THE ANDREWS STRAIGHT WIRE

APPLIANCEBy

Dr. Nilofer

Introduction…

The Straight Wire Appliance is conceptually any fully programmed appliance. It was initially designed by Lawrence F. Andrews, D.D.S.

Dr. Andrews has engaged in independent research, teaching, and publishing since 1960. Research spanning ten years led to The Six Key to Optimal Occlusion, quantifying the tooth positions of naturally optimal dentitions, and the Straight-Wire Appliance. This information has been documented in a text titled Straight Wire, The Concept and Appliance (L. A. Wells, 1989).

Lawrence F Andrews Will Andrews

1980's - 1990's research led to finding the Six Elements of Orofacial Harmony. They are the characteristics found to be shared by individuals with both optimal occlusion and balanced faces. They are proposed as optimal goals for orthodontic treatment and as the bases for a new correct classification system.

Evolution of straight wire appliance (AJO,1978,May)

1927 —Angle angulated brackets and tubes to effect tipping movement. He also suggested to angulate posterior brackets to produce desired tooth movement.

1952 —Holdaway angulated bracket on teeth adjacent to extraction spaces to aid in paralleling the roots and also used as a method of setting up posterior anchorage unit into tip back or anchorage prepare positions.

Jarabak and Fizzel in 1960 demonstrated a modified edgewise technique which incorporated second (tip) and third order (torque) mechanics in the appliance and they called it “building treatment into the appliance”

In 1960 Lee developed a series pretorqued brackets to be used on upper and lower incisors to eliminate the need for adding torque to the anterior part of the arch wire.

In 1960s manufacturers raised the base of lateral incisor to eliminate the need for lateral offset bends.

They also began to offer biangulated tube that incorporated 10 degree torque as well as rotational controls for the molars.

Lawrence Andrews basically gave the straight wire appliance because of the Inconsistencies in treatment results existing at the

time. Extensive & elaborate wire bendings because

each bracket was the same but optimal positions differ for most tooth types in a dentition.

Edgewise was basically intended only for non-extraction cases.

with extraction the wire bendings required were even more elaborate.

At the same time disadvantages of Begg were many namely

Root recovery sometimes from extreme angles were unfavourable.

Inability to use rectangular archwires denied accurate molar control and buccal segment torque

Straight Wire Appliance The concept that an edgewise appliance

could be fully programmed evolved thru a series of five steps by Andrews these includes:-

1)Examination of post treatment occlusion.

2)Study of naturally occurring optimal occlusion from 120 normal samples.

3)Discovering the six characteristics that were present in 120 normal samples.

4)Crown measurements in 120 samples,5)Comparison of treated occlusion with normal

occlusion.

On the hypothesis that naturally occurring optimal occlusion would be worthy of evaluation,120 casts of such dentition were collected based on the following criteria:--

Have never been subjected to orthodontic treatment.

Are well aligned and pleasing in appearance.

Appear to have excellent occlusion.

Would not benefit from orthodontic treatment.

It took 14 Research Projects to show to develop this very popular appliance.

One led to to the 6 key elements in optimum occlusion.

5 led to the concept of SWA 8 research projects were designed to

explain & justify the concept.

Examination of post treatment occlusion

Andrews examined hundreds of post treatment dental cast displayed by members of the American board of orthodontics and the Tweed foundation to assess the quality of American orthodontics in terms of static occlusion. consistently found features were:-

Incisors were not rotated No cross bite or over jet Class I molar relationship

Except for these consistencies following variation in the treatment results were

found:--

Articulation of the occlusal surface of the teeth were not proper.

Long axis of the tooth on either side of the extraction site were not always parallel.

Variation of inclination and angulation among patients treated by different orthodontists.

The permanent 2nd molar were not routinely included in the treatment.

Interdental spaces existed frequently at extraction sites and other locations and there was no articulation of the dental cast to assess the functional occlusion.

Study of Normal models The measurements which were made in

this study include – Vertical crown contour. crown inclination maxillary molar offset horizontal crown contour facial prominence of each crown Depth of curve of Spee

The results of this were compared with

1150 treated cases. And unlike Angle’s conviction

Orthodontia’s best did not match Nature’s best.

Features The basic feature of SWA is that the Slot

planes indirectly represent the planes of the crown’s.

Tooth positions are referenced from the crown’s facial axis and not the tooth/ crown’s long axis as is the more traditional view.

The main advantage is that it eliminates the need for wire bends.

However Wire forming is a procedure still required here.

Rectangular slot- narrow side towards the incisal edge of tooth Two point contact Accepts rectangular arch wire - edgewise

In/Out adjustments & finishing angulations of tip &torque were given in the bracket itself

Hence the requirement of bending the finishing torque into the rectangular arch wire was eliminated.

Objectives of Andrews basically was – 1. To minimize the variables

1. Bracket siting variables2. Wire bending variables and side effects

2. To take advantage of similarities. 1. Similarities seen in patients2. Similarities in wire bending for each patient

and every wire

Answer was not the wire, but the bracket

If correct tooth position was built into the

bracket

It removed the variables

It removed wire bending side effects

And it reduced the workload.

