (14), postoperative pain (15), periodontal health (16, 17), and esthetic appearance (18). Although, the subject has been heavily debated with active proponents for both approaches (6, 19), the cumulative evidence regarding their overall comparative performance in terms of clinically relevant outcomes has not yet been objectively assessed according to the principles of evidence-based orthodontics. Two systematic reviews on the subject have been performed, but the first (and older one) did not find any eligible trials to include (20), while the second only focused on the periodontal health of impacted canines with no clinically relevant differences between the open and closed technique (17). Objectives The aim of this systematic review was to critically evaluate existing clinical evidence and assess whether considerable differences in the primary outcome of treatment duration and other secondary treatment outcomes exist between impacted canines treated surgically-orthodontically with an open or closed exposure technique. To this end, the present systematic review attempts to answer the following question: When compared with a closed exposure technique, what are the comparative effectiveness and harms of the open exposure technique in the management of impacted canines in patients of any age or sex? Materials and methods Protocol and registration The review’s protocol was made a priori following the PRISMA-P statement (21), registered in PROSPERO (CRD42016051916), and all post hoc changes were appropriately noted. This systematic review was conducted and reported according to Cochrane Handbook (22) and PRISMA statement (23), respectively. Eligibility criteria According to the Participants Intervention Comparison Outcome Study design schema (PICOS), we included randomized and prospective controlled non-randomized trials (S) on human patients of any age or sex with at least one impacted canine (P) comparing an open (I) versus a closed surgical approach (C) for the exposure and orthodontic management of impacted canines. The primary outcome (O) of this systematic review was treatment duration, of either the initial alignment of the impacted canine to the occlusion or the complete fixed appliance phase, extracted from the patient records in months. The secondary outcomes focused on clinical relevance to the patient or the orthodontist and included the need for canine re-exposure, adverse effects to the canine (including ankylosis and discoloration), and patient-reported outcomes (including overall satisfaction, pain, and disruption of the function). Excluded were non-clinical studies, retrospective studies, case reports, animal studies, and studies that did not directly compare both approaches. Information sources and literature search Nine electronic databases were systematically searched by one author (SNP) without any limitations from inception up to December 12th, 2016 (Supplementary Appendix 1): MEDLINE (searched via PubMed), Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, Cochrane Database of Abstracts of Reviews of Effects, Embase, Virtual Health Library, Scopus, Web of Knowledge, and ClinicalTrials.gov. Additionally, five sources (Google Scholar, International Standard Registered Clinical/soCial sTudy Number Registry, Directory of Open Access Journals, Digital Dissertations, and metaRegister of Controlled Trials) and the reference/citation lists of included trials were manually searched for any additional trials. Authors of included trials were contacted for additional missed or ongoing trials. No limitations concerning publication language, publication year, or publication status were applied. Study selection The eligibility of identified studies was checked sequentially from their title, abstract, and full-text against the eligibility criteria by one author (CC) and were subsequently checked independently by a second one (SNP), with conflicts resolved by a third author (TE). Data collection and data items Study characteristics and numerical data were extracted from included trials independently by two authors (CC, SNP) using pre-defined and piloted extraction forms including: (i) study characteristics (design, clinical setting, country), (ii) patient characteristics (age, sex, number and localization of impacted canines, extraction of any teeth as part of the treatment plan), (iii) any orthodontic co-interventions, and (iv) study outcome measures. Piloting of the forms was performed during the protocol stage until over 90 per cent agreement was reached. Missing or unclear information was requested by the trials’ authors and re-analyzed firsthand, whenever possible. Risk of bias in individual trials The risk of bias of included RCTs was assessed using Cochrane’s risk of bias tool (22); the risk of bias of included prospective non-randomized studies (NRS) was assessed using the Downs and Black checklist (24) with appropriate modifications. A main risk of bias assessment was included in the systematic review pertaining to each trial’s primary outcome. Data synthesis Meta-analysis was performed if similar interventions and control groups were compared and similar outcomes were measured. As outcome of canine exposure and alignment is bound to be affected by patient age (25), localization of the canine (26, 27), the orthodontic mechanotherapy (27), and biologic variation in tooth movement (28), a random-effects model was judged as clinically and statistically appropriate (29). The novel random-effects model proposed by Paule and Mandel was preferred a priori over the more widely known DerSimonian and Laird (30) method to estimate all pooled data, according to empirical evidence (31). Mean Differences (MD) for continuous outcomes and Odds Ratios (OR) for binary outcomes and their corresponding 95 per cent Confidence Intervals (CI) were calculated. Statistically significant results of binary meta-analyses were translated clinically using the Number Needed to Treat (NNT). For included trials with clustered data, we tried to contact the trial’s authors to ask for adjusted outcomes or raw data. The extent and impact of between-study heterogeneity was assessed by inspecting the forest plots and calculating the tau2 and the I2, respectively; I2 defines the proportion of total variability in the result explained by heterogeneity, and not chance (32). We roughly categorized heterogeneity as low moderate, and high to I2 values of 25, 50, and 75 per cent (32), although we also judged the heterogeneity’s localization on the forest plot. Additionally, the 95 per cent CIs around tau2 and I2 were calculated (33) to quantify our uncertainty around these estimates. Ninety-five per cent predictive intervals were calculated for meta-analyses of ≥3 trials to incorporate existing heterogeneity and provide a range of possible effects for a future clinical setting (34). All analyses were conducted in Stata SE version 14.2 (StataCorp LP, College Station, Texas, USA) by one author (SNP). A two side P ≤ 0.05 was considered significant for hypothesis-testing, except for P ≤ 0.10 used for tests of between-studies or between-subgroups heterogeneity (35). Quality of evidence The overall quality of clinical recommendations for each of the main outcomes was rated using the Grades of Recommendations, Assessment, Development, and Evaluation (GRADE) approach, as very low, low, moderate, or high (36). The minimal clinical important (37), large, and very large effects were defined as half, one, and two standard deviations (using the average standard deviation for an outcome across the control groups of included trials), respectively. Arbitrary cut-offs of 1.5, 2.5, and 4.3 were adopted for the OR. The produced forest plots were augmented with contours denoting the magnitude of the observed effects (38). Additional analyses and sensitivity analyses Reporting biases (including the possibility of publication bias) were planned in the protocol to be assessed, but could not be performed due to the limited number of included trials. Robustness of the meta-analyses was planned a priori to be checked with sensitivity analyses based on (i) exclusion of trials with high risk of bias, (ii) improvement of the GRADE classification, (iii) exclusion of non-randomized trials, and (iv) exclusion of trials with reporting biases. Results Study selection A total of 476 and 9 papers were identified through electronic and manual searches, respectively (Figure 1). After removal of duplicates and initial screening, 37 papers were assessed using the eligibility criteria, and 11 papers were included in this systematic review (Figure 1; Supplementary Appendix 2). In two instances, multiple publications pertaining to the same trial were grouped together; thus, a total of 8 unique trials from 11 publications were finally included in the systematic review. Several authors were contacted for clarifications or additional data (Supplementary Appendix 3) with only limited success. In one instance of a trial including both impacted canines and impacted incisors (14), the authors were contacted and graciously provided the raw study data that enabled the exclusion of impacted incisors and the inclusion of the study. Figure 1. View largeDownload slide Flowdiagram for the identification and selection of studies in this systematic review. Figure 1. View largeDownload slide Flowdiagram for the identification and selection of studies in this systematic review. Study characteristics The characteristics of the included trials can be seen in Table 1. Of the eight included trials, four (50%) were randomized and four (50%) were prospective non-randomized trials, conducted in eight different countries. They included a total of 433 patients (mean 54 patients per trial; range 24–96) with male patients being the 30.1 per cent (52/173 patients among the three trials that reported patient sex), and with an average age of 15.2 years. A total of 453 impacted canines were included in the identified trials, 220 (48.6%) of which were treated with an open exposure and 233 (51.4%) with a closed exposure (Table 1). Table 1. Characteristics of the included trials. AA  Trial  Design; setting  Patients (M/F); mean age; malocclusion; uni/ bilateral IC  No of ICs  Jaw/side  Exs (prim/perm)  Ortho measures; timing  Eligible outcome  CoI  1  Chaushu 2005  pNRS; university; Israel  OT: 30 (6/24); 14.8 years; uni/bil ICs CT: 30 (13/17); 16 years; uni/bil ICs  OT: 32 CT: 25  OT: Max/LAB-PAL CT: Max/LAB-PAL  —  OT: Ortho-T; 1 week post-OP (OT) CT: Ortho-T; post-OP  SurgDur; Pain, oral function, general activity and other symptoms  NR  2  Gharaibeh 2008  RCT; university; Jordan  OT: 16 (2/14); 17.3 years; uni ICs CT: 16 (2/14); 17.6 years; uni ICs  OT: 16 CT: 16  OT: Max/PAL CT: Max/PAL  —  OT/CT: Ortho-T; 1 week post-OP (OT/CT)  SurgDur; pain  