Comparison of 3D Accuracy of Conventional Cast Metal to Milled Zirconia Implant-Supported Full-Arch Fixed Dental Prosthesis Frameworks.

PURPOSE: To compare the 3D accuracy of conventional and digital workflows in the fabrication of implant-supported full-arch fixed dental prosthesis (FAFDP) frameworks for an edentulous mandible.

MATERIALS AND

METHODS

A heat-polymerized polymethyl methacrylate (PMMA) master model simulated an edentulous mandible to be restored with a fixed prosthesis supported by five implants (implants A to E). A conventional open-tray, splinted-coping polyether impression was poured with type 4 dental stone to produce a stone model, which was scanned with a dental laboratory scanner to produce a virtual model. Zirconia (Zr) full-contour (ZFC) (n = 5) and Zr cutback (ZCB) (n = 5) frameworks were fabricated with CAD/CAM. The stone model was used as a working model to fabricate conventional noble metal frameworks (CNB) (n = 5). Each test framework was attached to five implants with application of 35-Ncm torque. Test models were fabricated with type 4 dental stone and were allowed to set completely before removing the test frameworks. Centroid positions and central axes of the implants in master and test models were measured with a coordinate measuring machine and compared. The local coordinate system comprised implant A (right posterior implant) as the origin; implants A, C (central incisor implant), and E (left posterior implant) as the xy-plane; and implants A and E as the x-axis. Three linear distortion parameters (dx, dy, and dz), one global linear distortion parameter (dR), two angular distortion parameters (dθx and dθy), and 3D distance distortion values (ΔR and %ΔR) were assessed.

RESULTS

The magnitude of mean dx, dy, dz, and dR values ranged from 39.9 ± 26.4 µm (CNB-B) to 263.3 ± 94.6 µm (CNB-E) for dx; from 56.9 ± 5.4 µm (ZFC-B) to 124.5 ± 37.6 µm (ZCB-C) for dy; from -8.3 ± 27.6 µm (ZFC-D) to -24.6 ± 17.3 µm (ZCB-D) for dz; and from 80.6 ± 29.4 µm (CNB-B) to 263.3 ± 94.6 µm (CNB-E) for dR. The magnitude of mean dθx and dθy ranged from 0.025 ± 0.486 degrees (ZFC-C) to 1.490 ± 0.383 degrees (CNB-C) and from -0.050 ± 0.171 degrees (ZCB-B) to 1.263 ± 0.501 degrees (ZFC-C), respectively. One-way analysis of variance (ANOVA) found differences among groups for dx, dy, dz, dθx, and dθy at some implants, but there was no clear pattern on the poorest group. For global linear distortion (dR), CNB-D fared the worst. However, CNB exhibited the worst accuracy in ΔR and %ΔR for all reference distances, except implant A to implant E.

CONCLUSIONS

There were no differences between ZFC and ZCB for all parameters. CNB fared poorest for ΔR and %ΔR for three of the four reference distances (A-B, A-C, and A-D), as well as for dR for one of five implant positions (implant D).