Reverse scan body: The scan pattern affects the fit of complete-arch prototype prostheses

Area of Science:

• Digital Dentistry
• Prosthodontics
• CAD/CAM Technology

Background:

• Complete-arch implant-supported prostheses require precise fit for optimal function and longevity.
• Extraoral scanning with reverse scan bodies offers an alternative to intraoral scanning for digital fabrication.
• Evaluating different scanning strategies is crucial for refining digital workflows.

Purpose of the Study:

• To determine the impact of various extraoral scan patterns on the fit of implant-supported complete-arch prototype prostheses.
• To assess the efficacy of a complete digital extraoral protocol using reverse scan bodies.

Main Methods:

• A reference mandibular cast with multi-unit abutment analogs was used.
• A polymethylmethacrylate interim prosthesis was scanned using three extraoral patterns: occlusal (O-group), intaglio (I-group), and helix (H-group).
• CAD/CAM technology was employed to mill prototype prostheses, and their fit was evaluated using screw-resistance and radiographic methods.

Main Results:

• The occlusal scan pattern (O-group) yielded a 100% prosthesis fit.
• The intaglio (I-group) and helix (H-group) scan patterns resulted in 80% and 53% fit, respectively.
• The differences in fit between the scan patterns were statistically significant (p = 0.008).

Conclusions:

• The occlusal scan pattern is superior for achieving accurate fit in milled prototype prostheses fabricated via extraoral scanning with reverse scan bodies.
• This digital workflow eliminates the need for intraoral implant data acquisition.
• Optimizing scan patterns is key to successful CAD/CAM fabrication of implant prostheses.