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I had an interesting conversation with a good friend of mine the other day. He works for a large lab and gets to see all sorts of lab work that is sent into the lab from dentists and the work that is done by the lab and sent back out to the dentists. He talked mainly about two dentists who send in work to the lab.

One dentist, we will call him Dr. Malpractice sends in crown preps that look absolutely horrible. Crooked margins, too much tooth structure removed in some places and not enough in other places. There is no rhyme or reason as to what the dentist is trying to do (as far as the lab can tell). This may be slightly exaggerated, but you get the point. On the other hand there is another dentist, we’ll call him Dr. Millionaire, that sends in his work and every single prep is a masterpiece. Crowns are easy to read and the exact amount of tooth structure has been removed which makes the labs job easy.

I wondered what would make the difference between these two dentists. Education? Age? Patient demographics? I know most of the readers of this blog won’t care, so I have decided to talk about my crown practical and relate it to these two dentists. The first crown prep you make will look like Dr. Malpractice’s prep. After a few (maybe 20) tries in the fake mouth you will create a decent looking tooth. Then you get to move onto the maxillary (upper) arch and relearn everything backwards looking in your mirror. Top that off by the fact that you have no suction so your mirror get water on it as soon as you start to drill and you can’t see anything anyway…

I am not trying to scare you, school will strike the fear into your heart all by itself, I am just preparing you mentally. I was reading the blog by Ping about how they had to set dentures in less than 3 hours for one of their practicals. I am sure that must have been quite the experiance.

Last Monday we had to do a crown prep for our practical and I felt like I did alright. It was one of those practicals where you grade your own work and then the instructor grades your work. You aren’t penalized for the grade you give yourself, so I always give myself one check. What I wanted to talk about is the intricacy required to do a proper crown prep. Have you ever sat down and looked at ruler with a mm measurement on it? One mm. Go and look. It is small. A tooth has functional cusps (cusps that fit into the central groove of the opposing arch) and non functional cusps (these do not fit into the opposing arch cusps) and each of these have to be reduced a certain amount. 1.5mm for functional cusps and 1mm for non functional cusps. The best way I have found out to gauge this depth is to make depth cuts into the tooth at intervals so I know how deep I am going (this is also the method taught at Temple).

Next would be axial reduction. Axial reduction is the sides of the teeth. This is reduced by .75 mm and can be difficult when using a large bur. It has been recommended to us as students to get the 850 diamond bur to do crown preps. i don’t exactly know why we just didn’t get this bur in our kit to begin with, but it costs 5.50 cents in our dental school store. (If you want a box, let me know, I get discounts on everything!)

So after all of these technical measurements and drilling (measure twice, cut once!) you should end up with a beautiful crown prep that you would be proud to put into your own mouth and make Dr. Millionaire jealous. While I am not close to making Dr. Millionaire envious of my work (I DO still work on plastic teeth) I would like to think I am better than Dr. Malpractice which, from my friends description, isn’t very hard.