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Functional appliances (FA).

1. Mode of action of functional appliances

There are three mechanisms of action of functional appliances, namely:

• skeletal changes;

• dentoalveolar changes;

• soft tissue changes.

FA generate forces which are delivered primarily to the teeth. A posteriorly directed force acts upon the upper arch and anteriorly directed force acts upon the lower arch. The sites where FA induces facial changes are the maxillary complex, the mandible and the glenoid fossae.

The skeletal changes can be considered in two dimensions, namely anteroposterior

and vertical, and are:

1) additional overall growth of the mandible;

2) accelerated growth of the mandible, but not necessarily additional growth;

3) a change in the direction of the growth of the mandible;

4) a change in the position of the mandibular condyle and glenoid fossae;

5) restricted growth of the maxilla.

The dentoalveolar changes include:

1) retraction of the upper incisors (palatal tipping);

2) proclination of the lower incisors;

3) overbite reduction by reducing lower incisor eruption while permitting buc­cal segment tooth eruption;

4) mesial movement of lower buccal segment teeth, occurs because they move mesially as they continue to erupt;

5) distal movement of the upper buccal segment teeth - in combination with mesial movement of the lower buccal segment teeth, the molar relationship can be altered to a Class I relationship;

6) expansion of the upper arch.

Some functional appliances have the long-term effect on the soft tissues. Functional regulator appliances in combination with lip exercises might influence the position and functions of lips and cheeks to move the teeth into correct positions.»

2. Timing of treatment with functional appliances.

Traditionally FA have been fitted prior to the pubertal growth. This will usually be somewhere between 10-12 years of age in girls and 12-14 years of age in boys. Once fitted, the overall treatment time lasts 9-12 months, depending on the size of the initial overjet. The average rate of overjet reduction is approximately 1 mm per month.

Recently the treatment has been started at 8 - 9 years of age, but it is supposed to be a two- stage treatment. It begins with an initial phase of FA therapy, followed by a second fixed-appliance phase.

3. Classification of functional appliances.

FA can be classified according to:

• their component parts;

• whether they are primarily tooth-borne or tissue-borne;

• the malocclusion in which they are used (Class II or Class III incisor relation­ship);

• the degree of soft tissue stretch they induce when in place.
There are two basic types of FA:

1. Myotonic FA.

2. Myodynamic FA.

4. Myotonic functional appliances. Their components and main types.

In myotonic FA the elastic recoil within the stretched soft tissues generates the forces that move the teeth. The main components of FA are cheek shields, lip pads, pilots and tongue cribs. One of the typical myotonic FA is the Frankel appliance or the functional regulator (FR). It has acrylic shields in the buccal sulci and little or no acrylic lingually, but in common with all FA it induces mandibular posturing. The buccal shields are intended to cause expansion of the arches by holding the cheeks away from the teeth and also to enlarge the alveolar process by stretching the perio­steum in the depth of the sulcus, thus causing bone to be laid down on the buccal as­pect.



There are three main variants of the appliance. The FR I is for treatment of Class II division 1 malocclusions and incorporates lip pads labial to the lower incisors to al­low forward development of the mandibular alveolar process. The cheek shields al­low normalizing the width of the upper arch. In case of infantile swallowing it can include a tongue crib. The FR II has in addition a palatal wire to procline the upper incisors and is intended for Class II division 2 malocclusions. The FR III is for the treatment of Class III malocclusions, having lip pads labial to the upper incisors, which together with a palatal arch, procline them, and a lower labial bow retroclining the lower incisors.

5. Myodynamic functional appliances. Their components and main types.

The forces that move the teeth are generated by stimulation of masticatory muscles and use of their strength while wearing FA. The main components of myodynamic FA are inclined planes, occlusal shelves and bite planes. As an example of the myodynamic FA is a twin-block appliance. It is constructed in two parts, as, separate upper and lower appliances. Forward mandibular posturing is achieved by incorporat­ing buccal blocks with interlocking inclined planes, with the lower blocks engaging in front of the upper ones. The appliance is often used with headgear to the upper arch.

 

Fixed appliances

1. General principles and indications for the use of.

Fixed appliances, also referred to as braces, are combination of bands, brackets and auxiliaries that can move a tooth on six directions: mesially, distally, lingually, facially, apically, and occusially. Fixed appliances are attached to the teeth and, thus, are capable of greater range of tooth movements than is possible with removable appliances. Not only does the attachment on the tooth surface (called a bracket) allow the tooth moved vertically or tilted, but also a force couple can be generated by the interaction between the bracket and archwire running through the bracket. The interplay between the archwire and the bracket slot determines the type and direction of movement achieved.

The edgewise bracket is rectangular in shape and is typically described by the width of bracket slot, usually 0.018 or 0.022 inch. The depth of the slot is commonly between 0.025 and 0.032inch.

A round wire in a rectangular slot of bracket will give a degree of control of mesio-distal tilt, vertical height, and rotational position. The closer the fit of the archwire in the bracket, the greater is the control gained. However, with a round wire only tipping movements in a bucco-lingual direction are possible. When a rectangular wire is used in rectangular slot, a force couple can be generated by the interaction between the walls of the slot and sides of the archwire and bucco-lingual apical movement produced. Thus fixed appliances can be used in conjunction with a rectangular archwires to achieve tooth movement in all three spatial planes. In orthodontics these are described by the types of bend that are required in an archwire to produce each type of movement:

· First-order bendsare made in the plane of the archwire to compensate for differing tooth width.

· Second-order bendsare made in the vertical plane to achieve correct mesiodistal angulation or tilt of the tooth.

· Third- order bendsare applicable to rectangular wires only. They are made by twisting the plane of the wire so that when it is inserted into the rectangular bracket slot the bucco-lingual force is exerted on the tooth apex. This type of movement is also known as torque.

In the original edgewise appliance these bands were placed on the archwire during treatment so that the teeth were moved into their correct position. Modern bracket systems have average values for tip and torque built into the bracket slot itself, and the bracket bases are of different thicknesses to produce an average bucco-lingual crown position (known as in-out). These pre-adjusted systems have the advantage that the amount of wire bending required is reduced. For initial alignment flexible archwire are used , but to minimize unwanted movements, progressively more rigid archwires are necessary.


Date: 2016-04-22; view: 1460


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