Clinical Crown Length Changes Following Maxillary Molar Distalization: The Role of Three-Dimensional Tooth Movement...

Maxillary molar distalization is widely used for space gain and anterior retraction. However, gingival recession may occur around the maxillary second molar following distalization, and the tooth movement factors associated with changes in clinical crown length (CCL) remain unclear. This study investigated the associations of CCL changes with three-dimensional movement of the maxillary second molar and the position of the maxillary third molar.

This retrospective study included 58 maxillary second molars from 30 adult patients who underwent skeletal anchorage-assisted maxillary total arch distalization. CCL changes and three-dimensional tooth movements were evaluated using CBCT and digital intraoral scans obtained before and after treatment. Linear mixed-effects models were used to evaluate the associations between CCL changes and second molar movement. Gingival margin displacement was additionally analysed in relation to second molar vertical displacement. In patients with a third molar (n = 38), the associations between CCL changes and the three-dimensional position of the third molar were evaluated. Third molar status was also evaluated by classifying third molars as missing, impacted, or erupted.

The mean CCL change was 0.36 ± 0.70 mm. Greater second molar intrusion was significantly associated with decreased CCL (β = -0.108, p = 0.020), whereas distal and transverse movements were not significantly associated with CCL change. With greater second molar intrusion, the gingival margin also moved in the direction of intrusion, but significantly less than the tooth itself (β = 0.793, p = 0.002). In the third-molar subgroup, greater second molar intrusion remained significantly associated with decreased CCL (β = -0.111, p = 0.022), whereas a more buccally positioned third molar was associated with increased CCL (β = 0.132, p = 0.016). Third molar status and third molar angulation were not significantly associated with CCL change.

CCL changes during maxillary molar distalization were associated with second molar intrusion and the buccolingual position of the third molar. Greater second molar intrusion was associated with decreased CCL, whereas a more buccally positioned third molar was associated with increased CCL. These findings suggest that vertical movement of the second molar and the three-dimensional position of the third molar should be considered when planning maxillary molar distalization.