Functional orthodontic appliances / for orthodontists by Almuzian

Functional Orthodontic Appliances/Growth Modification
Appliance/Myofunctional Appliance
Mohammed Almuzian
2013

Mohammed Almuzian, 2013 1
List of the contents
Table of Contents
Definition .....................................................................................................................................3
History .........................................................................................................................................3
Classification................................................................................................................................3
I. According to mode of action...............................................................................................3
II. According to mode of retention...........................................................................................4
III. Hunt’s Classification ......................................................................................................4
Indications ....................................................................................................................................4
Problems with functional appliances...............................................................................................6
1. Rebound of overjet.................................................................................................................6
Aetiology .....................................................................................................................................6
Solutions ......................................................................................................................................6
2. Incisor proclination ................................................................................................................8
Studies .........................................................................................................................................8
Solutions ......................................................................................................................................8
3. Lateral open bite ....................................................................................................................9
Compliance with different type of functional appliance .................................................................10
Problems with functional appliance studies ...................................................................................10
Effects and Mode of action ..........................................................................................................12
Dentoalveolar modification .........................................................................................................12
Skeletal effect.............................................................................................................................13
Soft tissue effect.........................................................................................................................17
Habit breaker..............................................................................................................................19
Comparing the functional appliance regarding the skeletal effect....................................................19
If there are no skeletal changesby functional appliance,so,whythe functional applianceis
still recommendedhighlyingrowingpatient?Andwhatisthe factorinfluencingthe timingof
treatment with myofunctional appliances ....................................................................................22
Factor influencing the Choice of appliance of myofunctional appliances.........................................26
Types of myofunctional appliances ..............................................................................................27
I. Myofunctional appliances for treatment of Deep overbite .......................................................27
II. Myofunctional appliances for treatment of openbite ...............................................................27
III. Myofunctional appliances for treatment of Class III............................................................28
Frankel FR3................................................................................................................................28
Class 3 twin-blocks .....................................................................................................................28

IV. Myofunctional appliances for treatment of Class II.............................................................28
a. History of TB ......................................................................................................................46
b. Indications of TB.................................................................................................................46
c. Advantage of TB.................................................................................................................46
d. Disadvantage of TB.............................................................................................................46
e. Design ................................................................................................................................47
f. Advancement.......................................................................................................................51
g. Clinical tips.........................................................................................................................52
h. Effectiveness of the Twin-block appliance compared to normal..............................................52
i. Profile changes:...................................................................................................................52
j. Psychosocial benefits of early orthodontic treatment with the Twin-block appliance.................52
FAQ aboutfunctional appliance...................................................................................................53
I. Treatment duration .......................................................................................................53
II. Advantages of two stage treatment with the functional appliance.....................................53
III. Advantages of one stage treatment with the functional appliance..................................54
IV. Stability of myofunctional appliances results ............................................................54
V. SAQs...........................................................................................................................54
Mouthguard advice by BOS................................................................Error! Bookmark not defined.
Definition .........................................................................................Error! Bookmark not defined.
Prevalence of trauma.........................................................................Error! Bookmark not defined.
Materials ..........................................................................................Error! Bookmark not defined.
Types of mouthguard........................................................................Error! Bookmark not defined.


Functional Orthodontic Appliances/Intraoral Growth Modification
Appliance/Myofunctional Appliance
Definition
A removable or fixed orthodontic appliance which use or eliminate the force
arising from the masticatory, facial muscles & peridodontium to alter the skeletal
and dental relationship. (Mills, 1991).The term “myofunctional appliance” is
preferable as they all depend for their action upon the activity of the orofacial
musculature.
History
 Kingsley in 1879 used the bite jumping appliance.
 Inclined bite plane first used in 19th century In Spain by Catalan.
 Monobloc appliance developed 1902 Pier Robin
 “Norwegian system “ Andreasen appliance (activators), developed from
URA retainers used with inclined bite planes and mandibular lingual
extensions when Andreasen prescribed it to his daughter during her long
schoolholidays in Norway. (Andreasen and Haupl,1936)
 Balter Bionator 1950
 Frankle appliances 1966
 TB appliances were originally described by William Clark (1982 and
1988).
Classification
I. According to mode of action by Vig and Vig 1974.
1. Myotonic: Work by passive muscle stretch through large mandibular opening
(8-10mm). eg. Harvold
2. Myodynamic: Work by stimulation of the muscle activity with medium
mandibular opening (<5mm). eg Andreasen, Bionator, MOA

II. According to mode of retention
1. Toothborne:
 Passive tooth borne eg Andreasen, Bionator
 Active tooth borne eg twin block, Herbst.
2. Tissue borne eg Frankel
III. Hunt’s Classification
1. Removable: good for deep overbite / short face cases. Andreasen, Bionator,
Harvold, MOA, Function Regulator.
2. Removable functional headgear appliances: good choice in high angle cases,
CTB (Clark, 1982) with HG, Van Beek, Bass appliance with HG, Teuscher
or headgear activator Teuscher appliance (HATA)
3. Fixed: can be classified as either
A. Flexible (Flexible Fixed Functional Appliance – FFFA) AdvanSync
B. Rigid (Rigid Fixed Functional Appliance – RFFA)Dynamax
C. Hybrid types- Herbst (Pancherz)
Indications
1. Interceptive treatment for trauma: Functional appliances are frequently
advocated for early treatment to reduce the overjet early which subsequently
might reduce trauma. This had been disapproved by (Kurlock 2004)
2. Psychological advantages in young patient: Functional appliances are
frequently advocated for early treatment to reduce the overjet early which
subsequently might reduce teasing problems. (O’Brien 2003)

