THE JOURNAL OF PROSTHETIC DENTISTRY VOLUME 83 NUMBER 6The smoothest composite surface that is important in esthetic restorations can be obtained with a celluloid strip. 1 However, a discoloration study revealed that composite surfaces polymerized under matrix discolored more than surfaces polished after 48 hours of light curing. 2 Higher tendency of discoloration on the celluloid strip-covered composite surface, even though it has a smoother surface, may be related to lower physical property on the surface.A previous study showed microhardness of the celluloid strip-finished composite to be lower than the polished subsurface, 3 and the celluloid strip-covered composite surface showed lower conversion than the composite bulk. 4 Thus, it was recommended that composites should be finished and polished, despite the smooth finish of the celluloid strip. 5-8 However, from a clinician's point of view, he is reluctant to polish the celluloid strip-finished composite surface with an instrument, especially when an esthetic result is the prime concern to the patient.It would be helpful for the clinicians to find a way to minimize the drawbacks of celluloid strip-finished composite surface. Discovering the physical properties of the celluloid strip-finished composite surfaces would be the first step in minimizing these disadvantages. In the composite, the physical property is closely related to the degree of conversion, and the hardness measurement is an effective way to evaluate the degree of composite cure. 9 The purpose of this study was to evaluate the changes in the microhardness of composite surface over time, which was cured under celluloid. Purpose. This study tested the hypothesis that the celluloid strip-finished composite surface did not cure enough compared with the polished composite surface.Methods and material. The composite was placed in a 1.5-mm thick aluminum mold and the upper surface was covered with a celluloid strip. Composite was light cured for 60 seconds, then a layer of approximately 200 µm thick was ground away from the lower surface and polished. The hardness of the upper composite surface that was polymerized under a celluloid strip and the polished lower surface were measured with Vickers hardness measuring instrument 15 minutes, 6 hours, and 6 days after light curing. The hardnesses of polished and celluloid strip-finished surfaces were compared using a paired t test. Oneway ANOVA and Tukey was used for tests for the significant differences in hardnesses between 15 minutes, 6 hours, and 6 days after light curing for a given surface.Results. Microhardness of the celluloid strip-finished composite surface was 380.6 N/mm 2 at 15 minutes, 442.5 N/mm 2 at 6 hours, and 519.2 N/mm 2 at 6 days after light curing. Microhardnesses of the polished composite surface was 476.6 N/mm 2 at 15 minutes, 511.7 N/mm 2 at 6 hours, and 535.0 N/mm 2 at 6 days after light curing. The hardness of the celluloid strip-opposed composite surface was significantly lower than that of the polished surface 15 minutes...