Influence of diphenyliodonium hexafluorophosphate salt (DPI) and ion-releasing glass fillers (45S5) on physical, mechanical and chemical properties of model resin composite formulations

Abstract

Recurrent dental caries is a major reason for resin composite restoration replacement. 45S5 Ion-releasing glass (IRG) fillers are promising for functionalizing resin composites. They aid in hydroxyapatite deposition and remineralization of dental tissues. Diphenyl iodonium hexafluorophosphate (DPI) is a UV light initiator that replenishes Camphorquinone (CQ) by replacing inactive radicals with phenyl active radicals. The aim of this research was to explore the interactive effect of DPI and IRG on short and long-term material properties. Model resin-composites with varying amounts of IRG were prepared using a UDMA/TEGDMA resin system and either a unary or binary (includes DPI) photo-initiator system. Polymerization related properties such as degree of conversion (DC), shrinkage strain (SS) and depth of cure (DoC) were measured. IRG negatively impacted DC and DoC when higher content was used while DPI improved both DC and DoC. The SS was lower in the unary group and with higher IRG content confirming an inverse relation between DC and SS. Martens hardness (HM) and related parameters, indentation modulus (EIT) and creep (CIT), as well as the effect of storage in water or ethanol on these parameters were tested. HM and EIT decreased and CIT increased linearly as the amount of IRG is increased. Deterioration of HM and EIT through aging was more pronounced in specimens containing higher IRG amount. DPI showed higher HM, EIT and lower CIT only at higher IRG content compared to the unary group. Water sorption, solubility, hygroscopic dimensional changes and ions release were assessed. IRG significantly increased water sorption, solubility and hygroscopic expansion. Inclusion of DPI reduced water sorption, solubility and hygroscopic expansion. Release of calcium, sodium and phosphate were dose dependent on IRG. This study concluded that 45S5 IRG, while offering potential means of remineralisation, diminished the material’s overall properties. The inclusion of DPI enhanced the polymerization and overall properties of the tested model resin composites.