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Roth prescription.ppt

The document discusses Roth prescription and the development of the MBT bracket system. It describes how Roth observed that teeth will move after appliance removal and proposed overcorrection. This led to the development of the Roth prescription, which involves increased torque, tip, and in/out values compared to straightwire. The document then outlines how the MBT bracket system was developed by modifying the Roth prescription values based on new research. Key modifications included reduced anterior tip and lower posterior torque values. The document also discusses MBT bracket placement technique and methods for anchorage control.

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ROTH PRESCRIPTION
DR. Ronald Roth after using the Straightwire appliance for many years, raised a question:- "If we were clever enough to get the teeth into ideal position at the end of the treatment using Straight wire appliance, would the teeth remain in those positions?“ Probably not!
• He said " I have never seen a case with fixed appliance in which the teeth did not move or settle into occlusion after appliance removal".
He noted that following changes occur after appliance removal: • Teeth will move after appliance removal, no matter where they are placed. • Curve of spee will return or deepen after appliance removal. • As the teeth in buccal segments settle they will tip mesially. • Teeth adjacent to an extraction site will tend to rolate & tip towards extraction site.
• Because these factors seems to occur most of the time, it seems only logical to plan for these things to happen during treatment & set up a goal that will overcome these factors. • The obvious choice is Overcorrection, which he gave in the form of Roth prescription.
• incisors - Torque is increased to reduce wire bending in the later stages . • canine - Torque is increased to keep the root away from cortical plate • Molars - Tip is reduced - to get bracket wings parallel with buccal groove of the tooth
Lower teeth
• Lower second molar torque is increased to avoid rolling back of the teeth lingually which was commonly observed.
Bracket placement: X is the value of FACC at FA in the first molar
MBT
After using the Straightwire appliance system by Andrew and Roth prescription system for more than 8 years and reviewing more recent research on measurements of the dentition Bennet, Mc.Laughlin and Trevisi determined that further modifications were needed to optimize treatment efficiency. Together they developed the MBT Versatile + appliance system.
Upper anterior tip: • The anterior tip measurements for the original SWA are all greater than those found in Andrew research. • This was done to control what Andrews referred to as "Wagon wheel" effect that torque places on the anterior crown tip. • He said that as the palatal torque is added to the anterior segment, the mesial crown tip is reduced giving the wagon wheel effect.
• But MBT observed that with light continuous force mechanics, tip is well controlled by the PEA. • By using lacebacks and bendbacks during leveling and aligning and elastic module tiebacks during space closure, very little adverse tipping occurs during these stages of treatment. • So in the MBT Versatile+ appliance, the anterior tip is reduced.
Upper posterior tip: • For the MBT Versatile appliance, 0 degree tip, as opposed to 2 degree tip has been selected for all the premolar brackets. • This places the crowns of these teeth in slightly more upright position, which is more in the direction of class I. • It also provides for slightly reduced anchorage needs for these teeth.
• The reference for crown tip in the upper molar is the buccal groove. • This buccal groove shows a 5 degree angulation to a line drawn perpendicular to the occlusal plane. • Usually a 5 degree bracket is used with the bands seated more gingivally at the mesial aspect.
• When this 5 degree bracket is placed parallel to the occlusal plane, it actually provides 10 degree tip to the upper first molars which is excessive. • In MBT versatile+ appliance, the tip for the upper molar is 0 degrees with the band and bracket slot placed parallel to the occlusal plane. • This introduces the correct 5 degree tip in the upper first and second molars as measured from the buccal groove
Lower posterior tip: • MBT prefers the same tip to that of the Andrews in the premolars, since angling these teeth slightly forward in this manner moves them more into the class I direction. • Zero degree tip is preferred in the lower first and second molars. • Similar to the upper molars, 2 degree tip is derived when the band and bracket is placed parallel to the occlusal plane.
Anterior torque: The palatal torque in the upper incisors and the labial torque in the lower incisors is increased, since it is the most common requirement in the orthodontic cases and thereby reducing the need for wire bending.
While the upper canine torque is same to that of the Andrews, lingual torque in the lower canine is reduced. This is done so that the root is placed more closer to the center of the alveolar process.
Upper posterior torque: • The torque values for the premolar is same to that of the Andrews. • The upper molars frequently show excessive buccal crown torque with palatal cusps "Hanging down" and creating centric, balancing side and working side interferences. • For this reason, MBT prefer -14 degree torque of buccal root torque in these teeth, as opposed to - 9 degree of buccal root torque.
• For this reason, MBT prefer -14 degree torque of buccal root torque in these teeth, as opposed to -9 degree of buccal root torque.
Lower posterior torque: The lingual tip in the lower premolar and the molar teeth is reduced. This is because: - Many orthodontic cases demonstrate narrowing in the maxillary arch with lower posterior segments that are compensated towards lingual. -These cases benefit from buccal uprighting of the lower posterior segments.
• It has been consistently observed that lower second molars with -35 degree of torque that consistently "roll in" lingually. • Therefore MBT have chosen to reduce lingual crown torque in the lower cuspids, bicuspids, first molar and second molar.
In-out modifications • Upper second bicuspids are frequently smaller in size than upper first bicuspids. • For this reason an upper Second bicuspid bracket has been provided with additional 0.5 mm of in-out compensation
MBT system comes witht three different types ofbrackeytypes: • Victory series bracket:- This is the mid sized bracket which is beneficial in cases with smaller teeth and minimal to moderate degrees of difficulty.
• Unitek Full sized Twin brackets:- This bracket is larger in size and beneficial in cases with larger teeth, patients with difficult malocclusions where control is essential and with patients who are prone to breakage. • Clarity brackets:- This is ceramic bracket, beneficial in terms of esthetics.
ARCH FORM: • MBT also gave three different types ofarchforms which can be effectively used to fabricate archwires. Theyare:
l. Tapered arch form:- • This arch form provides the most narrow intercuspid width and is indicated in patients with narrow, tapered arch forms
2. Square arch form:- • This arch form is indicated in cases with broad arches. • It is also indicated, in treatment, in cases requiring buccal uprighting of the lower posterior segment and expansion of the arch
3. 0void arch form:- • This arch form is preferred when using multi strand wires, 0.014 and 0.016 stainless steel round wires and all Niti and heat activated Niti wires.
Buccal tubes: • The buccal tubes which is used in the molars can be of different types. • In the maxillary buccal tubes, 3 compartments are seen - Headgear tube, Rickett's tube and Archwire tube.
• Headgear tube is used to insert inner bow of headgear • Rickett's tube is used to insert additional appliance like utility arch • Archwire tube is used to insert regular archwire.
