[Cone-beam CT evaluation of temporomandibular joint in skeletal class Ⅱ female adolescents with different vertical patterns]

To compare temporomandibular joint (TMJ) morphology and position among skeletal class Ⅱ female adolescents with different vertical patterns using cone-beam CT (CBCT).

Diagnostic CBCT images of 80 female patients aged 11 to 14 years were assessed retrospectively. According to subspinale-nasion-supramental angle (ANB) and Frankfort horizontal plane-gonion-gnathion angle (FH-GoGn), the participants were categorized into four groups (20 subjects each), i.e. class Ⅰ normal angle (group 1, 0°≤ANB < 4°, 22°≤FH-GoGn≤32°), class Ⅱ low (group 2, ANB≥4°, FH-GoGn < 22°), normal (group 3, ANB≥4°, 22°≤FH-GoGn≤32°) and high angle (group 4, ANB≥4°, FH-GoGn > 32°). Cephalometrics, morphology and position of TMJ were measured in Dolphin software. Using paired-samples t test to analyze TMJ symmetry, One-way analysis of variance (One-way ANOVA) and Chi-square tests to detect differences among the groups. The correlations between cephalometrics and TMJ measurements were also analysed within the skeletal class Ⅱ patients.

(1) Analysing TMJ morphologic symmetry, some measurements differed statistically although the mean diffe-rences were negligibly relative to their values. No statistically significant difference was found among the groups though group 4 showed the highest probability of condylar position asymmetry (65%). (2) Comparing group 1 with group 3, statistical difference was found in condylar position (χ²=6.936, P < 0.05) instead of morphologic measurements. Anterior and concentric condylar position were more frequently observed in group 1, yet posterior position was more prevalent in group 3. (3) In groups 2, 3, and 4, statistically, group 2 had the deepest glenoid fossa depth (H_2&4=10.517, P=0.002), biggest superior (LSD-t_2&3=3.408, LSD-t_2&4=5.369, P < 0.001) and lateral (LSD-t_2&3=2.767, LSD-t_2&4=3.350, P=0.001) joint spaces, whereas group 4 showed the shortest condylar long axis diameter (H_2&4=13.374, P < 0.001), largest glenoid fossa vertical distance (LSD-t_2&4=4.561, P < 0.001, LSD-t_3&4=2.713, P=0.007), smallest medial (LSD-t_2&4=-4.083, P < 0.001) and middle (LSD-t_2&4=-4.201, P < 0.001) joint spaces. The posterior condylar position proportion gradually increased from groups 2 to 3 to 4. Correlation analysis revealed ANB correlated with anterior joint space positively (r=0.270, P=0.037) and condylar long axis angle negatively (r=-0.296, P=0.022). FH-GoGn correlated with superior (r=-0.488, P < 0.001), posterior (r= -0.272, P=0.035), mesial (r=-0.390, P=0.002), middle (r=-0.425, P=0.001), and lateral (r=-0.331, P=0.010) joint spaces, articular eminence inclination (r=-0.259, P=0.046), as well as condylar long axis diameter (r=-0.327, P=0.011) negatively, and glenoid fossa depth (r=0.370, P=0.004) positively.

TMJ characteristics of skeletal class Ⅱ sagittal pattern mainly reflected in condylar position rather than morphology. TMJs of different vertical patterns differed more in joint spaces, position of condyle and glenoid fossa than in morphologic measurements. Vertical position of glenoid fossa and proportion of posterior condyle increased gradually from hypodivergent to hyperdivergent. Highest glenoid fossa position, maximum ratio of posterior positioned condyle, smallest joint spaces, shallowest glenoid fossa depth, and narrowest condylar long axis diameter were found in skeletal class Ⅱ high angle group, which means that patients with this facial type have considerable joint instable factors, and we should especially pay attention when orthodontic treatment is carried out on them.