Dental Adhesives - an Evaluation of Test Methodologies

Phillips, Ralph

Abstract

Development of a truly adhesive restorative material has long been a high priority goal in biomaterials research. Although progress has been made in the area of adhesion to tooth structure, the present systems suffer a number of shortcomings, i.e. low strength and bond instability. Due to the importance of the area, research continues unabated to develop biocompatible treatments to render the tooth more receptive to adhesion and to formulate improved adhesive systems. A problem that has persisted since the beginning of this research is the precise evaluation of the adhesive bond. Measured values for bond strength are extremely sensitive to test methodology and almost every laboratory has designed its own test apparatus and procedure. Thus the test methodologies vary widely from one laboratory to another, as do the data reported for the same materials. Variations exist with respect to storage media, thermal stress, substrate (human or bovine teeth) and the mechanical test, i.e. stress mode, (shear or tensile), instrument design, alignment and loading rate. The need for a standardized test for adhesion to the tooth to permit comparison of data from one facility to that from another has long been recognized. However, to date there has not been a great deal of progress in this area. Requisite to the development of a standard test is the determination of the effect of the numerous variables on adhesive test values. As a first step toward achievement of this goal, this research proposes to evaluate, in a systematic manner, the influence of a series of variable associated with the mechanical tests and the test substrate. Representatives of current adhesive systems will be tested both in tension and shear. Two different shear apparatus and two tensile apparatus will be compared. The members of each pair differ with respect to the potential for malalignment and hence the introduction of other stress components. The effect of loading rate will be determine in both stress modes. Results obtained on human enamel and dentin will be compared to those obtained on bovine teeth. The effect of dentin depth as related to dentin-enamel junction will be evaluated.