抄録
Purpose : This study investigated the effect of the cross-sectional dimensions on the deflection of the lingual bars in Ti-6 Al-7 Nb and Co-Cr removable partial denture frameworks and of the stress distributions in the frameworks and the underlying oral mucosa.
Materials and Methods : Three-dimensional finite element models (FEM) of nine lingual bars with different dimensions (thickness : 1.5, 2.0, or 2.5 mm ; height : 4, 5, or 6 mm) including the underlying mucosa were produced for a Kennedy Class II case. Each framework included occlusal rests on the first premolars of both arch sides. The bottom surface of the mucosa and the rest on the edentulous side were fixed in a vertical direction. The rest on the tooth-supported side was fixed in all directions. Elastic moduli of 200 and 123 GPa were input into the program as values for the Co-Cr and Ti-6 Al-7 Nb alloys, respectively. A 30° buccally oblique biting force of 20 N was directed toward each of the three missing tooth locations.
Results : The Ti-6 Al-7 Nb frameworks resulted approximately 1.2 times the maximum stress in the mucosa compared to the Co-Cr frameworks with the same cross-sectional dimensions. The framework displacement and stress in the mucosa decreased as the thickness or the height of the bars increased. The maximum principal compressive stress within the mucosa was estimated to be 1.84 MPa at the posterior ridge crest when the smallest cross-sectional Ti-6 Al-7 Nb bar was used.
Conclusion : The rigidity of the Ti-6 Al-7 Nb lingual bars was comparable to that of the Co-Cr lingual bars when the cross-sectional dimensions of the former were 0.5 mm thicker or 2.0 mm higher than the latter.
