CAD/CAM Denture Fabrication

CAD/CAM History

• CEREC was introduced in 1985.
• The first recorded use of CAD/CAM to fabricate a complete denture was in 1994.
• Initially, CAD/CAM systems were closed, requiring the purchase of all components from a single manufacturer.
• Advances in digital scanning, 3D printers, and open system software have revolutionized CAD/CAM dentures recently.

General Workflow

• The fabrication of a denture requires three general steps: data acquisition, design, and manufacturing.

Data Acquisition

• Data needed to fabricate an upper and lower denture includes recreation of the upper and lower edentulous arches and relationship of the arches and esthetic information.
• Conventionally, data acquisition is performed with impressions, stone casts, wax rims, and bite registration.
• In digital workflow, data is acquired by scanning master casts with interocclusal records or directly scanning the upper and lower arches with an intraoral scanner.
• Directly scanning edentulous arches presents challenges because intraoral scanners are designed for static objects.
• Capturing denture borders is difficult due to border molding movements.
• Soft tissue movement and limited keratinized tissue in the lower jaw complicate scanning.
• Relating digital models of the upper and lower arches is difficult in a purely digital workflow.
• Unlike fixed prostheses, edentulous cases lack stable relationships or landmarks between the upper and lower jaw for the software to use.
• Digitally recording a patient's interocclusal record is difficult and requires conventional wax rims without an existing denture.
• Scans and 3D printers, however, can produce record bases quickly for interocclusal record appointments.

Design

• Historically, denture design involved setting teeth in wax.
• Design software can recreate the "setting teeth" process digitally.
• Multiple proprietary denture design software versions exist, such as 3Shape, Planmecca, and Exocad.
• Dentures can be designed in-house or sent to a lab.
• Digital denture design follows conventional principles but is more streamlined.
• Designing digital dentures is more involved than CEREC for fixed prosthetics currently.

Manufacturing

• Conventional denture manufacturing involves flasking, investing, and processing with PMMA.
• Digital denture manufacturing uses additive (3D printing) or subtractive (milling) technologies.
• Subtractive manufacturing involves milling a prosthesis from a solid block and is used for CEREC fixed prostheses.
• Additive manufacturing is relatively new and involves 3D printing the prosthesis layer by layer.
• Subtractive manufacturing is popular for definitive complete digital dentures.
• A mill fabricates the denture base from a monolithic block of cured resin after the design is complete.
• Cured resin bases do not shrink during processing, which make them more accurate than conventional methods.
• Artificial teeth are milled with the base or are prefabricated and bonded to the milled base and can be milled from functionally superior materials.
• Additive manufacturing uses methods to 3D print dentures.
• Additive manufacturing is cost-effective and produces less waste.
• Additive manufacturing has inferior dimensional stability, flexural strength, and surface hardness compared to conventional and milled dentures because of the materials that are used and cured.
• Additive manufacturing still requires labor to print, trim, and bond denture bases to teeth.
• Additive manufacturing is best for immediate or interim dentures, record bases, or wax try-ins.

Digital Denture Advantages

• Can use materials functionally superior to PMMA.
• Superior fit due to no polymerization shrinkage.
• Fewer appointments.
• Easy refabrication with digital records.
• Less expensive materials such as VPS are used.
• True mucostatic impression because no pressure is exerted on the tissue being captured.

Digital Denture Disadvantages

• High learning curve with labor intensive design.
• Capturing mobile or poorly keratinized tissue is difficult, especially in the mandible.
• Capturing denture borders, centric relation, lip profile, and occlusal plane is hard.
• 3D printed dentures are functionally inferior to conventional and milled ones.
• Depending on the amount of work performed in-house, the initial costs can be much higher.

Detailed Workflow Options

• There are many possible workflow options that use digital technology due to system differences and decisions about in-house versus lab processing.
• Three workflow options are: 5-step, 3-step, and 2-step.

5-Step Workflow

• Similar to conventional denture fabrication, but uses scanners to design and manufacture the components.
• The digital workflow is to scan master impressions to create digital casts, print record bases for wax rims, scan modified wax rims after interocclusal record appointment, articulate casts, and 3D print or mill try-in and definitive dentures.
• In the 5-step method, clinical steps are the same, but lab steps are all completed digitally.

5-Step Workflow Advantages

• The learning curve is easiest because clinical steps are similar to conventional methods.
• Lowest initial overhead because no hardware is required if not completing any work in-house.
• Easy to ease into the digital process by scanning, sending to lab, and purchasing more equipment.
• Milled dentures can be created, which are stronger and have better fit.

5-Step Workflow Disadvantages

• Minimal time savings.
• Higher the lab complete, the higher the cost per case.

3-Step Workflow

• The clinical step is to scan upper and lower arches and relate them using a centric tray to record bite registration.
• The lab step is to scan the centric tray and use digital scans and design software to create models and a try-in denture.
• After the try-in is evaluated and modified, the final denture is milled or printed.

3-Step Workflow Advantages

• Streamlines workflow.
• Saves chair time.
• Reduces costly materials such as VPS.
• Process can be controlled end-to-end to avoid lab bills.
• Dentures can be milled from physically superior materials.

3-Step Workflow Disadvantages

• Larger initial overhead (intraoral scanner required).
• May require additional 3D printer, mill, design software.
• In-house fabrication is more time-consuming than CEREC for fixed.
• Requires specific tools like a papillameter and bite fork with a universal transfer system (UTS).

2-Step Workflow

• Suitable for patients with existing dentures.
• The existing denture is used as a custom tray, and VPS wash and bite registration are captured in the first clinical step.
• This information is scanned with patient feedback, and a new denture is designed, milled, and delivered.

2-Step Workflow Advantages

• A better idea to capture esthetics.
• Quickest turnaround and lowest chair time.
• No need to send the patient's denture to the lab if scans are done in-house.

2-Step Workflow Disadvantages

• An existing denture is required.
• New centric record may need to be captured if denture worn or VDO is reduced.

Summary

• Digital technology streamlines denture fabrication.
• Digital technology has varying levels of digital integration
• Be wary of individual product claims, as essential information is needed to fabricate a prosthesis without guessing.