Effect of etchant variation on wet and dry dentin bonding primed with 4-META/acetone

Objective: To collect data that explains the advantage, if any, of wet bonding versus dry bonding to dentin, and to more clearly understand the mechanism of wet bonding. Methods: Bovine dentin samples were prepared with #600-grit paper and were divided into four groups of six each. The first six specimens were etched with 10% citric acid and 3% ferric chloride for 10 s then rinsed and blot-dried (Gr. 1: 10-3:W). The second six were etched with 10% citric acid and 3% ferric chloride then rinsed and air-dried (Gr. 2: 10-3:D). The third six were etched with 10% citric acid for 10 s, rinsed and blot-dried (Gr. 3: 10-0:W). The fourth group of six samples was etched, rinsed and air-dried (Gr. 4: 10-0:D). All groups were primed with 5% 4-methacryloyloxyethyl trimellitate anhydride (4-META) in acetone for 60 s and an acrylic rod was bonded to the samples using a 4-META/methyl methacrylate (MMA)-tri-n-butyl borane (TBB) resin. The samples were fashioned into dumbbell-shaped specimens and stressed in tension until bond failure, to determine tensile bond strengths. Fractured surfaces were examined by scanning electron microscopy. Results: The mean tensile bond strengths of specimen groups were found to be 18.9 (8.1) MPa (Gr. 1: 10-3:W), 18.1 (1.7) MPa (Gr. 2: 10-3:D), 11.9 (4.4) MPa (Gr. 3: 10-0:W) and 5.4 (2.8) MPa (Gr. 4: 10-0:D). There was no statistically significant difference between Grs. 1 and 2 (p>0.01), or between Grs. 1 and 3 (p>0.05). The TBS of Gr. 4 (10-0:D) was significantly lower than the others (p<0.01). The 5% 4-META in acetone primer was apparently quite effective in improving monomer impregnation into demineralized dentin resulting in increased resin content within the hybridized dentin. Significance: Effective dentin bonding depended upon the etchants employed. 10-0 etching and air-drying caused the demineralized dentin to collapse in which case wet bonding became necessary to obtain good TBS data. The specimens demineralized with 10-3 did not collapse, even when air-dried; consequently both wet and dry bonding proved effective for obtaining high tensile bond strength data.