Azeri Orthodontic Society
Fixed Functional Appliances - A Classification
Yazan: Korrodi Ritto (D.D.S., Ph.D.)

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Functional orthopedic treatment seeks to correct malocclusions and harmonize the shape of the dental arch and oro-facial functions.


Removable functional appliances are normally very large in size, have unstable fixation, cause discomfort, lack tactile sensibility, exert pressure on the mucous (encouraging gingivitis), reduce space for the tongue, cause difficulties in deglutition and speech and very often affect aesthetic appearance. The alteration in the mandibular posture creates added difficulties. These adverse effects make the adaptation and acceptance of these appliances more difficult1,2 (Oliver and Knappman, 1985; Ngan et al., 1989). Fixed functional appliances first appeared in 1900 when Emil Herbst3 (Herbst E., 1910) presented his system at the Berlin International Dental Congress. Since then and up to the seventies, very little was published on this appliance. It was at that time that Hans Pancherz4 (Pancherz H., 1979) brought the subject back into discussion with the publication of several articles on the Herbst.

It was only in the eighties that several systems derived from Herbstís work started to appear. A number of fixed appliances have gained popularity in recent years to help achieve better results in non-compliant patients.

Fixed functional appliances are normally known as "non-compliance Class II correctors" giving a false idea about the co-operation necessary during treatment. In reality, when we compare them to removable appliances, we can clearly recognize fixed appliances as non-compliance devices. However, for treatment to be successful, good co-operation is always necessary, especially if skeletal modifications instead of dentoalveolar compensation are desired. The aim of this article is to update the classification of fixed functional appliances, published in 2000 in "The Functional Orthodontist". Their clinical applications will be listed and a description of how they work will be given. The advantages that some have over others will also be discussed.

CLASSIFICATION
Fixed functional systems have some advantages over removable systems. They are designed to be used 24 hours a day, which means that there is a continuous stimulus for mandibular growth. They are smaller in size permitting better adaptation to functions such as a mastication, swallowing, speech and breathing.

Fixed functional appliances are usually described as non-compliance Class II devices, which are able to treat Class II malocclusions successfully, while reducing the need for patient co-operation and overall treatment time. It is possible to treat this type of malocclusion with minimal effort. Just as the name implies, what distinguishes them from removable appliances is that it is impossible for the patient to remove them. What we have therefore, is an appliance that allows greater control by the orthodontist.

These appliances are fixed on the upper and lower arches. Since the application of force is transmitted directly to the teeth through a support system, the main disadvantage that may be encountered is dental movement that takes place during treatment which may not be the most suitable for the type of malocclusion in question. In an attempt to avoid this unwanted dental movement and as a way of finding an appliance that allows easy adaptation by the patient, various fixed functional appliances have appeared in recent years.
Fixed functional appliances can be classified as either flexible (Flexible Fixed Functional Appliance - FFFA) or rigid (Rigid Fixed Functional Appliance - RFFA).

Flexible Fixed Functional Appliances
Flexible fixed functional appliances (FFFA) can be described as an inter-maxillary torsion coils, or fixed springs. Elasticity and flexibility are the main characteristics of flexible appliances. They allow great freedom of movement of the mandible. Lateral movements can be carried out with ease. The major drawbacks with these appliances are the propensity with which fractures can occur both in the appliance itself (mainly in areas that have more acute angles) and in the support system (mainly in the lower arch). If on one hand flexibility is an advantage, on the other hand it does tend to produce fatigue in the springs. Another drawback is the tendency of the patient to chew on the appliance, possibly contributing to breakage or damage. While it is not possible for the patient to completely open his mouth, depending on the way the system is fixed onto the lower arch, good opening can be achieved.

It is important to tell patients to avoid opening their mouths too widely because this could result in breakage. Also, they are not very aesthetic appliances. When the curvature of the spring is accentuated, some protuberances can appear in the cheeks. Several appliances have come on to the market since the eighties featuring variations on the covering and type of springs, method of fixation and replaceability of fractured components. The covering used on the springs makes the appliance more comfortable and hygienic as food does not accumulate inside the spring. A disadvantage is that the covering can degrade quite quickly, especially if the patient bites on the appliance. The ability to replace components is important, as fractures are an unavoidable reality. These appliances are expensive, therefore, a system that allows the replacement of some of its components can reduce the cost of treatment. This leads to another disadvantage: the inventory of material that must be kept. Almost all are sold in kits of various sizes which contain components for both the left and right side. It is not always possible to treat a patient with only one size making it necessary to replace it with a larger size. Once again, this increases costs.

