Torque in pre adjusted e.w.a /certified fixed orthodontic courses by Indian dental academy


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Torque in pre adjusted e.w.a /certified fixed orthodontic courses by Indian dental academy

  1. 1. • INDIAN DENTAL ACADEMY Leader in continuing dental education GOOD MORNING ALL !!
  4. 4. •Position of maxillary and mandibular incisors have long been recognized as useful guides in diagnosis and treatment planning. •Incisor protrusion and inclination are generally considered to influence stability of orthodontic results and aesthetics of lips relative to chin and nose. •Proper buccolingual inclination of both posterior and anterior teeth is considered essential for providing stability and proper occlusal relationship in orthodontic treatment. •In orthodontic terms ‘torque’ can be defined as the buccolingual or labiolingual root tipping in which the movement of the crown is minimized and the root apex is maximized. •In terms of engineering principles ‘torque’ is defined as a force causing twist in a structure. The resulting twist of the mechanical part is called ‘torsion’.
  5. 5. BIOMECHANICS OF TORQUE •Torque or root movement of a tooth is achieved by keeping the crowns stationary and applying a moment to force only to the root. •This basic concept is better understood if the role of moment to force ratio is known. •The centre of rotation of a tooth is at the incisal edge in case of root movement. •The M/F ratio should at least be 12:1 to achieve root movement. •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
  6. 6. Proffit has stated that the perhaps 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). •MC/MF = 0 results in PURE TIPPING •MC/MF < 1 results in CONTROLLED TIPPING •MC/MF = 1 results in TRANSLATION •MC/MF >1 results in TORQUE When a rectangular wire is twisted and inserted into the slot, the opposite sides of the wire contacts the slot which creates a couple and generates a moment large enough for root movement.
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  8. 8. Evolution of torque incorporation from edgewise to PEA Angle (1928) – Introduced the edgewise appliance with basic components of a metal bracket with a rectangular slot whose original size was a 0.022 x 0.028 inch. The unique feature of the rectangular wire in the rectangular slot was that twisting or torquing the wire could be imparted to the arch wire to control axial inclination of the teeth. He also suggested angulating the posterior brackets to produce desired tooth movement.
  9. 9. •Tweed (1941) advocated arch wire bends to obtain correct axial inclinations and called it ‘artistic positioning’. •Holdaway (1958) suggested angulating all brackets and also gave three reasons to support the same : i) As an aid in the paralleling of roots adjacent to extraction spaces ii) To tip back posterior segment for anchorage iii) To obtain correct axial inclinations for artistic positioning Ivan Lee attempted to devise a pre angulated bracket by milling torque into the face of the edgewise bracket slot. Jarabak and Fizzel (1963) incorporated ‘built in’ second and third order movements into edgewise brackets. They suggested that brackets of upper incisors be angulated as well as torqued. Lawrence Andrews (1970) was the first to develop a fully pre adjusted appliance. The term ‘straight wire’ was coined by him as a name for the appliance he invented that eliminated or minimized arch wire adjustments to dictate tooth positions. With this inventory, the era of PEA was officially launched.
  10. 10. TORQUE NORMS IN VARIOUS PRESCRIPTIONS ANDREWS STRAIGHT WIRE APPLIANCE (SWA) • Considered as the first generation of PEA • This appliance was constructed on the basis of a collection of 120 non orthodontic models selected on the basis of occlusions that could not be anatomically improved upon with orthodontic therapy. • The average values from the non orthodontic normal sample were used to construct a hybrid edgewise appliance in which all three dimensions for tooth positioning for each tooth was built directly into the bracket. • On the basis of consistent findings in the non orthodontic normal sample he devised the six keys of occlusion which eventually became Rx objectives: 4. Absence Of Rotations 1. Inter Arch Relationship 5. Tight Contacts 2. Crown Angulation 6. Curve Of Spee 3. Crown Inclination
  11. 11. Average crown inclination in SWA : -9 ° -9 ° -7 ° -7 ° -7 ° +3 ° +7 ° 7 6 5 4 3 2 1 -35 ° -30 ° -22 ° -17 ° -11 ° -1 ° -1 ° Upper Lower •Maxillary incisors have a positive inclination •Mandibular incisors have a slight negative inclination •Upper canines and premolars are negative and quite similar. •Inclination of the maxillary first and second molars are also similar and negative. •Inclinations for the mandibular teeth are progressively more negative from the incisors to the molars. Standard Brackets Fully Programmed Brackets Translation Series
  12. 12. •Standard brackets were designed to treat only non extraction cases with an ANB angle difference of less than 5° without the necessity of putting offset bends into the wire. •Andrews recommended different bracket slot inclinations for three different types of skeletal bases +12° +2° +7° Upper III II I Class -6° +4° -1° Lower •He also emphasized the ‘wagon wheel effect’ where tip was lost as torque was added. Hence he chose to add additional tip to anterior brackets in his SWA.
