myofunctional or functional appliances

Lec. 7 Myofunctional or Functional Appliances

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Myofunctional or Functional Appliances

Introduction

Functional /Myofunctional Appliances are devices that alter patient's functional

environment in an attempt to influence and permanently change the surrounding

hard tissue. Most of the functional appliances are mainly designed to correct

skeletal class II relationship by positioning the mandible downward and forward

to enhance mandibular growth. All functional appliances are intraoral devices.

Functional appliances may be removable or fixed.

Definition

By Proffit—"Functional appliances are appliances which alter the posture

of the mandible, holding it open or closed and forward or backward."

Functional appliances are appliances which act by either harnessing the

muscular forces or by preventing aberrant muscular forces.

Advantages of Functional Appliances

1. They are effective in vertical control of increased overbite.

2. They can be used in the mixed dentition.

3. They require minimal chairside adjustment.

Disadvantages of Functional Appliances

1. The success of functional appliances therapy solely depends on patient

cooperation.

2. Precise tooth movement is not possible with functional appliances.

3. Treatment duration of functional appliances is often prolonged.

4. Functional appliances often need two phases treatment to complete the

treatment. Functional appliances may be used for definitive treatment or

as phase 1 of two phase treatment. Phase 1 treatment is aimed at reducing

the overjet, overbite and to correct sagittal jaw relationship, while phase 2


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treatment is aimed at completing the final alignment using fixed

mechanotherapy.

Classification of Functional Appliances

Functional appliances can be divided into removable or fixed functional

appliances. Removable functional appliances can be classified into removable

tooth borne and removable tissue borne functional appliances. The fixed

functional appliances are tooth borne

Removable Functional Appliances

Removable functional appliances include removable tooth borne and removable

tissue borne functional appliances.

Removable Tooth Borne Appliances

These appliances depend on the stretch of the soft tissues caused by the

mandible being positioned downward and forward, as well as by the muscle

activity generated by the mandible attempting to return to its original position.

Examples Activator, Bionator and Twin block appliance.

Removable Tissue Borne Functional Appliances

These appliances are used to minimize unwanted tooth movement and to

recontour the facial soft tissue adjacent to the teeth as well as posture of

mandible downward and forward. Example: Functional regulator /functional

corrector/ Frankel appliance.

Fixed Tooth Borne Functional Appliances

The fixed tooth borne functional appliances are fitted on the teeth and cannot be

removed by the patient at will. Example: Herbst appliances.


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Effects of Functional Appliances

Effects of functional appliances include effect on the dentition, skeletal and

muscular structures.

Effects of Functional Appliance on Dentition

Functional appliances typically cause some intrusion of maxillary incisors. This

is caused by a lingual force transmitted from the labial bow against these teeth

when the mandible attempts to reposition back to its normal position. This

natural repositioning attempt by the mandible causes protrusion of mandibular

incisors caused by a labial force transmitted from the portion of the appliance

lingual to these teeth.

Effect of Functional Appliances on Skeletal Structures

Functional appliances are designed to stimulate the growth in the condylar

region and can also produce change in the direction of growth of the jaws.

Functional appliances can also bring about downward and forward remodeling

of the glenoid fossa. Functional appliances are also capable of restricting the

growth of the jaws.

Effect of Functional Appliances on Muscular Structures

Functional appliances are designed to improve the tonicity of orofacial

musculature.

Principles of Functional appliances treatment

1. Most of the functional appliances are used to correct early Class II

malocclusions and some cases of Class III malocclusion, deepbite and

openbite.

2. A Class II division 1 malocclusion caused by a prognathic maxilla is not

a good case for functional appliance therapy. While, retrognathic

mandible are generally cases indicated for functional appliance therapy.


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3. Functional appliances can be utilized in the correction of Class II division

2 malocclusions if the growing patients with a mild to moderate Class II

skeletal pattern. In such cases it may be helpful to have a pre-functional

phase to procline the retroclined upper incisors, this can be achieved by

using a removable appliance.

4. Functional appliances should be used when the patient is growing. As

girls complete their growth slightly earlier than boys, functional

appliances can be used a little later in boys. It has been suggested that

treatment should, if possible, coincide with the pubertal growth spurt (10-

14 years for girls, 12-16 years for boys). Generally it is better to start the

Functional appliance treatment in the late mixed dentition, provided there

is still growth remaining. This means that the patient is ready to progress

onto the fixed appliance stage which typically follows the functional

appliance. If the functional, appliance is started too early then there will

be delay while waiting for the remaining deciduous teeth to exfoliate.

