Wednesday, May 20, 2009

Frequently asked questions

In space closure, if after a couple of months of space closure, we still have a couple of mm of space in the upper anteriors and no spacing in the lower arch, the occlusion is a solid ClassI with little or no overjet, is it correct to assume that we have a tooth size discrepancy? There seems to be 2 ways to deal with this remaining space, either bond composite to the upper teeth to close it or perform ARS on the lowers? What would you do in this situation?

Studies show that in 60% of cases, there is a tooth size discrepancy where there is more tooth mass on the lower arch than on the upper. This is usually due to small upper laterals or large lower laterals. We call this the 60% problem. The solution to this is to do what you suggest. In 20% of all cases, there is excess tooth mass on the upper. This is called the 20% problem; it can also be corrected by IPR, but in this situation, it is the upper arch that is reduced. In my practice, I often do the ARS on the premolars because stripping in that area does not affect the esthetics as much.
The interesting point about this discussion is that only 20% of all cases have no tooth size- arch length discrepancy, so the problem you describe is present in a lot of cases. However, in many cases with a discrepancy the problem is too small to be clinically relevant, so not all of the cases with a discrepancy need interproximal tooth reduction or bonding.


If we are to call the diagnostic arch length the existing mandibular form, taken from the molar buccal cusp tips and anterior incisal edges, and not expand, how do we substantial crowding?
Another way to put my question-when we unwind all of the crowding, don't we need a longer arch length, or distal drive the molars? Creating a Roman arch form and advancing anteriors will not strictly maintain this existing arch length, right?

If you keep your arch length the same, the only way you can relieve crowding is to remove tooth structure. Tweed wrestled with this problem 70 years ago and ended up extracting 4 bis in 90% of his cases.
We base our arch width on a line 3mm wider than the cusp tips/incisal edges to account for bracket thickness. We can change arch form (expand or labially advance teeth) to relieve crowding. How much of this can you do? Different practitioners will alter arch form different amounts. The more you change arch form, the less stable the final result will be, but the more you alter arch form, the less extractions you have to do.
From a philosophical standpoint, I am not a big fan of distalization, especially on the lower. I don't like pre-determined arch forms, and I don't like to do a lot of expansion. This is why I extract teeth. Over the last 15 years, I extracted some combination of bicuspids in a little over 21% of my cases. This is a little bit lower than the 26% national average as reported by the AAO, but as a GP doing ortho, I do refer some of the more difficult cases that present in my office. These difficult cases are usually extraction cases, so factoring in these cases to my overall percentage would bring my extraction percentage closer to the national average.


I have evaluated cases involving Class II elastics and I remember what you said about the use of Class II elastics,that is, Class II elastics really work but if you use them you may be "selling your soul because of some of the side effects that may occur”. I've looked at a few of my cases and I think you meant Class II elastics may distort everything we've worked to achieve up to this point in treatment. I see mostly lateral open bites, especially molars out of occlusion. So what should or could we do to remedy the ill effects of Class II elastics? Do we use single elastics on each side and use less aggressive means (I've been using 2 elastics on each side 3/16 med full time wear)? Do we accept this problem as side effects of Class II elastics and deal with it after the Class II has been corrected? I'm thinking using Class II finishing elastics with vertical elastics on the 6's or maybe even bracketing the 7's. What are your thoughts on this matter?


There are certainly many side effects associated with Class II elastics. To minimize the side effects, I try to use them only in .019x.025 st steel with the bite opened to the desired level. Then,the elastics act as minor repositioning devices. This, hopefully, will eliminate the lateral open bite problem. If lateral open bite still occurs, go to a lighter wire after the Class II is corrected and the occlusion should settle.
I like to use ¼” medium elastics, with full time wear. This provides a constant repositioning force and maximizes the speed of correction. If correction doesn’t occur with this force, I increase the force by using 2 elastics per side, but this may lead to the side effects you described, especially in weak muscled patients. Vertical finishing elastics are a good way to close lateral open bites; bracketing the 7’s in cases that can tolerate the bite opening will also help.
The bottom line is Class II elastics are a good way to correct Class II, IF you can stand the side effects. Many ways exist to handle the side effects, but these ways may be a bit mechanically complex.

I noticed that a case of mine has a tooth size discrepancy, with wide mand lateral incisors, and wide mand second bi's. Much more crowing exists on the lower than the upper, and the molars are Class I, but with only 2 mm of overjet in the anteriors. Initial leveling and aligning will probably advance the lower anteriors. Do we wait to do IPR on these type of cases after crowding and rotations are relieved, or can do IPR before initial aligning? She is not a weak muscled patient, but I still would prefer not creating edge to edge in anteriors and opening the bite. But I guess that it comes with the territory that the teeth may look worse before they look better.

Good job in picking out the tooth size discrepancy before treatment starts. I like to align before I do IPR, even if it means the occlusion will be edge to edge for awhile. The reason I do it this way is because when the teeth are aligned, it is easier to strip the contact points and shape the teeth correctly. When crowding exists it is tough to get at the contact points accurately. In addition you never quite know how the leveling and aligning will play out, so I always like to get things lined up before I do something irreversible. So, get into at least .016st steel before doing any reduction.

Temporary Anchoring Devices or mini implants are something we've never talked about. They are gaining in popularity among orthodontists. Are you currently using them? Do you think this will decrease treatment time? What kind of cases are they indicated, deep bites cases, open bite cases ?
What are your feelings towards TAD?

TAD's are all the rage these days. They are easy to insert and remove and provide reliable anchorage. They are used for space closure, distalization, intrusion, as well as attachment points for interarch elastics so the mechanical advantage of the elastics is greater. They are often used for bite opening and bite closing. I see their use greatly increasing over the next few years.

2 comments:

abhiquick said...

There are some important things you need to know about surgical tooth extraction and process of pain free dentistry. Things You Need To

Know About Surgical Tooth Extraction

Blogger said...

I've just installed iStripper, so I can watch the best virtual strippers on my desktop.