  13. 13. Translation series brackets (Xn cases) • Included all qualities of the standard brackets. •Additional slot siting features: •Power arms. •Counter mesiodistal tip •Counter rotation •Maxillary molar bracket included a counter bucco lingual tip Minimum Translation Translation Series Brackets Medium Translation Maximum Translation Depending on the distance the teeth have to be translated
  14. 14. ROTH PHILOSOPHY •With the intent to reduce the number of brackets and simplify the straight wire appliance ,Roth selected brackets from Andrews SWA set up and developed the Roth treatment and prescription. •These were made available in 1976 and they are considered as the second generation of PEA. •The three main reasons for the Roth prescription were as follows: •To reduce the need for a large and expensive inventory where one set of brackets could be used for a wide variety of cases •Anchorage Loss: Roth believed that mesially angulated brackets on posterior teeth tend to tip the teeth mesially and let them migrate forward resulting in possible anchor loss. •Over Correction : Roth propagated a therapy goal in which at the end of treatment all teeth were positioned slightly overcorrected and from which the would most likely settle into a non orthodontic normal position.
  15. 15. TORQUE SPECIFICATIONS -14 ° -14 ° -7 ° -7 ° -2 ° +8 ° +12 ° 7 6 5 4 3 2 1 -35 ° -30 ° -22 ° -17 ° -11 ° -1 ° -1 ° Upper Lower •Compared to SWA in the upper arch • The incisor torque is increased (5º) • Canine torque is decreased (5º) • The molar buccal root torque is increased (5º) •The lower arch values are similar to the SWA. •Super Torque Series • Extra torque incorporated from canine to canine in the following case scenarios: •Two upper first premolar extraction cases •Also used in Class II div 2 cases and in any cases that require 6mm or more upper anterior retraction
  16. 16. TIP IN ROTH PHILOSOPHY •Compared to SWA, incisor tip was kept the same. • Canine tip was increased in both upper and lower arches to counteract for the increase in incisor torque. •Upper buccal segments had 0° tip whereas lower buccal segments had -1 ° distal tip to conserve anchorage The Roth treatment was developed on a clinical trial and error basis starting with standard Andrew’s brackets and then altering the values and some of the anterior bracket positions.
  17. 17. MBT PHILOSOPHY •Mclaughlin, Bennett and Trevisi redesigned the entire standard bracket system to complement their proven treatment philosophy and to overcome the inadequacies of SWA. •They re-examined Andrew’s original findings and took into account of additional research input from Japanese sources •This 3rd generation bracket system is designed for use with light continuous forces, lacebacks,bendbacks and sliding mechanics.
