Classification of edentulous mandibular alveolar ridges based on the finite element analysis on the dynamic behavior of the complete dentures.

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The purpose of this study was twofold : development of a new method to make finite element model from digitized 3-dimensional shape of the alveolar ridge and a wax denture automatically as much as possible, and classification of the mandibular alveolar ridge based on the dynamic behavior of the denture calculated by finite element method.We measured three-dimensional shape of a master cast and a wax denture with 3D laser scanner LPX-250 (Roland DG Co.Ltd.). It was posssible to make FE model quasi-automatically with a software we developed in C++ programming language. The FE models was considered to have sufficient reproducibility with the denture mobility under loads comparing with another clinical method to measure denture mobility.With this method, we made FE models from 16 master casts and corresponding wax dentures, and analyzed denture mobilities under unilateral loads. We performed principal component analysis (PCA) with displacement of three representative nodes. The PCA showed that about 84 % of the three-dimensional displacement of dentures can be explained with three principal components-antero-posterior translation, rotation in horizontal plane, and amount of sinking at the molar region.The cluster analysis with principal component scores showed that there was at least 6 independent clusters. However, since most of the clusters consisted of a couple of cases, more cases were considered to be necessary to develop new classification system of edentulous mandibular ridge.