Are Posterior Teeth Overerupted or Is the Mandibular Ramus Shorter? - A CBCT Study of Skeletal Class II Hyperdivergent Patients Compared With Class I.

Objective

The aim of this study is to investigate posterior tooth height and mandibular ramus height in skeletal Class II hyperdivergent patients using cone-beam computed tomography (CBCT) and to assess their associations with the hyperdivergent pattern.

Methods

CBCT data from 60 adult skeletal Class II hyperdivergent patients and 60 adult Class I average-angle patients were analysed. Vertical measurements of posterior teeth and mandibular ramus heights were performed and compared between the two groups using independent samples t-tests. Pearson correlation analyses were performed separately within each group to assess the relationships between posterior teeth heights and mandibular ramus height.

Results

Both ramus and condyle heights in the Class II hyperdivergent group were significantly shorter than those in the Class I average-angle group (p < 0.001). And the vertical heights of maxillary molars (U6-FH: 48.5 ± 2.9 mm; U7-FH: 44.8 ± 3.2 mm) in the Class II hyperdivergent group were significantly shorter than those in the Class I group (U6-FH: 49.8 ± 2.9 mm; U7-FH: 47.2 ± 3.0 mm; p = 0.013 and p < 0.001, respectively). Posterior tooth height showed positive correlations with mandibular ramus height in both groups. Correlations with condylar height were less consistent, particularly for the lower posterior teeth. Stronger correlations were observed for the upper posterior teeth.

Conclusions

No evidence of posterior tooth overeruption was observed in skeletal Class II hyperdivergent patients. Instead, a shorter mandibular ramus height was observed in the hyperdivergent group compared with the Class I group. Significant positive correlations were found between posterior tooth height and ramus height. These findings indicate an association between skeletal and dental measurements and do not support the previously hypothesized "struggle" dynamic.