By Dr. Eric McRory, DDS in collaboration with Nate Seimears
STEP 1: Planning
The first stage of any full-mouth case is proper planning. Planning where the teeth go starts at the dental office, by the dentist, not by hoping that the lab technician can re-create the smile that the dentist has envisioned for the patient in his/her own mind. Planning the case should be done with quality photographs of the patient prior to treatment and mounted study models. These photographs and models are used to communicate with the patient, in a pre-treatment consultation, what esthetic and functional changes are needed to achieve the treatment goals. Once the treatment goals and required treatment are reviewed with the patient, and the patient has consented to moving forward with treatment, a new set of mounted casts are obtained to do a diagnostic mock-up.
STEP 2: Diagnostic Mock-up
The desired outcome of dental treatment is first done using photographs and models. The “mock-up” can be done in an analog format, using solid casts and wax, or it can be done digitally by scanning the teeth or solid models into appropriate dental software. The dentist must use photos to determine if changes to the existing tooth length and positions are needed.
If there are changes that need to be made to tissue levels or the position of teeth, those changes are typically made at this stage of treatment by the periodontist, orthodontist, or oral surgeon. If specialty treatment is required, a new set of photographs and study models is obtained once this treatment is completed, so that final tooth morphology, incisal edge positions, and occlusion can be planned. Once again, these changes can be done with an analog wax-up or by using digital software.
Once the diagnostic mock-up is completed, the lab can create a digital model of the wax up, and from that scan can mill provisional restorations. There are various methods for making provisional restorations, but a common way to do this is re-lining of PMMA “eggshell” restorations intraorally. When using this method, it’s important that the model with the diagnostic wax-up have enough soft tissue land-area around the teeth so that the eggshells can be transferred to the mouth using a clear plastic stent. The land area acts as a stop for the plastic stent when it is seated into the mouth. The stent is used as a carrier for the eggshells with the reline material and keeps it from being under or over-seated, thus keeping the occlusal/incisal planes in the correct orientation. On the upper arch, the hard palate is the best land area, and on the lower arch, the buccal shelves and labial vestibule are good land areas.
Once the provisional restorations are completed, the esthetics have been approved, and the occlusion has been tested, photographs and mounted models of the provisional restorations are made. The upper model should be mounted with a facebow so that the incisal plane is parallel to the horizon with the dental midline centered in the facebow, thus giving the lab a level/centered reference to work from. The lower model should be mounted to the upper model in MIP, which ideally should be coincident with the FSCP (Fully Seated Condylar Position).
STEP 3: Impressions
Making accurate and clean impressions are imperative for the lab to be able to make well-fitting restorations. This is much easier to do if the gingival tissues are healthy and the impressions are not made on the same day that the teeth are prepared. Waiting a week or two after preparing the teeth for restorations gives the tissue a chance to heal, provided the patient is given good home care instructions and follows them. Obtaining accurate bite registrations are just as important as obtaining accurate impressions, as the working models need to be accurately transferred to the articulator, maintaining the same orientation as the mounted models of the provisional restorations. The provisional restorations are the lab’s reference of how to construct the final restorations. Here are the steps for obtaining bite registrations:
- Remove the lower posterior provisional restorations, leaving the anterior provisionals in place to maintain the VDO. Make a bite registration between the lower posterior prepared teeth and the upper posterior provisionals. After letting the bite registration material set up, trim the excess material away with a bur or a scalpel blade. Remove the lower anterior provisionals and place the trimmed bite registrations on the lower posterior tooth preparations. Have the patient bite gently into the bite registrations. Boxing wax can be used to keep the bite registrations from moving on the teeth as the patient practices this exercise. Make a second bite registration between the lower anterior prepared teeth and the upper provisionals. Now there is a complete set of bite registrations that can be used to mount the lower working cast to the upper provisional cast.
- Another set of bite registrations are needed to mount the upper working cast against the lower working cast. However, they must be mounted at the same VDO as the provisional restorations. This is done by removing the upper and lower posterior provisional restorations and leaving the anterior provisionals in place. The anterior provisionals maintain the proper VDO and they also help the patient bite into their FSCP, as there are no posterior occlusal interferences. Place bite registration material on the upper and lower posterior prepared teeth then guide the patient into occlusion on their anterior provisionals. After the material has set, trim the bite registrations. Remove the anterior provisionals and place the trimmed posterior bite registrations over posterior prepared teeth. Repeat the bite registration between the anterior prepared teeth with the posterior bite registrations in place, maintaining the proper VDO. It’s important to instruct the patient to bite gently so that the teeth are not compressed in the sockets and so that the bite registration material itself is not compressed. Rubbery materials such as Blue Mouse are unsuitable for this type of work. Use a rigid composite material such as Luxabite or a semi-rigid silicone material such as ACU-flow.
Now the lab has a way to mount both working casts and provisional cast against one and other:
- Upper provisionals against lower provisionals
- Upper working cast against lower provisionals
- Lower working cast against upper provisionals
- Upper working cast against lower working cast
With this information, the lab can create the final restorations with the same parameters as the provisional restorations, which the patient has tested and approved. This prevents any surprises to the patient on the seat date.