NR  3  Koutzoglou 2013  pNRS; private practice; Greece  OT: 46 (NR); NR years; uni/bil ICs CT: 50 (NR); NR years; uni/bil ICs  OT: 57 CT: 62  OT: Max-Mnd/LAB-PAL CT: Max-Mnd/LAB-PAL  OT: 47 pc CT: 47 pc  SOa OT/CT: Ortho-T; 1 week post-OP  Ankylosis; fibrous connective tissue  None  4  londhe 2014  RCT; university; India  OT: 16 (NR); NR years, uni/bil ICs CT: 15 (NR); NR years, uni/bil ICs  OT: 16 CT: 15  OT: Max/LAB CT: Max/LAB  —  SO OT/CT: Ortho-T; post OP  SurgDur; pain; recovery period; Tx duration; mobility; vitality; swelling; root integrity  None  5  Marzouk 1997  pNRS; hospital; Saudia Arabia  OT: 33 (NR); NR, NR years, uni/bil ICs CT: 33 (NR); NR, NR years, uni ICs  OT: 33 CT: 33  OT: Max/LAB-PAL CT: Max/LAB-PAL  Max 4s (in some cases)  SO; OT: Ortho-T; 1 week post-OP (OT) CT: Ortho-T; post-OP  Tx duration; attachment rebond need  NR  6  Parkin 2012; 2013; 2015  RCT; university; England  OT: 40 (13/27); 14.3 years; uni ICs CT: 41 (16/25); 14.1 years; uni ICs  OT: 40 CT: 41  OT: Max/PAL CT: Max/PAL  pc (if present)  OT/CT: Ortho-T; timing NR  SurgDur; pain; failure rate; esthetic outcome  None  7  Smailiene 2013a;b  RCT; university, Lithuania  OT: 22 (NR); NR years; uni ICs CT: 21 (NR); NR years; uni ICs  OT: 22 CT: 21  OT: Max/PAL CT: Max/PAL  —  OT: No Ortho-T CT: Ortho-T; 1 week post-OP  Tx duration; tooth shape, position, and colour  None  8  Szarmach 2006  pNRS; university; Poland  OT: 4 (NR); NR years; uni ICs CT: 20 (NR); NR years; uni ICs  OT:4 CT: 20  OT: Max/LAB-PAL CT: Max/LAB-PAL  —  OT/CT: Ortho-T; timing NR  Tx duration  NR  AA  Trial  Design; setting  Patients (M/F); mean age; malocclusion; uni/ bilateral IC  No of ICs  Jaw/side  Exs (prim/perm)  Ortho measures; timing  Eligible outcome  CoI  1  Chaushu 2005  pNRS; university; Israel  OT: 30 (6/24); 14.8 years; uni/bil ICs CT: 30 (13/17); 16 years; uni/bil ICs  OT: 32 CT: 25  OT: Max/LAB-PAL CT: Max/LAB-PAL  —  OT: Ortho-T; 1 week post-OP (OT) CT: Ortho-T; post-OP  SurgDur; Pain, oral function, general activity and other symptoms  NR  2  Gharaibeh 2008  RCT; university; Jordan  OT: 16 (2/14); 17.3 years; uni ICs CT: 16 (2/14); 17.6 years; uni ICs  OT: 16 CT: 16  OT: Max/PAL CT: Max/PAL  —  OT/CT: Ortho-T; 1 week post-OP (OT/CT)  SurgDur; pain  NR  3  Koutzoglou 2013  pNRS; private practice; Greece  OT: 46 (NR); NR years; uni/bil ICs CT: 50 (NR); NR years; uni/bil ICs  OT: 57 CT: 62  OT: Max-Mnd/LAB-PAL CT: Max-Mnd/LAB-PAL  OT: 47 pc CT: 47 pc  SOa OT/CT: Ortho-T; 1 week post-OP  Ankylosis; fibrous connective tissue  None  4  londhe 2014  RCT; university; India  OT: 16 (NR); NR years, uni/bil ICs CT: 15 (NR); NR years, uni/bil ICs  OT: 16 CT: 15  OT: Max/LAB CT: Max/LAB  —  SO OT/CT: Ortho-T; post OP  SurgDur; pain; recovery period; Tx duration; mobility; vitality; swelling; root integrity  None  5  Marzouk 1997  pNRS; hospital; Saudia Arabia  OT: 33 (NR); NR, NR years, uni/bil ICs CT: 33 (NR); NR, NR years, uni ICs  OT: 33 CT: 33  OT: Max/LAB-PAL CT: Max/LAB-PAL  Max 4s (in some cases)  SO; OT: Ortho-T; 1 week post-OP (OT) CT: Ortho-T; post-OP  Tx duration; attachment rebond need  NR  6  Parkin 2012; 2013; 2015  RCT; university; England  OT: 40 (13/27); 14.3 years; uni ICs CT: 41 (16/25); 14.1 years; uni ICs  OT: 40 CT: 41  OT: Max/PAL CT: Max/PAL  pc (if present)  OT/CT: Ortho-T; timing NR  SurgDur; pain; failure rate; esthetic outcome  None  7  Smailiene 2013a;b  RCT; university, Lithuania  OT: 22 (NR); NR years; uni ICs CT: 21 (NR); NR years; uni ICs  OT: 22 CT: 21  OT: Max/PAL CT: Max/PAL  —  OT: No Ortho-T CT: Ortho-T; 1 week post-OP  Tx duration; tooth shape, position, and colour  None  8  Szarmach 2006  pNRS; university; Poland  OT: 4 (NR); NR years; uni ICs CT: 20 (NR); NR years; uni ICs  OT:4 CT: 20  OT: Max/LAB-PAL CT: Max/LAB-PAL  —  OT/CT: Ortho-T; timing NR  Tx duration  NR  BR, brackets rebonding; CT, closed technique; CoI, conflict of interest; F, female; IC, impacted canine; LAB, labial; LIN, lingual; M, male; Max, maxilla; Mnd, mandible; NR, not reported; OT, open technique; Ortho-T; orthodontic traction; pNRS, prospective non-randomized study; PAL, palatinal; pc, primary canine; RCT, randomized controlled trial; RPE, rapid palatal expansion; SurgDur, duration of surgical procedure; SO, space opening; in, if needed; uNRS, unclear non-randomized study. aRapid maxillary expansion also performed on some patients (51 of 150 maxillary cases), but is not reported further. View Large Risk of bias within studies The risk of bias for the eight trials included is summarized in Figure 2 and given in detail in Supplementary Appendices 4–5. High risk of bias was found in all four RCTs included for at least one bias domain, with the most problematic domain being complete blinding of outcome assessments (missing in all four trials) and improper randomization (in one trial). All four non-randomized trials had also at least one problematic domain, with the most critical domains being incomplete reporting of follow-up and drop-outs, lack of blinding, and lack of proper confounder assessment. Figure 2. View largeDownload slide Summary of the risk of bias of the randomized (upper half) and non-randomized (lower half) trials included in this systematic review. C1, C2, C3…: criterion 1, criterion 2, criterion 3, … (for details see Supplementary Appendix 5). Figure 2. View largeDownload slide Summary of the risk of bias of the randomized (upper half) and non-randomized (lower half) trials included in this systematic review. C1, C2, C3…: criterion 1, criterion 2, criterion 3, … (for details see Supplementary Appendix 5). Results of individual studies and data synthesis The results of all outcomes reported in all included studies can be found in Supplementary Appendix 6. Additionally, the re-analyses of raw data available for the studies of Chaushu et al. (14) and Marzouk et al. (39) can be seen in Supplementary Appendices 7–10. The results of the meta-analyses for the review’s primary and secondary outcomes can be seen in Table 2. Table 2. Results of random-effects (Paule-Mandel) meta-analyses for the primary and secondary outcomes from all studies. Outcome  Studies  Effect  95% CI  P value  tau2 (95% CI)  I2 (95% CI)  95% prediction  Primary   Duration; surgical exposure  3a  Omitted  Omitted  Omitted  Omitted  Omitted     Duration; initial canine traction  3b  MD: –2.14  –4.23, –0.05  0.045  2.39 (0.27, 50.00)  74% (25%, 98%)  –7.35, 3.07   Duration; bond debond  1  MD: –3.78  –9.21, 1.65  0.172  na  na    Secondary   Failure; re-exposure need  2  RR: 2.91  0.49, 17.12  0.238  0.83 (0.00, 32.70)  48% (0%, 97%)     Ankylosis  1  OR: 0.15  0.03, 0.83  0.030  na  na     Colour difference  1  RR: 1.91  0.19, 19.52  0.586  na  na     Unoperated canine best; laypersons  1  MD: –1.73  –15.90, 12.44  0.811  na  na     Unoperated canine best; orthodontists  1  MD: –0.32  –15.10, 14.46  0.966  na  na     Pain; averaged  3  MD: 0.30  –0.52, 1.13  0.470  0.32 (0.00, 5.75)  60% (0%, 97%)  –8.68, 9.28   Difficulty in eating  2  MD: 0.54  –0.73, 1.80  0.404  0.44 (0.00, 46.22)  52% (0%, 99%)     Difficulty in speech  2  MD: 0.35  –0.73, 1.44  0.521  0.31 (0.00, 4.43)  50% (0%, 94%)    Outcome  Studies  Effect  95% CI  P value  tau2 (95% CI)  I2 (95% CI)  95% prediction  Primary   Duration; surgical exposure  3a  Omitted  Omitted  Omitted  Omitted  Omitted     Duration; initial canine traction  3b  MD: –2.14  –4.23, –0.05  0.045  2.39 (0.27, 50.00)  74% (25%, 98%)  –7.35, 3.07   Duration; bond debond  1  MD: –3.78  –9.21, 1.65  0.172  na  na    Secondary   Failure; re-exposure need  2  RR: 2.91  0.49, 17.12  0.238  0.83 (0.00, 32.70)  48% (0%, 97%)     Ankylosis  1  OR: 0.15  0.03, 0.83  0.030  na  na     Colour difference  1  RR: 1.91  0.19, 19.52  0.586  na  na     Unoperated canine best; laypersons  1  MD: –1.73  –15.90, 12.44  0.811  na  na     Unoperated canine best; orthodontists  1  MD: –0.32  –15.10, 14.46  0.966  na  na     Pain; averaged  3  MD: 0.30  –0.52, 1.13  0.470  0.32 (0.00, 5.75)  60% (0%, 97%)  –8.68, 9.28   Difficulty in eating  2  MD: 0.54  –0.73, 1.80  0.404  0.44 (0.00, 46.22)  52% (0%, 99%)     Difficulty in speech  2  MD: 0.35  –0.73, 1.44  0.521  0.31 (0.00, 4.43)  50% (0%, 94%)    CI, confidence interval; MD, mean difference; na, not applicable; OP, operation; OR, odds ratio; RR, relative risk. aHigh heterogeneity identified (I2 > 75%), which remained unexplained; meta-analysis of three studies [MD (95% CI) = –5.44 (–11.92, 1.03); P = 0.099; tau2 (95% CI) = 26.47 (10.84, 50.00); I2 (95% CI) = 83% (66%, 90%)] was omitted, as elimination of any single study was not straightforward (MDs of –8.56, –6.80, and 0). bInitial meta-analysis included three studies [MD (95% CI) = –2.26 (–4.91, 0.39); P = 0.094] with high heterogeneity [tau2 (95% CI) = 4.35 (1.85, 50.00); I2 (95% CI) = 84% (70%, 98%)]. As two studies (Parkin 2012; Smailiene 2013) included only palatally impacted canines and the third (Marzouk 1997) included both palatally and labially impacted canines, only the subsample of palatally impacted canines was included from the third study to achieve homogeneity. View Large As far as the primary outcome of treatment duration is concerned, data was available on two levels: first, the duration from surgical exposure to the initial alignment of the canine to the occlusal plane/dental arch and second, complete treatment duration from appliance insertion to appliance removal. Meta-analysis of three studies on the initial alignment of the impacted canine to the dental arch indicated that open exposure was associated with a statistically significant reduction in treatment duration by 2.14 months (95% CI: 0.05–4.23 months less; P < 0.05) compared to the closed exposure, with moderate heterogeneity (tau2: 2.39; I2: 74%; Table 2; Figure 3). Based on the 95 per cent prediction interval, this indicated that in a future setting initial canine alignment with the open technique might take 7.4 less to 3.1 months more than the closed technique. On the other side, one included trial reported a small reduction in overall treatment duration (bond to debond), but this was not statistically significant, probably due to low power (MD: –3.78 months; 95% CI: –9.21 to 1.65 months; P > 0.05). Figure 3. View largeDownload slide Contour-enhanced forest plot with random-effects (Paule-Mandel) meta-analysis of the review’s primary outcome (treatment duration in months). Figure 3. View largeDownload slide Contour-enhanced forest plot with random-effects (Paule-Mandel) meta-analysis of the review’s primary outcome (treatment duration in months). As far as the secondary outcomes are concerned, no statistically significant differences between open and closed exposure could be found for (i) re-exposure need, (ii) canine discoloration, (iii) post-operative pain, (iv) difficulty in