Angle of Wire Entry

Implications in orthodontic treatmment

A textbook reference

Quotes from this book:

The farther the point of force application is from the center of resistance the greater the moment (rotational tendency) that is produced.

Couple

• Two forces that are equal, parallel, and non-collinear

• Translational effects cancel each other out and

pure rotational forces remain

Couple

•The moments are in the same direction and are additive

Rotation caused by a couple

• Center of resistance and center of rotation are the same

Commonly seen couple

• Wire contacts 2 of the 4 corners of the slot • A couple can produce a….

Moment of a couple

“Moment of a Couple”

• Rotation resulting from the moment of the couple is responsible for many tooth movements

• This rotation can affect one tooth or a group of teeth

Tom, age 13

Or Blake, age 13

Angle of Entry

Angle of entry can be affected by:

• Tip in the bracket (angle of bracket slot)• Tipped teeth due to malocclusion• Bend in the wire• Combination of all three

Appliance Prescription-Tip

Concepts to remember

• Greatest angle of entry produces greatest moment of couple

• The canine bracket, especially on the upper, has the most tip built in. Therefore, greatest angle of entry is most often at the canine bracket.

• Large variations in canine position are often present pretreatment. This can also result in large angle of entry changes

Assume a fully bracketed maxillary arch

What effect does a straight wire have on the incisors in each of these illustrations?

Remember Dr Prittinen’s angle of entry concept

R

R

L

L

R

R

L

L

The incisors intrude.

The incisors extrude.

Assume a fully bracketed maxillary arch

What effect does a straight wire have on the incisors in each of these illustrations?

Remember Dr Prittinen’s angle of entry concept

R

R

L

L

R L

The incisors will cant running downhill right to left.

RL

The incisors will cant running downhill left to right.

Normally positioned canine

Distally tipped canine

What happens?

• Combining the distal tipping of the tooth with the tip built into the bracket produces a VERY LARGE angle of wire entry.

Implications

• Extrusive force on the anteriors (expressed due to small root surface area)

• Intrusive force on posteriors (not expressed due to large root surface area, and because posterior intrusion is tough to do)

Net effect

• Bite deepens and becomes very difficult to open

• Intrusive and extrusive forces produced as a result of the moment of the couple results in tendencies for some teeth to flare and some to roll in lingually

Intrusive/Extrusive force results

• Vertical forces– Extrusive forces create the potential for LINGUAL

crown tipping– Intrusive forces create the potential for BUCCAL

(or LABIAL) crown tipping

These are the moments(rotational tendencies)

of the couple

Axial inclination of canines.Look at this example

Archwire at rest

Engaging wire produces these forces

Moment of couple on canine(greatest angle of wire entry)

• Creates extrusive force on the incisors

• Intrusive force on the molars

• Distally inclined cuspid crowns present a big mechanical problem

Distally inclined canine crowns

Note flared premolars (a result of intrusive force) and lingually

inclined anteriors (due to extrusive force)

Note flared premolars (a result of intrusive force) and lingually

inclined anteriors (due to extrusive force)

This is caused by the moment(rotational tendency) of the couple

Finally, always rememberNewton’s 3rd law

For every action, there is an equal and opposite reaction

It is amazing how this law can be used to predict tooth

movement

can be used to predict tooth movements

Distally inclined canine crowns

Another solution

• When angle of entry will be a problem, start the case by not bracketing the 4 anterior teeth– 6543-----3456 are bracketed• The angle of entry can’t affect anterior teeth if they are

not engaged

• Align the canines (this will take 3-4 months) then after canine angulation is more ideal, bracket and engage the anteriors.

What do you expect to happen here?

Does angle of entry make bite easier or more difficult to open?

How can this be controlled?

• Brackets could be positioned to negate these effects if desired.

• Horizontal, as well as vertical position of slot could be altered.

Effect of vertical forces

• Remember the moment• Extrusive forces result in lingual crown

movement• Intrusive forces result in facial (or buccal)

crown movement

Another example

Q#1. Does the greatest angle of entry encourage an intrusive or extrusive force on the upper anteriors?

Q#2 Would you expect flaring or de-torquing of those upper anteriors?

Another example

Q#1. Does the greatest angle of entry encourage an intrusive or extrusive force on the upper anteriors? (Intrusive)

Q#2 Would you expect flaring or de-torquing of those upper anteriors? (Flaring due to moment of the intrusive force)

3 months later

• Is what happened to the upper anteriors predictable?

Yes!

Melanie, Age 28

Bite opening is very difficult.

Initial arch wiresafter 2 mo (l) and 3 mo (r)

To summarize…

• The extrusive force imparted to the incisors because of the moment (rotational tendency) of the couple (angle of entry on the canine bracket) results in lingual crown movement.

Answer: Angle of wire entry.

