In vivo measurement of dental arch deformation during static tasks

Objective: If teeth are assumed to be rigid, the deformation of a dental arch (DA) can be depicted with the translation and rotation of all the teeth. This study aimed to develop a method to investigate DA deformation during static tasks.

Methods: An interocclusal record obtained with polyvinylsiloxane bite-registration material (Exabite III; GC, Japan), and a dental stone cast, which was divided into individual tooth parts in advance, were digitized with a three-dimensional optical scanner (Comet VarioZoom; Steinbichler Optotechnik, Germany). The DA model was fabricated with CAD software (PolyWorks; InnovMetric, Canada) by best-fitting the polygonal teeth models onto the surface form of the interocclusal record and then aligned to the coordinate system based on the incisal point, occlusal plane, and midline of the arch. DA deformation was investigated by calculating the translation and rotation of each tooth between the 2 DA models: during jaw closing and another static task. We utilized 3 dentate subjects and the lingual cusp of the premolars and the midpoint of the lingual cusps of the molars as landmark points. To ensure the accuracy of the best-fitting procedure, the locations of the points of the left first premolar and the first molar were measured repeatedly (n=10) in one subject. In addition, dimensional changes between the points of bilateral posterior teeth were investigated in 3 subjects during intercuspal (ICP) and insical (INC) clenching.

Results: The fitting error was 0.024±0.033mm and 0.022±0.031mm with regard to the premolar and molar, respectively. DA tended to compress during ICP and to expand during INC. Dimensional changes were greater in the posterior part of DA during both tasks. The magnitudes of DA compression and expansion were up to 0.42 and 0.27mm, respectively. Conclusion: Our method showed acceptable accuracy and can be used to investigate DA deformation during static jaw tasks.