Dentin Adhesion of Resins Containing Micron and Submicron Polylactide Capsules

Objectives: Micron and submicron polylactide (PLA) capsules were developed as a strategy to control and sustain drug (e.g. bioactives) delivery and ultimate enhance the stability of dentin-resin adhesive interfaces. Encapsulated bioactives are released through the controlled degradation of the capsule shell material. The aim of this study was to determine the effect of micro and nano PLA capsules on the dentin bond strength and adhesive layer thickness.

Methods: Polished dentin surface from human third molars (n=5) were etched with 35% glycolic acid, primed with a 15% enriched grape seed extract/HEPES solution for 1min. Then, two coats of an experimental methacrylate adhesive (BisGMA: 41.25%, TEGDMA: 12%, HEMA 6%, ethanol: 40% and photoinitiators) containing 0 (control), 1 or 1.5 wt% of micro (D₅₀: 1.4μm) and nano (D₅₀: 359nm) PLA spheres with rhodamine dye content was applied, air-dried for solvent evaporation and light cured for 40s. A commercial light-curable resin composite was used to incrementally build a crown. Specimens were immersed in distilled water for 24 h at 37°C before they were serially sectioned into specimens of 0.8±0.05 mm² cross-sectional area. The interface bond strength was assessed in tension (crosshead speed 1mm/min). The incorporation of rhodamine dye into the spheres assisted on capsule distribution visualization at the adhesive layer, as observed in fluorescence light microscopy. The adhesive layer thickness was measured through LASX software (Leica, Buffalo Grove, IL-USA). Data were statistically analyzed using ANOVA and post-hoc Tukey test (α= 0.05).
Results: There were no statistical differences (p=0.38) in the bond strength among experimental groups (average 45±9 MPa) and control (42±10 MPa). Thickness was significantly higher (22-29 μm) for the 1 wt% PLA capsules when compared to control (15 μm), regardless of capsule size (p=0.001).

Conclusions: While PLA capsules increase the adhesive layer thickness, it did not affect the resin-dentin bond strength.