[The effect of first premolar extraction on vertical dimension in skeletal Class I patients].

Purpose: To evaluate the vertical changes in Class I patients treated with first premolar extraction and to compare these changes with those without extraction.

Methods: Each group had 25 cases.One group was treated with first premolar extraction and the other without extraction. Lateral cephalograms were taken both pretreatment and posttreatment. All the films were traced and measured. To determine the vertical dimension changes due to treatment and to compare differences between the 2 groups, paired and unpaired t tests were performed with SPSS 16.0 software package, respectively.

Results: There was no significant difference in FH-MP, Yaxis, S-Go, S-Go/N-Me and ANS-Me/N-Me in both group after treatment. Both groups had increase in N-Me , but the change was comparatively greater in the extraction group. The extraction group showed more vertical movement of the mandibular first molars than the non-extraction group.Both groups showed mesial movement of the maxillary first molars and central incisors,but no significant difference was found.

Conclusions: Both groups have increase in linear vertical dimensions. The changes in vertical dimension is greater in the extraction group, but there is no further change in the mandibular plane angle.