Effects of chlorexidine/solvent solutions on bond strength to dentin

Objectives:  Studies have demonstrated that resin/dentin bonds degrade over time.  Breakdown of hydrophilic adhesives and denuded collagen by endogenous proteases (MMPs) are regarded as the main factors involved on degradation.  Chlorhexidine (CHX) has long been known as an MMP-nonspecific inhibitor.  Wet ethanol bonding has been shown to permit the use of hydrophobic resins for bonding.  The adjunctive use of ethanol-wet bonding with chlorhexidine could improve infiltration of hydrophobic resins and add benefits from CHX to preserve collagen.  We tested the hypothesis that water and ethanol-wet bonding are not affected by the adjunctive use of chlorhexidine.  Methods:  Four solutions were prepared (w/w):  water(Water); 1% chlorhexidine in water(CHX/Water); ethanol(Ethanol); and 1% chlorhexidine in ethanol(CHX/Ethanol).  Flat dentin surfaces were etched with 35% phosphoric acid (15s), rinsed with water (30s), and dried with absorbent paper.  The surface was re-wetted with the solutions and excess removed with tissue-paper.  The adhesives (ALL BOND 3, Bisco or EXCITE, Ivoclar-Vivadent) were applied, left undisturbed (30s), and light-cured for 20s (500 mW/cm²).  Four-mm resin build-ups were constructed incrementally.  After storage in water at 37°C for 24h, teeth were cut into beams for microtensile test (0.5mm/min).  Data were analyzed by two-way ANOVA and Tukey (α=0.05).  Results:  There was interaction between the factors in comparison.  Bond strength was not affected by the treatments for AB3, but treatments resulted in significant differences for EX adhesive.

Rewetting Solutions	Microtensile bond strengths(MPa)
	All Bond 3	Excite
Water	49.4±10.8(19)a	36.0±14.1(19)b
1% CHX in water	51.3±17.3(16)a	31.4±9.1(21)b
Ethanol	58.3±10.4(20)a	20.8±8.7(19)c
1% CHX in ethanol	53.1±15.8(21)a	46.3±7.0(18)a

Values are mean ± S.D. (number of specimens).  Different superscript values indicate significant differences (p<0.05).  CHX = chlorhexidine.

Conclusions:  All Bond 3 was not effected by any of the rewetting solutions, while bonds made by Excite were lower when ethanol was used but higher using 1% CHX in ethanol..