Confounders in epidemiological associations

The following description of a retrospective non-randomized study is given within a publication in a scientific journal: “A total of 54 consecutive patients (24 male / 28 female; mean age: 14.1 years) treated with sequential thermoplastic aligners during the last 12 months were identified from the archive of a private practice. They were compared to 52 consecutive patients treated with conventional fixed appliances during the same period, who were matched for age, sex, and case severity with the patients in the aligner group. The total duration of treatment in months was extracted from the patient files by a third party not involved in any way with their treatment. Initially, descriptive statistics were calculated for all patient characteristics and for the study’s primary outcome (treatment duration), consisting of means and Standard Deviations (SDs). Student’s t-tests for independent samples and chi-square tests were performed on patient age, sex, and case severity to confirm that the two groups were matched. Finally, a t-test for independent samples was performed on treatment duration to assess any differences between the aligner and the fixed appliance group at the 5% level." The authors of the study give the following table (Table 1) in their Results section and conclude that (i) the two groups were adequately matched, since no statistically significant difference was found for any baseline difference and (ii) aligners and braces are equally efficient, since no statistically significant difference was found for treatment duration

Evidence-based orthodontics: too many systematic reviews, too few trials

Why are there so many systematic reviews in orthodontics, and what are the negative consequences of this for our speciality as an academic discipline

Outcomes of comprehensive fixed appliance orthodontic treatment: A systematic review with meta-analysis and methodological overview

OBJECTIVE: The aim of this systematic review was to assess the occlusal outcome and duration of fixed orthodontic therapy from clinical trials in humans with the Objective Grading System (OGS) proposed by the American Board of Orthodontics. METHODS: Nine databases were searched up to October 2016 for prospective/retrospective clinical trials assessing the outcomes of orthodontic therapy with fixed appliances. After duplicate study selection, data extraction, and risk of bias assessment according to the Cochrane guidelines, random-effects meta-analyses of the mean OGS score and treatment duration were performed and 95% confidence intervals (CIs) were calculated. RESULTS: A total of 34 relevant clinical trials including 6,207 patients (40% male, 60% female; average age, 18.4 years) were identified. The average OGS score after treatment was 27.9 points (95% CI, 25.3-30.6 points), while the average treatment duration was 24.9 months (95% CI, 24.6-25.1 months). There was no significant association between occlusal outcome and treatment duration, while considerable heterogeneity was identified. In addition, orthodontic treatment involving extraction of four premolars appeared to have an important effect on both outcomes and duration of treatment. Finally, only 10 (39%) of the identified studies matched compared groups by initial malocclusion severity, although meta-epidemiological evidence suggested that matching may have significantly influenced their results. CONCLUSIONS: The findings from this systematic review suggest that the occlusal outcomes of fixed appliance treatment vary considerably, with no significant association between treatment outcomes and duration. Prospective matched clinical studies that use the OGS tool are needed to compare the effectiveness of orthodontic appliances

Functional appliance treatment for mandibular fractures: A systematic review with meta-analyses

OBJECTIVES Mandibular collum fractures among growing patients can lead to abnormal growth, function, esthetics and ultimately quality of life. Among the proposed treatment alternatives, orthopaedic treatment with functional appliances has been suggested, with encouraging results. Aim of the present systematic review was to critically appraise existing evidence on the outcome of functional appliance treatment among growing patients with mandibular collum fractures. MATERIALS AND METHODS Eight databases were searched up to October 2020 for randomised and non-randomised clinical studies assessing functional appliance treatment outcome for children with mandibular fractures. After duplicate study selection, data extraction and risk of bias assessment, random effects meta-analyses of mean differences (MD) and their 95% confidence intervals (CIs) were performed, followed by assessment of the quality of evidence with GRADE. RESULTS A total of 8 unique studies (one prospective and nine retrospective non-randomised) with 223 children could be identified. Functional appliance treatment was associated with greater anteroposterior condyle dimensions of the injured condyle compared with the contralateral healthy condyle (3 studies; MD = 0.87 mm; 95% CI = 0.30 to 1.45 mm; p = .003). No difference was found in the mesiodistal condyle size between the injured and the contralateral healthy joint (3 studies; MD = -0.05 mm; 95% CI = -1.05 to 0.95 mm; p = .92), but collum length was smaller at the injured side compared with the contralateral one (1 study; MD = -2.89 mm; 95% CI = -5.29 to -0.49 mm; p = .02). Treatment outcome might be influenced by patient age, patient sex and severity/localisation of the fracture, but the quality of evidence for all analyses was very low due to methodological limitations leading to bias. CONCLUSIONS While some evidence exists that functional appliances might lead to good clinical rehabilitation of fractured mandibular condyles, including considerable bone remodelling, available studies are small and have methodological weaknesses

Methods, transparency and reporting of clinical trials in orthodontics and periodontics

