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A cost-minimization analysis of large overjet reduction with two removable functional appliances based on a randomized controlled trial

A cost-minimization analysis of large overjet reduction with two removable functional appliances... Summary Objective The purpose of this study was to assess and relate the societal costs of reducing large overjet with a prefabricated functional appliance (PFA), or a slightly modified Andresen activator (AA), using a cost-minimization analysis (CMA). Design, settings, and participants A multicentre, prospective, randomized clinical trial was conducted with patients from 12 general dental practices. Ninety-seven patients with an Angle Class II, division 1 malocclusion, and an overjet of ≥6 mm were randomly allocated by lottery to treatment with either a PFA or an AA. The PFA and AA groups consisted of 57 and 40 subjects, respectively. Blinding was not performed. Duration of treatment, number of scheduled/unscheduled appointments, and retreatment were registered. Direct and indirect costs were analysed with reference to intention-to-treat (ITT), successful (S), and unsuccessful (US) outcomes. Societal costs were described as the total of direct and indirect costs, not including retreatments. Interventions Treatment with a PFA or an AA. Results The direct and societal costs were significantly lower for the PFA than for the AA group. The number of visits was lower in the PFA group, when ITT was considered, and for the US cases as well. No difference in retreatment rate could be seen between the groups. Limitations Costs depend on local factors and thus should not be generalized to other settings. Harms No harms were detected during the study. Conclusion The success rate of the both appliances was low. However, the PFA was the preferred approach for reduction of a large overjet in mixed dentition, since it minimized costs and there were no difference in clinical outcomes between PFA and AA. Registration This trial was registered at ‘FoU i Sverige’ (http://www.fou.nu/is/sverige), registration number: 97131. Protocol The protocol was not published before trial commencement. Introduction Dental health care in Sweden is free of charge for those below the age of 20 years. General dental practitioners (GDPs) are responsible for the diagnosis and selection of patients with malocclusions and, with the support of consulting orthodontists, also for some interceptive orthodontic treatments. Approximately, one-third of all children and adolescents in Sweden is offered orthodontic treatment (1, 2). Large overjet (>6 mm) as a feature of Class II malocclusions is seen in 14–15 per cent of 10-year-old Scandinavian children (3, 4). Early treatment has been suggested to reduce the incidence of incisal trauma to the upper permanent incisors in patients with large overjet, and/or incompetent lip closure (5–7). Treatment with removable functional appliances requires the patient’s interest, compliance, and considerable chair time with many additional visits. It has been stated that activators provide completely satisfactory results and ideal occlusion in only 33–35 per cent of cases treated (8, 9), and a recently published randomized controlled trial (RCT) confirmed this finding where successful (S) treatment outcomes (overjet 3 mm) were seen in 37 per cent of the subjects (10). Other studies, however, have presented success rates above 60 per cent when the treatment goal was less than ideal, or when treated by specialists, the latter possibly contributing to higher compliance (11, 12). Nevertheless, the method of choice for orthodontic treatment should depend on clinical skills and cost-effectiveness. A recent systematic review highlighted the need for orthodontic studies where both economic and clinical outcomes are presented (13). During the last 20 years, the interest for analysing costs of orthodontic treatment has increased and several studies have been published describing and comparing treatment costs following various orthodontic diagnoses and treatment circumstances (14–22). When allocating resources, including dental care and orthodontics, health service providers and financiers need to consider both the evidence of clinical effectiveness of the treatment procedures as well as the related costs, i.e. ‘value for money’ (23). A health-economic evaluation is characterized by the concern for the relationship between costs (inputs) and consequences (outputs), when different diagnostic or therapeutic options are considered. Four main techniques are available: cost-minimization analysis (CMA), cost-effectiveness analysis, cost-utility analysis, and cost–benefit analysis (24, 25). Economic assessments with a societal perspective comprise calculations of direct and indirect costs. Direct costs are those related to diagnostic or treatment interventions, whereas indirect costs are the loss of production due to the absence from work and travel expenses to the clinics. Societal costs are expressed as the sum of direct and indirect costs. Cost-effective healthcare requires valuation of the economic effects of interventions (26). The overall costs of treating large overjet have, thus far, not been clarified in an RCT. A recently published RCT of patients with large overjet, treated with a prefabricated functional appliance (PFA), or a slightly modified Andresen activator (AA), with a 1-year, post-retention follow-up, showed that both treatment approaches achieved comparable clinical outcomes (10). As both approaches accomplished similar clinical outcomes, a CMA was an appropriate form of economic evaluation. A CMA is applicable when two or more treatment methods achieve the same clinical outcomes (i.e. reduction of overjet), and the aim was to identify the least expensive method. Thus, the purpose of this study was to assess and relate the costs of reducing a large overjet by a PFA, and a slightly modified AA, using a CMA. It was hypothesized that not only the treatment effect in correcting large overjet was similar for both appliances but also the societal costs would be comparable. Subjects and methods Trial design and ethics This CMA was based on a multicentre, randomized, and controlled study that assessed the effectiveness of overjet reduction, including a 1-year follow-up (10). Informed written consent was obtained from parents before their children were enrolled in the study. The CMA was also based on a questionnaire survey of parental leave of absence and travel costs for dental visits during their child’s orthodontic treatment. The Research Ethics Committee at the University of Gothenburg approved this study (Dnr: 437-07), following the guidelines of the Declaration of Helsinki (27). Registration This trial was registered in the Research and Development database in Sweden (‘FoU i Sverige’, http://www.fou.nu/is/sverige), registration number 97131. Subjects and randomization The sample consisted of 97 subjects (44 girls, 53 boys), with a mean age of 10.3 years (7–14 years, SD 1.64). Patients fulfilling the criteria below were invited to participate in the study. Informed written consent was obtained from the parents, and randomization was performed by lottery. At each clinic, two envelopes were available, one for girls and one for boys with 5 AA and 5 PFA notes for each gender. If all notes were used, 240 participants would be available for the RCT (Figure 1). The following inclusion criteria were applied: 6–14 years of age with central incisors erupted, Angle Class II div 1, increased overjet ≥6 mm, and no previous orthodontic treatment. Patients with other malocclusions, e.g. crossbite, severe crowding, or agenesis that needed more extensive orthodontic treatment, were not included. Figure 1. View largeDownload slide Flow chart of the participants in the study. Figure 1. View largeDownload slide Flow chart of the participants in the study. The study was designed as intention-to-treat (ITT), and patients were randomly allocated to treatment with either a PFA or an AA (Figure 1). Detailed information on the trial design and treatment methods was published in a previous article (10). Interventions Appliances: The AA was a standardized, custom-made, slightly modified activator, with an opening in the frontal region to enable mouth breathing. All AAs were made at the same orthodontic dental laboratory according to a given prototype (Figure 2). The PFA (Myobrace®, Myofunctional Research Co, Australia) was available in seven sizes. The size of the appliance was chosen according to the manufacturer’s recommendation. All PFAs were ordered from the same company (Figure 2). Figure 2. View largeDownload slide Andresen activator (AA) standardized but custom-made, slightly modified with opening in the front to make it easier to wear for mouth breathers. Prefabricated functional appliance (PFA; myobracebrace®, Myofanctional Research Co, Australia). Figure 2. View largeDownload slide Andresen activator (AA) standardized but custom-made, slightly modified with opening in the front to make it easier to wear for mouth breathers. Prefabricated functional appliance (PFA; myobracebrace®, Myofanctional Research Co, Australia). Participants were instructed to use the appliance nightly and 2 hours during the day for a total of 12–14 hours. Outcomes Orthodontic outcome measures When a participant’s overjet had been reduced to ≤3 mm, the treatment was regarded as S, and the patient then continued to wear the appliance as a retainer only at night for 6 months. The treatment was classified as unsuccessful (US) if there was no reduction in overjet by 6 months and/or if they refused to use the appliance or keep appointments. Cost measures ‘Direct costs’ included chair time during the treatment and retention period, as well as material costs. Chair time costs comprised dental equipment and disposable items, premises, cleaning, maintenance, staff