Abstract:

Objective    To analyze the the stress of its periodontal tissues in different conditions by establishing the three-dimensional finite element model of an embedded tooth, and provide  experimental reference to the orthodontic traction of embedded teeth in the clinic．Methods    A patient with a canine completely embedded in the maxillary bone was chosen．The three dimensional finite element model of the canine and its surrounding tissues was established by means of the finite element method (FEM) and spiral CT. On the basis of the dental cusp stable，the canine axis were changed to reach different angles of traction ．Finally，the forces of 50g、100g and 150g were  exerted to the three models with different angles at 0°、45° or 90°.  Equivalent stress clouds of the periodontal membrane and the wink movement clouds of the tooth were observed. Results    At 0°, the wink movement of the embedded tooth was to follow the direction of the force, and the movement was integral. There was a stress concentration area at apical and cusp of the tooth, and the biggest stress emerged at the cusp; At 45° and 90°，the wink movement of the embedded tooth was to follow the traction, but, an angel appeared between the two directions with rotation center at dental cervix. There were stress concentration areas at the apical and the side facing traction forces, and the biggest stress also emerged at the cusp. The stress of periodontal tissues increased following with the growth of the drawing stress at the same traction direction，however, no obvious change of the stress concentration area was found. Conclusions    When the traction direction is in line with the tooth axis，the embedded tooth is to move integrally, and the periodontal stress distribution is homogeneous, which benefits the traction. However, when the traction direction angls with the tooth axis, the tooth is inclined to move to one side and the periodontal stress distribution is not homogeneous, which is adversary to the traction. Less drawing stress is suitable to tract the embedded tooth.

Key words: Embedded canine; Finite element method; Wink movement; Equivalent stress