INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
INTRODUCTION • • • • • •
Last 5 decades Sudden negative growth Little knowledge of Biomechanics Efficiency in bite opening Works like a simple machine Base arch wire-main component www.indiandentalacademy.com
• Edgewise -two point contact at both the ends-moment at both the ends-two couple system • Begg –two point contact at one end ,one point contact at other end-force at one end and moment at other end-one couple system
â€˘ V-bend principle
Special features of Begg mechanics The difference between the design of the Begg bracket and the edgewise bracket, as also the difference in the philosophies of the two treatment modalities must be taken into account for enunciating the Begg biomechanics.
Begg Mechanics Dr. Srinivas
Behavior of the Begg bracket in the first, second and third order mechanics â€˜Unipointâ€™ bracket Bracket slot behaves differently in the three planes First order mechanics Second order mechanics Third order mechanics
Differences between the mechanics of the two therapies
When groups of teeth are rigidly held together forces are applied on the tooth surface away from the bracket Forces and moments employed are relatively low The Begg slot is closer to the tooth than the edgewise slot
Vertical deflection in the arch wire will generate a force but no moment unlike in an edgewise bracket
Rotational Control in Refined Begg â€˘ â€˘
In the horizontal plane (First order) is the least (especially with full size wires). For second order (mesio-distal) is relatively greater (more so with Stage I pins). The freedom for third order displacement on a round wire is maximum www.indiandentalacademy.com
Basic Begg Movements • • •
Incisor intrusion Tipping Root movements
Mechanics of intrusion More easily understood by considering the net intrusive force magnitude and direction instead in terms of M/F ratio Lack of true intrusion of the maxillary incisors was one of the major weaknesses of traditional Begg (bite opening was mainly on account of molar extrusion and some intrusion of the lower incisors) www.indiandentalacademy.com
Anterior teeth can be intruded by orthodontic means only to the extent of 3-4 mm. An adult case of gummy smile requiring surgery cannot be converted to a non surgical orthodontic treatment However, cases of gummy smile during childhood can be successfully treated by partly intruding the incisors and partly by preventing the downward displacements of the alveolus / maxilla. www.indiandentalacademy.com
six anterior teeth are intruded together in Begg practice
Bite opening force from the anchor bends varying amounts of intrusion (translation) and labial crown-lingual root tipping (rotation). Such rotational displacement is generally undesirable (the exception being lingually inclined incisors as in Cl. II div. 2 cases), Interplay between the wire generated intrusive force and the elastic force determines both the magnitude and direction of the net resultant force acting on the teeth www.indiandentalacademy.com
Consideration of the magnitude of intrusive force â€˘ â€˘
Optimal intrusive force value For active intrusion the upper anteriors should receive approximately 60 gm net force in the midline after negating the extrusive component of Cl II elastics
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Role of light Class II elastics light elastic force for longer periods (from 2 to 5 days), a very light Cl. II force is provided most of the time Sims has suggested the use of 3/8″ ultra light elastics e.g., “road-runner elastics” suggested force values are only a rough estimate many variables www.indiandentalacademy.com
Consideration of the direction of the resultant force Hocevar: teeth respond only to the resultant of the forces, and not to the individual components of the force system â€˘ The direction and the magnitude of the resultant force both depend upon the interplay between â€˘ 1.The magnitude of the intrusive force â€˘ 2.The magnitude and direction both of the elastic force. www.indiandentalacademy.com
Arch wire design • • •
mild gingival curve incorporating a vertical step up bendSwain posterior segments of the archwire are kept gingival and the anterior segment is kept occlusal likely to tip the anchor molars distally
distal vertical elastics
Summary of Intrusion Mechanics â€˘ â€˘
Application of force is through the concerned centre of resistance (or very close to it). Careful manipulation of these two forces the magnitude and the direction of the resultant force can be so adjusted as to obtain a predominantly intrusive action, a predominantly retrusive action or a combination of the two
Extreme cases of proclination or retroclination After the inclination corrects, a varied strategy is employed which helps in keeping the resultant force close to the C Res
Mechanics of Begg tipping â€˘
uncontrolled tipping is undesirable because it can hasten root resorption, as emphasized by Reitan The few exceptions wherein uncontrolled tipping is beneficial for one or two visits
Controlled Lingual tipping of upper anteriors • •
Intrusion and tipping of upper incisors are intimately related the moments generated by both of them are in the same labio-lingual plane but act in opposite directions retractive force is crown lingual - root labial. intrusive force is crown labial - root lingual,
Provides a moment in the labio â€“ lingual plane by creating a force couple
Light forces generated by MAA against the crown surfaces Wire
Preventing Uncontrolled Tipping of Lower Incisors Intrusive force alone can flare the teeth Such flaring can be avoided by: a.Minimise the moment by reducing the intrusive force, or by placing the brackets as much gingivally as is permitted by hygiene considerations.