salaries, etc. All estimates of chair time costs were calculated in Swedish currency, at SEK 2000 (€212) per hour for a general practitioner according to the price list for general dentistry in the Public Dental Service (Folktandvården) in the Västra Götaland region. In addition, the number of appointments, scheduled and emergency appointments and cancellations were noted. However, broken appointments and cancellations were not included in the CMA. Material costs (i.e. laboratory invoices and fees for repairs) were collected and calculated according to the laboratory price list (TIC DPNova) for 2015. ‘Indirect costs’, i.e. loss of production when a parent took a leave of absence from work to accompany their child to the orthodontic appointment, were estimated as loss of income (salary plus employer charges to social insurance and collectively agreed private pension schemes). We conducted a questionnaire survey to collect data on travel time and costs, as well as national identification numbers for parents accompanying their child to the orthodontic treatment. National identification numbers were sent to the Swedish National Bureau of Statistics (http://www.scb.se) where they were matched with a longitudinal integration database for social insurance and labour market studies (LISA by Swedish acronym). The database presently contains annual registers and includes all registered residents in Sweden, 16 years of age or older. Outcomes from LISA provided the individual annual wages of the parents in SEK for 2013. Since the Consumer Price Index remained the same during the period 2013–2015, no adjustment for changes in cost of living was made. The average findings from the questionnaires and the LISA database are summed up in Table 1. Table 1. The average indirect costs in euros (€) and average duration based on a questionnaire survey for parents (n = 178) while accompanying the child to orthodontic treatment. Loss of income means salary plus employer charges to social insurance and collectively agreed private pension schemes. Loss of income €35/h Absent from work: 69 min  Appointment duration 20 min  Travelling time duration 49 min Travel costs €6/visit Loss of income €35/h Absent from work: 69 min  Appointment duration 20 min  Travelling time duration 49 min Travel costs €6/visit View Large Table 1. The average indirect costs in euros (€) and average duration based on a questionnaire survey for parents (n = 178) while accompanying the child to orthodontic treatment. Loss of income means salary plus employer charges to social insurance and collectively agreed private pension schemes. Loss of income €35/h Absent from work: 69 min  Appointment duration 20 min  Travelling time duration 49 min Travel costs €6/visit Loss of income €35/h Absent from work: 69 min  Appointment duration 20 min  Travelling time duration 49 min Travel costs €6/visit View Large The sum of direct and indirect costs was defined as ‘societal costs’. The cost analysis was based on the ITT principle, i.e. the analysis included data for costs of S and US cases. All costs were in 2015 prices and expressed in Euros (€), SEK 100 = €9.44 at a mean currency value (www.xe.se). Cost-minimization analysis The CMA was considered as follows: CMA = Societal costs divided by the number of patients in the ITT, S, and US groups, respectively. Post-retention follow-up All cases were followed up 4 years post-retention (Figure 1). Retreatment of large overjet with a removable functional appliance was documented during this period. No CMA was performed for retreatments. Sample size calculation According to a sample size analysis, 38 patients per group were required to obtain adequate power (80 per cent, at significance level P < 0.05 with an SD of 1.3, and with the loss of 10 patients), based on a clinically significant difference of 1 mm in overjet reduction between the study groups. The power was thus adequate to conclude that the clinical outcome was similar and comparable for the AA and the PFA appliances. Statistical analysis Statistical analyses were performed using SPSS for Windows 22.0 (SPSS, Inc., Chicago, IL, USA). Differences between the groups were analysed with chi-square and Fisher’s exact test for categorical variables, independent t-tests for continuous variables, and a Poisson distribution was assumed for count data (e.g. number of visits). In the analysis, the total sample was considered an ITT group, which comprised all subjects, a S group including participants who achieved an overjet ≤3 mm at end point, and an US group comprising participants discontinuing treatment, or not reaching the end point of the treatment. Parallel analyses were carried out in all three groups. P-values less than 0.05 were considered statistically significant. Broken appointments and cancellations were not included in CMA. Blinding was not performed. Results Participant flow and retreatment The PFA and AA group consisted of 57 (28 girls, 29 boys) and 40 subjects (16 girls, 24 boys), respectively. Figure 1 illustrates the flow of participants through the study. Successful treatment outcome (overjet ≤ 3 mm) was seen in 37 per cent of the subjects. No statistically significant difference in success rate, gender, age, or treatment time was found between the PFA and AA groups. The mean treatment time for the ITT group, including a retention period of 6 months, was 1.5 years (SD 0.70) in the AA group and 1.2 years (SD 0.60) in the PFA group. No statistically significant difference was seen between groups. The patients in the S treatment group had significantly (P < 0.001) longer treatment time (1.7 years) compared with the US (1.07 years) group. In the S group, retreatment of large overjet with a removable functional appliance was performed on one patient in the AA group due to relapse and none in the PFA group (Figure 3). Among the US cases in the AA and PFA group, 26 per cent and 36 per cent of the patients underwent retreatment of the large overjet, respectively (Table 2). The most common retreatment was performed with headgear activators on average 1.5 years post-retention (Table 3). No long-term follow-up monitoring was possible in three cases (Figure 3). Table 2. Mean number of regular and emergency visits, chair time during the treatment including retention period. A retreatment frequency of large overjet with removable appliances during a 4-year post-retention period. Intention-to-treat (ITT cases), successful cases (S), and unsuccessful cases (US). AA, Andresen activator; PFA, prefabricated functional appliance. AA PFA Group difference Mean (95% CI) SD Mean (95% CI) SD Mean (95% CI) P-value ITT AA (n = 40) PFA (n = 57) Number of visits 11.45 (10.4–12.6) 4.1 8.4 (7.7–9.2) 3.4 3 (1.5–4.5) <0.001 Emergency visits 0.7 (0.4–1.0) 0.9 0.1 (0.03–0.2) 0.4 0.6 (0.3–0.9) <0.001 Chair time (min) 245 (213–277) 100 167 (149–185) 67 78 (44–111) <0.001 Retreatment (%) 15% (4.3–27.7) 25% (13.1–36.3) 0.09 (−0.1–0.3) 0.317 S AA (n = 19) PFA (n = 17) Number of visits 13.1 (11.5–14.9) 3.6 11.2 (9.7–13.0) 3.1 1.9 (−0.4–4.1) 0.109 Emergency visits 0.8 (0.4–1.3) 1.0 0.1 (0.03–0.5) 0.5 0.7 (0.1–1.2) 0.034 Chair time (min) 276 (229–322) 97 213 (173–254) 79 63 (2–123) 0.043 Retreatment (%) 5% (0) 0% (0) 0.05 (−0.18–0.28) 1.000 US AA (n = 21) PFA (n = 40) Number of visits 10.0 (8.6–11.4) 4.0 7.2 (6.4–8.1) 2.8 2.7 (1.0–4.5) <0.001 Emergency visits 0.6 (0.3–1.0) 0.9 0.1 (0.02–0.2) 0.4 0.5 (0.2–0.8) 0.037 Chair time (min) 217 (173–261) 97 148 (131–164) 51 69 (32–107) <0.001 Retreatment (%) 26% (6.3–45.7) 36% (20.9–51.1) 0.1 (−0.19–0.33) 0.559 AA PFA Group difference Mean (95% CI) SD Mean (95% CI) SD Mean (95% CI) P-value ITT AA (n = 40) PFA (n = 57) Number of visits 11.45 (10.4–12.6) 4.1 8.4 (7.7–9.2) 3.4 3 (1.5–4.5) <0.001 Emergency visits 0.7 (0.4–1.0) 0.9 0.1 (0.03–0.2) 0.4 0.6 (0.3–0.9) <0.001 Chair time (min) 245 (213–277) 100 167 (149–185) 67 78 (44–111) <0.001 Retreatment (%) 15% (4.3–27.7) 25% (13.1–36.3) 0.09 (−0.1–0.3) 0.317 S AA (n = 19) PFA (n = 17) Number of visits 13.1 (11.5–14.9) 3.6 11.2 (9.7–13.0) 3.1 1.9 (−0.4–4.1) 0.109 Emergency visits 0.8 (0.4–1.3) 1.0 0.1 (0.03–0.5) 0.5 0.7 (0.1–1.2) 0.034 Chair time (min) 276 (229–322) 97 213 (173–254) 79 63 (2–123) 0.043 Retreatment (%) 5% (0) 0% (0) 0.05 (−0.18–0.28) 1.000 US AA (n = 21) PFA (n = 40) Number of visits 10.0 (8.6–11.4) 4.0 7.2 (6.4–8.1) 2.8 2.7 (1.0–4.5) <0.001 Emergency visits 0.6 (0.3–1.0) 0.9 0.1 (0.02–0.2) 0.4 0.5 (0.2–0.8) 0.037 Chair time (min) 217 (173–261) 97 148 (131–164) 51 69 (32–107) <0.001 Retreatment (%) 26% (6.3–45.7) 36% (20.9–51.1) 0.1 (−0.19–0.33) 0.559 View Large Table 2. Mean number of regular and emergency visits, chair time during the treatment including retention period. A retreatment frequency of large overjet with removable appliances during a 4-year post-retention period. Intention-to-treat (ITT cases), successful cases (S), and unsuccessful cases (US). AA, Andresen activator; PFA, prefabricated functional appliance. AA PFA Group difference Mean (95% CI) SD Mean (95% CI) SD Mean (95% CI) P-value ITT AA (n = 40) PFA (n = 57) Number of visits 11.45 (10.4–12.6) 4.1 8.4 (7.7–9.2) 3.4 3 (1.5–4.5) <0.001 Emergency visits 0.7 (0.4–1.0) 0.9 0.1 (0.03–0.2) 0.4 0.6 (0.3–0.9) <0.001 Chair time (min) 245 (213–277) 100 167 (149–185) 67 78 (44–111) <0.001 Retreatment (%) 15% (4.3–27.7) 25% (13.1–36.3) 0.09 (−0.1–0.3) 0.317 S AA (n = 19) PFA (n = 17) Number of visits 13.1 (11.5–14.9) 3.6 11.2 (9.7–13.0) 3.1 1.9 (−0.4–4.1) 0.109 Emergency visits 0.8 (0.4–1.3) 1.0 0.1 (0.03–0.5) 0.5 0.7 (0.1–1.2) 0.034 Chair time (min) 276 (229–322) 97 213 (173–254) 79 63 (2–123) 0.043 Retreatment (%) 5% (0) 0% (0) 0.05 (−0.18–0.28) 1.000 US AA (n = 21) PFA (n = 40) Number of visits 10.0 (8.6–11.4) 4.0 7.2 (6.4–8.1) 2.8 2.7 (1.0–4.5) <0.001 Emergency visits 0.6 (0.3–1.0) 0.9 0.1 (0.02–0.2) 0.4 0.5 (0.2–0.8) 0.037 Chair time (min) 217 (173–261) 97 148 (131–164) 51 