The impact of delayed placement and resin matrix composition on adhesion between layers of resin composites
DOI:
https://doi.org/10.2340/biid.v13.46529Keywords:
Composite–composite interface, delayed placement, interlayer adhesion, shear bond strength, oxygen inhibition layerAbstract
Objective: To investigate the effect of delay time in resin composite placement and resin matrix composition on interlayer adhesion between two successive composite layers.
Materials and methods: Three experimental resin composites were prepared by mixing 79 wt.% particulate filler with 21 wt.% dimethacrylate-based resin matrices (urethane dimethacrylate/
triethylene glycol dimethacrylate [UDMA/TEGDMA]; ethoxylated bisphenol-A-dimethacrylate/urethane dimethacrylate/triethylene glycol dimethacrylate [Bis-EMA/UDMA/TEGDMA]; bisphenol A-glycidyl methacrylate/triethylene glycol dimethacrylate [Bis-GMA/TEGDMA]). Fifteen groups of specimens were prepared (n = 6/group), consisting of a cured composite substructure onto which a successive surface layer was applied at different time intervals following light-initiated polymerization (0, 10 minutes, 1, 24, and 72 hours). After 2 days of dry storage at 37°C, interlayer adhesion was evaluated by measuring shear bond strength (SBS) using a universal testing machine. Failure modes were visually assessed. In addition, oxygen inhibition layer (OIL) thickness was measured microscopically, and Vickers hardness and viscosity were determined. Data were analyzed using two-way and one-way analysis of variance followed by Tukey Tukey’s Honestly Significant Difference (HSD) tests (α = 0.05).
Results: SBS values ranged from 10.3 ±2.4 to 24.5 ±3.0 MPa. Both placement delay time and resin matrix composition significantly affected SBS (p < 0.05). SBS decreased significantly when the application of the second successive layer was delayed beyond 1 hour, with the lowest values observed after 72 hours, particularly in Bis-GMA-based composites. The highest SBS was observed in the UDMA/TEGDMA group at 1 hour. Cohesive failure within the substructure was seen in all specimens. The UDMA/TEGDMA group exhibited the lowest OIL thickness (29.35 ± 0.69 µm).
Conclusion: Both incremental application timing and resin matrix composition significantly influenced composite interlayer adhesion. Short delays (10–60 minutes) enhanced interlayer adhesion, whereas prolonged delays (24–72 hours) resulted in a reduction in interlayer adhesion.
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