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

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.

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.

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.

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.