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) x 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 alpha = 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.