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[Factors influencing the changes of lower third molars' angulation and space/crown width ratio by orthodontic
Xiao-tong Li1, Dong-mei Zhang, Yan-qi Yang
1Department of Orthodontics, Peking University School, Beijing 100081, China. xiaotonglee@hotmail.com
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.