• In the mandibular buccal tubes, only 2 compartments are seen • Rickett's tube and • Conventional tube.
MBT BRACKET PLACEMENT TECHNIQUE
• Andrew recommended that pre- adjusted appliance brackets be placed with the twin bracket wings straddling, in a parallel fashion, to the vertical long the axis of the clinical crown, • And that the center of the bracket slot be placed on the center of the clinical crown.
• Potential errors or potential deviations from this desired position can occur as follows:
Horizontal errors: • Brackets can be placed to the mesial or distal of the vertical long axis of the clinical crown, leading to improper tooth rotation.
• Elimination of such errors can be best achieved by visualizing the vertical long axis of the crown directly from the facial surface, as well as from the incisal or occlusal surface with a mouth mirror. • It is even better to draw a line through the vertical long axis of the clinical crown for more accurate visualization.
Axial or paralleling errors: • Brackets can be rotated off the vertical long axis of the clinical crown if the bracket wings do not straddle the long axis of the crown in a parallel manner.
Thickness errors: • Such errors can occur if excessive adhesive is left underneath one portion of the bracket base, or if the contour of the tooth does not correspond accurately to the contour of the base of the bracket.
• Such errors can cause improper tooth torque or rotation, and can be eliminated by pressing the bracket against the tooth at placement, so that excessive adhesive flows from beneath the bracket, • or by contouring the bracket base to more accurately fit the tooth surface.
Vertical errors: • Vertical bracket placement errors occur when the bracket is placed gingival or incisal/occlusal to the center of the clinical crown.
• Such errors lead to extrusion or intrusion of teeth, as well as potential torque and in/out errors. • The human eye is quite accurate at bisecting and locating the center of a given object such as a crown. Therefore, brackets can be placed accurately using direct visualization on fully erupted and anatomically normal teeth.
• However, in the following clinical situations (which occur quite frequently), direct visualization is more difficult.
Gingival Concerns
1. Partially erupted teeth: • It is difficult to locate the center of the clinical crown on partially erupted teeth when treating young patients. • The tendency is to place the bracket too incisally or occlusally, especially with bicuspids and lower second molars.
2. Gingival inflammation: • Gingival inflammation causes foreshortening, with the tendency to place the bracket too occlusally or incisally.
3. Teeth with palatally or lingually displaced roots: • With such teeth, gingival tissue covers a greater portion of the clinical crown than normal, producing a shorter clinical crown. The tendency is to place the bracket too incisally or occlusally.
Incisal or Occlusal Concerns:
1. Incisal or Occlusal crown fractures or tooth wear: • It is difficult to visualize the center of the clinical crown since the apparent clinical crown is foreshortened.
• Correction of this problem can be made by either restoring the crown to its appropriate length, or by estimating how long the crown was before fracture or wear.
2. Crowns with long tapered buccal cusps: • Occasionally a crown on a tooth such as a cuspid or bicuspid will show an unusually long and tapered buccal cusp. • If the bracket is placed in the center of the clinical crown, adjacent marginal ridges will not be properly aligned. • This situation can be corrected by selectively reducing the height of the cusp prior to bracket placement.
BRACKET PLACEMENT CHART
• In an attempt to reduce the errors inherent in using only a direct visualization method of bracket placement, a study was carried out to provide a method that could serve as a supplement to the direct visualization technique. .
• The result of this study was the development of a bracket placement chart:
• Use of the Bracket Placement Chart eliminates potential gingival errors because measurements are made from the occlusal or incisal edge of the teeth. • This alone is a major advantage, since the majority of vertical bracket placement errors that do occur are the results of inability to accurately visualize the gingival half of the clinical crown.
• The only potential errors that cannot be avoided are on crowns with incisal or occlusal fractures or wear, or on crowns with unusually long tapered facial cusps. • When these situations occur, appropriate millimeter adjustment needs to be made to allow the crown to be properly positioned.
The technique that has been developed for bracket placement with this method is as follows: Step one • Divider and a millimeter ruler are used to measure the clinical crown heights on as many fully erupted teeth as possible on the patient's study models.
Step two • These figures are recorded, divided in half and rounded to the nearest .5mm Step three • The row on the bracket placement chart that contains the greatest number of recorded figures is selected for bracket placement.
Step four • At the time of banding and bonding, brackets are placed by visualizing the vertical long axis of clinical crowns (buccal groove on the molars) as a vertical reference and the estimated center of the clinical crown as a horizontal reference.
Step five: • A bracket placement gauge is then used to confirm that the brackets are at a height that represents the appropriate figures in the selected column of the bracket placement chart.
ANCHORAGE IN PEA
• Anchorage control in PEA means " The maneuvers used to restrict undesirable changes during the opening phase of treatment, so that the leveling and aligning is achieved without key features of malocclusion becoming worse" - Bennet & Mc.Laughlin.
• Bennet and Mc.Laughlin emphasize the need to consider anchorage in all three planes of space.
I.Horizontal anchorage control: • Limiting the mesial movement of the posterior segment and encouraging the distal movement of anterior teeth.
2.Vertical anchorage control: • Involves the need to try to influence vertical skeletal & dental development in the posterior segment [as with high angled cases] and at times attempt to limit vertical eruption of anterior segments or even intrude these segments.
3.Lateral or transverse anchorage control: • Involves the maintenance of expansion procedures, primarily in upper arch, and the avoidance of tipping or extrusion of the posterior teeth during expansion.
Anchorage control is done with • Extra oral - Headgears and face masks • Intra oral - Banding II molars, lacebacks, TPA, Holding arch, Lip bumpers, etc.
l.ANCHORAGE CONTROL IN HORIZONTAL SEGMENT: 1) Control of the anterior segment: -There is a tendency for the anteriors to incline forward during the initial phase of leveling and aligning. -Early attempts were made to eliminate or minimize the efforts by connecting anterior segments to posterior segments, usually with elastic forces.
But as the elastic forces were greater than the leveling force of the archwire, there was a tendency for the anterior teeth to tip & rotate distally, increasing the curve of spee & deepening the bite, This effect is known as "Roller coaster" effect.
• MBT introduced ''lacebacks" to reduce these effects. • These are constructed using 0.009 or 0.010 ligature wire tied in a figure of eight fashion. • They extend from most distally banded molars to the canines in all quadrant.
• Even though the initial purpose of the lace backs was to prevent canines from tipping forward, it was noted that the lace backs can also be effectively used to distalize the canines without the unwanted tipping which is known as 'walking canines'.
