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.