Effect Of Types Of Cements And The Timing Of Tooth Preparation On The Retention Of Cast Posts And Cores

Objective: The aim of this laboratory experiment was to study the effects of the timing of tooth preparation after cemented with different kinds of cements on the retention of cast posts and cores.Methods: 60 extracted intact mandibular human premolars with single root were involved in this study and randomly divided into 3 groups of 20 specimens each. Remo ved the crowns of them perpendicular the long axis of the roots with a separating disc 1 mm coronal to the cemento-enamel junction(CEJ). After endodontic treatment, all roots were embedded in the center of plastic cylinders and paralleled with the cylinder and stored in water of 37 ℃. A cast post and core was prepared for each root and cemented into the root canal with three different cements:zinc phosphate cement (ZPC);zinc poly crylate cement (ZPCC)and glass-ionomer cement(Ketac Cem,GIC). Within each group every 5 teeth's tooth preparation were respectively performed 10min,30min,1h and 24h after cement mixing and got four subgroups -A, B ,C,D. After one week of cement mixing the axial tensile strength values of each post were measured with the CMT5105 universal testing machine at a speed of 1 mm /min. Differences among the three groups and differences among subgroups A ,B,C,D were determined using SPSS11.5. Data were analyzed by one-way varience analysis and Student-Newman -Keuls (SNK) pairwise multiple comparisons.