Objective: The aim of this study was to explore the methods, reporting and transparency of clinical trials in orthodontics and compare them to the field of periodontics, as a standard within dentistry. Design/setting: Cross-sectional bibliographic study. Methods: A total of 300 trials published in 2017-2018 and evenly distributed in orthodontics and periodontics were selected, assessed and analysed statistically to explore key aspects of the conduct and reporting of orthodontic clinical trials compared to trials in periodontics. Results: Several aspects are often neglected in orthodontic and periodontic trials and could be improved upon, including use of statistical expertise (22.3% of assessed trials), blinding of outcome assessors (62.3%), prospective trial registration (12.0%), adequate sample size calculation (35.7%), adherence to CONSORT (14.3%) and open data sharing (4.3%). The prevalence of statistically significant findings among orthodontic and periodontic trials was 62.3%, which was significantly associated with several methodological traits like statistician involvement (odds ratio [OR] = 0.5; 95% confidence interval [CI] = 0.3-0.9), blind outcome assessor (OR = 0.5; 95% CI = 0.2-1.0), lack of prospective trial registration (OR = 2.8; 95% CI = 1.3-5.9) and non-adherence to CONSORT (OR = 4.5; 95% CI = 1.3-15.8). Conclusions: Although trials in orthodontics seem to be significantly worse compared to periodontics in aspects like trial registration, adherence to CONSORT and declaration of competing interests or financial support, their methods do seem to have improved considerably in recent years

Effect of four premolar extractions on the vertical dimension of the face : A retrospective cephalometric study

PURPOSE Adequate control of the vertical dimension is of great importance in orthodontic treatment. Although existing evidence is very limited, extraction of four premolars is thought to contribute towards improved control of anterior facial height compared with non-extraction treatment protocols. Thus, the aim of this retrospective cohort study was to compare the effect of fixed-appliance treatment with extraction of four premolars to non-extraction treatment on the skeletal vertical dimension. METHODS A consecutive sample of 76 children with skeletal hyperdivergence (49% male; mean age 11.9 years) was divided into two groups for treatment with either non-extraction (n = 31) or extraction of four premolars (n = 45). Baseline characteristics were comparable: overjet 5.1 ± 2.5 mm, overbite 2.4 ± 1.9 mm, ANB angle 4.6 ± 2.3°, and SN-ML angle 40.2 ± 3.5°. Patients were treated with standard edgewise fixed appliances with closing loops/sliding mechanics. Vertical skeletal and dental outcomes were measured on lateral cephalograms before and after treatment. Data were analyzed with linear regression at 5%. RESULTS Compared to non-extraction treatment, treatment with premolar extractions had no significant effect on the SN-ML angle (difference (Δ) = 0.07°; 95% confidence interval -0.90 to 1.01°; P = 0.88). Statistically significant changes between the extraction and non-extraction groups were only found for the parameters SNA (Δ -1.47°; P = 0.003), ANB (Δ -1.17°; P = 0.004), SN-OP (Δ -1.48°; P = 0.04), and L1-ML (Δ -6.39°; P < 0.001). CONCLUSION Orthodontic treatment of children with skeletal hyperdivergence using systematic extraction of four premolars had minimal effects on the vertical facial dimension compared to non-extraction treatment

What are the differences in protective characteristics of orthodontic mouthguards? An in vitro study

BACKGROUND Orthodontic patients wearing fixed appliances are susceptible to traumatic dental injuries during contact-sport. This laboratory study investigated the protective qualities of orthodontic mouthguards using impact-testing to a typodont fitted with a fixed appliance through peak load transfer and retention of the mouthguard. METHODS Seven orthodontic mouthguards [three custom-made (Medium-CM, Heavy-CM, Heavy-pro-CM); three commercially-available mouth-formed (Shock-Doctor® Ultra Braces, Opro® Ortho-Gold Braces, Opro® Ortho-Bronze Braces) and a Shock-Doctor® Instant-Fit] were fitted to a maxillary arch typodont bonded with a fixed appliance and impact-tested using 0.5 or 1 Joule (J) energy via hockey-ball, cricket-ball or steel-ball projectile. A load-cell recorded peak load transfer through mouthguard to typodont with retention scored in a binary manner dependent upon any displacement following impact. Differences across mouthguards were calculated with ANOVA or Kruskal-Wallis test for normal and non-normal data, respectively. Post hoc comparisons across mouthguards were conducted via Dunnett's test with Sidak correction. RESULTS Only the three custom-made and Opro® Ortho-Gold Braces were not displaced by impact-testing. For these, Opro® Ortho-Gold Braces transferred the smallest load for 3/6 impact-tests, followed by Medium-CM. Heavy-pro-CM performed poorly, ranking penultimate or worst for all impact-tests. Significant differences were found between mouthguards for cricket-ball and steel-ball set-ups. The Opro® Ortho-Gold Braces performed better than the Heavy and Heavy-pro-CM for 0.5 J cricket-ball impact-test (P < 0.05), whilst Medium-CM performed better than Heavy-pro-CM. For 1 J cricket-ball, there were significant differences between Medium-CM and Heavy-pro-CM (P < 0.05). For 0.5 J steel-ball, the Medium-CM performed significantly better than both Heavy-pro-CM and Opro® Ortho-Gold Braces (P < 0.05), whilst Heavy-CM performed better than the Heavy-pro-CM (P < 0.05). For the 1 J steel-ball, Medium and Heavy-CM performed better than Opro® Ortho-Gold Braces (P < 0.05). CONCLUSIONS Opro® Ortho-Gold and Medium-CM mouthguards offer the best protection for low-impact sports, whilst Medium or Heavy-CM mouthguards are recommended for high-impact sport