Chlorhexidine improves bond strength of Scotchbond 1XT: a 2-year study

Objectives: Dentinal MMPs have been claimed to play an important role in the auto-degradation of collagen fibrils within incompletely resin-infiltrated hybrid layers. This study investigated the effect of 0.2 and 2% chlorhexidine (CHX), as a therapeutic primer, on the long-term bond strength of an etch-and-rinse adhesive to human dentin.

Methods: Scotchbond 1XT (SB, 3M ESPE) was selected for the study. Exposed dentin of 30 extracted teeth was etched with 35% phosphoric acid (15 s) and rinsed with water. Teeth were randomly assigned to 3 groups (N=10): (1) 0.2% CHX + SB; (2) 2% CHX + SB; (3) SB-control. Irrespective of its concentration, CHX was applied onto the acid-etched dentin for 30 s and then blot-dried. Adhesive was applied according to the manufacturer's instructions. Filtek Z-250 (3M ESPE) was used to create resin composite build-ups. Specimens were prepared for microtensile bond strength test and either immediately pulled out or stored in artificial saliva for 2 years and then tested. Data were evaluated by two-way ANOVA and Tukey tests (p<.05). Additional specimens were prepared for interfacial nanoleakage analysis.

Results: Bond strength (in MPa) are expressed as Mean SD. Different superscript letters indicate statistical differences (p<0.05). CHX did not affect the immediate bond strength of SB to dentin (SB-control= 40.8±8.7^a; SB+0.2%CHX=39.2±9.3^a; SB+2%CHX= 41.2±9.6^a). However, after 2 years of in vitro storage, the bond strengths of SB-control group decreased 70% (SB-control=13.4±4.9^b), while in CHX-treated groups the decrease of bond strength was only about 25% (SB+0.2%CHX=32.6±8.3^a,c; SB+2%CHX=28.5±7.2^c). Nanoleakage was significantly reduced in CHX-treated specimens.

Conclusions: CHX significantly lowered the loss of bond strength seen in acid-etched resin-bonded dentin artificially aged for 2 years. The findings suggest that CHX inhibits the collagenolytic activity of dentin. The use of CHX as inhibitor of the hybrid layer auto-degradation processes should be validated by in vivo long term studies.