The effects of lubrication on the temperature rise and surface finish of glass-ionomer cements

Object Previous work [Jones CS. Factors influencing the finishing of direct filling materials. PhD Thesis, University of London; 2002] has shown that there is an optimum load, speed and time that produced the smoothest surface when finishing glass-ionomer cement using each of four grades of a disc system. This study looks at the effects of lubrication on the temperature produced in samples of GIC when finished dry and with different lubricants using these optimal loads, speeds and times. It also compares the surface finish produced using different lubricants. Materials and methods A thermocouple connected so that it permitted the display and recording of temperature against time was inserted 1mm into the base of samples of a glass-ionomer cement. The samples were finished and polished using each of the grades of a disc system in a specially constructed jig that mimicked oral finishing. After roughening, the pre-determined optimum loads, speeds and times were used sequentially for each of the four grades of disc. Five samples were tested for each method of finishing. Firstly run dry, then in turn lubricated with water, walnut oil and petroleum jelly. After the use of each abrasive disc the surface roughness was measured using a profilometer. One of the five samples was selected at random and prepared for examination in the scanning electron microscope. All results were subjected to non-parametric statistically analyses. Results Walnut oil and petroleum jelly produced significant temperature increases compared to both dry and with water finishing. Lubricated with water significantly reduced the temperature rise compared to dry. The Ra values of 0.5 μm was obtained for the coarse and a value of 0.3 μm for the medium discs run without lubrication. With lubrication the Ra increased although there was little difference between the lubricants. However the photomicrographs showed that walnut oil and petroleum jelly caused gross morphological changes indicating major surface destruction. Conclusions The practice of finishing GICs using petroleum jelly or similar lubricant appears to be detrimental. Further experimental work needs to be done to advise practitioners on finishing GICs to produce the smoothest surface possible.