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Next to the presence of (chemical) coupling between filler and resin, filler particle size is important for the mechanical coherence of dental resin composites which are used for posterior restorations. In the range of the current composites a smaller particle size is desirable. The better mechanical coherence for composites with smaller particles found in an in vitro erosive wear test is probably related to the size of food fibres, which are part of the erosive medium. It appears that there is a critical value of the filler particle size (1.3-1.5 microns), under which the food fibres are not able to penetrate in the interparticle space, so the erosive capability of the erosive medium will be reduced.

The denture base which is made from the acrylic resin often occurs the fracture during function, and it is known that this fracture is mainly occured by the fatigue fracture, which is happened by the crack growth from the location of high stress. Until now, the author discussed on the fatigue properties about the specimens with semi-circular notch as the model of the remaining natural teeth, but these results are not easily applied to the design of denture base because the shape of denture base, considering its function and esthetics, is not changed. So, for the improvement of the strength of denture base, the denture base might be used the reinforcement. And, used as a trial the organic fiber as reinforcement, and their effects were investigated from the sides of the bending moment at fracture and the strain distribution occurs the fracture at the posterios palatal area, and its strength is improved 190%. And the fracture of the complete denture happens in general at the location between two central incisors, therefore this problem should be considered as the notched effect. So, reinforcing the lingual part of maxillary anterior teeth using the organic fiber, its strength is improved 53% comparing with the general complete denture. Therefore, the effects of reinforcement were enough appeared, and the improvement of the strength of denture base is very expected in dental use.