title: Conversion, shrinkage, water sorption, flexural strength and modulus of re-mineralizing dental composites.
abstract: OBJECTIVE
  Cure, volumetric changes and mechanical properties were assessed for new dental composites containing chlorhexidine (CHX) and reactive calcium phosphate-containing (CaP) to reduce recurrent caries.
  
  
  METHODS
  20wt.% of light curable urethane dimethacrylate based liquid was mixed with 80wt.% glass filler containing 10wt.% CHX and 0-40wt.% CaP. Conversion versus depth with 20 or 40s light exposure was assessed by FTIR. Solidification depth and polymerization shrinkage were determined using ISO 4049 and 17304, respectively. Subsequent volume expansion and biaxial flexural strength and modulus change upon water immersion were determined over 4 weeks. Hydroxyapatite precipitation in simulated body fluid was assessed at 1 week.
  
  
  RESULTS
  Conversion decreased linearly with both depth and CaP content. Average solidification depths were 4.5, 3.9, 3.3, 2.9 and 5.0 with 0, 10, 20, and 40% CaP and a commercial composite, Z250, respectively. Conversions at these depths were 53±2% for experimental materials but with Z250 only 32%. With Z250 more than 50% conversion was achieved only below 1.1mm. Shrinkage was 3% and 2.5% for experimental materials and Z250, respectively. Early water sorption increased linearly, whilst strength and modulus decreased exponentially to final values when plotted versus square root of time. Maximum volumetric expansion increased linearly with CaP rise and balanced shrinkage at 10-20wt.% CaP. Strength and modulus for Z250 decreased from 191 to 158MPa and 3.2 to 2.5GPa. Experimental composites initial strength and modulus decreased linearly from 169 to 139MPa and 5.8 to 3.8GPa with increasing CaP. Extrapolated final values decreased from 156 to 84MPa and 4.1 to 1.7GPa. All materials containing CaP promoted hydroxyapatite precipitation.
  
  
  CONCLUSIONS
  The lower surface of composite restorations should both be solid and have greater than 50% conversion. The results, therefore, suggest the experimental composite may be placed in much thicker layers than Z250 and have reduced unbounded cytotoxic monomer. Experimental materials with 10-20wt.% additionally have volumetric expansion to compensate shrinkage, antibacterial and re-mineralizing components and competitive mechanical properties.
authors.affiliation: Division of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK.
authors.forename: A
authors.initials: A
authors.lastname: Aljabo
authors.affiliation: Division of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK.
authors.forename: W
authors.initials: W
authors.lastname: Xia
authors.affiliation: Division of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK.
authors.forename: S
authors.initials: S
authors.lastname: Liaqat
authors.affiliation: Division of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK.
authors.forename: M A
authors.initials: MA
authors.lastname: Khan
authors.affiliation: Division of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK.
authors.forename: J C
authors.initials: JC
authors.lastname: Knowles
authors.affiliation: Department of Paediatric Dentistry, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK.
authors.forename: P
authors.initials: P
authors.lastname: Ashley
authors.affiliation: Division of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, 256 Gray's Inn Road, London WC1X 8LD, UK. Electronic address: anne.young@ucl.ac.uk.
authors.forename: A M
authors.initials: AM
authors.lastname: Young
mesh_terms: D003188:Composite Resins; D003764:Dental Materials; D017886:Durapatite; D055119:Elastic Modulus; D008422:Materials Testing; D008689:Methacrylates; D018583:Pliability; D058105:Polymerization; D014867:Water
chemical_list: D003188:Composite Resins; D003764:Dental Materials; D008689:Methacrylates; D014867:Water; D017886:Durapatite
keywords: Antibacterial; Conversion depth; Dental composite; FTIR; Hydroxyapatite; Modulus; Mono and tri calcium phosphate; Shrinkage and expansion; Strength; Tooth remineralization