Effect of Layers of Bonding System on Dentin Bond Strength

Objectives:  It is known and accepted that using more tan two layers of dentin bonding agents increases bond strength. The purpose if this study was to evaluate the effect of additional layers of bonding systems on the bond strength to dentin.

Methods:  36 recently extracted caries and restoration free upper premolars, were cut and polished with 600 grit until superficial dentin was exposed. Teeth were divided into three groups to receive dentin bonding systems: ProtecBond (Kuraray), Single Bond 2 (3M ESPE) and an experimental one bottle no-etch bonding agent.  For each bonding system three sub-groups were made (n=4) to receive 2, 3 and 4 layers of bonding adhesive, all placed according to manufacturer's instructions. Composite Z-100 was placed over the bonding agent and 1mm² sticks were created from all teeth. 20 randomly selected stick from each group were selected to be evaluated in microtensile at 0.1 cm/min until failure. Data was recorded in MPa and evaluated with a two-way ANOVA. Scheffe's test for comparison among number of layers and bonding systems was also calculated at 0.05 significance level.

Results:  Means with standard deviations (in parenthesis) are shown in table. The experimental dentin bonding system was the only one that did not increase its bond strength to dentin with additional layers. ANOVA and Scheffe's test showed a significance difference between the bond strength with two and four layers, for all bonding systems. No difference was found among adhesives.

	Single Bond 2	EXL-759	Protec Bond
2 layers	22.4(2.4)	32.4(9.0)	29.0(7.1)
3 layers	35.5(11.7)	26.0(5.8)	30.1(9.5)
4 layers	38.2(6.6)	25.3(9.5)	36.8(7.6)

Conclusions:  The use of additional layers affects the bond strength of the system to dentin, but it may be a positive or negative effect depending on the bonding system.