The use of NaOCl to Increase Bond Strength

Objective:   To evaluate if the addition of 5.25% NaOCl followed by 37% H₃PO₄ etch will increase the bond strength by increasing the overall etched surface using a three-step etch-and-rinse adhesive system.

Method:   36 Human molars stored in 0.5% chloramine T were cut in half and prepared with a flat enamel surface.  Each tooth will represent one of 6 groups.  A) 37%  H₃PO₄ etch for 20 seconds. B) 37%  H₃PO₄ etch rubbed into enamel for 20 seconds.  C) 5.25% NaOCl for 30 seconds and 37%  H₃PO₄ etch for 20 seconds.  D) 5.25% NaOCl for 30 seconds and 37%  H₃PO₄ etch rubbed into enamel for 20 seconds.  E) 5.25% NaOCl for 60 seconds and 37%  H₃PO₄ etch for 20 seconds. F) 5.25% NaOCl for 60 seconds and 37% H₃PO₄ etch rubbed into enamel for 20 seconds.  A rinse step was performed between NaOCl and etching, and after etching.  The surfaces were dried and 1 coat of Optibond FL adhesive was applied and light cured for 20s.   A composite build-up of approximately 5 mm was made using Filtek Supreme, applied in 2 increments.  After 24-hour storage in water, the specimens were sectioned with a diamond saw in both the x and y directions.  Each rectangular stick had a cross section area of approximately 0.8mm.   At random 2 sticks from each tooth were subjected to tension at a crosshead speed of 1.0 mm/minute using a Zwick testing machine after 1 week and 3 months of storage in artificial saliva at 37^oC.

Results: One-ANOVA (alpha 0.05) revealed no statistically significant differences between groups ( p> 0.05).

                    Bond strength in MPa (SD)

A                             39.5 (5.9)

B                              33.7 (10.4)

C                              32.3 (13.5)

D                             33.2 (16.6)

E                              27.8 (14.2)

F                              32.8 (14.5)

Conclusion: The addition of NaOCl did not increase the long-term bond strength of composite to enamel.