  18. 18. TORQUE SPECIFICATIONS -14 ° -14 ° -7 ° -7 ° -7° 0° +7 ° +10 ° +17 ° 7 6 5 4 3 2 1 -10° -20 ° -17 ° -12 ° -6 ° 0 +6° -6 ° -6 ° Upper Lower
  19. 19. INCISOR TORQUE – •Palatal root torque of the upper incisors and labial root torque for the lower incisors were increased compared to previous generations due to : • Inefficiency of PEA brackets in delivering torque. •In class II cases, class II elastics can cause torque to be ‘lost’ on upper incisors and lower incisors can get flared. • In class I cases, correct incisor torque helps to achieve good anterior tooth fit. •In class III cases correct torque helps to compensate for mild class III dental bases
  20. 20. CANINE TORQUE Upper canines: • Torque in the upper canines are necessary because they are key elements in a mutually protected occlusion. •The goal is to deliver ideal tip and torque to the canines so that they can fulfill their role in lateral excursions and have a small amount of freedom in maximum intercuspation. •MBT uses two canine brackets for three torque options ( +7°, 0°, -7 °) Lower Canines: •Original SWA torque in canine is not satisfactory because -11 ° tends to leave lower canine roots too prominent in some cases. •MBT uses two canine brackets for three options (+6 °, 0 °,-6 °)
  21. 21. SELECTION OF CANINE TORQUE OPTIONS 1. ARCH FORMS Well developed arches and substantial tooth movement not required Upper Canine: -7 ° Lower Canine: -6 ° In cases of ovoid arch forms • Upper Canine: 0 ° • Lower Canine: 0 ° In cases of narrow (tapered) arch • Upper Canine: +7 ° • Lower Canine: +6 ° 2. CANINE PROMINENCE • -7 ° in the upper arch or -6 ° in lower arch canine torques are normally not correct if the patient has prominent canines or canine gingival recession at start of treatment, in these cases bracket with 0 ° or +7 °/+6 ° should be used.
  22. 22. 3. EXTRACTION DECISION: 0 ° brackets tend to maintain canine roots in the cancellous bone making tip control of roots easier. 4. OVERBITE: In some Class II div 2cases, there is a requirement to move lower canine roots labially and also centre the roots in bone. This is more easily achieved if 0 ° or +6 ° lower canine torque is used. 5. RAPID PALATAL EXPANSION CASES RPE of upper arch creates a secondary widening of the lower arch. There are torque changes associated with this. Values of 0 ° or +6 ° brackets are recommended to assist in the favourable change. 6. AGENESIS OF UPPER LATERAL INCISORS If one or both lateral incisors are missing, a decision may be made to close spaces and bring canines mesially. It is helpful to invert -7 ° upper canine 180 °, thus changing the torque to +7 ° with the tip remaining the same.
  23. 23. UPPER PREMOLAR AND MOLAR TORQUE •Upper premolar value of -7 ° has proven to be satisfactory in clinical use and the authors continue to work with it. •For upper molars, -9 ° of original SWA has proven to be inadequate. They prefer -14 ° as it gives better control on palatal cusps and prevents the cusps from hanging down LOWER PREMOLAR AND MOLAR TORQUE •Many orthodontic cases have narrow maxillary arches with lower arches showing compensatory narrowing. •These cases normally require buccal crown torque of lower premolars and molars. •The original SWA first molar torque (-35 °) torque (-30 °) and 2 nd allowed ‘rolling in’ of the lower molars.
  25. 25. VARIABILITY OF TORQUE IN PEA •Torque prescription varies from 7° for the maxillary central incisor in the SWA to 17° in MBT and 22 ° in Bioprogressive Rx. •This lack of uniformity may be attributed to : The value that the developer chose as the average normal inclination of the tooth surface. The expected ‘play’ in the bracket between the arch wire and the slot. Position of the bracket on tooth surface. The appliance meant to be placed rather gingivally have different torque values than one placed incisally. AJO DO 2004; 125:323-28
  26. 26. VARIABLES AFFECTING TORQUE IN PEA •Variation in the shape of individual tooth •‘Play’ of the arch wire •Variations in bracket placement •Manufacture errors in brackets and wires •Mode of ligation AJO DO 2004; 125:323-28
  27. 27. 1.VARIATION IN THE SHAPE OF INDIVIDUAL TEETH •Torque built into the brackets of Andrew’s original SWA was based on faciolingual data derived from a study of 120 non orthodontic models. •Theoretically for these brackets to apply torque implied by prescription, they should be positioned at the same point at which average torque values were first obtained - L.A point. •With basic morphologic differences in the individual tooth shape and different recommended bracket placement charts of various prescriptions, clinicians donot use the L.A. point and therefore torque applied to tooth varies from prescription. AJO DO 1989; 96:312-09 2.PLAY OF THE ARCH WIRE •Filling the bracket slot by incrementally increasing the wire cross section has been the basic sequence of therapeutic protocols. •Inevitably, a fraction of torque that is built into the bracket remains unexpressed owing to ‘play’ or ‘3rd order clearance’ or ‘slop’. •Inability in full expression of built in torque in PEA is perhaps one of its biggest shortcomings. The average ‘play’ values vary with different clinicians and researchers.
