A brief history and overview of treatment mechanics

Introduction 3

Fundamentals of treatment mechanics 3

Bracket design Bracket positioning Archwire selection Force levels

The work of Andrews 4 Wide range of brackets Center of the crown Various arch forms Heavy forces

The work of Roth 6

Roth brackets Center of the crown Wide arch form Articulators

McLaughlin and Bennett 1975 to 1993 7

Mainly standard brackets Center of the crown Ovoid arch form

Light forces and sliding mechanics

The work of McLaughlin, Bennett, and Trevisi between 1993 and 1997 8

Re-designed bracket system - MBT™

improved bracket positioning with gauges

The work of McLaughlin, Bennett, and Trevisi between 1997 and 2001 12

The decision to use three arch forms

Updated light forces and sliding mechanics

Overview of the MBTIM treatment philosophy 13

Bracket selection 13

Versatility of the bracket system 13

Accuracy of bracket positioning 13

Light continuous forces 13

The .022 versus the .018 slot 14

Anchorage control early in treatment 15

Group movement 16

The use of three arch forms 16

One size of rectangular steel wire 17

Archwire hooks 18

Methods of archwire ligation 20

Awareness of tooth size discrepancies 21

Persistence in finishing 21

Case SS 22

INTRODUCTION

FUNDAMENTALS OF TREATMENT MECHANICS

Andrews published his landmark article' in 1972, and subsequently designed an appliance based on his findings. However, soon after the introduction of the preadjusted appliance, it became clear that the bracket system required a whole new program of treatment mechanics and force levels to fully realize its potential. In turn, the new treatment mechanics and force levels brought about a need for modifications to the bracket system. Ultimately, it has become the mechanics and force levels that have determined the appliance design, and not vice versa. This chapter reviews the evolution of orthodontic treatment mechanics since the early 1970s (the start of the modern era), and goes on to review the principles of the method currently used.

Appliance design and treatment mechanics are closely inter-related. To some extent, bracket design can be scientific and based on research, so that bracket designs can be produced in a matter of months. However, development and refinement of appropriate treatment mechanics take years, and have to be based on experience with numerous treated cases. Consequently, the information on treatment mechanics is often anecdotal, and based on recommendations from experienced clinicians. F.ven well-structured investigations into treatment efficiency tend to be inconclusive.2,3

Orthodontic treatment mechanics are determined by four elements - bracket selection, bracket positioning, archwire selection, and force levels (Fig. 1.1). If a balanced combination of these elements is used, efficient and systemized treatment can be achieved. However, variation in one (for example archwire selection) can substantially influence the other elements and can undermine the effectiveness of the treatment approach.

/ Bracket

Archwire \

/ selection

selection \

\ Bracket

Force /

\ positioning

levels /

Fig. 1.1 Orthodontic treatment mechanics are determined by four elements.

THE WORK OF ANDREWS

Andrews is rightly regarded as the father of the preadjusted bracket system, and it is interesting to review his contribution in the light of experience over the last 25 years of clinical use.

When the original Straight-Wire Appliance® (SWA) became available in 1972, it was based on science, but included many of the traditional features of siamese edgewise brackets. Andrews' paper was based on the measurement of 120 non-orthodontic normal cases. He then used the data as a basis to design a bracket system.

Although the SWA was radically new, traditional heavy edgewise forces continued to be used. No special anchorage control measures, such as second order archwire bends, were employed. This may have been due to his clinical experience as an edgewise orthodontist and the force levels that were used. He also emphasized the 'wagon wheel effect' where tip was lost as torque was added. Hence, he chose to add additional tip to the anterior brackets. (Fig. 1.2).

Bracket positioning was based on the center of the clinical crown. Because less wire bending was needed with the new appliance, there was also a trend to standardize arch form. As a result of Roth's influence, there was a general movement toward a broad or square arch form, although Andrews continued to use the basal bone of the mandible as an arch form reference. Various arch forms were used because no clear direction was available.

Research tip

Research tip

Andrews Orthodontic Wire Bending

SWA tip

Research tip

Fig. 1.2 The original Straight-Wire Appliance® (SWA) was based on measurement of 120 non-orthodontic normal cases, although extra tip was built into the anterior brackets.

