As you have suggested, it can be measured. To me the more important question is how much you want to change the angulation of the tooth, in which case it might not be that you want a heavy force, but rather a lighter force that would be expressed over a longer range. Put another way, is it necessary to completely fill the slot? or would you be better off with an auxilliary spring added to a wire that does not fully sill the slot but would have a greater load deflection and, therefore, be active over a longer range: specifically, a Warren torquing auxiliary.

Dear William 

                           Thanks for answering the questing. But i said in full dimensions wire it can be measured but not in 19x 25 SS wire. Because many factors apart from play of the wire come into action on using a 19 x 25 SS wire. I believe MBT prescription on MBT mechanics is nothing but a joke.

About spring i do agree that its very effective in expressing torque.But using spring will bring us back to Angle time where experience matter and things go to personal opinion . in spring you never know how much torque is expressed it just a guesswork where seniors suggestion wins and junior guess is always wrong. when you full fill a slot than its not a guess . Filling the slot is fail safe .if its 7 degree torque there would be 7 degree torque expressed . But spring is never fail safe . A armature clinician can express more than required torque and put more than required force. if the patient miss visit things can get worse depending on spring activativation.

I agree that there are variables: consistencies with patient's presenting for appointments, patient's care of appliances, patient's hygiene, the degree to which the wire is secured within the wire, things the patient might do to the appliance, not to mention the side-effect on the adjacent tooth/teeth.  Forget about the "MBT mechanics;" it's not a joke, it's a SYSTEM. It is probably perfect for certain cases, but heaven forbid there should be a variation in crown face-to-root angulation. It seems silly to worry about the torque that is built in to an appliance. It is the response that matters.

In his last years Kokich was talking about "prescription orthodontics". No set prescription is going to fit every patient. Please consider reading the article:

http://www.angle.org/doi/pdf/10.2319/012413-76.1

Notice how the brackets are arranged in figure 2 on page 1096. Bear in mind that the torque on the lower molar brackets had zero degree torque and that there were pre-judged applications of variations of torque on the other teeth in order to get the desired response.

All of the permutations that you list in your response are real factors - ALL of which must you learn to accommodate. Just remember: from the yet-to-be released movie, Mouth of Dreams: "if you bend it, they will move."  Good luck.

Dear William 

                         Thanks for such a detailed answer. i have read the article. A very well finished cases with good professional skills. 

Sorry for bothering you but i want to refine my question and need a pinpoint answer. 

If the a MBT prescription is bonded on maxillary arch with 17 degree torque option for central and +7 degree option for canines. The inclination of all the teeth is 0 degree to occlusal plane perpendicular . All the brackets are bonded at same height and the arch is well aligned with normal labial morphology.How much torque would be expressed on maxillary incisors by using a 0.019"x0.025" wire in 0.022" slot. ?The slot bevel , wire bevel  and wire play make 10 degree play of the wire in the slot.

With best regards 

For your answer you would have to go to a scientist with sophisticated instrumentation. I am a clinician. Good luck.  

Thanks sir .

That's the point !!!  if it was a full dimensional wire instead of 19x25 it  would been the answer. limitation of full dimensional wires is another story.But the problem in modern orthodontic brackets is we don't  know how much torque we have expressed.

Sorry for bothering you 

Hi Haris,

The theoretical torque loss (slop) for a 19x25 wire in a 022 system is +/- 7.24°. However, this is modified by the bracket system. Many manufacturers do not have a precise slot size, to complicate this further many wires are not exact either or have bevelled edges which may contribute to slop.

When you add the mechanical factors of wire flex (especially in softer wires) and additional factors of biology, such as altered facial curvature of the tooth and cement thickness then the exactitude of bracket torque virtually flies out of the window. As Dr Northway correctly relates its the clinical results that matter, not what the company who designs what is essentially just a handle say. Thus we learn the important lesson that it is the skill of the clinician, not the system designer (MBT) or prescription that gets the results. Reliance completely on prescription would not make you a good clinician, however some advantage can be gained by using higher torque brackets or better still going to a 018 system that expresses torque earlier with lighter forces, but thats just down to personal preference.

If the theoretical model is all you need then read these 2 papers. The equations for calculating the torque are contained within (and should be part of any good postgrad program).

Mathematical Prediction of Torque Loss for Different Archwire Dimensions and Shapes in Different Bracket Slots Quang L. Nguyen, DMDa, Ronald A. Bell, DDS, Medb, Goodwin Thomas, DDSc

Archambault, A., Badawi, H., Carey, J., Flores-Mir, C., Lacoursiere, R., Major, P. W. Torque expression in stainless steel orthodontic brackets. Angel Orthodontist. 2010;80:201-210

Dear David 

                 Thanks for the input.First of all i mentioned torque play of 10 degree because its mentioned in systematized orthodontic treatment mechanics book .William proffit mention is 9.6 degree with reference to a German study.

i studied MBT system and my personal and only personal opinion its not a proper system if you consider the mechanics because you never know what torque would be express.

All these studies that measured torque use mathematical formulas or leaf gauges and many rudimentary techniques to measure wire play so the torque loss. But the measure this on single bracket. we all know passing wire through single bracket don't express torque. Atleast one and ideally both side tooth should have brackets to express effective torque. 

