Typodont Equilibration

For those who are taking Advanced Standing Entrance (practical) exams, during the on campus interviews, it is going to be a really good idea for you to be aware of what it takes to get a typodont in shape. That means that the proximal contacts are there and passive and the occlusion is reasonable and stable. I discussed in another post the difference between Columbia and Kilgore tpodonts, but didn't really get into how to make each of them good enough for an exam.

While the practical exams are mostly over for this year, the first one for 2010 will probably be in May - at least the Colorado exam was in early May this year, and this comes pretty fast. Those who didn't apply during this season or who are planning to apply next year, should start figuring out some of the issues right away - and one is control of the typodont.

In the next few months I will make a new videotape of typodont equilibration and put it on our DDSeClass.com website, so you can sign up and see how it is done. But there is no definite rule, except the same one that works in the patient's mouth - figure out what the problems are and then invent something that will fix them!

There is, however, a reasonably systematic approach to adjusting a typodont. I will go through some of it here and leave the rest of the details for the eClass. First, I will point out that the other day I equilibrated a student's typodont for the USC exam, and it was really a mess. The typodont was Columbia and only about 2-3 years old, but the teeth I have, which are newly manufactured, did not fit well at all. The problem is that when you put the teeth into the socket and look through the hole in the bottom of the typodont base, the screw hole in the tooth doesn't line up. In this instance the hole in the base must be enlarged so the screw will enter the tooth passively and not break the tooth.

Provided the holes all line up, we need first to tighten all of the screws on the typodont, so that if they are tightened later during equilibration, nothing changes. Also it will prevent rotation, which is a big problem on the anterior teeth. Then I will take out all of the second premolars and the maxillary lateral incisors. At this point I check to see how passive the contact is between the molars in all four quadrants. I also check to see how the contacts are anterior to the removed teeth. Also we need to know if there is room to put the second premolar back in the socket. Sometimes there is more than enough room, and sometimes, like the newer Columbia typodonts, there is not enough room. Then we have to decide which way to move the teeth anterior and posterior to the missing tooth so that there is just the right amount of space to return the premolar, and so that there are good contacts in the anterior and posterior regions, and they are passive contacts.

Sometimes a lot of tilting of the teeth is involved. Sometimes all of the proximal contacts in the anterior and posterior segments are fine, but there is not enough room to return the second premolar. In this case, the second premolar is usually recontoured to fit the space that is available.

I will describe here some techniques for tilting teeth, but I will save the occlusal adjustment for another posting.

If you wish to tilt a premolar mesially or distally, it is usually possible to cut the bottom of the tooth at an angle, so when the screw is tightened, the tooth will tilt accordingly. Sometimes the tooth won't tile because the head of the screw sits on the base in a bad way, so we recut the surface of the base where the head tightens at an angle. For molars it is generally best to take a small piece of aluminum foil (I generally use a strip from the edge of a scalpel blade package) and place it under the tooth, on one side or another. You can also use foil to raise a tooth into occlusion, or to raise AND tilt a tooth at the same time, by using different thicknesses of foil in two different locations. The scalpel foil can be folded a number of times to get different thicknesses. Sometimes I've had to use 5 layers on one side of a tooth and 7 layers on another to get it raised into occlusion, but without the facial cusp (say) too close to the opposing tooth surface.

When we get back into prime practical exam preparation "season" we'll be going over more of these things more carefully and I'll be answering more questions.

It is also relevant that typodont equilibration is important in some Regional Clinical Licensure Examinations, like the CRDTS, but a lot of people don't realize it due to the way the exam is graded.