69 (32–107) <0.001 Retreatment (%) 26% (6.3–45.7) 36% (20.9–51.1) 0.1 (−0.19–0.33) 0.559 AA PFA Group difference Mean (95% CI) SD Mean (95% CI) SD Mean (95% CI) P-value ITT AA (n = 40) PFA (n = 57) Number of visits 11.45 (10.4–12.6) 4.1 8.4 (7.7–9.2) 3.4 3 (1.5–4.5) <0.001 Emergency visits 0.7 (0.4–1.0) 0.9 0.1 (0.03–0.2) 0.4 0.6 (0.3–0.9) <0.001 Chair time (min) 245 (213–277) 100 167 (149–185) 67 78 (44–111) <0.001 Retreatment (%) 15% (4.3–27.7) 25% (13.1–36.3) 0.09 (−0.1–0.3) 0.317 S AA (n = 19) PFA (n = 17) Number of visits 13.1 (11.5–14.9) 3.6 11.2 (9.7–13.0) 3.1 1.9 (−0.4–4.1) 0.109 Emergency visits 0.8 (0.4–1.3) 1.0 0.1 (0.03–0.5) 0.5 0.7 (0.1–1.2) 0.034 Chair time (min) 276 (229–322) 97 213 (173–254) 79 63 (2–123) 0.043 Retreatment (%) 5% (0) 0% (0) 0.05 (−0.18–0.28) 1.000 US AA (n = 21) PFA (n = 40) Number of visits 10.0 (8.6–11.4) 4.0 7.2 (6.4–8.1) 2.8 2.7 (1.0–4.5) <0.001 Emergency visits 0.6 (0.3–1.0) 0.9 0.1 (0.02–0.2) 0.4 0.5 (0.2–0.8) 0.037 Chair time (min) 217 (173–261) 97 148 (131–164) 51 69 (32–107) <0.001 Retreatment (%) 26% (6.3–45.7) 36% (20.9–51.1) 0.1 (−0.19–0.33) 0.559 View Large Figure 3. View largeDownload slide Flow chart of the 4-year post-retention period. AA, Andresen activator; PFA, prefabricated functional appliance; US, unsuccessful group; S, successful group. Figure 3. View largeDownload slide Flow chart of the 4-year post-retention period. AA, Andresen activator; PFA, prefabricated functional appliance; US, unsuccessful group; S, successful group. Table 3. Number (n) of retreatment of large overjet with removable functional appliance used mean 1.5 years (0.5–3 years) post-retention. Retreatment with removable appliance n = 21 Appliance type:  Headgear activator (HA) n = 14  Removable plate (RP) n = 3  Combination (RP + HA) n = 4 Retreatment with removable appliance n = 21 Appliance type:  Headgear activator (HA) n = 14  Removable plate (RP) n = 3  Combination (RP + HA) n = 4 View Large Table 3. Number (n) of retreatment of large overjet with removable functional appliance used mean 1.5 years (0.5–3 years) post-retention. Retreatment with removable appliance n = 21 Appliance type:  Headgear activator (HA) n = 14  Removable plate (RP) n = 3  Combination (RP + HA) n = 4 Retreatment with removable appliance n = 21 Appliance type:  Headgear activator (HA) n = 14  Removable plate (RP) n = 3  Combination (RP + HA) n = 4 View Large Number of appointments The distribution of scheduled and emergency appointments is summarized in Table 2. The number of appointments was significantly higher in the AA group both for the ITT and US cases. The mean number of appointments for patients with S treatment outcomes showed no significant difference between the two groups, AA and PFA (P = 0.109), while the number of emergency visits was significantly higher (P < 0.001) in the AA than in the PFA group (Table 2). Costs Significant differences in direct, indirect, and societal costs were found between the AA and PFA for all subgroups, i.e. ITT, S, and US outcomes, in that costs were higher for the AA than for the PFA groups (P ≤ 0.001) (Table 4). Table 4. Mean direct costs of materials, direct costs for chair time, indirect costs, and societal costs in Euros (€). Intention-to-treat (ITT cases), successful cases (S), and unsuccessful cases (US) during the treatment including retention period. AA,Andresen activator; PFA, prefabricated functional appliance. AA PFA Group difference Mean (95% CI) SD Mean (95% CI) SD Mean (95% CI) P-value ITT AA (n = 40) PFA (n = 57) Direct costs—material 195 (171–219) 75 43 (39–47) 15 152 (132–172) <0.001 Direct costs—chair time 864 (751–977) 353 590 (527–652) 236 274 (155–393) <0.001 Indirect costs 489 (433–545) 176 341 (305–376) 134 148 (86–211) <0.001 Societal (total) costs 1548 (1366–1730) 569 974 (876–1071) 368 574 (385–764) <0.001 S AA (n = 19) PFA (n = 17) Direct costs—material 191 (152–229) 80 44 (37–52) 15 146 (107–187) <0.001 Direct costs—chair time 972 (943–1137) 342 753 (609–896) 279 220 (7–433) <0.001 Indirect costs 558 (488–628) 146 450 (381–519) 134 108 (13–203) <0.001 Societal (total) costs 1721 (1466–1976) 530 1247 (1035–1459) 411 160 (150–799) <0.001 US AA (n = 21) PFA (n = 40) Direct costs—material 199 (167–232) 72 42 (37–47) 15 157 (133–180) <0.001 Direct costs—chair time 766 (610–921) 341 521 (464–578) 178 245 (112–378) <0.001 Indirect costs 427 (344–509) 181 294 (261–328) 105 132 (59–205) 0.001 Societal (total) costs 1391(1132–1651) 570 857 (768–947) 281 534 (317–751) <0.001 AA PFA Group difference Mean (95% CI) SD Mean (95% CI) SD Mean (95% CI) P-value ITT AA (n = 40) PFA (n = 57) Direct costs—material 195 (171–219) 75 43 (39–47) 15 152 (132–172) <0.001 Direct costs—chair time 864 (751–977) 353 590 (527–652) 236 274 (155–393) <0.001 Indirect costs 489 (433–545) 176 341 (305–376) 134 148 (86–211) <0.001 Societal (total) costs 1548 (1366–1730) 569 974 (876–1071) 368 574 (385–764) <0.001 S AA (n = 19) PFA (n = 17) Direct costs—material 191 (152–229) 80 44 (37–52) 15 146 (107–187) <0.001 Direct costs—chair time 972 (943–1137) 342 753 (609–896) 279 220 (7–433) <0.001 Indirect costs 558 (488–628) 146 450 (381–519) 134 108 (13–203) <0.001 Societal (total) costs 1721 (1466–1976) 530 1247 (1035–1459) 411 160 (150–799) <0.001 US AA (n = 21) PFA (n = 40) Direct costs—material 199 (167–232) 72 42 (37–47) 15 157 (133–180) <0.001 Direct costs—chair time 766 (610–921) 341 521 (464–578) 178 245 (112–378) <0.001 Indirect costs 427 (344–509) 181 294 (261–328) 105 132 (59–205) 0.001 Societal (total) costs 1391(1132–1651) 570 857 (768–947) 281 534 (317–751) <0.001 View Large Table 4. Mean direct costs of materials, direct costs for chair time, indirect costs, and societal costs in Euros (€). Intention-to-treat (ITT cases), successful cases (S), and unsuccessful cases (US) during the treatment including retention period. AA,Andresen activator; PFA, prefabricated functional appliance. AA PFA Group difference Mean (95% CI) SD Mean (95% CI) SD Mean (95% CI) P-value ITT AA (n = 40) PFA (n = 57) Direct costs—material 195 (171–219) 75 43 (39–47) 15 152 (132–172) <0.001 Direct costs—chair time 864 (751–977) 353 590 (527–652) 236 274 (155–393) <0.001 Indirect costs 489 (433–545) 176 341 (305–376) 134 148 (86–211) <0.001 Societal (total) costs 1548 (1366–1730) 569 974 (876–1071) 368 574 (385–764) <0.001 S AA (n = 19) PFA (n = 17) Direct costs—material 191 (152–229) 80 44 (37–52) 15 146 (107–187) <0.001 Direct costs—chair time 972 (943–1137) 342 753 (609–896) 279 220 (7–433) <0.001 Indirect costs 558 (488–628) 146 450 (381–519) 134 108 (13–203) <0.001 Societal (total) costs 1721 (1466–1976) 530 1247 (1035–1459) 411 160 (150–799) <0.001 US AA (n = 21) PFA (n = 40) Direct costs—material 199 (167–232) 72 42 (37–47) 15 157 (133–180) <0.001 Direct costs—chair time 766 (610–921) 341 521 (464–578) 178 245 (112–378) <0.001 Indirect costs 427 (344–509) 181 294 (261–328) 105 132 (59–205) 0.001 Societal (total) costs 1391(1132–1651) 570 857 (768–947) 281 534 (317–751) <0.001 AA PFA Group difference Mean (95% CI) SD Mean (95% CI) SD Mean (95% CI) P-value ITT AA (n = 40) PFA (n = 57) Direct costs—material 195 (171–219) 75 43 (39–47) 15 152 (132–172) <0.001 Direct costs—chair time 864 (751–977) 353 590 (527–652) 236 274 (155–393) <0.001 Indirect costs 489 (433–545) 176 341 (305–376) 134 148 (86–211) <0.001 Societal (total) costs 1548 (1366–1730) 569 974 (876–1071) 368 574 (385–764) <0.001 S AA (n = 19) PFA (n = 17) Direct costs—material 191 (152–229) 80 44 (37–52) 15 146 (107–187) <0.001 Direct costs—chair time 972 (943–1137) 342 753 (609–896) 279 220 (7–433) <0.001 Indirect costs 558 (488–628) 146 450 (381–519) 134 108 (13–203) <0.001 Societal (total) costs 1721 (1466–1976) 530 1247 (1035–1459) 411 160 (150–799) <0.001 US AA (n = 21) PFA (n = 40) Direct costs—material 199 (167–232) 72 42 (37–47) 15 157 (133–180) <0.001 Direct costs—chair time 766 (610–921) 341 521 (464–578) 178 245 (112–378) <0.001 Indirect costs 427 (344–509) 181 294 (261–328) 105 132 (59–205) 0.001 Societal (total) costs 1391(1132–1651) 570 857 (768–947) 281 534 (317–751) <0.001 View Large Discussion Main findings This is the first study to evaluate the differences in costs between treatments with an AA and a PFA intending to reduce large overjet, based on outcomes of an RCT study. A health-economic valuation from a prospective RCT provides fewer biases. The random distribution of subjects reduces bias and confounding factors by ensuring that both known and unknown factors of outcome are equally distributed between subjects. The prospective design also assures that the baseline characteristics, treatment progression, treatment time, number of appointments, and side outcomes can be precisely controlled and observed. An ITT analysis was used, in which each patient record was evaluated, regardless of the effect of treatment. It is said that this method underestimates the extent of the treatment effects, since it includes data from patients who did not complete treatment. However, this is the suggested procedure for RCTs evaluating the average effect of treatment on the average patient (28, 29). As a result, the study outcomes are applicable to all patients who started treatment, rather than to only those who complied with treatment and achieved S results. The randomization process also reduces the risk of error due to factors such as selection bias, the clinician’s favoured treatment method, and the individual differences in skills of the general dental practitioner. However, overall clinical skills or lack of experience could still be a confounding factor in studies with small samples (30). Pietilä (31) conducted a cost and productivity analysis of orthodontic care in Finland. They found that there was a wide range in the cost of providing orthodontic care and that general dentists who had little orthodontic experience were associated with the highest costs (31). Contrary to