So if going to my above question the situation is as follow 

the a MBT prescription is bonded on maxillary arch with 17 degree torque option for central and +7 degree option for canines. The inclination of all the teeth is 0 degree to occlusal plane perpendicular . All the brackets are bonded at same height and the arch is well aligned with normal labial morphology.How much torque would be expressed on maxillary incisors by using a 0.019"x0.025" wire in 0.022" slot. ?The slot bevel , wire bevel and wire play make 10 degree play of the wire in the slot.

In this situation passing wire through both upper incisors wont express only torque as the wire have no twisting in the slots. Extending this wire through laterals having 10 degree torque wont express  any torque as the 7degree  twist in the wire is less than 10 degree play that can be accommodated in the brackets. Extending the wire in the canine will cause intrusion of the canine due to exiting effect of wire from lateral brackets in a semicircle arc  but a +7 degree can will twist the wire 3 degree which is less than 10 degree free play . Extending the wire with -7degree torque will express only 4 degree negative between canine and premolars most of which will go premolars .The small positve torque in canine may or may not cause lateral incisor torque change depending upon interbracket distance ,bone quality ,length of roots etc. 

But this is not the case in engaging full dimension wires. In full dimension wires full torque is expressed and clinician don't need a mathematician to make these calculations .But till the limitation of using full dimension SS remain we have live with uncertainty what our brackets did. We have simply taken away the brain of a preadjusted bracket so we can use our own. 

I know we all are doing good at what we are doing but there is always chance of simplicity and betterment.i still know some clinician that use standard edgewise appliances and do all the wire bending because they think it make them true orthodontist.

Regards

Hello Haris,

the effective torque can be measured. Please have a look at  attached file.

best wishes

U. Kritzler

Dear Ulrich 

          Thanks for sending me a dentaurum catalog page .Its is based on following article

Sernetz F. Qualität und Normung orthodontischer Produkte aus der Sicht des Herstellers. Kieferorthopädische Mitteilungen 1993; 7: 13-26.

William proffit also borrowed this article table in his book .

To the best of my understanding the article is based on measuring the wire play in a single bracket.wire play -built in torque = effective torque

In modern orthodontics you dont need this. You can easily use a computer softwae or print a picture after take snaps with good quality lens. The pictures are given. The pictures are from one of my upcoming book that is still in review and are copyright protected.

We all  know single brackets dont express torque .We need to pass wire atleast two and ideally 3 bracket for the middle bracket to express torque. The discussion how things work is given above.

Many question is based on clinical setting .In clinical because of many factors the 19x25 wire dont express  the required torque.

Give you kind comments if i am wrong. 

1. Archambault A, Lacoursiere R, Badawi H, Major PW, Carey J, Flores-Mir C. Torque expression in stainless steel orthodontic brackets. A systematic review. Angle Orthod. 2010 Jan;80(1):201–10.

Thanks for mentioning the article.But how many times you have felt a torsion of 20 degree while inserting a 19x25 wire . the central has 17 or 22 degree torque and lateral has 10 .until or unless severe proclination or retroclination or extreme morphological variation is not present you wont get a torsion necessary for effective torque. 

After going through that article what you think you much torque in passive or active self ligating brackets would be expressed in MBT prescription on maxillary incisors?

I neither use heavy steel wires nor bend additional torque into a steel wire to torque the incisors. In order to prevent severe root resorption  I use Warren springs or torquing untility arches instead. This approach is used by Bjorn Zachrisson too.

1. Bernstein L. Root Torque with Warren Springs. J Clin Orthod. 1971;5(03):167–9.

2. Deangelis V. A 50-year journey from Begg to straight wire and beyond: is orthodontics on the correct course today? J Mass Dent Soc. 2010 Jan;59(2):38–42.

3. Isaacson RJ, Rebellato J. Two-couple orthodontic appliance systems: torquing arches. Semin Orthod. 1995 Mar;1(1):31–6. 

4. DeAngelis V. Iatrogenic Damage To Dental Roots And Paradental Tissues. J Mass Dent Soc. 2012;(Spring 2012):1–5.

Best wishes

Ulrich Kritzler

Dear Ulrich

                           i also use torquing spring in case of special torque problem. Even we use heavy wires we don't get the required torque.We still resort to wire bending in SWA ! . its still a dream for us to have a fully preadjusted system. 

Regards

Do you know the following publications:

1. Thomas WW. Variable Torque for Optimal Inclination. Clinical impressions vol 17 no 2009;(1):1–9.

Thanks for the articles

I think the torque in prescription brackets serve mainly to guard against unwanted torque rather than to produce an effective torque. Nigel Harradine in AAO 2014 had a lecture addressing this issue. You may want to look it up but it focuses mainly on play.

Thanks Hassan i agree on this. Contemporary brackets with contemporary mechanics dont produce effective torque as claimed.

Slot dimensions are  more important for the transmission of torque than bracket design.

Dear Ulrich i do agree that slot dimension is important. All the articles you are sending are about wire play and thus effective torque in a single bracket.Because it is simple to measure them. Here i got a question about clinical setting. The theme of asking the question is to validate my personal opinion that contemporary  prescriptions like MBT is a commercial stunt if we use it with MBT mechanics.90% of our cases lack ideal tooth angulation . We buy preadjusted brackets to finish the case at specific tooth position and end the case at notion that we dont have to treat the number but the patient.

I hope after going through  all those articles you send me you cant tell by surety  that how much torque would be expressed in 19x25 wire in MBT in upper incisors bcz it just a wild guess. 

Hello Haris,

Michel Dalstra has published new research on torsional play.

Best wishes

U. Kritzler