3. Orthopaedic treatment
 Correction of AP in class II division 1 malocclusions or class II D2 with
incisors decompensation (for more details see below)
 CL III cases.
 AOB like Frankle 4
 Mild degree of facial asymmetry by using hybrid appliance
4. Compromise treatment: Some cases are not suitable for fixed appliance
treatment because of, for example, poororal hygiene, so the functional
appliance can offer an acceptable degree of occlusal and facial improvement.
5. Anchorage reinforcement: Turning a class II case into an easy class 1 case
6. Habit breaker (digit sucking) combined with one of the above problems.
7. Patient with gonial angle less than Franchi and Bacceti 2006. A Class II patient
at the peak in skeletal maturation (CS 3) with a pretreatment Co-Go-Me° smaller
than 125.5° is expected to respond favorably to treatment
Correctionof AP in class II division 1 malocclusions orclass II D2 with
functional appliances
'Classic'functional appliance cases is:
1. Growing patient
2. Motivated patient
3. Moderate to severe Class II D1 or class II D2 with incisors decompensation
4. Normal or low MMPA (average or increased OB)
5. Slightly proclined upper teeth.
6. Slightly retroclined lower incisors.
7. Well aligned or minimal crowded arches.
Class II cases notsuitable for functional appliances
1. Non-growing patient

2. High angled cases, posterior mandibular rotation, AOB
3. Cases with proclined LLS or retroclined ULS
4. Cases which can be treated by conventional fixed appliance on extraction or
non-extraction basis.
Problems with functional appliances
1. Rebound of overjet
2. Lower incisor proclination
3. Lateral open bite
In details
1. Rebound of overjet
Aetiology
I. A rebound of condylar position caused by atrophy of hyperatrphyed meniscus
II. Reduction in the activity of protractormuscle (lateral Pterygoid muscle)
III. Uprighting of ULS or LLS. LLS relapsed more.
IV. Unfavourable growth
Solutions
(DiBiase andFleming2007) wrote a comprehensive review article aboutthistopic.They
mentionedthe followingasa transition technique:
Technique Advantages Disadvantages
1. Over-correction. To counteractthe relapse
2. Reinforcing
anchorage Headgear
and palatal arches
To control molar buccal tipping during
alignmentstage.
3. Maintainingpostured
bite byinclinedURA
or clipoverURA (Plint
claspappliance).The
bite plane shouldbe
8mm deepand70
degree inclination
 Maintaintransverse
correction
 Allow settlingof occlusion
 MaintainclassII effect.
 Increased
proclinationof
LLS.
 Interference
withthe
placementof FA.

(SandlerandDiBiase,
1996).
4. Nightwearappliance. Advantages:
 Betterto predictrebound,
 Good time forpostured
condyle toadapt
 Good settlingof occlusion,
correction
5. Integrationof the
functional appliance
withthe fixed
appliance until rigid
AW inplace.
 Good settlingof occlusion,
correction
 Quickmethods
But thisneedsa
modificationinthe
functional appliance to
avoidinterference with
FA.
6. Early lightclassII
elasticsatan early
stage on lightwiresto
keepoverjet
controlled.
 Further
proclinationof
LLS and
retroclinationof
ULS.
 Extrusionof LBS
cause reduction
inthe OB
 Lingual tipping
and rollingof the
lowermolars
due to poor
rigidityof the
NiTi AW.
7. Appliance
prescription
(MBT is preferredbecause
 It correct LLS and ULS
inclination
 The zero tippingof the U6 and
U3 cause lessrebounding
effect
 Increase palatal roottorque of
buccal segmentwill
compensate fortippedmolar
due to expansion.
 Lastlythe reduce lingual
crown torque of L6 to
counteractthe lingual rolling
whenclassII elasticisused
8. The use of fixed
to avoidthe
transitional phase
Dynamax
FixedTB
AdvanSync
Herbst
9. Last optionisthe
immediate transition
withoutretainer.
It isa shorttreatmentoption Difficulttopredict
rebound,
No time forpostured

condyle toadapt
No settlingof occlusion
2. Increase in the incisor inclination (upper retroclination and lower
proclination)
Lower incisor proclination is a feature of almost all functional appliance
treatment. (Approximately 8-15 degree)
Studies
Studies show a wide range of proclination with any given appliance and a
wider range between different appliances.
• Appliances which are tooth-borne, such as the Herbst appliance, seem to
producegreater proclination (average 3.2 mm or 11 degrees in Koutsonas and
Pancherz, 1997).
• The Bass appliance which places no direct pressure behind the lower
incisors can producevery little labial incisor movement, albeit with slower
overjet reduction. Bass 2006
• Lund and Sandler (1998), reported average proclination of 8+7 degrees using
TB.
Solutions
1. Lower labial cap of acrylic on their twin blocks and reported average
proclination of 5.2+3.9 degrees (Young & Harrisson 2005). However this
might cause extensive decalcification in poorOH (Dixon 2005).
2. Trenouth & Desmond (2010) used Southern end clasps on the lower incisors
and reported almost no lower incisor proclination.
3. Other functional appliance like Dynamax

4. Headgear with functional appliance
5. Relief to the acrylic lingual to the lower incisors (Ball and Hunt, 1991)
6. Avoidance of labial bows in the upper arch
7. Extending the lower lingual acrylic as posterior as possible
8. Incremental advancement
9. Short time use or avoidance of class II elastic
10.Overcorrect the OJ and then use class III elastic
11.MBT prescription
12.Extraction
3. Lateral open bite
1. Lower incisor capping to prevent incisor overeruption.
2. Upper incisor capping or 'torquing' spurs to prevent incisor overeruption.
3. Grinding from the functional appliance to allow eruption. However this might
encourage the lower molars to erupt more mesially causing lower premolar
crowding as well as leading to more LLS crowding.
4. Night time wear. However it is important to mention that one intriguing
thought arises from work showing by Lee and Proffit (1995), that nearly all
human tooth eruption occurs between 8 pm and midnight. Should we get our
patients to wear the twin block just in the mornings once the overjet is
reduced and the remaining posterior open bite can usefully settle at night
when teeth erupt?
5. Stop and wait until settling of the occlusion
6. Steep and deep URA.
7. Other type of removable functional like Dynamax.
8. Claim that fixed functional produceless open bite problems

