Effect of thermal aging on the radiopacity of universal composite resins at two thickness levels

OBJECTIVES: The aim of this study was to investigate the effects of material type, specimen thickness, and thermocycling on the radiopacity of universal composite resins using equivalent aluminum thickness (mm Al). MATERIALS AND METHODS: Four universal paste-type (Filtek Z250 Universal Restorative; FZ250, Omnichroma; OC, Vittra APS Unique; VU, and G-aenial Universal A'Chord; GU) and three universal flowable composite resins (Omnichroma Flow; OCF, Vittra APS Unique Flow; VUF, and G-aenial Universal Flo; GUF) were tested. Disk-shaped specimens (12 mm diameter) were prepared at 1 mm and 2 mm thicknesses (n = 10 per group). Radiographic images were obtained using a digital X-ray system together with an aluminum step wedge and enamel-dentin references. Mean gray values (MGV) were measured using ImageJ software and converted to equivalent mm Al. Specimens were subjected to 10,000 thermocycles (5-55 °C). Data were analyzed using three-way ANOVA (p < 0.05). RESULTS: Radiopacity differed significantly among the tested materials (p < 0.001). FZ250 and VU exhibited the highest mm Al values at both thickness levels. Specimen thickness significantly affected radiopacity, with 2 mm specimens showing higher values than 1 mm specimens across all materials (p < 0.001). After thermocycling, statistically significant decreases were observed in the 2 mm specimens of the VU and VUF groups (p < 0.001). All materials exhibited radiopacity values equal to or greater than 1 mm Al at 1 mm thickness. CONCLUSION: All tested universal composite resins met the minimum ISO 4049 radiopacity requirement. Radiopacity was influenced by material type and specimen thickness. Thermocycling caused a decrease in radiopacity values in some composite resin groups. CLINICAL RELEVANCE: Thermocycling may affect radiopacity depending on material type and specimen thickness and should be considered by clinicians during radiographic evaluation of composite restorations.