Durability of Resins Bonded to Water Vs. Ethanol-Saturated Acid-Etched Dentin

Objective: The purpose of this study was to test the durability of acid-etched dentin bonded with experimental comonomer blends R1-5 that varied from very hydrophobic (R1) to very hydrophilic (R5).  Methods:  Using extracted, human third molars, the enamel and superficial dentin was removed with an Isomet saw.  After acid-etching with 37% phosphoric acid for 15s, the rinsed surfaces were wet with water or 100% ethanol.  Bonding was done with both neat resins and solvated primers.  Primers were made of 50 wt% ethanol/50% resin.  These were applied to water or ethanol-saturated dentin in two layers.  After evaporation of the solvent, a layer of the same neat resin was applied and light-cured, and covered with light-cured composite.  There were 20 teeth per resin, 10 for water-saturated dentin and 10 for ethanol-saturated.  Five of these 10 teeth were bonded with neat resins and 5 bonded with 50% ethanol/50% resin.  After 24h of water storage, the teeth were divided into 0.8 x 0.8 mm sticks. The sticks from all five teeth per subgroup were pooled and incubated for 1 day, 3, 6, 12 months.  At each experimental time, 20 sticks were removed for measurement of µTBS.  Results:  The neat resins bonded to ethanol-saturated dentin gave 30% higher bond strengths than to water-saturated dentin.  Neat and ethanol-solvated resins bonded to ethanol-saturated dentin did not fall over 1 yr.  Resin bonds made to water-saturated dentin all gradually fell over 1 yr.  TEM observations of water vs. ethanol-saturated dentin revealed that ethanol decreased the diameter of collagen fibrils (p<0.05) and increased the width of interfibrillar spaces, thereby allowing for more resin uptake.  Conclusions:  Durability of all but resin 1 increased when bonded to ethanol-wet dentin compared to water.  Supported by R01 DE014911 from the NIDCR to DHP (P.I.).