Advantages of the SWA

Andrews

1. No individual variation due to wire-

bending

1. More consistent results

2. Easier to attain superior results

3. No side effects of wire bending – wagon wheel

effect

2. Self limiting appliance – once wire is

straight - treatment stops

• No over treatment if patient misses an

appointment

3. Straight wire is an indication of treatment

goals

4. Easier to transfer cases

5. Better control of final position of teeth.

6. Better patient comfort.

7. Space closure with one set of wires.

8. Ease of ligation –tiewings away from

gingiva.

9. Ease of bracket placement.

Andrews Six Keys

Andrews Six Keys :

1. Molar inter arch relationship.2. Mesiodistal crown. 3. Labiolingual crown inclination.4. Absence of rotations.5. Tight interproximal contacts.6. Curve of spee.

TERMINOLOGIES

The following terms are necessary for discussing the six keys

Terms of importance : Andrews Plane : The surface or plane on

which the midtransverse plane of every crown in an arch will fall when the teeth are optimally positioned

The Clinical Crown : The amount of crown that can be seen intra-orally or with a study cast.

Orban’s def : Clinical crown is defined as Anatomic crown minus 1.8 mm

Also in cases of recession it would be Crown height upto CEJ minus 1.8 mm.

Facial axis of the clinical crown—(FACC)-for all teeth except molars ,the most prominent portion of the central lobe on each crown’s facial surface.

For molars , it is the buccal groove that separates the two large facial cusps.

Facial axis point -(FA)-The point on the facial axis that separate the gingival half of the clinical crown from the occlusal half.

Crown Angulation : This is evaluated

according to the line formed by the facial axis of the clinical crown (FACC) and a line drawn perpendicular to the occlusal plane.

The Crown angulation is

considered positive if

the occlusal portion of

the FACC is mesial to

the gingival portion.

Crown Inclination The angle

between the line perpendicular to the occlusal plane and a line that is parallel & tangent to FACC at its midpoint (the FA point ).

If the occlusal portion of the crown is facial to its gingival portion it is considered as positive.

Tooth class —a group of teeth having similar shape and function. classes are incisors , canines, premolars ,and molars.

Tooth type —a subordinate category within a class of teeth. Premolars are a class of teeth and mandibular first premolar is a type and is different from any other tooth type, such as mandibular second premolar.

INTER ARCH RELATIONSHIPS

1. Angles Class I molar relationship.

2. The distal marginal ridge of the maxillary Ist molar occludes with the mesial marginal ridge of the mandibular second molar.

3. The mesiolingual cusp of the maxillary Ist molar occludes with the central fossa of the mandibular Ist molar.

4. The buccal cusps of the maxillary premolars have cusp embrasure relationship with the mandibular premolars

5. The lingual cusps of maxillary premolars have a cusp embrasure relationship with the mandibular premolars.

6. The Maxillary canine has a cusp embrasure relationship with the mandibular canine & 1st premolar with the tip slightly mesial.

7. The maxillary incisors overlap the mandibular incisors and the midlines coincide

1. Improper molar relationship.

Source : Six Keys To Normal Occlusion (AJO-DO Vol 62(3)

2. Improved molar relationship.

3. More improvedmolar relationship.

4. Proper molar relationship.

Key II Crown Angulation In general all the crowns have a

positive angulation. Crown angulation (tip). The gingival

portion of the long axes of all crowns was more distal than the

incisal portion (Fig. 3). Crown tip is expressed in degrees,

plus or minus. The degree of crown tip is the angle between the long axis of the crown (as viewed from the labial or buccal surface) and a line bearing 90 degrees from the occlusal plane.

A “plus reading” is awarded when the gingival portion of the long axis of the crown is distal to the incisal portion. A “minus reading” is assigned when the gingival portion of the long axis of the crown is mesial to the incisal portion,

Why this MD tip is so very important can be explained with the help of a rectangle.

Crown angulation (tip)-long axis of crown measured from line 90 degrees to occlusion.

A rectangle occupies much more mesiodistal width when tipped than upright .

Normally occluded teeth demonstrate gingival portion of crown more distal thanocclusal portion of crown.

Key III Crown Inclination Consistent pattern of Most maxillary centrals having a positive

inclination and mandibular incisors having a slight negative inclination . The crown of maxillary incisors are more positively inclined relative to a line 90 deg to the occlusal plane.

The inclinations of premolar and molars is more and more negative.

Source AJO-DO Vol 62(6)

Crown inclination is determined by the resulting angle between a line 90 degrees to the occlusal plane and a line tangent to the middle of the labial or buccal clinical crown.

Spaces resulting from normally occluded posterior teeth and insufficiently inclined anterior teeth are often falsely blamed on tooth size discrepancy.

Tip Values 5 5 2 2 11 9 5

Torque

Torque

Tip Values 2 2 2 2 5 2 2

Tip and Torque.

Tip is the mesiodistal component whereas torque is the labiolingual component.

