Maxillary first permanent molar changes in buccolingual angulation and intermolar width for untreated subjects with Angle Class I and Class II molar relationships with growth

PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact [email protected]'s Thesis (MSD) --Boston University, Henry M. Goldman School of Dental Medicine, 2015 (Department of Orthodontics and Dentofacial Orthopedics).Includes bibliographic references: leaves 39-45.Background: Palatal inclination of maxillary first permanent molars and intermolar width dimension has been shown to increase with growth for subjects with Class 1 occlusion. Potential changes for growing untreated subjects with Class II molar occlusion has not yet been studied. Objective: To investigate the buccolingual inclination and intermolar width changes in untreated subjects with Angle Class I and Class II molar occlusions for six consecutive years. Material and Methods: The sample included the dental models of 55 untreated subjects from 9.4 to 14.4 years of age, 28 with Angle Class I and 27 with Angle Class II occlusion from the Forsyth twin study. Subjects with Angle Class I and Class II by 3 mm or more were included. Models taken every year for six consecutive years of each subject were scanned using the MotionView scanner, (Motionview, Chattanooga, TN). For each subject, three models were taken prior to the eruption of maxillary second molars and three after the eruption of maxillary second molars. All the scans for each subject were superimposed on the palatal rugae using Geomagic Control Software (Cary, NC). Superimposed images were exported to Mimics software (Materialise, Leuven Belgium) to calculate the buccolingual inclination of maxillary molars and the intermolar width. A reference plane was created from model I of each subject, which included the incisal papilla point and the gingival margin points. For each first molar, a buccolingual inclination plane was then established. The angle between the reference plane and the plane created for each molar connecting the lingual cusp tips and the lingual groove point (buccolingual inclination plane), was measured to calculate the molar buccolingual inclination at each time-point. The intermolar width at each time-point was calculated by measuring the distance between the lingual groove-point on each side. Results: All molars showed significant palatal inclination increasing over the 6 years, though Class II patients showed a greater change. In Class I patients, the left molar buccolingual inclination change mean was 4.95 degrees, while the right molar inclination change mean was 5.03 degrees. On the other hand, comparable amounts for Class II patients were 6.27 degrees and 6.24 degrees. Intermolar width showed a continuous increase over 6 years and was significantly greater at each time-point in Class I patients. When comparing Class I to Class II subjects, Class II molar occlusion subjects showed smaller intermolar width as well as less amount of change overtime compared to Class I subjects. Conclusions: - Palatal inclination of maxillary first permanent molars occurs continuously between ages 9.4 and 14.4, with Class II subjects showing larger change at each interval. - Intermolar width of maxillary first permanent molars increases steadily between ages 9.4 and 14.4. - Class II molar occlusion subjects showed smaller intermolar width as well as less amount of change overtime compared to Class I. Further studies with larger sample size and a study design that includes skeletal classification of subjects' malocclusion are needed to support our findings