Effect of the repeated firing on Dimensional Stability of Porcelain

Objectives: The effect of the repeated firing procedure in the porcelain on the dimensional stability was investigated using the digital photogrammetry which can measure the deformations in the three-dimension at micron level. Methods: Twenty metal-supported (Ivoclar classic, Vivadent) and twenty metal free (IPS Empress II, Vivadent) specimens were prepared. A mould composed of 4 parts to be used in preparing 1.5 mm thick standard porcelain specimens on die was prepared. Four reference point on the occlusal and four reference points on the axial were determined. Following the repeated-firing between the determined points in two different porcelain systems, the area, the circumference and the vectoral lengths were measured. The coordinates of the determined points on the specimens were determined using Pictran D and Pictran B programs. Repeated Measurements Anova test was administered to these values. Whether there was a difference between the first, second, and third firing values of the specimens, Paired T and Wilcoxon tests were used. In order to determine if there was difference between porcelain systems, an independent t and Mann Whitney U tests were used. Thus it was tested whether there was any difference between the percentages of the shrinkage in the metal supported and metal free specimens. Results: The repeated-firing procedure affected the dimensional stability. Axial sides were affected greater than the occlusal sides during the repeated-firing procedure in terms of dimensional stability. There was no difference between the two porcelain systems. Conclusions: The repeated firing during porcelain production causes some changes in the porcelain. The changes in the dimensions of the porcelain may cause undesired results in the occlusion and contour. Knowing the effects of the firing contributes significantly to related disciplines guiding the clinician and technicians.

This study is supported by Selçuk University Scientific Research Coordination (BAP).