Experimental HEMA-containing and HEMA-free dental adhesives with enhanced physical-chemical characteristics

Methods: The final FTIR/Raman degree of conversion (DC), DSC glass transition temperature (Tg) and the resin permeability (rP) were characterised at varying photo-curing times (0s, 10s, 20s, 60s, 120s) and the results were statistically analysed. For each specimen, the fluid flow across the resin specimens was then calculated as μLmin⁻¹ cm⁻² cm H₂O⁻¹.

Results: The inclusion of a hydrophilic ionic salt (DPIHP) increased the affinity between the amphiphilic monomers and the binary photoinitiator system enhancing the DC, Tg and resistance to fluid permeability (p<0.05), particularly in the HEMA-containing resin. In the HEMA-free adhesive, the presence of DPIHP allowed a higher DC at a photo-curing interval time of between 10-20s.   This may have been induced by the DPIHP phenyl iodide radical initiating the polymerization reaction. Additionally, the DPIHP active phenyl-radical may have subtracted an electron from the inactive CQ neutral radical regenerating it to the original molecule. A significant correlation was observed between rP, FTIR/Raman DC and Tg (p<0.05).  

Conclusions: New generation resin adhesives containing hydrophilic monomers and solvents should be formulated on a ternary photoinitiator system including hydrophilic ionic in order to achieve enhanced physical-chemical characteristics especially when light-cured in a relatively short period time (10-20s).