• There is initial tipping of the canines distally. • This is followed by a period of rebound, where the leveling effect of the arch wire will allow the roots of the canines to move distally.
Bend backs • MBT also introduced another method known as "Bend backs" where the arch wire is bent immediately behind the most distally banded posterior teeth, which will minimize the forward tipping of the incisors.
b. Control of posterior segments: 1. Upper posterior arch: The posterior anchorage control requirements are normally greater in the upper arch than in the lower arch due to 4 main factors: • Upper anterior teeth has larger teeth than the lower anterior teeth.
• Upper anterior brackets have a greater amount of tip built into them than the lower anterior brackets • Upper incisor require more torque control and bodily movement than lower incisors • Upper molars usually move mesially more readily than the lower incisors.
Extra oral force: • Extra oral force is normally the most effective way to provide posterior anchorage control in the upper arch.
• Even though 3 types of headgears are there - Occipital, Cervical & Combi pull, the most preferred one by MBT is -Combi pull. • This type of headgear allows a distal force to pass straight through the center of resistance of' the maxillary dentition. This is done by making the outer bow of the facebow angled upward by 15 degrees.
• MBT suggested a force level of 150-250 gm for occipital pull and 100-150 gm for cervical pull. • This slightly stronger pull on the occipital compartment will help the force directly slightly above the occlusal plane & simultaneously allowing effective distalization of the molars. • In the high angled cases only occipital pull should be applied and in the low angled cases, only cervical pull is advocated.
Trans Palatal Arch: • A Trans palatal arch can be used in moderate anchorage cases • This restricts the mesial movement of the maxillary molars
Nance holding arch: • The Nance holding arch reinforces anchorage during leveling and aligning, and canine retraction. • It can also be used immediately after distalization procedures to hold molars in place
Banding the second molars: • Banding the second molars is helpful in the moderate anchorage; cases, but it is not recommended in the high angled cases. • This is because banding the second molars will cause the extrusion of the second molars, which will further increase the MPA angle
Lower posterior arch: Lingual holding arch: • A lingual holding arch, fabricated from 0.045 or 0.051 round stainless steel wire is helpful during the initial phase of unraveling the crowded incisors with lacebacks.
LEVELING & ALIGNING WITH PEA
Wire selection: • Initial archwires should provide light continuous force. • Archwire should move freely within the bracket slot. There should be at least 0.002 clearance, and ideal is 0.004. • During initial alignment, rectangular wires can be avoided since it creates unnecessary root movement, which will increase the possibility of resorption.
• The archwire used for initial alignment requires a combination of excellent strength, good springiness, long range of action & low load deflection rate. • Austenitic Niti like copper Niti or Chinese Niti is much preferable. • Size of the archwire should be 0.016 or 0.018 depending upon the slot size.
• Sometimes a 0.015 or 0.017 multi strand stainless steel can be used initially. • The advantage is that there is less "Initial discomfort" for patients & some wire bending in additional to normal archform can be accomplished.
DEEP BITE CORRECTION WITH PEA
Although moderate deep bite cases gets corrected as a result of routine leveling & aligning procedures, a severe deep bite cases require different corrective procedures • Certain points should be considered in deep bite correction:
• In low angled deep bite cases with extraction, control of the overbite is very difficult. – This is because the strong muscle force in this situation makes it more difficult for the posterior teeth to move anteriorly into extraction site. – The anterior teeth tend to upright as they move posteriorly with subsequent further bite deepening.
• In high angled cases, care should be taken to avoid the extrusion of the posterior teeth since it further increases the Mandibular Plane angle and downward & backward rotation of the mandible.
Incisor position • When the incisors are retrusive and can be advanced, this helps in bite opening process. • When they are protrusive and need to be retracted, the bite tends to deepen & mechanics become more difficult.
l. BITE PLATE: • The use of anterior bite plate is most effective in the initial treatment stages of deep bite cases, especially in non extraction cases.
• It helps in the extrusion of lower posterior teeth & allows early placement of brackets in lower incisors. • It is contra indicated in high angled cases since extrusion of posterior teeth further increases the MP angle.
2.BITE OPENING CURVE: • At the end of initial leveling & aligning, a rectangular stainless steel archwire with bite opening curve can be placed. • A reverse curve in the lower archwire & accented curve in the upper archwire. • It may not be beneficial in all cases.
3.INTRUSION UTILITY ARCH: • Intrusion utility arch was devised by Ricketts with the help of basic biomechanical principles developed by Burstone. • This appliance consist of a continuous wire that extends across both buccal segments but engages only the first permanent molars and four incisors.
Components: • Molar segment, which is adapted into the auxiliary tube. • Posterior vertical segment • Vestibular segment, which runs in the buccal vestibule. • Anterior vertical segment • Incisal segment, which is adapted to the four incisors.
Wire selection:. • For 0.018 slot - Mandible - 0.016*0.022 or 0.016*0.016 Maxillary - 0.016*0.022 • For 0.022 slot - 0.019*0.025 for both the arches. • Rectangular wire is preferred to round wire to control torque and to prevent unwanted tipping of the incisors.
Fabrication: • The intrusion arch is stepped gingivally at the molars, passes the buccal vestibule and then it is stepped at the incisors to avoid distortion from the occlusal forces. • There should be 5 mm distance between the anterior border of the auxillary tube and posterior vertical segment.
Activation • Two types of activation can be done: – Retraction – Intrusion
Retraction: • Incisor retraction is achieved by bending down the end of the molar segment gingivally. This helps in prevention of protrusion of lower incisors during intrusion.
Intrusion • Intrusion is achieved by placing an occlusally directed gable bend in the posterior portion of the vestibular segment.
4.THREE PIECE INTRUSION ARCH: • This appliance was introduced by Shraff, Lindhauer & Burstone. • Along with the intrusion of anterior teeth, it helps in the retraction of the anterior teeth & thereby enhancing the space closure.
This appliance consists of : • Posterior segment, – Which is adapted into the molars and premolar. • Anterior segment with posterior extension, – which runs through the four incisors and canine • Intrusive cantilever spring, – which is placed between the anterior segment and posterior segment
• The posterior segment is made of 0.017*0.025 stainless steel • A T.P.A can also be given for more consolidation in the posterior teeth. • The anterior segment is placed, which is bent gingivally distal to the laterals, then horizontally creating a step of 3mm. • The distal part of the segment extends posterior to the distal end of the canine bracket, where it forms a hook.
The intrusion springs are fabricated -The wire is bent gingivally, mesial to the molar tube & a helix is formed. - On the mesial end of the spring, a hook is made through which it is attached to the anterior segment. -The spring is activated by making a bend mesial to the helix and then clinched back and attached to the anterior segment.