the findings in the present study, a higher cost (societal and direct) for early treatment performed by specialists was presented in an RCT from the UK, but indirect costs were similar to those reported in this study, €474 compared with €489 (32). The outcomes in the present study reject the null hypothesis that AA and PFA treatment will be equal in an economic valuation and showed that the PFA treatment is to be preferred. The main reason for this was the higher material costs in the AA group, including laboratory fabrication of the appliances by a dental technician, and significantly longer chair time for the AA group, probably due to the need for impressions and appliance adjustments, resulting in additional and longer appointments that led to higher direct and indirect costs for the AA appliance. For the S cases, however, an equal number of visits between groups was seen, but total chair time was shorter for the PFA group, probably due to the factors mentioned above. Furthermore, it is important to bear in mind that costs depend on how many appliances are used during treatment with the PFA. According to a new protocol by the company (Myobrace®, Myofunctional Research Co, Australia) manufacturing the PFA, two appliances should be used, first, one soft PFA, and second, a slightly harder PFA. If we had followed this protocol, the material cost difference between AA and PFA would be less (€195 for AA and €86 for PFA) but still with significantly higher costs for AA. The numbers of emergency visits were higher in the AA group. Except for breakage or loss of appliance, the hard acrylic material may create excess pressure on soft tissue, which might cause soreness of the oral mucosa, compared with the softer silicone elastomeric material of PFA, explaining the difference in the number of emergency visits. An additional recent retrospective and short-term study presented different outcomes when comparing a prefabricated appliance, Twin-block, and a headgear activator (21, 22). According to the study by Nilsson et al. (22), emergency appointments were less frequent in the PFA group compared with the Twin-block and Activator-Headgear appliance groups. This was in line with the results of the S group in the present study, although they only presented a 9 month treatment period in a specialist clinic, and only reported results for S cases. Economic valuation of orthodontic treatment provides important information to achieve ‘value for money’, when planning and organizing orthodontic dental care (19). A CMA measures and compares input costs and assumes outcomes to be equivalent. Thus, the types of interventions that can be evaluated with this method are limited. The prerequisite for the CMA lies in the acceptability by readers or evaluators that outcomes are judged as equivalent (18, 23). According to previous cost-minimizations studies, the average loss of income in Sweden was said to be €26/hour (14, 16), which is lower than our finding of €35/hour. However, we did not use estimates of wages, but instead a questionnaire to obtain more exact and individual data regarding salaries and parental absence from work. In contrast to the Swedish National Bureau of Statistics register, our patients only came from a city, meaning our results could be used solely for urban areas and large cities in Sweden. A recent retrospective study has evaluated treatment costs of a modified headgear activator (21). They reported longer treatment time, longer chair time, and more appointments compared with the results for the AA group found in the present study. This might be due to the retrospective design, not following standardized protocol with a defined cut-off point for US treatment, retention time, and different appliance design. Indirect costs were, however, lower than in this present study, probably because they used estimates of wages with no travel expenses included. The type of appliance, especially those requiring the patient’s co-operation, may have an effect on the duration of treatment (33). This was not in agreement with the present study that found no difference in treatment time between the AA and PFA. Activators may be difficult appliances to wear. Permert et al., (34) studied compliance of removable appliance treatment. They found that 70 per cent of those who discontinued treatment with removable appliances were treated with an activator. The reasons for discontinuing treatment were mainly due to problems with co-operation, lack of motivation, and lack of parental support (34). Higher failure rates for activator treatments have also been reported previously (20, 35). This is in line with findings of the earlier published clinical results of the present RCT (10). Growth modification therapies in early correction of Class II malocclusion with removable functional appliances have been investigated in several RCT, and systematic reviews showing that the correction of the molar and incisal relationship mainly depends on dentoalveolar changes (7). With this in mind, no cephalometric records were taken as only patient-centred clinical outcomes were used as an indicator for treatment success. Although success rate is rather low in our study, one should remember that investigations on treated cases are usually selective and not often presented as RCT, ITT studies as the present one. The criteria of reduction of overjet to as low as 3 mm could affect the success rate in this study compared with other studies with other values considered as S. In the present study, about 30 per cent of the US cases received retreatment and in most cases with a headgear activator. Retreatment was performed on an average of 1.5 years post-retention (Table 3). Although no cost valuation was done for retreatments, it is obvious that the costs increased. As there were no significant difference between AA and PFA groups in retreatment frequency, the increased costs in both groups should be comparable. Therefore, it would be useful to be able to identify the ‘at risk’ patient, i.e. the one who is likely to discontinue treatment since US treatments are very expensive interventions with no benefits to patients or society. Cost-minimization data will gradually become an important part of health care planning, particularly if the state is a major stakeholder. Thus, the characteristics of PFA might be economically beneficial to our dental health care system. Furthermore, dental impressions are often considered uncomfortable and in treatment with PFA, impressions are not needed. This might be a great advantage when treating young patients with large overjet aiming to reduce the risk for maxillary incisor trauma (7). Early treatment for trauma prevention needs to start soon after the eruption of the permanent incisors. Bauss et al. (36) and Caliskan and Turkun (37) all found that children aged 8 to 11, when early treatment usually occurs, had the highest prevalence of dental trauma, therefore, orthodontic treatment should preferably be started before that age. Generalizability One could argue that the close observation of patients in a trial provides positive outcomes that may not be applicable to everyday clinical conditions and that the data should, therefore, not be extrapolated to the general population. However, the patients taking part in the present RCT were treated by GDPs in local dental clinics under the supervision of a consultant orthodontist, simulating normal conditions for treatment of large overjet in the Swedish Dental Health Care system. The outcomes should therefore be expected in the general population. The treatment outcomes from a larger number of operators also make the patient-related treatment outcomes more general than if only one or two clinicians performed the treatment. Harms No harms were detected during the study. Limitations It is important to bear in mind that costs depend on local factors, thus the figures presented in the present study should not be directly extrapolated to other settings. Only general practitioners treated the patients in the present study. As these practices are often located closer to the patients’ homes than the orthodontic specialist clinic, the indirect costs could be lower, possibly compensating for more expensive direct costs if a specialist with a higher salary would have performed treatment. The costs incurred in studies from one country are seldom representative of another (23). Conclusions The results of this research reject the hypothesis that AA is as cost-effective as PFA. In terms of cost-minimization, PFA is the preferred approach for reduction of large overjet in the mixed dentition due to the following reasons: lower direct costs for materials and lower indirect costs, fewer appointments and less chair time and a lower likelihood for additional emergency visits. Both appliances (AA and PFA) showed a low success rate for overjet correction and no difference in frequency of retreatments. Funding This work was supported by The Council for Research and Development in the Västra Götaland Region, Gothenburg Dental Society; Swedish Dental Society. Conflict of Interest statement We have read and understood policy on declaration of interests and declare that we have no competing interests in the subject matter or materials discussed in this manuscript. Acknowledgments The authors wish to thank Senior Professor Björn Lindgren, Lund University and National Bureau of Economic Research, Cambridge MA, for contributing to the design of this study. 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( 2004 ) Prevalence of traumatic injuries to the permanent incisors in candidates for orthodontic treatment . Dental Traumatology , 20 , 61 – 66 . Google Scholar CrossRef Search ADS PubMed 37. Calişkan , M.K. and Türkün , M . ( 1995 ) Clinical investigation of traumatic injuries of permanent incisors in Izmir, Turkey . Endodontics & Dental Traumatology , 11 , 210 – 213 . 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 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

