torque in orthodontics

GOOD MORNING ALL

TORQUE IN ORTHODONTICS

Supervisor Dr Maher Fouda Prepared by Hawa Shoaib

TORQUE

1. Torque is a force system. It is produced by torsion in an arch wire that creates a couple when interacted with a bracket slot, which is the result of twist in the wire compared to the bracket slot.

2. Torque is not “in the wire”. Torque is not the angle of the bracket slot. Torque is not the axial inclination of the tooth.

3. Torque applied to a tooth created by torsion in the arch wire against the bracket slot spins the tooth around its center of resistance.

In orthodontics mechanics, 3rd order twist in the arch wire only produces a couple (torque).

4. A wire twisted to produce lingual ROOT torque to the maxillary incisors will also extrude the maxillary incisors

5. A wire twisted to produce labial root torque to the maxillary incisor will also intrude the maxillary incisors.

Mechanically, it refers to the twisting of a structure about its longitudinal axis, resulting in an angle of twist. Torque is a shear-based moment that causes rotation. Clinically, in orthodontics, it represents the

buccopalatal crown/root inclination of a tooth..

Angle Orthodontist, Vol 80, No 1, 2010

ANGLE ORTHODONTIST, VOL 82, NO 4, 2012

In orthodontic treatment, torque control is often required, particularly in the maxillary incisors, for an ideal inter incisal angle, adequate incisor contact, and sagittal adjustment of the dentition in order to achieve an ideal occlusion.

BIOMECHANICS OF TORQUE

1 .Torque or root movement is achieved by keeping the crowns stationary and applying a moment to force only to the root..

2 .The center of rotation of a tooth is at the incisal edge in case of root movement..

3. The M/F ratio should at least be 12: 1 to achieve root movement

4 .According to Dr. Ravindra Nanda : M/F ratio of 5:1 causes uncontrolled tipping M/F ratio of 7:1 causes controlled tipping M/F ratio of 10:1 causes translation M/F ratio of 12:1 causes ROOT MOVEMENT

PROFFIT has stated the simplest way to determine how a tooth will move is to consider the ratio between moment created when force is applied to crown (Mf) and counterbalancing moment generated by a couple within the bracket (MC)

The ratio between the moment produced by the force applied tomove a tooth (MF) and the counterbalancing moment produced by the couple used to control root position (MC) determines the type of tooth movement.

With no MC, (MC/MF = 0), the tooth rotates around the center of resistance (pure tipping). As the moment-to-force ratio increases (0 < MC/MF < 1), the center of rotation is displaced further and further away from the center of resistance, producing what is called controlled tipping. When MC/MF = 1, the center of rotation is displaced to infinity and bodily movement (translation) occurs. If MC/MF > 1, the center of rotation is displaced incisally and the root apex will move more than the crown, producing root torque.


torque expression is affected by the amount of play between the arch wire and the bracket slot and by variations in tooth anatomy, variations in bracket placement, inaccuracies in the bracket slot and arch wire dimensions ,mode of ligation of an arch wire, and stiffness of the arch wire

The MBT and Roth bracket prescriptions are the two commonly used preadjusted edgewise appliance systems in the United Kingdom..


There is no difference in the final inclinations of the upper central incisor, lower central incisor, and upper canine in patients treated with either

the MBT or Roth prescription preadjusted edgewise appliances.

TORQUE EXPRESSION 0.018 VS 0.020 SLOT

EXPRESSION OF TORQUE

THE MBT™ VERSATILE+ APPLIANCE SYSTEM

Inadequate torque expressed in the anterior teeth can result in torque loss in the upper incisors during over jet reduction or space closure and proclination of the lower incisors when leveling the Curve of Spee or treating for crowding in the lower arch.

The MBT™ Versatile+ Appliance System offers greater palatal root torque in the upper incisor area and greater labial root torque in the lower incisors. For increased versatility, two options are available for the upper central incisors: +17° or +22°, depending on the clinical need.