• This will cause anterior intrusion and the extrusion of the molars. • Along with this, a chain elastic can be attached from the hook of the anterior segment to the molar tube to get retraction along with the intrusion of the anteriors.
5.TIP BACK SPRINGS:
These springs are indicated in cases requiring true intrusion of the incisor and can be used in the following conditions: 1. Growing patients with forward growth rotations 2. For a very deep curve of spee in lower arch 3. Cases with a deep overbite due to extrusion of incisors 4. For a steep natural plane of occlusion
• These springs originally proposed by Burstone, are made of 0.017*0.025 TMA or 0.017*0.025 stainless steel wire. • The anchor molars are reinforced with a TPA in upper and a lingual holding arch in the lower. • The wire is bent gingivally mesial to the molar tube and then a helix is formed
• The mesial end of the spring is bent into a hook & is engaged into the main archwire distal to the lateral incisors which, according to Burstone, is the approximate center of resistance of the four incisors.
• Mesial end of the spring lies passively at the height of the mucobuccal fold and the spring is activated by pulling the hook down and engaging it into the arch wire, thereby causing intrusion of the upper incisors.
SPACE CLOSURE WITH PEA
One has to consider three main factors: • Whether canines & incisors are to be retracted separately or En masse • Whether sliding mechanics or frictionless mechanics should be used • Whether pure retraction or retraction with intrusion is to be used
Depending upon these factors, the appliance choice is made. • When the canines & incisors are retracted separately, it will help in conserving the anchorage especially when sliding mechanics are used. • The principle is that by retracting fewer teeth at a time, less stress is placed on the posterior anchorage.
• In En masse retraction, the method of anchorage is based on the types of tooth movement in the posterior & anterior segments and does not entirely depend upon the number of teeth in each segment.
Sliding mechanics: • In friction or sliding mechanics an elastic chain or thread is attached to the tooth & a continuous arch wire is placed.
• The elastic chain is the force component of the retraction assembly & the wire bracket interaction produces the moment. • Since the e chain is placed at the bracket level & not at the center of resistance, tooth experiences a moment in two-planes of space.
• One moment rotates the tooth mesial-out & the other causes distal tipping of the crown.
Advantages of sliding mechanics: • Complicated wire bending is not required. • Initial wire placement is less time consuming. • Enhances patient comfort • Since the space closure is slow, there is less chance of resorption & relapse
Disadvantages: • Confusion concerning the ideal force levels. • There are no essential guidelines concerning the amount of force to be used during space closure. • Tendency to over activate the elastic & spring forces, which cause initial tipping but gives inadequate rebound time for uprighting.
Wire selection: • A 0.016*0.022 stainless steel wire in a 0.018 slot • and a 0.017*0.025 stainless steel wire in a 0.022 slot is ideal for sliding mechanics. • The composition of bracket also affects sliding mechanics. – For example ceramic brackets create more friction than stainless steel brackets.
Canine retraction with sliding mechanics: • In maximum anchorage situations it would be ideal to retract the canines separately, consolidate the anchorage & then retract the incisors. • Minor cuspid retraction can be carried out with the use of lacebacks. • For the major cuspid retraction, an elastic chain may be attached to the power arm on the cuspid bracket.
• Since the force is passed close to the center of resistance of the canine, it helps to achieve the translatory movement.
• Due to the force of the elastic chain, the canine tooth initially tips distally, followed by a period of "rebound" due to the leveling effect of the archwire-bracket interaction, which causes distal uprighting of the root, thereby helping in the retraction.
Nickel Titanium springs: • Bennet & Mc. Laughlin say that the rate of space closure is significantly greater and more consistent with Nickel titanium springs than the elastic chains.
FRICTIONLESS MECHANICS: • In the frictionless mechanics, teeth are moved without the brackets sliding along the archwire & activating the loop produces the force, which helps in retraction
Advantages of Frictionless mechanics: • Offers more control than the sliding mechanics • Precise control over posterior & anterior anchorage. • Tooth will move only to the limit to which it is activated. • Differential tooth movement is possible
Disadvantages: • Precise understanding in mechanics is required, since minor error in mechanics can result in a major error in tooth movement. • More wire bending skills & chair time is required than sliding mechanics. • Loops may be uncomfortable to some patients.
T LOOP RETRACTION SPRING: • Burstone developed T Loop for the space closure in an extraction case. • He used 0.017*0.025 beta titanium wire in an 0.018 slot. • Advantage of T loop over the normal vertical loop is that the T loop produces a higher M/F ratio, a lower load deflection rate and delivers a more constant force & M/F ratio
PG RETRACTION SPRING: • This spring is constructed from 0.016*0.022 stainless steel wire. • The principal element of this spring is a double ovoid loop of 10mm in height. • It is included in order to reduce the load deflection of the spring & is placed gingivally so that the activation will cause a tipping of the short horizontal arm in a direction that will increase the couple acting on the tooth.
• The gentle round form avoids the effect of sharp bends on load deflection • A desirable force level of approximately l60 gm is obtained when the two sections of the double helix is separated at 1mm.
CONCLUSION • Straightwire appliance is not a computer software which can be downloaded from the bracket case & executed in the teeth to get desired results. • Preadjusted edgewise appliance will not diagnose cases, it will not set up treatment plan, and will not figure out the mechanics needed to correct the malocclusion. • But a properly placed Staightwire appliance will detail the tooth positions better, more consistently, and faster than one can by bending offsets into the archwire
• The key is to get the brackets properly placed. • This requires lot of self discipline & persistence, but the benefits are well worth the efforts. • It allows one to detail & finish cases more accurately. • Above all we should accept the fact that wire bending is always necessary in the Pre adjusted edgewise appliance!

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Roth prescription.ppt

  • 1.
  • 2.
    DR. Ronald Rothafter using the Straightwire appliance for many years, raised a question:- "If we were clever enough to get the teeth into ideal position at the end of the treatment using Straight wire appliance, would the teeth remain in those positions?“ Probably not!
  • 3.
    • He said "I have never seen a case with fixed appliance in which the teeth did not move or settle into occlusion after appliance removal".
  • 4.
    He noted thatfollowing changes occur after appliance removal: • Teeth will move after appliance removal, no matter where they are placed. • Curve of spee will return or deepen after appliance removal. • As the teeth in buccal segments settle they will tip mesially. • Teeth adjacent to an extraction site will tend to rolate & tip towards extraction site.
  • 5.
