Dimensional changes of three-unit implant-supported zirconia frameworks from scanning to sintering

Passive fitness of implant frameworks are important factors for long-term success of dental implant restorations. The aim of this in vitro study was to evaluate the dimensional changes of implant supported zirconia frameworks fabricated by Zirkonzahn CAD/CAM system during fabrication stages. The master model of 3-unit FDP was made of two implant abutments. The master model was scanned 12 times and data were saved as STL files (scanning groups). Using semi-sintered zirconia,
12 real-size frameworks (milling groups) and 12 enlarged frameworks which were then sintered (sintering group) were made in this system. Dimensions of master model and specimens of each stage were measured. The dimensional changes in respect to master model were calculated. Data were analyzed using Repeated measures ANOVA, independent t-test, and paired sample t-test at α=0.05 of significance. The milling stage showed greater dimensional changes comparing to the other stages (P<0.05). At all stages, the dimensional changes of premolar abutment height were greater than canine (P<0.001). Within the limitations of this study, the results suggested that the fabrication stages and size of abutments had significant effects on the dimensional changes of zirconia frameworks.