Effect of C-factor and LED Curing Mode on Microleakage of Class V Resin Composite Restorations Qasem Diefallah Alomaria Kefah Barrieshi-Nusairb Mohammad Alic AbstrAct Objectives: To investigate the effects of cavity C-factor and LED curing mode on microleakage of class V resin composite restorations. Methods: Eighty extracted human maxillary premolars were divided into four groups. In groups I and II, V-shaped class V cavities (C-factor ≈ 1.5) were prepared while box-shaped class V cavities (high C-factor ≈ 4) were prepared in groups III and IV. All the cavities were prepared on the vestibular surfaces of the teeth. All the cavities were prepared by one operator with specific dimensions. The same adhesive system (Excite) and the same restorative composite (Tetric Ceram) were used in all the groups. The restorations in groups I and III were cured with the fast curing mode of LED curing light, while the restorations in groups II and IV were cured with the soft-start mode of the same cur- ing light. The samples were thermocycled, immersed in a 0.5% basic fuchsin solution for 24 hours, and sectioned. The degree of dye penetration was measured quantitatively and then qualitatively at both enamel and dentin/cementum margins. Results: Quantitatively, there was no statistical difference in the degree of microleakage between the groups at the enamel margin (P>.05). At the dentin/cementum margin, group III showed signifi- cantly more dye penetration than the other groups (P<.001). Similarly, qualitative measurements of dye penetration showed that group III had higher microleakage at dentin/cementum margin than the remaining groups (I and III P<.001; II and III P<.01; III and IV P<.01). Paired sample statistics showed that microleakage at the dentin/cementum margin was not statistically different from enamel mi- croleakage (P>.05), except for group III (P<.000). Conclusions: Fast curing mode of LED curing light resulted in more microleakage at the gingi- val floor of class V cavities with high C-factor. There was no difference in dye penetration between enamel and dentin margins of the cavities except when the fast curing mode was used with high C-factor cavities. Both quantitative and qualitative measurements of microleakage gave the same results at both enamel and dentin margins. (Eur J Dent 2011;5:400-408) Key words: Resin composite; Microleakage; C-factor; LED curing units; Curing modes. a Department of Restorative Sciences, Faculty of Dentistry, Kuwait University, Kuwait. b Deceased. c Department of Diagnostic Sciences, Faculty of Dentistry, Kuwait University, Kuwait. Corresponding author: Qasem Diefallah Alomari Department of Restorative Sciences, Faculty of Dentistry, Kuwait University, P. O. Box 24923, Alsafat 13110, Kuwait. E-mail: qalomari@hsc.edu.kw qasemalomari70@yahoo.com 400 European Journal of Dentistry