Activator as a Myofunctional Appliance

What is a Myofunctional (Myofacial) Appliance?

The Activator

Classification - Where Does the Activator Fit?

Key Distinction: Myofunctional vs. Myofacial

• Myofunctional is the standard, widely accepted term in orthodontics for this class of appliances.
• Myofacial (or myofascial) is more commonly used in the context of pain/TMD or soft-tissue management, but the terms are sometimes used interchangeably in older orthodontic texts.
• The activator is unambiguously a myofunctional appliance - it is the prototype and most classical example of this entire appliance category.

How It Works (Mechanism)

1. A construction bite is taken with the mandible postured anteriorly (forward) and slightly open.
2. The appliance holds the mandible in this new position.
3. Stretched orofacial and masticatory muscles (especially the lateral pterygoid, masseter, and suprahyoid muscles) generate tensile/propulsive forces.
4. These forces are transmitted to the teeth and alveolar bone, stimulating condylar growth and correcting skeletal Class II relationships.

Indications

• Class II Division 1 and Division 2 malocclusion
• Class I deep bite / open bite
• Class III (reverse activator)
• Mixed dentition growth modification
• Habit-breaking, space maintenance, and retention

Myofunctional Appliances - Complete Overview

Definition

Classification Systems

A. By Removability (Most Common Classification)

B. Graber's Classification (by support)

C. Proffit's Classification (by force mechanism)

Individual Appliances - Details

REMOVABLE APPLIANCES

1. Activator (Andresen Appliance)

• Inventor: Viggo Andresen, 1908 (Denmark)
• Design: Loose-fitting, bulky, tooth-borne, covers palate and both arches with acrylic
• Mechanism: Holds mandible in protrusive position; stretched muscles generate propulsive forces
• Indication: Class II Div 1 and 2, deep bite, open bite, Class III (reverse activator)
• Key feature: The prototype of all myofunctional appliances

• Harvold-Woodside activator (high construction bite)
• Herren activator
• Kinetor (Stockfish) - adds elastic tubes
• Elastic open activator (Klammt)
• Hamilton activator

2. Bionator (Balters Appliance)

• Inventor: Wilhelm Balters, 1950
• Design: Reduced-bulk activator - acrylic removed from palate and replaced with a coffin spring; upper and lower components connected by wire
• Mechanism: Tongue-focused - positions tongue correctly to allow natural jaw development
• Types: Standard, open bite, Class III
• Advantage: Less bulky, better tolerated than activator

3. Monoblock

• Inventor: Pierre Robin, 1902 - the first functional appliance
• Design: Single vulcanite bite-jumping appliance
• Indication: Class II due to mandibular deficiency; originally for glossoptosis (Pierre Robin sequence)
• Historical significance: Pioneer of all modern functional appliances

4. Frankel Function Regulator (FR)

• Inventor: Rolf Frankel, 1957
• Design: Vestibular shields and lip pads - sits largely outside the dental arches in the vestibule
• Mechanism: Tissue-borne; eliminates abnormal muscle pressure from lips and cheeks, allowing arches to expand naturally
• Types:
  • FR-1: Class I and Class II Div 1
  • FR-2: Class II (most common)
  • FR-3: Class III
  • FR-4: Open bite
• Unique feature: Works by removing restrictive muscle forces rather than adding propulsive ones

5. Twin Block Appliance

• Inventor: William Clark, 1977
• Design: Two separate upper and lower acrylic blocks with inclined planes cut at 70° to the occlusal plane
• Mechanism: Occlusal inclined planes engage and direct mandible forward with every jaw closure
• Advantages: Two separate pieces - more comfortable, better tolerated, can eat with it in place, easier compliance, can be used day and night
• Most widely used removable functional appliance today

6. Bimler Appliance (Bimler Chewing Activator)

• Inventor: H.P. Bimler, 1949
• Design: Highly flexible, elastic framework - minimal acrylic, mostly wire
• Mechanism: Myodynamic - depends on active muscle contractions during chewing
• Types: Type A (Class II Div 1), Type B (Class II Div 2), Type C (Class III)

7. Vestibular Screen (Oral Screen)

• Design: Single acrylic plate placed in the vestibule between lips/cheeks and teeth
• Mechanism: Eliminates abnormal lip and cheek muscle pressure
• Indication: Habit breaking (thumb sucking, lip sucking), mouth breathing, mild Class II

8. Lip Bumper

• Design: Wire/acrylic device held in the vestibule by tubes in molar bands
• Mechanism: Keeps lips away from the teeth, eliminating lip pressure
• Indication: Lower arch space gaining, relieving anterior crowding, lip incompetence

FIXED (NON-COMPLIANCE) APPLIANCES

9. Herbst Appliance

• Inventor: Emil Herbst, 1909; re-popularized by Pancherz (1979)
• Design: Bilateral telescopic piston-and-tube mechanism attached to upper and lower bands
• Mechanism: Rigid - permanently holds mandible in protruded position 24/7
• Rigid Fixed Functional Appliance (RFFA)
• Advantage: No patient cooperation needed, continuous 24-hour effect

10. MARA (Mandibular Anterior Repositioning Appliance)

• Fixed, rigid appliance
• Uses elbows on the upper first molars to prevent the mandible from retracting
• Good for younger growing patients

11. Jasper Jumper

• Design: Flexible coiled spring connecting upper and lower arches
• Type: Flexible Fixed Functional Appliance (FFFA)
• Mechanism: Uses spring elasticity to push mandible forward
• Used alongside fixed braces for concurrent treatment

12. Forsus Fatigue Resistant Device

• Flexible fixed functional appliance
• Push rod and spring mechanism
• Can be used concurrently with fixed appliances

13. FFFA (Flexible Fixed Functional Appliances) - Group

• Use elasticity/flexibility for mandibular repositioning
• Allow freedom of mandibular movement
• More prone to breakage than rigid appliances

SPECIAL/HYBRID APPLIANCES

14. Functional Orthopedic Magnetic Appliances (FOMA)

• Use rare earth magnets (samarium-cobalt) to generate repelling or attracting forces
• No patient activation needed
• Generate continuous light forces

15. Pre-fabricated Myofunctional Trainers (Myobrace/T4K)

• Modern pre-fabricated silicone/polyurethane appliances
• Target orofacial muscle dysfunction (mouth breathing, tongue thrust, lip incompetence)
• Used in mixed dentition (ages 5-15)
• Examples: T4K (for kids), T4F, T4U (multifunctional trainer), Myobrace system

Summary Table