b.Provide a holding force by bending the diatal ends of the arch wire as suggested by Hocevar. c.Provide a counter moment by using a MAA for labial root torque or a reverse torquing auxiliary
Mechanics of root movement Predominantly root movements in a labiolingual or mesiodistal direction Auxiliary commonly used is the one made in 0.012 premium plus wire
Forces generated (in grams) by the commonly used four spur and two spur torquing auxiliaries with 5 mm spur length Wire
Forces produced by a 4 spur torquing auxiliary made in 0.012” wire are approximately twice of those from a MAA made in 0.009” wire The M/F ratio for root movements is about twice of that employed in controlled tipping during the initial stages
Forces generated by the uprighting springs (2 1/2 turns, the inner diameter of helical 0.036â€?, length of the arm 4 mm and angulation 135o ) Activation
Nikolai-greater moments are required for the mesio-distal root movements than for the bucco-lingual root movements Action of uprighting springs and torquing auxiliaries is in all the three planes namely sagittal, vertical and transverse
Does Begg appliance satisfy the appliance design criteria ? Burstone has set the following criteria for an efficient appliance design : • Force system • Precise M/F ratios for different types of tooth movement. • Constancy and low magnitude of moments and forces. • Ease of use. • Patient comfort. • Minimal patient co-operation www.indiandentalacademy.com
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Refined Begg appliance admirably satisfies all the above requirements. provide the required M/F ratios for controlled tipping in the initial stages and for root movements in the final stage. forces used are light and fairly constant. In fact the ultra-light forces advocated by Refined Begg are physiologically more acceptable. easy to practice and manipulate. The light forces are comfortable for the patient. Finally, one has to depend on patient’s cooperation only to a limited extent. www.indiandentalacademy.com
Problems in stage III • Multiple complex moments and forces • Tends to the generation of unintentional force systems • Anchor loss,bite deepening,flaring of molars ,space opening distal to molars
â€˘ Modification of materials: high L/D wires as base arch wire low L/D wires for springs and auxillaries â€˘ Design modifications: bends mesial and distal to canines constricted arch wires class II elastics All these add a new set of forces which can further complicate the mechanics www.indiandentalacademy.com
â€˘ Solution : Balancing of forces at either ends of the base arch wire â€˘ Distal tipping of molar-excellent anchorage preservation modality
Orthodontic force systems: Technical refinements for increased efficiency Richard A. Hocevar. The efficiency of the Begg technique suffers because Class II elastics overwhelm anchor bends, which normally do not yield enough force for vertical control of maxillary incisors. This can be improved by attention to detail and modifications. Bite-opening bends in the arch wires distal to canines and lateral incisors, long (6.5 mm.) mesiogingivally angulated molar tubes, and placement of intermaxillary elastics at the distal ends of the tubes are all helpful. Intermaxillary "check elastics," having one end over the posterior end of the maxillary arch wire, both strands under the end of the mandibular arch wire, and the other end up to the maxillary anterior teeth, reinforce anchor bends and extrude upper and lower molars while keeping them upright. They augment bite opening in Stage I and counteract the adversewww.indiandentalacademy.com affects of the auxiliaries in Stage III.
Vector analysis of forces. a, Arch wire anchor bend. b, Class II elastic. c, Vertical component of Class II elastic. d, Resultant of a and c. e, Horizontal component of elastic. f, Total resultant force. Vector lengths are proportional to force magnitudes. www.indiandentalacademy.com
Reducing this overjet without allowing the edge of the upper incisor to drop would require a balance of forces that is probably impracticable with www.indiandentalacademy.com conventional Begg technique.
Class II, Division 2 incisor relation. Force a, would produce only further retroclination in this situation. Intrusion would require that the total resultant force on the incisors act in direction b. Following intrusion, a posteriorly directed force and a couple to produce lingual root torque would be required to www.indiandentalacademy.com achieve the desired final position indicated by the shaded incisor.
Typical Begg arch wire tends to intrude canines and extrude incisors relative to each other. www.indiandentalacademy.com
Slight bite-opening bends (at arrows) mesial and distal to the canines help ensure efficient bite opening, level occlusal planes, and even occlusion. www.indiandentalacademy.com
If the resultant (c) of the arch wire expansion force (a) and the vertical component of the Class II elastic force (b) passed directly through CR, the lower molar would be likely to move occlusally and buccally (A). Molar extrusion without buccal movement (B) is probably accounted for by force b being considerably greater than a. Bone anatomy www.indiandentalacademy.com and muscle are also involved.
Forces on a lower molar produced by a Class II elastic hooked on the distal end of the arch wire (a) and a mesial hook (b) . The moment arm, and hence the moment tending to tip the molar mesially, may www.indiandentalacademy.com be much greater with distal elastic attachment.
Incorrect (A) and correct (B) molar tube designs. The mesial hook, optional, is for intramaxillary www.indiandentalacademy.com elastics only.
