12.4 CAD/CAM Restorations, Digital Workflows & Laboratory Case Management

12.4 CAD/CAM Restorations, Digital Workflows & Laboratory Case Management

Quick Answer: Competencies 5.11.6 and 5.11.7 cover computer-generated prostheses and restorations and the assistant's role in preparing, packaging, transferring digital information for, delivering and receiving laboratory cases. In CAD/CAM (computer-aided design / computer-aided manufacturing), the preparation is captured with an intraoral scanner (or a scanned impression or model), the restoration is designed in software, and it is milled from a block or 3D-printed. This can happen chairside on the same day or in a laboratory. Every lab case needs a complete written prescription (work authorization). Physical items are disinfected and labelled both outgoing and incoming. Digital files containing personal health information are sent through secure, encrypted channels.

1. The CAD/CAM Workflow

1. Data capture: an intraoral scanner records the preparation, the adjacent and opposing teeth, and the bite. Retraction, dryness and good isolation matter just as much as for a conventional impression, because scanners cannot "see" through blood, saliva or tissue covering the margin. Alternatively, a conventional impression or stone model is scanned in the laboratory.
2. Design (CAD): the software proposes a restoration from the scan. The dentist or technician adjusts margins, contacts, occlusion and anatomy.
3. Manufacture (CAM):
   • Subtractive milling: the restoration is cut from a prefabricated block or disc of lithium disilicate, zirconia, feldspathic or hybrid ceramic, composite resin or PMMA (for provisionals).
   • Additive manufacturing (3D printing): models, surgical guides, custom trays, splints, provisionals and some final restorations are built up layer by layer from resin.
4. Finishing: zirconia is sintered in a furnace (it shrinks as it densifies). Lithium disilicate may be crystallized in a furnace. Restorations are then stained, glazed or polished.
5. Delivery: try-in and cementation follow the same sequence as any indirect restoration (section 12.1): contacts, margins, internal fit, occlusion, then cementation and cleanup.

Digital file formats: scans are commonly exported as STL (surface geometry) or as formats that also carry colour and texture (for example PLY). Radiographs and CBCT use DICOM. Files must be named so they cannot be confused between patients.

2. Other Digital Prosthodontic Applications

• Digital dentures: scans or impressions are used to design and mill or print denture bases and teeth.
• Implant planning: CBCT data and intraoral scans are merged to plan the implant position and to print a surgical guide.
• Orthodontic models and aligners (section 15.5) are printed from scans.

3. The Laboratory Prescription (Work Authorization)

The dentist signs the prescription. The assistant checks that it is complete before the case leaves the office. It should include:

• the dentist's name, address, phone and registration number
• the patient's name or a case identifier
• the date sent and the date needed
• the tooth numbers (FDI) and the type of restoration or appliance
• the material, the shade and the stump (die) shade
• the margin, pontic and occlusal design
• any special instructions, such as photographs, a facebow or a custom shade appointment
• a list of every item enclosed
• the dentist's signature.

Keep a copy of the prescription in the patient's record. Labs commonly return the case with an invoice or a certificate listing the materials used. A prescription that is incomplete or unclear delays the case or produces the wrong restoration.

4. Preparing, Packaging and Sending a Case

1. Disinfect impressions, bite registrations, try-in dentures and appliances (section 11.1 and 5.4). Rinse, disinfect with a compatible intermediate-level disinfectant for the required contact time, rinse again, and bag and label each item "disinfected".
2. Pour or protect: pour models if the office does this, or protect the impression in a rigid container so that it is not distorted in transit (alginate should be poured, not shipped).
3. Package each item securely in a labelled case box with the prescription in a separate, clean envelope (not in the same bag as the impressions).
4. Digital cases: upload scans through the lab's secure portal or encrypted transfer. Include only the personal information needed. Confirm receipt, and note the upload in the patient's chart.
5. Record and track: log the date sent, the expected return date and the appointment booked for delivery. Schedule the patient's appointment only after confirming the lab's turnaround time.

5. Receiving a Case from the Laboratory

1. Check the case against the prescription: correct patient, tooth, material and shade, and all enclosed items returned.
2. Inspect for damage, voids, rough areas and fit on the model. Report problems to the dentist and the lab before the patient arrives.
3. Disinfect the restoration or appliance before try-in, using a method compatible with the material.
4. Store the case in a labelled case pan until the appointment, and record its arrival.
5. After delivery, file the lab slip or certificate in the patient's record, and return any items to the lab if remakes are needed.

6. Complications and Home-Care Instructions for Prosthodontic Cases (5.11.8, 5.11.9)

Home-care instructions:

• Clean around crowns and under bridge pontics with floss threaders, superfloss or interdental brushes.
• Avoid chewing ice or very hard foods.
• Wear a night guard if the patient grinds.
• Report a loose restoration, a change in bite or sensitivity that does not settle.
• Keep regular recall visits so that margins can be checked.