    • Because thesefactors seems to occur most of the time, it seems only logical to plan for these things to happen during treatment & set up a goal that will overcome these factors. • The obvious choice is Overcorrection, which he gave in the form of Roth prescription.
  • 7.
    • incisors -Torque is increased to reduce wire bending in the later stages . • canine - Torque is increased to keep the root away from cortical plate • Molars - Tip is reduced - to get bracket wings parallel with buccal groove of the tooth
  • 8.
  • 9.
    • Lower secondmolar torque is increased to avoid rolling back of the teeth lingually which was commonly observed.
  • 10.
    Bracket placement: X isthe value of FACC at FA in the first molar
  • 11.
  • 12.
    After using theStraightwire appliance system by Andrew and Roth prescription system for more than 8 years and reviewing more recent research on measurements of the dentition Bennet, Mc.Laughlin and Trevisi determined that further modifications were needed to optimize treatment efficiency. Together they developed the MBT Versatile + appliance system.
  • 13.
    Upper anterior tip: •The anterior tip measurements for the original SWA are all greater than those found in Andrew research. • This was done to control what Andrews referred to as "Wagon wheel" effect that torque places on the anterior crown tip. • He said that as the palatal torque is added to the anterior segment, the mesial crown tip is reduced giving the wagon wheel effect.
  • 15.
    • But MBTobserved that with light continuous force mechanics, tip is well controlled by the PEA. • By using lacebacks and bendbacks during leveling and aligning and elastic module tiebacks during space closure, very little adverse tipping occurs during these stages of treatment. • So in the MBT Versatile+ appliance, the anterior tip is reduced.
  • 17.
    Upper posterior tip: •For the MBT Versatile appliance, 0 degree tip, as opposed to 2 degree tip has been selected for all the premolar brackets. • This places the crowns of these teeth in slightly more upright position, which is more in the direction of class I. • It also provides for slightly reduced anchorage needs for these teeth.
  • 18.
    • The referencefor crown tip in the upper molar is the buccal groove. • This buccal groove shows a 5 degree angulation to a line drawn perpendicular to the occlusal plane. • Usually a 5 degree bracket is used with the bands seated more gingivally at the mesial aspect.
  • 19.
    • When this5 degree bracket is placed parallel to the occlusal plane, it actually provides 10 degree tip to the upper first molars which is excessive. • In MBT versatile+ appliance, the tip for the upper molar is 0 degrees with the band and bracket slot placed parallel to the occlusal plane. • This introduces the correct 5 degree tip in the upper first and second molars as measured from the buccal groove
  • 20.
    Lower posterior tip: •MBT prefers the same tip to that of the Andrews in the premolars, since angling these teeth slightly forward in this manner moves them more into the class I direction. • Zero degree tip is preferred in the lower first and second molars. • Similar to the upper molars, 2 degree tip is derived when the band and bracket is placed parallel to the occlusal plane.
  • 21.
    Anterior torque: The palataltorque in the upper incisors and the labial torque in the lower incisors is increased, since it is the most common requirement in the orthodontic cases and thereby reducing the need for wire bending.
  • 22.
    While the uppercanine torque is same to that of the Andrews, lingual torque in the lower canine is reduced. This is done so that the root is placed more closer to the center of the alveolar process.
  • 23.
    Upper posterior torque: •The torque values for the premolar is same to that of the Andrews. • The upper molars frequently show excessive buccal crown torque with palatal cusps "Hanging down" and creating centric, balancing side and working side interferences. • For this reason, MBT prefer -14 degree torque of buccal root torque in these teeth, as opposed to - 9 degree of buccal root torque.
  • 24.
    • For thisreason, MBT prefer -14 degree torque of buccal root torque in these teeth, as opposed to -9 degree of buccal root torque.
  • 25.
    Lower posterior torque: Thelingual tip in the lower premolar and the molar teeth is reduced. This is because: - Many orthodontic cases demonstrate narrowing in the maxillary arch with lower posterior segments that are compensated towards lingual. -These cases benefit from buccal uprighting of the lower posterior segments.
  • 26.
    • It hasbeen consistently observed that lower second molars with -35 degree of torque that consistently "roll in" lingually. • Therefore MBT have chosen to reduce lingual crown torque in the lower cuspids, bicuspids, first molar and second molar.
  • 27.
    In-out modifications • Uppersecond bicuspids are frequently smaller in size than upper first bicuspids. • For this reason an upper Second bicuspid bracket has been provided with additional 0.5 mm of in-out compensation
  • 28.
    MBT system comeswitht three different types ofbrackeytypes: • Victory series bracket:- This is the mid sized bracket which is beneficial in cases with smaller teeth and minimal to moderate degrees of difficulty.
  • 29.
    • Unitek Fullsized Twin brackets:- This bracket is larger in size and beneficial in cases with larger teeth, patients with difficult malocclusions where control is essential and with patients who are prone to breakage. • Clarity brackets:- This is ceramic bracket, beneficial in terms of esthetics.
  • 30.
    ARCH FORM: • MBTalso gave three different types ofarchforms which can be effectively used to fabricate archwires. Theyare:
  • 31.
    l. Tapered archform:- • This arch form provides the most narrow intercuspid width and is indicated in patients with narrow, tapered arch forms
  • 32.
    2. Square archform:- • This arch form is indicated in cases with broad arches. • It is also indicated, in treatment, in cases requiring buccal uprighting of the lower posterior segment and expansion of the arch
  • 33.
    3. 0void archform:- • This arch form is preferred when using multi strand wires, 0.014 and 0.016 stainless steel round wires and all Niti and heat activated Niti wires.
  • 34.
    Buccal tubes: • Thebuccal tubes which is used in the molars can be of different types. • In the maxillary buccal tubes, 3 compartments are seen - Headgear tube, Rickett's tube and Archwire tube.
  • 35.
    • Headgear tubeis used to insert inner bow of headgear • Rickett's tube is used to insert additional appliance like utility arch • Archwire tube is used to insert regular archwire.
  • 36.
    • In themandibular buccal tubes, only 2 compartments are seen • Rickett's tube and • Conventional tube.
  • 37.
  • 38.
    • Andrew recommendedthat pre- adjusted appliance brackets be placed with the twin bracket wings straddling, in a parallel fashion, to the vertical long the axis of the clinical crown, • And that the center of the bracket slot be placed on the center of the clinical crown.
  • 39.
    • Potential errorsor potential deviations from this desired position can occur as follows:
  • 40.
    Horizontal errors: • Bracketscan be placed to the mesial or distal of the vertical long axis of the clinical crown, leading to improper tooth rotation.
  • 41.
