Effects of chemical surface treatments of quartz and glass fiber posts on the retention of a composite resin

Statement of problem. Failure of a fiber post and composite resin core often occurs at the junction between the 2 materials. This failure process requires better characterization. Purpose. The purpose of this study was to evaluate the effect of 2 chemical solvents, hydrogen peroxide and methylene chloride, on the shear bond strength of quartz and glass fiber posts to a composite resin. Material and methods. Twenty-four posts (3 +/- 0.1 mm in length) were prepared for each quartz (LIGHT-POST (LP)) and glass fiber (Cytec blanco (CB)) post. Posts were horizontally embedded in acrylic resin with half of the post diameter exposed. The exposed surfaces were successively ground with 400-, 800-, and 1200-grit silicon carbide papers, to ensure uniform smoothness. The specimens were divided into 3 subgroups (n = 8) representing different surface treatment techniques, including application of silane for 60 seconds (S), etching with hydrogen peroxide for 20 minutes (H), and etching with methylene chloride for 5 seconds (M). Silane-treated specimens served as controls. A clual-polymerized composite resin (Tetric EvoCeram) was placed in a polytetrafluoroethylene mold (30 x 2 mm) positioned upon the post specimens and polymerized for 20 seconds with a light-emitting diode (LED) polymerization unit. The specimens were stored in water at 37 degrees C for 24 hours. Shear bond strength values (MPa) of posts and composite resin cores were measured using a universal testing machine with a crosshead speed of 0.5 mm/min. Data were analyzed by 2-way analysis of variance (ANOVA). Post hoc Tukey intervals for comparison among the 2 post materials and 3 surface treatment techniques were calculated (alpha = .05). The effect of the chemical surface treatments on glass and quartz fiber post surfaces were examined with a scanning electron microscope (SEM). Results. There were significant differences between the shear bond strength for LP and CB (P<.001). For all groups, the application of H showed the highest bond strength values. There was no significant difference between the S and M groups (P>.05). The SEM observations demonstrated that the fiber post surfaces were modified after chemical surface treatment techniques. Conclusions. The surface treatment of quartz and glass fiber posts with hydrogen peroxide significantly enhanced the shear bond strength of the composite resin tested due to its ability to dissolve the epoxy resin matrix used in each post. The lowest bond strength was obtained with M and S groups. Application of methylene chloride to the fiber post surfaces for 5 seconds was not effective in increasing the shear bond strength of the fiber post to composite resin.