Effects of Bioactive Restorative Materials on Bovine Dentine with Varying Gap Sizes under Demineralising and Remineralising Conditions

Abstract

Aim: To evaluate the demineralisation and remineralisation in gaps of varying dimensions between different bioactive restorative materials and bovine dentine. Methods: Four restorative materials, Cention® Forte (CF), RE-GEN™ (RG), ACTIVA™ Presto (AP), and GC Fuji VII (GIC) that claim to be bioactive, and an inert composite, Herculite™ XRV Kerr (HX), were selected for this study. Bovine dentine was used to investigate the effects of these five materials on the exposed surfaces. Silicon putty with a 10mm cylindrical hole in a 30ml plastic container was used to encase a 2mm-thick bovine dentine slice and the test materials. On one surface of the dentine, a stepped cellulose spacer, comprising five layers and measuring 250µm in thickness for each, was used to create a gradation space between the dentine and one of the materials. The whole container was then scanned using an X-ray microtomography scanner ( XMT), MuCAT2, at 3 time points. At T0, the original scan, the specimen was immersed in de-ionised water for storage. At T1, the specimen was immersed in demineralisation solution of acetic acid and sodium acetate at pH 4.5 for 6 weeks. At T2, following demineralisation, the specimen was immersed in a remineralisation solution containing calcium chloride, potassium phosphate, and potassium chloride at pH 7 for 6 weeks after demineralisation. After reconstruction, the images were standardised and aligned for qualitative and quantitative analysis. Results: CF, RG and GIC were shown to prevent mineral loss on the dentine surface with the gaps after demineralisation. In addition, mineral was formed and deposited on inside the gap. The dentine in the HX gap had aggressive demineralisation with no mineral deposition in the gap. The dentine in the AP gap was also demineralised but was less than that of HX. In the AP gap, some mineral was formed. After subsequent remineralisation, no obvious change of LAC was found in the CF and GIC gaps. There 5 was continuous mineral formation in the RG gap and the deposition was mainly on the material side. The LAC of the demineralised dentine next to the HX gap was increased, indicating some remineralisation. Small amount of mineral deposit was also found in the HX gap. No change of LAC was detected in the gap of AP. Variation of gap widths, 250 to 750 µm was not shown to have any noticeable effect. Discussion: The release of beneficial ions such as calcium, phosphate and fluoride from CF, RG and GIC has enough acid neutralising effect to prevent demineralisation and also new mineral formation in the gaps when they are subjected to acidic challenges. However, only RG, with the bioactive glass, Bioglass 45S5, has the ability to form mineral on its surface to fill the gap in a non-acidic environment. AP may have some ion release, but the concentration might not be enough to prevent demineralisation. HX, having no bioactive component, shows the classical demineralisation and remineralisation patterns. Conclusion: The bioactivity of RE-GEN™ is able to prevent demineralisation in the material-dentine interface if a restoration leaks. It also has self-repair potential to fill the unintentional gap created by clinicians in restorative procedures in acidic and non-acidic environment. Cention® Forte and GC Fuji VII are also materials that can prevent secondary caries formation. However, ACTIVA™ Presto claim on bioactive prevention cannot be upheld.