Date of Award

Spring 1996

Document Type

Thesis

Degree Name

Master of Science in Engineering Science- (M.S.)

Department

Committee for the Interdisciplinary Program in Materials Science and Engineering

First Advisor

Jaya Vaidyanathan

Second Advisor

David S. Kristol

Third Advisor

Richard Clyde Parker

Abstract

Typically, dental composites are used in different configurations and situations. When a cavity forms at the occlusal surface of a posterior tooth, a class I and class II filling is used, depending on the extent and nature of the cavity formed. These fillings have to be designed to resist mechanical abrasion and occlusal stress during chewing, bruxing and other tooth functions. Class IV fillings are also designed to resist biting stress. In these applications composites with high filler loading with filler particles of size >0.6μm are used. These composites are typically known as minifill or midifill composites. When more than one particle size range is used, they are also refereed to as hybrid composites. When the restorations are prepared on interior tooth surfaces not subject to direct application of occlusal or biting stresses (e.g., class III and class V fillings), the composites are designed with less emphasis on the abrasion resistance and mechanical properties of the composites.

Typically, microfill composites with limited filler loading of colloidal silica (of 0.4p.m size) is used for such applications. It has been reported in recent years that these fillings must be designed to flex with tooth function and hence should possess lower modulus of elasticity. The posterior restorations, on the other hand, must be sufficiently stiff to resist masticatory stresses. For these reasons, dynamic mechanical properties of minifill/midifill and microfill composites need elucidation. The dynamic mechanical response is best studied under flexural mode of dynamic deformation. Among the properties considered important for composite resins are viscoelastic properties such as storage modulus (E'), loss modulus (E") damping, glass transition, etc. In this study dynamic mechanical analysis using flexural mode of deformation in the temperature range of -50 to 180°C has been used to characterize the viscoelastic properties of four composites at 37°C with visible light cure.

The results indicate that hybrid composites have higher viscoelastic properties than the microfill system. The resin is characterized by higher storage modulus mode and loss modulus across the entire range of temperature investigated. The results indicate that the filler loading and cross linking effects may be responsible for the variation of viscoelastic properties as a function of different variables (e.g. filler loading, particle size).

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