CAD-CAM milled dentures: The Geneva protocols for digital dentures

Abstract

This technical report describes 2 workflows for fabricating computer-aided design and computer-aided manufacturing (CAD-CAM) milled complete dentures (CDs). The first technique illustrates a manufacturer-independent workflow using conventional clinical steps and a novel, custom modified tray to successfully fabricate CAD-CAM milled CDs. The second technique highlights a nearly digital workflow for manufacturing a CAD-CAM milled CD and a milled resin interim removable partial denture.

Initial attempts to fabricate complete dentures (CDs) with computer-aided design and computer-aided manufacturing (CAD-CAM) technology began in the 1990s ; since then, there has been an evolution of the techniques and the associated technologies. The infusion of CAD-CAM techniques into CD fabrication methods has led to the evolution of modified and easier clinical protocols, the use of materials with improved properties, better fit and retention of the CDs, reduction in the chairside and laboratory times, and overall reduction in clinical and laboratory costs. High patient and clinician satisfaction with CAD-CAM CDs has been reported.

The CAD-CAM clinical protocols used are modified versions of the conventional clinical steps followed during the fabrication of CDs. Although promoted by various manufacturers as being more straightforward and easier, the CAD-CAM protocols require extended time to learn the procedure and to digitize the analog clinical procedures. Elaborate instruments, depending on the manufacturing system, are often required to carry out these novel clinical protocols. Despite the numerous advantages, the currently practiced CAD-CAM methods for CDs still have limitations. Nevertheless, these protocols are rapidly evolving, and newer alternative protocols incorporating the conventional clinical steps in a manner best suited to satisfying all the required criteria for the successful fabrication of CAD-CAM CDs have been developed. The newer protocols continue to use analog clinical steps that are then digitized to accomplish the prosthesis. Attempts to use optical scans combined with conventional clinical procedures have demonstrated some success ; however, a completely digital clinical workflow for the fabrication of CDs has yet to be demonstrated.

The purpose of this technical report was to demonstrate an alternative, manufacturer-independent, clinical workflow that has been routinely used by the Clinic for Gerodontology and Removable Prosthodontics at the University of Geneva for manufacturing CAD-CAM milled CDs. This report further aimed to showcase a nearly digital workflow for fabricating a clinically acceptable CAD-CAM fully milled maxillary CD and a fully milled mandibular resin removable partial denture (RPD), without the use of any analog clinical procedures.

Technique 1: the Geneva protocol

This manufacturer-independent alternative clinical technique uses a modified clinical protocol to fabricate maxillary and mandibular CDs in just 3 clinical visits, by using a CAD-CAM milling technique. The various clinical procedures in the respective visits are described below:

Visit 1:

  • 1.

    Make preliminary impressions using irreversible hydrocolloid impression material (Blueprint; Dentsply Sirona) and stock impression trays (Schreinemakers).

  • 2.

    Measure the anterior and posterior heights of the existing dentures, if present ( Fig. 1 ), by using calipers (Inox; KNUTH GmbH) or a Gutowsky gauge (Mitutoyo Inc) and the upper lip length by using a Papillameter (AvaDent; Global Dental Science Europe BV).

    Figure 1
    Initial situation. A, Completely edentulous maxilla. B, Completely edentulous mandible. C, Measuring anterior height of existing denture.
  • 3.

    Pour dental stone in casts (Elite; Zhermack S.p.A.) and fabricate modified custom trays by using light-polymerizing polymethylmethacrylate resin (Profibase; VOCO GmbH) with integrated occlusal wax rims (Wax bite rims; Erkodent Erich Kopp GmbH). Position a small tray handle in the anterior part (approximately the width of 2 maxillary central incisors) as seen in Figure 2 A, B. Fabricate the wax rims to the measured height of the existing denture and/or the upper lip length.

    Figure 2
    Modified custom trays. A, Maxillary custom tray with occlusal rim and integrated handle. B, Mandibular custom tray with occlusal rim and integrated handle. C, Adjusting custom tray. D, Adding wax over resin tray handle to establish lip support.

Visit 2:

  • 4.

    Verify the fit of the modified custom trays in the mouth and make corrections if necessary ( Fig. 2 C, D). Evaluate the height of the maxillary tray handle and the occlusal rim; arbitrarily approximate it to the length of the upper lip. Then, verify the mandibular tray in the same manner and restrict the mandibular tray height to the lower lip.

