Anterior Open Bite: Determination of Dental Pulp Cavity Volume and Center of Resistance Using CBCT and Finite Element Method

Abstract

Anterior open bite is considered a malocclusion with no incisal contact between anterior teeth. In previous studies, occlusal hypofunction in anterior open bite malocclusion resulted in increased dental pulp size. Dental pulp is composed of soft connective tissue, vascular, lymphatic and nervous systems that located within the tooth. The volumes of dental pulp cavity were earlier reported in normal bite patients. However, the pulp cavity volume in anterior open bite malocclusion has not been reported in previous studies. Treatment procedures for anterior open bite correction are varied, mainly dependent on severity of malocclusion. In mild to moderate anterior open bite malocclusion, a camouflage orthodontic treatment is aimed at compensating the abnormal tooth position. Control of force vectors and moments is important to obtain the desired tooth movement. Center of resistance (Cres) is a reference point crossed by a force vector at which bodily tooth movement is achieved. The position of Cres depends upon several factors. Accordingly, the variation of tooth dimension and pulp cavity volume in anterior open bite malocclusion may also affect the position of Cres. The present study aimed to investigate the impacts of occlusal hypofunction on the tooth morphologies along with Cres locations in anterior open bite malocclusion. The main hypothesis of this study was that the occlusal hypofunction in anterior open bite malocclusion enlarged the dental pulp cavity and relocated the Cres locations of the tooth. Forty-six patients aged between 15 and 29 years were divided into 2 groups according to anterior overbite and skeletal vertical configurations. Cone-beam computed tomography (CBCT) images were imported into an image processing software for calculating pulp cavity and tooth volumes. Finite element (FE) models of right maxillary central incisor derived from CBCT images were investigated. Cres levels were presented as percentages of the root length from the root’s apex. The relationship between the location of Cres, and volume ratios were evaluated. The results indicated that the anterior open bite group depicted variation in tooth dimension, as indicated by increased dental pulp cavity and root canal volumes, decreased tooth volume and root volume of anterior teeth. The means of pulp cavity/ tooth volume ratio and root canal/ root volume ratio in anterior open bite group were significantly greater than those in anterior normal overbite group. However, no significant differences of the means of pulp chamber/ crown volume were found between groups. The average location of Cres in hypofunction maxillary central incisors was 0.62 mm (3.7%) apically from the normal group, measured from root apex. The difference was statistically significant (P < 0.01). There was a significant correlation between root canal/root volume ratio and Cres locations (r = -0.780, P < 0.001). In conclusion, occlusal hypofunction in anterior open bite malocclusion might lead to an increase of the pulp cavity volume. Moreover, the locations of Cres in hypofunctional group were located more apical than the functional group. As the pulp cavity volume increased, the levels of Cres apically shifted. Our results suggest that any dental procedures, for example, orthodontic treatment should be prudently determined in anterior open bite patient with hypofunctional teeth to avoid the incident of unpleasant tooth movement and root resorption during orthodontic treatment.