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Abstract
The purpose of this study was to evaluate the effect of chlorhexidine (CHX) on microtensile bond strength (µTBS) of dentin bonding systems.
Dentin collagenolytic and gelatinolytic activities can be suppressed by protease inhibitors, indicating that MMPs (Matrix metalloproteinases) inhibition could be beneficial in the preservation of hybrid layers. Chlorhexidine (CHX) is known as an inhibitor of MMPs activity in vitro.
The experiment was proceeded as follows:
At first, flat occlusal surfaces were prepared on mid-coronal dentin of extracted third molars. GI (Glass Ionomer) group was treated with dentin conditioner, and then, applied with 2% CHX. Both SM (Scotchbond Multipurpose) and SB (Single Bond) group were applied with CHX after acid-etched with 37% phosphoric acid. TS (Clearfil Tri-S) group was applied with CHX, and then, with adhesives. Hybrid composite Z-250 and resin-modified glass ionomer Fuji-II LC was built up on experimental dentin surfaces. Half of them were subjected to 10,000 thermocycle, while the others were tested immediately. With the resulting data, statistically two-way ANOVA was performed to assess the µTBS before and after thermocycling and the effect of CHX. All statistical tests were carried out at the 95% level of confidence. The failure mode of the testing samples was observed under a scanning electron microscopy (SEM).
Within limited results, the results of this study were as follows;
In all experimental groups applied with 2% chlorhexidine, the microtensile bond strength increased, and thermocycling decreased the microtensile bond strength (P > 0.05).
Compared to the thermocycling groups without chlorhexidine, those with both thermocycling and chlorhexidine showed higher microtensile bond strength, and there was significant difference especially in GI and TS groups.
SEM analysis of failure mode distribution revealed the adhesive failure at hybrid layer in most of the specimen, and the shift of the failure site from bottom to top of the hybrid layer with chlorhexidine groups.
2% chlorhexidine application after acid-etching proved to preserve the durability of the hybrid layer and microtensile bond strength of dentin bonding systems.
Figures and Tables
Figure 4
SEM images of fractured surfaces after microtensile bond strength testing of SM.
(A) No CHX/No Thermocycle (× 100) (B) No CHX/No Thermocycle (× 2000) (C) No CHX/10,000cycles (× 100) (D) No CHX/10,000cycles (× 2000) (E) CHX/No Thermocycle (× 100) (F) CHX/No Thermocycle (× 2000) (G) CHX/10,000 cycles (× 100) (H) CHX/10,000 cycles (× 2000)
A,B show adhesive failure. C,D show adhesive failure at the bottom of hybrid layer and resin tag are broken or left out of dentinal tubules. E,F show adhesive failure at hybrid layer intertubular dentin seems to be completely covered by adhesive (DT: dentinal tubule, C: composite resin, HL: hybrid layer).
Figure 5
SEM images of fractured surfaces after microtensile bond strength testing of SB.
(A) No CHX/No Thermocycle (× 100) (B) No CHX/No Thermocycle (× 2000) (C) No CHX/10,000cycles (× 100) (D) No CHX/10,000cycles (× 2000) (E) CHX/No Thermocycle (× 100) (F) CHX/No Thermocycle (× 2000) (G) CHX/10,000 cycles (× 100) (H) CHX/10,000 cycles (× 2000)
A,B show adhesive failure at hybrid layer. C,D show mixed failure at the bottom of hybrid layer. G,H show mixed failure at top of the hybrid layer.(HL: hybrid layer, DT: dentinal tubule)
Figure 6
SEM images of fractured surfaces after microtensile bond strength testing of TS.
(A) No CHX/No Thermocycle (× 100) (B) No CHX/No Thermocycle (× 2000) (C) No CHX/10,000cycles (× 100) (D) No CHX/10,000cycles (× 2000) (E) CHX/No Thermocycle (× 100) (F) CHX/No Thermocycle (× 2000) (G) CHX/10,000 cycles (× 100) (H) CHX/10,000 cycles (× 2000)
G,H show the shift of the failure site from the bottom to the top of the hybrid layer. (DT: dentinal tubule, HL: hybrid layer, C: composite resin)
Figure 7
SEM images of fractured surfaces after microtensile bond strength testing of GI.
(A) No CHX/No Thermocycle (× 100) (B) No CHX/No Thermocycle (× 2000) (C) No CHX/10,000cycles (× 100) (D) No CHX/10,000cycles (× 2000) (E) CHX/No Thermocycle (× 100) (F) CHX/No Thermocycle (× 2000) (G) CHX/10,000 cycles (× 100) (H) CHX/10,000 cycles (× 2000)
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