Written by Arvid Saunaitis, CDT, and Stephen J. Slomski, DDS Monday, 30 June 2003 19:00
Teamwork between doctors and technicians, along with trust in each other’s level of expertise, is an important aspect in the successful construction of any complicated partial denture. The doctor should not have to exert himself in figuring out the minor details involved in the construction of a partial denture framework, nor should the technician be responsible for taking an accurate impression. Instead, the doctor should skillfully perform the tasks related to the clinical phase, and the technician should do the same with the technical phase. Working as a team—and showing mutual respect and trust—will enhance the success rate of every case.
The following case illustrates what such teamwork can accomplish.
A 55-year-old male with severe attrition and wear presented for the restoration of his maxillary arch. He was missing teeth Nos. 3, 9, 13, 14, and 15. Teeth Nos. 5, 6, 7, 8, 10, and 11 had severe wear. The dilemma that presented was how to handle the existing natural teeth, which were sound periodontally but severely worn. The concern the doctor had with this patient was the likelihood of future fractures regardless of which treatment option was selected. Because the patient’s insurance coverage and financial situation prevented the reconstruction of both arches at the same time and because a round house bridge was not an option, the situation required careful planning.
The absence of teeth Nos. 17, 18, 20, 30, 31, and 32, which were needed for proper function, had over the years resulted in the severe attrition and loss of vertical dimension.
Because bonding the anterior teeth and replacing the posterior teeth with a partial denture would not restore posterior occlusion, the likelihood existed for future fractures and chipping in bonded areas. A conventional partial denture did not offer any additional benefits. After discussing the different options available, the doctor and technician decided that an all-cast partial denture was the only alternative.
The ensuing discussion between the laboratory technician and the doctor led to the following treatment plan. An all-metal framework/overlay partial denture was to be constructed. Teeth Nos. 5 through 11, instead of being restored to their natural size and form, were to be reduced. These teeth were reduced in size, removing all undercuts, much like teeth would be for metal copings. But instead of copings, the metal frame of the overpartial denture would be constructed to fit over the prepared teeth. Teeth would be processed onto this frame. The occlusion from teeth Nos. 5 through 12 would be in metal, and the vertical dimension of occlusion would be opened approximately 1 to 2 mm to allow for more natural length of the teeth. The metal occlusion would be used because it would be much stronger, especially considering the patient’s severe past wear. Also, the metal would diminish the likelihood of the teeth breaking off the partial denture (which would be more likely to happen in a conventional acrylic-based partial).
The only sure way to achieve a successful final result with a complicated partial denture such as the one discussed in this article is with the proper use of a surveyor and accurate study and opposing models. Unfortunately, because the study model is used for planning only, the care needed to maximize its accuracy is often not exercised. If the alginate impression is not poured up in the recommended amount of time, or if the impression material pulled away from the tray and a model was produced from the same impression, the accuracy of the model will be greatly compromised. Likewise, if any plaque or calculus buildup is not removed, or if there are other discrepancies in the undercut areas, a correct design of the framework cannot be determined.
|Figure 1. Articulated models showing severe attrition and wear on the maxillary arch.|
With the aid of the bite rim the doctor constructed on the opposing model, the technician articulated the study model (Figure 1). Using the back screw of the articulator, the vertical dimension was opened to allow the anterior teeth to be of proper length and the posterior teeth to have a proper plane of occlusion. The increase in vertical dimension was about 1 to 2 mm, which allowed the technician to select denture teeth of similar shape, size, and length necessary to compensate for the attrition and wear.
Estimating the minimum amount of tooth reduction needed in order to provide sufficient clearance for the partial denture, the technician reduced the teeth on the study model. To minimize the amount of reduction, setting one tooth at the time allowed the technician to reduce each tooth on the model just enough to provided needed clearance.
|Figure 2. Teeth set on prepared study model.|
Upon completion of the setup on the study model (Figure 2), the articulated models, along with a design that was determined with the use of a surveyor on the study model, were presented to the doctor for a consultation with his patient. Having the models mounted, the teeth set to the increased vertical dimension, and the required minimal tooth reduction provided the doctor with a visual image of the completed treatment plan.
|Figure 3. Teeth Nos. 5, 6, 7, 8, 10, 11 showing sharp edges and undercuts.|
After the doctor completed the necessary tooth reductions and removed all of the sharp edges and undercuts (Figure 3), an impression was taken and a new master cast was produced. Any undercut or sharp edge not removed can easily scrape off the model during the construction of the framework and contribute to the failure of the completed partial denture.
|Figure 4. New master cast rearticulated with the same opposing model to increased vertical dimension.|
At the laboratory, the articulated study model was substituted with the master cast, maintaining the vertical dimension determined earlier (Figure 4). Some doctors feel that if the vertical dimension needs to be opened, it should be done in the patient’s mouth. The authors do not find this to be true. The convincing proof is found with night guards or bruxism appliances. Years ago, when this co-author (Mr. Arvid Saunaitis) started making bruxism appliances, the models were mounted to the established vertical dimension using the bite provided by the doctor. After receiving numerous complaints about the inaccuracies of these mountings, I started to articulate the models by hand and open the vertical on the articulator. I discovered that, in many instances, when the vertical dimension is opened in the mouth, the patient protrudes, resulting in an inaccurate mounting. Mounting the models by hand and opening the vertical on the articulator, along with a few other techniques that I developed with bruxism appliances, resulted in appliances that do not require adjustments. They snap into place and have good retention without using ball clasps or wire arms.
