Effect of Cyclic Loading on Bond Strength to Worn Dentin

Objectives: The aim of this study was to evaluate the effect of cyclic loading on the micro-tensile bond strength (MTBS) of a self-etching adhesive system (Clearfil SE Bond) to worn dentin.  Methods: Flat dentin surfaces from human molars (n=20) were assigned to 8 experimental groups (table below) based on those with or without attrition, phosphoric acid etching (Clearfil K-etchant for 10 seconds), and cyclic loading (100,000 cycles, 75N). Resin composite paste (Clearfil AP-X) was placed and polymerized after the bonding procedure according to the manufacturer's instruction. Resin/tooth blocks were then serially sectioned into 1-mm thick slabs and trimmed to 1-mm-width beam specimens. The specimens were subjected to MTBS testing with a 0.5 mm crosshead speed.  Data were statistically analyzed with ANOVA and the Bonferroni test.  Results: Results presented in the table exhibited that minimum mean value of MTBS was 14.9MPa in the group without attrition and etching, and with loading, while maximum mean value of MTBS was 40.0MPa in the group without attrition and loading, and with etching.

Table Results of MTBS            Mean value (s.d.), Unit: MPa

w/ Attrition	w/ Etching	w/ Loading	32.4 (8.1) a b
		w/o Loading	38.7 (9.7) b
	w/o Etching	w/ Loading	29.2 (12.1) a
		w/o Loading	23.3 (9.2) a
w/o Attrition	w/ Etching	w/ Loading	24.0 (9.8) a
		w/o Loading	40.0 (6.7) b
	w/o Etching	w/ Loading	14.9 (6.4) c
		w/o Loading	29.2 (15.0) a

*Values with the same superscripts indicate no significant difference (p>0.05).

Conclusion: Based on the results, it was concluded that MTBS to dentin without attrition was significantly decreased by cyclic loading, but MTBS to dentin with attrition was not affected. The acid etching before the application of the self-etching primer improved MTBS to dentin regardless of the existence of dentin attrition.