THE INCI-DENTAL BLOG

When managing wear I split the treatment plan into 3 sections:

1)      Establishing which position to restore to

2)      Deciding how to manage anterior teeth and create stable occlusion

3)      Long term provision of posterior support

Which position should you restore to?

Pretty much no matter what the wear is like you only have a few options of where you can actually restore the bite to.

1) Conforming to the occlusion:

The intercuspal position (ICP) or Centric occlusion: is the occlusion a person makes when they close their jaw and fit their teeth together in maximum intercuspation. This position is rarely useful in restoring wear cases as the ICP is often in a protruded position. There will also be very little room in this position to replace tooth tissue, in fact there will be the minimum space as there is maximum intercuspation.

The only wear case I can think you might restore into ICP off the top of my head is a serious erosion case on the upper anterior which has progressed quickly so that the lower anterior teeth have not compensated and filled the space lost by the erosion. In this case you would just rebuild the palatal surface of the upper teeth in ICP with the material of your choice.

However outside wear situations ICP is the most likely position to restore to. In most simple crown work or trauma cases we always conform to the original occlusion and accept whatever slide from RCP to ICP that is present.

2) Setting occlusion to the Retruded contact position (RCP or centric relation):

When some people bite they have an initial contact and then slide into a position of maximum intercuspation (ICP). For most people this slide is small and non consequential. However in certain people it can be marked. Sometimes the initial contact is a real interference and the wear may be caused by the patient trying to grind past this initial contact into a more even occlusion. These patients are potential TMD sufferers and if the initial contact is on the tooth you’re trying to crown/ restore then beware as they are high risk for repeated fractures of your work. However I digress this will have to be the subject of another blog.

Sometimes in wear cases you can take advantage of the space between the RCP and ICP to give you a little room to restore in. Where you can do this you get advantage over increasing the Vertical dimension. That advantage is that you already have some contacts in this position which will help maintain the occlusal changes and reduce the amount of teeth you need to restore.

3) Increasing the vertical dimension:

In cases where you can’t use the ICP or get enough space in RCP then you only really have one option left? That is to restore the teeth to an increased vertical dimension. This can be relatively straightforward in mouths without posterior support but can be far trickier where a Dahl appliance or posterior shims are needed. I would say in general the more units you have to restore the harder it becomes.

With this technique you are making a new ICP wherever you like; the only rule is the new position has to be the RCP so picking this new ICP position is pretty easy. The difficulty is recording that position and translating it to your restorations.

When we increase the vertical dimension we can increase it by any amount we like, many studies and experience shows us that patients can tolerate pretty much any increase we choose. We therefore set the increase on two factors the anterior aesthetics and the amount of posterior disclusion we will leave. Therefore your aim would be to have the best anterior aesthetics with minimum posterior disclusion, N.B. The closer together the posterior teeth are the more likely Dahl compensation is to occur and the easier they will be to restore.

Our only limit to creativity is that the new ICP must be on the retruded arc of closure. That means with the condyle in its most superior position on closing. The reason we do this is that we want the new occlusion, wherever we choose it, to be in an RCP relationship (i.e. RCP =ICP). The reason is simple; If we are creating a new occlusion why would we want to have an RCP- ICP slide? Why risk TMD, interferences and potential loss of restorations if we don’t have to. It is by far the safest and best to make our new ICP a nice firm position and the first contact when we close.

Working to the retruded arc of closure also gives you the only really reproducible position for you to work to in lab. Without it there is no way you can predictably plan new position on study models and that means all wax ups would be fairly useless.

P.S.  It’s not that you absolutely can’t restore a new ICP which is not RCP the real question is why would you ever want to?! It might happen by mistake and the patient may develop an engram (jaw closing pattern) that compensates for any slide from RCP without causing TMD but that is a large risk to take. You are far better eliminating this slide and being certain your restorations will stay in place than crossing your fingers the patient can adapt favorably.

Examples of choosing restoring position:

I hope I’ve not lost everyone with that explanation of the 3 positions you can restore to. I’m hoping these 3 case examples might make the points easier to follow so bear with it. Sometimes the choice is easy to make but sometimes it is harder.

Case one:

The top picture shows the patient in ICP here the teeth are over closed with no room to restore the upper incisors. So ICP is not a useful position to restore to. However this patient has a huge slide from RCP to ICP. This has been caused by a relative loss of posterior support and the face that his RCP is so unstable.

The RCP position is shown in the bottom picture. You can clearly see that there is an initial contact between the 27 and 36 tooth but because that contact is unstable and has no chomp the patient slides forward (look at the wear groves in the 22) into the ICP.

Now when I had a good look at that RCP I could see that there was loads of space available to me in this position to restore the anterior teeth upper and lower. Obviously I’d have to provide posterior support to stop the slide to keep them but that is easily achieved with an upper denture.

Alternatively I could Increase the vertical dimension more than this if I wanted more room but why would I want to? If I do I lose this nice position I can work to and register to easily, I will need face bows and more accurate records to predict the new RCP position and worst of all I’ll have to shim or build up the 27,36 teeth to get back the contact I have at the moment.

Verdict: restore in RCP

Case 2:

This picture actually shows the patient in RCP. You can see from the wear patterns that the ICP (maximum intercuspation) would need the patient to protrude and grind to his left. I didn’t get a photo in ICP unfortunately but I think this shows pretty well that in this RCP note first contact between 13 and 43 there is not enough room to restore aesthetically.

We are therefore committed to open up the vertical dimension to a new RCP. I can choose whatever increase I want so I will level the lower incisors and make the upper incisors the correct length.  The reason this case is easier than some is that here we have literally no posterior support so I will not have to restore any posterior teeth no matter how much I open the bite.

Verdict: Increase vertical dimension

Case 3:

In this case I wasn’t sure weather to restore to RCP or increase the vertical dimension. You can see from the photo that the patient has a few posterior units but he just doesn’t have any opposing pairs. That’s why he has ground down the incisors to make a chewing platform.

Again this picture is not in ICP because in ICP the patient would be protruded as he is in function grinding the teeth. The picture therefore shows the patient in RCP. I’m not sure if it’s easy to see in this photo but in this RCP there is actually a fair bit of room between where the lower teeth hit the palatal surface of the upper teeth and the incisal tip.

This space is probably just big enough for me to add composite and lengthen the upper incisors without changing this RCP. If at this point I could provide some posterior support to stop the habitual grind forward I could maintain these restorations. However they might be a little thin.

Alternatively I could make a very small increase in the vertical dimension and build palatal shelves on the upper anterior teeth. This would only be a very minimal increase in VD but would give me more freedom to shape the teeth as I pleased and make the restorations more steady.

The final possibility is to increase the vertical dimension more add length to the worn lower teeth and add palatal shelves to the upper teeth thus improving aesthetics even more. However  it would require far more treatment and it’s not always easy to add length to lower incisors.

When the lower incisors have an even occlsual plane, unlike case 2, I often try to leave them alone providing the patient is not concerned about the aesthetics of short lower incisors (which they rarely are).

Verdict: Increase in VD (but a small one)

Clear as mud?

I’ll answer any questions if people have them but it’s a tricky subject to explain. I know I found it very confusing in the books and having tried to write this; I can see why!

However it’s really important to get a handle on what position you want to restore to so make sure you do get this before you try a wear case. Only when you’ve worked out the position you’re going to restore to you can start to plan how you will actually do it. In the next blog in this wear series I’ll go through the treatment planning options for case 2 and what I actually did.

All the best and sorry if this is a bit long!

Chris