Effects of lubrication on the retention of tapered and parallel cast post and cores

The effects of lubrication on the retention of parallel-sided and tapered cast post and cores cemented with zinc phosphate-cement (ZnPO₄) and glass ionomer cements were investigated. Seventy-two maxillary canine teeth of similar size were selected for direct, parallel-sided post and core castings. The canines were sectioned at the cementoenamel junction and mounted in resin blocks. A post space was prepared to 1.5 mm (d) × 10 mm (I) with a handpiece mounted in a surveyor. The teeth were divided into four groups: ZnPO₄ without lubricant, ZnPO₄ with lubricant rinsed with water, ZnPO₄ with lubricant removed by solvent, and ZnPO₄ with solvent alone. The same four groups were made by using glass ionomer cement. Retention was tested with a 4200 series Instron machine by pulling the castings out of the teeth. There were no significant differences in retention among the eight groups of parallel posts at α = 0.05. The testing procedure was repeated by using an 11 mm post with 6 degrees of taper. With tapered posts, a statistically significant reduction in retention was found in the lubricated samples when compared to the nonlubricated samples.