Bond strength of Self-adhesive Luting Cements to Zirconia after Thermocycling

Objectives: One major concern with indirect restorative materials is the long-term durability of bonding ability (Dent Mater, 2001;17:347-353).  The purpose of this study was to evaluate the effect of 20,000 thermocycles on bond-strengths to zirconia (Lava, 3M ESPE) of three self-adhesive luting cements (RelyX Unicem, 3M ESPE; Multilink Sprint, Ivoclar-Vivadent; SAC-A, Kuraray Medical) and one adhesive luting cement (ResiCem, Shofu). Methods: The surface of Lava was pretreated by sandblasting with 50 micron aluminum-oxide particles.  Specimens of ResiCem were pretreated by manufacturer's instructions.  A stainless-steel rod, 3.4 mm in diameter and 2 mm in height, was prepared and inserted into a Teflon mold, 3.6 mm in diameter and 2.0 mm in height, using the four luting cements.  The shear-bond strength between the Lava and stainless-steel rod was obtained with a universal testing machine after one-day storage (1-D) and after 20,000 thermocycles (TC 20k).  The flexural strength of four luting cements was measured with the same materials under the same conditions.  Statistical analyses were done by t-Test (1-D vs. TC 20k, p<0.05, S: significant difference, NS: no significant difference).

Results:

Table:    Shear bond strength, Flexural strength (MPa, Mean (S.D.), N=10)
	RelyX Unicem		Multilink Sprint		SAC-A		ResiCem
1-D	19.2(3.8)	68.8(4.4)	22.8(5.9)	102.7(7.1)	25.7(4.6)	98.1(6.5)	21.9(6.0)	118.6(6.2)
	NS	S	S	S	NS	S	S	S
TC 20k	16.0(4.8)	48.8(5.7)	16.9(3.7)	84.7(5.9)	23.5(4.6)	92.5(5.9)	15.3(4.4)	102.3(7.2)

Conclusions: The bonding ability of two self-adhesive resin cements to Lava and stainless-steel rod did not show significant differences after TC 20k compared to those of 1-D testing.  No relationship was found between bond strength to Lava and flexural strength of four luting cements, as the flexural strength of four luting cements after TC 20k was significantly reduced.