Evaluation of bone area in the posterior region for mandibular molar distalization in class I and class III patients

The aim of this study was to investigate the bone area in the posterior region, which is important for mandibular molar distalization in skeletal class I and class III individuals with normodivergent and hyperdivergent vertical growth patterns.

In this retrospective study, cone-beam computed tomography (CBCT) scans of 120 individuals divided into 4 groups as class I normodivergent (group-I), class I hyperdivergent (group-II), class III normodivergent (group-III), and class III hyperdivergent (group-IV). Retromolar area at crown level measurements was performed on CBCT-derived panoramic radiographs and axial sections. Retromolar area at the root level was measured 2 mm, 4 mm, 6 mm, 8 mm, and 10 mm apical to cemento-enamel junction at CBCT axial sections.

Retromolar area decreased towards the root apex in all groups and smallest retromolar area was level of CEJ_10mm in all groups. At any root level, the distal root of the mandibular second molar tooth was in contact with the mandibular inner or outer lingual cortex; 50% in group-I, 46.7% in group-II, 23% in group-III, and 23% in group-IV.

In normodivergent individuals, the retromolar area length at the root level is observed to be higher in class III than in class I at almost every level. In hyperdivergent individuals, on the other hand, only at CEJ_10mm level, it is higher in length in class III than in class I. Vertical growth pattern has no effect on the root and crown level retromolar area in class I and class III individuals.

CBCT provides more useful information than panoramic radiographs for patients who are scheduled for large mandibular molar distalization.