title: The influence of short and medium-term water immersion on the hydrolytic stability of novel low-shrink dental composites.
abstract: OBJECTIVE
  Differences in mechanical and physical properties exhibited by novel low-shrink resin-based composite (RBC) formulations compared with conventional methacrylate RBCs may contribute to the clinical success of the candidate material. The aim of the current study was to investigate the effect of water uptake characteristics and water solubility on the mechanical properties of two methacrylate (Z100 and Filtek Z250), an experimental oxirane (OXI) and silorane (SIL) RBC following short- and medium-term immersion.
  
  
  METHODS
  The water sorption/solubility and associated diffusion coefficients of each material (n=5) were measured using gravimetric analysis following short- (0.1, 0.5, 1, 4, 24 and 48 h) and medium-term (1, 4, 12 and 26w) immersion. The bi-axial flexure strength, associated Weibull moduli (n=20) and fracture analysis using scanning electron microscopy (SEM) of each material for similar immersion periods was also investigated.
  
  
  RESULTS
  Following 0.5h and each subsequent short- and medium-term immersion period the water sorption of Z100 and Filtek Z250 was decreased compared with OXI. A significant decrease in bi-axial flexure strength and associated increase in filler particle exfoliation identified through SEM was identified for OXI compared with Z100, Filtek Z250 and SIL following 26w immersion. SIL exhibited the significantly lowest water sorption, solubility and associated diffusion coefficient following each immersion period.
  
  
  CONCLUSIONS
  The increase in water sorption, solubility and the associated diffusion coefficient of the experimental oxirane RBC, OXI was manifested as a significant decrease in bi-axial flexure strength and attributed to the decrease in synergy between the filler particles and resin matrix. The decreased water sorption, solubility and associated diffusion coefficient of the experimental silorane RBC, SIL may potentially improve hydrolytic stability of RBC restorations demonstrated by the non-significant decrease in bi-axial flexure strength following medium-term immersion.
authors.affiliation: Biomaterials Unit, School of Dentistry, University of Birmingham, St Chad's Queensway, Birmingham B4 6NN, UK. w.m.palin@bham.ac.uk
authors.forename: W M
authors.initials: WM
authors.lastname: Palin
authors.forename: G J P
authors.initials: GJ
authors.lastname: Fleming
authors.forename: F J T
authors.initials: FJ
authors.lastname: Burke
authors.forename: P M
authors.initials: PM
authors.lastname: Marquis
authors.forename: R C
authors.initials: RC
authors.lastname: Randall
mesh_terms: D000042:Absorption; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003188:Composite Resins / Q000737:chemistry*; D003764:Dental Materials / Q000737:chemistry*; D004058:Diffusion; D004548:Elasticity; D005027:Ethylene Oxide / Q000737:chemistry; D006801:Humans; D006868:Hydrolysis; D007101:Immersion; D008422:Materials Testing; D008689:Methacrylates / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D018583:Pliability; D012822:Silicon Dioxide / Q000737:chemistry; D012833:Siloxanes / Q000737:chemistry; D012995:Solubility; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D014867:Water / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C444701:Filtek Z250; D008689:Methacrylates; D012833:Siloxanes; C083568:Z100 composite resin; D014867:Water; D012822:Silicon Dioxide; D015040:Zirconium; D005027:Ethylene Oxide