eating, (v) difficulty in speech, and (vi) canine aesthetics. However, open exposure was associated with a significantly lower odds for ankylosis of the impacted canine (OR = 0.15; 95% CI 0.03–0.83; P < 0.05), which was statistically and clinically relevant. This was translated clinically to an NNT of 9 (95% CI 8–47), which indicates that for every nine impacted canines treated with a closed exposure technique, an additional ankylosis of the impacted canine would be observed than if an open technique had been favored. Quality of evidence Assessment of existing meta-evidence with the GRADE approach (Table 3) indicated that moderate quality evidence supported the shorter initial alignment duration with the open technique. For the rest of the outcomes, low to very low quality of evidence existed, due to the inclusion of non-randomized studies, their high risk of bias, and the imprecision stemming from the small number of included studies. Table 3. GRADE summary of findings table for the primary and secondary outcomes. OutcomeStudies (canines)  Relative effects (95% CI)  Anticipated absolute effectsa (95% CI)  Quality of the evidence (GRADE)  What happens with open technique  Closed technique*  Open technique  Difference  Tx duration (initial traction) three studies (135 canines)  —  9.7 months  —  2.1 months less (0.1–4.2 less)  ⊕⊕⊕◯ moderatea,b due to bias  Shorter initial traction of impacted canines  Tx duration (bond-debond) one study (43 canines)  —  32.2 months  —  3.8 less months (1.7 more to 9.2 less)  ⊕⊕◯◯ lowb,c due to bias and imprecision  There may be little or no difference  Failure; re-exposure need two studies (118 canines)  RR 2.91 (0.49, 17.12)  10.1%  29.4% (4.9–100.0%)  19.3% more canines needing re-exposure (5.2% less to 89.9% more)  ⊕◯◯◯ very lowb,c,d due to bias and imprecision  There may be little or no difference  Failure; canine ankylosis one study (119 canines)  OR 0.15 (0.03–0.83)  14.5%  2.5% (0.5–12.3%)  12.0% less ankylosed canines (2.2–14.0% less)  ⊕⊕◯◯ lowe due to bias  Greatly reduces the risk of ankylosis  Color difference one study (43 canines)  RR 1.91 (0.19, 19.52)  4.8%  9.2% (0.9–93.7%)  4.4% more canine with different colour (3.9% less to 88.9% more)  ⊕⊕◯◯ lowb,c due to bias and imprecision  There may be little or no difference  Unoperated canine best; laypersons (VAS scala)f one study (67 canines)  —  5.9/10 points in VAS  —  0.2 less (1.2 less to 1.6 more)  ⊕⊕◯◯ lowb,c due to bias and imprecision  There may be little or no difference  Unoperated canine best; orthodontists (VAS scala)f one study (67 canines)  —  6.1/10 points in VAS  —  <0.1 less (1.5 less to 1.5 more)  ⊕⊕◯◯ lowb,c due to bias and imprecision  There may be little or no difference  Post operative pain (VAS scala) three studies (143 canines)  —  3.7/10 points in VAS  —  0.3 points more (0.5 less to 1.1 more)  ⊕◯◯◯ very lowb,c,d due to bias and imprecision  There may be little or no difference  Difficulty in eating (VAS scala) two studies (112 canines)  —  4.1/10 points in VAS  —  0.5 points more (0.7 less to 1.8 more)  ⊕◯◯◯ very lowb,c,d due to bias and imprecision  There may be little or no difference  Difficulty in speech (VAS scala) two studies (112 canines)  —  2.3/10 points in VAS  —  0.4 points more (0.7 less to 1.4 more)  ⊕◯◯◯ very lowb,c,d due to bias and imprecision  There may be little or no difference  OutcomeStudies (canines)  Relative effects (95% CI)  Anticipated absolute effectsa (95% CI)  Quality of the evidence (GRADE)  What happens with open technique  Closed technique*  Open technique  Difference  Tx duration (initial traction) three studies (135 canines)  —  9.7 months  —  2.1 months less (0.1–4.2 less)  ⊕⊕⊕◯ moderatea,b due to bias  Shorter initial traction of impacted canines  Tx duration (bond-debond) one study (43 canines)  —  32.2 months  —  3.8 less months (1.7 more to 9.2 less)  ⊕⊕◯◯ lowb,c due to bias and imprecision  There may be little or no difference  Failure; re-exposure need two studies (118 canines)  RR 2.91 (0.49, 17.12)  10.1%  29.4% (4.9–100.0%)  19.3% more canines needing re-exposure (5.2% less to 89.9% more)  ⊕◯◯◯ very lowb,c,d due to bias and imprecision  There may be little or no difference  Failure; canine ankylosis one study (119 canines)  OR 0.15 (0.03–0.83)  14.5%  2.5% (0.5–12.3%)  12.0% less ankylosed canines (2.2–14.0% less)  ⊕⊕◯◯ lowe due to bias  Greatly reduces the risk of ankylosis  Color difference one study (43 canines)  RR 1.91 (0.19, 19.52)  4.8%  9.2% (0.9–93.7%)  4.4% more canine with different colour (3.9% less to 88.9% more)  ⊕⊕◯◯ lowb,c due to bias and imprecision  There may be little or no difference  Unoperated canine best; laypersons (VAS scala)f one study (67 canines)  —  5.9/10 points in VAS  —  0.2 less (1.2 less to 1.6 more)  ⊕⊕◯◯ lowb,c due to bias and imprecision  There may be little or no difference  Unoperated canine best; orthodontists (VAS scala)f one study (67 canines)  —  6.1/10 points in VAS  —  <0.1 less (1.5 less to 1.5 more)  ⊕⊕◯◯ lowb,c due to bias and imprecision  There may be little or no difference  Post operative pain (VAS scala) three studies (143 canines)  —  3.7/10 points in VAS  —  0.3 points more (0.5 less to 1.1 more)  ⊕◯◯◯ very lowb,c,d due to bias and imprecision  There may be little or no difference  Difficulty in eating (VAS scala) two studies (112 canines)  —  4.1/10 points in VAS  —  0.5 points more (0.7 less to 1.8 more)  ⊕◯◯◯ very lowb,c,d due to bias and imprecision  There may be little or no difference  Difficulty in speech (VAS scala) two studies (112 canines)  —  2.3/10 points in VAS  —  0.4 points more (0.7 less to 1.4 more)  ⊕◯◯◯ very lowb,c,d due to bias and imprecision  There may be little or no difference  Effectiveness and adverse effects of interventions to surgically expose and rehabilitate impacted canines. Patient or population: patients with labially or palatally/lingually impacted permanent canines. Settings: university clinics (England, India, Israel, Jordan, Lithuania, Poland), private practice (Greece), and hospital (Saudi Arabia). CI, confidence interval; GRADE, Grading of Recommendations Assessment, Development and Evaluation; OR, odds ratio; RR, relative risk; VAS, visual analogue scale. *Response or risk in the control group is based on the average of included studies. aShould start from low due to the inclusion of the non-randomized study of Marzouk 1997, but exclusion of this (Table 3) lead only to effect magnification. Therefore, it was judged safe to start from high GRADE, as no bias could be identified. bDowngraded by one due to the high risk of bias of included studies. cDowngraded by one due to imprecision, judged by the small number of included studies with limited sample sizes and the wide confidence intervals. dStarts from low due to the inclusion of the non-randomized study of Chaushu 2005. eGRADE would be upgrade by one for confounding (as confounders were assessed through multivariable regression modelling) and by one due to very large effect magnitude; given however that the trial was not free of risk of bias, we decided not to upgrade. fTranslated from 100 mm VAS to 10 cm VAS for consistency. View Large Additional analyses Additional analyses were undertaken in order to assess the possible impact of impaction-related characteristics on treatment outcomes. As such, data from two included studies were re-analyzed post hoc for this systematic review with multiple regressions (including explorative interaction terms) to assess potential differences in outcomes between labially and palatally impacted canines (Supplementary Appendices 7–10). According to these, the initial alignment of the impacted canine to the dental arch took significantly longer for palatally than for labially impacted canines (8.87 versus 4.17 months, respectively; Supplementary Appendices 9), with an adjusted difference of 4.70 months less for labial impactions compared to palatal impactions (P < 0.001). However, open exposure was found to be consistently superior to closed exposure for both labial and palatal impactions (P > 0.05 for interaction of impaction localization and exposure technique; Supplementary Appendix 10). Other than that, no significant difference was found in any of the treatment outcomes according to impaction localization, with the sole exception of intraoperative need for surgical bone removal (P = 0.042 for interaction of impaction localization and exposure technique; Supplementary Appendix 11). Stratified analysis by canine localization indicated that open exposure of palatal canines was tendentially associated with greater bone removal need than closed exposure, while the opposite tendency seen for labially impacted canines. However, the results of the stratified analysis were not statistically significant, presumably due to the loss of power from stratifying an already limited sample. Additional analyses were planned in the review’s protocol regarding various patient-, impaction-, or treatment-related factors, but the majority of them could not be performed, due to limited data. One included study indicated that increasing patient age and impaction severity were both associated with higher odds of ankylosis of the impacted canine (P < 0.05) (40). Re-analysis of the provided Chaushu et al. (14) data indicated that patient gender was significantly associated with post-operative swelling, the ability to enjoy food, and complaints of bad taste/smell after the exposure surgery (Supplementary Appendix 8). Additionally, a tendency for intraoperative greater bone removal need in older patients and a subsequent greater difficulty in speech in those cases was observed (Supplementary Appendix 4). Finally, a sensitivity analysis was performed by excluding non-randomized trials (Table 4), which indicated that the shorter duration of initial canine relocation with open exposure was robust to the inclusion of non-randomized trials, as the effect magnitude was actually enlarged (3.50 months less compared to the initial 2.14 months less of the original analysis). The decreased ankylosis risk with open exposure on the other side could not be confirmed, as no randomized trial reported this outcome. No further sensitivity analyses, nor any assessments of reporting biases, including small-study effects and publication bias, could be performed due to limited studies. Table 4. Sensitivity analysis including only randomized clinical trials for the primary and secondary outcomes. Outcome  Studies  Effect  95% CI  P value  tau2 (95% CI)  I2 (95% CI)  Primary   Duration; surgical exposure  3  Same as Table 2   Duration; initial canine traction  2  MD: –3.50  –6.23, –0.78  0.012  2.09 (0.00, 0.00)  51% (0%, 0%)   Duration; bond debond  1  Same as Table 2  Secondary   Failure; re-exposure need  1  RR: 3.39  0.37, 31.02  0.280  na  na   