#2 "Pre-crown prep" preparation! part A

It is a habit that we tend to all have to sometimes narrow our focus so much on our task, we don't see the "forest for the trees" or however that goes.
I was blissfully going along with my 2 hour crown preps (after all, if you do it fast, it has to be sloppy, right?) and my search for perfection when I had the opportunity to share a common lab tech with Michael Schuster back in 1984 or so. There was a dedicated lab tech named Pat Choate who had attended the lab training at the Pankey Institute and since I had just completed a week long course, I had to find a Pankey trained lab, so I looked up the list and was delighted to find one right there in my home town of Prescott Arizona.
I was over at his lab one day (in the days we used to do that!) and noticed that a couple of the cases he had were from the now famous Michael Schuster of the Scottsdale based "Center For Professional Development". I was a little surprised/ impressed that Pat was doing this work. As it turned out, Schuster's regular lab man was ill or temporarily out and he had called the Pankey institute and gotten Pat Choat's name. since we lived in Prescott and it was less than 100 miles from Scottsdale, I guess it was the closest one.
How does this apply to this post? Well, we were discussing the cases that Schuster sent, and I was very impressed that he practiced what he preached. they were mounted on a Denar DII semiadjustible articulator with facebow transfer and CR bite records just like we had just learned.
I was looking at the opposing teeth on a 4 unit single crowns on the bottom and noticed that the upper teeth looked strangely flat and appeared to be heavily ground off. I asked Pat why and he matter of fact explained to me, "those teeth were supererupted and Dr Schuster didn't want to duplicate that error in the new restorations.
so, lesson learned, Duh, I had never thought of pre-adjusting the opposing teeth and then take an impression of that "pre-equilibration that he was doing, so the simple "pre-restorative, pre-crown prep" steps and areas to look for became todays topic, or part A:
look at the opposing tooth for supereruption, obviously sharp, thin cusps, "plunger" cusps that will go deep into the lower occlusal anatomy
There are several good reasons to do this:
1. If the opposing tooth has been opposite a space you are now bridging, if there has been any significant length of time, depending on the age of the patient, density of their bone, etc, it will usually be both sticking down too far AND rotated around the palatal cusp if it is an upper molar, thus, creating an opposing that will:
a. not usually allow any, if much anatomy of the new crown
b. require more than is really needed of central pit reduction (thus closer to the pulp)
c. create marginal ridge discrepancies, adding to food impaction liklihood
d. and overall just make it hard to do!

2. If the opposing has been wearing due to the current tooth's filling eroding, the end result is a hidden supereruption where the "plunger cusp" (usually lingual upper, buccal lower) continues to grow into the deminishing filling and tooth structure of the current tooth. If this occurs:
a. many of the same problems occur as in #1 except to a lesser degree
b. often as the wear occurs, the height of the non-working (buccal upper, lingual lower) cusps is artificially higher than normal and it is easy to get complacent and reduce what you think is a lot, and you are just taking off the supererupted portion (when you place a pilot groove for instance) illustration to follow soon