Shear Bond Strength to Enamel and Flexural Strength of Different Fiber-reinforced Composites

Purpose: To assess the shear bond strength to unground human enamel (ESBS) and flexural strength (FS) of different reinforcing fibers used in combination with a flowable composite resin. Materials and Methods: For ESBS testing, 90 human molars were selected and randomly divided into 9 groups (n = 10) according to the reinforcing fiber to be tested: 1. RTD Quartz Splint additionally impregnated at chair-side with Quartz Splint Resin (RTD); 2. RTD Quartz Splint without additional impregnation; 3. Ribbond- THM (Ribbond) impregnated with OptiBond FL Adhesive; 4: Ribbond Triaxial (Ribbond) impregnated with OptiBond FL Adhesive; 5. Connect (Kerr) impregnated with OptiBond FL Adhesive; 6. Construct (Kerr) impregnated with OptiBond FL Adhesive; 7. everStick PERIO (Stick Tech); 8. everStick C&B (Stick Tech); 9. nonreinforced composite Premise flowable (Kerr). Cylinders of flowable composite reinforced with the fibers were bonded to the intact buccal surface of the teeth. After 24 h of storage, shear loading was performed until failure occurred. FS was assessed performing three- point bending test according to ISO Standard 4049/2000. ESBS and FS data were analyzed using one- way ANOVA, followed by Tukey's HSD test for post- hoc comparisons (p < 0.05). Results: For each group, the ESBS and FS, respectively, in MPa were: 1. 17.07 +/- 4.52 and 472.69 +/- 30.49; 2. 14.98 +/- 3.92 and 441.77 +/- 61.43; 3. 18.59 +/- 5.67 and 186.89 +/- 43.89; 4. 16.74 +/- 6.27 and 314.41 +/- 148.52; 5. 14.38 +/- 4.14 and 223.80 +/- 77.35; 6. 16.00 +/- 5.55 and 287.62 +/- 85.91; 7. 16.42 +/- 3.67 and 285.35 +/- 39.68; 8. 23.24 +/- 5.81 and 370.46 +/- 29.26; 9. 12.58 +/- 4.76 and 87.75 +/- 22.87. For most fibers, no significant difference in ESBS was found compared to the control group, except for everStick C&B, which yielded higher ESBS. Nonreinforced composite exhibited the lowest FS, while all fibers positively affected the FS. Conclusions: Fiber reinforcement of flowable composite does not affect its ESBS. The flexural strength of FRCs is significantly influenced by fiber composition and pattern.