For every 4 deg lingual crown torque given there is a mesiodistal tip of 1 deg i.e 1 deg of mesial tip of the gingival portion of the crown.

Therefore 4 deg of lingual Crown torque = -1 deg Crown tip

This phenomenon is aptly described by the Wagon Wheel effect.

The wagon wheel. Anterior arch wire torque negates arch wire tip in a ratio offour to one.

A mechanical problem can occur because of this because if a lingual torque of 20 deg is given to a central incisor then a negative -5 deg convergence is seen near the gingival area (tip:torque 1:5 )to combat this a +10 deg tip would be given since we want a ultimate +5 deg tip.

Key IV : Rotations The fourth key to normal occlusion is that the

teeth should be free of undesirable rotations. An example of the problem is seen in a superimposed molar outline showing how the molar, if rotated, would occupy more space than normal, creating a situation unreceptive to normal. occlusion.

Key V : Tight ContactsThe fifth key is that the contact points should betight (no spaces). Persons who have genuine

tooth-size discrepancies pose special problems, but in the absence of such abnormalities tight contact should exist. Without exception, the contact points on the nonorthodontic normals were tight.

Key VI : Curve Of SpeeThe planes of occlusion found on the non-orthodonticnormal models ranged from flat to slight curves of

Spee. Even though not all of the non-orthodontic normal

cases had flat planes of occlusion, Andrew believed that a flat plane should be a treatment goal as a form of overtreatment.

There is a natural tendency for the curve of Spee to deepen with time, for the lower jaw growth downward and forward sometimes is faster and continues longer than that of the upper jaw, and this causes the lower anterior teeth, which are confined by the upper anterior teeth and lips, to be forced back and up. Resulting in crowded lower anterior teeth and/or a deeper overbite and deeper curve of Spee.

At the molar end of the lower dentition, the molars (especially the third molars) are pushing forward, even after growth has stopped, creating essentially the same results.

Intercuspation of teeth is best when the plane of occlusion is relatively flat.

A deep curve of Spee results in a more confined area for the upscreating spillage of the upper teeth progressively mesially and distally.

A flat occlusion is most receptive to normal occlusion.

A reverse curve of Spee resultssive room for the upper teeth.A reverse curve of Spee is an

Few more points of importance :

Intercuspal position & retruded jaw position /relation should be coincident.

Anterior guidance in mandibular protrusion should be guided by the incisors . There should be disocclusion of all other teeth..

Canine guidance Lateral movements of the mandible should be guided by the working side canines. There should be disocclusion of all other teeth working/ nonworking side.

Cusp embrasure contact The inter – cuspal position should be

even throughout both buccal segments.

The 4th study that lead to development of the first fully programmed appliance involved thousands of measurements of the crowns in 120 samples.

The purpose of this study was to learn the extent to which position and in certain ways, shape was constant within each tooth type , and how relative size was consistent within an arch.

The Crown Measurements

Following measurements were made

The height and width of potential bracket area on facial aspect of each crown.

Vertical crown contour Crown angulation Crown inclination Horizontal crown contour Depth of the curve of spee. Maxillary molar offset Facial prominences of each crown

Naturally optimal versus treated occlusion

When dentitions with naturally optimal occlusions were compared with dentition treated by orthodontists the following conclusions were apparent:-

Few of the post treatment results meet the six keys standard.

Treatment priorities and results of a given orthodontist share characteristic features not always observed in the results of other orthodontists.

A quarter century of clinical experience and research devoted to naturally optimal and treated occlusions has yielded not only the quantified six key objectives for orthodontic treatment but also several principles fundamental to the fully programmed appliance.

These principles are:-

Each tooth type is similar in shape from one individual to other.

The size of the normal crowns within a dentition has no effect on their optimal angulation or inclination, or on the relative prominences of their facial surface.

Most individuals have normal teeth regardless of whether their occlusion is flawed or optimal.

Jaw must be normal and correctly related to permit the teeth to be correctly positioned and related.

Dentition with normal teeth and in jaws that are or can be correctly related can be brought to optimal occlusal standards.

Arch lines and treatment strategies

The six keys are more readily attained with any appliance when the clinician understands that there are three arch lines and not just one and each must be optimal for occlusion to be optimal.

These three arch lines are:- Core line Midsagittal line Perimeter line

Core line The arch core line is an imaginary line that best represents the length of the dental arch at its core.

It passes mesiodistally through the center of each crown whose alignment conforms to the arch form. it extends to the distal surface of the last teeth in each arch to be included in the treatment.

It is short when its length is less than the sum of the mesiodistal diameter of normal crowns at their contact points. And optimal when it equals that sum.

Mid sagittal line

It is an imaginary line that best represent the anteroposterior length of an arch.

It is measured in the midsagittal plane of an arch from the anterior limit of the core line to a line connecting the most distal aspect of the core line.

The midsagittal line is optimal when the core line’s length and form are optimal.

The midsagittal line is short when the core line is short or when the core line’s occlusogingival or buccolingual form are incorrect.

Perimeter line It is also an

imaginary line that best represent the length of the occlusogingival portion of the dental arch.

