Efficacy of experimental dual cure resin cement for clinical orthodontics

Objectives: The chemical-curing 4-META/MMA-TBB resin cement has been widely used for orthodontic direct bonding system, even though the curing time is significantly longer than the light cure system. To improve the clinical handling of chemical-cure resin cement, a dual-cure resin cement system composed of MMA, UDMA and light activator was developed. The purpose of this study was to estimate the efficacy of an experimental dual-cure resin cement by measuring the shear bond strength (SBS) to the human enamel. Methods: One hundred and twenty extracted human incisors were embedded in an epoxy resin and the facial enamel surface was made flat using a wet silicon carbide paper #600. The enamel surface was etched for 15 sec with Transbond XT Etching Gel (3M Unitek, USA). After rinsing and drying, a commercial composite bracket 18-901(Mitsuba, Japan) was bonded to the teeth with one of eight resin cements; 1, Unifast II (Uni II; GC, Japan) 2, Unifast II containing Comphor quinone (Uni-CQ) 3, Transbond XT (TB; 3M Unitek, USA) 4, Orthomite Superbond (SB; Sunmedical, Japan) 5, Unifast LC (Uni-LC; GC, Japan) 6, Experimental dual-cure resin cement-S1 (7.9wt% UDMA), S2 (13.2wt% UDMA) and S3 (21.2wt% UDMA). Five minutes after the cementation, the SBS of all of the bonded brackets was measured using the universal testing machine with the cross-head speed of 1 mm/min. The SBS were analyzed statistically using Duncan's test (p<0.05). Results: The SBS of the tested cements were statistically divided in three groups, the highest cement (Uni-LC, 25.8 ± 4.7 MPa), the next group (S1,S2,S3,SB and TB) and the lowest group (UniII and Uni-CQ). Conclusions: It was possible to conclude that the dual-cure resin cement-S1, S2 and S3 were useful in practice because they exhibited a bonding efficacy comparable to that of SB and the cementing time could be controlled by light irradiation.