Ankylosis  0  —  —  —  —  —   Colour difference  1  RR: 1.91  0.19, 19.52  0.586  na  na   Unoperated canine best; laypersons  1  MD: –1.73  –15.90, 12.44  0.811  na  na   Unoperated canine best; orthodontists  1  MD: –0.32  –15.10, 14.46  0.966  na  na   Pain; averaged  2  MD: 0.17  –0.58, 0.92  0.653  0.16 (0.00, 32.00)  47% (0%, 99%)   Difficulty in eating  1  MD: 0.40  –0.74, 1.54  0.490  na  na   Difficulty in speech  1  MD: 0.40  –0.70, 1.50  0.475  na  na  Outcome  Studies  Effect  95% CI  P value  tau2 (95% CI)  I2 (95% CI)  Primary   Duration; surgical exposure  3  Same as Table 2   Duration; initial canine traction  2  MD: –3.50  –6.23, –0.78  0.012  2.09 (0.00, 0.00)  51% (0%, 0%)   Duration; bond debond  1  Same as Table 2  Secondary   Failure; re-exposure need  1  RR: 3.39  0.37, 31.02  0.280  na  na   Ankylosis  0  —  —  —  —  —   Colour difference  1  RR: 1.91  0.19, 19.52  0.586  na  na   Unoperated canine best; laypersons  1  MD: –1.73  –15.90, 12.44  0.811  na  na   Unoperated canine best; orthodontists  1  MD: –0.32  –15.10, 14.46  0.966  na  na   Pain; averaged  2  MD: 0.17  –0.58, 0.92  0.653  0.16 (0.00, 32.00)  47% (0%, 99%)   Difficulty in eating  1  MD: 0.40  –0.74, 1.54  0.490  na  na   Difficulty in speech  1  MD: 0.40  –0.70, 1.50  0.475  na  na  CI, confidence interval; MD, mean difference; na, not applicable; OP, operation; OR, odds ratio; RR, relative risk. View Large Discussion Summary of evidence This systematic review summarized existing evidence from eight randomized and prospective non-randomized trials that included a total of 433 patients and a total of 453 impacted canines treated with either an open or closed surgical exposure. As far as the primary outcome of treatment duration is concerned, existing evidence indicated that open approach was associated with substantial gains in the duration of initial canine alignment to the dental arch compared to the closed technique (gain of 2.1 or 3.5 months less according to the original and the sensitivity analysis, respectively) (Tables 2 and 4). This might be associated with the lack of a repositioned flap over the exposed canine, which could act as an obstacle to the tooth’s eruption. On the other side, it might be that open exposure technique is used selectively for canines located directly under the mucosa surface (13), which might add confounding, as these canines have per se a shorter eruption path to the dental arch. This was the case for the included non-randomized trial of Szarmach et al. (41), where exposure technique was chosen ‘depending on the impaction zone and the distance to the occlusal plane’. However, the sensitivity analysis, excluding this trial and including only trials where impacted canines were randomly allocated to a technique irrespective of their localization, found actually larger time gains for the open exposure (3.5 versus 2.1 months, Tables 2 and 4). These results seem to be in agreement with a previous retrospective study, which reported higher alignment failure of the impacted canines with the closed technique and attributed this to scar tissue, improper traction direction, or the presence of dense connective tissue in the eruption way of the canine (42). Additionally, exposure of impacted canines with an open technique was associated with significantly lower odds of ankylosis (OR = 0.15; 95% CI 0.03–0.83; P < 0.05), which was independent of patient age, sex, impaction side (labially or palatally) or grade of impaction (40). This could be a direct effect due to trauma of the periodontal ligament or root cementum by the low-speed bur, chemical trauma from the etching gel (43), or the use orthodontic forces of high magnitude or inappropriate direction (40). Alternatively, this could be an indirect effect resulting from the shorter traction time, where potentially damaging heavy orthodontic forces are applied. Furthermore, canine localization was found to be significantly associated to treatment duration according to the re-analysis of Marzouk et al. (39) data, which indicated that palatally impacted canines needed on average 4.70 months longer to align than labially impacted ones (Supplementary Appendix 10). This is in agreement with retrospective data (27) and could be due to the fact that palatally impacted canines may lie a lot further from the occlusal plane than labially impacted ones, resulting in a longer eruption path. Finally, limited evidence indicated that older patients were associated with higher odds of tooth ankylosis than younger patients, irrespective of canine localization, impaction grade, or exposure technique (40). This is in agreement with other retrospective studies not included in this review, which reported that patient age seemed to be associated with prolonged duration (42) and less favorable prognosis (44) for the alignment of the impacted canine. Strengths and limitations The strengths of this systematic review consist of the a priori registration in PROSPERO (45), an extensive and unrestricted literature search, use of robust review procedures for qualitative/quantitative data synthesis (46), exclusion of biased study designs (47), use of a novel estimator for random-effects variance (31), clinical translation of the meta-analysis results (34), and assessment of cumulative meta-evidence with the GRADE approach (36). However, some limitations are also present in this study. First and foremost, this systematic review included some non-randomized trials, and although sensitivity analyses indicated that this did not affect the results, moderate to high risk of bias was observed for all trials. Additionally, predominantly small trials were included, which could influence the results of the meta-analyses (48). Furthermore, clarifications or individual patient data couldn’t be obtained from attempts to communicate with trialists [except for one case (14)], thus re-analysis to take into account baseline confounding and clustrering effects were precluded. It is important to note that for many comparisons with non-significant results wide 95 per cent CIs existed, which indicate high uncertainty around these estimates and more trials need to be added to the evidence base to reduce this uncertainty. Finally, the limited number of included trials did not enable robust assessments of heterogeneity, subgroup analyses, small-study effects, and reporting biases for most of the outcomes. Conclusions Based on a limited number of relatively small randomized and prospective non-randomized trials, open surgical exposure of impacted canines seems to be superior to the closed approach in terms of reduced initial alignment duration and decreased risk of ankylosis. No other significant differences in adverse effects or patient-oriented outcomes could be found between the two exposure techniques. Recommendations for further research Additional parallel or cluster-randomized trials compliant with the CONSORT statement (49) are needed to fill current evidence gaps. These pertain to the feasibility of each exposure technique according to the specific localization of impacted canines [jaw, side, and height of impaction (50)], differences between various modifications of the two techniques, and the relative effectiveness of various orthodontic mechanotherapy alternatives (including the timing of force application). Finally, future trials should employ a priori sample size calculation to ensure adequate statistical power and take into account the clustering of multiple canines within patients (51). Supplementary material Supplementary material is available at European Journal of Orthodontics online. Conflicts of Interest None to declare. 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European Journal of Orthodontics , 35, 669– 675. Google Scholar CrossRef Search ADS 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 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The European Journal of Orthodontics Oxford University Press

Open versus closed surgical exposure for permanent impacted canines: a systematic review and meta-analyses

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© 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
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10.1093/ejo/cjx047
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Abstract

Summary Background Permanent canines are amongst the teeth most affected by impaction and ectopic eruption. Although impacted canines are often subjected to surgical exposure and alignment with either the open or the closed technique for many decades, their treatment effects have not yet been systematically asssessed. Objectives The aim of this systematic review was to critically assess whether significant differences exist in the outcomes of the open or closed surgical exposure of impacted canines. Search methods An unrestricted electronic search of nine databases from inception to December 2016 was performed. Selection criteria methods Included were randomized or prospective non-randomized studies comparing open versus closed exposure of impacted canines in human patients. Data collection and analysis After duplicate study selection, data extraction, and risk of bias assessment according to the Cochrane guidelines, random-effects meta-analyses of mean differences (MDs) and odds ratios (ORs), including their 95 per cent confidence intervals (CIs) were performed, followed by subgroup and sensitivity analyses. Results A total of eight unique studies and a total of 433 (30.1% male/59.9% female) patients were included, with an average age of 15.2 years and a total of 453 impacted canines (48.6% and 51.4% in the open and closed exposure, respectively). Open exposure of impacted canines was associated with reduced duration of canine alignment (two studies; MD = –2.14 months; 95% CI = –4.23 to –0.05 months; P < 0.05; moderate heterogeneity and moderate quality) and lower odds of tooth ankylosis (one study; OR = 0.15; 95% CI = 0.03–0.83; P < 0.05; low quality) compared to closed exposure; both findings being independent of canine localization. However, initial alignment of palatally impacted canines took overall significantly longer than labially impacted canines (8.87 versus 4.17 months). Conclusions Based on existing evidence, open surgical exposure seems to be superior in treatment duration and ankylosis risk over the closed technique. Due to the limited number of small included trials, further research is needed for robust clinical recommendations. Registration PROSPERO (CRD42016051916). Introduction Rationale The permanent canine is, after the third molars, the tooth with the highest incidence of impaction with prevalence ranging between 0.3 and 2.4 per cent (1, 2). Canine impaction shows a predilection for the palatal over the labial side (3) and has