[Effect of three types of cements and the timing of tooth preparation on the retention of cast posts and cores].

PURPOSE

The aim of this laboratory experiment was to study the effects of the timing of tooth preparation after cemented with three kinds of cements on the retention of cast posts and cores.

METHODS

Sixty extracted intact mandibular human premolars with single root were involved in this study. Cast posts and cores were fabricated for each tooth and randomly divided into three groups of 20 specimens each,cemented with three different cements: zinc phosphate cement (ZPC), zinc poly crylate cement (ZPCC)and glass-ionomer cement (GIC). Three groups were then randomly divided into four subgroups of 5 specimens each which were subjected to preparation of their cores at 10 minutes, 30 minutes, 1 hour and 24 hours after cement. After one week of cement, each post core system was subjected to an axially directed removal force using an universal testing machine at a speed of 1 mm /min. Difference among the three groups was determined using SPSS11.5 software package. The data was analyzed by one-way variance analysis and Student-Newman-Keuls (SNK) pairwise multiple comparisons.

RESULTS

Retention of cast posts significantly increased as the timing of tooth preparation increased for both groups, the value of group D (24h) was significantly greater than the other three groups, P<0.05; the posts cemented with ZPC provided significantly greater retention, ZPC>ZPCC, P<0.01; ZPC>GIC, P<0.01; GIC>ZPCC, P<0.05.

CONCLUSIONS

The timing of tooth preparation has a significant effect on the retention of cast posts and cores; tooth preparation at 24 hours after cementation is suggested. And in the same timing of tooth preparation, the posts cemented with ZPC provided significantly greater tensile resistance, ZPC is still a high-performance cement to cement post compared to other cements.