Inside Dental Technology
July/August 2011, Volume 2, Issue 7
Published by AEGIS Communications
Replacing What Has Been Lost
With a solid understanding of prosthetic principles, technicians can replicate form and function.
"That which is striking and beautiful is not always good, but that which is good is always beautiful." ~Ninon de L’Enclos
This quote is so true, and so applicable to our industry of prosthetics, when we attempt to replace what is lost with our materials and knowledge. And, many times, we can lose sight of nature and function to restore, using only the eye, what looks good to us. We can admire the beauty and yet have no eye for the beauty of function.
I hope to illustrate in this article how we can achieve both, which, in my opinion, is what nature intended. Yes, there can be dysfunction in nature, but many times in this day and age everyone wishes to have the "Hollywood Smile." Perhaps we should remember that Hollywood is full of special effects that are not real, but let us see if we can work with nature to construct a beautifully functional smile.
It is most advantageous if we can receive a fully contoured wax rim from the dental office. But because this is not always the case, I will explain two different methods to help us achieve success; the first method is for the contoured rim, and the second is for an uncontoured rim or no rim at all. The second method may sound ridiculous, but not having a contoured rim is much the same as having no rim at all. The only thing we may have is an occlusal relationship, such as it is.
Many times we do not exploit all of the benefits of a contoured wax rim. I know I did not for years; now I feel I am getting a better grasp on all the benefits that are given to us. And, often we do help or instruct our accounts on how to give us this treasure chest of information. We should definitely study the technique and be able to teach it to our dental offices.
So we begin with the contoured wax rim, and we are going to assume that the dental office has taken a bite registration using the bi-manual method per Dr. Pete Dawson, or an intraoral bite recorder, or Dr. Massad’s method. There are other methods, but these three have seemed to work well for me over the years. Now that we have an occlusal registration, we have properly articulated the models set to the "Campers Line," on a Bonwill-friendly semi-adjustable articulator, hopefully using a facebow (Figure 1).
These next two steps can make all the difference in the world if you wish to use all the information the contoured rim can give you.
First, with the mandibular rim removed, or if the mandibular arch is dentate, proceed to the next step. Hand-mix a small amount of Optosil® Lab Putty (Heraeus, www.heraeusdentalusa.com) and place it on the anterior section of the lower arch, and slowly close the articulator with the maxillary rim in place into the putty.
Note that you will need to contour the unset putty to be even with the incisal of the maxillary rim. Using a scalpel, make the midline before the Optosil sets fully. Now we have the length of the incisors as well as the midline. This next step is very important. Index the model base with a large round bur or something similar—do not place long, vertical indexes. With the maxillary rim in place, again mix a small amount of Optosil and apply it to the facial surface of the wax rim, making sure to make it even with the incisal edge and filling the indexes in the model base. Now we have the much-overlooked facial contour: the inclination. Many times, both clinical and technical dental professionals will overlook this important piece of information and the result is not only undesirable, but also difficult to regain once we miss this critical step. Once we have this critical information, we can now, and only now, place the teeth in the correct position. We have the accurate models, articulated in accordance with the patient, and now we have the contours of the facial and buccal, as well as the inclination of the anterior section.
But—what if we do not have the perfectly contoured wax rim? Then, we rely upon the knowledge that, hopefully, we have been taught.
The incisal edge of the maxillary centrals should be within the 6-mm to 8-mm distance from the maxillary incisal papilla. Note that men lean more toward the 6-mm distance and women usually (but not always) lean toward the 7-mm to 8-mm distance. Next, the maxillary cuspids should follow the "long branch rugae." This is vital (Figure 2). Now we can place our anterior teeth with no contoured rim. Trust me, these are only guides and are no substitute for the anterior teeth being set chairside or with a contoured rim. Keep these principles in mind though when setting all maxillary teeth.
At this point we should proceed to perform our model analysis, marking our ridges of course, as well as borders, post dam, muscle attachments, etc. Also, using the Heraeus Palameter®, we will mark the lowest point in the mandibular ridge, right and left. This unique device makes the job quick and easy (Figure 3). There are numerous reasons for finding and marking this portion of the model; one very important one is that we never wish to set teeth beyond this line because doing so places teeth on the ascending ramus and will cause instability in the denture. Many times it is not advisable to place four posterior teeth. By performing this analysis at this stage and transferring this line to the maxillary cast, we can more accurately select and place Heraeus Mondial® posterior teeth (Figure 4).
As we go forward, we think again of function and esthetics—how do we get both? We already have the principles we’ve already mentioned. These are basic placement, and now we begin the esthetics. Think of a smile—a very friendly smile—how nice, and how natural it seems.
The maxillary Mondial anterior teeth should not be forward of the vermillion boarder of the lower lip, unless the case is an Angle Class II or Angle Class III. Also, the "smile line," the slight curve of the maxillary teeth, should also follow the curve of the lower lip. My thoughts are that the maxillary anterior teeth should be ever so slightly asymmetrical, to reflect light and contour to the eyes. The symmetrical smile is a rare find in the natural world. That being said, I am not suggesting you set your teeth in a haphazard way, but rather, place them just "slightly misaligned" (Figure 5). This, of course, should apply as well to the poor misunderstood lower anteriors.
With all of these esthetic concerns, will function still work? Yes. All esthetics and function can and will work together (Figure 6). As we can see, in protrusive movement the Mondial anteriors slightly touch, and in right and left lateral movement the cuspids slightly contact.
Now, on to the mechanics of the posterior teeth and their proper function. I personally prefer the "lingualized" posterior concept, and while there is much written about its many benefits, this is the concept I will illustrate in this article. Bear in mind though that this is my preference, and that Mondial posteriors can be set very easily in a functional, or working and balancing, occlusal method. We must remember to articulate the models either with a facebow or using the "Campers Line." From here we create the Curve of Spee, with no Wilson Curve. We create this simply by remembering two things: the occlusal plane is no higher than halfway up the retro-molar pad, and the most anterior segment is no higher than the mandibular cuspid. So, now we place the mandibular first bicuspid slightly lower distally than the adjacent cuspid, the second bicuspid mesially lower yet, and the mandibular first molar matching the mesial of the second bicuspid and slightly lifted distally (Figure 7). Now we have our Curve of Spee, again with no Wilson Curve. As we set the maxillary posteriors, we need to bear in mind that the lingual cusps should rest in the mandibular fossae, clear of the mandibular buccal cusps. This should be easily achieved because the mandibular teeth have no Curve of Wilson.
So, now in centric occlusion, we should see maxillary posterior contact in the mandibular fossae (Figure 8). And in lateral movements, there should be no buccal contacts in the posterior—only lingual contacts for balancing. The anterior contact, again, should only slightly contact so that in lateral excursive movements, the anterior and posterior are mutually protected.
We can achieve beauty and function by using these tools, a Bonwill-compliant articulator, the Heraeus Palameter, and Mondial teeth. Along with contoured rims, proper bite registrations, and knowledge of tooth placement, we can produce a "striking and beautiful, and good" prosthesis (Figure 9).
About the Author
T.G. Hornischer Jr., CDT, is the recipient of the NADL’s Excellence in Education Award and Merit Award. T.G. earned his degree in Dental Technology in 1979, and received his National Board Certification in 1981. He has completed numerous implant and prosthetic courses, and conducts courses in the United States, Canada, and Europe.
The manufacturer provided the preceding material. The statements and opinions contained therein are solely those of the manufacturer and not of the editors, publisher, or the Editorial Board of Inside Dental Technology.
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