1 Page : 181-198
Author(s) : Chawasri Poonvutikul, Piyarat Apivatanagul, Niramol Chamnannidiadha
Keyword(s) : extraction orthodontic cases,mandibular position,skeletal Class I normal bite
Manuscript Type : Original Article (บทวิทยาการ)
Page : 181-198
This study’s objectives were to investigate the changes of mandibular positions in pre-molar extraction orthodontic cases and to seek the correlation coefficients of the changes in the positions of mandible, first molars and incisors. The non-randomized selected sample consisted of 32 adult females; mean aged 22.03 years (18-33 years) showing a skeletal Class I, normal bite malocclusion with ANB= 3۬ degrees and SN-GoMe = 33ۯ degrees. All patients were treated orthodontically with four premolar extractions. Pre- and post-treatment standardized lateral cephalometric radiographs were taken on the same machine and cephalometric data were analyzed. MPA (SN-GoMe),Y-axis angle (NSGn) and SNPog angles were examined to evaluate the vertical and sagittal changes of the mandibular position. The changes of the mesial height of contour of the maxillary and mandibular first molars andthe incisal edge of incisors were recorded relatively to pre-treatment functional occlusal plane, vertically and sagittally. There is a statistical significant difference (Paired t-test, p < .05) of the pre- and post-treatment position of mandible. There are correlations between the increase of MPA and the decrease of SNPog angle and the extrusion of maxillary incisor position (r= 0.55, p < .01, r= -0.42, p < .05, respectively) and the backward movement of maxillary incisor position too. (r=-0.46, p < .05, r= 0.61, p < .01, respectively). There are correlations between the increase of Y-axis angle and the backward movement of maxillary incisor position and the extrusion of mandibular first molar position (r= -0.57, p < .01, r= 0.42, p < .05, respectively). There is a correlation between the decrease of Y-axis angle and the forward movement of maxillary first molar position (r= 0.45 , p < .05) . There are correlations between the decrease of Y-axis angle and the increase of SNPog angle and the backward movement of mandibular incisor position (r= 0.41, p < .05 and r= -0.52, p < .01, respectively). And there is correlation between the decrease of SNPog angle and the extrusion of mandibular incisor position (r= -0.55, p < .01). In summary, there is a statistical significant difference (pair t-test, p < .05) of the pre- and post-treatment positions of mandible in skeletal Class I, normal bite malocclusion adult females sample (mean age 22.03 years). The vertical and sagittal changes of mandibular positions are correlated to the changes of incisor and first molar positions.