SWA tip

Research tip

Difficulties were encountered with treatment mechanics in the early years, due to the heavy forces and possibly due to the increased tip in the anterior brackets. Consequently, deepening of the anterior bite, with creation of a lateral open bite, was seen in many cases, and this became known as the 'roller coaster' effect (Figs 1.3-1.6).

Fig. 1.3 In the early years of the preadjusted appliance, heavy forces were used, and these were associated with deepening of the anterior bite and creation of a lateral open bite which became known as the 'roller coaster' effect.

Roller Coaster Effect Orthodontics

Figs. 1.4 to 1.6 The treatment sequence above shows the 'roller coaster' effect developing in an early treatment with the original SWA. The unwanted deepening of the overbite was due to excess force and the use of elastic retraction mechanics.

Figs. 1.4 to 1.6 The treatment sequence above shows the 'roller coaster' effect developing in an early treatment with the original SWA. The unwanted deepening of the overbite was due to excess force and the use of elastic retraction mechanics.

These early clinical experiences led Andrews to introduce a series of modifications, and after using the original 'standard' Straight-Wire Appliance® for a period of time, he recommended a wide range of brackets. For example, he determined that for extraction cases, canine brackets with anti-tip, anti-rotation and power arms were needed (Fig. 1.7). He also recommended the use of three different sets of incisor brackets, with varying degrees of torque for different clinical situations.

/ Wide range

Various \

j of brackets

archforms \

. Brackets

I

\ positioned at

Heavy force /

\ the center of the

levels /

\ clinical crown

JF

Fig. 1.7 Orthodontic treatment mechanics in the early years of the SWA.

Fig. 1.7 Orthodontic treatment mechanics in the early years of the SWA.

THE WORK OF ROTH

Following his early experiences with the original SWA, Roth introduced measures to overcome day-to-day shortcomings which he had found in clinical use. Whereas Andrews, with the first generation of preadjusted brackets, was recommending a large range of bracket specifications, Roth was anxious to avoid the inventory difficulties of a multiple bracket system. He therefore recommended a single appliance system, consisting primarily of minimum extraction series brackets, which he felt would allow him to manage both extraction and non-extraction cases.

This has been described as the second generation of preadjusted brackets, and Roth's recommendations were widely accepted by clinicians, some of whom had experienced similar difficulties in treatment mechanics and were confused by the wide variety of available brackets. The appliance prescriptions developed by Andrews and Roth were based on the overall treatment mechanics used in their practices.

The Roth treatment approach emphasized the use of articulators for diagnostic records, for early splint construction, and for the construction of gnathological positioners at the end of treatment (Fig. 1.8). This approach was used to aid in establishing correct condyle position. He used the center of the clinical crown for bracket positioning, as advocateoby Andrews. As slated above, his arch form was wider than Andrews' in order to avoid damage to canine tips during treatment and to assist in obtaining good protrusive function.

Roth Gnathological
Fig. 1.8 Roth selected a range of brackets to create a single appliance system.

www.allislam.net Problem

THE WORK OF MCLAUGHLIN AND BENNETT BETWEEN 1975 AND 1993

Although they evaluated many bracket variations, including the Andrews' 'translation' series, in the period 1975 to 1993 McLaughlin and Bennett preferred to work mainly with the standard SWA bracket system. Instead of initially modifying the basic bracket design, for more than 15 years they developed and refined treatment mechanics based on sliding mechanics and continuous light forces, mainly using standard SWA brackets. These mechanics were published initially as a series of papers in the early 1990s4'5'6 and then as a book in 1993' (Pig. 1.9) and have seen widespread acceptance.

Their treatment mechanics recommendations included accurate bracket positioning, and lacebacks and bendbacks for early anchorage control, with light archwire forces (Fig. 1.10). Sliding mechanics were recommended on .019/.025 steel rectangular wires, with light .014 finishing wires.

They used the middle of the clinical crown for bracket positioning during this development period. A medium-sized standard ovoid arch form was used for the majority of cases, and the size reflected the fact that many of their patients were children with malocclusions, unlike Andrews' sample of 120 normals, which were non-extraction adults with large arches.

