Selection of photo-curing protocol (high intensity vs soft-start) and matrix type (transparent vs metal) did not influence the margin quality and marginal seal of Class II resin-based composite restorations. SUMMARYThis study determined the influence of light curing protocols and matrix type on the margin quality and marginal seal of Class II resin-based composite restorations.In extracted human molars, box-shaped MOD cavities with 1 mm wide interproximal bevels were prepared with cervical margins located at least 1 mm coronal to the cemento-enamel junction. The prepared teeth were mounted in a jig featuring artificial training teeth that served as adjacent teeth. A contoured sectional metal matrix band was placed in one interproximal area, and a section of a contoured transparent matrix band was placed in the opposite interproximal area. Both were kept in position using 98Operative Dentistry margin quality before and after TC was analyzed in SEM using the replica technique, and the marginal seal was determined using the dye penetration test (50% AgNO 3 , 2 hours) at the end of the study.The matrix type did not significantly influence the quality and seal of the respective margins. For the complete restoration margin, one of the high intensity protocols (APO) produced a higher percentage of "continuous margin" compared to pulse delay irradiation after TC and lower percentages of "marginal opening" compared to halogen standard irradiation before and after TC. Halogen step irradiation produced a superior marginal seal compared to pulse delay curing at the occlusal margins; equivalent results were observed for all curing modes at the cervical margins. Neither a general advantage of soft-start irradiation nor a general disadvantage of high intensity curing was confirmed.