title: Shrinkage stress kinetics of Bulk Fill resin-based composites at tooth temperature and long time.
abstract: To determine the shrinkage stress kinetics at up to 12h after light exposure and at tooth temperature during placement of selected Bulk Fill resin-based composites (RBCs).
  
  
  
  Five representative Bulk Fill RBCs from four companies were chosen with a wide range of viscosity and filler volume content. The shrinkage stress kinetics at T=33°C was measured continuously over a period of 12h using a modified tensometer with the ability to measure the cantilever beam deflection to better than 40nm accuracy at a sampling rate of up to 200 samples/s, and thermally stable resulting in a measurement accuracy better than 0.05MPa at 12h. The tensometer compliance was 0.105μm/N. A custom made heater was used to control the RBC sample temperature at T=33°C with a temperature gradient across the sample of less than 1°C. The samples were irradiated for 20s with irradiance of 1.1W/cm2and total energy density of 22J/cm2. Three samples (n=3) were used for each RBCs.
  
  
  
  The shrinkage stress at 12h for the five Bulk Fill RBCs ranged from 2.21 to 3.05MPa, maximum stress rate ((dS/dt)M) varied from 0.18 to 0.41MPa/s, time at which the maximum stress rate occurred (tMax) were between 1.42 to 3.24s and effective gel time (tgel) varied from 50 to 770ms. Correlations were observed between (dS/dt)Mand tMax(r=-0.946), tMaxand filler volume fraction (r=-0.999), and between the shrinkage stress at 12h and tgel(r=0.994). However, no correlation was observed between the stress at 12h and filler volume fraction.
  
  
  
  The shrinkage stress for four of the five Bulk Fill RBCs were not significantly different (p<0.05) at 6h and beyond after photo-curing and that fully developed stress induced by photo-cured RBCs may only be reached at times longer than 12h.
authors.affiliation: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada.
authors.forename: David
authors.initials: D
authors.lastname: Kalliecharan
authors.affiliation: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada.
authors.forename: William
authors.initials: W
authors.lastname: Germscheid
authors.affiliation: Department of Dental Clinical Sciences, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada.
authors.forename: Richard B
authors.initials: RB
authors.lastname: Price
authors.affiliation: Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309-0596, United States.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Stansbury
authors.affiliation: Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada. Electronic address: daniel.labrie@dal.ca.
authors.forename: Daniel
authors.initials: D
authors.lastname: Labrie
mesh_terms: D003188:Composite Resins; D007700:Kinetics; D008027:Light; D013696:Temperature; D014070:Tooth; D014783:Viscosity
chemical_list: D003188:Composite Resins
keywords: Kinetics; Polymerization; Resin composite; Shrinkage; Stress; Temperature; Tensometer