Terry Fohey, CDT
It has always amazed me how many dentists fear the day they deliver their restorations! They are not sure if the patient is going to like them or how much time they are going to have to spend adjusting them. Practicing this way can lead to disgruntled patients, remakes, reworks and high stress for the dental team. The most amazing thing about it is there is a definitive way to avoid this trap.
The Tap Roots of Success
Although the current literature will not reflect these views, there are some basic facts that will bring predictability to a level that will astound you.
Fact Number 1: The TMJ does have something to do with occlusion.
Fact Number 2: Centric relation is a repeatable position when recorded by using bilateral manipulation.
Fact Number 3: Equilibration creates harmony and stability, which translates into predictability. These observations come from 20 years of clinical experience studying success and failure. If you want predictable results, this is the treatment modality to use. Everything else is a crap shoot.
Visualize the End Result
Understanding the TMJ, centric relation and equilibration are the tap roots of success. The foundation for restorative dentistry would be to envision the end result before you ever start-just as any good architect would. The treatment goal for the dentist and technician should be to do every case three times. Every case should be done as a wax-up, an approved provisional and a final restoration. In order to achieve excellent results, the dentist and technician should have a shared knowledge base. A true master dentist understands laboratory procedures and a true master technician understands the masticatory system, thereby creating a shared knowledge base that allows them to act as an architect/builder team to design the best possible treatment for each patient.
In Figure 1, a sample of a diagnostic wax-up demonstrates that the technician has fulfilled the dentist`s treatment plan on a set of duplicate models. The areas marked with magic marker indicate where the technician has equilibrated the cast in order to achieve centric relation and maximum intercuspal position being coincident. The technician then has created the esthetic changes and returned the case with a letter explaining what he/she has done so that the treating physician can approve and begin treatment. This is a very important phase of treatment in that potential roadblocks you may be faced with are exposed. Attending to them at this point is much easier than tap dancing at the end of the chair on the day of delivery. Figure 2 illustrates a provisional (Duracryl or Lang`s) made from the wax-up. This demonstrates several points about diagnostic wax-ups (Ivory Presentation Wax-Black Marlin Dental Products):
1. All the effort is not wasted. You will be able to make a provisional using the Putty Matrix Technique (Ivoclar Siltec Putty).
2. Your alginate impression must be accurate in order for this process to work.
3. Phonetics, esthetics and lip-closure path must be worked out in the patient`s mouth.
What exactly is an approved provisional? The patient has told you he/she likes the way the provisionals look, feel and sound. Now, how do we transfer all of this information to the technician and how do we keep it relative to the patient`s masticatory system? Do we hand-articulate the temp model? Maybe in the simplest cases we can get rather close; however, most dentists are not willing to accept mediocrity for their patients. So, if you want to build your practice on clinical excellence, make sure you understand the concepts of model interchangeability.
Simple Case Model Interchangeability
Since we know that centric relation is a precise position, then it is repeatable. All bite registrations are taken in centric relation with the patient having been equilibrated prior to restorative treatment. Figure 3 illustrates a bite registration that articulates with the approved provisional model and the master die model on this simple anterior case. Note that the same bite articulates both casts. The bite registration was taken with an open vertical. The equilibration process will ensure that the teeth have equal intensity holding contacts. The same contacts will exist on the cast when you remove the bite and close the pin on the (Denar) articulator. Figures 4 and 5 illustrate the matrices and how they are relevant to both technician and dentist.
This is easy enough to perform on a simple case such as six anteriors. As a point of information, most of the restorations in our lab are completed with Classic (Ivoclar) porcelain.
Complex Case Model Interchangeability
The posteriors are prepared first; then the equilibration process is completed on the anterior teeth. Figure 6 illustrates how the bite registration (Blue Mousse) is taken with anterior contact and the patient in centric relation. This now supplies the technician with a bite that will articulate the approved provisional model, as well as the fully prepared model (Figure 7) in exactly the same position. This will allow the technician to create an anterior guide table (Figure 8) that duplicates the anterior guidance with which the patient is comfortable, as well as matrices for lip-closure path and incisal-edge position.
Transfer Base Registration-The Pearl of Predictability
Figure 9 illustrates a very common dilemma for the technician. Note the difference in interocclusal space between the approved provisional and the master die model. It illustrates that the dies actually are in front of the provisional. Figures 10 and 11 illustrate what a transfer base is and what a transfer base impression looks like. Many dentists do not understand the difficulty labs have in articulating these cases.
Actually, taking the bite is relatively easy with no posteriors in the way. What dentists do not realize is that technicians do not have the condyles to act, as the back two legs of the tripod and the cast will rock, the bites will compress or the bite will fit the approved provisional model differently than it fits the master die model, creating unnecessary challenges for the technician. The transfer bite will fit the models exactly like it fits the mouth as shown in Figure 12. The purpose of a transfer base is to support the areas that have missing teeth. The transfer bite is lined with a light-body impression material to increase its stability during the bite registration and impression process (Vinyl Poly Siloxane Impression Material-Bayer). The occlusal surface should be notched so you can remove the bites before drawing the transfer base in the impression. This process is very much like drawing a removable partial denture in an impression. These transfer bases should be fabricated before you take diagnostic models, creating the benefit of interchangeable models throughout the entire case. The choice material is Ivoclar Ivolen.
For dental team members to achieve predictable results, they must understand and implement these concepts or be willing to deliver less than their best.
About the Author
Terry Fohey, CDT, has a restorative practice of dental laboratory technology in Athens, GA, and St. Petersburg, FL. He is a motivational leader, author and seminar leader in the areas of restorative dentistry, management and communication. He is a faculty member at the Center for Advanced Dental Study in St. Petersburg, Florida, and CEO of Black Marlin Dental Products, a consulting and dental-education company. For further information, Mr. Fohey can be reached at 112 Park Avenue, Athens, GA, phone (800) 241-8614.