BUT, the Kilgore and Columbia typodonts are significantly different in several important ways. The nature of the ideal preparations, of course, does not change, but the sensitivity of each typodont to any overextension or carelessness in margin placement is very different.
Mostly, we are looking at Kilgore typodonts for the Northern California schools, but there are others as well. Be sure to ask what typodont they are expecting you to use, and if you supply your own or not. Remember that ALL typodonts have problems with positioning of teeth so that there is good proximal contact, or at least some, and it is not ACTIVE, and that there is good occlusion, with solid vertical stops for posterior preparations.
But you must be aware that for the Kilgore typodont the proximal contacts are positioned much farther toward the facial than for Columbia, and the occlusogingival width of the contact is very small, typically, for the Kilgore. This means that the box for a class II is shifted to the facial with respect to the isthmus, and that very little gingival extension is required to get gingival clearance. In fact, if you are not careful about your pulpal depth, you may have gingival clearance before even making the box!
For the Kilgore, it is generally easier to cut a crown preparation through the proximal contact area without coming too near the adjacent tooth, because the gingival embrasures are so large, but the preparations tend to be shorter than for Columbia, because of the smaller clinical crown. This makes over reduction of the marginal ridges a more serious problem, due to the short resultant walls and limited retention.
For the Columbia, active proximal contacts is a continuing problem - necessitating adjustment of the bottom of the tooth at an angle, recutting the seat of the screw on the back of the base, or placing aluminum foil under one side or the other of the bottom of the tooth, mostly molars in this case. If the adjacent tooth shifts while cutting a class II box, it can cause real problems. To say nothing of the very large contacts occlusogingivally for Columbia, often requiring very deep boxes to get gingival clearance. The newer Columbia typodonts use a different plastic for the base than they used to - exchanging Melamine for, I think, Nylon. This new base does not lend itself well to the adjustments that are necessary to get teeth to fit with only passive proximal contact.
A few days ago I equilibrated an older typodont - only 2 years old - and had to replace most of the teeth with new ones. Normally this would cause difficulties, having to adjust ALL proximal contacts in a sequential fashion, but in this case it was doubly complex, because almost all of the teeth did not fit the screw holes in the base. That is, when you look at the bottom of the tooth through the screw hole in the base, the hole in the tooth is not centered, often points so that the screw will hit the side of the hole in the base (hence tipping the tooth), or the screw will not even go into the tooth. In this case I had to recut the holes in the base in all of these cases - if that were not done and the screw could be tightened into the tooth, the tooth would almost always break. Some of you might have had this problem before - but it is becoming more frequent with Columbia typodonts recently!
If you read this post and find the subject of typodont equilibration important for you now or in the future, with a little encouragement I will make a videotape of the procedure for a couple of typodonts so that you can see some of the techniques that are necessary. Realistically, most students that see how complex this can be, elect to have me do it for them if they are to take their own typodont to an exam. If you use a typodont supplied to you by the school, know at least enough to check it and see if it will make your life more complicated because they did not equilibrate it well enough!