lec.4 types of ortodontic appliances lec.4 + 5

Lec.4 Types of Ortodontic appliances

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Lec.4 + 5 Orthodontics د.سهى علي

Types of Orthodontic appliances

Orthodontic appliances can be classified in a number of ways. The most common and

practical way is to divide them into two categories:

Passive appliances.

Active appliances.

Ideal Requirement of Orthodontic Appliances

All appliances should be comfortable to wear and readily acceptable by the patient.

The ideal requirements of any orthodontic appliances are as follows :

1. Biologic requirement: It should be well tolerated by the oral tissue, and it

shouldn’t interfere with the normal growth or function, i.e. mastication, deglutition,

and phonetics.

2. Mechanical requirements: The appliance should be able to deliver controlled

forces of desired intensity, for a desired duration and in the desired direction.

3. Esthetic requirements: The appliance should be esthetically acceptable and it

shouldn’t draw attention to the patient.

I. Passive appliances: They are appliances designed to prevent the

development of malocclusion, and maintain the position of the teeth like:

a. Space maintainers: these devices commonly designed for space maintenance

after premature loss of deciduous teeth. e.g. prevent the mesial movement of the first

molars after the early loss of the deciduous molars. Space maintainers can be fixed or

removable, depending on the age of the patient and the location of the space

maintenance problem.

b. Habit breakers: are removable or fixed appliances designed to prevent or stop

bad oral habits especially thumb sucking, or placing the tongue in between the front

teeth. e.g.: tongue crib.

c. Retainers: They are removable appliances designed to keep the tooth movement

achieved by the active appliances. They are used for 3 to 12 months depending on the

treated malocclusion.


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II. Active appliances: They are appliances designed to correct malocclusion

by actually applying force to move teeth or direct growth of the dental bases. Their

types are:

1. Fixed appliances.

2. Removable appliances.

3. Combination between removable and fixed appliance.

4. Myofunctional appliances.

5. Orthopedic appliances (Extra-oral).

Fixed appliance Removable appliance

They are a combination of the use of a removable appliance with some components of the fixed

appliance (bracket or band).


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Andresen appliance (monoblock) Frankel appliance

(Myofunctional appliances)

(Orthopedic appliances)

Removable appliance: These appliances can be removed from the mouth by

the patient. The patient can insert and remove these appliances to brush their teeth or

eat without the intervention of a clinician. It can be used to do tipping tooth

movements and correct rotations of less than 90°. It is basically made of:

1. Stainless steel wire.

2. Acrylic.

3. Others: as screws and elastics.


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Action of Removable appliance: A removable appliance applies a single-point

contact force to the crown of a tooth, so it can basically perform only tipping tooth

movement (labio-lingual or mesio-distal) and can correct tooth rotations less than 90°

(couple force system). However, with some modifications it has a limited capacity to

do the other tooth movements.

Advantages of Removable appliance:

1. Its components are relatively cheep.

2. Its comparatively simple and should be within the scope of the dental practitioner

for carefully selected cases.

3. It takes less chair side time because it is fabricated in the laboratory.

4. Since the appliance is removable the problems of oral hygiene should not be any

greater than normal.

Disadvantages of Removable appliance:

1. Single point of force application which means that only limited types of tooth

movements such as tipping movements and minor tooth rotation, so it can be used in

only selected simple cases.

2. Usually only a few teeth should be moved at any one time.

3. It is uncomfortable to the patient and affects speech in the first few days.

4. It needs a high degree of patient compliance.

Components of a removable appliance:

Removable orthodontic appliance consists of the followings four components:

1. Active components: Which produce force for tooth movement, as springs.

2. Retentive components: responsible for holding the appliance inside the mouth, as

clasps.

