Degree of conversion of experimental resin composites containing bioactive glass 45S5: the effect of post-cure heating

Matej Par,Thomas Attin,Tobias T Tauböck,Nika Spanovic,Zrinka Tarle

doi:10.1038/s41598-019-54035-y

Matej Par, Thomas Attin + Show 3 more

Open Access

https://doi.org/10.1038/s41598-019-54035-y

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Abstract

Resin composites containing reinforcing inert glass fillers combined with bioactive glass (BG) can aid in the prevention of secondary caries, which is a major cause of failure of contemporary composite restorations. A series of previous studies on experimental resin composites filled with BG 45S5 has demonstrated that methacrylate resin polymerization can be impaired by the addition of unsilanized BG, leading to lower degrees of conversion (DC). In order to distinguish whether the polymerization inhibition is caused by a direct (temperature-independent) effect of BG or an indirect (temperature-dependent) effect of restricted mobility of reactive species, this study used Raman spectroscopy to evaluate the DC values of experimental composites post-cured at 37 °C and 150 °C. The potential of BG to adversely affect DC was highly dependent on the resin system. The highest DC reduction was observed in the resin system based on ethoxylated bisphenol A dimethacrylate (Bis-EMA), followed by bisphenol A glycidyl methacrylate (Bis-GMA). In contrast, the DC for urethane dimethacrylate (UDMA) was not compromised by BG. Increasing the mobility of reactive species by heating at 150 °C showed limited potential for increasing the DC in the Bis-EMA and Bis-GMA resin systems, indicating a direct inhibitory effect of BG on polymerization.

Highlights

Resin composites containing reinforcing inert glass fillers combined with bioactive glass (BG) can aid in the prevention of secondary caries, which is a major cause of failure of contemporary composite restorations
Of most practical importance was the interaction between the factors “resin system” and “BG amount”, which indicates that the investigated resin systems responded differently to the replacement of inert fillers with BG
A series of studies performed on the experimental BG-containing composites similar to those based on the bisphenol A glycidyl methacrylate (Bis-GMA) resin system in the present study has indicated that unsilanized BG fillers can diminish the degrees of conversion (DC) in a dose-dependent manner[10,11,12]

Summary

Introduction

Resin composites containing reinforcing inert glass fillers combined with bioactive glass (BG) can aid in the prevention of secondary caries, which is a major cause of failure of contemporary composite restorations. For the same experimental compositions, BG fillers were demonstrated to impair mechanical properties[11,13] and increase water sorption and solubility[14] These properties were affected by the presence of BG fillers through two main mechanisms: (I) a direct effect of unsilanized, hydrophilic and water-soluble BG particles, which cannot reinforce the material structure, and (II) an indirect effect of BG fillers mediated by the DC reduction. Unsilanized filler particles that are incapable of chemical linking with the polymeric network tend to improve resin mobility and enhance final DC values[20] These considerations are inconsistent with previous reports of DC being diminished by replacing smaller silanized inert fillers with larger unsilanized BG particles[10,11,12] unless the polymerization was affected by some phenomenon other than mobility restrictions. The free radical-mediated polymerization of various resins has been shown to be inhibited by unsilanized glass fillers, which leads to an inferior DC24,25

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