It is measured along a line that connects the most facial points of the occlusal surface of the crowns that are on the core line and extends as far distally as does the core line.

Factors affecting the arch line. Arch Line Components

Inclination Angulation Rotation Mesiodistal position Labiolingual position Occlusogingival position Inter jaw relation

In the maxillary arch the perimeter line is long when incisors inclination is excessively positive, optimal when inclination is moderately positive and short when inclination is negative.

Inclination

In the mandibular arch the perimeter line is long when the incisors are inclined positively, optimal when inclination is slightly negative, short when inclination is excessively negative.

Positively inclined mandibular incisors lengthen the perimeter line, causing the posterior to have a class II tendency if the incisor interarch relationship is CLASS I and there is no maxillary interdental space.

Optimal perimeter lines occur when maxillary incisor inclination is moderately positive and mandibular incisor inclination is slightly negative.

AngulationThe Angulation of maxillary incisors can affect the core, midsagittal and perimeter lines. If viewed buccally the mesial and distal ends of the posteriors conform to the shape of a circle .Similarly when viewed facially the lower incisors look like an isosceles triangle. These particular teeth class and type if angulated more or less than optimal wont affect the three arch lines. However if the mesial and distal surface of the Maxillary central incisor crowns are seen in the area of potential contact then they are seen potentially as Trapezoids and when their mesiodistal angulations are altered they change the arch perimeter.

The mesiodistal diameter of a maxillary central incisor is approximately 0.15mm greater when angulated 5 deg than at 0 deg.

Similarly 0.25 mm for lateral incisors when angulated at 9 deg.

The core line is 0.8 mm less when the maxillary incisors are upright than when they are optimally angulated.

(Unpublished Study By L. Andrews. 1986 )

Rotation

Rotation First premolar, canine & incisors will not affect immediately the arch core lines as will the 2nd premolars, & molars.

But rotated incisors may cause drift due to broken contacts which would alter all 3 lines.

If Second premolars/1st molars were rotated by 20 deg mesially the core line average was increased by 0.268mm for second premolars and0.317mm for 1st molars. (Unpublished Study By L. Andrews. 1987 )

Mesiodistal Position

Long arch lines occur when there are interdental spaces assuming no missing teeth or tooth size discrepancy.

Faciolingual Position

Changing this in the buccal segment affects the core and the perimeter lines.

Palate splitting will increase the core and perimeter lines in the maxillary arch.

Facial tipping of buccal segments will increase the core and perimeter lines in either of the two arches.

Lingual tipping will decrease core and perimeter lines in both arches.

Facial or lingual tipping of all four incisors will affect all three arch lines..

Occlusogingival Position

Change in occlusogingival height of an isolated tooth will not affectthe arch lines immediately.

If the length of the Arch core line is correct but the form is convex or concave ,the midsagittal line will be short.

With the same circumstances with adequate interdental space for leveling the midsagittal line would be correct.

Class I JAW presents the full range of alveolar bone for attaining optimal incisor inclination and class I incisors

Inter Jaw Relationships

A class III jaw precludes coincidental class I incisors and optimal inclination.

There is excessively negative mandibular inclination &excessively positive maxillary inclination ..causing decreased arch perimeter in lower & increased arch perimeter in upper

Class I incisors with incorrect inclination

Optimal incisor inclination class III relationship.

Regardless of the etiology part of our job as orthodontists is to correct the archlines by correcting the tooth positions and interarch relationships.

Attaining optimal arch lines efficiently depend greatly upon treatment strategies, which includes goals, appliance selection and prescription, bracket and slot sitting and certain treatment procedures.

NON- PROGRAMMED APPLIANCE

Need for new appliance

Shortcomings of standard edgewise:-for tooth movement not involving translation six factors cause the slot of non programmed edgewise brackets to be sited in ways that always require arch wire bends.

Each factor may cause the slot to be misdirected by more than 2 degree from its optimum angulation and inclination and by more than 0.5mm, occlusogingivally, mesiodistally, and faciolingually.

These six factors are:--

Bracket bases are perpendicular to the bracket stem.

Bracket bases are not contoured occlusogingivally

Slots are not angulated Bracket stems are of equal faciolingual

thickness Maxillary molar offset is not built in. Bracket sitting techniques are

unsatisfactory.

•Bracket bases are perpendicular to the bracket stem.•The base of the non- programmed bracket is perpendicular to the faciolingual axis Cause problems of slot siting & occlusogingival positioning.

Bracket bases are not contoured occlusogingivallySlots are not angulatedWhen such bracket is being attached to a crown either directly or with a band, it can unintentionally be rocked occlusally or gingivally.

In such cases additional compensatory bends would have to be made in the arch wire.

The potentioal inclination range that the bracket can rock for each tooth is greater than 2 deg.

When the Base of the slot Is placed parallel to the FACC and the base point is affixed correctly to the FA point the angle of the slots will vary to that many different positions

The incomplete lines show the optimal position

Stems of Equal Prominence : The distance from the bracket base to

the center of the slot is same for each bracket .

