Effects of core preparation time on the retention of cemented cast post Dr. O. Savabi Isfahani*-Dr. K. Khosravi**- Dr. M. Ebrahimi***- Dr. P. Hosseini***- Dr.MR. Malekipoor**** *- Associate Professor of Prosthodontics Dept.-Faculty of Dentistry – Isfahan University of Medical Sciences. **- Associate Professor of Operative Dentistry Dept.-Faculty of Dentistry – Isfahan University of Medical Sciences. ***- Dentist, Graduated in Faculty of Dentistry - Tehran Islamic Azad University. ****- Assistant Professor of Operative Dentistry Dept.-Faculty of Dentistry – Khorasgan Islamic Azad University. Background and Aim: Core preparation following cast post cementation is necessary. It seems that bur vibration may result in cracks and interfere with cement setting procedure. The aim of this study was to investigate the effects of different core preparation times on the retention of cemented cast post. Materials and Methods: Forty – eight intact canines were selected. After root canal theory posts and cores were fabricated for all samples. The specimens were randomly divided into four groups of twelve teeth. All posts and cores were cemented with zinc phosphate cement according to the manufacturer's instructions. In the first group (control) no preparation was made after cementation but cores of three other groups were prepared at different intervals (15 minutes, 30 minutes and 24 hours) after cementation. The preparations were made for 30 seconds incisally, 60 seconds palatally and 120 seconds axially. Then all specimens were stored in an incubatore for one week. An instron machine was used to determine the tensile force required for each post dislodgement. Data were subjected to one – way ANOVA at 0.05 level of significance. Results: The mean tensile forces for groups 1 to 4 were 650.58, 641.58, 616.45 and 549.87 Newton, respectively. The differences were not statistically significant. Conclusion: Considering the limitations of the present study, it can be concluded that with respect to the applied cement, different intervals of high – speed preparation have no significant negative effects on cast posts retention. Key words: Cast post and core – Retention – Zinc phosphate cement - Preparation | 