higher prevalence in female patients (2). Canine impaction can be associated with functional or esthetic impairment, while impacted canines might also lead to root resorption of adjacent permanent teeth (4). Therefore, a definitive diagnosis of an impacted canine is often directly followed by an attempt to tackle the impaction, if needed. Common approaches for the management of impacted canines include early interceptive measures (5, 6) or late intervention, including extraction (7), autotransplantation (8), and surgical exposure of the canine’s crown with a subsequent orthodontic alignment of the tooth (9). Given the high aesthetic and functional value of canines, the combined surgical/orthodontic approach to relocate the impacted canine in its proper place in the dental arch is considered often, with two major surgical techniques: the open and the closed technique. The open technique includes the surgical exposure of the crown by either complete removal of bone and soft tissue directly overlying the impacted canine (10) or the use of an apically repositioned gingival flap (11). Afterwards, surgical pack might be used to cover the wound, while the canine can be either left to spontaneously erupt or an orthodontic attachment is directly bonded on the canine in order to directly apply traction. The contemporary closed technique on the other side involves raising a full mucoperiostal flap, exposing the canine crown, and bonding an attachment on it (12). Afterwards, the flap is repositioned and orthodontic traction is applied after initial healing, until the canine erupts in the oral cavity and is subsequently guided to the dental arch. Although, both approaches are versatile, can be adapted to each case (13), and have been used extensively for many years, reports about their comparative performance are mixed. Several studies have evaluated various aspects of their performance, including surgical duration and postoperative recovery time (14), postoperative pain (15), periodontal health (16, 17), and esthetic appearance (18). Although, the subject has been heavily debated with active proponents for both approaches (6, 19), the cumulative evidence regarding their overall comparative performance in terms of clinically relevant outcomes has not yet been objectively assessed according to the principles of evidence-based orthodontics. Two systematic reviews on the subject have been performed, but the first (and older one) did not find any eligible trials to include (20), while the second only focused on the periodontal health of impacted canines with no clinically relevant differences between the open and closed technique (17). Objectives The aim of this systematic review was to critically evaluate existing clinical evidence and assess whether considerable differences in the primary outcome of treatment duration and other secondary treatment outcomes exist between impacted canines treated surgically-orthodontically with an open or closed exposure technique. To this end, the present systematic review attempts to answer the following question: When compared with a closed exposure technique, what are the comparative effectiveness and harms of the open exposure technique in the management of impacted canines in patients of any age or sex? Materials and methods Protocol and registration The review’s protocol was made a priori following the PRISMA-P statement (21), registered in PROSPERO (CRD42016051916), and all post hoc changes were appropriately noted. This systematic review was conducted and reported according to Cochrane Handbook (22) and PRISMA statement (23), respectively. Eligibility criteria According to the Participants Intervention Comparison Outcome Study design schema (PICOS), we included randomized and prospective controlled non-randomized trials (S) on human patients of any age or sex with at least one impacted canine (P) comparing an open (I) versus a closed surgical approach (C) for the exposure and orthodontic management of impacted canines. The primary outcome (O) of this systematic review was treatment duration, of either the initial alignment of the impacted canine to the occlusion or the complete fixed appliance phase, extracted from the patient records in months. The secondary outcomes focused on clinical relevance to the patient or the orthodontist and included the need for canine re-exposure, adverse effects to the canine (including ankylosis and discoloration), and patient-reported outcomes (including overall satisfaction, pain, and disruption of the function). Excluded were non-clinical studies, retrospective studies, case reports, animal studies, and studies that did not directly compare both approaches. Information sources and literature search Nine electronic databases were systematically searched by one author (SNP) without any limitations from inception up to December 12th, 2016 (Supplementary Appendix 1): MEDLINE (searched via PubMed), Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials, Cochrane Database of Abstracts of Reviews of Effects, Embase, Virtual Health Library, Scopus, Web of Knowledge, and ClinicalTrials.gov. Additionally, five sources (Google Scholar, International Standard Registered Clinical/soCial sTudy Number Registry, Directory of Open Access Journals, Digital Dissertations, and metaRegister of Controlled Trials) and the reference/citation lists of included trials were manually searched for any additional trials. Authors of included trials were contacted for additional missed or ongoing trials. No limitations concerning publication language, publication year, or publication status were applied. Study selection The eligibility of identified studies was checked sequentially from their title, abstract, and full-text against the eligibility criteria by one author (CC) and were subsequently checked independently by a second one (SNP), with conflicts resolved by a third author (TE). Data collection and data items Study characteristics and numerical data were extracted from included trials independently by two authors (CC, SNP) using pre-defined and piloted extraction forms including: (i) study characteristics (design, clinical setting, country), (ii) patient characteristics (age, sex, number and localization of impacted canines, extraction of any teeth as part of the treatment plan), (iii) any orthodontic co-interventions, and (iv) study outcome measures. Piloting of the forms was performed during the protocol stage until over 90 per cent agreement was reached. Missing or unclear information was requested by the trials’ authors and re-analyzed firsthand, whenever possible. Risk of bias in individual trials The risk of bias of included RCTs was assessed using Cochrane’s risk of bias tool (22); the risk of bias of included prospective non-randomized studies (NRS) was assessed using the Downs and Black checklist (24) with appropriate modifications. A main risk of bias assessment was included in the systematic review pertaining to each trial’s primary outcome. Data synthesis Meta-analysis was performed if similar interventions and control groups were compared and similar outcomes were measured. As outcome of canine exposure and alignment is bound to be affected by patient age (25), localization of the canine (26, 27), the orthodontic mechanotherapy (27), and biologic variation in tooth movement (28), a random-effects model was judged as clinically and statistically appropriate (29). The novel random-effects model proposed by Paule and Mandel was preferred a priori over the more widely known DerSimonian and Laird (30) method to estimate all pooled data, according to empirical evidence (31). Mean Differences (MD) for continuous outcomes and Odds Ratios (OR) for binary outcomes and their corresponding 95 per cent Confidence Intervals (CI) were calculated. Statistically significant results of binary meta-analyses were translated clinically using the Number Needed to Treat (NNT). For included trials with clustered data, we tried to contact the trial’s authors to ask for adjusted outcomes or raw data. The extent and impact of between-study heterogeneity was assessed by inspecting the forest plots and calculating the tau2 and the I2, respectively; I2 defines the proportion of total variability in the result explained by heterogeneity, and not chance (32). We roughly categorized heterogeneity as low moderate, and high to I2 values of 25, 50, and 75 per cent (32), although we also judged the heterogeneity’s localization on the forest plot. Additionally, the 95 per cent CIs around tau2 and I2 were calculated (33) to quantify our uncertainty around these estimates. Ninety-five per cent predictive intervals were calculated for meta-analyses of ≥3 trials to incorporate existing heterogeneity and provide a range of possible effects for a future clinical setting (34). All analyses were conducted in Stata SE version 14.2 (StataCorp LP, College Station, Texas, USA) by one author (SNP). A two side P ≤ 0.05 was considered significant for hypothesis-testing, except for P ≤ 0.10 used for tests of between-studies or between-subgroups heterogeneity (35). Quality of evidence The overall quality of clinical recommendations for each of the main outcomes was rated using the Grades of Recommendations, Assessment, Development, and Evaluation (GRADE) approach, as very low, low, moderate, or high (36). The minimal clinical important (37), large, and very large effects were defined as half, one, and two standard deviations (using the average standard deviation for an outcome across the control groups of included trials), respectively. Arbitrary cut-offs of 1.5, 2.5, and 4.3 were adopted for the OR. The produced forest plots were augmented with contours denoting the magnitude of the observed effects (38). Additional analyses and sensitivity analyses Reporting biases (including the possibility of publication bias) were planned in the protocol to be assessed, but could not be performed due to the limited number of included trials. Robustness of the meta-analyses was planned a priori to be checked with sensitivity analyses based on (i) exclusion of trials with high risk of bias, (ii) improvement of the GRADE classification, (iii) exclusion of non-randomized trials, and (iv) exclusion of trials with reporting biases. Results Study selection A total of 476 and 9 papers were identified through electronic and manual searches, respectively (Figure 1). After removal of duplicates and initial screening, 37 papers were assessed using the eligibility criteria, and 11 papers were included in this systematic review (Figure 1; Supplementary Appendix 2). In two instances, multiple publications pertaining to the same trial were grouped together; thus, a total of 8 unique trials from 11 publications were finally included in the systematic review. Several