Changes in Occlusal Contact Area Following Orthodontic Treatment: At Time of Debond and Into Retention

Abstract

Introduction: The purpose of this study was to evaluate changes in occlusal contact surface areafrom pre-treatment (T1), post-treatment (T2), and into retention (T3) using 3D models acquired when patients presented for retainer replacement. The influence of patient demographics, treatment characteristics, time since debond and retention types on occlusal contact changes were analyzed. Methods: Patients treated in the University of Washington Orthodontics clinic who obtained an intra-oral scan for the fabrication of new retainers were screened. Inclusion criteria were a history of orthodontic treatment of the permanent dentition with fixed appliances and without orthognathic surgery, the availability of good quality intra-oral scans prior to and after orthodontic treatment, and the absence of restorative treatment since debond. Occlusal contact surface area on the intra-oral scans was analyzed using 3D analysis software across a range of - 1mm to 1mm of inter-occlusal distance between the maxillary and mandibular dentition. Three categories were differentiated: open (0.46 to 1 mm), near (0.21-0.45 mm), and tight (0-0.2 mm) contacts. Surface areas were evaluated for the anterior, posterior, and total dentition at each of the three time points. Changes in occlusal contact surface area were assessed between the three time points (T1-T2, T2-T3 and T1-T3) with subgroup analyses based on age, malocclusion, extraction status, retainer type, and retention time. Results: 60 patients met the inclusion criteria (mean age 15.8 years, 57% female, 43% male, mean time since debond 20.3 months). From T1 to T2, tight and near contact surface area decreased, while open contact surface area increased in the anterior, posterior, and total dentition. From T2 to T3, tight and near contact surface area increased, while open contact surface area decreased in the anterior, posterior, and total dentition. The majority of occlusal contact changes during retention occurred within the first 24 to 36 months following appliance removal. From T1 to T3, there was no significant net change overall for tight, near, and open contacts in the anterior, posterior, and total dentition. Age, extraction status, and retainer type demonstrated limited influence on occlusal contact changes. Class II and III malocclusions exhibited greater increases in near contact surface area and greater decreases in open contact surface area compared with Class I malocclusions, primarily in the total dentition. Conclusions: Orthodontic treatment with fixed appliances temporarily disrupts close occlusal contacts, while retention allows for occlusal settling which increases the occlusal contact areas with a return toward pretreatment values obtained after 24 to 36 months following appliance removal.