Thisin vitrostudy evaluated the volumetric change (VC) and gap formation (GF) in Class V composite restorations after light-curing and aging. Thirty-six extracted human premolars were used. Standardized Class V cavities (3 mmx3 mmx1.5 mm) were prepared. G-Premio Bond was applied. The teeth were randomly assigned into six groups (n = 6): Group FZ: Filtek Z250(microhybrid), Group SP: SDR Plus Bulk Fill Flowable (low-viscosity bulk-fill), Group EB: Estelite Bulk Fill Flow (low-viscosity bulk-fill), Group GI: G-aenial Universal Injectable (highly-filled low-viscosity), Group AF: Admira Fusion (ormocer), Group SX: Solare X (nanohybrid). Each specimen was scanned four times with micro-CT (SkyScan 1174v2, Belgium): after cavity preparation, before and after light-curing, and after aging. The VC (%) and GF (mm(3)) parameters were quantified and analysed. Then, VC after light-curing was verified with AcuVol video image analyser (n = 6). The specimens were submitted to 10,000 thermocycles (5-55 degrees C) and 100,000 load cycles (50N). The data were statistically analysed using the Kruskal-Wallis, Wilcoxon and Dunn tests (p < 0.05). After light-curing, Group AF and FZ showed significantly lower VC than Group GI. Group GI showed significantly higher total GF than Group AF, EB, FZ and SX. Group GI showed significantly higher GF than Group AF, EB and FZ in cervical region. After aging, a significant increase in the volume of the gap (VG) in cervical region was found for Group FZ and GI (p < 0.05). After light-curing, ormocer and microhybrid composites exhibited lower VC and GF than highly-filled low-viscosity composites. After aging, an increase in VG was observed for microhybrid and highly-filled low-viscosity composites for cervical region.