|Date:||Fri, 22 Sep 2006 02:26:14 -0500|
|From:||"ESCO automatic digest system" <LISTSERV@LISTSERV.UIC.EDU>|
|Subject:||ESCO Digest - 19 Sep 2006 to 21 Sep 2006 (#2006-29)|
There are 4 messages totalling 2105 lines in this issue.
Topics of the day:
1. Re: Tip-Edge and Torquing
2. Torquing with TipEdge- part 2
3. Torquing with TipEdge
4. Super Class II
|Date:||Wed, 20 Sep 2006 07:39:57 +0100|
|From:||"Paul M Thomas" <p.thomas@EARTHLINK.NET>|
|Subject:||Re: Tip-Edge and Torquing|
Dear Esco Folks,
In reference to the ongoing discussion regarding Tip-Edge and torquing, I would offer the following comment as well. Tip-Edge Plus retains the ability to use the Sidewinder springs when desired as an alternative to threading the deep tunnel archwire. These can assist significantly in anchorage preservation when necessary (as Richard would say) to "put on the brakes". Of course it may take a bit more thought than threading the tunnel in regards to counterclockwise versus clockwise springs, but then isn't orthodontics meant to involve a bit of thought? :o) For all-out anchorage cases, we have mixed and matched being "equal opportunity employers". Tip-Edge works nicely with the temporary anchorage devices or orthodontic bone anchors (attached). The light forces and ability to tip/upright the teeth reduces some of the load on the anchor screws and decreases the likelihood of failure. I can speak out of both sides of my mouth since my grad clinic supervision cases are divided roughly 50/50 between MBT and Tip-Edge. We are fortunate to have Richard still be willing to provide a yearly Tip-Edge course for our grads to introduce them to a technique which works wonders with some of the Brit "whopper" class II malocclusions. I admit that Richard is a bit of a cheerleader for the technique which may foster a bit of the "us and them" mentality, but he is enthusiastic (passionate, perhaps) about life in general....whether poodling along at 4mph in his narrowboat or at 140mph on his motorbike. I personally have enjoyed seeing the grads have the experience with each system. Both produce excellent results when used as intended.
Paul M Thomas
|Date:||Tue, 19 Sep 2006 20:22:11 -0300|
|Subject:||Re: Torquing with TipEdge- part 2|
Another possibility of what the Tip Edge colleagues may be referring to is this: although moments are independent, the rotation of a body in one plane can cause reaction forces that are not in the same plane, which, in turn, cause rotation in another plane. In 2D, of course. this is not possible, but it is in 3D. For instance, let's consider an upper right incisor. If there is a buccal crown twist in the archwire inside an its bracket that does not express itself as 3rd order moment because of play, and someone applies a mesial crown tipping moment to it, the two reaction forces in the bracket slot will be separated by an antero-posterior distance. What this means is that now we are applying both a second order and third order moment at the same time. Now, it's not the round wire doing it. It's the rectangular wire doing it as a reaction to the changed position of the bracket. The round wire continues delivering only a second order moment, it doesn't "torque" the teeth. The third order couple that we just described will tend to move the crown buccally. If you apply a distal tipping moment to the crown, the same happens, and a couple that tips the molar bucally will appear created by the rectangular archwire. The reason is that the anterior and posterior edges of the archwire have a height discrepancy when it is twisted. So, when the tooth tips in 2nd order, at a certain point in time it contacts the posterior edge of the archwire distally, and the anterior edge mesially, or vice-versa. In our everyday mechanics, this happens during common rectangular archwire leveling with any bracket- not just the tip edge bracket. In a tip edge bracket, this has to be done separately, with the uprighting auxiliary (or round wire), because they increased the 2nd order play to improve leveling efficiency. The effect and "torque gain or loss" is the same got by the regular edgewise bracket, unless you apply more 2nd order moment than you should to "overcorrect" the 2nd order position). The regular edgewise bracket does both at the same time. I see this more as a "lack of control" of 3D archwire leveling than as an general advantage, because the " twists" along the rectangular archwire vary greatly during leveling. In addition, from the same perspective, it is important to know that the opposite is also true: third order moments can change 2nd order positions by means of the same mechanism. When you initially level with tip edge, you have the advantage of having more second order play, so you miss some of the torque that you could get with a regular edgewise bracket. In the end, it's the same "torquing" expression of the regular edgewise, after the uprighting springs. If there is another argument I missed in this matter, please let me know. Thanks, r. "I dream of a world where orthodontists will care more learning biomechanics than purchasing a new bracket."
Old Chinese Proverb
|Date:||Tue, 19 Sep 2006 19:06:18 -0300|
|Subject:||Re: Torquing with TipEdge|
Hello Dr. Tribo Thanks a lot for your figure. If you look at it closely, you will observe that from the beginning to the end there are still 2 contact points for the 3rd order expression of the archwire on the slot (one for the force pointing to the gingiva and one for the force pointing to the incisal). Nothing changes in 3rd order from the first to last picture, from the Statics point of view. You do not get an increase in torque by getting additional contact points- this assumption is a mechanical fallacy. Why? Because more contact points will simply divide the force into a "load" which is simply that force distributed along all contact points. There's a similar fallacy related to friction- some people think more area of contact means more friction. It doesn't matter. The total force magnitude is still the same. You will realize that this idea is mechanically impossible if you think of a second order moment vector perpendicular to the third order moment vector. They do not affect each other. I don't know about other schools, but I don't think any of our basic orthodontic biomechanics students here in Indiana or any engineer would buy this idea. Rotations in second order (couple of forces in the frontal plane) do not cause rotations in third order (couple of forces in the sagittal plane). If you have a couple of forces (opposite sense, same magnitude) , and one acts on the mesial of the bracket, and the other on the distal, the only situation where this would cause a third order moment is if there is a distance between these forces antero-posteriorly. From another perspective, a resultant extrusive or intrusive force on the bracket, if far from the center of resistance, can change the inclination of the tooth in 3rd order and reduce (or increase) the play between the slot and the archwire. But this can be done using any bracket (with an overlay intrusion or extrusion base arch), not only tip edge. Maybe what happened to the person that wrote the book is that he/she had such a resultant force during 2nd order tipping and generalized it to all cases. I am sure tip edge has some good points, but this is certainly not one of them.
|Date:||Tue, 19 Sep 2006 15:52:41 -0400|
|From:||"charles ruff" <orthodmd@MAC.COM>|
|Subject:||super class II|
Hullo Group, I have patient(14-M)here whose molar relationship on left side is: Mesiobuccal cusp of upper second molar occluding with the mesio buccal groove of the lower first molar. The distal slope of the distal cusp of the upper first molar occludes with the mesial slope of the mesiobuccal cusp of the lower first molar.The photo is enclosed. What term shall we designate to his molar relationship ? Super class II Hyper class II Two cusp class II
Your views/suggestions welcome. Jayaram Mailankody. Calicut, INDIA
Concerning the severe Class II molar discrepancy, the most precise way is to measure the discrepancy in millimeters instead of making up a name for it.
That response is fine and certainly correct but usually when we classify malocclusions it is for the purpose of quickly alerting ourselves to the kind of problem we are dealing with.
For instance, if I called this "super class II" I would know that I have to either be very lucky or I have to do more than normal if I hope to correct this class II problem.
So for me, I would call it "super class II" and know what I needed to know