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
• Early systems were closed, requiring all components (trays, scanners, software, printers) from a single manufacturer, making them expensive
• Recent advances in digital scanning, 3D printers, and open-source design software have revolutionized CAD/CAM dentures and reduced costs

General Workflow

• Whether using conventional or digital methods, fabricating a denture involves three main steps
• These steps are data acquisition, design, and manufacturing

Data Acquisition

• Fabricating upper and lower dentures requires various data, including the re-creation of edentulous arches, the relationship between arches, and esthetic information
• Traditionally, data capture involves impressions, stone casts, wax rims, and bite registrations

Digital Data Acquisition

• Digital workflows can capture data in one of two ways
• A scanner is used to scan master casts and interocclusal records to digitally recreate conventional records
• An intraoral scanner is used to directly scan the upper and lower arches to create a digital master impression
• Many practitioners are still taking impressions and then scanning them
• Intraoral scanners, being cameras, are designed to capture static objects, which poses a challenge when scanning dynamic edentulous ridges
• Border molding during eccentric movements is difficult to capture accurately and repeatedly
• Mobile soft tissue leads to inconsistent tissue capture as the patient or scanner moves
• Tongue movements and limited keratinized tissue in the lower jaw make scanning the mandible challenging
• Relating the upper and lower digital arches is difficult to do in a purely digital workflow
• The CEREC system relies on a stable relationship between the upper and lower jaw with landmarks (teeth) for software orientation
• In edentulous cases, there is no stable relationship or landmarks between the upper and lower jaw, hindering data capture
• Digitally recording a patient's interocclusal record is difficult without conventional wax rims
• Scans and 3D printers can quickly and easily print accurate record bases for interocclusal record appointments

Design

• Historically, denture design involved setting teeth in wax for try-ins and manually manipulating their position on record bases
• Design software allows for digital recreation of this teeth-setting process
• Proprietary denture design software includes 3Shape, Planmecca, and Exocad
• Designs can be completed in-house or sent to a lab using physical or digital records
• Denture design follows similar principles to conventional dentures, like position over the ridge and angulation, though software can streamline the process
• Designing digital dentures currently involves more processes than CEREC for fixed prostheses

Manufacturing

• Traditionally, dentures are manufactured conventionally through flasking, investing, and processing with PMMA

Digital Manufacturing

• Two digital manufacturing methods exist: additive and subtractive
• The subtractive method involves milling a prosthesis from a solid cured block, as done with CEREC for fixed prostheses
• The additive method involves 3D printing the prosthesis layer by layer, and is relatively new at the consumer level

Subtractive Manufacturing Specifics

• Subtractive manufacturing is currently more popular for fabricating definitive complete digital dentures
• A mill creates the denture base from a monolithic block of cured resin
• Because the resin is pre-cured, there is no acrylic shrinkage during processing, leading to more accurate bases than conventional methods
• Artificial teeth can be either milled with the base or prefabricated and bonded to the milled base
• Functionally superior materials can be used compared to traditional dentures

Additive Manufacturing Specifics

• Additive manufacturing 3D prints dentures
• It is more cost-effective than subtractive manufacturing and generates less waste
• Materials and curing methods can lead to inferior dimensional stability, flexural strength, and surface hardness compared to conventional and milled dentures
• Printing, trimming, and bonding denture bases to teeth can be labor-intensive
• Additive manufacturing is best suited for immediate or interim dentures, or for fabricating record bases or monolithic wax try-ins

Advantages of Digital Dentures

• Digital dentures use materials that can be functionally superior to PMMA
• They offer a superior fit due to the absence of polymerization shrinkage compared to conventional dentures
• Patients require fewer appointments
• Data facilitates the refabrication of new dentures
• Digital dentures involve less use of expensive materials like VPS
• The digital method allows for a true mucostatic impression, as no pressure is exerted on the tissue during capture

