Effects of different sizes of occlusal metal on curing depth of light-cured orthodontic band cement

Introduction: Sufficient penetration and quantity of light are necessary to cure band cement. It is doubtful whether this occurs when bands are cemented to teeth restored with large pieces of occlusal metal. The purpose of this in-vitro investigation was to examine the curing depth and degree of conversion from monomer to polymer of light-cured adhesives when used to cement bands to ceramic blocks covered with metal restorations. Methods: Two resin adhesives-Transbond Plus (3M Unitek, Monrovia, Calf) and Ultra Band-Lok (Reliance Orthodontic Products, Itasca, Ill)-and 3 curing methods were used. The upper surfaces of ceramic blocks (13 × 10 × 15 mm), used instead of human molars, were restored by using metal pieces of different sizes (4 × 8 × 2, 6 × 8 × 2, and 8 × 8 × 2 mm). The curing depth of the cement along the lateral surface of the block was measured at the middle of its width with slide calipers. Fourier transform infrared spectrometry was used to evaluate the degree of conversion of the adhesives. Results: There was unpolymerized resin in the deep area of the cement on curing with central irradiation from the occlusal surface. However, the amount of unpolymerized resin was significantly (P < .05) decreased with the boundary and circle irradiation methods. Conclusions: The curing depth of band cement was significantly affected by the size of the occlusal metal restoration and the irradiation method. Therefore, a suitable irradiation method is essential for complete curing of resin for cementing bands to teeth with large metal restorations.