Therefore the slots are not of equal prominence.

Maxillary Molar Offset Not Built In: Since this is not given in the bracket

itself we have to incorporate it in the wire bending itself.

Just as the non programmed brackets have at least six design shortcomings that affect the accurate slot sitting, the land marks traditionally used for sitting the bracket have their own deficiency.

Unsatisfactory Landmarks

Even when cases were transferred the orthodontist use to reposition the brackets to suit himself/herself.

During bracket positioning the land marks used are

Angulation landmark

Long axis of crownLong axis of tooth

Incisal edges

Marginal ridges

Contact points

Long axis of crown: Not reliable Since they run thru center of the teeth. Contact Points :Though easy since not

inside the tooth cannot be referenced easily.

Incisal Edges : Limited help since they are too far away from the bracket slots.

Plus posterior teeth have cusp tips.

Inclination landmark

Long axis of the crown or tooth

Bracket height from cusp tip or incisal tip

Long Axis of the tooth just as unreliable for similar reasons plus the fact that facial axis of the crown does not parallel the the axis either.

Also no two sites on the crowns facial surface have the same angular relation to to the plane of the occlusal surface/ crowns mid transverse plane or to the occlusal plane of the arch when the teeth are optimally positioned

The diversity of bracket sitting techniques for inclination is evident when the literature is reviewed.

Tweed recommends sitting brackets a specified no. of millimeters from the incisal edge or cusp tip.

Saltzmann recommends bracket location at middle third of the crown except for maxillary laterals.

Holdaway advocates the bracket sitting can be altered according to characteristics of malocclusion.

Open bite cases----within the gingival 1/3 Deep bite cases—within the occlusal1/3

A/c to Jarabak bracket sites for inclination should be determined by the shape of the crown.

Ovoid crowns--- bracket site should be in middle 1/3

Tapering crowns ---1-2mm away from the incisal edges.

Square form —should be close to the incisal edges as possible.

Lindquist recommended marginal ridges of the posterior teeth as reference to locate the brackets.

WIRE BENDING

E.g•In a tooth slot inclination can differ up to 45 degree depending on which portion of the crown is chosen as bracket site.

Excessive wire bending

Non programmed brackets are simple in design, easily manufactured and inexpensive but unfortunately they are difficult to use because considerable wire bending is needed throughout the treatment.

Next to shortcomings of bracket design and landmarks, the most obvious reason for so much bending is that the brackets are all the same but the positions of most tooth types are different.

With non programmed appliances there are four reasons to bend (1st,2nd,3rd order) the wire in

each of three planes:-

To initiate or maintain movement of the teeth

To compensate for slot sitting errors caused by inadequate bracket design or incorrect bracket sitting.

To compensate for the side effects of wire bending and wire forming

To correct for earlier human error inaccuracies in wire bending.

Primary wire bends

According to Andrews a primary arch wire bend is a first order, second order or third order bend intended for the most direct movement of teeth

The slot of the bracket is intended to indirectly represent the crown landmarks chosen by the orthodontist for angulation, occlusogingival position, inclination and facial prominences.

If the slots does accurately represent the crown landmarks, even then the primary bends required for each tooth.

Secondary wire bends

These are any bends for tooth guidance that are not primary bends.

These bends are needed to compensate for slot sitting irregularities caused by bracket design and unreliable bracket sitting technique wire bending and wire forming side effects and judgment errors in bending.

Tertiary wire bends

A tertiary bend is one placed for any reason other than guidance

Examples are omega loops for stops, loops for increasing wire flexibility and loops for elastics.

Orthodontist often encounter slot sitting problems caused by bracket design and bracket sitting

Personal skills in wire manipulation vary According to Thurow there is no such

thing as an isolated orthodontic act. More effort and knowledge is required to prevent or control unwanted movements than to apply primary forces.

Some of these events cannot be perceived clinically but any one of them can affect tooth position beyond the established .5mm or 2degree error limits.

Brackets designed to work with sitting system that ensures locating them within the 0.5mm and 2 degree guidelines.

An appliance whose design and sitting system offers these features will reduce or eliminate the need for wire bending .

It will also stimulate greater emphasis on diagnosis, treatment planning and execution of treatment

FULLY PROGRAMMED APPLIANCE

1958 John Stifter came up with a bracket with a male and female component.

female component was attached to the tooth with interchangeable male components which had various combinations of inclinations, angulations and torque values.

Summary : This was the FIRST EDGEWISE BRACKET designed to build guidance into all three planes of space.

For Bracket Siting The Crowns FA point was selected

because 1. No interference with gingiva/ tooth.2. The angulation & inclination of the

crown at this site had a consistent angular relationship to the plane of each tooth’s occlusal surface at all times and to the occlusal plane of the arch.

3. The middle of each FA point shared the same plane/surface when the teeth in an arch was optimally positioned.

The FACC is taken as a landmark because :

1. Can be easily seen and marked.2. Easy to inspect the angulation of a

crown before treatment.3. During treatment the FACC can be easily

visualised thru the vertical components, designed to parallel and straddle the FACC.

