Influence Research Of The Different Expansion Coefficient Plaster Cast Material On Resin Denture Accuracy And Physical Properties

Objective To evaluate the influence of the different expansion coefficient plaster cast material on the denture accuracy and physics properties.Methods The study is to compare the difference of denture base resin cured by three kinds of plaster cast materials of different expansion coefficient on the denture accuracy:High expansion coefficient,medium expansion coefficient, low expansion coefficient.The dimensional accuracy between the posterior border of upper complete denture and standardized cast at five different positions are measured by scanning electron microscopy. Specimens sized 50mm×6.0mm×5.0mm are made for impact strength test. Specimens with 64mm×10mm×3.5mm are made for measuring flexural strength and flexural modulus. Specimens with 30mm×10mm×6.0mm are made for measuring Hardness and Surface roughness.Results The posterior border gaps between the upper complete denture and standardized cast range from 280μm-344μm ,198μm-220μm and 50μm-122μm, respectively cured by three methods. The gaps at B, D are lower than those of A, C, E. Impact strength , flexural strength and Surface Hardness of specimens cured by High expansion coefficient plaster cast material are lower than those of Medium expansion coefficients' and low expansion coefficients' (P<0.01). Flexural Modulus of specimens cured by low expansion coefficient plaster cast material are lower than those of High expansion coefficients' (P<0.01). The surface roughness of specimens invested for low expansion coefficient are lower than those of High expansion coefficients' and Medium expansion coefficient plaster cast material (P<0.01).Conclusions(1).The accuracy of resin denture made by low expansion coefficient plaster cast material is highest.(2). Physical properties of specimens made by low expansion coefficient are higher than those of Medium expansion coefficients' and High expansion coefficients'.(3). The surface roughness of specimens invested for low expansion coefficient are lower than those of High expansion coefficients' and Medium expansion coefficient plaster cast material.