ORTHODONTIC TREATMENT MECHANICS

<md the

P READ J U STE D APPLIANCE

ORTHODONTIC TREATMENT MECHANICS

<md the

P READ J U STE D APPLIANCE

John C Bennett • Kicturd l* McLaughlin

Fig. 1.9 Orthodontic Treatment Mechanics and the Preadjusted Appliance was published in 1993.

John C Bennett • Kicturd l* McLaughlin

/ Standard

Ovoid \

/ SWA bracket

archwire \

/ selection

selection \

\ Brackets

Light force /

\ positioned at

levels and sliding J

\ the center of the

mechanics J

\ clinical crown

Fig. 1.10 Orthodontic treatment mechanics evaluated by McLaughlin and Bennett from 1975 to 1993.

Fig. 1.9 Orthodontic Treatment Mechanics and the Preadjusted Appliance was published in 1993.

Fig. 1.10 Orthodontic treatment mechanics evaluated by McLaughlin and Bennett from 1975 to 1993.

THE WORK OF MCLAUGHLIN, BENNETT, AND TREVISI BETWEEN 1993 AND 1997

Having established an overall approach and a successful system of treatment mechanics using the preadjusted bracket system in its standard form, McLaughlin and Bennett then worked withTrevisi to re-design the entire bracket system to complement their proven treatment philosophy and to overcome the perceived inadequacies of the original SWA. They re-examined Andrews' original findings, and took into account additional research input from Japanese sources"-''1 when designing the MBT™ bracket system.

This third-generation bracket system retained all that was best in the original design, but at the same time introduced a range of improvements and specification changes to overcome the clinical shortcomings. Its design was based on a balance of basic science and many years of clinical experience. MBT™ is a version of the preadjusted bracket system specifically for use with light, continuous forces, lacebacks and bendbacks, and it was designed to work ideally with sliding mechanics.

The original system of dots and dashes was superseded by laser numbering of standard size metal brackets, and the rectangular shape was replaced by the rhomboidal form. This reduced the bulk of each bracket and coordinated perspective lines through only two planes, thereby assisting accuracy of bracket placement. The bracket system was made available in standard metal (Fig. 1.11), mid-sized, and clear forms (Fig. 1.12). It had sufficient versatility to deal with most clinical situations, and to limit inventory levels.

As previously stated (p. 4), the anterior tip specifications for the original SWA were all greater than the research findings. Additional tip had been built in, over and above the scientific means. For example, the important upper canine carried 11° in the first-generation (SWA) and then 13° in the second-generation (Roth)10 system, compared with the research finding of 8°.

Roth Brackets Placement

Fig. 1.11 Standard metal MBT™ brackets give optimal tooth control.

Fig. 1.12 This case has Clarity™ brackets on the upper anterior teeth and mid-sized metal brackets on the lower anterior teeth. The three different bracket options of standard metal, midsized metal and clear forms may be used in combination for the same patient.

Fig. 1.11 Standard metal MBT™ brackets give optimal tooth control.

Fig. 1.12 This case has Clarity™ brackets on the upper anterior teeth and mid-sized metal brackets on the lower anterior teeth. The three different bracket options of standard metal, midsized metal and clear forms may be used in combination for the same patient.

Mbt Torque Figure

Fig. 1.13 The recommended tip measurements for the MBT™ bracket system are based on Andrews' original research figures, and these features give less distal root tip in the upper and lower anterior segments.

SWA tip

Recommended tip

Additional anterior tip was a disadvantage for three reasons:

1. It created a significant drain on antero-poslerior (A/P) anchorage.

2. It increased the tendency to bite deepening during the alignment stage.

3. It brought the upper canine root apex too close to the first premolar root in some cases.

As lighter forces were being used in all stages of treatment, this additional 'anti-tip', or second-order compensation, was not needed. Therefore, when designing the MBT™ bracket

Fig. 1.13 The recommended tip measurements for the MBT™ bracket system are based on Andrews' original research figures, and these features give less distal root tip in the upper and lower anterior segments.

system, it was decided to base the anterior tip on the original research values. These assist treatment mechanics because they reduce the anchorage control needs, reduce the tendency to bite deepening in the early stages of treatment, and put less demand on patient cooperation. When the original research values for tip are used for incisors and canines, a total of 10° less distal root lip in the upper anterior segment and 12° less distal root tip in the lower anterior segment is needed, compared with the original SWA (Fig. 1.13). As the MBT" measurements are based on Andrews' original research figures, there is no compromise in ideal static occlusion. And if the condyles are in centric relation, there is no compromise in ideal functional occlusion as described by Roth.