    • Elimination ofsuch errors can be best achieved by visualizing the vertical long axis of the crown directly from the facial surface, as well as from the incisal or occlusal surface with a mouth mirror. • It is even better to draw a line through the vertical long axis of the clinical crown for more accurate visualization.
  • 42.
    Axial or paralleling errors: •Brackets can be rotated off the vertical long axis of the clinical crown if the bracket wings do not straddle the long axis of the crown in a parallel manner.
  • 43.
    Thickness errors: • Sucherrors can occur if excessive adhesive is left underneath one portion of the bracket base, or if the contour of the tooth does not correspond accurately to the contour of the base of the bracket.
  • 44.
    • Such errorscan cause improper tooth torque or rotation, and can be eliminated by pressing the bracket against the tooth at placement, so that excessive adhesive flows from beneath the bracket, • or by contouring the bracket base to more accurately fit the tooth surface.
  • 45.
    Vertical errors: • Verticalbracket placement errors occur when the bracket is placed gingival or incisal/occlusal to the center of the clinical crown.
  • 46.
    • Such errorslead to extrusion or intrusion of teeth, as well as potential torque and in/out errors. • The human eye is quite accurate at bisecting and locating the center of a given object such as a crown. Therefore, brackets can be placed accurately using direct visualization on fully erupted and anatomically normal teeth.
  • 47.
    • However, inthe following clinical situations (which occur quite frequently), direct visualization is more difficult.
  • 48.
  • 49.
    1. Partially erupted teeth: •It is difficult to locate the center of the clinical crown on partially erupted teeth when treating young patients. • The tendency is to place the bracket too incisally or occlusally, especially with bicuspids and lower second molars.
  • 50.
    2. Gingival inflammation: •Gingival inflammation causes foreshortening, with the tendency to place the bracket too occlusally or incisally.
  • 51.
    3. Teeth withpalatally or lingually displaced roots: • With such teeth, gingival tissue covers a greater portion of the clinical crown than normal, producing a shorter clinical crown. The tendency is to place the bracket too incisally or occlusally.
  • 52.
  • 53.
    1. Incisal orOcclusal crown fractures or tooth wear: • It is difficult to visualize the center of the clinical crown since the apparent clinical crown is foreshortened.
  • 54.
    • Correction ofthis problem can be made by either restoring the crown to its appropriate length, or by estimating how long the crown was before fracture or wear.
  • 55.
    2. Crowns withlong tapered buccal cusps: • Occasionally a crown on a tooth such as a cuspid or bicuspid will show an unusually long and tapered buccal cusp. • If the bracket is placed in the center of the clinical crown, adjacent marginal ridges will not be properly aligned. • This situation can be corrected by selectively reducing the height of the cusp prior to bracket placement.
  • 56.
  • 57.
    • In anattempt to reduce the errors inherent in using only a direct visualization method of bracket placement, a study was carried out to provide a method that could serve as a supplement to the direct visualization technique. .
  • 58.
    • The resultof this study was the development of a bracket placement chart:
  • 59.
    • Use ofthe Bracket Placement Chart eliminates potential gingival errors because measurements are made from the occlusal or incisal edge of the teeth. • This alone is a major advantage, since the majority of vertical bracket placement errors that do occur are the results of inability to accurately visualize the gingival half of the clinical crown.
  • 60.
    • The onlypotential errors that cannot be avoided are on crowns with incisal or occlusal fractures or wear, or on crowns with unusually long tapered facial cusps. • When these situations occur, appropriate millimeter adjustment needs to be made to allow the crown to be properly positioned.
  • 61.
    The technique thathas been developed for bracket placement with this method is as follows: Step one • Divider and a millimeter ruler are used to measure the clinical crown heights on as many fully erupted teeth as possible on the patient's study models.
  • 62.
    Step two • Thesefigures are recorded, divided in half and rounded to the nearest .5mm Step three • The row on the bracket placement chart that contains the greatest number of recorded figures is selected for bracket placement.
  • 63.
    Step four • Atthe time of banding and bonding, brackets are placed by visualizing the vertical long axis of clinical crowns (buccal groove on the molars) as a vertical reference and the estimated center of the clinical crown as a horizontal reference.
  • 64.
    Step five: • Abracket placement gauge is then used to confirm that the brackets are at a height that represents the appropriate figures in the selected column of the bracket placement chart.
  • 65.
  • 66.
    • Anchorage controlin PEA means " The maneuvers used to restrict undesirable changes during the opening phase of treatment, so that the leveling and aligning is achieved without key features of malocclusion becoming worse" - Bennet & Mc.Laughlin.
  • 67.
    • Bennet andMc.Laughlin emphasize the need to consider anchorage in all three planes of space.
  • 68.
    I.Horizontal anchorage control: • Limitingthe mesial movement of the posterior segment and encouraging the distal movement of anterior teeth.
  • 69.
    2.Vertical anchorage control: • Involvesthe need to try to influence vertical skeletal & dental development in the posterior segment [as with high angled cases] and at times attempt to limit vertical eruption of anterior segments or even intrude these segments.
  • 70.
    3.Lateral or transverseanchorage control: • Involves the maintenance of expansion procedures, primarily in upper arch, and the avoidance of tipping or extrusion of the posterior teeth during expansion.
  • 71.
    Anchorage control isdone with • Extra oral - Headgears and face masks • Intra oral - Banding II molars, lacebacks, TPA, Holding arch, Lip bumpers, etc.
  • 72.
    l.ANCHORAGE CONTROL IN HORIZONTALSEGMENT: 1) Control of the anterior segment: -There is a tendency for the anteriors to incline forward during the initial phase of leveling and aligning. -Early attempts were made to eliminate or minimize the efforts by connecting anterior segments to posterior segments, usually with elastic forces.
  • 74.
    But as theelastic forces were greater than the leveling force of the archwire, there was a tendency for the anterior teeth to tip & rotate distally, increasing the curve of spee & deepening the bite, This effect is known as "Roller coaster" effect.
  • 75.
    • MBT introduced''lacebacks" to reduce these effects. • These are constructed using 0.009 or 0.010 ligature wire tied in a figure of eight fashion. • They extend from most distally banded molars to the canines in all quadrant.
  • 76.
    • Even thoughthe initial purpose of the lace backs was to prevent canines from tipping forward, it was noted that the lace backs can also be effectively used to distalize the canines without the unwanted tipping which is known as 'walking canines'.
  • 77.
    • There isinitial tipping of the canines distally. • This is followed by a period of rebound, where the leveling effect of the arch wire will allow the roots of the canines to move distally.
  • 78.
