FATIGUE FAILURE IN DENTURE BASE POLYMERS

Although well-fitting dentures of adequate thickness seldom exhibit fatigue failure in service, a very small percentage of the millions of denture wearers have well-fiting dentures. Fatigue failure is a very real problem in these dentures, in the well-fitting single upper denture occluding against natural lower teeth, and in all dentures with soft liners. We can make dentures more resistant to fatigue failure by using a few precautions. First, the heat-curing resins are much more resistant to this failure; therefore, use of a heat-curing acrylic resin is indicated. Second, fine-polymer beads increase fatigue strength many times, so a fine-grained polymer should be used. Finally, stress concentrators should be avoided. Most important would be the elimination of sharp surface contours, such as deep notches for low frenum attachments, and prominent rugae patterns. A prominent frenum attachment has little function and is not beneficial to the completely edentulous individual. It is a simple procedure to eliminate the frenum at the time of extraction of the anterior teeth. Any particle acts as a stress concentrator; therefore, acrylic dentures should be fabricated in a relatively dust-free atmosphere such as that used for porcelain work. Fibers and the surface defects that they produce act as stress concentrators, and this should be recognized if a material with fibers is used. Rayon or nylon fibers are used commercially.20 The use of acrylic fibers should correct this weakness. © 1969.