Effect of different vertical positions of palatal expansion-screw: Finite element analysis

Objectives: The aim of the study was to determine the effect of different vertical positions of the expansion screw in a palatal expander on stress in the periodontium of the maxillary first molar, using the finite element method. Methods: The 3-D finite element model comprised the metal frame of a palatal expander, maxillary first molar, periodontal ligament (PDL), and bone. The model consisted of 6530 nodes and 5234 elements. A palatal expansion force (300g) was applied to the metal frame of different vertical heights. The position of expansion screw was raised 7 mm from the initial location toward the palate. Results: The stress pattern in the periodontal ligament was analyzed to determine the degree of buccal tipping of the molar in response to different vertical heights of the screw. The results showed that the lower position (away from palate) of the frame caused higher concentration of compressive stress around the cervical region of buccal side of the PDL. As its position moved higher toward the palate, the stress in the PDL became more evenly distributed, which indicates that more buccal tipping of the tooth occurred with lower position. Conclusions: This study demonstrated that the stress distribution in the PDL of the maxillary first molar was sensitive to the vertical position of the screw, and that more bodily movement occurred with higher position of the expansion screw in the palate.