9. Fixed appliance
Compliance with different type of functional appliance
In general the TB fail in 1 out of 5 patients
Failure rate
TB in pre-adolescent 18% O’Brien 2003
TB in adolescent 25%
33%
9%
O’Brien 2003 b (with
herbest)
Lee et a 2007
Incremental and one
go advancement TB
The first one has half of
the failure of the latter
Bank 2004
Fixed TB 3% Read, 2001
Dynamx 9% Lee et a 2007
Dynamx 84% Bader Thiruvenkatachari,
2010
Herbst appliance 13% O’Brien 2003
Frankle appliance 42% in female and 24%
in male
Ghafari 1998
HG 5% for female and 25%
for male
Ghafari 1998
Schafer K, Ludwig B, Meyer-Gutknecht H, Schott TC. Quantifying patient
adherence during active orthodontic treatment with removable appliances using
microelectronic wear-time documentation. Eur J Orthod 2015;37:73-80

Removable appliances are a common treatment modality used in both active
and retentive phases of orthodontic treatment. It is well known that patient
adherence is imperative for optimal therapeutic success.Until recently, it has
been almost impossible for orthodontists to objectively evaluate how
consistently patients were adhering to their prescribed wear times. The aim of
this study was to quantify the adherence of active removable appliances during
the first 3 months of treatment. This was a multicenter, prospective cohort
study that evaluated how wear time was influenced by age, sex, device type,
location of treatment, and health insurance status. One hundred forty-one
patients were divided into 3 age groups:7-9, 10-12, and 13-15 years. Each
patient was treated either in one of 3 private practices in Germany or at the
University Hospital of Tubingen, Germany. A temperature-sensitive
microsensor, TheraMon Sensor, was placed in a standard activator, a Class III
activator, or a maxillary expander, and the stored data were transferred at
routine visits. The overall median wear time was 9.7 hours per day compared
with the prescribed wear time of 15 hours per day; only 7.8% of the patients
reached the prescribed 15 hours. Statistically significant differences were seen
based on sex, age, location, and health insurance. Wear time decreased as age
increased, with the youngest patients wearing their appliances for a median of
12.1 hours per day, and the oldest wearing them for 8.5 hours a day. Girls
wore their devices longer in each age group by 1.3 hours. Wear times were
significantly higher in patients with private health insurance during the first
3 months and in each month separately. There was no significant difference
between device types.
Problems with functional appliance studies
1. Small samples
2. No controls:
 No controlling to differentiate treatment effect from normal growth effect.
 If involved historic controlit is considered invalid for the today
population
 Also the randomization is absent which would not involve the bias in the
confounding factors.
3. Retrospective so the best cases tend to be selected.

4. Unmatched samples for age and gender
5. Different appliances
6. Different operators
7. Different lengths of study
8. Inaccuracies in measurement
9. Most based on cephalometric.
10.Animal studies may not be relevant to humans. This is because:
 Animal are different species
 Animal has no class II problems
 Unrealistic prolong use of functional in animal
On the other hand, the retrospective are weak studies because:
 Only good cases were shown
 Only enthusiastic clinician are involved
So the RCT are the gold standard
Mode of action
 Stretch and activate the muscle of mastication and facial muscle
 Stretching of periosteal
 Relieve softtissue effect (Frankle appliance)
 Disocclude the occlusion
Effects
Effect With Against
Dentoalveolar modification
We should employ the knowledge that a large proportion of their effect is via
upper incisor retroclination and distal movement of upper molars
1. ULS retroclined

2. LLS proclined
3. Distalization of U molars.
4. Mesilaization of L molar
5. Inhibition of the eruption of upper posterior teeth
6. OB: Differential eruption of the teeth by encouragement of the eruption of
lower posterior teeth which cause reduction in the OB and increase LAFH.
7. Transverse expansion if screw is incorporated
The evidences are:
1. Tulloch et al 1997
2. Tulloch et al 1998
3. Lund and Sandler 1998
4. Keeling et al 1998
5. Ghafari 1998
6. O’Brien et al 2003
7. Dolce et al 2007
8. O’Brien in 2009
These dental effects are due to the stretching of the muscle of mastication and facial
tissue as well as alteration of the soft tissue balance when the mandible is postured.
Skeletal effect
Effect With Against
Redirection of condylar
growth (altering growth
direction, mainly vertically)
which is more stable over a
long period of time
Mills, 1991
Deflection of ramal form
Remodeling of the

gonial angle in
responseto altered
muscle activity and
tone in the
pterygomasseteric
sling has been found
in animal
experiments
(Woodsideet al,
1983; Joho, 1968,
1973; Altuna, 1979;
Harvold, 1960) and
human functional
appliance studies
(Harvold, 1960;
Hutchison, 1982).
Condylar position changes
within the fossa results
mainly due to condyle
remodelling and glenoid
fossaremodelling
Petrovic 1990 suggested
that the functional would
increase the activity of
the lateral pterygoid
which helps in
enhancing growth of the
condyle by increasing
the number of
proliferative cells.
An MRI study by Ruf and
Pancherz (1998) showed no
mean change in condylar
position within the fossa
Mandibular effect:
Enhancement of mandibular
Animal Studies,
McNamara 1987
Human Studies on long
term

