[Experimental study on the influence of various dental luting cements on the crown elevation during cementation].

Cementing manipulation is an important final step in adapting crown prosthesis to various oral environments. Preventing elevation of full cast crowns during cementation and improving adaptability of the margin after cementation are especially critical. The purpose of this article is twofold: 1) To clarify the relationship between the viscosity of dental cement and the extent of crown elevation, with special attention to viscosity changes occurring in various cement materials during the hardening process. 2) To study the effects on cemented-crown elevation of the space created between the abutment tooth and the crown, which may be partly related to dental cement behavior during cementation. A total of 4 cement materials was used: Elite Cement 100 as a zinc-phosphate cement, Super Bond C & B and Chemiace as MMA-resin cements containing 4-META, and Panavia EX as a phosphoricester cement. Viscosity was measured by means of MR-3 Soliquidmeter with a cone and plate system (Reheology Engineering). A brass material was processed to experimental crowns cemented to abutment teeth of brass. Crown elevation was measured by comparator (Measurescope Model II, Nikon). In addition, effects of the resistance of dental cement during cementation on crown elevation were studied for the sake of a comprehensive understanding of the elevation phenomenon. 1. Changes in dental-cement viscosity during the hardening process 1) Elite Cement 100 demonstrated the highest initial steady flow coefficient of viscosity. It was followed by Super Bond C & B, Chemiace, and Panavia EX, in that order. The t-test revealed significant differences among these cement materials (significance taken to be 1%). 2) As experimental temperature increased, the viscosity of all tested cement materials increased with progressive hardening. 3) With the passing of time, changes in torque, which represents a change pattern in viscosity, indicated that the tested cement materials have different viscosity-change patterns during the initial setting period. 4) From a clinical viewpoint, Super Bond C & B and Elite Cement 100 had very limited working time, whereas Chemiace and Panavia EX had relatively long working time. 2. Elevation after cementation of experimental crowns 1) For Elite Cement 100, mean elevation was 334microns, for Super Bond C & B 281 microns, for Chemiace 164microns, and for Panavia EX 130microns. The t-test revealed significant differences among these cement materials (significance taken to be 1%). 2) In all the cement materials tested, with a reliability of 99%, sequential correlation was observed between crown elevation and steady flow coefficient of viscosity.(ABSTRACT TRUNCATED AT 400 WORDS)