title: Dental Composites with Calcium / Strontium Phosphates and Polylysine.
abstract: OBJECTIVE
  This 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.
  
  
  METHODS
  Experimental 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.
  
  
  RESULTS
  Monomer 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.
  
  
  CONCLUSIONS
  The 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.
authors.affiliation: Department of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, London, United Kingdom.
authors.forename: Piyaphong
authors.initials: P
authors.lastname: Panpisut
authors.affiliation: Department of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, London, United Kingdom.|Interdisciplinary Research Centre in Biomedical Materials (IRCBM), COMSATS, Lahore, Pakistan.
authors.forename: Saad
authors.initials: S
authors.lastname: Liaqat
authors.affiliation: Department of Restorative Dentistry, Unit of Prosthodontics, UCL Eastman Dental Institute, London, United Kingdom.
authors.forename: Eleni
authors.initials: E
authors.lastname: Zacharaki
authors.affiliation: Department of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, London, United Kingdom.
authors.forename: Wendy
authors.initials: W
authors.lastname: Xia
authors.affiliation: Department of Restorative Dentistry, Unit of Prosthodontics, UCL Eastman Dental Institute, London, United Kingdom.
authors.forename: Haralampos
authors.initials: H
authors.lastname: Petridis
authors.affiliation: Department of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, London, United Kingdom.
authors.forename: Anne Margaret
authors.initials: AM
authors.lastname: Young
mesh_terms: D002130:Calcium Phosphates / Q000737:chemistry*; D019245:Compressive Strength; D003764:Dental Materials / Q000737:chemistry*; D055119:Elastic Modulus; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D010710:Phosphates / Q000737:chemistry*; D011107:Polylysine / Q000737:chemistry*; D058105:Polymerization; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D013324:Strontium / Q000737:chemistry*
chemical_list: D002130:Calcium Phosphates; D003764:Dental Materials; D010710:Phosphates; D011107:Polylysine; C052774:strontium phosphate; D013324:Strontium