Characterizing Curing Efficiency of EGCG-Encapsulated Halloysite Nanotube Modified Adhesives for Durable Dentin–Resin Interfaces

Matrix metalloproteinase (MMP)-induced collagen degradation at the resin-dentin interface remains a significant challenge for maintaining the longevity of dental restorations. This study investigated the effects of epigallocatechin-3-gallate (EGCG), a potent MMP inhibitor, on dental adhesive curing efficiency when encapsulated in halloysite nanotubes (HNTs). EGCG-loaded HNTs were incorporated into a commercial dental adhesive (Adper Scotchbond Multi-Purpose) at 7.5% and 15% w/v concentrations. To isolate the effects of each component, the study included three control groups: unmodified adhesive (negative control), adhesive containing only HNTs, and adhesive containing only EGCG (0.16% and 0.32%, equivalent to the EGCG content in EGCG–HNT groups). Degree of conversion (DC), polymerization conversion (PC), and Vickers micro-hardness (VHN) were assessed to evaluate curing efficiency. The addition of 7.5% EGCG-encapsulated HNTs maintained curing properties similar to the control, showing no significant differences in DC (80.97% vs. 81.15%), PC (86.59% vs. 85.81%), and VHN (23.55 vs. 24.12) (p > 0.05). In contrast, direct incorporation of EGCG at 0.32% significantly decreased DC (73.59%), PC (80.63%), and VHN (20.56) values compared to both control and EGCG–HNT groups (p < 0.05). Notably, HNT encapsulation mitigated these negative effects on polymerization, even at higher EGCG concentrations. These findings demonstrate that EGCG encapsulation in HNTs can maintain the curing efficiency of dental adhesives while potentially preserving the MMP-inhibitory benefits of EGCG.