Marginal and internal fit of CAD/CAM frameworks in multiple implant-supported restorations: Scanning and milling error analysis.

Abstract

Despite computer-aided design and computer-aided manufacturing (CAD/CAM) technology improving prosthesis fit, errors inherent to digital workflow still exist. To measure scanning/milling errors, and identify factors influencing marginal (MD) and internal discrepancy (ID). After scanning, 22 conical abutments in 5 master casts, 6 suprastructures with more than 2 implants (3, 4, and 6) were CAD designed. Angular deviation and errors in the vertical/horizontal planes were analyzed using a coordinate measuring machine (CMM). CAD suprastructures were milled and MD/ID evaluated with micro-computed tomography (CT) and optic microscopy (OM) at one screw test (OST) and final fit test (FFT). Mean scanning errors, at the vertical/horizontal planes, and angulation error were 3 μm ± 13, 44 μm ± 34, 0.3° ± 0.2°, respectively. Angulation errors nearly double in structures >3 abutments (0.26°vs 0.4°). OM MD in FFT/OST was 57.7 μm ± 13.9/100.7 μm ± 34.6, respectively. Micro-CT FFT-MD was 38.9 μm ± 12.8. Lineal/perimetral ID was 49.6 μm ± 11.9 and 108.2° ± 41.8, respectively. Structures >3-implants were 2.3 times more likely to present higher MD (CI95%:0.4-13.6). Nearly all the internal horizontal gap was due to scanning errors (44 of 49.6 μm). Horizontal scanning errors were three times more likely to present greater ID (CI95%:0.5-17.4). Horizontal plane scanning errors are greater than vertical errors. Scanning angulation/milling errors are higher for suprastructures>3implants. Scanning/milling errors are associated with ID/MD, respectively, leading to micro-gap formation. A CMM reduces scanning errors in >3-implant-frameworks before milling the final piece.