Effect of disk thickness on sintering distortion of fixed dental prostheses fabricated from unshaded
Syuntaro Nomoto1, Mizuho Hirano1, Hideshi Sekine1
1Department of Fixed Prosthodontics, Tokyo Dental College, Tokyo, Japan.
Purpose:
To evaluate the effect of disk thickness on sintering distortion in four-unit fixed dental prostheses (FDPs) fabricated from unshaded multi-composition layered (MCL) zirconia disks.
Methods:
Unshaded MCL disks with different thicknesses (14, 18, 22, and 26 mm) were used to fabricate simplified four-unit FDPs. For each thickness, FDPs were milled from three vertical regions within the disk. Areas I, II, and III corresponded to the enamel side, central region, and cervical side, respectively. Seven FDPs were prepared under each condition. The FDPs were scanned before and after final sintering under manufacturer-recommended conditions. Using computer-aided design software, this study analyzed buccolingual midline cross-sections to quantify pre- to post-sintering changes in the external angle α.
Results:
The disk thickness and milling area significantly affected the sintering distortion, with a significant interaction, indicating that the milling area effect differed according to the disk thickness. Area I showed increased angle α, whereas Area II showed decreased α across all disk thicknesses. Area III showed the greatest increase in α in the 26 mm group. The 14 mm disk, closest to the prosthesis height, showed a smaller area-dependent variation than the 18 and 22 mm disks.
Conclusions:
The disk thickness influenced the magnitude and direction of sintering distortion in the four-unit FDPs fabricated from unshaded MCL disks. This pattern may be associated with the differences in the range and relative proportions of compositional layers incorporated into the prosthesis. A disk thickness close to the prosthesis height was associated with a smaller area-dependent variation.
