Dental Composites with Calcium / Strontium Phosphates and Polylysine

Abstract

PurposeThis study developed light cured dental composites with added monocalcium phosphate monohydrate (MCPM), tristrontium phosphate (TSrP) and antimicrobial polylysine (PLS). The aim was to produce composites that have enhanced water sorption induced expansion, can promote apatite precipitation and release polylysine.Materials and MethodsExperimental composite formulations consisted of light activated dimethacrylate monomers combined with 80 wt% powder. The powder phase contained a dental glass with and without PLS (2.5 wt%) and/or reactive phosphate fillers (15 wt% TSrP and 10 wt% MCPM). The commercial composite, Z250, was used as a control. Monomer conversion and calculated polymerization shrinkage were assessed using FTIR. Subsequent mass or volume changes in water versus simulated body fluid (SBF) were quantified using gravimetric studies. These were used, along with Raman and SEM, to assess apatite precipitation on the composite surface. PLS release was determined using UV spectroscopy. Furthermore, biaxial flexural strengths after 24 hours of SBF immersion were obtained.ResultsMonomer conversion of the composites decreased upon the addition of phosphate fillers (from 76 to 64%) but was always higher than that of Z250 (54%). Phosphate addition increased water sorption induced expansion from 2 to 4% helping to balance the calculated polymerization shrinkage of ~ 3.4%. Phosphate addition promoted apatite precipitation from SBF. Polylysine increased the apatite layer thickness from ~ 10 to 20 μm after 4 weeks. The novel composites showed a burst release of PLS (3.7%) followed by diffusion-controlled release irrespective of phosphate addition. PLS and phosphates decreased strength from 154 MPa on average by 17% and 18%, respectively. All formulations, however, had greater strength than the ISO 4049 requirement of > 80 MPa.ConclusionThe addition of MCPM with TSrP promoted hygroscopic expansion, and apatite formation. These properties are expected to help compensate polymerization shrinkage and help remineralize demineralized dentin. Polylysine can be released from the composites at early time. This may kill residual bacteria.

Monomer conversion, dimensional stability, biaxial flexural strength, and fluoride release of resin-based restorative material containing alkaline fillers

“…Where ∆B0 and ∆Bt were the absorbance of the C-O peak (1,320 cm −1 ) above background level at 1,335 cm −1 initially and after time t 21) . Peak of C=C stretch (1,637 cm −1 ) of methacrylate group was not used to calculate degree of monomer conversion because this peak also represents O-H stretch of absorbed water in the setting RMGICs 22) .…”

“…Gravimetric studies were used to assess mass and volume changes of all materials (n=3) 14,21) . Disc specimens were prepared 14) .…”

“…The ball-on-ring testing jig were used to measured BFS and BFM of the tested materials (n=8) 21) . Disc specimens were prepared according to section 2.2 and immersed in a tube containing 10 mL of deionized water.…”

“…Furthermore, the absorbed water also enables release of ions from hydrophilic/reactive fillers. The water sorption induced expansion of polymer-based materials could be governed primarily by the flexibility of polymer matrix and the addition of hydrophilic components 14,16,21) .…”

“…Low diffusion coefficient of water sorption induced expansion observed in CN and Z350 could be due to the high rigidity of UDMA and Bis-GMA polymer network in both CN and Z350 which may limit water sorption resulting in the low mass and volume changes 21) . High mass and volume increase observed with RMGICs (RL and FL) could be due primarily to their hydrophilic and flexible HEMA polymer and polyacrylic salts network facilitating diffusion of water into materials 34) .…”