title: Development of viscoelastic stability of resin-composites incorporating novel matrices.
abstract: OBJECTIVE
  To study the effect of resin matrix and maturation time (1 and 24 h) on the creep deformation of resin-composites, two of which have matrix-forming monomers that are either bis-GMA free or have an ormocer structure between the CC groups.
  
  
  METHODS
  Five resin-composites: four commercial and one experimental were investigated. Six specimens were prepared for each material and were divided into two groups (n=3) according to the maturation time and condition. Group A was stored dry at room temperature for 1 h and Group B was stored for 24 h in distilled water to allow post-curing at 37°C. Each specimen was loaded (20 MPa) for 2 h and unloaded for 2 h. The strain deformation was recorded continuously for 4h. Statistical analysis was performed using one-way ANOVA and the Bonferroni post hoc test at a significance level of a=0.05.
  
  
  RESULTS
  The maximum creep-strain % after 1 h ranged from 1.32% to 2.50% and was reduced after 24h post-cure to between 0.66% and 1.47%. Also, the permanent set after 1h ranged from 0.70% up to 1.27% (Group A) and after 24 h ranged from 0.53% up to 1.20% (Group B).
  
  
  CONCLUSIONS
  Creep deformation and maximum recovery for all resin-composites decreased with time, demonstrating improvement in viscoelastic stability. However, there was no significant difference between the permanent set at different times, except for Herculite XRV Ultra. Composites with novel matrices showed comparable properties to existing bis-GMA based materials.
authors.affiliation: Biomaterials Science Research Group, School of Dentistry, University of Manchester, Manchester, UK; College of Dentistry, King Saud University, Riyadh, Saudi Arabia.
authors.forename: Khold
authors.initials: K
authors.lastname: Al-Ahdal
authors.affiliation: Biomaterials Science Research Group, School of Dentistry, University of Manchester, Manchester, UK.
authors.forename: Nick
authors.initials: N
authors.lastname: Silikas
authors.affiliation: Biomaterials Science Research Group, School of Dentistry, University of Manchester, Manchester, UK; Photon Science Institute, University of Manchester, Manchester, UK. Electronic address: david.watts@manchester.ac.uk.
authors.forename: David C
authors.initials: DC
authors.lastname: Watts
mesh_terms: D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D003799:Dental Stress Analysis; D004548:Elasticity; D008422:Materials Testing; D013314:Stress, Mechanical; D014783:Viscosity
chemical_list: D003188:Composite Resins; D003764:Dental Materials
keywords: Creep; Mechanical properties; Resin-composites; Viscoelasticity