Reference-based surface agreement of customized implant abutments: a comparison of two workflows

This in vitro study compared reference-based surface agreement of customized implant abutments fabricated using an industrial computer numerical control (CNC) machining workflow (CG) and a dental computer-aided design/computer-aided manufacturing (CAD-CAM) milling workflow (MG).

A resin model with molar, premolar, and incisor implant sites was used. Sixty abutments (30 per workflow) were organized into 10 three-abutment scan datasets per workflow. CG specimens were machined from titanium bar stock, including the implant-abutment connection, whereas MG specimens were milled from pre-milled blanks only above pre-machined connections. Scans were aligned to a computer-aided design (CAD)-derived reference using retained non-abutment tooth structures. Deviation was assessed using root mean square (RMS, mm) and in-tolerance rate (inTOL, percentage of points within ± 50 µm). Curve-derived tooth-level RMS was the primary endpoint.

Overall surface-based RMS was lower in CG than in MG, whereas inTOL showed near-ceiling values in both groups. In the tooth-level analysis, CG showed lower RMS and higher inTOL in the molar and premolar conditions; neither outcome differed significantly in the incisor condition. In the curve-level analysis, differences favoring CG were concentrated in axial regions, whereas differences favoring MG were limited to molar Curve 2 (RMS and inTOL) and molar Curve 8 (RMS only).

Under laboratory conditions, CG showed closer agreement on the measured surfaces, particularly in the molar and premolar conditions and in the axial region. Because the workflows differed in starting stock and machining scope, these findings represent workflow-level differences and do not establish clinical superiority.