authors were contacted for clarifications or additional data (Supplementary Appendix 3) with only limited success. In one instance of a trial including both impacted canines and impacted incisors (14), the authors were contacted and graciously provided the raw study data that enabled the exclusion of impacted incisors and the inclusion of the study. Figure 1. View largeDownload slide Flowdiagram for the identification and selection of studies in this systematic review. Figure 1. View largeDownload slide Flowdiagram for the identification and selection of studies in this systematic review. Study characteristics The characteristics of the included trials can be seen in Table 1. Of the eight included trials, four (50%) were randomized and four (50%) were prospective non-randomized trials, conducted in eight different countries. They included a total of 433 patients (mean 54 patients per trial; range 24–96) with male patients being the 30.1 per cent (52/173 patients among the three trials that reported patient sex), and with an average age of 15.2 years. A total of 453 impacted canines were included in the identified trials, 220 (48.6%) of which were treated with an open exposure and 233 (51.4%) with a closed exposure (Table 1). Table 1. Characteristics of the included trials. AA  Trial  Design; setting  Patients (M/F); mean age; malocclusion; uni/ bilateral IC  No of ICs  Jaw/side  Exs (prim/perm)  Ortho measures; timing  Eligible outcome  CoI  1  Chaushu 2005  pNRS; university; Israel  OT: 30 (6/24); 14.8 years; uni/bil ICs CT: 30 (13/17); 16 years; uni/bil ICs  OT: 32 CT: 25  OT: Max/LAB-PAL CT: Max/LAB-PAL  —  OT: Ortho-T; 1 week post-OP (OT) CT: Ortho-T; post-OP  SurgDur; Pain, oral function, general activity and other symptoms  NR  2  Gharaibeh 2008  RCT; university; Jordan  OT: 16 (2/14); 17.3 years; uni ICs CT: 16 (2/14); 17.6 years; uni ICs  OT: 16 CT: 16  OT: Max/PAL CT: Max/PAL  —  OT/CT: Ortho-T; 1 week post-OP (OT/CT)  SurgDur; pain  NR  3  Koutzoglou 2013  pNRS; private practice; Greece  OT: 46 (NR); NR years; uni/bil ICs CT: 50 (NR); NR years; uni/bil ICs  OT: 57 CT: 62  OT: Max-Mnd/LAB-PAL CT: Max-Mnd/LAB-PAL  OT: 47 pc CT: 47 pc  SOa OT/CT: Ortho-T; 1 week post-OP  Ankylosis; fibrous connective tissue  None  4  londhe 2014  RCT; university; India  OT: 16 (NR); NR years, uni/bil ICs CT: 15 (NR); NR years, uni/bil ICs  OT: 16 CT: 15  OT: Max/LAB CT: Max/LAB  —  SO OT/CT: Ortho-T; post OP  SurgDur; pain; recovery period; Tx duration; mobility; vitality; swelling; root integrity  None  5  Marzouk 1997  pNRS; hospital; Saudia Arabia  OT: 33 (NR); NR, NR years, uni/bil ICs CT: 33 (NR); NR, NR years, uni ICs  OT: 33 CT: 33  OT: Max/LAB-PAL CT: Max/LAB-PAL  Max 4s (in some cases)  SO; OT: Ortho-T; 1 week post-OP (OT) CT: Ortho-T; post-OP  Tx duration; attachment rebond need  NR  6  Parkin 2012; 2013; 2015  RCT; university; England  OT: 40 (13/27); 14.3 years; uni ICs CT: 41 (16/25); 14.1 years; uni ICs  OT: 40 CT: 41  OT: Max/PAL CT: Max/PAL  pc (if present)  OT/CT: Ortho-T; timing NR  SurgDur; pain; failure rate; esthetic outcome  None  7  Smailiene 2013a;b  RCT; university, Lithuania  OT: 22 (NR); NR years; uni ICs CT: 21 (NR); NR years; uni ICs  OT: 22 CT: 21  OT: Max/PAL CT: Max/PAL  —  OT: No Ortho-T CT: Ortho-T; 1 week post-OP  Tx duration; tooth shape, position, and colour  None  8  Szarmach 2006  pNRS; university; Poland  OT: 4 (NR); NR years; uni ICs CT: 20 (NR); NR years; uni ICs  OT:4 CT: 20  OT: Max/LAB-PAL CT: Max/LAB-PAL  —  OT/CT: Ortho-T; timing NR  Tx duration  NR  AA  Trial  Design; setting  Patients (M/F); mean age; malocclusion; uni/ bilateral IC  No of ICs  Jaw/side  Exs (prim/perm)  Ortho measures; timing  Eligible outcome  CoI  1  Chaushu 2005  pNRS; university; Israel  OT: 30 (6/24); 14.8 years; uni/bil ICs CT: 30 (13/17); 16 years; uni/bil ICs  OT: 32 CT: 25  OT: Max/LAB-PAL CT: Max/LAB-PAL  —  OT: Ortho-T; 1 week post-OP (OT) CT: Ortho-T; post-OP  SurgDur; Pain, oral function, general activity and other symptoms  NR  2  Gharaibeh 2008  RCT; university; Jordan  OT: 16 (2/14); 17.3 years; uni ICs CT: 16 (2/14); 17.6 years; uni ICs  OT: 16 CT: 16  OT: Max/PAL CT: Max/PAL  —  OT/CT: Ortho-T; 1 week post-OP (OT/CT)  SurgDur; pain  NR  3  Koutzoglou 2013  pNRS; private practice; Greece  OT: 46 (NR); NR years; uni/bil ICs CT: 50 (NR); NR years; uni/bil ICs  OT: 57 CT: 62  OT: Max-Mnd/LAB-PAL CT: Max-Mnd/LAB-PAL  OT: 47 pc CT: 47 pc  SOa OT/CT: Ortho-T; 1 week post-OP  Ankylosis; fibrous connective tissue  None  4  londhe 2014  RCT; university; India  OT: 16 (NR); NR years, uni/bil ICs CT: 15 (NR); NR years, uni/bil ICs  OT: 16 CT: 15  OT: Max/LAB CT: Max/LAB  —  SO OT/CT: Ortho-T; post OP  SurgDur; pain; recovery period; Tx duration; mobility; vitality; swelling; root integrity  None  5  Marzouk 1997  pNRS; hospital; Saudia Arabia  OT: 33 (NR); NR, NR years, uni/bil ICs CT: 33 (NR); NR, NR years, uni ICs  OT: 33 CT: 33  OT: Max/LAB-PAL CT: Max/LAB-PAL  Max 4s (in some cases)  SO; OT: Ortho-T; 1 week post-OP (OT) CT: Ortho-T; post-OP  Tx duration; attachment rebond need  NR  6  Parkin 2012; 2013; 2015  RCT; university; England  OT: 40 (13/27); 14.3 years; uni ICs CT: 41 (16/25); 14.1 years; uni ICs  OT: 40 CT: 41  OT: Max/PAL CT: Max/PAL  pc (if present)  OT/CT: Ortho-T; timing NR  SurgDur; pain; failure rate; esthetic outcome  None  7  Smailiene 2013a;b  RCT; university, Lithuania  OT: 22 (NR); NR years; uni ICs CT: 21 (NR); NR years; uni ICs  OT: 22 CT: 21  OT: Max/PAL CT: Max/PAL  —  OT: No Ortho-T CT: Ortho-T; 1 week post-OP  Tx duration; tooth shape, position, and colour  None  8  Szarmach 2006  pNRS; university; Poland  OT: 4 (NR); NR years; uni ICs CT: 20 (NR); NR years; uni ICs  OT:4 CT: 20  OT: Max/LAB-PAL CT: Max/LAB-PAL  —  OT/CT: Ortho-T; timing NR  Tx duration  NR  BR, brackets rebonding; CT, closed technique; CoI, conflict of interest; F, female; IC, impacted canine; LAB, labial; LIN, lingual; M, male; Max, maxilla; Mnd, mandible; NR, not reported; OT, open technique; Ortho-T; orthodontic traction; pNRS, prospective non-randomized study; PAL, palatinal; pc, primary canine; RCT, randomized controlled trial; RPE, rapid palatal expansion; SurgDur, duration of surgical procedure; SO, space opening; in, if needed; uNRS, unclear non-randomized study. aRapid maxillary expansion also performed on some patients (51 of 150 maxillary cases), but is not reported further. View Large Risk of bias within studies The risk of bias for the eight trials included is summarized in Figure 2 and given in detail in Supplementary Appendices 4–5. High risk of bias was found in all four RCTs included for at least one bias domain, with the most problematic domain being complete blinding of outcome assessments (missing in all four trials) and improper randomization (in one trial). All four non-randomized trials had also at least one problematic domain, with the most critical domains being incomplete reporting of follow-up and drop-outs, lack of blinding, and lack of proper confounder assessment. Figure 2. View largeDownload slide Summary of the risk of bias of the randomized (upper half) and non-randomized (lower half) trials included in this systematic review. C1, C2, C3…: criterion 1, criterion 2, criterion 3, … (for details see Supplementary Appendix 5). Figure 2. View largeDownload slide Summary of the risk of bias of the randomized (upper half) and non-randomized (lower half) trials included in this systematic review. C1, C2, C3…: criterion 1, criterion 2, criterion 3, … (for details see Supplementary Appendix 5). Results of individual studies and data synthesis The results of all outcomes reported in all included studies can be found in Supplementary Appendix 6. Additionally, the re-analyses of raw data available for the studies of Chaushu et al. (14) and Marzouk et al. (39) can be seen in Supplementary Appendices 7–10. The results of the meta-analyses for the review’s primary and secondary outcomes can be seen in Table 2. Table 2. Results of random-effects (Paule-Mandel) meta-analyses for the primary and secondary outcomes from all studies. Outcome  Studies  Effect  95% CI  P value  tau2 (95% CI)  I2 (95% CI)  95% prediction  Primary   Duration; surgical exposure  3a  Omitted  Omitted  Omitted  Omitted  Omitted     Duration; initial canine traction  3b  MD: –2.14  –4.23, –0.05  0.045  2.39 (0.27, 50.00)  74% (25%, 98%)  –7.35, 3.07   Duration; bond debond  1  MD: –3.78  –9.21, 1.65  0.172  na  na    Secondary   Failure; re-exposure need  2  RR: 2.91  0.49, 17.12  0.238  0.83 (0.00, 32.70)  48% (0%, 97%)     Ankylosis  1  OR: 0.15  0.03, 0.83  0.030  na  na     Colour difference  1  RR: 1.91  0.19, 19.52  0.586  na  na     Unoperated canine best; laypersons  1  MD: –1.73  –15.90, 12.44  0.811  na  na     Unoperated canine best; orthodontists  1  MD: –0.32  –15.10, 14.46  0.966  na  na     Pain; averaged  3  MD: 0.30  –0.52, 1.13  0.470  0.32 (0.00, 5.75)  60% (0%, 97%)  –8.68, 9.28   Difficulty in eating  2  MD: 0.54  –0.73, 1.80  0.404  0.44 (0.00, 46.22)  52% (0%, 99%)     Difficulty in speech  2  MD: 0.35  –0.73, 1.44  0.521  0.31 (0.00, 4.43)  50% (0%, 94%)    Outcome  Studies  Effect  95% CI  P value  tau2 (95% CI)  I2 (95% CI)  95% prediction  Primary   Duration; surgical exposure  3a  Omitted  Omitted  Omitted  Omitted  Omitted     Duration; initial canine traction  3b  MD: –2.14  –4.23, –0.05  0.045  2.39 (0.27, 50.00)  74% (25%, 98%)  –7.35, 3.07   Duration; bond debond  1  MD: –3.78  –9.21, 1.65  0.172  na  na    Secondary   Failure; re-exposure need  2  RR: 2.91  0.49, 17.12  0.238  0.83 (0.00, 32.70)  48% (0%, 97%)     Ankylosis  1  OR: 0.15  0.03, 0.83  0.030  na  na     Colour difference  1  RR: 1.91  0.19, 19.52  0.586  na  na     Unoperated canine best; laypersons  1  MD: –1.73  –15.90, 12.44  0.811  na  na     Unoperated canine best; orthodontists  1  MD: –0.32  –15.10, 14.46  0.966  na  na     Pain; averaged  3  MD: 0.30  –0.52, 1.13  0.470  0.32 (0.00, 5.75)  60% (0%, 97%)  –8.68, 9.28   Difficulty in eating  2  MD: 0.54  –0.73, 1.80  0.404  0.44 (0.00, 46.22)  52% (0%, 99%)     Difficulty in speech  2  MD: 0.35  –0.73, 1.44  0.521  0.31 (0.00, 4.43)  50% (0%, 94%)    CI, confidence interval; MD, mean difference; na, not applicable; OP, operation; OR, odds ratio; RR, relative risk. aHigh heterogeneity identified (I2 > 75%), which remained unexplained; meta-analysis of three studies [MD (95% CI) = –5.44 (–11.92, 1.03); P = 0.099; tau2 (95% CI) = 26.47 (10.84, 50.00); I2 (95% CI) = 83% (66%, 90%)] was omitted, as elimination of any single study was not straightforward (MDs of –8.56, –6.80, and 0). bInitial meta-analysis included three studies [MD (95% CI) = –2.26 (–4.91, 0.39); P = 0.094] with high heterogeneity [tau2 (95% CI) = 4.35 (1.85, 50.00); I2 (95% CI) = 84% (70%, 98%)]. As two studies (Parkin 