A cost-minimization analysis of large overjet reduction with two removable functional appliances based on a randomized controlled trial

The European Journal of Orthodontics , Volume 40 (4) – Aug 1, 2018
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Abstract

Summary Objective The purpose of this study was to assess and relate the societal costs of reducing large overjet with a prefabricated functional appliance (PFA), or a slightly modified Andresen activator (AA), using a cost-minimization analysis (CMA). Design, settings, and participants A multicentre, prospective, randomized clinical trial was conducted with patients from 12 general dental practices. Ninety-seven patients with an Angle Class II, division 1 malocclusion, and an overjet of ≥6 mm were randomly allocated by lottery to treatment with either a PFA or an AA. The PFA and AA groups consisted of 57 and 40 subjects, respectively. Blinding was not performed. Duration of treatment, number of scheduled/unscheduled appointments, and retreatment were registered. Direct and indirect costs were analysed with reference to intention-to-treat (ITT), successful (S), and unsuccessful (US) outcomes. Societal costs were described as the total of direct and indirect costs, not including retreatments. Interventions Treatment with a PFA or an AA. Results The direct and societal costs were significantly lower for the PFA than for the AA group. The number of visits was lower in the PFA group, when ITT was considered, and for the US cases as well. No difference in retreatment rate could be seen between the groups. Limitations Costs depend on local factors and thus should not be generalized to other settings. Harms No harms were detected during the study. Conclusion The success rate of the both appliances was low. However, the PFA was the preferred approach for reduction of a large overjet in mixed dentition, since it minimized costs and there were no difference in clinical outcomes between PFA and AA. Registration This trial was registered at ‘FoU i Sverige’ (http://www.fou.nu/is/sverige), registration number: 97131. Protocol The protocol was not published before trial commencement. Introduction Dental health care in Sweden is free of charge for those below the age of 20 years. General dental practitioners (GDPs) are responsible for the diagnosis and selection of patients with malocclusions and, with the support of consulting orthodontists, also for some interceptive orthodontic treatments. Approximately, one-third of all children and adolescents in Sweden is offered orthodontic treatment (1, 2). Large overjet (>6 mm) as a feature of Class II malocclusions is seen in 14–15 per cent of 10-year-old Scandinavian children (3, 4). Early treatment has been suggested to reduce the incidence of incisal trauma to the upper permanent incisors in patients with large overjet, and/or incompetent lip closure (5–7). Treatment with removable functional appliances requires the patient’s interest, compliance, and considerable chair time with many additional visits. It has been stated that activators provide completely satisfactory results and ideal occlusion in only 33–35 per cent of cases treated (8, 9), and a recently published randomized controlled trial (RCT) confirmed this finding where successful (S) treatment outcomes (overjet 3 mm) were seen in 37 per cent of the subjects (10). Other studies, however, have presented success rates above 60 per cent when the treatment goal was less than ideal, or when treated by specialists, the latter possibly contributing to higher compliance (11, 12). Nevertheless, the method of choice for orthodontic treatment should depend on clinical skills and cost-effectiveness. A recent systematic review highlighted the need for orthodontic studies where both economic and clinical outcomes are presented (13). During the last 20 years, the interest for analysing costs of orthodontic treatment has increased and several studies have been published describing and comparing treatment costs following various orthodontic diagnoses and treatment circumstances (14–22). When allocating resources, including dental care and orthodontics, health service providers and financiers need to consider both the evidence of clinical effectiveness of the treatment procedures as well as the related costs, i.e. ‘value for money’ (23). A health-economic evaluation is characterized by the concern for the relationship between costs (inputs) and consequences (outputs), when different diagnostic or therapeutic options are considered. Four main techniques are available: cost-minimization analysis (CMA), cost-effectiveness analysis, cost-utility analysis, and cost–benefit analysis (24, 25). Economic assessments with a societal perspective comprise calculations of direct and indirect costs. Direct costs are those related to diagnostic or treatment interventions, whereas indirect costs are the loss of production due to the absence from work and travel expenses to the clinics. Societal costs are expressed as the sum of direct and indirect costs. Cost-effective healthcare requires valuation of the economic effects of interventions (26). The overall costs of treating large overjet have, thus far, not been clarified in an RCT. A recently published RCT of patients with large overjet, treated with a prefabricated functional appliance (PFA), or a slightly modified Andresen activator (AA), with a 1-year, post-retention follow-up, showed that both treatment approaches achieved comparable clinical outcomes (10). As both approaches accomplished similar clinical outcomes, a CMA was an appropriate form of economic evaluation. A CMA is applicable when two or more treatment methods achieve the same clinical outcomes (i.e. reduction of overjet), and the aim was to identify the least expensive method. Thus, the purpose of this study was to assess and relate the costs of reducing a large overjet by a PFA, and a slightly modified AA, using a CMA. It was hypothesized that not only the treatment effect in correcting large overjet was similar for both appliances but also the societal costs would be comparable. Subjects and methods Trial design and ethics This CMA was based on a multicentre, randomized, and controlled study that assessed the effectiveness of overjet reduction, including a 1-year follow-up (10). Informed written consent was obtained from parents before their children were enrolled in the study. The CMA was also based on a questionnaire survey of parental leave of absence and travel costs for dental visits during their child’s orthodontic treatment. The Research Ethics Committee at the University of Gothenburg approved this study (Dnr: 437-07), following the guidelines of the Declaration of Helsinki (27). Registration This trial was registered in the Research and Development database in Sweden (‘FoU i Sverige’, http://www.fou.nu/is/sverige), registration number 97131. Subjects and randomization The sample consisted of 97 subjects (44 girls, 53 boys), with a mean age of 10.3 years (7–14 years, SD 1.64). Patients fulfilling the criteria below were invited to participate in the study. Informed written consent was obtained from the parents, and randomization was performed by lottery. At each clinic, two envelopes were available, one for girls and one for boys with 5 AA and 5 PFA notes for each gender. If all notes were used, 240 participants would be available for the RCT (Figure 1). The following inclusion criteria were applied: 6–14 years of age with central incisors erupted, Angle Class II div 1, increased overjet ≥6 mm, and no previous orthodontic treatment. Patients with other malocclusions, e.g. crossbite, severe crowding, or agenesis that needed more extensive orthodontic treatment, were not included. Figure 1. View largeDownload slide Flow chart of the participants in the study. Figure 1. View largeDownload slide Flow chart of the participants in the study. The study was designed as intention-to-treat (ITT), and patients were randomly allocated to treatment with either a PFA or an AA (Figure 1). Detailed information on the trial design and treatment methods was published in a previous article (10). Interventions Appliances: The AA was a standardized, custom-made, slightly modified activator, with an opening in the frontal region to enable mouth breathing. All AAs were made at the same orthodontic dental laboratory according to a given prototype (Figure 2). The PFA (Myobrace®, Myofunctional Research Co, Australia) was available in seven sizes. The size of the appliance was chosen according to the manufacturer’s recommendation. All PFAs were ordered from the same company (Figure 2). Figure 2. View largeDownload slide Andresen activator (AA) standardized but custom-made, slightly modified with opening in the front to make it easier to wear for mouth breathers. Prefabricated functional appliance (PFA; myobracebrace®, Myofanctional Research Co, Australia). Figure 2. View largeDownload slide Andresen activator (AA) standardized but custom-made, slightly modified with opening in the front to make it easier to wear for mouth breathers. Prefabricated functional appliance (PFA; myobracebrace®, Myofanctional Research Co, Australia). Participants were instructed to use the appliance nightly and 2 hours during the day for a total of 12–14 hours. Outcomes Orthodontic outcome measures When a participant’s overjet had been reduced to ≤3 mm, the treatment was regarded as S, and the patient then continued to wear the appliance as a retainer only at night for 6 months. The treatment was classified as unsuccessful (US) if there was no reduction in overjet by 6 months and/or if they refused to use the appliance or keep appointments. Cost measures ‘Direct costs’ included chair time during the treatment and retention period, as well as