THE BOND STREGTH OF ADHESIVE RESIN CEMENT: TIME DIFFERENTIAL BETWEEN CEMENTATION AND FINISHING OF CAST DOWEL-CORES By Purnima Joan Shahani, D.D.S., M.S.A Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Dentistry at Virginia Commonwealth University.Virginia Commonwealth University, 2003Major Director: Peter C. Moon, M.S., PhDDirector of VCU Dental Biomaterials LaboratoryThis study compared the retention of cast dowel-cores cemented with Panavia® 21 subjected to immediate versus delayed high-speed finishing. Conventionally, finishing is delayed for 24 hours to one week to allow for optimal setting and ultimate strength of the cement. Forty-five recently extracted human maxillary canines were used. Teeth were divided among 3 groups: a control group (n=15, no finishing), an immediate finishing group (n=15, high-speed cutting of the cores performed five minutes after cementation) and a delayed finishing group (n=15, high-speed finishing performed 48 hours post-cementation). Tensile load to failure was applied using an Instron® at a crosshead speed of 0.05 inches/minute. A statistical test of equivalence was performed. The average retention force associated with failure after immediate finishing was not found to be inferior to delayed finishing failure force. In fact, post-hoc comparisons indicated that immediate finishing has statistically significant greater mean retentive force when compared to this force for delayed finishing at p = 0.00001.

Indiana University-Purdue University Indianapolis (IUPUI) / The purpose of this study was to evaluate the fracture resistance of three post and core systems in endodontically treated teeth by loading to failure, and to measure marginal gaps before and after cyclic loading. Sixty extracted canines were assigned to three groups. The groups tested were: 1) Single cast post and core (Group CP). 2) Prefabricated metal post and composite resin core (Group MR). 3) Glass fiber post and composite resin core (Group FR). All teeth were obturated and prepared to receive a post and core with a coping. Thirty teeth (10 from each group) were loaded to failure, and the other 30 teeth were fatigue-loaded. The marginal gaps on the facial and lingual surface of the fatigue-loaded group were measured before and after cyclic loading. There were two hypotheses for this study. The first was that the FR group would have less marginal gap opening on the lingual surface than the other groups. The second was that the CP group would have a higher load at failure than the other groups. Group CP was found to have a significantly smaller pre-loading marginal gap than group FR (p = 0.0265) and group MR (p = 0.0273), while groups FR and MR did not have a significantly different pre-loading marginal gaps (p = 0.86). Group FR had significantly less change in marginal gap than group MR (p = 0.0013). Groups CP and MR did not have significantly different changes in marginal gap (p = 0.09). Groups CP and FR did not have significantly different changes in marginal gap (p = 0.11). The three post types did not have significantly different maximum loads to failure (p= 0.49), moments of inertia at cervical area (p = 0.75), or moments of inertia at fracture site (p=0.12). There was no significant difference between groups CP, FR, and MR in the load-to-failure test. Group CP demonstrated the highest load-to-failure values; however, the highest load-to-failure mean was for group MR. All fractures observed in this study were catastrophic. Group FR demonstrated better stress distribution and caused no early fractures in the fatigue-loading group. All groups demonstrated significant marginal gap changes on the lingual surface after fatigue loading; however, group FR demonstrated <45 μm marginal gap opening. In group FR, the reduced marginal gap opening was attributed to the use of Panavia 21 with the proper surface treatments to bond to the tooth structure, the resin composite, and the metal coping.