Treatment for Class III and open bite cases should usually start sooner

than for Class II problems.

5. Functional appliances should be preferably fitted on well aligned dental

arches.

6. There are two major principles applied in the use of functional

appliances; force elimination e.g. oral screen and force application e.g.

the Activator appliance.

7. Functional appliance should be worn for 12-16 hours per day. Most

growth occurs during evening hours when growth hormone is being

secreted, typically between 8 pm and midnight or 1am, so it is suggested

that children wear functional appliances from after the evening meal until

they awake in the morning which should be approximately 12 hours per

day.


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8. There are two major principles applied in the use of functional

appliances; force elimination e.g. oral screen and force application e.g.

the Activator appliance.

Activator

Viggo Andresen, in 1908 in Denmark, designed a loose fitting appliance, which

he first used on his daughter. He used this appliance on his daughter who was

going on a three month vacation. On her return three months later, he found a

marked sagittal correction and improvement of the facial profile. Although it

was developed more than 70 years ago, the Andresen appliance, which is also

known as an activator or monobloc, has been successfully used by many

generations of orthodontists. The activator is generally used for the treatment of

Class II div I malocclusion. The disadvantages of Activator are fully rely on

patient cooperation, bulky and uncomfortable.

Components of the Activator

1. Acrylic portion

2. Upper and/or lower labial bow

3. Jack screw: Optional (fitted to maxillary arch).

Fig. 1: Activator

Indications

1. Class I malocclusion with deep bite

2. Class II malocclusion with open bite

3. Class II division 1 malocclusion


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4. Class II division 2 malocclusion after aligning the incisors

5. Class III malocclusion (reverse activator)

Contraindications

1. Crowded arch

2. Increase lower facial height

3. Severe proclined lower incisors

Fabrication

1. Impressions: The impressions should reproduce the whole alveolar process

to the depths of the sulci.

2. Bite Registration

• Before taking the wax bite, the study models can be used to help decide if the

overjet can be corrected with one activator or whether a second one will be

needed. If the overjet is 8 mm or more two activators will normally be required

• If the overjet is less than 8 mm, it can be corrected with one activator

appliance. For these cases, the wax bite can be taken with the mandible

protruded sufficiently to bring the incisors almost edge-to edge (Fig. 2).

• A piece of good quality pink wax of approximately 6x8 cm dimensions is

warmed in hot water and folded over two or three turns to make a soft sausage

of wax. A slightly more bulky sausage will be needed for deep bite low angle

cases.

• The softened wax is pressed onto the upper teeth and then the lower jaw

protruded. Then the wax bite is cooled and if necessary, trimmed with a sharp

knife. It should be checked on the study modes and in the mouth, possible (Fig.

3).


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Fig. 2: If the overjet is less than 8 mm it can be corrected with one activator

appliance. For these cases the wax bite can be taken with the mandible

protruded sufficiently to bring the incisors almost edge-to-edge

Figs 3: A to D: The softened wax is pressed onto the upper teeth and

then the lower jaw protruded, then the wax bite is cooled and if

necessary, trimmed with a sharp knife. It should be checked on the

study models

3. Casting the Impressions: The impressions are poured in dental stone and

carefully mounted on a plane line articulator ensuring that the bite is correct.

Bionator

The bionator was developed in Germany by Wilhelm Baiter in the early 1950s

to increase patient's comfort and facilitate daytime wear to increase the

functional use of the appliance. Baiter accomplished this by drastically reducing

acrylic bulk of the appliance.


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Indications

Bionator is mainly indicated for the treatment of Class II division 1

malocclusion with mild to moderate skeletal discrepancy (mandibular

deficiency) for growing patient.

Types of Bionator

There are three basic types:

• Standard appliance.

• Open-bite appliance.

• Class III or reverse bionator.

Fig. 4: Standar bionator -side view

Uses of Bionator

1. Class II malocclusion.

2. Class III malocclusion.

3. Deep bite cases.

4. Open bite cases.

Frankel Appliance

The function regulator (FR) appliances are developed by "Rolf Frankel". The

function regulators (FR) are orthopedic exercise devices that aid in the

maturation, training and reprograming of orofacial neuromuscular system.

