Occlusion Roundtable
William “Bo” Bruce, DMD, maintains a private practice in Simpsonville, South Carolina, that is geared towards solving complex restorative and esthetic problems.
John C. Cranham, DDS, PC, maintains a private practice in Chesapeake, Virginia, that delivers unsurpassed general dentistry, cosmetic dentistry, and restorative dentistry, including TMJ therapy and dental implant services.
James R. McKee, DDS, maintains a private practice in Downers Grove, Illinois, that emphasizes predictable restorative dentistry and the diagnosis and treatment of TMJ dysfunction.
When do you use an adjustable articulator versus a quadrant tray?
William “Bo” Bruce, DMD | John C. Cranham, DDS, PC | James R. McKee, DDS
William “Bo” Bruce, DMD: That is the all-important question, which leads us to another question: why mount models with an articulator in the first place? To answer that question, it is important to understand that for most of our patients, their maximum intercuspation is not the same as centric relation. A semi-adjustable articulator allows us to reproduce the patient’s maxillary and mandibular relationship with the condyles fully seated in the glenoid fossa and, hopefully, with the disc in place. This allows us to reproduce how the mandibular arch closes into the maxillary arch with pinpoint accuracy. The maxillary arch is mounted using a facebow or Kois analyzer. It is critical that the mandibular arch is mounted to the maxillary arch using a centric relation bite record. This mounting allows the visualization of the patient’s first point of contact in centric relation and any corresponding slide to maximum intercuspation. If models are not mounted, the operator has no idea where that contact is and may misdiagnose the case. This also allows the development of good anterior guidance in centric relation to prevent unwanted eccentric contacts.
Can we use a triple tray? Sometimes we can. More than 90% of all dentistry is done in maximum intercuspation, and yes, we get away with it most of the time. Remember, utilizing a quadrant tray does not take into account any occlusal disharmony that the patient may have or condylar position. I would not suggest using quadrant trays when restoring second molars, multiple teeth, or anterior teeth. Additionally, temporomandibular joint (TMJ) health should always be evaluated before beginning treatment.
John C. Cranham, DDS, PC: Whenever I’m studying the patient’s occlusion, I’ll use a semi-adjustable articulator that accepts a facebow and allows me to mount the mandibular cast in a treatment position. During diagnostics, I’ll mount models on an articulator in centric relation to study the occlusion. In addition, I’ll also use a semi-adjustable articulator for cases in which I want to visualize the occlusion when I am doing prosthodontics.
If I’m redesigning an occlusion by working things out in provisionals and plan on carrying that out through the case, then I’m going to be doing that on a semi-adjustable articulator.
Typically, when I’m doing prosthetics or crown and bridge implant cases, more teeth are involved. Once I get beyond two or three teeth, it’s easier to work out the occlusion on the instrument. That way, when I bring it into the patient’s mouth, there is less work to do.
I’ll use triple trays and quadrant trays when I’m accepting the patient’s bite. This could be on a patient with very low functional risk who has an acceptable maximum intercuspation that I’m going to work with. Or, it could also be when I’m doing a crown or two on a patient who has been equilibrated and has ideal occlusion, and I’m comfortable getting a nice static bite in the patient’s initial occlusion and working from there.
Whenever I’m working on a quadrant type impression on an articulator that doesn’t accept a facebow, I’m always going to need to check the excursive movements in the mouth carefully, and I will probably have more work to do than if I was working on an articulator.
As dentistry moves forward, we’re going to see a push towards virtual articulation, and we’ll be doing a lot of our analysis on digital articulators. We’ll be able to see all of the excursive movements, how the teeth fit together, and how it relates to a stable seated joint position.
We’ll also be designing what we’re going to be doing more than ever before. This could be adjusting the bite, or moving the teeth, or doing wax-ups completely on the instruments before either printing or milling a provisional. The best part is that we’ll be able to digitally duplicate what we’re doing in the mouth. The profession is rapidly moving in that direction, and that is very exciting to see.
James R. McKee, DDS: I use a fully adjustable articulator for diagnostic study models. The models are obtained using an intraoral scanning device, and the digital files are sent to a lab where the models are fabricated using a 3D printer. With some of the new 3D printers that are available today, the fabrication of the models can also be done in the office by a staff member. During the diagnostic records appointment, the facebow is obtained along with an interocclusal record indexing how the mandibular arch fits to the maxillary arch in a fully seated condylar position. The models are duplicated and cross-mounted at the same vertical dimension of occlusion. After the mounting accuracy has been verified by comparing the initial points of contact on the models and in the mouth, they are finished and polished.
In terms of quadrant impressions, the landscape has changed with the advent of intraoral scanners. During the last 18 months of using an intraoral scanner, I’ve scanned the interocclusal record for most of my posterior restorations. The restorations have been fabricated from the digital files, and the results have been extremely impressive. The accuracy of the occlusal contacts and interproximal contacts has been very consistent. For anterior restorations or full-arch restorations, the scanned models are printed and mounted on a fully adjustable articulator using conventional techniques. In most cases, fully adjustable articulators are used as semi-adjustable articulators because most articulator settings are not adjusted for each individual case.
The next step in articulators is the development of a digital facebow that is easy to use and reasonably priced that could interface with both virtual and analog articulators. This and other future improvements in technology will result in increased predictably in diagnosis and treatment for our patients.
