The colour measurement of ceramic samples using a commercial colour measuring device and a laboratory spectrophotometer

Abstract

The selection of shade for a porcelain crown is a subjective process and mode of fabrication is known to have an effect. This investigation sought to determine the accuracy of a commercially-available shade-matching device (IdentaColor II) when used to measure the colour of proprietary, custom-made all-ceramic and custom-made metal-ceramic samples of shades B1, A3 and D4 under different calibration and lighting conditions as well as over time. The findings from the first part of the study led to an investigation of the influence of fabrication technique on the colour co-ordinates recorded for the ceramic samples measured previously. Colour measurements were made using a laboratory spectrophotometer, Spectraflash SF600 and were used as a comparator for the IdentaColor II. The reproducibility of these colour measurements was also assessed. The fabrication variables investigated were shade, thickness of ceramic, type of ceramic sample, number of firing cycles, operator, and method of condensation. An attempt was made to determine the correlation between fabrication technique, porosity and colour co-ordinates. The results indicated that IdentaColor II used a measurement system for colour values that conformed to no known standard which made validation difficult. Differences in the colour values were found between different calibration and lighting conditions and over time but these differences were clinically inconsequential. The results from IdentaColor II were reproducible but with limitations: the colours recorded were generally lighter than the chosen standard, there was a preponderance of “A” shades and the device never recorded the intended shade of a sample. The limitations of the colour scale used by IdentaColor II made its further investigation difficult and comparisons with colour-reference standards impossible. The results for the samples which had been measured by IdentaColor II and v Spectraflash SF600 were different: (1) the colour scales used by the two devices were different, (2) the scale used by IdentaColor II had a larger range, (3) the measurements from Spectraflash SF600 were more consistent both within each data set and over time and (4) the trends in the recorded colour co-ordinates when the ceramic thickness increased were different. The colour co-ordinates (C.I.E. L*a*b*) from Spectraflash SF600 for samples ostensibly of the same shade of ceramic were affected by the mode of fabrication which in turn influenced porosity. The colour coordinates generally decreased as the ceramic thickness of metal-ceramic samples of shades B1, A3 and D4 increased and as the amount of pre-sintered slurry condensation increased of metal-ceramic tabs of shades B1 and A3. Metal-ceramic tabs were a closer colour match to the shade tabs than all-ceramic samples of the same thickness.