Sheffield Peter, SODT. IN-tendo P.I.B. U.K.Antonopoulos Georgios, SDT, A.D.O.M.E., Greece

The relationship of height and thickness according to changing anterior torque

in Lingual Indirect Bonding.

 This Poster shows how the change of torque directly effects the positioning of a lingual bracket when the same slot height is measured from the incisal edge of a central incisor.

Purpose

 Using a cast model of a real Central incisor in Orthotype Class IV stone and customizing a root shape to retain the tooth example in modeling clay (fig 2) to clearly see the relationship. The instruments from IN-tendo system, T.A.D. (fig. 1) and B.P.D. (fig. 3) and the adjustable surveyor base (fig. 2). Hand held digital Vernier calipers.

Materials

fig. 1 fig. 3fig. 2

We can see clearly that differences in torque change the bracket position on the tooth’s lingual surface. Keeping this in mind we have to evaluate the loss in torque expected between the finishing / torque wires and the slot. For example if a 017 x 025 TMA wire was to be used then we can expect around 5 degrees of play (slop) between the bracket slot and the wire. This is known as the “Torque Trap” (see an article in the AJO 2013 by Prof Earl Johnson) and many other papers referring to this like the one from Thomas Stamm (Volume 1 No 3 Journal of Lingual Orthodontics Year 2000).

Conclusions

1.Anterior morphology and it’s effect on Torque, EJO 27, 2005, M.Van Leonel, J Degrieck,G.Depaun, L.Dermaut .2. Invisible Orthodontics 2003 Scuzzo/Takemoto.3. Vertical forces in Lingual and Labial Orthodontics Applied on the maxillary Incisors-A Theoritical Approach.4.Silvia Geron, Rafi Ramano and Tamar Brosh.5.Systemized Orthodontic Treatment Mechanics, Mc Laughlin, Bennet and Trevisi 2001.6. Prescription based Precision Full Arch Indirect Bonding. Dr John T.Kalagne 2007 Elsevier.7.Changes in Third Order Inclination resulting from Vertical Variation in Lingual Bracket Placements, Michael Knosel, Klaus Jung et al.8.Normal Torque of the buccal surface of mandibular teeth and its relationship with brackrt positioning. A study in Normal Occlusion, Brazil 2006.9. Marcel Antoonio Mestiner, C.Enoki and J. Mucha10.Relationship between Second and Third order problems in Lingual Orthodontics. Vol1 No 3 Journal of Lingual Orthodontics, Thomas Stamm.11.Selecting custom Torque prescriptions for the straight – wire appliance, AJO-DO 2013 Earl Johnson.

References

Assistance in Dental &Orthodontic Mechanical Engineering

A.D.O.M.E.

SODT PETER SHEFFIELD

IN-tendo P.I.B.

It is clear to see in the images provided how Torque has a direct relationship to the vertical height from the incisal edge. As the tooth proclines the vertical surface of the lingual morphology is shortened and this in turn leads to a more gingival placement of the bracket at higher torque settings, with the same height measurement. We may even make a prognosis by choosing the right values and through them select the desired wire plain that will determine our final Orthodontic result and teeth positioning. But is it so simple? Do we need the prescriptions and the standard values of the Orthodontic charts? Or do we have to look at every case separately and base our prescription on knowledge and observation on the patients characteristics? We have to focus on the ‘’signs’’ that nature gives us every time, as the guide lines of our process? And if so what is the protocol we have to follow for the lingual indirect bonding systems with regards to Morphology v’s Torque? Studying all these values and examining them due to the changing morphology of the teeth we are able to create many math charts and diagrams that explain all the ‘logical’ steps we have to do to specify the final bracket positioning. Thinking of all these we are already on the way for more studies and researches that will help us to understand better the ‘cause and effect chain 'of our indirect bonding work.

Results

We cut a single tooth from Class IV Ortho stone and trimmed it to represent a root with crown clearly defined. The root is just for retention within a block of sturdy modelling clay (fig. 2), so we could clearly see from the side any bracket relationship with the lingual surface.

The LACC (Long Axis of the Clinical Crown) was marked on the labial surface and the crown divided into 2 parts to find the midpoint and a mark made for the reference of the midpoint of the instruments blade.