MODE OF LIGATION

CLASS || MALOCCLUSION AND TORQUE

CASE REPORT 1 An 11-year-old girl had crooked and proclined front teeth. She had a convex profile and a deep mentolabial fold. mandible was retrognathic. Severe proclined maxillary incisors were obvious in photographs that showed her smiling

Intraoral photographs indicated a half-cusp Class II canine relationship on the left and a one-cusp Class II canine relationship on the right, with a deep overbite and a 10-mm overjet. Extraction was indicated because of the proclined maxillary anterior teeth and 3-mm crowding in the maxillary arch and the excessive curve of Spee and 2-mm crowding the mandibular arch

Initially we used Australian 0.016-inch wire with multiple helical vertical loops among maxillary anterior teeth and circle loops flush mesial to the canines, so that the resolution of anterior crowding and distalization of the canines could be realized simultaneously. During this stage Class II elastics, between mandibular first molars and the vertical loops distal to the lateral incisors, were used with light force, around 2 oz The flush circle bend then pushed the canine distally

High-torque brackets were used in the maxillary arch (22-degree torque for the maxillary central incisors) because the maxillary incisors were prone to retroclination during retraction.

Low-torque brackets were chosen for the mandibular arch (–6-degree torque for the mandibular incisors) because the negative torque prescription in the mandibular incisors could counteract the side effect of anterior proclination caused by Class II elastics.

TORQUE CONTROL IN VARIOUS TREATMENT STEPS

1 .LEVELING AND ALIGNING

2 .SPACE CLOSURE AND TORQUE

BITE OPENING CURVES AND TORGUE

SPEE CURVE LEVELING WITH REVERSE CURVES

When we use reverse curves to level a deep curve of Spee, we find that the intrusive forces exercised in the anterior and posterior sectors are balanced with the extrusive forces that are exercised in the premolar region. Another effect is that the intrusive forces are going to provoke at the molar level a positive torque and a distal inclination of the crowns and a mesial movement of their roots; on the other hand the intrusive forces exercised at the incisor level will provoke a buccal movement of these (positive torque).

DEFFRENTIAL TORQUE

TORQUE ( CLEARANCE)

CLEARANCE is the amount of play between the bracket and arch wire which depends on the size of the arch wire.

For example, a 0.017-inch × 0.025-inch stainless steel arch wire has approximately 12 to 14 degrees of play in a 0.022-inch slot, assuming that the wire is completely passive when retraction starts, while a 0.016-inch × 0.022-inch stainless steel arch wire has 16 to 18 degrees of play . Then will show greater amounts of tipping and a prolonged phase I and phase II of retraction compared to the former. A clinician should judiciously select the arch wire for space closure.

So if the anterior teeth are flared at the beginning,more tipping is required; hence a thicker wire will be of limited use, as the effective play will be less. If instead the teeth are upright and there is a need for more control on the incisors, a thicker wire should be the choice..

INTRUSION AND TORQUE CONTROL UTILITY ARCH OR CTA

The utility arch is similar in design to the CTA. It is stepped down at the molars, passes through the

buccal vestibule, and is stepped up at the incisors to avoid distortion from occlusal forces. The difference is that for intrusion the utility arch is tied into the incisor brackets, which create a two-couple force system the moment of which tends to tip the incisor crowns facially and the molar distally

the facial tipping of incisors can be avoided by cinching or tying back the intrusion utility arch, any force that tends to bring the anchor teeth mesially is undesirable. Incorporating a “twist” or “torque bend” in the incisor segment is another way of controlling the tendency of the teeth to tip facially;

Another problem is that, unlike the CTA, this being a two-couple system means that it is impossible to accurately determine the magnitude of the reactive forces (statically indeterminate), which makes it rather impossible to adjust the arch wire to prevent side effects. Therefore in our clinical practice we prefer to use the CTA. Also, considerable chair time is saved as the CTA involves no wire bending and needs minimal adjustment So CTA IS BETTER FOR CONTROL OF TORQUE

a ‘‘bi dimensional-slot’’ technique. In the bidimensional slot technique, the pre torqued 0.018-inch brackets are placed on the incisors, while the 0.022-inch brackets are placed on other teeth. When a 0.018 / 0.022-inch SS arch wire is engaged, it ‘‘full-sizedly’’ fits into the anterior brackets, but leaves a clearance of 0.004 inch within the buccal brackets.

