Introducing surface-to-surface matching technique to evaluate mandibular symmetry: A retrospective study

Abstract

Objectives: This study introduced a three-dimensional (3D) surface-to-surface matching technique to evaluate the mandibular symmetry of teenagers and adults with unilateral second molar scissor bite.

Methods: The targets came from 73 cone-beam computed tomography (CBCT) images with unilateral second molar scissor bite, including teenagers (n = 30) and adults (n = 43). 73 images without scissor bite and matched in sex and age were selected as controls. The scans were developed into 3D mandible models and seven mandibular functional unit models, including condylar process (Co), coronoid process (Cr), mandibular ramus (Ra), mandibular angle (Ma), alveolar process (Ap), mandibular body (Mb) and chin process (Ch). The surface-to-surface matching technique was introduced. 3D deviation analysis and matching percentages calculation were performed and compared to evaluate the symmetry of the mandible.

Results: Comparisons were made between the study samples and control samples. For teenagers, the matching percentages of the entire mandible (55.31 ± 7.24%), Mb (69.04 ± 9.22%) and Co (65.19 ± 10.67%) in the study group were lower than that of the entire mandible (60.87 ± 6.38%) (P <0.01), Mb (75.0 ± 8.71%) (P <0.05) and Co (70.25 ± 8.20%) (P <0.05) in the control group. While Ap, Ra, Ch, Cr and Ma showed no statistically significant differences (P >0.05). For adults, the matching percentages of the entire mandible (48.88 ± 9.77%), Ap (65.83 ± 11.21%), Mb (64.43 ± 12.03%), Ch (79.17 ± 10.29%), Ra (64.11 ± 9.84%) and Co (61.08 ± 11.64%) in the study group were lower than the entire mandible (59.28 ± 5.49%) (P <0.01), Ap (73.65 ± 9.10%) (P <0.01), Mb (71.66 ± 8.40%) (P <0.01), Ch (83.86 ± 5.59%) (P <0.05), Ra (68.54 ± 7.87%) (P <0.05) and Co (66.20 ± 10.62%) (P <0.05) of the control group. Only Cr and Ma showed no statistically significant differences (P >0.05).

Conclusion: Mandibular asymmetry was observed in both teenagers and adults with unilateral second molar scissor bite. Moreover, compared with teenagers, more mandibular units of adult patients were affected.

Clinical significance: Based on the surface-to-surface matching technique, the symmetric and morphological information of the mandible can be converted into visual color maps and quantitative descriptions. This method can bring convenience to the study of the growth of mandible, orthodontic treatment and orthognathic surgery design.

Keywords: Cone-beam computed tomography; Scissor bite; Second molar; Three-dimensional imaging.

Figure 1

The flow chart of the research.

Figure 2

(a) CBCT data was imported to the Mimics software. (b) The initial segmentation mask. (c) The mandible part was calculated. (d) The original mandible model was developed. (e) The mirrored mandible model was developed. (f) Best Fit Alignment.

Figure 3

3D Surface deviation analysis of mandibles. (a) teenager study group. (b) adult study group.

Figure 4

Mandibular functional units construction. Co, condylar process; Cr, coronoid process; Ra, mandibular ramus; Ma, mandibular angle; Ap, alveolar process; Mb, mandibular body; Ch, chin process.

Figure 5

3D Surface deviation analysis of mandibular functional units. Co, condylar process; Cr, coronoid process; Ra, mandibular ramus; Ma, mandibular angle; Ap, alveolar process; Mb, mandibular body; Ch, chin process.

Figure 6

Matching percentages of the mandibular functional units. The level of significance was set at 0.05. ∗ = p <0.05; ∗∗ = p <0.01.