Mechanical stability of resin-dentin bond components.

Objectives: To evaluate the effects of long-term storage on the mechanical properties of the components of resin-dentin bonds, that is, resin composite, adhesive system, demineralized and mineralized dentin.

Methods: Specimens of resin composite (Z250) and adhesive systems (Single Bond-SB; One-Step-OS and Clearfil Liner Bond 2V-CL) were cast in molds. Dentin specimens were prepared from dentin discs obtained from the crowns of extracted human molars. Specimens of demineralized dentin were obtained by immersion of dentin discs for 6 days in 0.5 mol/l EDTA (pH 7.0). Both dentin and resin-based substrates were shaped to hourglass or I-beam specimens that were used to determine the true stress (TS) or apparent modulus of elasticity (E), respectively. Control specimens were subjected to tensile testing at 0.6 mm/min after 24 h of immersion in distilled water. Experimental specimens were stored at 37 degrees C in either distilled water or mineral oil and tested after 12 months. The data of each group were individually analyzed by ANOVA and Tukey's test.

Results: Both TS and E of the resin-based materials decreased significantly after 12 months of storage in water (p < 0.05) except the TS of SB (p > 0.05). No changes were observed for specimens of mineralized dentin, regardless of storage condition (p > 0.05). Storage of demineralized dentin in water did not cause any significant effect in either TS or E (p > 0.05), however, significant reductions of TS and E of demineralized dentin occurred after storage in oil for 1 year (p < 0.05).

Significance: Storage time and medium may be deleterious to the mechanical properties of the resin-dentin bond components, which ultimately could compromise the durability of resin-dentin bonds.