Hybrid Layer, Shear Bond Strength, and Fracture Patterns of Titanium Dioxide–Doped Phosphate Glass–Filled Universal Dental Adhesives

Objectives The aim of the study was to explore the potential effects of incorporating 5 and 10 wt% of TiO₂-doped phosphate glass powder as fillers into the universal adhesive system. Materials and Methods Human permanent premolars and molars were used in the study. Five and 10 wt% of TiO₂-doped phosphate glass powder as fillers were added into the universal adhesive system. Unmodified universal adhesive was used as control. The effects of the added filler in the universal adhesive were examined on hybrid layer formation at the resin composite and dentine interface (mesio-occlusal-distal [MOD] cavities) under scanning electron microscope (SEM), shear bond strength (SBS) of resin composite to dentine using shear bond testing machine, and the patterns of fracture at the resin composite–dentin interface, which were examined under stereomicroscope. The SBS analyses were performed with (8 samples per group, n ¼ 24) and without (8 samples per group, n ¼ 24) 5,000 cycles of thermocycling. Statistical Analysis One-way analysis of variance (ANOVA) was used to analyze the data of the SBS. For bond strength, the effects of adding fillers into the universal adhesive were analyzed. Results The SEM images showed that the hybrid layers were similar in all the groups of unmodified and modified adhesives. An ANOVA test revealed that the SBSs of control and modified adhesives were not significantly different before (p ¼ 0.15) or after (p ¼ 0.39) thermocycling for all the groups. The patterns of fracture revealed various types of fracture in all adhesive groups including composite resin, adhesive, and dentine failure. Composite resin fractures are the most encountered pattern of fracture. Conclusion Adding 5 and 10 wt% of TiO₂ into universal adhesive did not adversely affect the hybrid layer, SBS, or mode of failure of composite resin to dentine. The pattern of fracture at the resin composite and dentine interface showed a favorable bonding with more cohesive than adhesive failure, particularly with the 5 wt% glass-modified adhesive group.