Initiator and Primer Photopolymerization Effects on Bonding with PMDM/HEMA-based Primers

An experimental adhesive primer based on the monomers PMDM and HEMA in acetone as a solvent and activated with a diacylphosphine oxide (PO, Irgacure 819) photoinitiator was previously evaluated and achieved >30 MPa mean composite-dentin shear bond strength (SBS). OBJECTIVE: This study was designed to evaluate the effect of substituting the redox photoinitiator camphorquinone (CQ) plus ethyl 4-dimethylaminobenzoate (4E) for PO in the same primer mixture for composite-dentin SBS testing. METHODS: Coronal enamel was removed from caries-free third molars and mounted in polycarbonate holders for SBS testing. The bonding protocol followed: 1) Dentin ground with 320 grit SiC paper was conditioned with 38% H₃PO₄ for 15s and rinsed with de-ionized H₂O for 10s. 2) The experimental primer consisting of 7.5% PMDM/42% HEMA plus 0.5 % photoinitiator (all mass %) in acetone was applied to moist dentin, air dried and light polymerized (10s) for Group 1 (PO) and Group 3 (CQ/4E). Group 2 (PO) and Group 4 (CQ/4E) primers were not polymerized. N=10 for all groups. 3) A Bis-GMA/HEMA (60/40 mass %) bonding resin activated with CQ/4E was applied and light-cured (10s). A 4.0 mm Teflon-coated iris was placed on the treated dentin through which a resin composite was applied and light polymerized (60s). After 24 h storage in distilled H2O specimens were tested in shear with a universal testing instrument at a cross head speed of 0.5 mm/min. Data was analyzed using 2-way ANOVA and Tukey post hoc test (á=0.05). RESULTS: Mean dentin SBS's (MPa): Group 2 (35.3±6.8) > Group 1 (27.8±9.8) >Group 4 (19.1±6.8) > Group 3 (18.7±8.8). CONCLUSIONS: Substituting CQ:4E for diacylphosphine oxide significantly decreased SBS (p < 0.001); however, eliminating photopolymerization of the primer had no significant effect on shear bond strengths. SUPPORT: NNMC, NIST, and ADAF