This study aims to evaluate the effect of experimental primers containing carbodiimide (EDC) on the total MMP activity, collagen degradation and stability of adhesive interfaces produced on sound and caries-affected dentin. Two hundred forty dentin beams (1x1x6 mm) will be obtained from 80 sound third molars. Half of them (n=120) will be subjected to a microbiological protocol for artificial caries induction. Sound and caries-affected specimens (n=10 per group) will be acid etched for 15s followed by 60s of treatment with: water (control), 0.5M EDC solution, experimental primer (50% HEMA in water), experimental primer containing 0.5M EDC, Scotchbond MP primer (SBMP) or SBMP containing 0.5M EDC. The total MMP activity will be determined immediately after the treatments using a colorimetric assay (SensoLyte). The ten remaining beams in each group will be used to analyze the dry mass (DM) loss and hydroxyproline (HYP) releasing. The beams will be completely demineralized in 10% phosphoric acid for 18h. DM loss and HYP will be evaluated immediately before the treatments described above and after 7 days in artificial saliva. Flat dentin surfaces will be produced on additional eighty third molars. Half of them will be submitted to the artificial caries induction protocol. Sound and caries-affected teeth will be divided into 5 groups (n=8) according to the surface treatment: SBMP, 0.5M EDC solution, experimental primer, primer experimental with 0.5M EDC or SBMP with 0.5M EDC. After the treatments the Scotchbond MP bond will be applied for all groups and the crown will be reconstructed in composite resin. The teeth will be sectioned in specimens (0.81 mm2 cross-section) and stored in artificial saliva for 24h or 6 months prior to microtensile mechanical testing. A slab from each tooth will be selected for nanoleakage analysis using SEM. Statistical tests will be defined based on the distribution and homoscedasticity of each dataset (response variables). All tests will be considered at the pre-established level of significance of 5 %.
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