Intrusion v Crown Lengthening of Upper Anteriors

Janis McAloon
March 2005

Any time you do a crown you are getting rid of enamel so it is always going to be on dentine. I think this is an important issue and would like to tell you all a little story.

Imagine you had a central incisor crown that started life at 8mm x10mm but wore down to 8mm x 8mm then overerupted to compensate. So far it has escaped the dentist’s drill so it’s a nice tooth with an intact pulp. The patient still had a gummy smile and the (effective) incisal edge position was still about 1mm too long.

The roots were nice and long so you crown lengthened 3mm and decided to make a 10mm crown or veneer (8-1+3) so everything would like just perfect.

Either way you want a translucent incisal edge so you remove 3mm of tooth structure (1 to change the incisal edge + 2 for porcelain). That’s still a bit conservative from a porcelain point of view but you realise you are 5mm (2+1+2) from the original (unworn) incisal edge and you expect the pulp could be getting close.

The tooth structure you just removed? You did that keeping your bur parallel to the incisal table. It was 3mm wide (labio-palatally) when you started, its now 5mm wide. You would prefer not to have a really thick incisal edge. If it’s a crown you are doing, you decide to take quite a bit off the palatal to reduce this width (you have to anyway because your prep goes 3mm up the root). The palatal is looking a bit pink so you stop there.

Interproximally you give yourself a very fine margin because you know the pulp horns are close and you don’t want to deepen your margin as you go higher up because of this. Gerard Chiche has this in his book.

Thank goodness the technician is going to be overcontouring because you won’t be able to give her room for a nice porcelain shoulder and you certainly won’t want opacious porcelain on display (let alone a gold margin). So you keep a a shallow chamfer all around the tooth.

After you finish you look at your nice smooth preparation – you think to yourself how much smaller the preparation is than you usually do. You are glad you left a lot on the cingulum otherwise you wouldn’t have had any where near enough resistance form. Maybe a veneer would have been better. But maybe not…

If it’s a veneer you are doing, you have no choice but to accept the very thick incisal edge. You start reducing interproximally. You are doing the adjacent teeth and as you try to take your margins interproximally you notice the adjacent teeth are getting further and further apart.

You have to “slice” through the proximal because you want porcelain right up at the gingival margin on both sides. You seem to be running out of tooth structure and your margin is going more and more towards the palatal. There is no chamfer. The preparation almost looks like a crown preparation when viewed from the front, with knife-edged slices at the sides.

There is no enamel on the interproximal surfaces or up on the labial root surface (of course). Height wise, you have 5mm of enamel (8-1-2) to hold your 10mm veneer. That’s just in the centre of course. So its not just porcelain hanging off the edge, it’s hanging off the sides as well.

Thank goodness the tooth didn’t have any restorations, and thank goodness the patient isn’t a bruxer (you ignore the fact that it was tooth grinding that got you here in the first place). Nevertheless, you are worried, so you probably sit the patient up and suggest you convert to a crown preparation.

Sometimes when I am thinking of doing a procedure I go through and try to visualise it in as much detail as I can. That way I can make mistakes in my head without doing permanent damage to someone’s tooth. I hope you will all think just a bit more about this and whether it really is worth doing some intrusion first before cutting back a worn tooth.