The theories of the bi dimensional approach—that the full-size engagement at the anterior segment cangive the utmost play to the pre torque in these brackets, while the clearance at the buccal segments can facilitate the wire sliding in space closure—probably make sense.

Lead to

So use

1 .The active self-ligating brackets seem to have better torque control, a direct result of their active clip forcing the wire into the bracket slot.

2. The amount of arch wire bracket slop was considerably less for active self-ligating brackets than passive self-ligating brackets.

3. The active self-ligating brackets expressed higher torque values than the passive self-ligating brackets at clinically usable torsion angles (0°-35°)..

Application of a second-order couple through a bracket to a longitudinally twisted arch wire will set up a small third-order couple. This couple will have a restraining effect on the third-order wire-bracket interaction.

CASE REPORT 2

Anterior labial root torque When upper anterior teeth, particularly lateral incisors, are in

cross bite, they often need labial root torque. Normally positioned lateral incisor brackets, due to the torque built into those brackets, encourage the expression of lingual root torque. In cases where labial root torque is desired, the laterals never look quite right when normal torque expression occurs. My answer to this problem is to place the lateral incisor brackets on upside down. Flipping the brackets changes the torque expression from predominately lingual root torque to predominately labial root torque when rectangular wire is used.

THE PROCEDURE TO ENCOURAGE LABIAL ROOT TORQUE IS AS FOLLOWS:

1) Create space in the arch form for the blocked out lateral incisor. This can be done on the initial arch wire by packing open coil spring between the central and canine in non-extraction cases, or by using a combination of coils and/or lacebacks in extraction cases . use a slightly larger (about 2mm) piece of coil each month until enough space in the arch form is created to accommodate the blocked out tooth.

2) Once sufficient space is created, bracket the blocked out tooth (in our example, the upper lateral incisor). Place the bracket on upside down and engage the tooth. A light flexible arch wire must be used because that wire must be deflected a significant amount to engage the tooth. Often, as in the case shown here, a tandem arch wire set up is used.

3) This set-up will result in labial movement of the crown. Because round wire is being used, no torque expression occurs as a result of torque in the bracket slot. At this stage of treatment it doesn't matter what the torque in the bracket slot is. Once the crossbite is corrected, remove the composite from the occlusal surface of the lower molars. The overbite will help retain the labial crown movement.

4)Once initial aligning is complete, begin torque expression by using a low load deflection rectangular arch wire. I often use 019x025 heat activated nickel titanium (HANT) followed by 021x025 HANT. Filling the slot encourages the expression of torque. The upside down bracket means the torque in the bracket slot encourages labial root/lingual crown torque. Because of anterior overbite, occlusion helps the crown retain its position while labial root torque occurs. Usually about 10 weeks of 021x025 HANT is necessary to achieve full torque expression. Leave the bracket on upside down for the whole treatment. That way correct torque expression is encouraged throughout the whole treatment.

Periodontal Ligament Hydrostatic Pressure

with Areas of Root Resorption afterApplication of a Continuous Torque

Moment

Angle Orthodontist, Vol 77, No 4, 2007

Resorption lacunae (arrows) are visible on the lingual sides of the lingual (LR) and buccal (BR) root parts.

application of a torque of 6 N mm, the root resorption was greater than for the teeth that received 3 N mm of torque in the in vivo experiments.

Good control in the retraction of anterior teeth during space closure is essential for successful orthodontic treatment. The incorporation of hooks in the retraction arch allows one to adjust the height of the line of action of the force by means of different lengths of soldered hooks..

The group with the 6 mm hook presented better results probably due to the fact that the system produced more bodily movement (translation) than palatal inclination, however the greater difficulty in moving the root in the distal direction simultaneously to the crown, probably requires a longer retraction time, or greater force application..

» Arches with vertical 6 mm high soldered hooks allowed approximation of the line of action of force to the center of resistance of the incisors, providing better mechanical control.