SWA tip

Recommended tip

The preadjusted appliance system is a development of the edgewise bracket, which is relatively inefficient in delivering torque. When designing the MBT™ bracket system, it was therefore necessary to build extra torque into the important incisor and molar regions in order to meet clinical goals in these areas with a minimum of wire bending (Pigs 1.14 & 1.15). This design feature helps to overcome the fundamental shortcoming of the original edgewise bracket.

Brackets with three options for canine torque were needed to deal with different patient arch forms and other clinical variables. Andrews' research finding of-7° torque in the upper canines, and a reduced torque figure of -6° (from -11°) in the lower canines, is satisfactory for the canines in many cases. I lowever, a typical orthodontic caseload is a different sample from the 120 non-extraction adults. Hence there is a need for three canine torque options.

It was decided that upper canine brackets would be available with -7°, 0° and +7° torque values in the new MBT" system, because versatility was needed. The 0° and +7° options are preferred for cases with narrow maxillary bone

-1 3 -1 Original SWA

-1 3 -1 Original SWA

Mclaughlin Bracket Placement

yy v

Fig 1 15 Original SWA Recommended torque

Figs. 1.14 and 1.15 Extra torque was built in to the MBT™ bracket system in the important incisor and molar regions compared with the original SWA.

form and/or prominent canine roots (Fig. 1.16). Lower canine torque is -6°, but 0° or even +6° is available for some cases (Fig. 1.17), if needed.

In the period from 1993 to 1997, McLaughlin and Bennett also revised their recommendations on bracket positioning, to improve vertical accuracy, in the early years, they had used the middle of the clinical crown for bracket positioning, but they subsequently" developed a better system. This accepted the principles advocated by Andrews, but also used gauges to ensure greater vertical accuracy (p. 62). Their work on the revised bracket designs and the new bracket positioning technique was incorporated into a second book,12 published in 1997 (Fig. 1.18).

0"torque

0"torque

+7 torque

+7 torque

/\

I la ml i

Lv

Fig. 1.17

-6° torque

0° torque

+-6" torque

Figs. 1.16 and 1.17 Versatility was needed for canine torque, and therefore three options were made available for upper and lower canines.

Figs. 1.16 and 1.17 Versatility was needed for canine torque, and therefore three options were made available for upper and lower canines.

Overview The Dentitions

Fig. 1.18 Orthodontic Management of the Dentition with the Preadjusted Appliance was published in 1997 and is scheduled to be republished in January, 2002.

ÄM ORTHODONTIC

MANAGEMENT OF THE DENTITION WITH I "IHE PREADJUSTÉD !ü§ APPLIANCE

til <" li: mu ll . kiiliarlJ I' Mi-ti.ii>4iliii i •- u .r. a

/ New range

Ovoid \

/ of MBTr"

archwire \

/ brackets

selection \

\ Brackets positioned

Light force j

\ with the help

levels and sliding /

\ of gauges

mechanics /

Fig. 1.19 Orthodontic treatment mechanics developed by McLaughlin, Bennett, and Trevisi up to 1997.

Fig. 1.18 Orthodontic Management of the Dentition with the Preadjusted Appliance was published in 1997 and is scheduled to be republished in January, 2002.

Fig. 1.19 Orthodontic treatment mechanics developed by McLaughlin, Bennett, and Trevisi up to 1997.

THE WORK OF MCLAUGHLIN, BENNETT, AND TREVISI BETWEEN 1997 AND 2001

In order to complete a modern systemized method of treatment mechanics, it became necessary to address the subjects of archwire selection and force levels.