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  29. 29. 3. VARIATIONS IN BRACKET PLACEMENT • • • • • • With PEA brackets, the position of brackets on crown determines the tooth’s final tip, torque, height and rotation. Poorly positioned brackets result in poorly positioned teeth and necessitate many more arch wire adjustments. This can lead to an increase in treatment time or final occlusion that is less than ideal. Errors in the vertical dimension can alter the torque values built into the appliance Meyer and Nelson stated that the mandibular 1st premolar has the greatest occlusogingival curvature of any tooth and that a 3 mm displacement of the bracket results in a 10 ° alteration in applied torque In addition thickness of composite and cement material under brackets and tubes may be another factor that changes the effective torque AJO DO 1978; 73:485-90 AJO DO 2001; 119:76-80
  30. 30. 4. VARIABILITY OF ACTUAL vs REPORTED TORQUE • Manufacturing of brackets allows for an acceptable variation in their size and characteristics including dimensional accuracy and torque consistency. •Wires and slots cannot be made precisely every time. Manufacturing tolerances result in 0.018” slots ranging from 0.017” to 0.019” whereas 0.022” slots ranging from 0.021” to 0.023” AJO DO 1993; 104:8-20 •Bracket manufacturing process involving casting, injection moulding etc. can affect the accuracy of prescribed torque values. •Various bracket slot manufacturing defects such as incorporation of metal particles in the slot, enlargement of the slot or decrease in the wire cross section can prevent the full engagement of the wire into the bracket slot which affects the torque expression. •Other means taken to prevent the undesirable event is the rounding and bevelling the edges of both arch wire and slot. This makes insertion of wire easier •In a study done by William Brantley et al (1984), it was found that in 0.022 slot the 0.019” x 0.025” β Titanium wire produced a play of 22 ° as compared to 12 ° in stainless steel.
  31. 31. •They concluded that edge bevel is expected to be a critical factor for actual torque expression by specific round or rectangular wire. So increase in edge bevel means increase in play. 5. MODE OF LIGATION • A source of torque control loss is force relaxation in elastomeric ligatures. Elastomeric ligatures have shown a force degradation pattern characterized by initial decrease of nearly 40 % in the first 24 hrs. Thus the engagement of the wire to slot is flexible and incomplete resulting in further reduced expression of the already compromised torque. •The use of steel ligatures has been found to diminish slot wire clearance. So as a bottom line, a clinician might actually require more torque than incorporated into the currently available PEA and alternatively sufficient activation should be applied to arch wires to compensate for play, various manufacturing defects and clinical procedures which counteract the expression of torque built into the bracket.
  32. 32. TORQUE CONTROL IN VARIOUS TREATMENT STEPS LEVELING AND ALIGNING •Contrary to popular belief torque is not expressed only in rectangular SS wires. •Flexibility of the rectangular HANT wires allows early placement and this allows easier torque control than was possible when only steel wires were available
  33. 33. BITE OPENING CURVES AND TORQUE •In majority of the cases after rectangular stainless steel wires have been in place for 4-6 weeks, arches are normally aligned and adequate bite opening would have taken place if 2nd molars were banded , if this is not so then bite opening curves can be placed in rectangular steel wires •Placing bite opening curves in the upper arch wire increases palatal root torque to upper incisors. • This is beneficial in majority of cases and it is usually unnecessary to add any additional torque bends. • When a reverse curve is placed in the lower rectangular wire result is proclination of lower incisors. This generally is not indicated. Thus before placement of bite opening curves in lower wire approximately 10 ° to 15 ° of labial root torque can be added
  34. 34. SPACE CLOSURE AND TORQUE •All research evidence shows the de merits of using Ni Ti coil springs for more rapid space closure. If space is closed too rapidly, incisor torque is lost and requires several months to regain the lost torque. •Loss of torque control results in upper incisors being too upright at the end of space closure with spaces distal to the canines and a consequent unaesthetic appearance. •Also rapid mesial movement of the upper molars can allow the palatal cusps to hang down resulting in functional interferences. •Rapid movement of the lower molars causes ‘Rolling in’ of molars.
