Dynamic Determinants of Incisal Display

Abstract

The principal objective of this study was to use computer aided design (CAD) to better illustrate and quantify the relationship of mandibular arch depth, mandibular arch width, overbite, and overjet in the presence of mandibular dental crowding. To date, there has been no research examining how changes in the mandibular arch limit the orthodontist\u27s ability to control overbite and overjet. Understanding how to effectively manage overbite and overjet are crucial to the clinician\u27s ability to manipulate incisal display. Polyvinyl siloxane impressions of both maxillary and mandibular arches of a Caucasian patient were taken and used to pour dental stone models. Models were then potted, scanned, manipulated, and measured using Insignia™ (Ormco Corporation, Glendora, CA). Five different groups of maloccluded, diagnostic set-ups were subsequently constructed based upon location of crowding in the arch. For all groups, regression analysis revealed similar linear relationships (R2=0.963-0.999) for arch depth, arch width, and overjet changes versus dental crowding. In contrast, overbite changes displayed linear, quadratic, and cubic relationships (R2 = 0.688-0.997). Results suggest that lingual contours of maxillary incisor crowns are smile arc determinants and rate determining factors of overbite change. Guidelines for managing overbite and incisal display are offered