Three-dimensional analysis of mandibular functional units in adult patients with unilateral posterior crossbite: A cone beam study with the use of mirroring and surface-to-surface matching techniques

Abstract

Objectives: To use three-dimensional (3D) mirroring and surface-to-surface techniques to determine any differences in mandibular functional unit shape and morphology between the crossbite side and non-crossbite side in adult patients with posterior unilateral crossbite who had not received any corrective treatment for malocclusion.

Materials and methods: Cone-beam computed tomography (CBCT) records from 24 consecutive adult white patients (mean age, 27.5 years; range 22.6-39.7 years; 14 women and 10 men) seeking treatment for maxillary transverse deficiency were assessed in this study. The control group comprised CBCT scans from age- and sex-matched patients. Segmentation masks were generated to obtain 3D surface mesh models of the mandibles and analyze the six skeletal functional units, which were further analyzed with reverse engineering software.

Results: Statistically significant differences in the mean surface distance when comparing the study sample and the control sample were found at the condylar process, mandibular ramus, angular process (P ≤ .0001), and alveolar process (P ≤ .01); no statistically significant differences were found for the coronoid process, the chin, and the mandibular body (P ≥ .5).

Conclusions: The condylar, angular, and alveolar processes plus the mandibular ramus appear to play a more dominant role than did the body, the coronoid, and the chin units in the asymmetry of the mandible in patients with unilateral crossbite.

Keywords: CBCT; Crossbite; Mandible; Surface-to-surface matching.

Figure 1.

The segmentation mask is manually selected in the axial view of the CBCT patient scans using the Threshold function of the Materialise Mimics software.

Figure 2.

First registration of mandibular images on the apical tip of the mandibular lingula and the geometric center of mental foramina/ LMF indicates left mental foramina; LML, left mandibular lingula; RMF, right mental foramina; LML, left mandibular lingual.

Figure 3.

To delineate the Co and the Cr, a perpendicular line to Sg-Li passing through Sg is drawn. This line represents the inferior border of the Co and Cr functional units. The Ra is bounded by the perpendicular to Sg-Li at the top and by two lines at the bottom: the Go1.0-Gor2.0 and the Go1.0-Gob2.0 lines, respectively. The Ap-Ga is delimited at the top by the Go1.0-Gor2.0 and the Go1.0-Gob2.0 lines. The Mb is bounded posteriorly by Go1.0-Rm and Go1.0-Gob2, anteriorly Mb is delimited by a line drawn through point B and Me1.5. The Cp is delineated posteriorly by the line drawn through point B and Me1.5. The Ap is delimitated posterior by a line Go1.0-Rm and inferiorly by the line Go1.0-B (A). The functional mandibular units are then separated (B–D). AP, indicates alveolar process; Ap-Ga, angular process; Co, condylar process; Cp, chin process; Cr, coronoid process; Ra, mandibular ramus; Mb, mandibular body.

Figure 4.

The mandibular functional units from the crossbite side and non-crossbite side of SS and from the right and left side of CS are superimposed using the “best fit” algorithm (A–G).

Figure 5.

3D deviation analysis is carried out using the surface-to-surface technique. A scale bar is shown on the right side. Green color shows the range of tolerance (0.5 mm), red and blue show, respectively, the minimum and maximum deviation values (A–G).