  35. 35. •According to Raymond Siatkowski (1999) there is an average torque loss of 5 ° in the retraction of 1.3mm in maxillary arch and 1.2mm in the mandibular arch. •This means that there is an average of 15 ° torque loss for 4mm of retraction.
  36. 36. TORQUE IN FINISHING AND DETAILING •Torque in maxillary incisors is critical in establishing an aesthetic smile line, proper anterior guidance and a solid Class I relationship. •Under torqued incisors deprive the dental arch of space. •It has been shown that for every 5 ° of anterior inclination 1mm of arch length is generated.Under torqued posterior segment has a constricting effect on the maxillary arch. (BJO 1999;26:97-102) •A major finishing consideration in the horizontal plane is co ordination of tooth fit in the anterior and posterior areas. Any discrepancy in the tip, torque or tooth size can affect tooth fit.
  37. 37. Providing adequate incisor torque Torque control is the weakness of PEA . Three factors responsible are. 1. Area of torque application • Approximately 1mm segment of rectangular steel wire is placed in a bracket slot of about the same dimension. • This segment is required to carry out rather difficult tooth movement which involves moving an entire portion of root through alveolar bone. 2. ‘Play’ between arch wire and slot. 3. Upper and Lower anterior torque need of different patients vary greatly. So,there is a need to place additional palatal root torque in upper incisors and labial root torque in the lower incisors.
  38. 38. Providing adequate posterior torque Though the MBT bracket system has been provided with additional buccal root torque compared to SWA, extra buccal root torque needs to be added to posterior segments of upper arch wire in certain cases. To provide adequate buccal root torque in the upper arch, it is also important to have a wide enough maxilla. If the maxilla is not wide enough, then buccal cortical plates will not allow for incorporation of appropriate amount of buccal root torque. This in turn leads to palatal cusps that create interferences during labial excursions and compromises to functional occlusion. This need to be evaluated carefully at the beginning of treatment
  39. 39. 0.018 or 0.022 slot? •The earliest slotted bracket appliances relied on precious metal wires for activation. Gold wires were efficient and resilient in the first standardized slot size : the 0.022 inch. •In the 1930’s stainless steel alloys were introduced and orthodontists soon replaced gold alloys with cheaper SS wires despite the realization that steel wires were less flexible than the equivalent sizes in gold. •Clinicians in the 1950’s began employing smaller sized wires in the 0.022 inch slot. The mood was now right for a downsizing of edgewise slot dimension from 0.022 to 0.018 to allow light forces with SS. •Some edgewise folks switched, some did not! Indeed the slot size dichotomy persists even today: 0.018 or 0.022!?
  40. 40. TORQUE EXPRESSION : 0.018” Vs 0.022” SLOT • The 0.018” brackets usually has 0.017” x 0.025” as working wire which has a slop of 6°. Thus theoretically torque expression in the 0.018” slot maybe better than in an 0.022” slot. • But the 0.018” slot has a host of other short comings: i) Torque prescription for the 0.018” slot tends to be more conservative. ii) There is an obvious limitation in choice of wires and treatment mechanics employed. iii) They are not efficient in sliding mechanics since the 0.017” x 0.025” wire does not have sufficient clearance and can be deflected . Loop mechanics has its own side effects of excessive forces and operator errors.
  41. 41. •In the 0.022” slot, the slop of 10 ° with a 0.019”x0.025” arch wire must be counteracted by adding torque (10 °- 15 °) into the arch wire for utilizing complete built in prescription. •In PEA the 0.022” slot is preferred because of the following advantages: •During leveling and aligning, these slots have definite advantage in choice of alignment wires. •0.022” slots are designed for sliding mechanics which is proven to be more efficient in space closure. •As adjunct with PEA, ( fixed functional, orthopedic forces, surgical cases) we require stiff, full size arch wires to avoid deflection. Thus 0.022” slots are more efficient.
