[Factors influencing the changes of lower third molars' angulation and space/crown width ratio by orthodontic treatment].

OBJECTIVE

To investigate the factors which influence the changes of lower third molars' angulation and space/crown width ratio by orthodontic treatment.

METHODS

Pretreatment and posttreatment panoramic radiographs of 120 orthodontically treated cases were taken. The lower third molars' angulation and space/crown width ratio were examined and the relative factors on changes were analyzed.

RESULTS

(1)The changes of the lower third molars' angulation and space/crown width ratio after orthodontic treatment were quite different among the cases. (2)The factors which influenced these changes mainly included extraction, mandibular plane angle, angulation and space/crown width ratio of lower third molar before orthodontic treatment. (3) Extraction was the most significantly variable associated with lower third molars' upright (angulation <30 degree) after orthodontic treatment.

CONCLUSION

Orthodontic extraction is helpful to upright the lower third molars and to increase the space for third molars; and the pre-treatment lower third molars' angulation and space/crown width ratio are important variables for the changes after treatment; cases with lower mandibular plane angle are apt to greater possibility for the lower third molars' upright.