|Date:||Sat, 10 Jun 2006 00:14:30 -0500|
|From:||"ESCO automatic digest system" <LISTSERV@LISTSERV.UIC.EDU>|
|Subject:||ESCO Digest - 31 May 2006 to 9 Jun 2006 (#2006-17)|
Topics of the day:
1. retracting canines
2. En masse v. sequential retraction
4. Re: anchorage
|Date:||Mon, 5 Jun 2006 10:56:07 -0400|
|From:||"Charles Ruff" <orthodmd@MAC.COM>|
I, for one, as you know Mort, don't retract canines individually except when I have a Nance in place which is less and less with the use of TADs. I would hate it if my close friends and colleagues thought I was brain dead just because I'm teaching at Harvard. :-)
The reason most instructors at Harvard retract canines individually and not en masse are for two reasons:
1. they were taught to do it that way when they were Harvard residents. We inbreed just like most programs. 2. as a group orthodontists are lemmings and do very little independent, critical thinking. there are exceptions to that general statement but unfortunately not many.
|Date:||Thu, 1 Jun 2006 09:04:34 -0700|
|From:||"Stanley M Sokolow" <overbyte@EARTHLINK.NET>|
|Subject:||En masse v. sequential retraction|
Morton & ESCO:
I don't know the history of this concept in orthodontics. Although we as a profession aspire to scientific treatment protocols, in reality as we all know, much of what we do is more of an art and craft than science. Ideas that are introduced into the professional thinking process by charismatic or influential orthodontists ("gurus") are not often well substantiated by scientifically validated research, but rather are based upon ". . . in my hands . . ." and "clinical experience" which often is anecdotal. So, although an idea is long-standing and used by most orthodontists, nevertheless it may have no validity. That said, where did this idea of canine retraction followed by incisor retraction come from?
I suspect it has its roots in the notion that retraction this way is "less taxing" on the anchorage. The idea being that first you use the second bicuspids and first (or first and second) molars as anchorage to retract the canines, then you tie the canines to the other anchorage to make a bigger anchorage unit, and retract the incisors. Since you are pitting the 6 or 8 posterior teeth (canines, bi's, and molars) against just the 4 incisors, you would think you have less anchorage loss. Also, during the first stage, the idea was to place a stop on the mesial of the molar tube, so that the molars would not "blow anchorage" by moving mesially. Of course this stop causes the mesial force on the molars to be transferred to the incisors during the first stage, so the incisors actually are moving slightly in the wrong direction in the canine retraction stage, but I don't think the proponents of this scheme ever added up the total effect. Apparently the soon-to-be-published study that I cited will show that the net effect of this process results in no better retraction result than just doing en masse retraction of canine through canine once these six teeth can be aligned on the archwire.
Why would this retraction be thought of as "less taxing" on the anchorage? I suspect that idea comes from Begg's differential force theory, which held that there is an ideal amount of force to move a tooth, one which produces a maximum rate of retraction. Below that force level or above that force level, the theory claims, the tooth will move more slowly than at the optimum force. In graphical terms, this means that when you plot rate of movement on the y-axis and applied-force on the x-axis, there would be a peak on the graph. Applying this theory to canine and incisor retraction, the idea would be that the retraction force could be adjusted to provide the optimal force on the teeth being retracted, but since this would be distributed among more anchorage teeth with bigger roots, the force on each anchor tooth would be sub-optimal, so there would be less anchorage loss than if the six anteriors (canine through canine) are retracted against the four posteriors (second bi's and first molars) where the forces would be more equally distributed between anchor and teeth being retracted. A few years ago, I was intrigued by the idea of making a mathematical model of the retraction process, so I looked up the studies that had been done on whether there is any validity to the idea that there is an optimum force. Decades ago, Ernie Hixon of the University of Oregon did a small study with only a few teeth, but it showed that there was no validity to the idea. The harder he pulled on the canine, the faster it moved. There didn't seem to be any point on the rate versus force curve above which the movement slowed down. His graph was a ramp -- no peak. As I recall now, there have been other studies on this but a published review of them showed that there is no optimum force.
Old ideas die hard. We often just keep doing something because that's what we learned or were told by a guru, and since most of what we do works to some extent no matter how you do it, we don't really have any reason to look critically at whether we're doing it the best way. Indeed, clinical orthodontists (as opposed to the research orthodontists) are not in a good position to do such research because we don't have the tools or technical skills to make scientifically valid comparisons of our techniques.
What we could do as clinicians is provide a vast database of clinical cases that could be mined by researchers to answer some of our basis questions. A central Internet repository of cases containing details of what we did, when we did it, what direction it was done, when landmark events (such as completion of a retraction stage) occurred, along with x-rays, digitized casts, etc., would be a valuable resource to the profession worldwide. Perhaps even our own office management computer systems would be able to do sophisticated searches and analyses of the data in such a database when we have clinical questions. We're a long way from that day.
|Date:||Thu, 1 Jun 2006 06:41:55 -0400|
|From:||"Ron Parsons" <ronparsons@MINDSPRING.COM>|
According to James Mah, DDS, MSc, MRCD, MDSc , who presented at the AAO in Vegas this year (referring to his handout), a full mouth series of xrays has an effective dose of 30-170 microsieverts (a measurement of effective dose). A CBCT has 40-135 microsieverts , which is about the same. Assuming the CBCT technology does not change, it is not clear that effective dose is a concern.
I wonder if we would feel the same about CBCT if we could diagnose caries, ankylosis, and vertical fractures with CBCT.
Finally, while we may be unnecessarily excited about this new technology, CBCT's could go the way of the microjets (light weight jets) or fax machines.
Thanks for all the commentators on the ESCO for sharing.
Atlanta , GA
|Date:||Fri, 2 Jun 2006 13:45:05 -0400|
|From:||"Dr. Zeit" <gzeit@SYMPATICO.CA>|
Mort asked an interesting question about why many orthodontists retract canines first in severe anchorage cases even though clinical research suggests there is no anchorage benefit in doing so. In " severe anchorage" cases orthodontists are more likely to use adjuncts (elastics? headgear?) That means more variables As orthodontists part of what we do is apply forces to teeth but another part of the job is to monitor progress (and be prepared to modify treatment if progress is poor). This may seem trivial, but maybe the preference for canine retraction exists because it is easier for many of us to assess where we are and how the treatment is progressing when we do things this way. The fact that most orthodontists do something a certain way may tell us more about human nature than about how teeth move.