  • 5.

    Border molding in a single step ( Fig. 3 A) performed by using a medium-viscosity elastomeric impression material (Impregum; 3M ESPE). Check for any tray exposures and trim the exposed regions of the impression ( Fig. 3 B, C); repeat the procedure until border molding is complete and satisfactory.

    Figure 3
    Single-step border molding and definitive impressions. A, Initial single-step border molding for maxilla. B, Tray exposures detected and marked. C, Correcting tray exposures. D, Completed definitive impression of intaglio surface.
  • 6.

    Make the definitive impressions ( Fig. 3 D) by using a low-viscosity elastomeric impression material (Impregum; 3M ESPE).

  • 7.

    Establish the labial fullness, occlusal plane, and occlusal vertical dimension and record the arbitrary centric jaw relation (CR). Then, verify the CR with gothic arch tracing by using intraoral tracers ( Fig. 4 A-C). The gothic arch tracing is an essential step for fragile or functionally impaired edentulous patients. It can be omitted at the discretion of the clinician in younger edentulous patients.

    Figure 4
    Jaw relations. A, Establishing anterior plane of occlusion with Fox plane. B, Establishing posterior occlusal plane. C, Verifying labial fullness, support, and esthetics. D, Verifying centric relation using gothic arch tracing.
  • 8.

    Mark the reference lines (midline and canine line) on the wax rims and register the CR using an elastomeric occlusal registration material (Jet Bite; Coltène). Note the shape, size, form, and shade of the tooth. Obtain relevant photographs.

  • 9.

    Scan the block comprising the definitive impressions and the jaw-relation records and store the resultant scan data in standard tessellation language (STL) file format. Transfer the STL files, photographs, and laboratory work authorization form with specific instructions to the digital denture laboratory through a connection software program (AvaDent Connect; Global Dental Science Europe BV).

  • 10.

    Import the scan data into a design software program (AvaDent Design; Global Dental Science Europe BV), align the scans, and establish the peripheral boundaries ( Fig. 5 A-C).

    Figure 5
    Digitizing clinical records and virtual tooth arrangement. A, Scanned maxillary edentulous impression. B, Scanned mandibular impression. C, Scanned jaw relation record. D, Digital preview of virtual tooth arrangement.
  • 11.

    Generate a virtual tooth arrangement for a digital preview ( Fig. 5 D). Evaluate the digital preview and modify if necessary.

  • 12.

    Transfer data to a CAM software program, mill the prostheses, and finish and polish the dentures.

Visit 3:

  • 13.

    Inspect the received dentures for manufacturing defects or flaws ( Fig. 6 A).

    Figure 6
    Definitive result. A, CAD-CAM milled complete dentures. B, Intraoral retracted frontal view of inserted dentures. C, Frontal view of smile with dentures in place. D, Profile view of smile with dentures in place. CAD-CAM, computer-aided design and computer-aided manufacturing.
  • 14.

    Deliver the dentures after clinical adjustments ( Fig. 6 B-D); give postinsertion instructions along with denture hygiene and maintenance information to the patient.

Technique 2: a nearly digital workflow for fabricating CAD-CAM CDs

Construction of a CAD-CAM milled maxillary CD and a CAD-CAM milled mandibular resin interim RPD by using a nearly digital workflow is presented.

Visit 1:

  • 1.

    Scan the patient’s completely edentulous maxillary and partially edentulous mandibular arches by using an intraoral scanner (3Shape TRIOS; 3Shape A/S) ( Fig. 7 ). During scanning, approximate the peripheries and retract the soft tissues and frenal attachments with the thumb and index finger. Obtain assistance from a second operator during the scanning of the mandibular arch.

    Figure 7
    Initial situation and optical scans. A, Completely edentulous maxilla. B, Optical scan of edentulous maxilla. C, Partially edentulous mandible (Kennedy Cl. II div. 2). D, Optical scan of edentulous mandible.
  • 2.

    Measure the lip length by using a Papillameter (AvaDent; Global Dental Science Europe BV). Verify the lip length measurement in different views; exercise care to maintain the labial fullness while establishing the lip length ( Fig. 8 ).

Jan 12, 2020 | Posted by in Prosthodontics | Comments Off on CAD-CAM milled dentures: The Geneva protocols for digital dentures
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