2012; Smailiene 2013) included only palatally impacted canines and the third (Marzouk 1997) included both palatally and labially impacted canines, only the subsample of palatally impacted canines was included from the third study to achieve homogeneity. View Large As far as the primary outcome of treatment duration is concerned, data was available on two levels: first, the duration from surgical exposure to the initial alignment of the canine to the occlusal plane/dental arch and second, complete treatment duration from appliance insertion to appliance removal. Meta-analysis of three studies on the initial alignment of the impacted canine to the dental arch indicated that open exposure was associated with a statistically significant reduction in treatment duration by 2.14 months (95% CI: 0.05–4.23 months less; P < 0.05) compared to the closed exposure, with moderate heterogeneity (tau2: 2.39; I2: 74%; Table 2; Figure 3). Based on the 95 per cent prediction interval, this indicated that in a future setting initial canine alignment with the open technique might take 7.4 less to 3.1 months more than the closed technique. On the other side, one included trial reported a small reduction in overall treatment duration (bond to debond), but this was not statistically significant, probably due to low power (MD: –3.78 months; 95% CI: –9.21 to 1.65 months; P > 0.05). Figure 3. View largeDownload slide Contour-enhanced forest plot with random-effects (Paule-Mandel) meta-analysis of the review’s primary outcome (treatment duration in months). Figure 3. View largeDownload slide Contour-enhanced forest plot with random-effects (Paule-Mandel) meta-analysis of the review’s primary outcome (treatment duration in months). As far as the secondary outcomes are concerned, no statistically significant differences between open and closed exposure could be found for (i) re-exposure need, (ii) canine discoloration, (iii) post-operative pain, (iv) difficulty in eating, (v) difficulty in speech, and (vi) canine aesthetics. However, open exposure was associated with a significantly lower odds for ankylosis of the impacted canine (OR = 0.15; 95% CI 0.03–0.83; P < 0.05), which was statistically and clinically relevant. This was translated clinically to an NNT of 9 (95% CI 8–47), which indicates that for every nine impacted canines treated with a closed exposure technique, an additional ankylosis of the impacted canine would be observed than if an open technique had been favored. Quality of evidence Assessment of existing meta-evidence with the GRADE approach (Table 3) indicated that moderate quality evidence supported the shorter initial alignment duration with the open technique. For the rest of the outcomes, low to very low quality of evidence existed, due to the inclusion of non-randomized studies, their high risk of bias, and the imprecision stemming from the small number of included studies. Table 3. GRADE summary of findings table for the primary and secondary outcomes. OutcomeStudies (canines)  Relative effects (95% CI)  Anticipated absolute effectsa (95% CI)  Quality of the evidence (GRADE)  What happens with open technique  Closed technique*  Open technique  Difference  Tx duration (initial traction) three studies (135 canines)  —  9.7 months  —  2.1 months less (0.1–4.2 less)  ⊕⊕⊕◯ moderatea,b due to bias  Shorter initial traction of impacted canines  Tx duration (bond-debond) one study (43 canines)  —  32.2 months  —  3.8 less months (1.7 more to 9.2 less)  ⊕⊕◯◯ lowb,c due to bias and imprecision  There may be little or no difference  Failure; re-exposure need two studies (118 canines)  RR 2.91 (0.49, 17.12)  10.1%  29.4% (4.9–100.0%)  19.3% more canines needing re-exposure (5.2% less to 89.9% more)  ⊕◯◯◯ very lowb,c,d due to bias and imprecision  There may be little or no difference  Failure; canine ankylosis one study (119 canines)  OR 0.15 (0.03–0.83)  14.5%  2.5% (0.5–12.3%)  12.0% less ankylosed canines (2.2–14.0% less)  ⊕⊕◯◯ lowe due to bias  Greatly reduces the risk of ankylosis  Color difference one study (43 canines)  RR 1.91 (0.19, 19.52)  4.8%  9.2% (0.9–93.7%)  4.4% more canine with different colour (3.9% less to 88.9% more)  ⊕⊕◯◯ lowb,c due to bias and imprecision  There may be little or no difference  Unoperated canine best; laypersons (VAS scala)f one study (67 canines)  —  5.9/10 points in VAS  —  0.2 less (1.2 less to 1.6 more)  ⊕⊕◯◯ lowb,c due to bias and imprecision  There may be little or no difference  Unoperated canine best; orthodontists (VAS scala)f one study (67 canines)  —  6.1/10 points in VAS  —  <0.1 less (1.5 less to 1.5 more)  ⊕⊕◯◯ lowb,c due to bias and imprecision  There may be little or no difference  Post operative pain (VAS scala) three studies (143 canines)  —  3.7/10 points in VAS  —  0.3 points more (0.5 less to 1.1 more)  ⊕◯◯◯ very lowb,c,d due to bias and imprecision  There may be little or no difference  Difficulty in eating (VAS scala) two studies (112 canines)  —  4.1/10 points in VAS  —  0.5 points more (0.7 less to 1.8 more)  ⊕◯◯◯ very lowb,c,d due to bias and imprecision  There may be little or no difference  Difficulty in speech (VAS scala) two studies (112 canines)  —  2.3/10 points in VAS  —  0.4 points more (0.7 less to 1.4 more)  ⊕◯◯◯ very lowb,c,d due to bias and imprecision  There may be little or no difference  OutcomeStudies (canines)  Relative effects (95% CI)  Anticipated absolute effectsa (95% CI)  Quality of the evidence (GRADE)  What happens with open technique  Closed technique*  Open technique  Difference  Tx duration (initial traction) three studies (135 canines)  —  9.7 months  —  2.1 months less (0.1–4.2 less)  ⊕⊕⊕◯ moderatea,b due to bias  Shorter initial traction of impacted canines  Tx duration (bond-debond) one study (43 canines)  —  32.2 months  —  3.8 less months (1.7 more to 9.2 less)  ⊕⊕◯◯ lowb,c due to bias and imprecision  There may be little or no difference  Failure; re-exposure need two studies (118 canines)  RR 2.91 (0.49, 17.12)  10.1%  29.4% (4.9–100.0%)  19.3% more canines needing re-exposure (5.2% less to 89.9% more)  ⊕◯◯◯ very lowb,c,d due to bias and imprecision  There may be little or no difference  Failure; canine ankylosis one study (119 canines)  OR 0.15 (0.03–0.83)  14.5%  2.5% (0.5–12.3%)  12.0% less ankylosed canines (2.2–14.0% less)  ⊕⊕◯◯ lowe due to bias  Greatly reduces the risk of ankylosis  Color difference one study (43 canines)  RR 1.91 (0.19, 19.52)  4.8%  9.2% (0.9–93.7%)  4.4% more canine with different colour (3.9% less to 88.9% more)  ⊕⊕◯◯ lowb,c due to bias and imprecision  There may be little or no difference  Unoperated canine best; laypersons (VAS scala)f one study (67 canines)  —  5.9/10 points in VAS  —  0.2 less (1.2 less to 1.6 more)  ⊕⊕◯◯ lowb,c due to bias and imprecision  There may be little or no difference  Unoperated canine best; orthodontists (VAS scala)f one study (67 canines)  —  6.1/10 points in VAS  —  <0.1 less (1.5 less to 1.5 more)  ⊕⊕◯◯ lowb,c due to bias and imprecision  There may be little or no difference  Post operative pain (VAS scala) three studies (143 canines)  —  3.7/10 points in VAS  —  0.3 points more (0.5 less to 1.1 more)  ⊕◯◯◯ very lowb,c,d due to bias and imprecision  There may be little or no difference  Difficulty in eating (VAS scala) two studies (112 canines)  —  4.1/10 points in VAS  —  0.5 points more (0.7 less to 1.8 more)  ⊕◯◯◯ very lowb,c,d due to bias and imprecision  There may be little or no difference  Difficulty in speech (VAS scala) two studies (112 canines)  —  2.3/10 points in VAS  —  0.4 points more (0.7 less to 1.4 more)  ⊕◯◯◯ very lowb,c,d due to bias and imprecision  There may be little or no difference  Effectiveness and adverse effects of interventions to surgically expose and rehabilitate impacted canines. Patient or population: patients with labially or palatally/lingually impacted permanent canines. Settings: university clinics (England, India, Israel, Jordan, Lithuania, Poland), private practice (Greece), and hospital (Saudi Arabia). CI, confidence interval; GRADE, Grading of Recommendations Assessment, Development and Evaluation; OR, odds ratio; RR, relative risk; VAS, visual analogue scale. *Response or risk in the control group is based on the average of included studies. aShould start from low due to the inclusion of the non-randomized study of Marzouk 1997, but exclusion of this (Table 3) lead only to effect magnification. Therefore, it was judged safe to start from high GRADE, as no bias could be identified. bDowngraded by one due to the high risk of bias of included studies. cDowngraded by one due to imprecision, judged by the small number of included studies with limited sample sizes and the wide confidence intervals. dStarts from low due to the inclusion of the non-randomized study of Chaushu 2005. eGRADE would be upgrade by one for confounding (as confounders were assessed through multivariable regression modelling) and by one due to very large effect magnitude; given however that the trial was not free of risk of bias, we decided not to upgrade. fTranslated from 100 mm VAS to 10 cm VAS for consistency. View Large Additional analyses Additional analyses were undertaken in order to assess the possible impact of impaction-related characteristics on treatment outcomes. As such, data from two included studies were re-analyzed post hoc for this systematic review with multiple regressions (including explorative interaction terms) to assess potential differences in outcomes between labially and palatally impacted canines (Supplementary Appendices 7–10). According to these, the initial alignment of the impacted canine to the dental arch took significantly longer for palatally than for labially impacted canines (8.87 versus 4.17 months, respectively; Supplementary Appendices 9), with an adjusted difference of 4.70 months less for labial impactions compared to palatal impactions (P < 0.001). However, open exposure was found to be consistently superior to closed exposure for both labial and palatal impactions (P > 0.05 for interaction of impaction localization and exposure technique; Supplementary Appendix 10). Other than that, no significant difference was found in any of the treatment outcomes according to impaction localization, with the sole exception of intraoperative need for surgical bone removal (P = 0.042 for interaction of impaction localization and exposure technique; Supplementary Appendix 11). Stratified analysis by canine localization indicated that open exposure of palatal canines was tendentially associated with greater bone removal need than closed exposure, while the opposite tendency seen for labially impacted canines. However, the results of the stratified analysis were not statistically significant, presumably due to the loss of power from stratifying an already limited