Abstract
The wedge-shaped defect (WSD) is frequently observed in the cervical region of tooth, especially on the buccal surface. It has been long demonstrated that WSD might be attributed to the incorrect or excessive toothbrushing. Recently, however, a new concept of WSD induced by occlusal forces has been proposed. The present study examined the stress bearing in the premolar cervical region for applied occlusal forces using a strain gauge in vitro and also observed the existence of WSD and facets in 304 extracted maxillary premolars in order to estimate the possibility of such a cause of WSD. The WSD was found in 198 teeth out of 304 (65.1%), in which 185 teeth (93.4%) had the defect in their buccal cervical region. Regardless of the presence of WSD, one or multiple occlusal facets were detected in most of the teeth. Only 15 teeth exhibited no facet. There was also no WSD in them. Among the teeth having WSD, the frequency of those which were accompanied by the facets at the buccal or lingual triangular ridge and/or the tip of lingual cusp was predominant, indicating a possibility that they might have occurred by a common action of occlusal force. From the strain measurement, on the other hand, it was found that the buccal cervical region was subjected to a considerable tensile or compressive stress when a load was separately applied on the areas showing facets mentioned above. These findings suggest that the occlusal force may cause complicated stresses to be a potential factor inducing WSD in the buccal cervical region.
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