4. Can be used for angulation and inclination of both anterior and posterior teeth.

Accuracy in the technique required is such that the the bracket should be sited within 2 deg if the FACC and base point of the bracket to within 0.5mm of the FA point.

The concept of programming tooth guidance into the bracket rather than into the wire is based on the fact that extensive similarities prevail in the basic morphology of normal tooth types.

Design features of : a) Correct amount of slot angulation.b) inclination.c) Facial Prominence.Are included in Partly programmed

appliances since they do not target the slot within 2 deg and 0.5 mm.

Whereas fully programmed brackets include the above plus convenience features and auxilliary features.

Types Of Fully Programmed Appliances

a) Standard Fully Programmed Appliance

b) Translation Fully Programmed Appliance

Types of Brackets

Standard brackets Incisor relation - Class I Class II Class

IIIMolar relation Class I Class II

Extraction series brackets or translation brackets Minimum Medium Maximum

STANDARD FULLY PROGRAMMED APPLIANCE.

Standard Brackets

Standard BracketsDef: A fully programmed bracket designed for

teeth that do not require translation. Non extraction cases. Same values of built in features as normals One Standard bracket for each tooth, except

incisors & max. molars.For incisors there are 3 9with differing inclinations)

and Max molars – 2 types of brackets – Class I molars Class II molars

Design of fully programmed standard brackets

Fully programmed standard brackets produce slot siting features of the quality required and also if it is not required for treatment with unbent arch wires.

These features will be required in midtransverse midsagittal and mid- frontal planes of each tooth and

brackets and not in relation to the planes of patient’s head.

Slot features in midtransverse plane

Feature 1 —the midtransverse plane of the slot, stem and crown must be the same.

Feature 2 —the base of the bracket for each tooth type must have the same inclination as the facial plane of the crown at the FA point

•Feature 3 ---each bracket’s inclined base must be contoured occlusogingivally to match the curvature of the crown

If features 1 through 3 are incorporated into the bracket

design and the brackets are sited correctly, each slot’s midtransverse plane will be aligned with that of the crown, regardless of crown’s position.

When the teeth are optimally positioned, the midtransverse planes of all the crowns, stems and slots in an arch will coincide with the Andrews plane.

These 3 slot siting features eliminate the need of several kind of bends—2nd order bends to deal with occlusogingival disharmony in slot sitting, 3rd order bends for inclination and other bends to deal with inherent side effects of wire bending

Slot features in midsagittal plane

Feature 4 —the midsagittal plane of slot ,stem and crown must be the same.

Feature 5 —the plane of the bracket base at its base point must be identical to the facial plane of the crown at the FA point.

In all the crowns the angle is 90 degree except for maxillary molars it is 100 degree to the midsagittalplane.

In the maxillary molars the extra 10 degree prosthetically equalizes the unequal facial prominences of molar buccal cusps.

Feature 6 —the base of the each bracket must be contoured to match the mesiodistal radius of the area of the crown it is designed to fit.

conformity of crown and bracket base curvature prevents any play between the base and the crown that might cause the midsagittal of the bracket to be directed mesially or distally to the crown’s midsagittal plane.

Feature 7---in each fully programmed bracket, the vertical components( mesial and distal borders of bracket stem and tie wings) are designed to parallel one another. these components , when the parallel and midpoint bracket siting technique is used, are to parallel and straddle the vertical landmark of the crown—the FACC.

The horizontal components of the bracket i.e. superior and inferior sides of the bracket stem are sited equidistant from the crown’s gingiva and cusp’s tip the base point of the bracket will mate with the crown’s FA point.

Features in mid frontal plane

Feature 8 —within an arch ,all slots points ( c ) must have the same distance between them and the crown’s embrasure line (a).

At the same time the distance between the slots points and the face of the each crown (bc), when measured along their respective midtransverse planes, must be inversely proportional to the distance between each crown’s face and its embrasure line (ab).

This feature in the bracket eliminates the first order bends to accommodate for varying crown prominences.

Bracket Base Inclination Cl I Cl II

Cl IIIMaxillary CI : 7 deg 2 deg

12 deg

LI : 3 deg -2 deg 8 deg

Mandibular CI & LI -1 deg 4 deg

-6 deg

Convenience features

Convenience feature do not play a role in slot sitting but they make the appliance easier for the orthodontist to use and sometimes more comfortable for the patient.

The gingival tie wings on posterior brackets are designed to extend farther laterally than they do on non-programmed brackets.

This facilitates ligation and eliminates gingival impingement

The bases of fully programmed brackets are inclined so on mand.premolars and molars the stem and tie wings are directed more gingivally than they are in non programmed brackets.

This slot sitting features eliminates or reduces occlusal interferences that often occurs with brackets whose bases are not inclined.

Similarly facial surface of incisor and canine brackets are designed to parallel their bases ,which in turn parallel the crown’s faces.

This feature is for lip comfort and also helps in preventing occlusal interferences.

Auxiliary features

They contribute to the biological aspect of the treatment ,even though they are not involved in siting the slot .

