[Reinforcement for overdentures on abutment teeth]

This study investigated the effect of the position of reinforcement wires, differences in artificial teeth, and framework designs on the breaking strength of overdentures.

The basal surfaces of composite resin teeth and acrylic resin teeth were removed using a carbide bur. A reinforcement wire or a wrought palatal bar was embedded near the occlusal surface or basal surface. Four types of framework structures were designed : conventional skeleton (skeleton), housing with skeleton (housing), housing plus short metal backing (metal backing), and housing plus long metal backing (double structure). After the wires, bars, and frameworks were sand-blasted with 50 microm Al(2)O(3) powder, they were primed with a metal primer and embedded in a heat-polymerized denture base resin. The breaking strengths (N) and maximum stiffness (N/mm) of two-week aged (37 degrees C) specimens were measured using a bending test (n=8). All data obtained at a crosshead speed of 2.0 mm/min were analyzed by ANOVA/Tukey's test (alpha=0.01).

There were no statistical differences between the two kinds of artificial teeth (p>0.01). The wrought palatal bar had significantly higher strength than the reinforcement wire (p<0.01). Greater strengths were found for specimens with frameworks than those without frameworks (p<0.01). The breaking strength of the wrought palatal bar embedded near the occlusal surface was higher than that on the basal surface (p>0.01). The breaking strength and maximum stiffness of the double structure framework were significantly greater (p<0.01) than those of the conventional frameworks.

The breaking strengths of overdentures were influenced by the size and position of the reinforcement wires. Double structure frameworks are recommended for overdentures to promote a long-term prognosis without denture breakage.