Bond Strength and Interface Between a Self-adhesive Resin and Dentin

Objectives: To evaluate the Knoop microhardness (KHN), morphological characteristics and micro-tensile bond strength (mTBS) of an adhesive interface between a self-adhesive resin and sound or caries-affected dentin, comparing to interfaces formed by an universal adhesive system and a resin-modified glass ionomer cement.
Methods: Occlusal surface of human molars were removed until dentin exposure. Half of the pulp wall was isolated to preserve sound dentin, while the other half was exposed to microbiological cariogenic challenge. Teeth were restored according to the groups: SB- Scotchbond Universal (3M Oral Care) + Filtek Z350 Flow (3M Oral Care); GI- Fuji II LC (GC); and VF- Vertise Flow (Kerr). Transversal KHN test (n = 5), mTBS test (n = 10), scanning electron microscopy (SEM) (n = 3) and confocal laser scanning microscopy (CLSM) (n = 10) were done. Data was analyzed with two-way analysis of variance and Tukey post hoc tests (p<0.05). Morphological characteristics were described after qualitative analysis.
Results: The substrate did not influence the materials hardness (p>0.05). The hybrid layer between SB and sound dentin presented higher KHN results (KHN = 33.7 ± 1.3). There were no significant differences between the hybrid layer formed by the tested materials and caries-affected dentin (p≥0.05). For both SEM and CLSM images, the hybrid layer between caries-affected dentin and the tested materials evidenced failure and gap formation. GI and SB presented no significant differences in mTBS results, that were higher than VF results (p<0.05). The mTBS results for caries-affected dentin was lower than for sound dentin when SB and GI were used (p<0.05).
Conclusions: Hybrid layers formed by the tested materials and caries-affected dentin presented lower KHN and greater number of failures. The mTBS was influenced by the substrate, except for the self-adhesive resin, that presented the lowest results, independently of the substrate.