  42. 42. TORQUE IN FACE VS TORQUE IN BASE •Torque in base was an important issue with the 1st and 2nd generation PEA brackets because level slot line up was not possible with brackets designed with torque in the face. •Torque in base ,as said by Andrews, is a pre requisite for a fully programmed appliance. •Albert H Owen (1980) conducted a study comparing Roth prescription and Vari Simplex Discipline. He concluded that while torque in base had a strong theoretical basis, its effectiveness is greatly influenced by clinician’s success in accurately placing brackets. •Torque in base means that bracket stem is parallel and coincides with long axis of bracket slot •The torque in face, slot is cut at an angle to the bracket stem. The long axis of slot does not coincide with bracket system.
  43. 43. UNDESIRABLE EFFECTS OF HAVING TORQUE IN THE FACE: i) Bracket having torque in the face affects the final vertical positioning of tooth. ii) Level slot line up is not possible. iii) Bracket wings could bend or distort under various forces of ligation. •Torque in the bracket base allows flexibility of design. It enhances bracket strength and other features such as depth of the wing and labio lingual profile. • Modern bracket systems including MBT system have been developed using CAD CAM tech. Brackets may be finished with torque in the base ( full size or clear) or combination of torque in base or face ( mid size) with absolutely no difference in slot position.
  44. 44. DOES ONE PRESCRIPTION APPLY TO ALL? • Factors such as age, sex, ethnic group are important in making a proper orthodontic treatment plan. Another important factor is the facial growth pattern and its general clinical characteristics. •Faciolingual inclinations in PEA are relative to the occlusal plane. Occlusal planes are oriented differently in head when extreme variations in vertical growth proportionally occurs. •Use of any PEA will orient the dentition to an occlusal plane that is different in different growth patterns •High angle skeletal patterns: upright maxillary incisors and increased buccal inclination of posterior teeth •Low angle skeletal pattern: More proclined maxillary incisors related to the SN plane and increased lingual inclination of the posterior teeth. AJO DO 1993; 104:8-20 AJO DO 1990; 98:422-9
  45. 45. VARYING FACES …………….. VARYING TORQUE!!!!!! Finishing protocols in torque should be decided by the orthodontist and not left to the appliance used!!
  46. 46. CEPHALOMETRIC NORMS FOR TORQUE • With the advent of ceph head films many ceph analyses were developed in an attempt to more objectively define the direction of treatment. • Dental and skeletal normals were established for general populations in certain analyses such as Tweed, Downs, Steiners etc • Problems associated with these: i) Assumption was made that if dental and skeletal values were normal face would also be normal. ii) Normals were obtained from patient samples with malocclusions. iii) Position of dentition was related to cranial base structures which showed significant variability of position in patients with more severe facial disharmony. • Arnett and Bergman (1993) drew attention to shortcomings of the cranial base for facial planning with their two part paper. • Arnett et al (1999) suggested a method of STCA and STCP. This new analysis was based on the true vertical line (TVL).
  47. 47. •Incisor torque norms acc. To Dr Arnett •Upper Incisor Lower Incisor •F: 57º ± 2.5° M: 58º ± 3° F: 64º ± 3.2° M: 64 ± 4° •Why use maxillary and mandibular OP?? •Incisor measurements to distant landmarks such an Sella Nasion, FH plane , A-Po line may produce misleading measurements. •Mandibular and palatal planes themselves are altered by surgical procedures so these are not good references for surgical cases.
  48. 48. CONCLUSION •Torque in edgewise wire is probably the most important and potent force which enables the orthodontist to control axial inclinations of teeth and to place them in harmonizing positions that are so desirable for a nicely finished result. •Perhaps third order control is one of the biggest limitations of PEA.
  49. 49. Maybe it is high time that we as orthodontists stopped strapping up cases with universal appliances and allow nature to take its course in treatment. We need to learn to look at patients with a wider perspective in relation to facial aesthetics and not just as mere subdivisions of malocclusions !!!!!!!!
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