Objectives: The aim of this study was to check the influence of the thickness ratio of the different layer on the final color of PFM restorations by the use of a clinical spectrophotometer.
Methods: One ceramic system (Vita VM13, Vita Zahnfabrik, Germany) in 2M3 shade was selected for the study. 3 different total ceramic thickness (A=1,3mm; B=1,6mm; C=2,0mm) were tested. Different layering pattern (a-f) were used for the thickness ratio between the various component of the layering (Base Dentine, Dentine, and Enamel). 5 samples were fabricated for each combination of total thickness/layering pattern, for a total of 30 specimens. To control the thickness of the various layer, a proprietary steel mould was used, and each layer was checked after firing with a digital calliper. The thickness of Base Dentine was 0.30-0.90mm, Dentine 0.40mm-0.75mm, Enamel 0.20mm-0.50mm. Easyshade (Vita Zahnfabrik, Germany) clinical spectrophotometer was used for colour comparison. “Restoration” mode was selected in order to compare the specimen colour with the reference colour stored in the device.
Results:
Sample | DE | DL | DC | DH |
Aa | 0,72±0,08 | -0,54±0,08 | -0,40±0,07 | -0,66±0,05 |
Ab | 1,70±0,14 | 1,60±0,14 | 0,20±0,07 | -1,30±0,04 |
Bc | 2,32±0,13 | 0,04±0,13 | -2,18±0,13 | -2,28±0,08 |
Bd | 1,08±0,04 | -0,44±0,04 | -0,20±0,14 | -2,60±0,07 |
Ce | 4,24±0,05 | -0,36±0,05 | -3,96±0,09 | -4,26±0,09 |
Cf | 2,52±0,04 | -0,54±0,04 | -2,32±0,04 | -2,56±0,05 |
One-way Analysis of Variance of DeltaE values showed a statistically significant difference between groups (p<0,05).
Conclusions: in order to achieve the color correspondence with the selected shade, at 1.3 ceramic thickness the layer of Base Dentine should be equal to the Dentine's one leaving the thickness of the Enamel layer as thin as possible. When the ceramic thickness raise to 1.6mm and 2.0mm, the ratio between Base Dentine and Dentine should be 2:1, the Enamel layer should not exceed 0.5mm.