| Abstrakt: |
PURPOSE: To study the influence of the first premolar extraction on the angulation and eruption space of third molar. METHODS: One hundred and twenty patients cases of Class 1 malocclusions were divided into 2 groups by age, who were treated with extraction and non-extraction respectively. The following values was measured: angle of cusp line between the second and third molar(α angle),impact state and depth, distance from Rickett's Xi to distal cusp of third mandibular molar along the occlusal plane (Xi-LTM), anterior border of ramus to the third mandibular molar (R-LTM), distance from projection of distal contact point of maxillary third molar to intersection of pterygoid vertical on occlusal plane (PTV-UTM). The change between pre- and post-treatment was calculated and analyzed with SPSS10.0 software package. α angle, Xi-LTM, R-LTM, R-LTM were tested with independent-sample t test, impact state and depth was tested with Chi-square test. Influence of age on the values was also evaluated. RESULTS: In younger group, changes of mandibular a angle and Xi-LTM in extraction group was 7.16°and 3.22mm, but in elder group, these changes was 2.42° and 2.10mm, all values were significantly larger than non-extraction group (P<0.05). Impact state and depth of third mandibular molar improved in extraction group, while there was no significant changes in the maxilla. CONCLUSIONS: The third mandibular molar becomes upright and distal movement after first premolar extraction. The possibility of the third mandibular molar impaction is decreased, hut the effect on the maxilla is not significant. [ABSTRACT FROM AUTHOR] |