FFFAs can be used in the treatment of Class I, II division 1 and 2 and III malocclusions. The intention when they first appeared was for the treatment of Class II, both in malocclusions characterized by a mandibular deficiency as well as in cases where a dental problem predominated. Later on, their application extended to Class I problems especially when treatment including extraction was foreseen. The appliance was used as an anchorage reinforcement or even for molar distalization. The appliance is also used in a reverse type for treatment of Class III malocclusions, as well as in cases of midline discrepancy. The type of the force exercised by FFFAs is continuous and elastic in nature. The amount of force is variable in accordance with the skeletal pattern of the patient, the type of movement desired and the size of the cusps. Normally, in brachyfacial cases, due to their strong musculature, it is necessary to use more force (greater activation) than in dolicofacial cases. The height of the dental cusps is a factor to bear in mind when treating with FFFAs. If the patient has high cusps with good intercuspation, it will be necessary to exert greater activation on the spring. If the large size of the cusps is linked to a brachyfacial skeletal pattern with strong musculature, we can predict a difficult clinical scenario and the appliance will be prone to fracture.

If an advance of the mandible is required as when treating a retromandibular case, the force exerted has to be greater than that used when only dental movement is desired to distalize the upper molar and procline the lower incisors. If the goal of the treatment is to achieve dentoalveolar movements, the appliance should be activated minimally by placing a slight bow in the force module. To maximize the dentoalveolar movements in the upper arch and minimize any loss of anchorage in the lower, the upper archwire is not tied back. FFFA produces a "headgear" effect on the maxillary dentition due to the intrusive force applied to the maxillary posterior segments and produces an anterior intrusive force on the lower dentition. It can be used to obtain maximum anchorage, holding upper molars back as the upper incisors are retracted. Due to the intrusive force on the upper molars, a posterior open bite is common as well as posterior expansion due to the deflected force module. Another unwanted common movement is the tendency for the lower molar to rotate mesiobuccally, causing a mild posterior crossbite especially when the second molars have not been banded. Some buccal expansion in the upper and lower arches is to be expected, and placing bands on the second molars will aid final alignment. Placing a transpalatal or lingual arch during the force activation stage will help control unwanted buccal expansion of both arches. Loss of occlusion adds to instability, especially in the transverse dimension.

The most unwanted dental movement is proclination of lower incisors. To avoid this effect, good anchorage preparation should be carried out. However, in a brachyfacial pattern with strong musculature this movement would be expected. To increase anchorage to avoid unwanted dental movements, various additional systems can be used, such as a transpalatal bar, lingual arches or lower incisor brackets with lingual torque. It is advantageous to start the treatment in adolescent patients when the majority of permanent teeth have erupted and 12-year molars can be banded. FFFAs are not recommended in mixed dentition, especially late mixed dentition to avoid unwanted dental movements. Proper anchorage preparation is critical to achieving successful results. It is necessary to align and level arches before placing the final wire and activating the force module. A .017" x .025" or .018" x .025 stainless steel archwire should be placed before inserting the FFFA. By fully engaging the brackets in both arches, especially the lower, anchorage is maintained during the activation of the force module, preventing unwanted mesial movement of the lower incisors and distal movement of the uppers. When proclining the lower incisors is desired as in in Class II division 2 it may be advantageous to use a .016" x .022" stainless steel archwire as a final wire.

All FFFAs allow the patient to close in centric relation.

When the patient closes in centric relation, the contour of the bow should be significantly increased. By slightly overactivating the appliance in centric relation, the patient will automatically position the mandible forward. This is a natural response to decrease the force module and alleviate discomfort. The upper archwire should be cinched to increase anchorage and minimize dentoalveolar movements. Despite the clinical references available in published work about skeletal effects produced by a bite-jumping mechanism with a FFFA, no current scientific research would be found. Very few articles were published and these only report clinical cases. This is in contract to the data available for the RFFA 14-23.

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