THE EDITOR'S CORNER

Have you ever run across an idea that puzzled you and then kept coming back periodically to puzzle you again momentarily and leave again? It almost haunts you. You can spend years with this idea coming to mind occasionally and fading away unresolved each time. I have one of these. It is the observation of Hayes Nance that you most often can't increase the lower cuspid-to-cuspid width even if the lower first bicuspids have been extracted.

What makes this so strange is that logically we think that we are moving the cuspids back into the space vacated by the first bicuspids and, therefore, that they are moving to a wider portion of the arch.

If the observation is correct, and I believe that it substantially is, you would think that the reason would not be hard to find.

You probably have to reject muscle alone--the action or interaction of tongue and cheek--unless you can show that the tooth movement creates some change in the soft tissue environment.

A simpler and better explanation might rest on the difference in lingual anatomy between a cuspid and a first bicuspid, with the tongue better able to hold the bicuspids in a wider span. This is not a strong idea considering the nondescript lingual cusp of the average lower first bicuspid.

An even better anatomical explanation is that cuspation does it, with the lingual cusp of the upper bicuspid holding out the buccal cusp of the lower first bicuspid. There is no lingual cusp on the upper cuspid to hold the lower cuspid. That's not a bad thought and should be checkable on cases of missing upper cuspids.

Another idea is a little wild, but not impossible. It is that when we think we are moving cuspids distally into the first bicuspid spaces, everything else is coming forward and the cuspids alone are maintaining their position in space and therefore their intercuspid width.

Are there any other ideas around?