growth (True condylar
growth). It is probable that
an average 1-2 mm of extra
short-term mandibular
growth can be obtained.
There is a great individual
variation regarding this
issue. This is clinically
worthwhile, but it would not
be sufficient to obviate
orthognathic surgery in those
cases deemed to require it
before the start of treatment.
The increasing evidence is
that the long-term gain in
mandibular growth is very
small or non-existent.
showed that the
mandible of monkeys
grow by 5-6mm more
than control.
1. Weislander (1993)
showed 2mm skeletal
changes lost after 2
years
2. Keeling et al (1998),
Bionator, one year
after active treatment,
all changes lost.
3. The long-term results
of the groups in the
RCT by Keeling et al
have been published
(Dolce et al 2007)
and they show no
long-term differences
4. Tulloch et al (1997)
using Bionator
showed a small (0.6
degrees/year)
enhancement of
mandibular growth in
the short term, then
Tulloch et al (1998)
none in the after 1
year
5. Tulloch et al (2004)
the growth
modification group
Human Studies on long
term, Lund and Sandler
(1998) they found
cephalometric evidences
of mandibular growth
when measured as
Articulare-Pogonion but
could not attribute this
growth or just
repositioning.

were lost.
6. O’Brien et al (2003)
using TB, growth in
the mandible of
approximately1.2
mm per year. This
small change was
stable 12 months
after treatment.
7. O’Brien in 2009
long-term results
there were no
differences of
skeletal pattern
8. Harrsion 2007
Maxillary skeletal changes:
Restriction of the maxillary
growth. An average 1-2 mm
of long-term maxillary
restraint seems possible,
although many studies fail to
find this. There is some
evidence that this does not
relapse after active
treatment, but may continue
and even increase.
on long term,
 The study by
Weislander (1993)
showed that
maxillary growth
restraint actually
increased relative
to controls after
the end of active
treatment using a
combined
Herbest-HG
appliance.
No significant maxillary
restraint, with Frankel
appliance Keeling et al
(1998) or with the modified
Bionator (Tulloch 2004).

 O’Brien et al
(2003) found
0.88mm restraint
in the TB gp.
3. Soft tissue effect
In general, Functional appliances are said to modify
the neuromuscular environment of the dentition and
associated bones. Adaptive processes may include:
 Elongation of muscle fibers (McNamara,
1973; Golspink, 1976) or tendons (Muhl and
Grimm, 1974).
 Migration of muscle attachments along bony
surfaces (McNamara, 1973; Symons, 1954;
Van der Klauuw, 1963; Rayne, 1975)
 Changes in muscle dimensions due to bone
displacements and rotations (Altuna, 1977,
1979, 1985; McNamara, 1973).
 Certain muscles of mastication may adapt by
changing the proportion of specific muscle
fiber types and fiber diameters (Altuna,
Herbert and Woodside, 1983).
1. Muscles of face: Frankel reported to restrain the
muscles of face
2. Muscle of mastication: Other appliances
stretching the muscle of mastication specially
lateral pterygoid. So the force will be
transmitted to the dentition causing a
dentoalveolar changes, condylar adaptation and
growth

3. Tongue: functional appliance can remove tongue
adaptively.
4. Lip muscle: Functional appliance can eliminate
lip trapping which is a cause of proclination
All these effect producedental and skeletal changes by
altering position of balance (Bishara & Ziaja, 1989).
The softtissue changes include: (Sharma and Lee
2003, 2005).
1. Increased commissure width
2. Increased LFH,
3. Retrudes the upper lip.
4. Increased lower lip height & projection,
5. Increased projection of ST pog
Effect on Oropharyngeal airway: Özbek, (1998) suggested that mandibular
deficiency may be a factor in reduced oropharyngeal airway (OAW) dimensions and
related impaired respiratory function. The purpose of the study was to evaluate the use
of functional-orthopaedic devices in increasing OAW dimensions in children with
Class II skeletal patterns (ANB>4) and clinically deficient mandibles. Comparisons
were made between two groups, one comprising 26 treated patients and the other
comprising 15 controls. Compared with controls, OAW dimensions increased
significantly in treated patients, especially those with sagittally smaller and more
retrognathic maxillomandibular complexes and smaller OAW dimensions.

4. Habit breaker:By occupying the spacewhich might be a spacefor the digit and
or tongue in case of habit.
NB:
Summary of the evidences:
 The increasing evidence is that the long-term gain in mandibular growth is very
small or non-existent. It is probable that an average 1-2 mm. of extra short-term
mandibular growth can be obtained. This is clinically worthwhile, but it would
not be sufficient to obviate orthognathic surgery in those cases deemed to
require it before the start of treatment.
 An average 1-2 mm of long-term maxillary restraint seems possible, although
many studies fail to find this. In contrast to the mandibular effect, there is some
evidence that this does not relapse after active treatment, but may continue and
even increase. Headgear may well be more effective for maxillary restraint.
 We should remember the large variability of growth - both with and without
treatment.
 Some uncertainty remains about the influence of the pubertal growth spurt on
growth enhancement.
 We should employ the very large occlusal benefits of functional appliances in
the knowledge that a large proportion of their effect is via upper incisor
retroclination and distal movement of upper molars. 75% dentoalveolar and
25% short term skeletal changes.
 We should keep in mind that the skeletal changes might be relapsed after
finishing FA treatment. For example a patient use TB to correctclass II D1
malocclusion, in general he will gain a lot of dentoalveolar changes as well as
some skeletal changes. According to the evidence the skeletal changes will lost
in average two years after functional treatment. So this is one of the causes of
relapse after treatment as well as one of the reasons for continuous use of active
retainer in a form of steep and deep or activator. The aims of using it after
active treatment are to enhance more dentalveolar compensation when the
skeletal changes relapsed.
Individual variation in effects
Woodside (1998) has outlined “prominent reasons” for individual variation in
results:
Patient compliance

