Publications by authors named "David Kalliecharan"

2 Publications

  • Page 1 of 1

Photo-polymerization kinetics of a dental resin at a high temporal resolution.

J Mech Behav Biomed Mater 2021 Dec 7;124:104884. Epub 2021 Oct 7.

Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada. Electronic address:

Objectives: This study: 1) aims to measure with high temporal resolution the intrinsic rate of the degree of conversion (DC) of a dental resin-based composite (RBC) photo-cured at two irradiances; 2) aims to determine the transition time at which the DC rate is maximum; 3) used two different irradiances to measure the shift in transition time; 4) aims to compare transition times measured using DC and shrinkage strain.

Methods: Samples (n = 20) 1 mm thick by 10 mm diameter of Filtek One bulk-fill restorative A2 shade (3M Oral Care) were photocured for 20 s with a single emission peak (wavelength centered at 455 nm) light-emitting-diode-based light-curing unit at irradiance levels of 890 mW/cm and 209 mW/cm, and initial sample temperature of T = 23 °C. The DC was measured in real-time using Attenuated Total Reflection (ATR) FTIR spectroscopy with a sampling rate of 13 DC data points per second. The data were analyzed within a phenomenological autocatalytic model. In addition, the axial shrinkage strain was measured using 3 samples of the RBC with the same outer dimensions and under similar experimental conditions using the bonded disk method and an interferometric technique.

Results: For the 890 mW/cm and 209 mW/cm irradiance levels, the DC with time was found to agree with the model enabling the determination of transition times of 0.66 ± 0.05 s and 2.3 ± 0.2 s, and the DC at these times of 5.5 ± 0.2% and 6.4 ± 0.2%. The maximum linear strain rate at 0.76 ± 0.01 s and 1.98 ± 0.02 s for the 890 mW/cm and 209 mW/cm irradiance levels, respectively, are within two standard deviations of the corresponding transition times.

Significance: At an irradiance level much greater than 1000 mW/cm, the photo-polymerization kinetics of a dental RBC may be too fast to be measured accurately using ATR-FTIR spectroscopy. A viable alternative to monitor the kinetics is through the measurements of the axial shrinkage strain employing the bonded disk method and an interferometric technique.
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December 2021

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

Dent Mater 2016 11 21;32(11):1322-1331. Epub 2016 Aug 21.

Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada. Electronic address:

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/cm and total energy density of 22J/cm. 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)) varied from 0.18 to 0.41MPa/s, time at which the maximum stress rate occurred (t) were between 1.42 to 3.24s and effective gel time (t) varied from 50 to 770ms. Correlations were observed between (dS/dt) and t (r=-0.946), t and filler volume fraction (r=-0.999), and between the shrinkage stress at 12h and t (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.
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November 2016