Functional Appliances in Orthodontics

• Functional appliances use natural orofacial and masticatory musculature forces.
• They are based on Moss's Functional Matrix Theory.
• Stretching muscles creates pressure that is transmitted to dental and skeletal structures, moving teeth and modifying growth.
• These appliances derive force from orofacial musculature.
• These appliances transmit forces, eliminate and guide natural muscular forces, tooth eruption and growth, correcting malocclusion.
• The most functional appliances work by posturing the mandible forward in growing patients.
• They modify anteroposterior relationships between upper and lower arches, effectively in patients with mild to moderate class 2 skeletal discrepancies.
• They are not effective at correcting tooth irregularities and malalignments, often followed by fixed appliance treatment.

Functional Appliances Actions

• Modify jaw growth
• Change spatial relationship of jaws
• Change direction of growth
• Change dental relations
• Functional appliances change the mandible's posture, causing the patient to hold it open and/or forward.
• Muscle and soft tissue stretch pressures transmit to dental and skeletal structures through function or appliances, moving teeth and modifying growth.

Force Application and Elimination

• Force application involves compressive stress and strain on involved structures, resulting in a primary alteration in form and secondary adaptation in function.
• Force elimination involves eliminating abnormal and restrictive environmental influences on dentition and jaws.

Skeletal and Dentoalveolar Changes

• Skeletal and dentoalveolar changes are produced by these components:
  • Guides Eruption pattern
  • Linguofacial muscle balance
  • Mandibular repositioning
• Functional appliances are used in growing patients (late mixed dentition just before growth spurt).
• Treatment should coincide with a pubertal growth spurt.
• Cervical vertebral maturity indicators (CVMI) are used to determine patient maturity.

CVM Stage Determination

• Baccetti's method is used for cervical stages.

Bite Registration

• Tools used are boxing wax, a wooden spatula, and hot water.

Mandible Advancement

• Functional appliances advance the mandible in class II malocclusion and rotates it downwards in class III malocclusion.

Class 2 Malocclusions

• Applicances can fix class 2 malocclusions due to retrognathic mandible
• They are for growing and compliant patients.
• They work best with a normal/low angle.
• and patients with normally inclined or retroclined lower incisors.

Functional Appliance Changes

• Orthopedic changes
• Dentoalveolar changes
• Muscular changes
• Functional appliances utilize a forced mandible posture transmitting forces to teeth and jaws.

Bite plane Action

• Bite planes produce differential eruption
• The appliances have modest effects, such as a change in the size of the mandibular overall length
• Reorientation of maxilla and mandible, facilitated by clockwise tipping of the occlusal plane and rotation of either of the jaws or both
• Reduction in forward growth of maxilla

Efficacy of Functional Appliances

• They are effective in vertical control of increased overbite (class2 div 1, class2 div 2)
• Functional appliances modify patient growth.
• They can be used in mixed dentition
• Minimal chair side adjustment is needed
• They can sometimes save the patient from jaw surgery if intervened at the right time, along with patient compliance and favorable growth
• Functional appliances can correct the curve of Spee
• Functional appliances correct class 2 dental relation

Treatment success

• Success depends on patient cooperation.
• There is no precise tooth movement.
• Treatment duration is often prolonged.
• Two treatment phases are needed to complete treatment and precision in tooth positioning.
• They increase vertical proportions of the face and inclination of lower incisors.
• Appliances have to be worn fulltime.
• They are not seen as aesthetic, may cause discomfort and are subject to breakages.

Functional Appliance Usage:

• Treatment should start before the pubertal growth spurt.
• Treatment is most effective at the time when the mandible exhibits increased growth.
• Functional appliances should be worn fulltime except during brushing or eating.
• Appliances should be worn at nighttime when growth takes place.

Removable Functional Appliances

• Tooth-borne appliances
• Active appliances are modifications that use screws and springs. -Passive examples: Bionator, Twinblock, Herbst
• Tissue borne appliances (Frankel function regulator)
• Fixed Functional Appliances (Herbst, MARA)

Key Components: Functional and Tooth Controlling

• Functional components generate forces by altering mandible posture, changing soft tissue pressures against teeth, or both (mandible+teeth):
  • Examples include lingual flanges, sliding pins and tubes, tooth supporting ramps, and lip pads.
• Tooth controlling components consist of
  • Arch expansion: Buccal shields, Buccinators bow and shield, and Expansion screws /spring
  • Vertical control: Occlusal/incisal stops, Bite blocks, lingual shield. -Stabilizing : Clasps, labial bow, Anterior torquing springs

Tooth-Born Appliances

• Tooth born appliances have no intrinsic force generating components like springs or screws.
• They depend on soft tissues stretch and muscular activity to produce the desired movement.
  • Bionator -Activator -Twin block -Herbst -Herbst appliances force the mandible to be positioned forward not by pressure against the mucosa, but by holding the teeth
• Stimulation forward posturing of mandible
• Vertical control of teeth happens as lower anterior teeth are covered with acrylic to act as a bite plane, holding the bite open, and preventing anterior supraeruption.

Mandibular Advancement

• Mandibular advancement is used for class II correction.
• The mandible is postured forward by it.
• Maxillary and mandibular portions are configured
• Vertical bite control is applied though components
• Often incorporates expansion screws and headgear tubes

MARA Appliance

• Holds the mandible forward, using a pin-and-tube device.
• This is a fixed functional appliance

Expansion Activator Appliances

• Includes tooth moving mechanical components such as screws or springs to provide intrinsic force for transverse or antero-posterior changes.
• This is called an Expansion activator

Frankel Functional Regulators

• Functional regulators of Frankel are located in the vestibule and have little or no contact with the dentition, holding the lips and cheeks away from the dentition.
• Mandible repositioning happens
• The regulators are Located mainly in vestibule
• Appliances causes arch expansion

Lip Bumper Appliance

• Used to shield the lips away from the teeth.
• It is considered a 'combined removal-fixed appliance'.
• Lip bumpers are used in cases of lip sucking patients, hyperactive mentalis activity.

Maxillary Appliance Uses

• Maxillary appliance can augment anchorage
• Maxillary appliance causes distalization of first molars, named Denholtz appliance.

Appliance Effects and Success

• Functional appliances posture the mandible forward and is best for adolescence patients.
• They are used for correction of mild to moderate class 2 malocclusions.
• In most cases are following by a second phase of fixed appliance treatment
• They produce mainly dentoalveolar changes with some skeletal changes, and are successful in 80% of cases.
• A 20% appliance failure rate is usually due to poor compliance.