16.4 Communicating Case Design to the Dental Laboratory

Communicating Case Design to the Dental Laboratory

Why this matters on the INBDE: This is a named Clinical Content area in its own right. The laboratory technician cannot see the patient, cannot see the opposing arch in function, and cannot know what you intended — everything they know arrives on the prescription and in the case.

The Dentist Retains Responsibility

The dentist, not the laboratory, is legally and clinically responsible for the restoration delivered to the patient. Consequences that follow directly:

• Every returned case must be evaluated on the cast and intraorally before delivery — margins, contacts, occlusion, contour, shade, and surface finish.
• A restoration that does not meet the standard is not delivered, regardless of the laboratory's schedule or the patient's inconvenience.
• Delegating fabrication does not delegate liability. A prescription that says only "PFM crown, #30" leaves every design decision to a technician who has never met the patient — and the dentist owns the result.
• Laboratory technicians in the United States are generally not licensed and may not practice dentistry; they may not take impressions, adjust restorations intraorally, or communicate treatment decisions to patients.

Elements of a Complete Laboratory Prescription

A prescription is a legal document and, in most jurisdictions, a work authorization required by law. It should be legible, dated, signed, and retained.

Enclose what the technician needs: accurate impressions or scans of both arches, an interocclusal record, a facebow record when the case requires it, the shade photographs, a diagnostic wax-up or its matrix, and the approved provisional as a template when the provisional design has been validated in the mouth.

The single most common cause of a remake is a prescription that names a material without specifying occlusal clearance, margin design, and contour. A technician given 0.8 mm of clearance and asked for layered porcelain will either return a thin, fracture-prone restoration or one that is high in occlusion.

Communicating Material Selection

Specify the alloy category on any metal case — high-noble, noble, or predominantly base metal — because it affects cost, biocompatibility (nickel allergy), and the porcelain bond.

Infection Control and Cross-Contamination

The pathway between operatory and laboratory carries contamination in both directions.

1. Rinse impressions, bite registrations, and prostheses under running water to remove blood and saliva.
2. Disinfect with an EPA-registered intermediate-level disinfectant compatible with the material, following the manufacturer's contact time. Immersion is preferred where the material tolerates it; alginate is sensitive to prolonged immersion and is usually sprayed and bagged.
3. Package in a sealed bag, labeled to indicate that the item has been disinfected, and document that it was.
4. On return, disinfect again before intraoral placement — a case that has been handled, pumiced, and polished in the laboratory is contaminated even if it arrived clean.
5. Use fresh pumice with a disinfectant additive and a separate laboratory pan for each case; shared pumice is a documented cross-contamination route.
6. Keep the laboratory area physically separate from the operatory and the sterilization area, with its own personal protective equipment, eye protection, and local exhaust for grinding.

Regulatory and Disclosure Obligations

• Dental prostheses are medical devices under the Food and Drug Administration, and manufacturers — including dental laboratories — must be registered and follow good manufacturing practice requirements applicable to their class.
• Patients must be able to determine the origin and material composition of their device. Many states additionally require written disclosure of where the restoration was fabricated, including offshore fabrication, and of the materials used.
• Materials must be traceable; retain the laboratory's material and manufacturing documentation with the patient record.
• The dentist is responsible for verifying that a laboratory used for a case, domestic or offshore, meets these requirements.

Evaluating the Returned Case

Before the patient is seated:

1. On the cast — marginal fit, contour, contacts, absence of nodules on internal surfaces, and correspondence to the prescription.
2. Check the occlusion on the articulator against the opposing cast.

Intraorally, in this order:

1. Seat completely — verify with a disclosing medium; an incomplete seat makes every subsequent check invalid.
2. Margins — explorer for open or overhanging margins; radiograph interproximal margins when access is limited.
3. Proximal contacts — floss should pass with resistance and not shred.
4. Occlusion — static contacts first, then excursive guidance; adjust and repolish any adjusted ceramic surface, because an unpolished adjusted surface abrades the opposing dentition.
5. Esthetics — shade, translucency, contour, surface texture, with the patient's own approval before cementation.
6. Cleansability — embrasure form and pontic-tissue relationship the patient can actually clean.

Feedback closes the loop. When a case is remade, tell the laboratory precisely why, with photographs. A laboratory that never learns why a case failed will produce the same case again.