Examples are power arms. hooks. face bow tubes. utility tubes and rotation wings.

Fully programmed translation brackets

Translation is defined as uniform motion of a body in a straight line.

For such movement to occur the force must actually or effectively be applied to the object’s center of resistance.

The Advantage of Translation fully programmed brackets over non-programmed ones is that by using these the teeth come more or less within the 2 deg and 0.5 mm permissible limit.

A bracket located on the crown’s face is in the wrong place in two ways:----•The bracket is occlusal to the tooth center of resistance ( b ). •So when a mesial or distal force is applied the tooth instead of translating ,it will tend to tip around its horizontal center of rotation (a ).

The bracket is also located laterally to the center of resistance ,

so instead of translating when a mesial or distal force is applied , the tooth will tend to rotate around its vertical center of rotation

In addition to this ,whenever a mesially directed force is applied to maxillary molars it also has tendency to tip buccally because of the drag imposed by the tooth dominant lingual root.

The Translation Fully Programmed Series have the same features as the standard one i.e.

The placement of brackets according to Midtransverse, midsagittal and mid frontal planes

+Slot Siting features of Counter mesiodistal tip, Counter rotation, Counter buccolingual tip (max

6) + Power Arm

Definition : “ A Slot Siting feature that

counteracts rotation during translation and then overcorrects ”

Counter rotation

The slot siting feature for counter rotation involves rotating the slot in specified amounts around its vertical axis depending upon amount of translation needed.

This feature coupled with the flex of wire counteracts tooth rotation caused by mesial or distal force during mesial or distal translation.

To transfer the force efficiently from bracket slot to center of crown the mesio-distal length of a bracket should equal the distance from the slot point to the tooth’s vertical axis.

Relative to a line 90 degree to the crown’s midsagittal plane, the mesiodistal axis of a standard slot is not rotated— 0 degree line.

however for translation brackets the slot’s mesiodistal axis is rotated 2,4, or 6 degree around the slot point.

When a mesial or distal force is applied, the resulting rotation moment (M) is controlled by the counter moment (CM) produced by the rotated slot and flexed arch wire.

When translation is complete, the rotated slot provides rotation overcorrection

For efficient rotation control the mesiodistal bracket length (b) should equal the distance ( c ) from slot point ( a) to the tooth's vertical axis ( d ).

Counter mesio-distal tip

The slot sitting feature for counter mesio-distal tip involves rotating the slot according to the translation distance around its facio-lingual axis.

Mesiodistal slot length ( a ) is less than the distance ( b ) from the bracket ( c ) to the tooth’s center of resistance ( d ).

When a mesio distal force is applied to a bracket, the counter moment ( CM ) and moment ( M ) are out of balance and the tooth tends to tip.

The counter moment produced by the angulated slot and flexed arch wire counters some but not all of the tendency for the root to lag behind the crown when a mesial or distal force is applied to the crown.

Optimal lever length for translating a tooth equals the distance ( b ) from the tooth bracket site ( c ) to the tooth’s center of resistance ( d ).

Optimal lever length produces a balanced countermoment and moment.

Counter moment and moment are out of balance when the counter moment is produced from the power arm alone without assistance from the wire and slot.

It happens because the power arm length ( e ) is shorter than is the distance ( b ) from the bracket ( c ) to the tooth’s center of resistance ( d ).

Translation occurs when both the slot and power arm are activated.

Together they provide a counter moment equal to the moment.

The combined lengths of the slot ( a ) and power arm ( e ) equal the distance ( b ) between the bracket ( c ) and tooth’s center of resistance ( d ).

When translation is complete the extra slot angulation provides angulation overcorrection.

Standard slot angulation for maxillary canine is 11 degree for canine however for canine translation brackets the standard slot angulation is increased to 13,14 or 15 degree.

Amount of translation

2mm or less

More than2mm but less than 4mm

More than 4mm

Degree of counter mesio-distal tip

+2 degree-mesial

-2 degree-distal

+3degree-mesial

-3 degree-distal

+4degree-mesial

-4degree-distal

Counter buccolingual tip

whenever a mesially directed force is applied to maxillary molars it also has tendency to tip mesially as well as buccally because of the drag imposed by the tooth dominant lingual root.

Counter buccolingual tip is achieved by increasing negative base inclination which cants the slot mid transverse plane relative to the crown’s mid transverse plane.

Partly programmed appliance

In 1970s after the introduction of straight wire appliance these brackets were developed with more than one programmed slot-sitting feature.

Patent restrictions allowed them to reproduce no more than 4 of 8 vital slot sitting feature that appear in fully programmed brackets.

Despite their major design divergences from the straight wire appliances, partly programmed appliances are being loosely called straight wire appliances.

By definition a partly programmed appliance lacks at least one slot sitting feature. For this reason alone, it would fail to fully direct each slot to its tooth’s slot site.

Actually the inadequacy in both quantity and quality of slot siting features makes wire bending necessary.

