To test whether levels of OPG can be changed during orthodontic treatment. Alveolar bone samples will be collected from partially impacted third molars after orthodontic uprighting for different period of time in volunteers. In situ hybridization and immunohistochemistry analysis for OPG and RANKL will reveal their roles in this physiological process.

Long treatment time is a major factor causing high fee for orthodontic treatment. Patients would have dental caries or periodontitis resulted from improper oral hygiene care during this long treatment period. Therefore, how to speed up the tooth movement which determines the duration of orthodontic treatment, can help more people to obtain good occlusion and esthetics. Orthodontic force on tooth induces bone resorption on the compression side and bone deposition on the tension side, thus bone remodels and then tooth moves. Bone resorption is a complex process. Osteoblasts play an important role during initiation of bone resorption.

Changes OPG expression of osteoblasts under mechanical stimulation can play a role in bone remodeling. In order to test this hypothesis, the following specific aims will be achieved:

1. To test whether levels of OPG can be changed during orthodontic treatment. Alveolar bone samples will be collected from partially impacted third molars after orthodontic uprighting for different period of time in volunteers. In situ hybridization and immunohistochemistry analysis for OPG and RANKL will reveal their roles in this physiological process.
2. To optimize the regulation by changing magnitude and frequency of pressure, and characterize the time table for these changes..

Inclusion Criteria:

• patients with two mandibular impaction third molars containing at least one mesially angular impaction with crown exposed to the oral cavity

Exclusion Criteria:

• pregnancy or diseases with abnormal bone metabolism