Disadvantages of Digital Dentures

• Digital dentures can have high initial costs depending on the amount of in-house work performed
• There is a steep learning curve and the design process can be labor-intensive
• Capturing mobile or poorly keratinized tissue, especially in the mandible, can be difficult
• Difficulty capturing denture borders, centric relation, lip profile, and occlusal plane is common
• 3D printed dentures can be functionally inferior to conventional and milled methods

Detailed Workflows

• Digital technology offers numerous workflow options depending on the system, desired in-house processing, and budget
• Common workflows are the 5 Step, 3 Step, and 2 Step workflows

5 Step Workflow

• Overall closely resembles conventional denture fabrication
• The difference is that scanners allow components to be designed and manufactured digitally

5 Step Digital Workflow

• Digital workflow consists of scanning master impressions to create digital master casts, printing record bases for wax rim fabrication
• Requires scanning modified wax rims after the interocclusal record appointment to articulate digital master casts
• Followed by 3D printing or milling to evaluate the prosthesis and finally 3D printing or milling a definitive prosthesis once try-in is confirmed
• Clinical steps remain the same, but lab steps are all completed digitally

Five Step Workflow Advantages

• The easiest learning curve, because the clinical steps are virtually the same as the conventional method
• The lowest initial overhead cost does not require purchase of any hardware to complete anything in-house
• Allows incremental adoption, scanner can be purchased and scans can be sent to labs before purchasing items like printers to print trays
• Creation of milled dentures, which are stronger and have shown improved fit due to lack of resin shrinkage is possible

Five Step Workflow Disadvantages

• The method does not save clinicians much time compared to conventional methods
• The more you have the lab complete, the higher the cost, per case

Three Step Workflow

• Scanning of upper and lower arches and relating the two arches is step one
• The relationship between arches is captured using a "centric tray" to record the bite registration
• Scanning the centric tray creates articulated upper and lower models using digital design software
• A try-in denture is then designed and fabricated
• This step can be completed in-house or by a lab
• The workflow is similar to the 5-step method from then, where a try-in denture is evaluated and modified for either delivery after being milled or printed

Three Step Workflow Advantages

• The method will vastly streamline the workflow process, and save lots of chair time
• Reduces the need for costly materials such as VPS
• Can control the process from end to end, avoiding the need for a lab bill completely
• Like the 5 step method, the method can mill a denture out of very physically superior materials

Three Step Workflow Disadvantages

• Larger initial overhead cost (at minimum you need a quality intraoral scanner)
• Depending on what is desired by a practice for in house production, they may need to purchase a 3D printer, mill, design software etc
• This can save a lab bill by fabricating in-house, but it must be considered that it will take time to design and fabricate, which can be much more time consuming than CEREC for fixed
• Key information about patient measurements can be missing, such as occlusal plane relation

Two Step Workflow

• Following this workflow, the patient's patient's incisal edge line is unknown and there is nothing to orient their occlusal plane to Camper's Line
• Specific tools are required, like a papillameter (measures from the maxillary edentulous ridge to the edge of the upper lip) and a bite fork using a universal transfer system (UTS)
• The use of these tools adds overhead cost

Two Step Workflow Method

• Best used when a patient has an existing denture
• The existing denture is used as a custom tray in the first clinical step
• Completion of VPS wash is done, as well as a bite registration of the upper and lower dentures
• Scans capture the impression and bite registration into design software
• All patient needs will be recorded
• A new denture will be designed, milled, and delivered

Two Step Workflow Advantages

• Share advantages of the 3 step method, but have a better idea of the esthetics since there is an existing denture to base it on
• Quickest turnaround for a new denture, with the lowest chair time
• No need to send a patient's denture back to the lab if scans are conducted in-house

Two Step Workflow Disadvantages

• Patient requirement includes having an existing denture
• Recapturing of new centroid record is needed, as heavily worn dentures and a significantly reduced VDO may be present

Summary

• Digital technology enhances the conventional denture fabrication process
• Individual products and technologies provide varying degrees of digital integration
• Be wary of the claims of individual products
• Specific steps must be taken to ensure proper final prosthesis fabrication