Effectiveness and durability of repaired acrylic resin joints

Abstract

T he fracture of acrylic resin dentures is an unresolved problem in removable prosthodontics. Attempts to determine the causes of the most frequent types of denture fractures has received little attention in the literature. The midline fracture of the lower denture is the most common.’ The breakage is usually mechanical or accidental. The mechanical causes are related to faulty design and fabrication and the improper use of materials. Fracture by accident is usually the result of expelling the denture from the mouth while coughing, dropping the denture, or excessive biting force. Denture breakage is prevalent among neuropsychiatric patients, especially those who also have neuromuscular disorders such as hemiparalytic muscular dystrophy and Parkinson’s disease.’ Broken dentures are repaired with autocuring acrylic resin or heat-curing acrylic resin.3,4 There is little scientific evidence as to which method is best. The fragments of a broken denture show an increase in internal stress. This increase is due to the breaking of molecular bonds at the points of fracture. Alteration of molecular forces within each fragment results in distortion of the fractured sections, which often causes difficulty in reassembling the broken pieces.‘x4 Regardless of the reason for the breakage or the method of repair, satisfactory repairs must fulfill the following criteria: (1) the repaired structure must have adequate strength; (2) the repair must be completed as rapidly as possible for convenience of the patient; and (3) the repaired denture must retain its dimensional accuraCY. Preparation of the pieces to be joined plays a significant role in controlling the quality of the completed repair. Sharp edges of broken pieces should be rounded with a rag-wheel and pumice to help minimize the stress concentration at the joint. Ware and Docking5 found that the transverse strength of smooth rounded edged repaired joints is superior to that of joints repaired with sharp edges and corners remaining. On the other hand, Tylman and Peyton6 recommended roughening the surface of the fractured material at the joined edges. The diversity of opinion is probably related to the