Partly programmed brackets have 4 slot-siting features:--

Slot inclination Slot angulation Prominences Horizontal base curvature

Slot inclination

In partly programmed appliance ,patents have restricted inclinations to be built in the face of the bracket which is different from the fully programmed appliance in which the inclination is built in the base of the bracket.

•Non programmed and partly programmed brackets have bases that are at right angles to the stem., thus when they are similarly cited, they site their slot points identically.

•In contrast ,the the inclined bases of fully programmed brackets locate the slot point on the crown’s midtransverse plane.

Slot angulation

Some partly programmed brackets use both slot angulation and slot inclination, so if such brackets are placed on the FACC and the FA point of optimally positioned crowns, the full and correct amount of angulation and inclination should be attained.

However the occlusogingival position of the slot is not directed to the Andrews plane .

Slot prominences

In most of the partly programmed brackets ,the prominences of the brackets varies in step with intention to eliminate or reduce the need of first order bends.

Several manufacturer indicate faciolingual prominences that is thicker or thinner than in their nonprogrammed brackets.

Because of lack of consistency in prominences incorporated in the bracket, a consensus is not evident.

If a clinician wants this information for a particular appliance, it can be obtained by contacting the manufacturer or by measuring the distance from base point to the slot point.

A difference of more than 0.5mm from the amount in the straight wire appliance can be considered clinically significant.

Horizontal base contour

Most partly programmed and some non programmed brackets have horizontal base contour.

However the measurements used for this slot siting feature are generally not published by the manufacturers and they may or may not be the same as for the straight wire appliance.

If they are not the same as the straight wire appliance ,then these appliance will not reliably locate the mid sagittal plane of the bracket stem and slot on the crown’s midsagittal plane.

Due to patent restriction of SWA none of the partly programmed appliances offer fully programmed translation brackets .

This means that unless treated with combination of wire bending and wire forming and possibly with auxiliary rotation devices non of the teeth requiring translation will translate, nor will they be sufficiently over inclined, over angulated or over rotated after translation.

Disadvantages and controversy associated with Andrews straight wire appliance

(1)-- It is difficult ,if not impossible, to place the brackets so exacting that the desired or built in angulations of the brackets will be properly expressed with unbent wires.

Andrews explanation

At the heart of every excellent treatment results lies a well placed appliance regardless of the type of appliance used.

One can not achieve a routine degree of excellence with a poorly placed appliance and this is particularly true with the edgewise appliance.

It is far easier and possible to control tooth positions with bracket placement than by bending wire.

If one were to take a perfectly positioned set of teeth and place a standard edgewise appliance on these teeth with all the brackets ideally positioned and then bend an upper and lower full size set of rectangular wires including first, second and third order bends, then for many orthodontists it will be difficult to place the wire and leave them in position for 2-3 months without moving some of teeth or all of the teeth from ideal occlusion.

On the other hand, if we were to place an appliance on this same perfect dentition in which brackets themselves had a very minimal amount of error and then place upper and lower unbent wire, we could be reasonably secure that very little if any untoward of these teeth would occur.

2.

Is straight wire appliance perfect for all the cases

Standard edgewise brackets that are inherently and grossly in error in all three plane of space on teeth.

So bending of wires required not only to move the teeth but also to overcome the inherent error built into the attachments.

Although the straight wire appliance is by no means perfect, the minimal amount of error built into the attachments for almost every case is minor enough to almost be overlooked in terms of the clinical end product.

To build into an appliance the desired tooth position for each tooth in all the three planes of space requires building of torque and in/out into specialized bracket bases of varying thickness that are specifically contoured to fit the bracket site area.

This can not be accomplished with the standard edgewise brackets regardless how one tips the bracket and torques the slot.

CONCLUSION Frequently the anticipated results of

treatment are not achieved by using straight wire. This is due to inaccurate bracket placement ,variation in tooth structure, variation in maxillary and mandibular relationships and tissue rebound. Clearly one straight wire prescription can not fit all the orthodontic patients .

Therefore it is still necessary for orthodontists to use their artistic senses and skills to make some first order ,second and third order bends in the arch wire to move the teeth to the desired positions ,however the no. of bends is not nearly the no. of bends necessary with standard edgewise appliance.

Urias D, Mustafa FI. -- Anchorage control in bioprogressive vs. straight-wire treatment.--Angle Orthod. 2005 Nov;75(6):987-92

Mavragani M, Vergari A, Selliseth NJ, Boe OE, Wisth PL.--A radiographic comparison of apical root resorption after orthodontic treatment with a standard edgewise and a straight-wire edgewise technique.Eur J Orthod. 2000 Dec;22(6):665-74

Miethke RR, Melsen B.--Effect of variation in tooth morphology and bracket position on first and third order correction with preadjusted appliances.Am J Orthod Dentofacial Orthop. 1999 Sep;116(3):329-35

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Taylor NG, Cook PA.The reliability of positioning pre-adjusted brackets: an in vitro study.Br J Orthod. 1992 Feb;19(1):25-34

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Andrews, L. F.: The six keys to normal occlusion, Am. J. Orthod1972. . 62:page-296-309

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