Quantitative evaluation of retromolar space in adults with different vertical facial types

To investigate the differences in mandibular retromolar space among skeletal Class I subjects with different vertical divergence using cone-beam computed tomography (CBCT).

A total of 123 skeletal Class I patients (aged 20-40 years) were categorized into hypodivergent, normodivergent, and hyperdivergent groups based on S-N/Go-Me and facial height index (FHI). Mandibular retromolar space was measured at four planes parallel to the occlusal plane along the sagittal line and molar cuspal line, respectively. The mandibular retromolar space was compared among the three vertical groups.

The hyperdivergent group had a significantly smaller mandibular retromolar space compared with the other two groups, while the hypodivergent group had the largest retromolar space. In addition, the hyperdivergent group had a larger number of subjects whose roots contacted the lingual cortex of the mandibular body.

The hyperdivergent group tends to exhibit the smallest mandibular retromolar space and highest risk of cortex contact. Clinicians should keep in mind that successful molar distalization requires sufficient retromolar space, especially for hyperdivergent subjects, which should be verified with CBCT.