The blade of the Torque and Angulation device (first created in 2005, now remodeled in 2014) was set into different tip and torque positions, by moving the two adjustment knobs illustrated. The values are expressed via the digital screen. (fig. 8a, left column). Then the tooth (Central Incisor with an average morphology) was moved into the correct corresponding position ‘in space’ according to the prescribed Tip and Torque. This technique is following the ‘axiom’ of the technique followed for decades before in the Ormco T.A.R.G technique. This is done by moving the height of the blade via the ‘fine height adjustment screw’ and the tooth by rotating the adjustable surveyor base until the midpoint and long axis correspond to the blade. (fig 4 & fig. 5). The tooth and surveyor base are now transferred to the B.P.D. (Bracket Positioning Device) so that we can measure the bracket height and ‘thickness’ (distance from the bracket slot to the vestibular face of the tooth). An ORG central incisor bracket from the ORJ Company was used in this test. We chose this bracket as it is of an average size and incorporates a hook. The bracket is placed with the slot on the bracket holder which has sprung jaws to hold it firmly in place.

The gross height of the bracket holder was adjusted to be close enough to the incisal edge for a ‘light’ touch without damaging the stone, then locked into position. Now the fine height adjustment screw is used as we do during the bonding process. The jaws of the bracket holder were lowered to the incisal edge and the dial test indicator for reading height was reset to zero by pushing the button on the Mitutoyo dial.

Now using the fine adjustment screw we moved the bracket position down to a pre-determined height for the test. Midpoint of the tooth. (the process is shown in fig 8a, fig.8b, fig. 9, fig. 10, fig 11, fig. 12) and was repeated for each new tip and torque setting exactly the same way until the final values were derived for each torque setting (fig.13, fig 14, fig. 15). The positions of the bracket and the new thickness recorded in the charts below. We measured the last movement (of 5 degrees) from 12 to 17 degrees torque in the tooth position to drop the incisal edge (which is our reference for zero height) by 0.6 mm which would concur with the results of Thomas Stamm’s paper indicating 1.2 mm for 10 degrees of Torque loss.

However we measured the distance from the middle of the incisal edge down the lingual surface to the top of the bracket base to compare the changes that occurred each time the bracket position was changed (slot height) (fig. 6 & fig. 7)

a) (fig. 16, fig 17) : 0 degrees HL2 = 2.78 mm, b)7 degrees HL2 = 3.80 mm, c)12 degrees HL2 = 4.33 mm, d)17 degrees HL2 = 5.11 mm (HL2=the height from the incisal edge to the slot line measured on the lingual surface)

Method

Therefore if there is a big torque movement needed we can expect a rotation of a central incisor (for example in an extraction case where high torque compensation is required) to retrocline by 5 degrees before being stopped by the wire. When this happens then the level of the visible incisal edge will appear to drop…dumping / rabbiting are terms commonly used for this. If we want to counter this effect then we should make the suitable height changes which will help control this phenomenon.

This is a common fault in Lingual Orthodontics when torque movements are required and will need skillful finishing by the Orthodontist to correct it. When we are looking at the bracket positioning from our Indirect Bonding Service, either on the master model or in the mouth and see what we think are height errors, we have to ask ourselves, what is happening in the big picture, what about torque and the final inclination's of the teeth? ...we need to use "Imagineering" to visualize what will be our final result!

fig. 4 fig. 5 fig. 6 fig. 7

fig. 8b

fig. 12

fig. 11 ( 00 LAB TORQUE)

fig. 10

fig. 9

fig. 15 (MBT TORQUE )

fig. 14 ( ROTH TORQUE)

fig. 13(ANDREWS TORQUE)

fig. 8b

fig. 16

 CHART

 LAB ANDREW

S ROTH MBT

TORQUE (degrees) 0 +7 +12 +17

THICKNESS (mm) 4.74 5.25 6.22 7.73

HL2(mm) 2.78 3.80 4.33 5.11

         

fig. 17

In –Tendo Laboratory

The Instruments

Andrews Torque Prescription Chart

B.P.D.Bracket Positioning Device

Roth Torque Prescription Chart

MBT Torque Prescription Chart

T.A.D.Torque & Angulation Device