Night-time wear vs full-time wear. Full-time wear requires appliance
designs that will not unduly affect the patient’s facial appearance and
speech.
Wavelike fashion of mandibular growth –accelerations followed by
quiescent periods. If treatment is applied during a quiescent period,
significant orthopaedic changes may not occur.
Improper diagnosis. Severe cases are probably future surgical cases, we
can’t expect growth control to exceed certain limits.
Type of mandibular rotations
Problems with Cephalometrics in Measuring the Orthopaedic Effect:
[Aelbers and Dermaut, 1996]
 A cephalogram is a magnified two-dimensional image of a 3-D object.
 Maxillary and mandibular lengths are often used to show possible
orthopaedic effects. Condylion, gnathion and pogonion are mandibular
points used, however, it is often difficult to define the head of the
condyle on a cephalogram. Results have indicated that the open mouth
method does not significantly change the recognition of condylion,
others have found improvement in landmark identification.
 Articulare is sometimes used because of the high reproducibility of this
landmark. Articulare does not, however, show full mandibular length,
and a change in the amount or direction does not necessarily create the
same positional change of articulare. Anterior positioning of the
condyles out of the glenoid fossae could be interpreted as an increase in
mandibular length.
 Maxillary length can be measured using PTm point, spinal point (ANS)
or point A. These landmarks can not be accurately identified. Point A is
influenced by dental changes. Because most functional appliances
induce a large dentoalveolar change, point A has a limited value to
evaluate orthopaedics.
 Angular measurements, such as SNA, SNB and ANB, may increase or
decrease when the incisor position changes, although no skeletal change
occurs, rendering the results invalid (Woodside, 1998).
 Statistical significance may not necessarily correlate to clinical
significance. Small statistically significant amount may be clinically
insignificant in the total malocclusion correction (Woodside, 1998).
 Implant studies are limited by ethics and small sample sizes.

Comparing the functional appliance regarding the skeletaleffect
1. Fixed and removable functional appliances: (Pacha, Fleming and Johal a
systematic review 2015
 There is little difference in the dental and skeletal effects of fixed and
removable functional appliances.
 Most of the correction of the overjet is by dento alveolar movement, but
there is a small amount of skeletal change (1-2mm).
 There is greater co-operation with fixed functional appliances but this is
not 100%. There is no such thing as non compliance orthodontic
treatment!
 Only one study reported on patient centred outcome and these should be
included in all trials in addition to some cephalometric and dental
measurements.
2. TB versus Bionator by Harrsion 2007 statistic difference in the reduction of
ANB when TB compared to bionator, however, there was no difference in
regard to the final OJ.
3. Comparison of Herbst with twin-block appliances in preadolescent patients,
O’Brien 2009, Treatment with the Herbst appliance resulted in a lower failure-
to-complete rate for the functional appliance phase of treatment (12.9%) than
did treatment with Twin-block (33.6%). Herbest appliance where more
effective in reducing OJ than TB. However, there were no differences in
treatment time between appliances, There were no differences in skeletal and
dental changes
4. Comparison of Twin-block and Dynamax appliances. ,
 Lee et al 2007, similar compliance rate. More breakage with Dynamax.
Forward movement of the chin and Pogare similar. More vertical skeletal
changes with TB (6mm compared to 5mm), ANB changes in TB 2 degree and
in Dynamax 1 degree.

 Thiruvenkatachari Bader, 2010, The incidence of adverse events was greater in
the Dynamax group (82%) than in the Twin-block group (16%). The Twin-
block appliance was more effective than the Dynamax appliance
Factor influencing the timing oftreatment with myo-functional
appliances
 Dental factors
 Growth spurt
 Trauma prevention
 Psychological factors
 Patient compliance
Factors With Against
Dental factors Better to start when the
permanent teeth have erupted for
better clasping of the appliance.
Treatment whilst deciduous teeth
are being shed may poseminor
problems of appliance retention,
discomfort or a delay in the
shedding of deciduous teeth.
Growth spurt
The principle
issue to start
functional
appliance is to
try to
synchronize the
treatment with
Treatment during growth spurt
may cause slight difference from
that earlier or later in that it has
little dental tipping, more skeletal
growth and stable results as well
as better occlusal settling.
Pancherz (1985) and Baccetti
(2000).
But neither Tulloch 1997
using hand wrist or
O’Brien 2003 using
CVM failed to relate the
skeletal changes to
skeletal maturity.
An important point is
that the growth spurt

pubertal growth
spurt.
Stephens and Houston (1985)
stated that a growing patient
has greater potential for:
 Dentoalveolar effect of the
 Overbite reduction
 Occlusal settling
 Spaceclosure
 Maxillary expansion
 Distalization or mesialization
of posterior teeth.
All of these make changes by
functional appliance as well as
the second phase fixed appliance
efficiently and fast.
cannot be predicted with
clinically useful
accuracy. Even with
longitudinal monitoring
of stature, Sullivan
(1983) has shown that
our prediction will still
be more than one year
incorrect in 33% of
cases.
The timing of treatment
seems to have minimal
impact (0.6 mm) on the
treatment outcome
(Baccetti, 2009
Franchi, 2000)
Trauma
prevention
A definite
potential
advantage of
starting
treatment early
is the reduced
incidence of
trauma to
prominent
High trauma with increased
overjets >9mm (Todd & Dodd
1983) (45% 10 yr olds with OJ
more than 9mm have traumatised
incisors compared to 27% if the
OJ was less than 9mm especially
if the lip is incompetent. Nuygen
1999 systematic review
However this had be
contradicted by Korluk
in 2004.The same results
by O’Brien 2009. But
the latest Cochrane
review by
Thiruvenkatachari in
2013 confirm the trauma
prevention benefits of
early treatment.

