Functional appliances can be used to treat Class II malocclusions by altering mandibular posture. They work by stretching soft tissues and generating corrective forces through intermaxillary traction. This causes dentoalveolar changes like incisor angulation as well as skeletal effects like increased mandibular length. Common functional appliances include the twin block, functional regulator II, and bionator, which guide mandibular positioning through occlusal coverage or soft tissue contacts. The Herbst appliance is fixed to achieve rapid correction through an immovable telescopic connection between upper and lower components.

1. Functional a ppliances
Nay Aung, BDS PhD
24.12.2022

2.  A functional appliance can be defined as an appliance that alters the posture of the mandible,
causing stretching of the facial soft tissues, to produce a combination of dental and skeletal
changes.
 Functional appliances are most commonly used in the management of Class II malocclusion,
however, they are occasionally used in Class III malocclusion.
 This presentation will focus on the use of functional appliances for the treatment of Class II
malocclusion.
Functional appliances

3.  These appliances may be classified according to whether they are tooth-borne or mucosa-
borne (e.g. the functional regulator II (FRII)).
 Tooth-borne appliances maybe classified as passive (e.g. bionator), if they carry no active
components, or active (e.g. twin block) if they carry active components such as expansion
screws and/or springs.
Functional appliances

4.  The following criteria should be fulfilled to prescribe a functional appliance:
 A significant Class II skeletal discrepancy with mandibular retrognathia.
 A growing patient. Ideally, treatment should be carried out during the pubertal growth spurt
(males 14±2 years; females 10±2 years) for maximum response. The magnitude of the skeletal
response declines following this.
 A compliant patient. Functional appliances can be difficult to tolerate and patients must
attend for regular appointments.
Patient selection

5.  Functional appliances work by posturing the mandible forwards, which causes soft tissue
stretching.
 This generates Class II intermaxillary traction forces.
 The resultant correction in overjet is produced by combination of tooth movement (70%) and
skeletal change (30%).
 The effects of functional appliances are:
 Dento-alveolar changes
 Increased mandibular length
 An increase in lower anterior face height (LAFH)
 Forward remodeling of the glenoid fossa
 Restraint of maxillary growth
Mode of action

6.  Dentoalveolar changes – these include retroclination of the maxillary incisors and proclination
of the mandibular incisors due to the Class II traction forces developed between the arches,
and because the upper incisors come under the control of the lower lip with anterior
mandibular posturing.
 Increased mandibular length – due to downward and forward translation of the condyle
which may encourage backward compensatory growth. In the short term, mandibular length
may increase by 2-4mm although there is great individual variation. There is evidence from
long-term studies that the early growth benefit may be lost with time.
Mode of action

7.  An increase in lower anterior face height (LAFH) – due to a combination of molar eruption
and downwards mandibular growth. This is useful where there is a deep overbite (OB)/short
LAFH, and detrimental in those with a reduced OB/increased LAFH.
 Forward remodeling of the glenoid fossa – this occurs secondary to anterior condylar
repositioning.
 Restraint of maxillary growth – due to the Class II traction forces acting on the maxilla.
Incorporation of headgear into functional appliance treatment increases this effect.
Mode of action
(B) The mechanism of action of functional appliances.
(A) Vertical and anterior posturing of the
mandible results in muscular and soft
tissue stretching.
This produces forces which act on the
dentition, through the appliance, to
produce tooth movement.

8.  One common feature between all the appliances described below is that they are constructed
from a bite registration taken with the mandible postured forwards.
Types of functional appliances

9.  The twin block appliance is suitable for Class II cases with a reduced or normal vertical
dimension.
 High-pull headgear should be used in those with an increased face height to limit vertical
maxillary growth.
 It is a two-piece appliance that is intended to be worn full-time.
 An advantage of the two-piece design is that it allows lateral mandibular excursions during
wear that may increase comfort and improve compliance.
 The mandibular appliance consists of an acrylic baseplate with Adams clasps placed onto the
first permanent molars and first premolars.
 The bite blocks cover the occlusal surface of the premolars.
The twin block appliance

10.  The maxillary appliance consists of an acrylic baseplate, with a mid-line expansion screw,
incorporating Adams clasps in a similar manner to the mandibular appliance.
 The bite blocks cover the occlusal surface of the premolars and molars.
 Some clinicians incorporate a labial bow to aid retraction of the maxillary incisors and
appliance retention.
 On insertion of both appliances, the bite blocks, which interdigitate at 45-70°, force the
mandible to posture anteriorly.
The twin block appliance
The twin block appliance.
(i) Upper component
(ii) Lower component
(iii) Side view
The blocks interdigitate at 45-70° to
posture the mandible forwards (note the
edge-edge incisor relationship).

11.  Rolf Frankel described a number of functional regulator appliances of which the functional
regulator II is the most popular.
 Frankel believed that the capacity to regulate facial growth resided in the soft tissues.
 The appliance aims to remove the restrictive soft tissue forces which limit normal maxillary
and mandibular development.
The functional regulator II appliance
(D) The functional regulator II appliance
(i) The various components:
1= buccal shield
2= labial pad
3= lingual pad
4= labial bow
(ii) The functional regulator II in situ

12.  The appliance is mainly used in Class II cases with a lip trap or in the mixed dentition as the
appliance is mocosa-borne and retention is not affected by shedding deciduous teeth.
 The role of the buccal shields is to limit cheek pressure on the maxillary buccal segments and
allow expansion under unopposed tongue pressure.
 The buccal shields are vertically overextended into the buccal sulcus in an attempt to cause
periosteal stretch, which is thought to encourage lateral maxillary bone deposition.
 The labial pad removes restrictive forces from hyperactive mentalis activity.
 The lingual pad contacts the lingual mucosa creating an avoidance reflex which results in
anterior mandibular posturing.
The functional regulator II appliance

13.  The original bionator appliance has undergone numerous modifications but essentially
consists of a lingual horseshoe of acrylic with molar facets to posture the mandible forwards
and guide molar eruption.
 A labial bow extends posteriorly to act as a buccal shield.
 There are a number of designs depending on whether the aim is to open, close or maintain
the overbite by encouraging or inhibiting molar and/or incisor eruption.
The bionator
(E) The bionator appliance.

14.  The Herbst appliance is a fixed functional appliance which has the advantage of producing
rapid occlusal changes as it cannot be removed by the patient.
 It consists of a metal framework cemented to the upper and lower arches and connected
bilaterally by a piston-and-tube telescopic device that forces the mandible forwards.
The Herbst appliance

15. Thank you so much for your kind attention.