Objective: The aim of this study was to determine the influence of occlusal rest position of RPDs on displacement of the abutment tooth and stress distribution in the periodontal ligament. Methods: Three-dimensional finite element models of the mandibular first and second premolars were created. A layer of the periodontal ligament and a medial or distal occlusal rest were produced for the second premolar (abutment). Material properties were determined based on in vivo tooth mobility data reported by M¨¹llemann. Contact phenomena both at the proximal teeth surfaces and at the contact between the rest and the abutment were simulated. The zero displacement was prescribed on the outer surface of the periodontal ligament and the first premolar crown. In each simulation, the rest was displaced 0.05 mm vertically to the apical direction, with or without restriction of horizontal movements. Movements of the abutment and the stress distributions in each model were calculated. Results: The maximum posterior displacement of the abutment crown of 42µm and the compressive stress of 0.35 MPa in the periodontal ligament were shown when the distal rest was used without the restriction of the horizontal movement. The restriction of the horizontal movement of the rests was effective to reduce the stress created in the ligament. However, the stresses were within the physiological limitations of the tissues. Conclusion: The single vertical load exerted from either the mesial or the distal occlusal rest on the abutment was unlikely to cause a mechanical damage to their supporting tissues.

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