Bonding effectiveness of adhesive luting agents to enamel and dentin

ObjectivesThe bonding effectiveness of five adhesive luting agents to enamel and dentin using different application procedures was determined using a micro-tensile bond strength protocol (μTBS).MethodsEnamel/dentin surfaces of human third molars were flattened using a high-speed diamond bur. Composite resin blocks (Paradigm, 3 M ESPE) were luted using either Linkmax (LM; GC), Nexus 2 (NX; Kerr), Panavia F (PN; Kuraray), RelyX Unicem (UN; 3M ESPE) or Variolink II (VL; Ivoclar-Vivadent), strictly following manufacturers’ instructions. For some luting agents, modified application procedures were also tested, resulting in four other experimental groups: Prompt L-Pop + RelyX Unicem (PLP + UN; 3 M ESPE), Scotchbond Etchant + RelyX Unicem (SE + UN; 3 M ESPE), Optibond Solo Plus Activator + Nexus 2 (ACT + NX; Kerr) and K-Etchant gel + Panavia-F (KE + P; Kuraray). The experimental groups were classified according to the adhesive approach in self-adhesive (UN), etch-and-rinse (ACT + NX, NX, KE + P, SE + UN and VL when bonded to enamel) and self-etch adhesive luting agents (LM, PLP + UN, PN and VL when bonded to dentin). The specimens were stored for 24 h in distilled water at 37 °C prior to μTBS testing. The Kruskal–Wallis test was used to determine pairwise statistical differences (p < 0.05) in μTBS between the experimental groups.ResultsWhen bonded to enamel, ACT + NX (15 MPa) and UN (19.6 MPa) scored significantly lower than VL (49.3 MPa), LM (49.2 MPa), PN (35.4 MPa) and SE + UN (35.2 MPa), while PLP + UN (23.5 MPa) showed a significantly lower μTBS than VL (49.3 MPa) and LM (49.2 MPa). No significant differences were noticed between VL (49.3 MPa), LM (49.2 MPa), NX (37.9 MPa), KE + PN (38.8 MPa), PN (35.4 MPa) and SE + UN (35.2 MPa). Regarding the bonding effectiveness to dentin, all luting agents bonded equally effectively (UN: 15.9 MPa; LM: 15.4 MPa; PN: 17.5 MPa; NX: 22.3 MPa), except VL (1.1 MPa), SE + UN (5.9 MPa) and ACT + NX (13.2 MPa). VL revealed an exceptionally high number of pre-testing failures, most likely due to a combined effect of not having cured the adhesive separately and an insufficiently light-cured luting agent.SignificanceFollowing a correct application procedure, the etch-and-rinse, self-etch and self-adhesive luting agents are equally effective in bonding to enamel and dentin. Several factors negatively influenced bond strength such as bonding RelyX Unicem to enamel without prior phosphoric acid etching; no separate light-curing of a light-polymerizable adhesive prior to cementation, use of a light-polymerizing adhesive converted into a dual-polymerizing adhesive, and use of a dual-cure luting agent with a low auto-polymerizable potential.