» Association of palatal torque on the retraction arches of anterior teeth is suggested to increase vertical control and diminish the palatal inclination of the incisors during the movement of retraction.

THE MOST COMMON SITUATIONS AND RECOMMENDED BRACKET PRESCRIPTIONS INCLUDE

1-Upper incisors

Negative bracket torque prescription (If they become available

A) advancement of upper crowding in non-extraction cases B) open bite prevention C) advancement of upper incisors in non-extraction cases

needing Cl III elastics

Positive bracket torque prescription;

A) non-extraction cases where the upper incisor start out being retroclined

B) Class II cases where the upper arch is extracting and the upper incisor will be retracted

C) Cases where there are gingival display concerns

2-Lower IncisorsNegative bracket torque prescription

A) advancement of lower crowding in non-extraction cases

B) advancement of lower incisors in non-extraction cases needing Class II elastics

C) Class III non-extraction cases to minimize the lower incisor advancement

Positive bracket torque prescription

A) Class I cases where lower bicuspids are extracted to add lower anterior anchorage

B) Class II cases where lower bicuspids are extracted to add lower anterior anchorage

Non-extraction Class II cases planning to use Class II elastic mechanics also could benefit from using Negative torque prescription to prevent excessive proclination lower incisors. This can result in more stability and a better periodontal prognosis.

Torque is affected only when 2 edges of rectangular wire touch the walls of the bracket slot. But there cannot be excessive binding such that arch wires are not permitted to move easily for alignment and to allow sliding mechanics(Andrews, 1972)

This is a central dilemma of bracket design: friction is the enemy of some tooth movements such as alignment and sliding mechanics while it is our best friend for other tooth movements like application of torque.

To balance this dilemma manufactures machine up to 20 degrees of wire spin when .019”x.025”ss wire is engaged into a .022” slot bracket and 6 degrees on a .021”x.025”ss wire. (Archambault, et al., 2010)

Light wire auxiliaries with pre-adjusted edgewise

appliance to control individual incisor torque

the torque spurs have been used to torquethe incisor roots as required but they have inherentdisadvantages such as excessive torque expression and lingual displacement of the tooth if the attachment to main archwire breaks.

Looped torque auxiliaries have been used for progressive torquing of the incisor roots..

These auxiliaries deliver light, continuousforces without reactivation and produce little, if

any, patient discomfort. Despite their advantages,,some orthodontists refrain from using them becauseof esthetic and hygienic concerns.

The MAA is constructed in a circular shape, when the MAA is pulled open and tied to the lower incisor bracket using a ligature wire a couple is generated with the incisal part of the box applying a lingual force on the tooth and gingival part of the box applying a labial force.

An 18-year-old female ..chief complaint of irregularlyplaced upper front teeth. The initial clinical examination revealed the following extra oral features: mesocephalic, mesofacial, mild convex profile with mild posterior divergence and competent lips . Intraoral examination revealed Class I molar relation bilaterally, overjet of 1 mm, upper and lower anterior crowding and crossbite in relation to 12 and 43 and in relation to 22 and 33 and instanding 42.

MAA OFFERED SEVERALADVANTAGES:

• Biomechanically more efficient for torque delivery than conventional PAE techniques.

• No need to step down the wire since it generates the labial force itself.

• In upper arch, use of MAA in cases of instanding incisors eliminates the need to reverse the bracket to get a labial root torque.

• Eliminates the need to make individual torque bends in the archwires,

The spring unit is fabricated from a segment of .016" × .022" beta titanium wire in a squaredU shape, with two vertical arms connected by a horizontal segment. The spring is preactivated by applying torsion to the connecting segment, forming an angle of 25 - 60° (depending on the amount of torque needed) between the two vertical arms.

The GTS is a small torquing spring that may be placed anywhere on the archwire to move the roots of the tipped teeth into alignment

Rectangular wire of 16×22 or 18×25 works best with the spring in either nitinol or stainless steel. The spring may also be used on 18 or 20 square wire

torque in orthodontics

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