Aim: This study evaluated the influence of acid-etching time on collagen exposure in adhesive interfaces established on primary and permanent dentin. Materials and methods: Flat dentin surfaces were produced on sound primary molars and premolars (n = 8). The surfaces were divided into mesial and distal halves, and each half was etched with phosphoric acid for 5 or 15 seconds. The teeth were randomly allocated into two groups according to the adhesive system applied: Prime & Bond NT or Prime & Bond 2.1. After the adhesive application, the specimens were processed for Goldner's trichrome staining. The thickness of the uninfiltrated collagen zone (UCZ) in the hybrid layer was measured under optical microscopy. Data were analyzed by analysis of variance and Tukey tests (α = 0.05). Results: The thickness of UCZ was adhesive dependent. Within the same substrate, the specimens treated with Prime & Bond 2.1 presented thicker UCZ when etched for 15 seconds. Collagen exposure was significantly higher for the primary teeth etched for 5 seconds and treated with Prime & Bond 2.1. Conclusion: The thickness of UCZ in hybrid layers is directly affected by acid-etching time and by the adhesive system applied. Primary dentin seems to be more susceptible to collagen exposure than is permanent dentin. Clinical significance: Both acid-etching time and adhesive system can influence the amount of exposed collagen interferin on resin-dentin bond quality, especially on primary dentin.
- Hybrid layer
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