3. Anchorage: It is an imaginary component resisting the unwanted tooth movements.

4. Acrylic base plate: as a major connector connecting the components.


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1-Active components: The active components of a removable appliance are

responsible for producing the desired tooth movement. They can be categorized as

springs, bows, screws and auxiliary elastics. Active components can be subdivided

according to the direction of the tooth

A. Labial (buccal) movement:

1. Z-spring

2. Recurved z spring

3. T-spring

B. Palatal (lingual) movement:

1. Hawley arch

2. Robert's retractor (simple and sleeved)

C. Mesio-distal movement:

1. Finger spring (simple and modified)

2. Buccal canine retractor (simple and modified).

Couple force system: It is used to derotate incisors less than 90°. It is a combination

of:

1. Labially directed force (Z-spring or recurved spring)

2. Palatally directed force (Hawley arch)

2-Retentive components: The success of a removable appliance mainly depends

upon good retention of the appliance, which is achieved by incorporating certain wire

components that get engaged into the undercuts on the teeth. These wire components

that help in the retention of a removable appliance are called clasps:

Adam's clasp (universal clasp): It is the major retentive component that provides

excellent retention, found in almost all removable appliances.

Fitted labial arch: It prevents tilting of the appliance incisally and hence makes

the molars and incisors one unit, and thus reinforces anchorage.

Hawley Arch: Gives anterior retention and enforce the anchorage.


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C-clasp: It is mainly used on deciduous teeth as a supporting clasp, made of 0.7-

0.8 mm round stainless steel wire; it should be kept clear of occlusal contact.

Ball end clasp: Mainly used in conjugation with fixed appliance or in quite

specialist situations such as in the Twin Block functional appliance around the

lower incisors.

3-Anchorage: It is an imaginary component resisting unwanted tooth movement. In

other words, it is what stops the wrong teeth from moving. Newton’s Third Law of

Motion states that: ‘To every action there is an equal and opposite reaction’.

We increase anchorage in the removable orthodontic appliances by:

1. Full extension of the acrylic to engage many teeth

2. Adding retentive components (Adam's clasp and FLA) to adapt the acrylic to the

teeth and palate.

4- Acrylic Base plates: The design of base plate varies with the type of removable

appliance; cold cure (self polymerizing) acrylic resins are used for the fabrication of

base plate.

Uses of acrylic base plate

1. It carries and unites both the retentive and active components of the removable

appliance into a single functional unit.

2. It helps in the retention of the appliance in the mouth.

3. It helps anchorage by resisting unwanted drift during tooth movement.

4. It transmits forces from the active components uniformly throughout the area.

5. It protects the palatal springs against distortion in the mouth.

6. Bite planes can be incorporated into the base plate and used to treat specific

problems.

Modifications of acrylic base plate

I. Flat anterior bite plane: A thickening of acrylic base plate behind the upper

anterior teeth on palatal rugae extending usually till the canine such that the lower

anterior teeth may bite on it. The extension should be flat and parallel to the occlusal


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plane. The bite plane should be high enough to disocclude the posterior teeth by

about 23mm.

Uses:

It corrects deep bite by separating the molars allowing them to over-erupt and so

decreasing the overbite.

It can be used where a tooth is to be moved along the arch, i.e. mesially or distally,

to get rid of any occlusal interference.

It can be used to free cuspal interferences to correct posterior crossbite of a single

tooth.

II. Inclined anterior bite plane: It is a modification of the anterior bite plate

inclining downward and inferiorly used in cases where there is a retroclination of

lower anterior teeth with increased overjet.

The bite plate is inclined so that the lower anterior teeth is proclined as it contacts the

slopping bite plane, and the mandible is guided to be held in the forward position,

thus may guide the mandible to grow forward like the myofunctional appliance.

It corrects deep bite and increased overjet as well by allowing

the molars to over-erupt and proclininig lower incisors.

III. Posterior bite plane: It is an extension of the acrylic

base plate used to open the bite anteriorly and free posterior

occlusion. The posterior bite plane should cover all the

premolars and molars to prevent their over-eruption.


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Uses:

It opens the bite anteriorly to allow correction of anterior cross bite.

It used in the correction of posterior crossbite either unilateral or bilateral.