    Bend backs • MBTalso introduced another method known as "Bend backs" where the arch wire is bent immediately behind the most distally banded posterior teeth, which will minimize the forward tipping of the incisors.
  • 79.
    b. Control ofposterior segments: 1. Upper posterior arch: The posterior anchorage control requirements are normally greater in the upper arch than in the lower arch due to 4 main factors: • Upper anterior teeth has larger teeth than the lower anterior teeth.
  • 80.
    • Upper anteriorbrackets have a greater amount of tip built into them than the lower anterior brackets • Upper incisor require more torque control and bodily movement than lower incisors • Upper molars usually move mesially more readily than the lower incisors.
  • 81.
    Extra oral force: •Extra oral force is normally the most effective way to provide posterior anchorage control in the upper arch.
  • 82.
    • Even though3 types of headgears are there - Occipital, Cervical & Combi pull, the most preferred one by MBT is -Combi pull. • This type of headgear allows a distal force to pass straight through the center of resistance of' the maxillary dentition. This is done by making the outer bow of the facebow angled upward by 15 degrees.
  • 83.
    • MBT suggesteda force level of 150-250 gm for occipital pull and 100-150 gm for cervical pull. • This slightly stronger pull on the occipital compartment will help the force directly slightly above the occlusal plane & simultaneously allowing effective distalization of the molars. • In the high angled cases only occipital pull should be applied and in the low angled cases, only cervical pull is advocated.
  • 84.
    Trans Palatal Arch: •A Trans palatal arch can be used in moderate anchorage cases • This restricts the mesial movement of the maxillary molars
  • 85.
    Nance holding arch: •The Nance holding arch reinforces anchorage during leveling and aligning, and canine retraction. • It can also be used immediately after distalization procedures to hold molars in place
  • 86.
    Banding the second molars: •Banding the second molars is helpful in the moderate anchorage; cases, but it is not recommended in the high angled cases. • This is because banding the second molars will cause the extrusion of the second molars, which will further increase the MPA angle
  • 87.
    Lower posterior arch: Lingualholding arch: • A lingual holding arch, fabricated from 0.045 or 0.051 round stainless steel wire is helpful during the initial phase of unraveling the crowded incisors with lacebacks.
  • 88.
  • 89.
    Wire selection: • Initialarchwires should provide light continuous force. • Archwire should move freely within the bracket slot. There should be at least 0.002 clearance, and ideal is 0.004. • During initial alignment, rectangular wires can be avoided since it creates unnecessary root movement, which will increase the possibility of resorption.
  • 90.
    • The archwireused for initial alignment requires a combination of excellent strength, good springiness, long range of action & low load deflection rate. • Austenitic Niti like copper Niti or Chinese Niti is much preferable. • Size of the archwire should be 0.016 or 0.018 depending upon the slot size.
  • 91.
    • Sometimes a0.015 or 0.017 multi strand stainless steel can be used initially. • The advantage is that there is less "Initial discomfort" for patients & some wire bending in additional to normal archform can be accomplished.
  • 92.
  • 93.
    Although moderate deepbite cases gets corrected as a result of routine leveling & aligning procedures, a severe deep bite cases require different corrective procedures • Certain points should be considered in deep bite correction:
  • 94.
    • In lowangled deep bite cases with extraction, control of the overbite is very difficult. – This is because the strong muscle force in this situation makes it more difficult for the posterior teeth to move anteriorly into extraction site. – The anterior teeth tend to upright as they move posteriorly with subsequent further bite deepening.
  • 95.
    • In highangled cases, care should be taken to avoid the extrusion of the posterior teeth since it further increases the Mandibular Plane angle and downward & backward rotation of the mandible.
  • 96.
    Incisor position • Whenthe incisors are retrusive and can be advanced, this helps in bite opening process. • When they are protrusive and need to be retracted, the bite tends to deepen & mechanics become more difficult.
  • 97.
    l. BITE PLATE: •The use of anterior bite plate is most effective in the initial treatment stages of deep bite cases, especially in non extraction cases.
  • 98.
    • It helpsin the extrusion of lower posterior teeth & allows early placement of brackets in lower incisors. • It is contra indicated in high angled cases since extrusion of posterior teeth further increases the MP angle.
  • 99.
    2.BITE OPENING CURVE: •At the end of initial leveling & aligning, a rectangular stainless steel archwire with bite opening curve can be placed. • A reverse curve in the lower archwire & accented curve in the upper archwire. • It may not be beneficial in all cases.
  • 100.
    3.INTRUSION UTILITY ARCH: •Intrusion utility arch was devised by Ricketts with the help of basic biomechanical principles developed by Burstone. • This appliance consist of a continuous wire that extends across both buccal segments but engages only the first permanent molars and four incisors.
  • 101.
    Components: • Molar segment,which is adapted into the auxiliary tube. • Posterior vertical segment • Vestibular segment, which runs in the buccal vestibule. • Anterior vertical segment • Incisal segment, which is adapted to the four incisors.
  • 102.
    Wire selection:. • For0.018 slot - Mandible - 0.016*0.022 or 0.016*0.016 Maxillary - 0.016*0.022 • For 0.022 slot - 0.019*0.025 for both the arches. • Rectangular wire is preferred to round wire to control torque and to prevent unwanted tipping of the incisors.
  • 103.
    Fabrication: • The intrusionarch is stepped gingivally at the molars, passes the buccal vestibule and then it is stepped at the incisors to avoid distortion from the occlusal forces. • There should be 5 mm distance between the anterior border of the auxillary tube and posterior vertical segment.
  • 104.
    Activation • Two typesof activation can be done: – Retraction – Intrusion
  • 105.
    Retraction: • Incisor retractionis achieved by bending down the end of the molar segment gingivally. This helps in prevention of protrusion of lower incisors during intrusion.
  • 106.
    Intrusion • Intrusion isachieved by placing an occlusally directed gable bend in the posterior portion of the vestibular segment.
  • 107.
    4.THREE PIECE INTRUSIONARCH: • This appliance was introduced by Shraff, Lindhauer & Burstone. • Along with the intrusion of anterior teeth, it helps in the retraction of the anterior teeth & thereby enhancing the space closure.
  • 108.
    This appliance consistsof : • Posterior segment, – Which is adapted into the molars and premolar. • Anterior segment with posterior extension, – which runs through the four incisors and canine • Intrusive cantilever spring, – which is placed between the anterior segment and posterior segment
  • 109.
