9. Extrinsic energy sources affect hardness through depth during set of a glass-ionomer cement.
O’Brien T, Shoja-Assadi F, Lea SC, Burke FJ, Palin WM.
Biomaterials Unit, School of Dentistry, College of Medical and Dental Sciences, University of Birmingham, St Chads Queensway, Birmingham B4 6NN, UK.
Abstract
OBJECTIVE: To investigate the effect of various energy sources on the upper and lower surface hardness of a setting glass ionomer with various thicknesses.
METHOD: Cylindrical specimens (4 mm diameter by 1, 2 or 4 mm thickness) of a glass-ionomer cement were prepared with no applied energy source (control), by preheating GIC capsules in a waterbath prior to mixing, application of light with high irradiance or ultrasonic excitation with a scaler tip. The upper and lower surface hardness was measured 0.5 h, 4 h and 1 week following material mixing. The increase in temperature towards the lower surface of each specimen was monitored throughout the first 5 min of setting.
RESULTS: No significant differences in hardness between upper and lower surfaces or varying thicknesses were identified for control and preheated samples at any post-mix time (p>0.05). At 0.5 h post-mix, the upper surface hardness of preheated, light and ultrasonic treatments was significantly increased compared with that of the control groups. Following 4 h post-mix, the overall hardness of preheated samples was significantly greater (p<0.001) than other sample groups, which were not statistically different (p=0.684). No significant differences in hardness between test groups were identified following 1 week (p>0.05).
CONCLUSIONS: Preheating GIC capsules prior to mixing resulted in superior hardness values through depth up to and including 4 h post-mix compared with specimen surfaces treated with light irradiation or with an ultrasonic scaler tip.
Copyright 2010 Elsevier Ltd. All rights reserved.
PMID: 20302904 [PubMed – indexed for MEDLINE]
1. J Dent. 2010 Jun;38(6):490-5. Epub 2010 Mar 17.