IMPACT STRENGTH OF ACRYLIC RESIN DENTURE BASE MATERIALS WITH SURFACE-DEFECTS

The first part of this study involved the development of a method for evaluating the effect of small surface defects (3.0 mu m - 80.0 mu m) on the impact strength of acrylic denture base materials. The method w as used to compare the properties of 12 denture base materials, some o f which are described as ''high-impact strength'' products. The defect s were introduced by drawing the specimens over abrasive papers of var ying grit sizes or by notching with a craft knife. Flexural toughness tests were also carried out in order to evaluate the materials under b oth rapid (impact) and slow (flexural) rate test conditions. The impac t resistance of acrylic resins was significantly reduced by the presen ce of very small surface defects (e.g., <16 mu m), and this was partic ularly noticeable for so-called high-impact resins. The latter have va lues of impact strength only slightly higher than standard acrylic pro ducts when defects are present. Testing ''notched'' specimens with sma ll surface defects was a simple method of obtaining reproducible resul ts. This test was sensitive enough to differentiate among several type s of currently available denture base resins.