Laser-induced acoustic emissions in experimental dental composites

A laser thermoacoustic technique was innovated to evaluate laser-induced ac oustic emissions (AEs) in experimental dental composites aged with 75% etha nol solution. Experimental composite systems of 75/25 BisGMA/TEGDMA resin f illed with 0, 12.6, 30.0, and 56.5 vol% of 8-mu m silanized and unsilanized BaSiO6 were analyzed. The sample size was 4.65 mm (diameter) x 0.5 mm (thi ck). Aging effects of immersing in 75% ethanol for up to 14 h on AEs were t hen evaluated. A continuous-wave CO2 laser was used to heat the samples. Ac oustic emissions were collected as a function of filler fraction, laser pow er, silanization, and immersion time. Onset of burst-pattern acoustic signa ls characteristic of fracturing occurred at different laser powers for diff erent tested groups. Acoustic emissions generally increased with laser powe r, in which lower laser powers produced low-amplitude (45-50 dB) signals; t he amplitude distribution (50-85 dB) became more extensive as laser powers increased. After immersion, the lower laser powers could produce the same p henomenon. The higher the filler fraction, the fewer AEs generated. A large percentage AE reduction due to silanization was noted as a function of fil ler fraction. Unsilanized specimens showed more thermal damages than did si lanized ones. (C) 2000 Elsevier Science Ltd. All rights reserved.