An In Vitro Study on Effect of Ceramic Thickness and Multiple Firings on Colour of Metal Ceramic Restorations

Abstract

Preparation of porcelain restorations that match the natural dentition has been a subject of great concern for many years. An understanding of the process by which the colour and translucency of fixed restorations are planned and obtained so as to replicate the colour of its adjacent teeth is important for achieving an esthetic restoration. This study was done to study the effect of fabrication procedures such as ceramic thickness and number of firing cycles on the colour of metal ceramic restorations. Metal ceramic samples with three different ceramic thicknesses; 0.5, 1 and 1.5 mm (N = 30, n = 10 per group) were fabricated. A3 shade of [VMK 95, VITA Zahnfabrik, Bad Sackingen, Germany] ceramic was used for the fabrication of samples. Samples were subject to multiple firing cycles and colour was measured after 2nd, 3rd, 4th, 6th, 8th and 10th firing cycle. Colour measurement was done objectively using spectrolino (Gretag Macbeth Inc., Germany) spectrophotometer. 'Repeated measures ANOVA' test was used for doing statistical analysis. No significant change was noticed in any of the four colour parameters between the baseline reading after second firing uptil the tenth firing for any of the three groups with different ceramic thicknesses. There was a consistent rise in L* or lightness of colour as the thickness of ceramic increased. Between group I and group III there was a consistent shift of a* axis towards the blue green side and there was a consistent shift in b* axis towards purple-blue with an increase in ceramic thickness. It was observed that there was a change in ΔE with a change in ceramic thickness. There was a change of about two units between group I and group II and a change of about one unit between group II and group III. Change in ΔE between group I and group III was the most significant, being about three units. It was concluded from the study that multiple firing cycles during fabrication of metal ceramic restorations do not have any effect on colour while colour varies with change in ceramic thickness.

Effect of multiple firings on optical and mechanical properties of Virgilite-containing lithium disilicate glass-ceramic of varying thickness

“…This finding was coherent with another study [ 30 ], which investigated the effect of multiple firings (3 firings only) on glass ceramics with different thickness (0.6 mm and 1.0 mm) and found that the change in translucency was only significant with thinner sections. On the other hand, other studies [ 31 , 32 ] investigated the effect of multiple firings on the translucency of ceramic materials and they found that multiple firings did not affect translucency parameters, making their findings in disagreement with our study. The reason for the different findings is that both studies used veneering porcelain build-up to framework rather than a monolithic block as the case in the present study.…”

Comparison of photographic and conventional methods for tooth shade selection: A clinical evaluation

“…Systematic education and training are necessary to be imparted to the laboratory technicians involved in the production of esthetic and accurate restorations. [ 38 ] By providing digital photographs with details of the patients tooth to be reproduced, the quality of restorations fabricated by the laboratory can be of superior quality. Even though this study did not evaluate the impact of the learning curve for the spectrophotometric color-matching system and the influence of individual laboratory technician's skill on the outcome, it would be interesting to evaluate the same in future studies.…”

Role Of Digital Photography as a Tool for Shade Selection in Prosthodontics

“…In addition, systematic education and training need to be imparted to laboratory technicians involved in production of aesthetic and accurate restorations. 23 The limitations of this study are the shade matching was done by a single dental technician and the results would have been more reliable if the study was done by more than one dental technician. The digital colour analysis of shade guides of the same manufacturer was found to be different in daylight as well as in studio environments.…”