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

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.

A New Customized Bioactive Glass Filler to Functionalize Resin Composites: Acid-Neutralizing Capability, Degree of Conversion, and Apatite Precipitation

“…Previous studies showed that the DC of resin composites could be impaired by the addition of BG 45S5 [22][23][24]. This phenomenon was confirmed in the present study for the composite series functionalized with BG 45S5, which showed a dose-dependent DC decline.…”

“…The degree of conversion (DC) represents a fundamental parameter governing mechanical properties and biocompatibility of polymer-based materials [18][19][20][21]. Previous studies indicated that BG 45S5 can impair the DC of experimental resin composites [22][23][24]. Since the present study is the first to investigate a particular novel BG composition, the possibility of it exerting a negative effect on DC was evaluated.…”

Bioactivity and Physico-Chemical Properties of Dental Composites Functionalized with Nano- vs. Micro-Sized Bioactive Glass

“…This indicates that the resin mobility was not hindered by the high surface area of nano-sized BG any more than the 30 times lower surface area of micro-sized particles. A dose-dependent potential of BG 45S5 for diminishing the DC of experimental composites has been observed in a previous study [27]. The present study demonstrated that downsizing the BG fillers exerted no inhibitory effect on resin polymerization.…”

“…The usual trade-off between bioactivity and mechanical properties can be fine-tuned by varying relative amounts of reinforcing and reactive fillers [25]. Resin matrix composition can be adjusted to optimize hydrophilicity [26] and degree of conversion (DC) [27]. Additionally, BG fillers can be downsized from micrometric to nanometric scale [21,[28][29][30][31][32].…”

Light Transmittance and Polymerization of Bulk-Fill Composite Materials Doped with Bioactive Micro-Fillers

“…The degree of conversion is an essential material characteristic of dental resin composites, affecting both physical and mechanical as well as biological polymer properties [34][35][36][37][38][39][40][41]. In the current study, the added micro-fillers did not affect the degree of conversion at the specimens' top surface, irrespective of the bulk-fill composite used.…”