Effect of C-factor and LED curing mode on microleakage in microleakage has been demonstrated between The use of the soft-start exponential mode of two cylindrical class V cavities of different dimen- LED curing lights was found to reduce microleak- sions, but of the same C-factor.15 Therefore, it was age at both enamel and dentinal margins of class concluded that microleakage is more closely re- II cavities, when compared to the continuous light lated to the volume of the restoration rather than polymerization mode.23 In our study, the soft-start to the C-factor.14 Our results were very interesting, mode did not affect enamel microleakage in all of as class V cavities with higher C-factor had more the groups, but it was able to reduce microleakage microleakage than class V cavities with lower C- at the dentin/cementum margin only for high C- factor only when the fast curing mode was used. factor cavities. It is difficult to compare our results On the other hand, there was no difference in the with previous findings, as we prepared class V cav- amount of microleakage when the soft-start cur- ities and other researchers used class II cavities. ing mode was used, regardless of the value of the Other causes of difference could be related to the C-factor. In all groups, the volume of the restora- resin composite that was used and the placement tions was the same. These results can be explained technique followed in both studies. by the fact that fast curing mode produces higher Bonding of resins to dentin is far more difficult stresses at the adhesive system, and these stress- and less predictable than bonding to enamel. Den- es have the worst effect in case of unfavorable cav- tin not only has a more complex histological struc- ity design (i.e. high C-factor). ture than enamel, but also varies more with loca- One could speculate that the variation between tion.33 Although our results showed that the degree the results of different studies can be attributed of enamel microleakage was less than that of den- to variations in methodology, for example, type of tin/cementum, this difference was not statistically cavity prepared in each study (class I vs. class II different except for group III (when the C-factor vs. class V), type of teeth used (human vs. bovine was high). In this group, the amount of microleak- vs. models), restorative materials used, the cur- age at the dentinal/cementum margins was sta- ing protocols employed in addition to the type of tistically higher than at the enamel margins. This adhesive system and the way it has been manipu- result is supported by a previous study by Ozturk et lated. Another important factor is the way the in- al.25 In their study, they prepared box-shaped class vestigators change the C-factor of the cavity, i.e., V cavities of the same dimensions used in the study by increasing the depth or the width of the cavity, at hand. They found higher microleakage at dentin/ as using cavities of different depths results in dif- cementum margins compared to enamel margins, ferent dentinal properties, which can affect mi- regardless of the curing unit (conventional halogen croleakage. In our study, we purposely changed curing unit, high intensity curing unit, and plasma the C-factor by changing the shape of the cavities, arc curing unit). Clinically, clinicians should use keeping the volume and the depth of the cavities the proper techniques to overcome this problem by constant in all the tested groups. manipulating the curing modes or by using rein- One LED curing light was used in this study, but modified glass ionomer liners.3 with two curing modes. Although the curing time The radiation exposure for all of the cavities was was different between the two curing modes used, 16.5 J/cm2. As we attempted to keep the volumes the total energy delivered was the same (16.5 J/ of the two types of cavities uniform, this resulted in cm2). Previous studies demonstrated that soft- differences in their surface areas. The box-shaped start curing delivers low levels of energy initially, cavities had smaller surface areas, and therefore, allowing the resin composite to flow. This releases their radiation exposure was less. Nonetheless, the stresses of polymerization shrinkage, resulting they had higher dye penetration values. Correction in reducing microleakage.7,31,32 High polymerization of the radiation exposure to correspond to the sur- stresses have been shown to increase leakage in face area is difficult to do in the settings of curing class V cavities.12 On the contrary, Hofmann and light used. Hunecke6 showed no difference between high in- Clinically, research regarding the effect of soft- tensity curing lights with soft-start curing, with re- start polymerization was equivocal. One study gard to margin quality and marginal seal of class II showed that it can reduce postoperative sensitivity resin composite restorations. following placement of resin composite restora- 406 European Journal of Dentistry