material costs. Chair time costs comprised dental equipment and disposable items, premises, cleaning, maintenance, staff salaries, etc. All estimates of chair time costs were calculated in Swedish currency, at SEK 2000 (€212) per hour for a general practitioner according to the price list for general dentistry in the Public Dental Service (Folktandvården) in the Västra Götaland region. In addition, the number of appointments, scheduled and emergency appointments and cancellations were noted. However, broken appointments and cancellations were not included in the CMA. Material costs (i.e. laboratory invoices and fees for repairs) were collected and calculated according to the laboratory price list (TIC DPNova) for 2015. ‘Indirect costs’, i.e. loss of production when a parent took a leave of absence from work to accompany their child to the orthodontic appointment, were estimated as loss of income (salary plus employer charges to social insurance and collectively agreed private pension schemes). We conducted a questionnaire survey to collect data on travel time and costs, as well as national identification numbers for parents accompanying their child to the orthodontic treatment. National identification numbers were sent to the Swedish National Bureau of Statistics (http://www.scb.se) where they were matched with a longitudinal integration database for social insurance and labour market studies (LISA by Swedish acronym). The database presently contains annual registers and includes all registered residents in Sweden, 16 years of age or older. Outcomes from LISA provided the individual annual wages of the parents in SEK for 2013. Since the Consumer Price Index remained the same during the period 2013–2015, no adjustment for changes in cost of living was made. The average findings from the questionnaires and the LISA database are summed up in Table 1. Table 1. The average indirect costs in euros (€) and average duration based on a questionnaire survey for parents (n = 178) while accompanying the child to orthodontic treatment. Loss of income means salary plus employer charges to social insurance and collectively agreed private pension schemes. Loss of income €35/h Absent from work: 69 min  Appointment duration 20 min  Travelling time duration 49 min Travel costs €6/visit Loss of income €35/h Absent from work: 69 min  Appointment duration 20 min  Travelling time duration 49 min Travel costs €6/visit View Large Table 1. The average indirect costs in euros (€) and average duration based on a questionnaire survey for parents (n = 178) while accompanying the child to orthodontic treatment. Loss of income means salary plus employer charges to social insurance and collectively agreed private pension schemes. Loss of income €35/h Absent from work: 69 min  Appointment duration 20 min  Travelling time duration 49 min Travel costs €6/visit Loss of income €35/h Absent from work: 69 min  Appointment duration 20 min  Travelling time duration 49 min Travel costs €6/visit View Large The sum of direct and indirect costs was defined as ‘societal costs’. The cost analysis was based on the ITT principle, i.e. the analysis included data for costs of S and US cases. All costs were in 2015 prices and expressed in Euros (€), SEK 100 = €9.44 at a mean currency value (www.xe.se). Cost-minimization analysis The CMA was considered as follows: CMA = Societal costs divided by the number of patients in the ITT, S, and US groups, respectively. Post-retention follow-up All cases were followed up 4 years post-retention (Figure 1). Retreatment of large overjet with a removable functional appliance was documented during this period. No CMA was performed for retreatments. Sample size calculation According to a sample size analysis, 38 patients per group were required to obtain adequate power (80 per cent, at significance level P < 0.05 with an SD of 1.3, and with the loss of 10 patients), based on a clinically significant difference of 1 mm in overjet reduction between the study groups. The power was thus adequate to conclude that the clinical outcome was similar and comparable for the AA and the PFA appliances. Statistical analysis Statistical analyses were performed using SPSS for Windows 22.0 (SPSS, Inc., Chicago, IL, USA). Differences between the groups were analysed with chi-square and Fisher’s exact test for categorical variables, independent t-tests for continuous variables, and a Poisson distribution was assumed for count data (e.g. number of visits). In the analysis, the total sample was considered an ITT group, which comprised all subjects, a S group including participants who achieved an overjet ≤3 mm at end point, and an US group comprising participants discontinuing treatment, or not reaching the end point of the treatment. Parallel analyses were carried out in all three groups. P-values less than 0.05 were considered statistically significant. Broken appointments and cancellations were not included in CMA. Blinding was not performed. Results Participant flow and retreatment The PFA and AA group consisted of 57 (28 girls, 29 boys) and 40 subjects (16 girls, 24 boys), respectively. Figure 1 illustrates the flow of participants through the study. Successful treatment outcome (overjet ≤ 3 mm) was seen in 37 per cent of the subjects. No statistically significant difference in success rate, gender, age, or treatment time was found between the PFA and AA groups. The mean treatment time for the ITT group, including a retention period of 6 months, was 1.5 years (SD 0.70) in the AA group and 1.2 years (SD 0.60) in the PFA group. No statistically significant difference was seen between groups. The patients in the S treatment group had significantly (P < 0.001) longer treatment time (1.7 years) compared with the US (1.07 years) group. In the S group, retreatment of large overjet with a removable functional appliance was performed on one patient in the AA group due to relapse and none in the PFA group (Figure 3). Among the US cases in the AA and PFA group, 26 per cent and 36 per cent of the patients underwent retreatment of the large overjet, respectively (Table 2). The most common retreatment was performed with headgear activators on average 1.5 years post-retention (Table 3). No long-term follow-up monitoring was possible in three cases (Figure 3). Table 2. Mean number of regular and emergency visits, chair time during the treatment including retention period. A retreatment frequency of large overjet with removable appliances during a 4-year post-retention period. Intention-to-treat (ITT cases), successful cases (S), and unsuccessful cases (US). AA, Andresen activator; PFA, prefabricated functional appliance. AA PFA Group difference Mean (95% CI) SD Mean (95% CI) SD Mean (95% CI) P-value ITT AA (n = 40) PFA (n = 57) Number of visits 11.45 (10.4–12.6) 4.1 8.4 (7.7–9.2) 3.4 3 (1.5–4.5) <0.001 Emergency visits 0.7 (0.4–1.0) 0.9 0.1 (0.03–0.2) 0.4 0.6 (0.3–0.9) <0.001 Chair time (min) 245 (213–277) 100 167 (149–185) 67 78 (44–111) <0.001 Retreatment (%) 15% (4.3–27.7) 25% (13.1–36.3) 0.09 (−0.1–0.3) 0.317 S AA (n = 19) PFA (n = 17) Number of visits 13.1 (11.5–14.9) 3.6 11.2 (9.7–13.0) 3.1 1.9 (−0.4–4.1) 0.109 Emergency visits 0.8 (0.4–1.3) 1.0 0.1 (0.03–0.5) 0.5 0.7 (0.1–1.2) 0.034 Chair time (min) 276 (229–322) 97 213 (173–254) 79 63 (2–123) 0.043 Retreatment (%) 5% (0) 0% (0) 0.05 (−0.18–0.28) 1.000 US AA (n = 21) PFA (n = 40) Number of visits 10.0 (8.6–11.4) 4.0 7.2 (6.4–8.1) 2.8 2.7 (1.0–4.5) <0.001 Emergency visits 0.6 (0.3–1.0) 0.9 0.1 (0.02–0.2) 0.4 0.5 (0.2–0.8) 0.037 Chair time (min) 217 (173–261) 97 148 (131–164) 51 69 (32–107) <0.001 Retreatment (%) 26% (6.3–45.7) 36% (20.9–51.1) 0.1 (−0.19–0.33) 0.559 AA PFA Group difference Mean (95% CI) SD Mean (95% CI) SD Mean (95% CI) P-value ITT AA (n = 40) PFA (n = 57) Number of visits 11.45 (10.4–12.6) 4.1 8.4 (7.7–9.2) 3.4 3 (1.5–4.5) <0.001 Emergency visits 0.7 (0.4–1.0) 0.9 0.1 (0.03–0.2) 0.4 0.6 (0.3–0.9) <0.001 Chair time (min) 245 (213–277) 100 167 (149–185) 67 78 (44–111) <0.001 Retreatment (%) 15% (4.3–27.7) 25% (13.1–36.3) 0.09 (−0.1–0.3) 0.317 S AA (n = 19) PFA (n = 17) Number of visits 13.1 (11.5–14.9) 3.6 11.2 (9.7–13.0) 3.1 1.9 (−0.4–4.1) 0.109 Emergency visits 0.8 (0.4–1.3) 1.0 0.1 (0.03–0.5) 0.5 0.7 (0.1–1.2) 0.034 Chair time (min) 276 (229–322) 97 213 (173–254) 79 63 (2–123) 0.043 Retreatment (%) 5% (0) 0% (0) 0.05 (−0.18–0.28) 1.000 US AA (n = 21) PFA (n = 40) Number of visits 10.0 (8.6–11.4) 4.0 7.2 (6.4–8.1) 2.8 2.7 (1.0–4.5) <0.001 Emergency visits 0.6 (0.3–1.0) 0.9 0.1 (0.02–0.2) 0.4 0.5 (0.2–0.8) 0.037 Chair time (min) 217 (173–261) 97 148 (131–164) 51 69 (32–107) <0.001 Retreatment (%) 26% (6.3–45.7) 36% (20.9–51.1) 0.1 (−0.19–0.33) 0.559 View Large Table 2. Mean number of regular and emergency visits, chair time during the treatment including retention period. A retreatment frequency of large overjet with removable appliances during a 4-year post-retention period. Intention-to-treat (ITT cases), successful cases (S), and unsuccessful cases (US). AA, Andresen activator; PFA, prefabricated functional appliance. AA PFA Group difference Mean (95% CI) SD Mean (95% CI) SD Mean (95% CI) P-value ITT AA (n = 40) PFA (n = 57) Number of visits 11.45 (10.4–12.6) 4.1 8.4 (7.7–9.2) 3.4 3 (1.5–4.5) <0.001 Emergency visits 0.7 (0.4–1.0) 0.9 0.1 (0.03–0.2) 0.4 0.6 (0.3–0.9) <0.001 Chair time (min) 245 (213–277) 100 167 (149–185) 67 78 (44–111) <0.001 Retreatment (%) 15% (4.3–27.7) 25% (13.1–36.3) 0.09 (−0.1–0.3) 0.317 S AA (n = 19) PFA (n = 17) Number of visits 13.1 (11.5–14.9) 3.6 11.2 (9.7–13.0) 3.1 1.9 (−0.4–4.1) 0.109 Emergency visits 0.8 (0.4–1.3) 1.0 0.1 (0.03–0.5) 0.5 0.7 (0.1–1.2) 0.034 Chair time (min) 276 (229–322) 97 213 (173–254) 79 63 (2–123) 0.043 Retreatment (%) 5% (0) 0% (0) 0.05 (−0.18–0.28) 1.000 US AA (n = 21) PFA (n = 40) Number of visits 10.0 (8.6–11.4) 4.0 7.2 (6.4–8.1) 2.8 2.7 (1.0–4.5) <0.001 Emergency visits 0.6 (0.3–1.0) 