Types of Frankel Appliance

There are five types of Frankel's Appliances:

1. FR-I is further divided into three types: FR-Ia, FR-Ib and FR-Ic.

2. FR-II

3. FR-III

4. FR-IV

5. FR-V.


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Indications of Various Types of Frankel Appliances

1. FR-1 a appliance of Frankel: Treating Angle's class I malocclusion with

deep bite.

2. FR-I b appliance of Frankel: Indicated for treating the cases of Angle's

class II division 1 malocclusion where the overjet does not exceed 5 mm.

3. FR-I c appliance of Frankel: Indicated for treating the cases of the Angle's

class II division 1 malocclusion where the overjet is more than 7 mm.

4. FR-II appliance of Frankel: Indicated for treating cases of Angle's class II

division 1 malocclusion and class II division 2 malocclusion.

5. FR-III appliance of Frankel: Indicated for Angle's class III malocclusion.

6. FR-IV appliance of Frankel: Indicated for treating bimaxillary protrusion

and open bite.

7. FR-V appliance of Frankel: It is used with headgear.

Fig 5: Frankel Appliance

Twin-Block Appliance

The twin block appliance was developed by Clark in 1977, and it consists of

upper and lower parts that fit together using posterior bite blocks with

interlocking inclined bite planes, which posture the mandible forwards.The

appliance became popular due to a number of advantages over other functional

appliances namely:


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1. Have greater freedom of movement arid cause less interference with normal

oral function as it is constructed in two parts.

2. Appearance is noticeably improved.

3. Less bulk, therefore, better patient compliance.

4. Can be used in later stages of growth (late mixed dentition/early permanent

dentition).

5. It can be easily modified to correct dental problems.

Indication

It is mainly used for correction of CI II division 1 cases (mandibular deficiency)

for growing patients.

Fig. 6: Twin Block Appliance

Herbst Appliance

It is a fixed functional appliance. It consists of bilateral telescopic mechanism

(rigid arms) attached to the upper and lower buccal segment teeth that maintains

the mandible in a protruded position. As it is a fixed appliance, it removes some

(but not all) compliance factors. The disadvantages are the increased breakages

and higher cost of the Herbst appliance. It is mainly used for correction of CI II

cases with mandibular deficiency.


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Fig. 7: Herbst Appliance

Oral Screen (Vestibular Screen)

Newell in 1912 introduced oral screen. It is composed of acrylic base material,

which fits in the buccal/labial vestibule of the mouth.

Indications

1. Oral habits, such as

a. Thumb sucking

b. Mouth breathing

c Tongue thrusting

d. Lip biting

2. In the cases of mild proclination of maxillary anterior teeth

Mechanism of Action

• Oral screen acts like a mechanical barrier between teeth and lips, tongue,

thumb and thereby help in correcting the oral habits, such as mouth breathing,

thumb sucking, lip biting and tongue thrusting.

• Oral screen is made to contact the proclined teeth when it is used to retrocline

the incisors. It transmits the forces of periooral musculature to the teeth and

these by retroclining the proclined anterior teeth.

• It is also used as a muscle exerciser to stimulate the hypotonic perioral

muscles.


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Figs 8 A to D: (Ai and ii) Oral screen, (B i and ii) Oral screen with wholes

can be used to treat mouth breathing habit, (C) Double oral screen, (Di, ii

and iii) Hotz type of oral screen. This type of oral screen can be used to

treat mild proclination of upper anterior teeth and also can be used to treat

habit, such as thumb sucking habit and digit sucking


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Lip Bumper

The lip bumper is a fixed functional orthodontic appliance that works by

altering the equilibrium between cheeks, lips and tongue and by transmitting

forces from perioral muscles to the molars where it is applied (Fig. )

Uses

Uses of lip bumper include (Fig. 9):

a. Lip bumper is used to treat lip suckling habit.

b. Lip bumper is used to treat lip biting habit.

c. Lip bumper is used as a molar anchorage.

d. Lip bumper is used for space gaining in the lower arch.

Fig.9: Lip bumper in conjunction with fixed orthodontic appliance

myofunctional or functional appliances

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