Although an ovoid arch form had proved useful in the early years, because of previous and current arch form research, it was recommended (Fig. 1.20) that three basic siiapes of arch form - tapered, square, and ovoid - would be required (p. 74). When superimposed, they vary mainly in inter-canine and inter-premolar width, giving a range of approximately 6 mm. Inter-molar widths of the three shapes are quite similar, but the molar areas of wires can be widened or narrowed as needed, by easy wire bending. Recommendations were published concerning arch form and archwire selection.13

This third book brings all the four treatment mechanics essentials together. It covers bracket design, bracket placement, and archwire selection, and it re-defines force levels (for example to incorporate recommendations for the use of heat-activated nickel-titanium (HAJMT) wires), re-stating the overall treatment philosophy. It describes a well-tested and effective system of treatment mechanics for the preadjusted appliance system.

/ New range / of MBT™ / brackets

Ovoid, tapered \ and square \ archwire \ selection \

\ Brackets positioned \ with the help \ of gauges

Updated light force / levels and sliding / mechanics j

Fig. 1.20 Orthodontic treatment mechanics developed by McLaughlin, Bennett, and Trevisi up to 2001.

Fig. 1.20 Orthodontic treatment mechanics developed by McLaughlin, Bennett, and Trevisi up to 2001.

OVERVIEW OF THE MBT™ TREATMENT PHILOSOPHY

The following elements make up the MBT™ treatment philosophy, and in the remainder of this chapter each will be reviewed in turn:

• Bracket selection

• Versatility of the bracket system

• Accuracy of bracket positioning

• Light continuous forces

• Anchorage control early in treatment

• The use of three arch forms

• One size of rectangular steel wire

• Archwire hooks

• Methods of archwire ligation

• Awareness of tooth size discrepancies

• Persistence in finishing

Bracket selection

At the heart of the technique is a high quality, versatile bracket system. A range of standard metal, mid-sized, and clear brackets is available. The exact bracket specifications are important, and attempts to use 'something similar' can adversely affect the balance of the treatment mechanics, and may not produce the desired treatment result.

The orthodontist's time is the most valuable commodity in the orthodontic clinic. There is a need for the orthodontist to have complete confidence in a reliable bracket system, which gives consistent performance, and can be used to save chairside time in the finishing stages of treatment.

Versatility of the bracket system

The system's full name is MBTrM Versatile-!- and as the name implies, it is designed to be versatile, in order to deal with most treatment challenges. This versatility (pp 39-5 I) is useful in both controlling inventory costs and avoiding needless wire bending.

Accuracy of bracket positioning

This is a cornerstone of the treatment approach. Every effort should be made to ensure accuracy, and it is part of (he technique to reposition brackets if necessary as treatment progresses. Gauges and individual bracket-positioning charts are recommended. Interestingly, the search for accuracy has led to an upsurge of renewed interest in indirect bonding (p. 69).

Light continuous forces

The technique requires the use of light continuous forces. The authors believe this is the most effective way to move teeth, being comfortable for the patient and minimizing the threat to anchorage. Light forces are especially important at the start of treatment, when the bracket tip puts demand upon anteroposterior (A/P) anchorage, and when it is important to minimize patient discomfort.

It is not possible to exactly quantify the term 'light forces'. Traditionally, forces in the range below 200 gm were referred to as light forces, and forces in the range above 600 gm were referred to as heavy forces! Essentially there is a need for the orthodontist to use thin, flexible wires early on, with minimal deflection, and to avoid too frequent archwire changes. Also, the clinician needs to recognize the signs of excess force, such as tissue blanching, patient discomfort, and unwanted tooth movements (for example roller coaster effect), and take steps to avoid these.

Later in treatment, during sliding mechanics, light continuous forces are applied using active tiebacks and rigid .019/.025 steel working wires (p. 254). In the finishing stages, light wires such as .014 steel or .016 IIANT are used for detailing of tooth positions and settling.

Although 'light forces' cannot be defined or quantified, it is hoped that careful study of this text and the various case reports will give clear clinical guidelines on this subject to the reader.

The .022 versus the .018 slot

The preadjusted appliance seems to perform best in the .022 form. The larger slot allows more freedom of movement for the starting wires, and hence helps to keep forces light (Fig. 1.21). Later in treatment, the steel rectangular working wires of .019/.025 have been found to perform well (Fig. 1.22). With the .018 slot, the main working wire is normally .016/.022 or .017/.025. These wires are more flexible and hence show greater deflection and binding during space closure14 with sliding mechanics (p. 259).

