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 microns-80.0 microns) on the impact strength of acrylic denture base materials. The method was used to compare the properties of 12 denture base materials, some of which are described as "high-impact strength" products. The defects were introduced by drawing the specimens over abrasive papers of varying grit sizes or by notching with a craft knife. Flexural toughness tests were also carried out in order to evaluate the materials under both rapid (impact) and slow (flexural) rate test conditions. The impact resistance of acrylic resins was significantly reduced by the presence of very small surface defects (e.g., < 16 microns), and this was particularly noticeable for so-called high-impact resins. The latter have values of impact strength only slightly higher than standard acrylic products when defects are present. Testing "notched" specimens with small surface defects was a simple method of obtaining reproducible results. This test was sensitive enough to differentiate among several types of currently available denture base resins.