Shrinkage stress kinetics of Bulk Fill resin-based composites at tooth temperature and long time

Dent Mater. 2016 Nov;32(11):1322-1331. doi: 10.1016/j.dental.2016.07.015. Epub 2016 Aug 21.

Abstract

Objective: 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).

Methods: 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/cm2 and total energy density of 22J/cm2. Three samples (n=3) were used for each RBCs.

Results: 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)M and tMax (r=-0.946), tMax and 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.

Significance: 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.

Keywords: Kinetics; Polymerization; Resin composite; Shrinkage; Stress; Temperature; Tensometer.

MeSH terms

  • Composite Resins*
  • Kinetics
  • Light
  • Temperature*
  • Tooth
  • Viscosity

Substances

  • Composite Resins