upper incisors.
Psychological
factors
Unless for psychosocialreasons
(increase self-concept, reduce
negative experience and improve
self esteem) (O’Brien 2003),
which can result from teasing,
early treatment with functional
appliances is not indicated.
OIIRR In the UNC study (Brin 2003),
the percentage of children with
more than one incisor with
moderate to severe in the two-
phase group was 5% in the
functional group and 12.5% in
the headgear group. In the single-
phase treatment group, the
incidence was 20.4%.
Does severe OIIRR
affect the longevity of
the affected teeth? In a
long-term evaluation
(average of 14.1 years)
of longevity of teeth
with severe OIIRR (>
1/3 loss of root length),
it was found that even
the most severely
affected teeth were
functioning in a
reasonable manner many
years after orthodontic
intervention.( Remington
1989) This is not
surprising because the
apical portion of the

tooth plays only a minor
role in overall
periodontal support. It
has been reported that 3
mm of apical root loss is
equivalent to 1 mm of
crestal bone loss
(Kalkwaf 1989).
Patient
compliance
The studies by O’Brien et al
(2003) showed a significantly
lower failure-to-finish rate in the
younger patients when treated by
the same operatorwith the same
appliance. Similarly, the study by
Banks et al (2004), found that
patients younger than 12.3 years
were three times more likely to
complete functional treatment
with twin-blocks.
Summary
1. Dental factors are important. We usually want to start treatment as soon
as the eruption of the permanent teeth permits and this is in the late
mixed dentition.
2. Enhancement of growth is on average small and seems to be only
marginally related to the pubertal growth spurt. However, it is probable
that regardless of growth enhancement effect, treatment is faster rapid
growth. Treatment during growth spurt is aiming to
a. Borrow the potential mandibular growth when needed

b. Provide a better environment for dentoalveolar compensation
c. Disoccluding the unfavourable occlusion that might interfere with
the potential growth leading to dysmorphic compensation (Kim and
Nanda 2002, You 2001 using Burlington sample).
However there is no evidence comparing adolescent patients with TB
treatment to control because of the equipoise. Again the long term
effect involve limited AP changes and more attractive profile
(O’Brien 2009 a & b) with increase VH, dental and occlusal changes
and favourable ST changes for low angle cases.
3. An early treatment in large class 2 discrepancies may be moderately
significantly advantageous in terms of dental trauma
4. An earlier start than this in large class 2 discrepancies may be
advantageous in terms of psychosocial benefits
5. Cooperation with functional appliances is better before 12.5 years of age
Factorinfluencing the Choice of appliance of myofunctional appliances
1. Patient factors
• Patient compliance
• Type of malocclusion
• OH
• Preference
2. Clinician factors preference
• Familiarity
• Laboratory facilities
• Available evidences

Types of myofunctional appliances
I. Myofunctional appliances for treatment of Deepoverbite
1. The Anterior Bite Plane (ABP)
It is the simplest form of a myofunctional appliance. Its types;
1. Upper horizontal bite-planes
2. Upper inclined bite-planes
3. A lower inclined bite-plane can be used in deep bite class III cases.
II. Myofunctional appliances for treatment of open bite
 Frankle IV
 Intrusive splint
 The oral screen
A. Design
This very simple functional appliance lies in the
labial vestibule. The oral screen has no place in
modern orthodontics.
B. Indication:
1. It has been used to discourage thumb-sucking
and to correctthe associated malocclusion.
2. Prevention of trauma during contactsportactivity.
3. It has also been used for lip training in patients with incompetent lips.

III. Myofunctional appliances for treatment of Class III
1. Frankel FR3
2. Class 3 twin-blocks
FrankelFR3
1. Not commonly used
2. Holding away of the softtissues from the upper incisors would stimulate
maxillary growth through stretching the periosteum.
3. Most of the effects are dentoalveolar.
Class 3 twin-blocks
1. Not commonly used
2. In this case, the mechanism is a reversal of the conventional orientation of
interlocking blocks used to posture the mandible forward in class 2 cases.
3. Most of the effects are dentoalveolar.
IV. Myofunctional appliances for treatment of Class II
1. Lip bumper
2. The Andresen appliance (or activator)
3. The Bionator
4. Harvold appliance
5. The Palatal and Labial Medium Opening Activators (MOA)
6. The Frankel appliance
7. The Intrusive Myofunctional Appliances
8. Teuscher appliance
9. Hybrid appliance
10.Mini-block appliance
11.Twin-block type appliances

12.Fixed twin block
13.The Herbst appliance
14.The Dynamax appliance
15.The AdvanSync appliance
16.Fixed magnetic appliance
In details
The Andresen appliance (or activator)
The activator was popularized by the publication of Andresen in 1936. It is a
loose appliance.
A. Mode of action:
 It is loosely fitting act as an exercise appliance resulting in passive tension of
the muscle and moderately displaces the mandible forwards (passive tooth
borne)
 Moderately bite opening (Myodynamic) <5mm
B. Indications: Useful in mild to moderately severe class II cases with no
crowding
C. Instruction for Use: The patient is
instructed to wear the appliance
for 10-12 hours in every 24: this
will be at night with 2-4 hours'
wear in the evening
D. Design:
 Upper labial bow.
 Upper and lower baseplates sealed together.
 The acrylic caps the lower incisor edges to prevent them from over erupting
 In the upper arch these slope guided the teeth distally and buccally as they
erupt with the oppositein the lower arch.

