In vitro fracture resistance of glass-fiber and cast metal posts with different lengths.

STATEMENT OF PROBLEM: Dental fractures can occur in endodontically treated teeth restored with posts.

PURPOSE: The purpose of this study was to evaluate the in vitro fracture resistance of roots with glass-fiber and metal posts of different lengths.

MATERIAL AND METHODS: Sixty endodontically treated maxillary canines were embedded in acrylic resin, except for 4 mm of the cervical area, after removing the clinical crowns. The post spaces were opened with a cylindrical bur at low speed attached to a surveyor, resulting in preparations with lengths of 6 mm (group 6 mm), 8 mm (group 8 mm), or 10 mm (group 10 mm). Each group was divided into 2 subgroups according to the post material: cast post and core or glass-fiber post (n=30). The posts were luted with dual-polymerizing resin cement (Panavia F). Cast posts and cores of Co-Cr (Resilient Plus) crowns were made and cemented with zinc phosphate. Specimens were subjected to increasing compressive load (N) until fracture. Data were analyzed with 2-way ANOVA and the Tukey-Kramer test (alpha =.05).

RESULTS: The ANOVA analysis indicated significant differences (P<.05) among the groups, and the Tukey test revealed no significant difference among the metal posts of 6-mm length (26.5 N +/-13.4), 8-mm length (25.2 N +/-13.9), and 10-mm length (17.1 N +/-5.2). Also, in the glass-fiber post group, there was no significant difference when posts of 8-mm length (13.4 N +/-11.0) were compared with the 6-mm (6.9 N +/-4.6) and 10-mm (31.7 N +/-13.1) groups. The 10-mm-long post displayed superior fracture resistance, and the 6-mm-long post showed significantly lower mean values (P<.001).

CONCLUSIONS: Within the limitations of this study, it was concluded that the glass-fiber post represents a viable alternative to the cast metal post, increasing the resistance to fracture of endodontically treated canines.