.018 slot

.018 slot

.022 slot

Fig. 1.21 The .022 slot allows more freedom of movement for the starting arch wires, and this helps to keep forces light.

016/.022

.019/025

Fig. 1.22 The .019/.025 steel rectangular working wires are more rigid than .016/.022 or .017/.025 wires and perform better during space closure and overbite control.

Anchorage control early in treatment

In the early stages of treatment, the main threat to anchorage comes from the influence of anterior bracket tip. The MBT™ brackets have reduced tip compared with earlier generations of the preadjusted appliance. This, combined with light archwires, results in reduced anchorage needs in the all-important opening stages of treatment. Orthodontists who are new to the treatment approach are often surprised by the reduced demands on anchorage, and gradually find less need for traditional headgear, or palatal and lingual arches.

Lacebacks (Fig. 1.23) are routinely used to assist control of canine crowns in premolar extraction cases, and in some non-extraction cases.

Bendbacks (Fig. 1.24) are used in most cases at the start of treatment, except where there is a need to increase arch length. Bendbacks ensure that the ends of the archwire are comfortable in the molar area, and help to prevent mesial movement of the anterior teeth, which is undesirable in most cases except Class 11/2 and some Class III cases. Bendbacks and lacebacks are normally continued throughout tooth leveling and aligning until the rectangular steel archwire stage.

Laceback Mbt Orthodontic
Fig. 1.23 Canine lacebacks are an important feature of the MBT™ treatment philosophy and are used to assist in control of canine crowns during leveling and aligning.
Mbt LacebacksDental Arch

Fig. 1.24 Bendbacks help to prevent mesial movement of the anterior teeth and ensure comfortable positioning of the archwire ends in the molar regions.

Group movement

The use of three arch forms

Where possible, teeth are managed in groups (Fig. 1.25). In preparation for group movement in premolar extraction cases, for example, lacebacks are used to control canines and retract them sufficiently to allow alignment of the incisors. In the lower arch, canines are retracted with lacebacks until anterior crowding is resolved. After this, the lower anterior segment is managed en masse, as a group of six or eight teeth. In the upper arch, canines are not normally retracted away from lateral incisors. However, it is important to maintain a Class ! canine relationship. Therefore, a laceback should be continued in the upper arch to maintain the Class I canine relationship, even if it means moving the canine away from the lateral incisor (Case JN, p. 123). It is also necessary to move the canine away from the lateral incisor in situations where a lateral incisor is small, and will require future buildup, and in some cases with a midline shift.

Until the mid-1990s the ovoid arch form (p. 76) was preferred for most of the authors' cases. They regarded it as a reliable form for a high percentage of preadjusted appliance cases.

During the late 1990s, the authors found it beneficial to use a tapered arch form for many cases, and sometimes a square arch form. The tapered form has the narrowest inter-canine width and is obviously indicated for patients with narrow, tapered arch forms. The square arch form is indicated in cases with broad arch forms and for cases that require buccal uprighting of the lower posterior segments and expansion of the upper arch. Currently, the recommended technique is to create an individualized form for all patients, based on the ovoid, tapered, or square forms (pp 78-79).

Ovoid Tapered Square Arch

Fig. 1.25 Where possible, group movement is carried out, and the upper and lower anterior segments are managed as a group of six or eight teeth. In situation A, the space has been closed by mesial movement of molars and premolars - a minimum anchorage treatment. In situation B, the incisors and canines have been retracted into the available space - a maximum anchorage situation as might occur in a Class III case or a bimaxillary protrusion case.

Fig. 1.25 Where possible, group movement is carried out, and the upper and lower anterior segments are managed as a group of six or eight teeth. In situation A, the space has been closed by mesial movement of molars and premolars - a minimum anchorage treatment. In situation B, the incisors and canines have been retracted into the available space - a maximum anchorage situation as might occur in a Class III case or a bimaxillary protrusion case.

One size of rectangular steel wire

Only one size of steel rectangular wire is used in normal treatment, and this is .019/.025. Larger, full thickness steel wires have been evaluated, but although they provide greater control, they are less effective for sliding mechanics. Occasionally .021/.025 wires in steel or HANT may be considered in the later stages of treatment, to obtain full expression of the bracket system. The technique is a 'full arch' approach, and closing loops (p. 252) or sectional wires are seldom used.