    • The posteriorsegment is made of 0.017*0.025 stainless steel • A T.P.A can also be given for more consolidation in the posterior teeth. • The anterior segment is placed, which is bent gingivally distal to the laterals, then horizontally creating a step of 3mm. • The distal part of the segment extends posterior to the distal end of the canine bracket, where it forms a hook.
  • 110.
    The intrusion springsare fabricated -The wire is bent gingivally, mesial to the molar tube & a helix is formed. - On the mesial end of the spring, a hook is made through which it is attached to the anterior segment. -The spring is activated by making a bend mesial to the helix and then clinched back and attached to the anterior segment.
  • 111.
    • This willcause anterior intrusion and the extrusion of the molars. • Along with this, a chain elastic can be attached from the hook of the anterior segment to the molar tube to get retraction along with the intrusion of the anteriors.
  • 112.
  • 113.
    These springs areindicated in cases requiring true intrusion of the incisor and can be used in the following conditions: 1. Growing patients with forward growth rotations 2. For a very deep curve of spee in lower arch 3. Cases with a deep overbite due to extrusion of incisors 4. For a steep natural plane of occlusion
  • 114.
    • These springsoriginally proposed by Burstone, are made of 0.017*0.025 TMA or 0.017*0.025 stainless steel wire. • The anchor molars are reinforced with a TPA in upper and a lingual holding arch in the lower. • The wire is bent gingivally mesial to the molar tube and then a helix is formed
  • 115.
    • The mesialend of the spring is bent into a hook & is engaged into the main archwire distal to the lateral incisors which, according to Burstone, is the approximate center of resistance of the four incisors.
  • 116.
    • Mesial endof the spring lies passively at the height of the mucobuccal fold and the spring is activated by pulling the hook down and engaging it into the arch wire, thereby causing intrusion of the upper incisors.
  • 117.
  • 118.
    One has toconsider three main factors: • Whether canines & incisors are to be retracted separately or En masse • Whether sliding mechanics or frictionless mechanics should be used • Whether pure retraction or retraction with intrusion is to be used
  • 119.
    Depending upon thesefactors, the appliance choice is made. • When the canines & incisors are retracted separately, it will help in conserving the anchorage especially when sliding mechanics are used. • The principle is that by retracting fewer teeth at a time, less stress is placed on the posterior anchorage.
  • 120.
    • In Enmasse retraction, the method of anchorage is based on the types of tooth movement in the posterior & anterior segments and does not entirely depend upon the number of teeth in each segment.
  • 121.
    Sliding mechanics: • Infriction or sliding mechanics an elastic chain or thread is attached to the tooth & a continuous arch wire is placed.
  • 122.
    • The elasticchain is the force component of the retraction assembly & the wire bracket interaction produces the moment. • Since the e chain is placed at the bracket level & not at the center of resistance, tooth experiences a moment in two-planes of space.
  • 123.
    • One momentrotates the tooth mesial-out & the other causes distal tipping of the crown.
  • 124.
    Advantages of sliding mechanics: •Complicated wire bending is not required. • Initial wire placement is less time consuming. • Enhances patient comfort • Since the space closure is slow, there is less chance of resorption & relapse
  • 125.
    Disadvantages: • Confusion concerningthe ideal force levels. • There are no essential guidelines concerning the amount of force to be used during space closure. • Tendency to over activate the elastic & spring forces, which cause initial tipping but gives inadequate rebound time for uprighting.
  • 126.
    Wire selection: • A0.016*0.022 stainless steel wire in a 0.018 slot • and a 0.017*0.025 stainless steel wire in a 0.022 slot is ideal for sliding mechanics. • The composition of bracket also affects sliding mechanics. – For example ceramic brackets create more friction than stainless steel brackets.
  • 127.
    Canine retraction withsliding mechanics: • In maximum anchorage situations it would be ideal to retract the canines separately, consolidate the anchorage & then retract the incisors. • Minor cuspid retraction can be carried out with the use of lacebacks. • For the major cuspid retraction, an elastic chain may be attached to the power arm on the cuspid bracket.
  • 128.
    • Since theforce is passed close to the center of resistance of the canine, it helps to achieve the translatory movement.
  • 129.
    • Due tothe force of the elastic chain, the canine tooth initially tips distally, followed by a period of "rebound" due to the leveling effect of the archwire-bracket interaction, which causes distal uprighting of the root, thereby helping in the retraction.
  • 130.
    Nickel Titanium springs: •Bennet & Mc. Laughlin say that the rate of space closure is significantly greater and more consistent with Nickel titanium springs than the elastic chains.
  • 131.
    FRICTIONLESS MECHANICS: • Inthe frictionless mechanics, teeth are moved without the brackets sliding along the archwire & activating the loop produces the force, which helps in retraction
  • 132.
    Advantages of Frictionless mechanics: •Offers more control than the sliding mechanics • Precise control over posterior & anterior anchorage. • Tooth will move only to the limit to which it is activated. • Differential tooth movement is possible
  • 133.
    Disadvantages: • Precise understandingin mechanics is required, since minor error in mechanics can result in a major error in tooth movement. • More wire bending skills & chair time is required than sliding mechanics. • Loops may be uncomfortable to some patients.
  • 134.
    T LOOP RETRACTIONSPRING: • Burstone developed T Loop for the space closure in an extraction case. • He used 0.017*0.025 beta titanium wire in an 0.018 slot. • Advantage of T loop over the normal vertical loop is that the T loop produces a higher M/F ratio, a lower load deflection rate and delivers a more constant force & M/F ratio
  • 136.
    PG RETRACTION SPRING: •This spring is constructed from 0.016*0.022 stainless steel wire. • The principal element of this spring is a double ovoid loop of 10mm in height. • It is included in order to reduce the load deflection of the spring & is placed gingivally so that the activation will cause a tipping of the short horizontal arm in a direction that will increase the couple acting on the tooth.
  • 137.
    • The gentleround form avoids the effect of sharp bends on load deflection • A desirable force level of approximately l60 gm is obtained when the two sections of the double helix is separated at 1mm.
  • 138.
    CONCLUSION • Straightwire applianceis not a computer software which can be downloaded from the bracket case & executed in the teeth to get desired results. • Preadjusted edgewise appliance will not diagnose cases, it will not set up treatment plan, and will not figure out the mechanics needed to correct the malocclusion. • But a properly placed Staightwire appliance will detail the tooth positions better, more consistently, and faster than one can by bending offsets into the archwire
  • 139.
    • The keyis to get the brackets properly placed. • This requires lot of self discipline & persistence, but the benefits are well worth the efforts. • It allows one to detail & finish cases more accurately. • Above all we should accept the fact that wire bending is always necessary in the Pre adjusted edgewise appliance!