sample. Additional analyses were planned in the review’s protocol regarding various patient-, impaction-, or treatment-related factors, but the majority of them could not be performed, due to limited data. One included study indicated that increasing patient age and impaction severity were both associated with higher odds of ankylosis of the impacted canine (P < 0.05) (40). Re-analysis of the provided Chaushu et al. (14) data indicated that patient gender was significantly associated with post-operative swelling, the ability to enjoy food, and complaints of bad taste/smell after the exposure surgery (Supplementary Appendix 8). Additionally, a tendency for intraoperative greater bone removal need in older patients and a subsequent greater difficulty in speech in those cases was observed (Supplementary Appendix 4). Finally, a sensitivity analysis was performed by excluding non-randomized trials (Table 4), which indicated that the shorter duration of initial canine relocation with open exposure was robust to the inclusion of non-randomized trials, as the effect magnitude was actually enlarged (3.50 months less compared to the initial 2.14 months less of the original analysis). The decreased ankylosis risk with open exposure on the other side could not be confirmed, as no randomized trial reported this outcome. No further sensitivity analyses, nor any assessments of reporting biases, including small-study effects and publication bias, could be performed due to limited studies. Table 4. Sensitivity analysis including only randomized clinical trials for the primary and secondary outcomes. Outcome  Studies  Effect  95% CI  P value  tau2 (95% CI)  I2 (95% CI)  Primary   Duration; surgical exposure  3  Same as Table 2   Duration; initial canine traction  2  MD: –3.50  –6.23, –0.78  0.012  2.09 (0.00, 0.00)  51% (0%, 0%)   Duration; bond debond  1  Same as Table 2  Secondary   Failure; re-exposure need  1  RR: 3.39  0.37, 31.02  0.280  na  na   Ankylosis  0  —  —  —  —  —   Colour difference  1  RR: 1.91  0.19, 19.52  0.586  na  na   Unoperated canine best; laypersons  1  MD: –1.73  –15.90, 12.44  0.811  na  na   Unoperated canine best; orthodontists  1  MD: –0.32  –15.10, 14.46  0.966  na  na   Pain; averaged  2  MD: 0.17  –0.58, 0.92  0.653  0.16 (0.00, 32.00)  47% (0%, 99%)   Difficulty in eating  1  MD: 0.40  –0.74, 1.54  0.490  na  na   Difficulty in speech  1  MD: 0.40  –0.70, 1.50  0.475  na  na  Outcome  Studies  Effect  95% CI  P value  tau2 (95% CI)  I2 (95% CI)  Primary   Duration; surgical exposure  3  Same as Table 2   Duration; initial canine traction  2  MD: –3.50  –6.23, –0.78  0.012  2.09 (0.00, 0.00)  51% (0%, 0%)   Duration; bond debond  1  Same as Table 2  Secondary   Failure; re-exposure need  1  RR: 3.39  0.37, 31.02  0.280  na  na   Ankylosis  0  —  —  —  —  —   Colour difference  1  RR: 1.91  0.19, 19.52  0.586  na  na   Unoperated canine best; laypersons  1  MD: –1.73  –15.90, 12.44  0.811  na  na   Unoperated canine best; orthodontists  1  MD: –0.32  –15.10, 14.46  0.966  na  na   Pain; averaged  2  MD: 0.17  –0.58, 0.92  0.653  0.16 (0.00, 32.00)  47% (0%, 99%)   Difficulty in eating  1  MD: 0.40  –0.74, 1.54  0.490  na  na   Difficulty in speech  1  MD: 0.40  –0.70, 1.50  0.475  na  na  CI, confidence interval; MD, mean difference; na, not applicable; OP, operation; OR, odds ratio; RR, relative risk. View Large Discussion Summary of evidence This systematic review summarized existing evidence from eight randomized and prospective non-randomized trials that included a total of 433 patients and a total of 453 impacted canines treated with either an open or closed surgical exposure. As far as the primary outcome of treatment duration is concerned, existing evidence indicated that open approach was associated with substantial gains in the duration of initial canine alignment to the dental arch compared to the closed technique (gain of 2.1 or 3.5 months less according to the original and the sensitivity analysis, respectively) (Tables 2 and 4). This might be associated with the lack of a repositioned flap over the exposed canine, which could act as an obstacle to the tooth’s eruption. On the other side, it might be that open exposure technique is used selectively for canines located directly under the mucosa surface (13), which might add confounding, as these canines have per se a shorter eruption path to the dental arch. This was the case for the included non-randomized trial of Szarmach et al. (41), where exposure technique was chosen ‘depending on the impaction zone and the distance to the occlusal plane’. However, the sensitivity analysis, excluding this trial and including only trials where impacted canines were randomly allocated to a technique irrespective of their localization, found actually larger time gains for the open exposure (3.5 versus 2.1 months, Tables 2 and 4). These results seem to be in agreement with a previous retrospective study, which reported higher alignment failure of the impacted canines with the closed technique and attributed this to scar tissue, improper traction direction, or the presence of dense connective tissue in the eruption way of the canine (42). Additionally, exposure of impacted canines with an open technique was associated with significantly lower odds of ankylosis (OR = 0.15; 95% CI 0.03–0.83; P < 0.05), which was independent of patient age, sex, impaction side (labially or palatally) or grade of impaction (40). This could be a direct effect due to trauma of the periodontal ligament or root cementum by the low-speed bur, chemical trauma from the etching gel (43), or the use orthodontic forces of high magnitude or inappropriate direction (40). Alternatively, this could be an indirect effect resulting from the shorter traction time, where potentially damaging heavy orthodontic forces are applied. Furthermore, canine localization was found to be significantly associated to treatment duration according to the re-analysis of Marzouk et al. (39) data, which indicated that palatally impacted canines needed on average 4.70 months longer to align than labially impacted ones (Supplementary Appendix 10). This is in agreement with retrospective data (27) and could be due to the fact that palatally impacted canines may lie a lot further from the occlusal plane than labially impacted ones, resulting in a longer eruption path. Finally, limited evidence indicated that older patients were associated with higher odds of tooth ankylosis than younger patients, irrespective of canine localization, impaction grade, or exposure technique (40). This is in agreement with other retrospective studies not included in this review, which reported that patient age seemed to be associated with prolonged duration (42) and less favorable prognosis (44) for the alignment of the impacted canine. Strengths and limitations The strengths of this systematic review consist of the a priori registration in PROSPERO (45), an extensive and unrestricted literature search, use of robust review procedures for qualitative/quantitative data synthesis (46), exclusion of biased study designs (47), use of a novel estimator for random-effects variance (31), clinical translation of the meta-analysis results (34), and assessment of cumulative meta-evidence with the GRADE approach (36). However, some limitations are also present in this study. First and foremost, this systematic review included some non-randomized trials, and although sensitivity analyses indicated that this did not affect the results, moderate to high risk of bias was observed for all trials. Additionally, predominantly small trials were included, which could influence the results of the meta-analyses (48). Furthermore, clarifications or individual patient data couldn’t be obtained from attempts to communicate with trialists [except for one case (14)], thus re-analysis to take into account baseline confounding and clustrering effects were precluded. It is important to note that for many comparisons with non-significant results wide 95 per cent CIs existed, which indicate high uncertainty around these estimates and more trials need to be added to the evidence base to reduce this uncertainty. Finally, the limited number of included trials did not enable robust assessments of heterogeneity, subgroup analyses, small-study effects, and reporting biases for most of the outcomes. Conclusions Based on a limited number of relatively small randomized and prospective non-randomized trials, open surgical exposure of impacted canines seems to be superior to the closed approach in terms of reduced initial alignment duration and decreased risk of ankylosis. No other significant differences in adverse effects or patient-oriented outcomes could be found between the two exposure techniques. Recommendations for further research Additional parallel or cluster-randomized trials compliant with the CONSORT statement (49) are needed to fill current evidence gaps. These pertain to the feasibility of each exposure technique according to the specific localization of impacted canines [jaw, side, and height of impaction (50)], differences between various modifications of the two techniques, and the relative effectiveness of various orthodontic mechanotherapy alternatives (including the timing of force application). Finally, future trials should employ a priori sample size calculation to ensure adequate statistical power and take into account the clustering of multiple canines within patients (51). Supplementary material Supplementary material is available at European Journal of Orthodontics online. Conflicts of Interest None to declare. Acknowledgements The authors would like to thank S. Chaushu (Hebrew University, Jerusalem, Israel) for providing raw data from their study, and S. Koutzoglou (Private practice, Rethymno, Greece), P. Benson (University of Sheffield, UK), D. Smailiene (Lithuanian University of Health Sciences, Kaunas, Lithuania) for responding to communication attempts. References 1. Takahama, Y. and Aiyama, Y. ( 1982) Maxillary canine impaction as a possible microform of cleft lip and palate. European Journal of Orthodontics , 4, 275– 277. Google Scholar CrossRef Search ADS PubMed  2. Sacerdoti, R. and Baccetti, T. ( 2004) Dentoskeletal features associated with unilateral or bilateral palatal displacement of maxillary canines. The Angle Orthodontist , 74, 725– 732. Google Scholar PubMed  3. Johnston, W.D. ( 1969) Treatment of palatally impacted canine teeth. American Journal of Orthodontics , 56, 589– 596. Google Scholar CrossRef Search ADS PubMed  4. Rimes, R.J., Mitchell, C.N. and Willmot, D.R. 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The European Journal of OrthodonticsOxford University Press

Published: Feb 1, 2018

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