Does Planned Molar Intrusion with Aligners Assist with Closure of Anterior Openbite?

Abstract

Introduction: Anterior openbite (AOB) treatment is commonly regarded as a challenging malocclusion to treat and retain long-term. Aligners have become an increasingly popular AOB treatment modality due to the theory that they exert a “bite-block” effect on molars, thus helping with AOB correction. In addition, practitioners can specifically plan intrusive molar movements and use virtual posterior bite blocks on the occlusal surfaces of molars, which some believe augment the intrusion. However, we do not know whether prescribed molar intrusion, with or without bite blocks, results in actual molar intrusion and whether these features assist with AOB closure. Methods: 42 AOB patients were recruited from 5 private practices and from the University of Washington Graduate Orthodontics Clinic. All patients were treated with Invisalign® aligners. Patients were divided into two groups based on the presence of a virtual bite “jump” in the approved ClinCheck® software treatment simulation. Patients who were prescribed molar intrusion, with or without accompanying incisor extrusion, had a virtual bite “jump” at the last stage of the simulated treatment, and were assigned to the planned molar intrusion (PMI) treatment group. Patients without prescribed molar intrusion did not have a virtual bite “jump” and were assigned to the no planned molar intrusion treatment (No-PMI) treatment group. PMI patients were further categorized by the presence or absence of virtual posterior bite blocks on the occlusal surfaces of molars (PMI-BB and PMI-No BB, respectively). Patient and treatment characteristics were evaluated using descriptive statistics. Treatment success was determined based on positive vertical incisor overlap in post-treatment cephalograms. Treatment changes were assessed using pre- (T1) and post-treatment (T2) cephalometric radiographs (Welch Two-Sample T-Test, 95% confidence interval, p=0.05). Patients were invited to return to their offices at least 1-year post-treatment (T3) for an intraoral frontal photograph to assess treatment stability using the Photographic Openbite Severity Index (POSI). Results: In the retrospective arm of the study, there were 18 No-PMI and 24 PMI patients (total N=42). The PMI treatment group had more severe pre-treatment openbites, greater pre-treatment crowding, and longer treatment times. The mean overbite change was 2.6 mm (SD=1.1) for No-PMI and 3.2 mm (SD=1.7) for PMI patients (p=0.15). All patients had positive vertical incisor overlap in T2 cephalograms, indicating 100% treatment success. The openbites were corrected primarily by incisor retroclination and extrusion in both treatment groups. Small amounts of molar intrusion were observed for PMI patients (0.1-0.6 mm), and reached statistical significance after controlling for potentially confounding variables (p=0.034). The amount of planned molar intrusion was not well correlated with the amount of measured molar intrusion, mandibular plane closure, or decrease in AFH. 15 patients from the original sample returned for T3 intraoral frontal photographs and were included in the POSI analysis. Of those, 12 (80%) had a POSI score of 0, 2 (13.3%) had a POSI score of 1, and 1 (6.7%) had a POSI score of 4. Conclusion: Prescribing molar intrusion for openbite patients appears to result in a small, statistically significant amount of mean molar intrusion (less than 1 mm), and may be of some assistance with openbite closure. However, the majority of the correction appears to be the result of incisor retroclination and extrusion. Patients undergoing aligner therapy exhibited a high success rate for openbite closure. Based on our limited sample, treatment stability was similar to that reported for fixed appliances; however, larger sample sizes and longer follow-up periods are necessary.