Some doctors also believe that the vertical should be opened gradually to see what the patient can tolerate. Unfortunately, this may not be possible with every case, and experience indicates that this is not necessary. By opening the vertical just enough to restore what was lost, the patient will be able to tolerate it. In addition, by having a try-in to the restored vertical, the doctor will be able to assess by examining the freeway space.
Because the partial denture with facings and metal occlusals cannot be tried in to determine the correct centric relation and aesthetics, making changes to the completed partial denture may not always be possible. Even if the doctor and patient previously approved the setup on the study model, no one can predict how it will look in the patient’s mouth. To reduce the risk factor associated with all-cast partials, it is advisable to try in the setup before the framework is cast.
|Figure 5. Teeth set on an acrylic base with indentations reproduced of the opposing dentition.|
In this case, on the articulated master cast, an acrylic base was adapted, and by closing the articulator, indentations of the opposing teeth were produced in areas of teeth Nos. 5, 6, and 11. The denture teeth, which were previously prepared for facings and set on the study model, were reset onto the newly constructed base and sent to the doctor for a try-in (Figure 5).
|Figure 6. Doctor and the patient examine aesthetics during try-in.|
Using thin articulating paper, the doctor had the patient close into centric relation, making sure that each acrylic occlusal in the area of teeth Nos. 5, 6, and 11 had good contacts with the opposing teeth and prevented the articulating paper from pulling out. After the centric relation was determined to be correct, the doctor examined the midline and plane of occlusion, and had the shade and aesthetics approved by the patient (Figure 6).
Following this procedure eliminates any unsuspected surprises after the all-cast partial denture is completed. For example, if—during the try-in—the plane of occlusion is not correct, the doctor can use a marker to draw a line on the denture teeth in the patient’s mouth, duplicating the angulation. Also, if the patient changes his mind about the shade or wants to have certain changes made, it is less troublesome to reset the denture teeth than to make changes to the completed all-cast partial denture.
When, during the try-in, it is discovered that the centric relation is not correct, it usually means that the mounting is incorrect, the bite taken is incorrect, or the opposing model is not accurate. Each of these problems is discussed in the following text.
MOUNTING IS INCORRECT
During mounting, if the stone behind the retromolar pad on the lower model touches the stone behind the tuborosity on the upper model, there will not be proper contact with the opposing teeth, resulting in an incorrect mounting. In addition, if bubbles were present and were not removed from the model on the occlusal and cingulum surfaces of the teeth before the models were mounted, this will also result in an incorrect mounting.
BITE TAKEN IS INCORRECT
This can occur when centric relation was recorded and the patient protruded the mandible, closed to the side, or both.
OPPOSING MODEL IS NOT ACCURATE
Sometimes, when the im-pression is taken to produce the opposing model and the patient is wearing a partial denture, the partial may have been displaced, causing the opposing model to be inaccurate. In addition, because the opposing model may not seem to be as important, not enough care may go into producing it. If the opposing model is inaccurate, no matter how many resets there are, the outcome of each try-in will be no different.
|Figure 7. Partial denture with facings cemented and posterior teeth set.|
At the laboratory, after the framework was cast and finished, opaque was placed on the facial surfaces of the metal, and denture teeth were cemented using mechanical as well as chemical bond. Posterior teeth were set, and the case was sent to the doctor for another try-in (Figure 7). Because after the partial denture is processed and finished the master cast is destroyed (and a duplicated model cannot reliably have 100% accuracy), it is important to have another try-in with the framework.
|Figure 8. Facings Nos. 5, 6, and 11 constructed with metal occlusals provided the patient with extra chewing surface.||Figure 9. View in relaxed position.|
|Figure 10. View when smiling.||Figure 11. The completed partial denture required no adjustments.|
When the doctor follows procedures properly and works with a quality dental laboratory, the outcome during the try-in and after the case is finished can be predictable (Figures 8 through 11).
Mr. Saunaitis is the president of Kromex Dental Laboratory in Chicago and author and presenter of “Forum for Prosthetic Dentistry” seminars. For the past 25 years, he has been researching and conducting experiments to determine why certain procedures fail and hasdeveloped techniques that eliminate remakes. He has combined his research knowledge into groups of seminars covering different subject matter. The first full-day seminar, for doctors and technicians, examines a combination case, including designs of crowns and bridgework to allow tried-and-true aesthetic clasps to be durable and for attachments to have proper clearance. He can be reached at (773) 436-9440.
Dr. Slomski, a 1984 graduate of the University of Illinois Dental College, is a member of the American Dental Association, the Illinois State Dental Society, and the Chicago Dental Society. He is also a member of the Academy of General Dentistry, the Dental Arts Club of Chicago, and the Omicron Kappa Upsilon Dental Honor Society. He can be reached at (773) 229-1303 or (708) 449-7585.
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