Innovative Light-curable Resin-based Restorative Materials Doped with Bioactive Micro-fillers

After minimally invasive caries removal, ideally one would employ bioactive restorative materials able to offer a therapeutic remineralising effect on the remaining partially demineralised tooth substrates. Nevertheless, bioactive materials often compromise mechanical properties due to their ability to turn into apatite. Thus, the aim of this study was to evaluate the mechanical properties, biocompatibility, bioactivity and alkalinising activity of light-curable resin-based materials containing tailored bioactive micro-fillers.

Method:

A control resin was formulated using monomers such as UDMA, BisGMA, TEGDMA, HEMA, photo-initiators and co-initiators. Different bioactive micro-fillers were mixed with the resin blend: i) 45S5 Bioglass(BAG); ii) polycarboxylated zinc-doped BAG(BAG-Zn); iii) βTCP-modified Portland cement(B-Port); iv) polycarboxylated zinc-doped B-Port(B-Port-Zn). The flexural strength(FS) and fracture toughness were determined at 24h and 1-month storage in SBF. The experimental resins were characterised using ATR/FTIR, XRD, SEM and the pH was monitored up to 1-month. The cytotoxicity was tested using an MTT assay. Bioactivity was evaluated using mineralisation and gene expression differentiation assays of Runx-2 & ALP.

Result:

The incorporation of bioactive microfillers had no effect on the biocompatibity apart from B-Port. The inclusion of zinc significantly (p<0.05) increased the gene expression. Lower FS was attained at 24h with zinc-polycarboxylated micro-fillers. However, after 1-month storage, all the experimental microfillers decreased in strength; FTIR, XRD & SEM analysis confirmed that they had induced apatite formation. The tested bioactive resins were able to create an alkaline pH in the storage media, in particular when in the presence of B-Port. 

Conclusion:

The decrease in FS of the resins containing zinc-polycarboxylated micro-fillers may be due to their higher opacity, making light-curing more challenging. However, these latter cements were bioactive, forming apatite and bio-inducing alkaline phosphatase formation in cells. Thus, these materials may be a suitable therapeutic solution in minimally invasive dentistry for the remineralisation of a partially demineralised substrate after selective caries removal.