A study conducted at the University of Oklahoma reports that long-term stability can be achieved by treating incisor crowding with or without premolar extractions.

Dental casts and cephalometric records of 98 patients were evaluated before treatment (T1), at post-treatment (T2), and at postretention (T3). Half of the patients had been treated with extractions, and half were treated nonextraction.

The results found that irregularity, as measured by the irregularity index, decreased 5.51 mm in the extraction group and 2.38 mm in the nonextraction group. Mandibular incisor irregularity increased 0.97 mm in the extraction group and 0.99 mm in the nonextraction group, respectively, in the postretention period. Maxillary incisor irregularity relapse was smaller than mandibular incisor relapse for both groups. Intercanine width expanded during treatment. At T3, mandibular intercanine width decreased in both groups, but the differences were not statistically significant.

The researchers also reported that at T3, intermolar width was stable, arch depth decreased, overbite and overjet slightly increased, SN mandibular plane angle decreased, and incisor positions in both groups tended to return to T1 values. Clinically acceptable stability was obtained. With the exception of the interincisal angle, no statistically significant differences were recorded between the extraction and nonextraction groups from T2 to T3.

The researchers concluded that no significant correlations were found between any variables studied and mandibular incisor irregularity at T1, T2, and T3.

[Biotech Business Week, 11/27/2006]