Aim: to quantify the effect of presence of enamel wall and thermocycling on
marginal microleakage of class V cavities restored with preheated bulk-fill or preheated
nano-filled composite. Methods: Class V cavities were prepared on the buccal surface
of forty-eight extracted maxillary first premolars. The teeth were divided into two groups
according to the type of preheated composite used (either bulk-fill or Nano-filled) and
further subdivided according to thermocycling or no thermocycling. The teeth were
immersed in 0.5% methylene blue dye solution for 24 hours at room temperature
and then sectioned buccolingually to examine the extent of microleakage by dye
penetration. Microleakage was assessed by a stereomicroscope at 40x magnification
and measured in micrometers depending on the extent of dye penetration for both
occlusal and gingival walls separately. Statistical analysis was done by Kruskal-Wallis
test for comparison between groups and Mann-Whitney test for comparing occlusal
and gingival dye penetration in each group. Results: preheated Nano-filled composite
subjected to thermocycling showed more significantly microleakage than other groups
(P < 0.05). Microleakage was significantly more (P < 0.05) in gingival (cervical)
walls of teeth compared to occlusal walls in all groups except preheated Nano-filled
composite directed to thermocycling which showed no significant difference between
gingival and occlusal walls (P > 0.05). Conclusions: thermocycling of preheated Nanofilled
composite produced more microleakage than thermocycling of preheated bulkfilled
composite. More microleakage was recorded in cervical areas than occlusal areas
of class V cavities.