 It is possible to reactivate the first appliance by trimming it away from the
lower teeth so that wax can be added to register the more advanced position
of the mandible.
E. Advantage of Andresen over TB (Bennet 2001)
1. Robust
2. Simple and cheap
3. Part time wear cause less dental effect and more skeletal
4. Easy to wear because not complicated and only 2-4mm opening of the bite
5. No lateral OB because eruption is allowable during its use and there is no
intrusive force on the postteeth, so less time for transient or supportive stage
The Bionator
A. History:
 Advocated by Balter Bionator 1950.
 This appliance is derived from Andresen's activator
but is greatly reduced in bulk.
 Although it has generally been neglected outside
Germany.
B. Mode of action:
 Looseappliance (passive tooth borne)
 Moderately displaces the mandible forwards & moderately bite opening
(Myodynamic) <5mm
C. Indication:
 Useful in mild to moderately severe class 2 cases with no crowding.
D. Instruction for Use:
 Worn full time apart from during meals and sports.
E. Design
Similar to the activator except:

 The palatal acrylic coverage is replaced by palatal loop 1.25mm to encourage
a forward postureof the tongue and mandible.
 Upper posterior teeth occlusal coverage while the lower are free to erupt
except the LLS which are capped.
 The vestibular bow 0.9mm contacts the upper incisors but is clear of the
buccalteeth by 2-3 mm to allow expansion.
F. Evidences
 The study by Tulloch et al 1997 (class II D1 OJ 7mm, HG, Bionator or CG for 15
months) concluded that the bionator produced some mandibular change, whereas,
with the headgear, there was some maxillary restraint. In the TG (HG or Bionator)
the improvement in the ANB in 70-80% while no improvement in 20%. In the CG
no improvement 50%, improvement 30% and worsening 20%.
 Then Tulloch 1998 followed the patient and found that skeletal improvement is
lost after 1 year.
 Keeling et al 1998 (HG/Biteplane, Bionator, CG, OJ 7mm for 2 years or until
class I achieved) suggested that a headgear biteplane combination resulted in no
restraint of the maxilla but forward positioning of the mandible while bionator
resulted in some mandibular growth that lost after 1 year follow up.
Harvold appliance
A. History: The Harvold appliance is
derived from the activator of Andresen.
It is similar to MOA except the amount
of opening is more.
B. Mode of action:
 The mandible is advanced a few millimetres less than the maximum the
patient can achieve.

 It is opened to give an interocclusal clearance of 10-20 mm measured at the
premolars. This is a myotonic appliance
C. Indication: Useful in mild to moderately severe class 2 cases with no
crowding and deep anterior bite due to deep COS.
D. Instruction for Use: 24h except meal time
E. Design:
 The upper labial bow
 Upper occlusal coverage
 Adam on U6 and U4
 Lower incisor capping
Medium Opening Activators (MOA)
A. Mode of action:
 Moderately displaces the mandible
forwards
 Moderately bite opening (Myodynamic)
<5mm
Indication: Useful in mild to moderately severe
class 2 cases with no crowding and deep anterior
bite due to deep COS.
B. Instruction for Use: 24h except meal time.
C. Design:
 The upper labial bow
 Upper occlusal coverage
 There are Adams cribs and occlusal rests present on the upper first
permanent molars and first premolars.
 Lower incisor capping

The Frankelappliance
A. History : This appliance, named after its
originator, Rolf Frankel of East Germany,
B. One of its advatages is using it in a mixed
dentition.
C. Mode of action &Design:
 It is a myodynamic loose tissue born
appliance, so it activate the lateral
pterygoid muscle.
 Frankel termed it a function regulator (FR) because it is intended to correct
functional anomalies in the circumoral musculature, which he holds
responsible for crowding and other aspects of malocclusion
 The buccalshields extend to produces 'periosteal stretch ‘and the teeth are
free of muscular pressures on the buccalbut not on the lingual surfaces.
 The lip pads (Pelotte wire) are also intended to
a. Produceperiosteal stretch
b. Alter and controllower lip activity,
c. The lip pads eliminate any trapping of the lower lip behind the upper incisors.
d. When the lip is displaced by the lip pad, it will force the appliance posteriorly
causing some headgear effect.
 The lingual pad contacts the alveolar mucosa on the lingual surface of the
mandibular alveolar process,butit is clear of the teeth. Thus a forward
mandibular postureis induced without any protrusive force on the lower
incisors.
D. Indication
1. Frankel 1a – Class 1
2. Frankel 1b – Mild Class 2/1

3. Frankel 1c – Moderate Class 2/1
4. Frankel 2 – Class 2/2
5. Frankel 3 – Class 3
6. Frankel 4 - AOB
E. Instruction for Use: the patient should wear it full time, except for meals and
sport
 The study by Ghafari et al 1998 suggested that headgear produces some
maxillary restraint and the Fränkel, mandibular growth increase.
Hybrid functional
 Used in the orthopaedic management of occlusal canting in growing patients
(Vig and Vig 1986).
 It consists of acrylic block at the side of overgrowth and no block at the
undergrowth site to allow differential eruption of the teeth at the
underdeveloped site.
 There is a buccal shield same like the one use in Frankle appliance to allow
arch expansion.
Lip bumper
A. Design:
 This is a functional component,
occasionally used in conjunction with a
lower fixed appliance.
B. Indication:
 The lip bumper can occasionally be useful
in Class 11, division 1 with lip trap interference.
 Distalization of lower molars
 Reinforce lower posterior teeth

 IO to avoid loss of spaceafter premature loss of primary teeth.
C. Mode of action
 Change in muscle balance
 Periosteal stretching.
The Dynamax appliance
Advantages
1. Little patient compliant.
2. No need for a postured bite
3. Incremental mandibular
advancement.
4. It can be used with fixed
appliance.
5. Minimal mouth opening - which may increase patient acceptance, especially
in high angle cases with less (the 'goldfish' look).
6. Upper incisor inclination is controlled by torque spring
7. Extra oral traction may be added.
8. Conversely, the posterior occlusal capping helps controlmolar eruption in
cases with reduced overbite. The aims of the postcapping are to
 Disoccluding the teeth,
 Allow even distribution of the HG force
 Prevent and intrude U postteeth.
9. Dynamx show better control of vertical height and insignificant less relapse
than TB (Lee 2007)
10.Little LLS proclination because the appliance works by avoidance's reflex
theory which might cause little LLS proclination.(Myodynamic passive tooth
borne appliance).
Disadvantages