Theoretically, there is approximately 10° of'slop' between the .019/.025 wire and the .022 slot (Fig. 1.26). However, in clinical use the wire performs better than expected, and this is presumed to be due to residual tip which remains uncorrected at the time of placement of the rectangular wire, and persists intermittently during treatment as teeth are moved (Figs 1.26-1.30).

mo

\ i

\ _—————

Figs 1.26 to 1.30 The .019/.025 steel rectangular wire performs better than expected. This is presumed to be due to residual tip at the time of placement of the rectangular wire, so that the torquing effect is produced at points X and Y.

Fig. 1.31 The .019/.025 steel rectangular wires normally have soldered hooks in the positions shown above. There is greater variability of hook position in the upper arch, and therefore a wider range of upper archwires needs to be stocked. The archwire hooks may be used in combination with the hooks on molar tubes or lower second premolar tubes (p. 52) to add versatility to the treatment mechanics. This versatility includes space closure with group movement (A) and tying space closed (B). Long (C) or short (D) Class II elastics are possible, as are Class III (E) and up-and-down elastics (F). See also Figures 1.32 to 1.37 opposite.

Archwire hooks

The working steel .019/.025 rectangular wires normally have soldered hooks, and these are useful for many aspects of treatment mechanics. The average hook positions are 36-38 mm in the upper arch and 26 mm in the lower arch (Fig. 1.31). There is greater variability of hook position in the upper arch, and this is assumed to be due to variation in upper lateral incisor size.

Fig. 1.31 The .019/.025 steel rectangular wires normally have soldered hooks in the positions shown above. There is greater variability of hook position in the upper arch, and therefore a wider range of upper archwires needs to be stocked. The archwire hooks may be used in combination with the hooks on molar tubes or lower second premolar tubes (p. 52) to add versatility to the treatment mechanics. This versatility includes space closure with group movement (A) and tying space closed (B). Long (C) or short (D) Class II elastics are possible, as are Class III (E) and up-and-down elastics (F). See also Figures 1.32 to 1.37 opposite.

Fig. 1.33 After completion of space closure, passive tiebacks are used to prevent spaces re-opening (Fig. 10.10, p. 286). The second premolar has a bonded tube (p. 52).

Fig. 1.32 Active tiebacks are applied to the soldered archwire hooks to achieve space closure. Information on tiebacks is available on pages 256 to 258.

Fig. 1.33 After completion of space closure, passive tiebacks are used to prevent spaces re-opening (Fig. 10.10, p. 286). The second premolar has a bonded tube (p. 52).

They are also used to apply (Mass II or Class III elastics (Figs 1.34 & 1.35), or for up-and-down elastics (Fig. 1.36), or for short Class II elastics (Fig. 1.37).

The soldered hooks may be used for space closure during sliding mechanics (Fig. 1.32) and for holding space closed (Fig. 1.33).

Class Elastics

Fig. 1.34 Class II elastics (Fig. 8.12, p. 225) applied to soldered archwire hooks.

Hooks Soldered Archwire

Fig. 1.36 Up and down elastics.

Kobyashi Hook

Fig. 1.37 Short Class lower first premolar.

elastics from a Kobyashi hook on the

Fig. 1.36 Up and down elastics.

Fig. 1.37 Short Class lower first premolar.

elastics from a Kobyashi hook on the

Methods of archwire ligation

With opening .016 HANT wires the authors favor elastomeric modules (Figs. 1.38 and 1.39) or ligature ties at the first visit, as it is not critical to tie the archwire fully into the bracket slot. At the first adjustment visit it is beneficial to fully tie in any areas where the wire is not completely seated in the bracket slot.

A similar approach is used at the first and second visits with rectangular IIANT wires. Any time a IIANT wire of any size is not fully engaged it can be helpful to cool the wire locally to assist full engagement.

The rectangular steel .019/.025 working wires are normally placed using elastomeric modules for the first 1 or 2 months. After that, .010 ligature wires may be used with ligature-tying pliers or hemostats and ligature directors (Fig. 1.38) to provide more positive archwire engagement. This allows the orthodontist to obtain better expression of the features built in to the bracket system.

