The purpose of this study is to analyze the mechanical stress and displacement during the simulated bilateral clenching task on the 3D finite element (FE) model of the dentated skull with unilateral molar loss.
For this study, the computed tomography (G.E.8800 Quick, USA) was used to scan the total length of human skull in the frontal plane at 2.0mm intervals. The fully assembled finite element model consists of the articular disc, maxilla, mandible, teeth, periodontal ligament and cranium. The FE model was used to simulate the bilateral clenching in intercuspal position. The loading condition was the force of the masseter muscle exerted on the mandible as reported by Korioth et al, degrees if freedom of the zygomatic region where the masseter muscle is attached were fixed as restraints. In order to reflect the actual action of the muscles force, the displacement of the region was attached where the muscle in connected to the temporal bone and restraint conditions were given values identical to values at the attachment region of the masticatory muscle but with the opposite direction of the reaction from when the muscle force is acted on the mandible.
Although the mandible generally has higher displacement and von Mises stress than the maxilla, its mandibular corpus on the molar-loss side has a higher stress and displacement than the molar-presence side. Because the displacement and von Mises Stress was the highest on the lateral surface of mandibular corpus with molar loss, the stress level of the condyle on the molar-loss side is greater than of the molar-presence side, which in turn caused the symphysis of the mandible to bend.
In conclusion, the unilateral posterior bite collapse with molar loss under para-functional activities such as bruxism and clenching can affect the stress concentration on the condyle and mandibular corpus. It is therefore necessary force while designing the occlusal scheme of restoration on alveolar bone with the posterior collapse.
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