0.9 0.1 (0.02–0.2) 0.4 0.5 (0.2–0.8) 0.037 Chair time (min) 217 (173–261) 97 148 (131–164) 51 69 (32–107) <0.001 Retreatment (%) 26% (6.3–45.7) 36% (20.9–51.1) 0.1 (−0.19–0.33) 0.559 AA PFA Group difference Mean (95% CI) SD Mean (95% CI) SD Mean (95% CI) P-value ITT AA (n = 40) PFA (n = 57) Number of visits 11.45 (10.4–12.6) 4.1 8.4 (7.7–9.2) 3.4 3 (1.5–4.5) <0.001 Emergency visits 0.7 (0.4–1.0) 0.9 0.1 (0.03–0.2) 0.4 0.6 (0.3–0.9) <0.001 Chair time (min) 245 (213–277) 100 167 (149–185) 67 78 (44–111) <0.001 Retreatment (%) 15% (4.3–27.7) 25% (13.1–36.3) 0.09 (−0.1–0.3) 0.317 S AA (n = 19) PFA (n = 17) Number of visits 13.1 (11.5–14.9) 3.6 11.2 (9.7–13.0) 3.1 1.9 (−0.4–4.1) 0.109 Emergency visits 0.8 (0.4–1.3) 1.0 0.1 (0.03–0.5) 0.5 0.7 (0.1–1.2) 0.034 Chair time (min) 276 (229–322) 97 213 (173–254) 79 63 (2–123) 0.043 Retreatment (%) 5% (0) 0% (0) 0.05 (−0.18–0.28) 1.000 US AA (n = 21) PFA (n = 40) Number of visits 10.0 (8.6–11.4) 4.0 7.2 (6.4–8.1) 2.8 2.7 (1.0–4.5) <0.001 Emergency visits 0.6 (0.3–1.0) 0.9 0.1 (0.02–0.2) 0.4 0.5 (0.2–0.8) 0.037 Chair time (min) 217 (173–261) 97 148 (131–164) 51 69 (32–107) <0.001 Retreatment (%) 26% (6.3–45.7) 36% (20.9–51.1) 0.1 (−0.19–0.33) 0.559 View Large Figure 3. View largeDownload slide Flow chart of the 4-year post-retention period. AA, Andresen activator; PFA, prefabricated functional appliance; US, unsuccessful group; S, successful group. Figure 3. View largeDownload slide Flow chart of the 4-year post-retention period. AA, Andresen activator; PFA, prefabricated functional appliance; US, unsuccessful group; S, successful group. Table 3. Number (n) of retreatment of large overjet with removable functional appliance used mean 1.5 years (0.5–3 years) post-retention. Retreatment with removable appliance n = 21 Appliance type:  Headgear activator (HA) n = 14  Removable plate (RP) n = 3  Combination (RP + HA) n = 4 Retreatment with removable appliance n = 21 Appliance type:  Headgear activator (HA) n = 14  Removable plate (RP) n = 3  Combination (RP + HA) n = 4 View Large Table 3. Number (n) of retreatment of large overjet with removable functional appliance used mean 1.5 years (0.5–3 years) post-retention. Retreatment with removable appliance n = 21 Appliance type:  Headgear activator (HA) n = 14  Removable plate (RP) n = 3  Combination (RP + HA) n = 4 Retreatment with removable appliance n = 21 Appliance type:  Headgear activator (HA) n = 14  Removable plate (RP) n = 3  Combination (RP + HA) n = 4 View Large Number of appointments The distribution of scheduled and emergency appointments is summarized in Table 2. The number of appointments was significantly higher in the AA group both for the ITT and US cases. The mean number of appointments for patients with S treatment outcomes showed no significant difference between the two groups, AA and PFA (P = 0.109), while the number of emergency visits was significantly higher (P < 0.001) in the AA than in the PFA group (Table 2). Costs Significant differences in direct, indirect, and societal costs were found between the AA and PFA for all subgroups, i.e. ITT, S, and US outcomes, in that costs were higher for the AA than for the PFA groups (P ≤ 0.001) (Table 4). Table 4. Mean direct costs of materials, direct costs for chair time, indirect costs, and societal costs in Euros (€). Intention-to-treat (ITT cases), successful cases (S), and unsuccessful cases (US) during the treatment including retention period. AA,Andresen activator; PFA, prefabricated functional appliance. AA PFA Group difference Mean (95% CI) SD Mean (95% CI) SD Mean (95% CI) P-value ITT AA (n = 40) PFA (n = 57) Direct costs—material 195 (171–219) 75 43 (39–47) 15 152 (132–172) <0.001 Direct costs—chair time 864 (751–977) 353 590 (527–652) 236 274 (155–393) <0.001 Indirect costs 489 (433–545) 176 341 (305–376) 134 148 (86–211) <0.001 Societal (total) costs 1548 (1366–1730) 569 974 (876–1071) 368 574 (385–764) <0.001 S AA (n = 19) PFA (n = 17) Direct costs—material 191 (152–229) 80 44 (37–52) 15 146 (107–187) <0.001 Direct costs—chair time 972 (943–1137) 342 753 (609–896) 279 220 (7–433) <0.001 Indirect costs 558 (488–628) 146 450 (381–519) 134 108 (13–203) <0.001 Societal (total) costs 1721 (1466–1976) 530 1247 (1035–1459) 411 160 (150–799) <0.001 US AA (n = 21) PFA (n = 40) Direct costs—material 199 (167–232) 72 42 (37–47) 15 157 (133–180) <0.001 Direct costs—chair time 766 (610–921) 341 521 (464–578) 178 245 (112–378) <0.001 Indirect costs 427 (344–509) 181 294 (261–328) 105 132 (59–205) 0.001 Societal (total) costs 1391(1132–1651) 570 857 (768–947) 281 534 (317–751) <0.001 AA PFA Group difference Mean (95% CI) SD Mean (95% CI) SD Mean (95% CI) P-value ITT AA (n = 40) PFA (n = 57) Direct costs—material 195 (171–219) 75 43 (39–47) 15 152 (132–172) <0.001 Direct costs—chair time 864 (751–977) 353 590 (527–652) 236 274 (155–393) <0.001 Indirect costs 489 (433–545) 176 341 (305–376) 134 148 (86–211) <0.001 Societal (total) costs 1548 (1366–1730) 569 974 (876–1071) 368 574 (385–764) <0.001 S AA (n = 19) PFA (n = 17) Direct costs—material 191 (152–229) 80 44 (37–52) 15 146 (107–187) <0.001 Direct costs—chair time 972 (943–1137) 342 753 (609–896) 279 220 (7–433) <0.001 Indirect costs 558 (488–628) 146 450 (381–519) 134 108 (13–203) <0.001 Societal (total) costs 1721 (1466–1976) 530 1247 (1035–1459) 411 160 (150–799) <0.001 US AA (n = 21) PFA (n = 40) Direct costs—material 199 (167–232) 72 42 (37–47) 15 157 (133–180) <0.001 Direct costs—chair time 766 (610–921) 341 521 (464–578) 178 245 (112–378) <0.001 Indirect costs 427 (344–509) 181 294 (261–328) 105 132 (59–205) 0.001 Societal (total) costs 1391(1132–1651) 570 857 (768–947) 281 534 (317–751) <0.001 View Large Table 4. Mean direct costs of materials, direct costs for chair time, indirect costs, and societal costs in Euros (€). Intention-to-treat (ITT cases), successful cases (S), and unsuccessful cases (US) during the treatment including retention period. AA,Andresen activator; PFA, prefabricated functional appliance. AA PFA Group difference Mean (95% CI) SD Mean (95% CI) SD Mean (95% CI) P-value ITT AA (n = 40) PFA (n = 57) Direct costs—material 195 (171–219) 75 43 (39–47) 15 152 (132–172) <0.001 Direct costs—chair time 864 (751–977) 353 590 (527–652) 236 274 (155–393) <0.001 Indirect costs 489 (433–545) 176 341 (305–376) 134 148 (86–211) <0.001 Societal (total) costs 1548 (1366–1730) 569 974 (876–1071) 368 574 (385–764) <0.001 S AA (n = 19) PFA (n = 17) Direct costs—material 191 (152–229) 80 44 (37–52) 15 146 (107–187) <0.001 Direct costs—chair time 972 (943–1137) 342 753 (609–896) 279 220 (7–433) <0.001 Indirect costs 558 (488–628) 146 450 (381–519) 134 108 (13–203) <0.001 Societal (total) costs 1721 (1466–1976) 530 1247 (1035–1459) 411 160 (150–799) <0.001 US AA (n = 21) PFA (n = 40) Direct costs—material 199 (167–232) 72 42 (37–47) 15 157 (133–180) <0.001 Direct costs—chair time 766 (610–921) 341 521 (464–578) 178 245 (112–378) <0.001 Indirect costs 427 (344–509) 181 294 (261–328) 105 132 (59–205) 0.001 Societal (total) costs 1391(1132–1651) 570 857 (768–947) 281 534 (317–751) <0.001 AA PFA Group difference Mean (95% CI) SD Mean (95% CI) SD Mean (95% CI) P-value ITT AA (n = 40) PFA (n = 57) Direct costs—material 195 (171–219) 75 43 (39–47) 15 152 (132–172) <0.001 Direct costs—chair time 864 (751–977) 353 590 (527–652) 236 274 (155–393) <0.001 Indirect costs 489 (433–545) 176 341 (305–376) 134 148 (86–211) <0.001 Societal (total) costs 1548 (1366–1730) 569 974 (876–1071) 368 574 (385–764) <0.001 S AA (n = 19) PFA (n = 17) Direct costs—material 191 (152–229) 80 44 (37–52) 15 146 (107–187) <0.001 Direct costs—chair time 972 (943–1137) 342 753 (609–896) 279 220 (7–433) <0.001 Indirect costs 558 (488–628) 146 450 (381–519) 134 108 (13–203) <0.001 Societal (total) costs 1721 (1466–1976) 530 1247 (1035–1459) 411 160 (150–799) <0.001 US AA (n = 21) PFA (n = 40) Direct costs—material 199 (167–232) 72 42 (37–47) 15 157 (133–180) <0.001 Direct costs—chair time 766 (610–921) 341 521 (464–578) 178 245 (112–378) <0.001 Indirect costs 427 (344–509) 181 294 (261–328) 105 132 (59–205) 0.001 Societal (total) costs 1391(1132–1651) 570 857 (768–947) 281 534 (317–751) <0.001 View Large Discussion Main findings This is the first study to evaluate the differences in costs between treatments with an AA and a PFA intending to reduce large overjet, based on outcomes of an RCT study. A health-economic valuation from a prospective RCT provides fewer biases. The random distribution of subjects reduces bias and confounding factors by ensuring that both known and unknown factors of outcome are equally distributed between subjects. The prospective design also assures that the baseline characteristics, treatment progression, treatment time, number of appointments, and side outcomes can be precisely controlled and observed. An ITT analysis was used, in which each patient record was evaluated, regardless of the effect of treatment. It is said that this method underestimates the extent of the treatment effects, since it includes data from patients who did not complete treatment. However, this is the suggested procedure for RCTs evaluating the average effect of treatment on the average patient (28, 29). As a result, the study outcomes are applicable to all patients who started treatment, rather than to only those who complied with treatment and achieved S results. The randomization process also reduces the risk of error due to factors such as selection bias, the clinician’s favoured treatment method, and the individual differences in skills of the general dental practitioner. However, overall clinical skills or lack of experience could still be a confounding factor in studies with small samples (30). Pietilä (31) conducted a cost and productivity analysis of orthodontic care in Finland. They found that there was a wide range in the cost of providing orthodontic care and that general dentists