Tooth Dimensions, Arch Width, and Treatment Outcomes after Mandibular Incisor Extraction

To evaluate treatment-related changes in tooth widths, ratios, and dental arch changes in patients treated with mandibular incisor extraction treatment (MIET).

Pre- (T1) and post-treatment (T2) digital dental casts of 24 patients (13 female, 11 male; mean age: 16.58±3.81 years) who underwent MIET were examined. Mesiodistal tooth widths, transverse dental arch widths, overjet, and overbite were measured, and the Bolton ratios were calculated using OrthoCAD software. Pre- and post-treatment values were compared. Correlations between post-treatment overjet and related parameters were analyzed.

Mesiodistal widths of the maxillary incisors decreased from T1 to T2, with a statistically significant decrease in the upper right lateral (-0.18±0.32 mm, p=0.010) and upper left central incisors (-0.20±0.36 mm, p=0.011). Mandibular intercanine width decreased (-2.56±3.39 mm; p<0.001), whereas maxillary and mandibular interpremolar width (2.91±2.06 mm, p<0.001; 1.57±2.68 mm, p=0.008) and mandibular intermolar width (1.09±1.94 mm, p=0.013) increased significantly. Overbite (-1.00±1.52 mm, p=0.004), the anterior Bolton ratio (-10.51±2.40%, p<0.001), and the overall Bolton ratio (-4.89±1.83, p<0.001) decreased during treatment. Post-treatment overjet was negatively correlated with the pre-treatment anterior and overall Bolton ratios and positively correlated with the pre-treatment arch length, the difference in intercanine width (T2-T1), and the pre-treatment overbite.

MIET caused a decrease in mandibular intercanine width and the anterior Bolton ratio, despite the interproximal reduction performed on the upper incisors. Given the potential consequences of these results on anterior and canine guidance, greater interproximal reduction in the maxilla and close attention to the torque and final positions of the mandibular canines may be recommended.