The effect of ultrasound on the setting reaction of zinc polycarboxylate cements

Abstract

The set of glass ionomer cement (GIC) is accelerated by application of ultrasound. Although GIC has somewhat displaced zinc polycarboxylate cement (ZPC) in dental applications the latter is still extensively used. Like GIC, it provides direct adhesion to tooth and can provide F release, but is more radiopaque and biocompatible than GIC. The aim of this study is to examine the effect of ultrasound on the setting of ZPC using Fourier transform infra red spectroscopy and any interaction with SnF₂ addition. ZPC with and without SnF₂ addition (+/−S) at luting (L) 2:1 P/L ratio and restorative (R) 4:1 P/L ratio consistencies. Ultrasound is applied to the cement using Piezon-Master 400, EMS, Switzerland at 60 s from start of mixing for 15 s. The ratios of absorbance peak height at 1,400 cm⁻¹ –COO^– to that at 1,630 cm⁻¹ –COOH were measured and compared those obtained for the cement not treated with US. These values were taken at the elapsed time at which no further change in spectrum [ratio] was observed at room temperature [10–20 min]. The US results are taken at 2 or 3 min. No US: R/+S (1.09), R/−S (1.2), L/+S (1.07), L/−S (1.04); US: R/+S (1.50), R/−S (1.64), L/+S (1.38), L/−S (1.05). The results show all four ZPC formulations are very sensitive to ultrasound whether with or without SnF₂. Reducing US to 10 s produces lower initial ratios but these increase up to 10 min when very high ratios (>2) are obtained. Previous studies with restorative GICs found that 40–55 s US was needed to produce the effect found with 15 s on ZPCs. ZPC powder is more basic than GIC glass; this may account for ZPC’s greater sensitivity to US. Ultrasound may provide a useful adjunct to the clinical use of ZPC both as luting agent and temporary restorative.