Making a removable appliance: The steps are:

1. Do the necessary wire bending.

2. Fix the springs and clasps to the cast by wax on the occlusal and labial surfaces of

the teeth, so that they do not move during fabrication of the acrylic. Wax is applied

on the coils and arms of Z-spring, recurved z-spring, T- and finger springs not to be

embedded in the acrylic base plate.

3. Soak the cast in water for about 5 minutes until no more air bubbles come out of

the cast. This is done to prevent the monomer from entering inside the cast and fusing

the acrylic with the stone of the cast.

4. Use orthocryl (cold cure acrylic) by the sprinkle method (salt and pepper) to

construct the acrylic base-plate by successively applying polymer and then monomer.

5- Cure in a hydroflask under 2 bar pressure to eliminate porosity. The hydro flask

contains water at 40oC to accelerate the curing reaction.

6- The wax is cleaned and the acrylic base plate is finished with a carbide bur and

polished with pumice.


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Advantages of Sprinkle method over Dough method:

1. The acrylic penetrates under the wires.

2. Does not dirty the fingers.

3. Less time consuming.

Advantages of using cold cure acrylic:

1- Easier technique (no waxing, wax elimination, and packing).

2- Less time consuming as it cures within 10-15 minutes.

Advantages of using orthocryl:

1 - Polymer composed of large particles which prevent the dripping of the

acrylic.

2 Acrylic curing is accelerated under pressure and heat under (40o) which gives

a long working time (hour if refrigerated) and short curing time (10-15

minutes).

3 Suitable for people with allergies (free of methyl methacrylate and dibenzoyl

peroxide).

Welding and soldering

Welding: It is the unity of two metal pieces using heat and pressure, the process

consists of raising the temperature of the pieces of metal to be joined until the metal

becomes plastic at the site of the joint and immediately applying pressure so that the

metal parts are squeezed together in their plastic state and become one. This is

accomplished by a welder machine.

The two wires are put in firm contact under pressure of the jaws of the welder and

then at a low voltage (2-10 V), and a high electrical current is passed through the

stainless steel wires which will soften and melt the surfaces of the wires and make

them fuse together under the influence of mechanical pressure, forming a weld joint.

Welded joints are generally weaker than soldered joints. Welding joints are stronger

when the wires are at right angle and not parallel because of the small contact area

that concentrates the electrical current and make the wire melt more making a

stronger joint.


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Soldering: Soldering entails heating the metals to be joined with a flame and

applying a solder which encases the pieces to be joined; oxidization of the solder and

metal is prevented by the use of a flux. The requirements of soldering are:

1. A heat source: usually a butane gas fine flamed torch.

2. Silver solder wires (low melting type, in the shape of wires 0.5-0.6mm in

diameter).

3. Flux either separately or incorporated in the solder wire. The purpose of the

flux is to dissolve any surface impurities, prevents oxidation during soldering,

dissolve metallic oxides as they are formed.

Application of soldering in orthodontics:

1. Repair fractured clasps.

2. Solder Hawley arch or buccal canine retractor to the bridge of the Adams clasp.

3. Solder a variety of modifications to the bridge of the Adams clasp (e.g. hooks for

elastics and face bow tubes).

4. Solder a variety of transpalatal bars, lingual bars, Hyrax expansion appliances,

quadhelix appliance, fixed habit breakers and tongue cribs to bands.

Steps in soldering:

1. Cleansing the surfaces to be joined from any dirt or other contaminants that may

weaken the solder joint.


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2. Assembling the wire parts to be joined by using dental plaster or stone to stabilize

the wires parts while maintaining 0.5 mm gap between them.

3.Selection of proper joint to have good soldering joint for example, when two wires

are being joined together it would be beneficial to wrap one wire around the other

rather than having a point contact.

4. Application of flux on the assembled units forming the joint and over an extended

portion of the metals to be joined.

5. Direct flame is used to heat the wires until they become red with adding the silver

solder to unite the two wires parts. Care must be taken not to overheat the

neighboring acrylic.

6. The soldering joint is immediately quenched in water to give the solder hardness.

7. Excess solder is removed by a bur and the joint is polished.


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lec.4 types of ortodontic appliances lec.4 + 5

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