The effect of toothbrushing on the physical, mechanical and chemical surface properties of resin composite CAD/CAM blocks

The properties of CAD/CAM resin composite blocks (RCBs) have improved over the years through modification in their composition including the addition of fluoride. However, there is currently limited data on their surface properties, biocompatibility and fluoride release following wear testing. Purpose: This study aimed to evaluate the surface hardness, roughness, gloss, monomer elution and fluoride release of two newly developed CAD/CAM Resin Composite Blocks with different filler contents and characteristics subjected to thermocycling and a 3-body wear test using a locally manufactured toothbrushing simulator. Materials and methods: Thirty samples each of edelweiss (EDL), KZR-CAD HR 3(KZR) RCBs, and CEREC felspathic block (CB) were sectioned into blocks measuring (14 x 12 x 18 mm). These were divided into 3 groups: No Treatment (NT), Toothbrushing (TB), and Thermocycling and Toothbrushing (TC+TB) for testing hardness, surface roughness, gloss, and monomer elution. To evaluate the fluoride release, 20 samples of Compoglass (COM) blocks measuring (14 x 12 x 5 mm) along with EDL and KZR RCBs were also divided into NT and TB groups, to evaluate fluoride release. All the parameters were separately analysed using repeated measures analysis of variance (ANOVA) with significance set at less than 0.05. Result: CEREC Blocs (CB) consistently showed higher VHN values than both Edelweiss (EDL) and KZR CAD HR3 (KZR) across all three intervention types (NT, TB, TC+TB). However, there were no significant differences between EDL and KZR suggesting that these materials exhibit similar VHN values regardless of the type of intervention applied. For surface roughness, KZR material appears to exhibit resilience to surface roughness particularly under thermocycling and toothbrushing conditions. The effect of toothbrushing (TB) and combination of thermocycling and toothbrushing (TC +TB) was found to significantly reduce the gloss values for all materials when compared to no treatment group (NT). Monomers were not detectable in any of the experimental groups suggesting that the levels of the monomers, if present, were below the detection limits of the HPLC method used in this study. Both EDL and KZR has the ability to release fluoride and KZR showed high fluoride release when subjected to toothbrushing. Toothbrushing and thermocycling significantly influenced the wear patterns of both fluoride containing RCB resulting in significant changes in the surface integrity of RCB. Conclusion: Both EDL and KZR showed similar results in hardness, gloss, and monomer elution. The hardness value comparable to dentine, optimal gloss, and biocompatibility in monomer release. However, KZR was more resistant to surface roughness and had higher fluoride release, especially after thermocycling and toothbrushing. Both materials showed evident wear and surface changes with toothbrushing and thermocycling.