Orthodontic Elastomeric Modules

Fig. 1.38 Conventional elastomeric modules.

Fig. 1.39 'Easy-to-tie' elastomeric modules.

Fig. 1.38 Conventional elastomeric modules.

Mechanecal Plier
Fig. 1.40 Coon ligature-tying pliers provide more positive archwire engagement than elastomeric modules.

Fig. 1.41 Hemostats or 'mosquito' pliers may also be used to apply wire ligatures to" brackets.

Awareness of tooth size discrepancies

It is pan of the technique to assess tooth size at the treatment planning stage and throughout treatment. In recent years, much more attention has been paid to tooth size discrepancies, because these can be an obstacle to achieving an ideal result in many cases. For example, it is accepted that enamel reduction among lower incisors is often necessary to obtain good tooth fit in the finishing stages as discussed in Chapter 10.

Persistence in finishing

Finally, in this chapter, it is worth remembering that persistence in finishing is needed, despite all the improvements in bracket design and the better understanding of treatment mechanics.

In the closing stages of treatment, light wires such as .014 steel are used, and archwire bends are frequently required. Also, it is necessary to resist the temptation to remove appliances too early. Time should be spent in finishing and settling using techniques recommended in Chapter 10, and this will be reflected in the final quality of the result.

REFERENCES

1 Andrews L F 1972 The six keys to normal occlusion. American Journal of Orthodontics 62:296-307

2 Reukers E 1997 Straight Wire Appliance versus conventional full edgewise, prospective clinical trial. University of Nijmegen, Nijmegen

3 Reukers H A J, Kuijpers-Jagtman A M 1996 Effectiveness of orthodontic treatment: a prospective clinical trial. European Journal of Orthodontics 18:424 (abstract)

4 McLaughlin R P, Bennett J C 1989 The transition from standard edgewise to preadjusted appliance systems. Journal of Clinical Orthodontics 23:142-153

5 Bennett J C, McLaughlin R P 1990 Controlled space closure with a preadjusted appliance system. Journal of Clinical Orthodontics 24: 251-260

6 McLaughlin R P, Bennett J C 1991 Finishing and detailing with a preadjusted appliance system. Journal of Clinical Orthodontics 25:251-264

7 Bennett J, McLaughlin R P 1993 Orthodontic treatment mechanics and the preadjusted appliance. Mosby-Wolfe, London (ISBN 0 7235 1906X)

8 Sebata E 1980 An orthodontic study of teeth and dental arch form on the Japanese normal occlusions. The Shikwa Gakuho 80(7):945-969

9 Watanabe K, Koga M, Yatabe K, Motegi E, Isshiki Y A 1996 A

morphometric study on setup models of Japanese malocclusions. The Shikwa Gakuho

10 Roth R H 1987 The Straight Wire Appliance 17 years later. Journal of Clinical Orthodontics 21:632-642

11 McLaughlin R P, Bennett J C 1995 Bracket placement with the preadjusted appliance. Journal of Clinical Orthodontics 29:302-311

12 Bennett J, McLaughlin R P 1997 Orthodontic management of the dentition with the preadjusted appliance. Isis Medical Media, Oxford (ISBN 1 899066 91 8). Republished in 2002 by Mosby, Edinburgh (ISBN 07234 32651)

13 McLaughlin R P, Bennett J C 1999 Arch form considerations for stability and esthetics. Revista Espana Ortodontica 29(2):46-63

14 Ouchi K, Koga M, Watanabe K, Issiki Y, Kawada E 2001 The effects of retraction forces applied to the anterior segment on orthodontic arch wires - changes in wire deflection with wire size. Presented to southern California component of Edward H Angle Society. In press.

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Responses

  • May Grubb
    Is modern form archwire = euroform archwire ?
    6 years ago
  • Selamawit
    How to avoid roller coaster effect Orthodontics?
    4 years ago
  • maura
    How to correct roller coaster effect in orthodontics?
    4 years ago
  • JOHNNY
    Why was tip reduced in mbt brackets?
    3 years ago
  • selina
    When was preadjusted applaince introduced by andrews?
    3 years ago

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