This illustrates one of the most important concepts in ortho

treatment: The same brackets, bands, and wires often produce

different treatment responses in different patients. These differences are usually

vertical dimension changes.

If distally positioned canine crowns result in bite deepening…

What happens with mesially inclined canine crowns?

Mesially inclined canine crowns

Mesially inclined canine crowns

Would this case make you nervous?

• Open bite tendency with mesially tipped canine crowns

• This bite may open excessively

YES!!!

Management

• Encourage mesial root movement of cuspid with mesio-gingival slot angulation

• Discourage bite opening by gingival bracket placement in anteriors (Question: Did I do this?)

Would this case make you nervous?

• Open bite tendency with mesially tipped canine crowns

• Again, the bite could open excessively without modifications to bracket positioning

YES!!!

Summary

• Positioning the slot to attain proper root angulation may increase the already large angle of entry

• If the greatest angle of entry is working against you, change the inciso-gingival and/or mesio-distal position to offset the angle of entry effect, or consider modifications to initial bracketing protocol

Summary, continued

• Use bite opening or bite closing techniques after root alignment or

• If you expect angle of entry side effects to be severe, do not bracket anteriors until after canines are uprighted, or use spring system as previously described

Bracketing Concept

• In the 1960’s, the best orthodontics was done by the best wire benders. Today, the best orthodontics is done by the best bracket positioners.

• Vertical control by bracket positioning….

Anteriors; inciso-gingival placement

• Deep bite patients– Position brackets 1 to 2 mm incisal to the center of

the tooth• Open bite patients– Position brackets 1 to 2 mm gingival to the center

of the tooth

Deep bite

Normal bite

Open bite

Premolars- inciso-gingival placement

• Deep bite cases– Position brackets 1 to 2 mm gingival to the center

of the tooth• Open bite cases– Position brackets 1 to 2 mm occlusal to the center

of the tooth

Deep bite

Open bite

Concept

• Step 1-Identify greatest angle of entry• Step 2-Vertically position brackets to

compensate for this, if necessary

Rule

• If I want the root to move to the distal, angle the slot disto-gingivally.

• If I want the root to move toward the mesial, angle the slot mesio-gingivally.

Hands-on demo

• Step 1- Outline 2nd bicuspid and “move” it (this represents pre-treatment position)

• We now want root to move to distal, and crown to mesial.

Another example

Bone Anatomy

• Thick cortical plate around canines make them the slowest moving teeth

• Angle of entry is most critical here

• Tip: palpate canine eminence to determine difficulty of movement

Bracket position modifications to this case?

Management

• Encourage mesial root movement of cuspid with mesio-gingival slot angulation

• Discourage bite opening by gingival bracket placement in anteriors

Mallory, age 12

Questions

• What will happen during initial leveling and aligning?

• What 2 things could you do to prevent this?

If angle of entry issues are not recognized, excessive bite opening will occur. To prevent this from happening, do not bracket the canines at the initial appointment.Also, compensate for bite opening by placing the anterior brackets gingivally.

Month 2

THIS IS WHAT HAPPENS WHENANGLE OF ENTRY ISSUES ARE

IGNORED.

Difficult!

Don’t bracket the incisors until the

canines are uprighted.

Evaluation

• Ben has a tougher initial level and align

• But angle of entry makes bite opening more difficult in Cory

After 6 months of treatment

Intrusive force on the premolars resulted in a moment (of the

couple) that encouraged flaring.This is totally expected.

Angle of entry

Case examples

Expected treatment response?

Expected treatment response?

Treatment modifications?

Indiscriminate leveling and aligning will cause occlusal plane canting. To prevent this, do not place brackets on the upper incisors until after the canines are uprighted.

Case 2 Anton

What is the expected treatment response in the upper anterior?

Why will this happen?

ARE THERE ANY TREATMENTMODIFICATIONS THAT COULDBE DONE TO PREVENT THIS?

Due to mesial canine angulation excessive bite opening may

occur. Again, stay off the upper anteriors until canine angulation

is more ideal.

EVALUATE THESE CASES

Chris, Age 14

Nicole, Age 15

Chris Nicole

Chris

• Excessive mesial inclination of canines could lead to excessive bite opening.

1st month of treatment-Chris

2nd month of treatment- Chris

Questions

• Is this the expected treatment response?

• Could anything have been done to prevent this? Explain.

Questions

• Is this the expected treatment response?

• Could anything have been done to prevent this? Explain.

• This is the expected response. Bracket positioning and bracketing scheme should have been altered to compensate for angle of entry issues.

Nicole- Month 1

Nicole-Month 2

Yes. Less extreme angle ofentry issues mean less

vertical problems initially.

Nicole: initial aligning complete

Chris: initial aligning complete

Chris Nicole

Are these theexpected treatment

responses?

YES: The same brackets, bands, and wires often produce

different treatment responses in different patients. The different treatment responses are usually

expressed in the vertical dimension.

THANK YOU!

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