Horizontal pins: a study of tooth reinforcement.

T he widespread use of pins to provide retention for amalgam restorations began with Markley’s’ description of cemented stainless steel pins. In 1966 the selfthreading pin technique was introduced.2 Unlike cemented pins, which rely on cement to hold them in place, self-threading pins are larger than the pinhole and are threaded into it. The cutting action of the threads retains self-threading pins but produces crazing of the dentin.’ Although self-threading pins induce damage to dentin they are five to six times more retentive than cemented pins.4 Numerous in vitro investigations have determined that posterior teeth are severely weakened by a cavity preparation with a width greater than one third the intercuspal distance. 5-9 Markley’ and Courtade”’ reported that weakened tooth structure could be strengthened with a combination of cemented pins and amalgam. Other articles suggested that placing pins into weakened cusps may prevent future cusp fracture, but no research data were offered to substantiate these claims.‘1-‘3 Collard et a1.14 suggested that while cemented pins effectively reinforce weakened tooth structure, self-threading pins placed in weakened cusps could create enough crazing during insertion to further weaken the cusp. The purpose of this study was to compare the load required to fracture a cusp with and without different types of horizontal pins. Crazing patterns produced by horizontal self-threading are described also.