who had little orthodontic experience were associated with the highest costs (31). Contrary to the findings in the present study, a higher cost (societal and direct) for early treatment performed by specialists was presented in an RCT from the UK, but indirect costs were similar to those reported in this study, €474 compared with €489 (32). The outcomes in the present study reject the null hypothesis that AA and PFA treatment will be equal in an economic valuation and showed that the PFA treatment is to be preferred. The main reason for this was the higher material costs in the AA group, including laboratory fabrication of the appliances by a dental technician, and significantly longer chair time for the AA group, probably due to the need for impressions and appliance adjustments, resulting in additional and longer appointments that led to higher direct and indirect costs for the AA appliance. For the S cases, however, an equal number of visits between groups was seen, but total chair time was shorter for the PFA group, probably due to the factors mentioned above. Furthermore, it is important to bear in mind that costs depend on how many appliances are used during treatment with the PFA. According to a new protocol by the company (Myobrace®, Myofunctional Research Co, Australia) manufacturing the PFA, two appliances should be used, first, one soft PFA, and second, a slightly harder PFA. If we had followed this protocol, the material cost difference between AA and PFA would be less (€195 for AA and €86 for PFA) but still with significantly higher costs for AA. The numbers of emergency visits were higher in the AA group. Except for breakage or loss of appliance, the hard acrylic material may create excess pressure on soft tissue, which might cause soreness of the oral mucosa, compared with the softer silicone elastomeric material of PFA, explaining the difference in the number of emergency visits. An additional recent retrospective and short-term study presented different outcomes when comparing a prefabricated appliance, Twin-block, and a headgear activator (21, 22). According to the study by Nilsson et al. (22), emergency appointments were less frequent in the PFA group compared with the Twin-block and Activator-Headgear appliance groups. This was in line with the results of the S group in the present study, although they only presented a 9 month treatment period in a specialist clinic, and only reported results for S cases. Economic valuation of orthodontic treatment provides important information to achieve ‘value for money’, when planning and organizing orthodontic dental care (19). A CMA measures and compares input costs and assumes outcomes to be equivalent. Thus, the types of interventions that can be evaluated with this method are limited. The prerequisite for the CMA lies in the acceptability by readers or evaluators that outcomes are judged as equivalent (18, 23). According to previous cost-minimizations studies, the average loss of income in Sweden was said to be €26/hour (14, 16), which is lower than our finding of €35/hour. However, we did not use estimates of wages, but instead a questionnaire to obtain more exact and individual data regarding salaries and parental absence from work. In contrast to the Swedish National Bureau of Statistics register, our patients only came from a city, meaning our results could be used solely for urban areas and large cities in Sweden. A recent retrospective study has evaluated treatment costs of a modified headgear activator (21). They reported longer treatment time, longer chair time, and more appointments compared with the results for the AA group found in the present study. This might be due to the retrospective design, not following standardized protocol with a defined cut-off point for US treatment, retention time, and different appliance design. Indirect costs were, however, lower than in this present study, probably because they used estimates of wages with no travel expenses included. The type of appliance, especially those requiring the patient’s co-operation, may have an effect on the duration of treatment (33). This was not in agreement with the present study that found no difference in treatment time between the AA and PFA. Activators may be difficult appliances to wear. Permert et al., (34) studied compliance of removable appliance treatment. They found that 70 per cent of those who discontinued treatment with removable appliances were treated with an activator. The reasons for discontinuing treatment were mainly due to problems with co-operation, lack of motivation, and lack of parental support (34). Higher failure rates for activator treatments have also been reported previously (20, 35). This is in line with findings of the earlier published clinical results of the present RCT (10). Growth modification therapies in early correction of Class II malocclusion with removable functional appliances have been investigated in several RCT, and systematic reviews showing that the correction of the molar and incisal relationship mainly depends on dentoalveolar changes (7). With this in mind, no cephalometric records were taken as only patient-centred clinical outcomes were used as an indicator for treatment success. Although success rate is rather low in our study, one should remember that investigations on treated cases are usually selective and not often presented as RCT, ITT studies as the present one. The criteria of reduction of overjet to as low as 3 mm could affect the success rate in this study compared with other studies with other values considered as S. In the present study, about 30 per cent of the US cases received retreatment and in most cases with a headgear activator. Retreatment was performed on an average of 1.5 years post-retention (Table 3). Although no cost valuation was done for retreatments, it is obvious that the costs increased. As there were no significant difference between AA and PFA groups in retreatment frequency, the increased costs in both groups should be comparable. Therefore, it would be useful to be able to identify the ‘at risk’ patient, i.e. the one who is likely to discontinue treatment since US treatments are very expensive interventions with no benefits to patients or society. Cost-minimization data will gradually become an important part of health care planning, particularly if the state is a major stakeholder. Thus, the characteristics of PFA might be economically beneficial to our dental health care system. Furthermore, dental impressions are often considered uncomfortable and in treatment with PFA, impressions are not needed. This might be a great advantage when treating young patients with large overjet aiming to reduce the risk for maxillary incisor trauma (7). Early treatment for trauma prevention needs to start soon after the eruption of the permanent incisors. Bauss et al. (36) and Caliskan and Turkun (37) all found that children aged 8 to 11, when early treatment usually occurs, had the highest prevalence of dental trauma, therefore, orthodontic treatment should preferably be started before that age. Generalizability One could argue that the close observation of patients in a trial provides positive outcomes that may not be applicable to everyday clinical conditions and that the data should, therefore, not be extrapolated to the general population. However, the patients taking part in the present RCT were treated by GDPs in local dental clinics under the supervision of a consultant orthodontist, simulating normal conditions for treatment of large overjet in the Swedish Dental Health Care system. The outcomes should therefore be expected in the general population. The treatment outcomes from a larger number of operators also make the patient-related treatment outcomes more general than if only one or two clinicians performed the treatment. Harms No harms were detected during the study. Limitations It is important to bear in mind that costs depend on local factors, thus the figures presented in the present study should not be directly extrapolated to other settings. Only general practitioners treated the patients in the present study. As these practices are often located closer to the patients’ homes than the orthodontic specialist clinic, the indirect costs could be lower, possibly compensating for more expensive direct costs if a specialist with a higher salary would have performed treatment. The costs incurred in studies from one country are seldom representative of another (23). Conclusions The results of this research reject the hypothesis that AA is as cost-effective as PFA. In terms of cost-minimization, PFA is the preferred approach for reduction of large overjet in the mixed dentition due to the following reasons: lower direct costs for materials and lower indirect costs, fewer appointments and less chair time and a lower likelihood for additional emergency visits. Both appliances (AA and PFA) showed a low success rate for overjet correction and no difference in frequency of retreatments. Funding This work was supported by The Council for Research and Development in the Västra Götaland Region, Gothenburg Dental Society; Swedish Dental Society. Conflict of Interest statement We have read and understood policy on declaration of interests and declare that we have no competing interests in the subject matter or materials discussed in this manuscript. Acknowledgments The authors wish to thank Senior Professor Björn Lindgren, Lund University and National Bureau of Economic Research, Cambridge MA, for contributing to the design of this study. 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Journal

The European Journal of Orthodontics – Oxford University Press

Published: Aug 1, 2018

References

  • Orthodontic care provided by general practitioners and specialists in three Swedish counties with different orthodontic specialist resources
    Bergström