Consistently correct mesiogingival angulation of molar tubes is achieved easily by making a scratch mark on the band parallel to the occlusal surface at the desired height and then welding the tube diagonally across the scratch so that the mesio-occlusal and distogingival points of the tube ends are on the line. This method automatically determines the correct position for the tube, no matter what the inclination www.indiandentalacademy.com of the molar in the malocclusion may be.
With short, horizontally oriented molar tubes (top), when arch wires are pinned into incisor brackets (broken lines), the anchor bends are so placed as to be very likely to be deformed by mastication. This is not the case with long, mesiogingivally angulated tubes (bottom). In both ,the arch wires are activated through the same range and thus deliver the same force to molars and incisors, but the degree of anchor bend in the top illustration is twice as great as that in www.indiandentalacademy.com the bottom one.
Maxillary molar tube having its distal end offset from the buccal surface facilitates control of molar rotation. www.indiandentalacademy.com
"check elastic" www.indiandentalacademy.com
SUMMARY • 1. Retraction of maxillary incisors deserves careful force system analysis and application, particularly in the many cases in which intrusion is desirable. • 2. Anchor bends, as commonly used in the conventional Begg technique, are not likely to have a significant effect on maxillary incisor movement. • 3. Slight bite-opening bends mesial and distal to the canines in all arch wires can help ensure that intrusive force is delivered primarily to incisors, and maintain level arches. • 4. Vertical intrusive force on mandibular incisors may cause proclination unless accompanied by www.indiandentalacademy.com some distal force.
• 5. There are many reasons for routinely cinching almost all arch wires at the distal ends of the buccal tubes throughout treatment. • 6. Positioning intermaxillary elastics at the posterior ends of arch wires, using long buccal tubes, and angulating all tubes mesiogingivally are important factors in efficient reduction of overbite. • 7. The use of maxillary molar tubes whose distal ends are set out from the buccal surface and arch wires with ''toe-in'' throughout treatment aids correction and control of maxillary molar rotations. www.indiandentalacademy.com
• 8. ''Check elastics'' can provide a potent mechanism for overbite reduction, causing extrusion of maxillary and mandibular molars and counteracting the tendency of the anchor bends to tip the molars distally, thus aiding incisor intrusion. • 9. A conventional Begg Stage III appliance tends to rotate the occlusal plane, and especially the maxillary arch, down in front and up in back and to deepen the overbite. • 10. The above tendency can be counteracted by routine use of check elastics in most cases. Cervical headgear to maxillary molars or anterior high-pull headgear may be preferable in a few cases of specific types. www.indiandentalacademy.com
Maxillary anterior intrusive forces generated by Begg Stage I appliances Charles B. Thornton, Robert J. Nikolai, Ph.D. â€˘ The capability of Begg mechanotherapy to produce intrusion of the maxillary anterior teeth, particularly the incisors, has been questioned. Although the Stage I appliance opens the bite, this can be the result of one or a combination of several occlusogingival displacements, and the manner of bite opening continues to be a subject of discussion. Support in favor of anterior maxillary intrusion exists, at least in part, because of the potential for extrusion of these teeth during Stage III. â€˘ The purpose of this experimental study was to quantify and compare the intrusion potentials of maxillary appliances www.indiandentalacademy.com
Significant results of the investigation may be summarized as follows: • 1. Appliance configurations generated initial mean values of intrusive force, distributed (although nonuniformly) over the four- or six-tooth segment, of approximately 40 grams. • 2. Anchor-bend size and Class II elastic-force magnitude were most influential in increasing and decreasing, respectively, anterior intrusive force. • 3. Within the 0.016-inch-wire sample, addition or deletion of a gable bend quantitatively affected intrusive force almost independently of the magnitude of Class II elastic force. • 4. Variation in the location of the anchor bend, up to 5 mm. mesial to the buccal tube, had a very small influence on the intrusive-force size. • 5. Increasing the wire diameter 25 percent, from 0.016 to 0.020 inch, resulted in dramatically raised intrusive-force www.indiandentalacademy.com values generated by the appliances.
The results of this study apparently warrant the following conclusions: • 1. The commonly used maxillary appliances of Begg Stage I mechanotherapy produce initially light but continuous force against the anterior segment. With no torque potential in the appliance, the teeth may seek the intrusive path of least resistance. • 2. Increasing (decreasing) the sizes of the anchor and/or gable bends may be equivalent to decreasing (increasing) the Class II elastic force with regard to the effect on intrusive potential. Not to be overlooked, however, is the fact that alterations in the elastic force also affect the horizontal action of the appliance, whereas the bends do not. • 3. In fabricating the appliances studied, with their common over-all design, the approximate magnitude of intrusive force desired should be approached from the low side through an appropriate combination of anchor-bend size and Class II elastic-force magnitude • 4. Because of long moment arms, even a light force against the anterior segment will result in sizable tipping moments against the molars. Accordingly, molar positions must be monitored while the appliance is active, and if unwanted displacements occur, anchorage www.indiandentalacademy.com reinforcement may be necessary.