Influence of Inhibitor Type on Shear Bond Strength to Dentin

Objectives: To evaluate the influence of various inhibitors at different concentrations in two part self-etching adhesive systems.  PartA is the primers in which two different inhibitors were used varying their concentrations (w%).  PartB is the adhesive system that stayed constant for all procedural testing.

Methods: Experimental primers were formulated using an acidic monomer,
2-hydroxyethyl methacrylate(HEMA), ethanol, water and either butylated hydroxytoluene(BHT) or hydroquinone monomethyl ether(MEHQ) inhibitor.  The experimental primers contained 0.05%BHT(Pri-1), 0.10%BHT(Pri-2), 0.15%BHT(Pri-3), 0.05%MEHQ(Pri-4), 0.10%MEHQ(Pri-5), and 0.15%MEHQ(Pri-6) by weight.  Primers were tested with the same PartB formulation, consisting of ethoxylated bisphenol-A(BisEMA)/dimer dicarbamate dimethacrylate(DDCDMA) in 70/30wt% ratio.  The Ultradent shear bond strength test (SBS) was performed on dentin of human third molars embedded in acrylic resin.  The SBS was tested (n=7) on an Instron mechanical tester after storage in de-ionized water (37^oC, 24 hours).  The dentin surfaces were treated with PartA and air dried with an oil/moisture free air source. PartB was then applied, air dried and photoactivated using a halogen lamp (500mW/cm²) for 10 seconds. Finally, the composite N’Durance (Septodont) was placed in two separate layers with each layer being cured for 40 seconds.  The data was statistically analyzed (ANOVA, Tukey’s, p<0.05).

Results:    For each column, similar letters indicate no statistical differences as well as for each row shown in parentheses.

 

Exp.	Type	%	SBS-Dentin	Exp.	Type	%	SBS-Dentin
Pri-1	BHT	0.05	29.7±3.36a(a)	Pri-4	MEHQ	0.05	28.9±1.51a(a)
Pri-2	BHT	0.10	28.9±3.14a(a)	Pri-5	MEHQ	0.10	24.6±3.57b(b)
Pri-3	BHT	0.15	18.7±3.71b(a)	Pri-6	MEHQ	0.15	23.2±3.49b(b)

Conclusions: Results demonstrate that as the amount of each inhibitor is increased in the primer, SBS to dentin decreases.  Statistical differences also exist between the two inhibitors of identical concentration.  These data trends will help in determining how much inhibitor is necessary in a primer system to achieve the desired shelf-life-stability without detriment to shear bond strength.