Clinical Evaluation of Mandibular Flexure during Mouth Opening with Digital 3-dimensional Analysis

Abstract

ABSTRACT

Background: Median mandibular flexure (MMF) is a phenomenon of flexure or deformation of the mandible which may affect prosthodontic treatments, specifically for full arch rehabilitation. During this phenomenon the mandible tends to flex in an inward and downward movement during maximum mouth opening. This flexure also occurs during other functional movements such as mouth closing, and lateral movements.

Objective: This study aimed to evaluate the 3-dimensional distortion of median mandibular flexure during maximum mouth opening and minimum mouth opening using a digital 3-dimensional analysis.

Methods: Twenty subjects with full dentition in the mandibular arch were recruited. Two intraoral scans were obtained with an optical scanner (Trios 4, 3Shape, Denmark). The first scan was executed with more than 35mm mouth opening. The second scan was performed with minimal mouth opening (less than 10mm). The two scans were exported from the intraoral scanner as Standard Tessellation Language (STL) files. The STL files were imported in the 3-dimensional inspection software (Geomagic Control X, 3D Systems, SC, USA). Superimpositions with Best-fit Algorithms were performed following the Initial Alignment. Linear measurements were made between the tip of canines, the buccal cusp tip of premolars, and the mesio-buccal cusp tip of first and second molars. 3D comparison of the two scans was calculated with the surface of teeth.

Results: The mean RMS deviation increased progressively from canine to molar: means (± standard deviations) were 0.037 (±0.014) mm for RMS 1 (canine), 0.053 (±0.019) mm for RMS 2 (premolar), and 0.083 (±0.029) mm for RMS 3 (molar). Significant differences were confirmed by both repeated-measures ANOVA and the Wilcoxon signed-rank test (p < 0.001). The linear measurements taken the maximum linear distance from the MxMO scan (Linear 1) had a mean (± standard deviation) of 48.29 mm (±2.28 mm), while the minimum linear distance from the MnMO scan (Linear 2) had a mean (± standard deviation) of 48.36 mm (±2.27 mm). A Shapiro-Wilk test indicated normality for RMS values but non-normality for linear measurements.

Conclusion: The mandibular flexure observed in the molar area had the highest degree of deviation and the canine area had the least. A significant difference in linear measurements between maximum and minimum mouth openings suggests variability in mandibular dimensions during movement, which has implications for procedures like prosthetics and implants. Median mandibular flexure is a noticeable phenomenon since there is evidence that there is a significant amount of deviation in the mandible and the extent of mandibular flexure is greatest in the molar region and progressively less towards the anterior region. Additionally, there is a significant change in the inter-molar distance between minimum mouth opening and maximum mouth opening. This confirms the importance of taking this deviation into consideration when diagnosing and treatment planning full arch mandibular case.