Effect of mandibular first molar mesialization on alveolar bone height: a split mouth study.

Objectives: To evaluate the risk of vertical alveolar bone loss (ABL) in mesialized mandibular permanent molars due to space closure in patients with unilateral second premolar agenesis. The contralateral side served as control.

Subjects And Methods: Twenty-five retrospectively selected subjects (median age 14.9, range 12.0, 31.9 years) were analyzed. Space closure (approximately 10 mm) was performed using skeletal anchorage. ABL was measured at mesial and distal sites of first molars in pre- and post-treatment panoramic radiographs. Measurements were corrected for distortion and magnification of radiographs. Molar angulation according to the occlusal plane was also evaluated. Permutational multivariate analysis of covariance (MANCOVA), followed by pairwise comparisons, was performed.

Results: MANCOVA resulted in no difference in ABL between the distal sites of mesialized molars and the control sites. On the contrary, there was statistically higher ABL, at the mesial sites of mesialized versus non-mesialized molars (p = 0.042; median 0.19 mm; range - 0.82, 1.33); though the difference was not clinically relevant. In the space closure side, mesially, only two patients had ABL higher that 1 mm. No patient had a severe bone level height defect (> 3 mm distance from the cementoenamel junction) at any point. When testing differences in molar angulation between sites and from pre- to post-treatment condition, no significant difference was detected (p > 0.05, median - 1.9°, range - 13.5, 6.2).

Limitations: This is a retrospective study on panoramic radiographs.

Conclusions: Space closure through extensive tooth movement was identified as a risk factor for vertical ABL, at the mesial sites of mandibular first molars. However, the amount of ABL was not clinically relevant, and thus this treatment option is considered safe in terms of ABL.