DEFORMATION OF RESTORATION AND FRACTURE OF LUTING CEMENT FILM

Objectives: Functional occlusal loading can generate complicated stres ses in the luting cement film between a restoration and its abutment. Such stresses may lead to cement fractures, which can promote cement d issolution and induce clinical problems. The purpose of this study is to determine the function of the cement film under loading, and to cla rify the relationship between the deformation of the restoration and t he cement fractures. Methods: Eccentric loads were applied onto model extension bridges which were cemented on brass dies with zinc phosphat e cement. Strain measurements were recorded using of a strain gauge me thod, ultimate strength by tensile tests, leakage by dye penetration t ests and cement fractures by ultrasonic microscopic analyses. Addition ally, the bridges which were just seated on their dies without cementa tion were loaded, and strain measurements were recorded. Results: The eases for linear strain increment with loading showed high tensile str ength and minimal dye penetration. The cases with non-linear strain be havior showed low tensile strength and considerable dye penetration. H owever, no fracture was observed in the occlusal cement film in both c ases. The cement fracture first occurred at the opposite marginal regi on to the loading side. Conclusions: One of the significant functions of the cement film is diminishing the deformation of restorations duri ng loading. The deformation of the restoration affects initiation and propagation of the cement fracture considerably. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.