 It has higher failure rate than TB (two times more failure rate).
Thiruvenkatachari, 2010.
 As well as more difficult to construct.
The Herbst appliance
A. History: It was first described by Dr. Herbst and popularized by Pancherz
1979.
B. Design:
 Fixed functional.
 Bands on upper and lower 6’s and 4’s.
 Palatal bar and lingual bar.
 Telescopic arms form upper 6’s to lower 4’s.
C. Advantages
According to O'Brien study in 2009, Herbst was superior to Twin Block when
we measured:
 Speech interference.
 Disturbance of sleep.
 Influencing schoolwork.
 Feelings of embarrassment.
 Better success rate than Twin Block.
 It can be used with fixed appliance. Recently a Flip-Lock Herbst
assembly with the 'male' attachments welded to rectangular tubing, which
is slid over a rectangular archwire. This mechanism is very simple to
install and to date is encouragingly robust.

D. Disadvantages
1. Expensive.
2. Breaks more significant and mechanical failure of piston assemblies.
3. Cement problem.
4. Removal difficulty.
5. Enamel decalcification.
6. Recommended in the permanent dentition only
7. If joined with FA treatment, it should use when full arch SS in use.
8. Inability to incorporate arch expansion during the functional phase
9. Do not grow mandibles and in contrast to others, there is evidence of
sufficient satisfaction with other simpler functional - in particular the twin-
block.
10.More lower incisor proclination
E. Indications
a. Dental Class II malocclusion.
b. Skeletal Class II mandibular deficiency.
c. Deep bite with retroclined mandibular incisors.
d. Pancherz (1995) also recommends its use in post-adolescentpatients, mouth-
breathers, uncooperative patients, and those that do not respond to removable
functional appliances
F. Contra-indications

a. Cases predisposed to root resorption.
b. Dental and skeletal open bites.
c. Vertical growth with high maxillomandibular plane angle and excess lower
facial height.
G. Effects of the Herbst Appliance
1. Restraining effect on maxillary growth
2. A stimulating effect on mandibular growth. The long-term effect on
mandibular growth is uncertain and may only have a short-term effect on
skeletal growth pattern (Pancherz and Fackel, 1990).
3. Dento-alveolar changes include lower incisor proclination, upper incisor
retroclination, lower posterior teeth mesialization and maxillary molar
distalization and intrustion. The changes are similar to those produced by high
pull headgear (Pancherz and Anehus-Pancherz, 1993).
4. Vertically, the overbite is reduced. This occurs by intrusion of lower incisors
and enhanced eruption of lower molars (Pancherz, 1995)
5. Hansen et al. (1990) found that the appliance did not have any adverse effects
on the temporomandibular joint (TMJ).
The AdvanSync appliance
A. History: Developed by Terry Dischinger in 2008

B. Design:
 This molar-to-molar fixed functional assembly
 The name of the appliance therefore reflects that the mandible can be postured
forward synchronously with the start of all the other fixed appliance tooth
movements.
 The appliance requires no laboratory work
 Molar band separation at one visit permits selection and cementation of the
molar attachments at the next visit.
 The telescoping arms have a long range of action and permit good lateral
excursion and are very easily advanced either by means of the alternative
screw position on the lower molars or via C rings which are crimped over the
pistons.
The Intrusive Myofunctional Appliances
As Tulloch points out, there is a widespread belief that children who grow
vertically will respond less well to class 2 treatment, but this is not well
documented or understood. The study by Ruf and Pancherz (1997) found no
evidence to support this view. The “hyperdivergent” cases in fact showed 1
mm. better mandibular response than the “hypodivergent” cases although this
was not statistically significant. This evidence suggests that ‘high angle’ cases
are no reason to avoid functional appliances because of the potential effects on
growth.
These appliances will be discussed below:
1. The BuccalIntrusion Splint (BIS)
 This appliance consists of an acrylic palatal baseplate which is clear of the
upper anterior teeth and with occlusal capping on the teeth in occlusion.

 There are double Adams cribs present on the upper first permanent molars
and second premolars and molar tubes embedded in the occlusal capping
acrylic to accept a Kloehn facebow near the area of maxillary rotation
(premolar area).
 There is a midline screw present in the palatal acrylic.
 This appliance is used to treat skeletal anterior open bites by intrusion of
the upper buccalsegment teeth.
2. The Maxillary Intrusion Splint (MIS)
• This appliance consists of an acrylic baseplate which extends over the occlusal
surfaces of all teeth and onto the incisal surfaces of the upper anterior teeth.
• There are Adams cribs present on the upper first permanent molars and first
premolars, along with a Southend clasp on the upper central incisors.
• There are headgear tubes present within the molar capping
• This appliance is designed to be used for patients with a Class II division 1
malocclusion and a "gummy smile" with an overjet of 6 to 8mm. .
3. The Maxillary Intrusion Splint and LowerTraction Plate (CONCORDE)
• This is a two part appliance which consists of a maxillary intrusion splint as
described above along with a lower appliance.
• The lower appliance consists of an acrylic baseplate with no occlusal or incisor
capping. There are double Adams cribs present on the lower first permanent
molars and second premolars, and a semi-fitted labial bow on the lower
incisors.
• There is a lingual hook on the lingual aspect of the acrylic baseplate to enable
elastics to be attached to the midpoint of the facebow.

• The selection criteria are the same as for the maxillary intrusion splint but
these combined appliances work more effectively at reducing overjet between
9 to 18mm than the maxillary intrusion splint alone.
• This appliance combination can also be used for the treatment of a severe
Class II division 1 malocclusion with a "gummy smile" and an average face
height.
4. The Intrusive Activator
a. The Van Beek appliance
 Described by Pfeiffer (1972).
 It consists of a simplified short outer arm
facebow embedded in the acrylic part of the
activator (Myotonic functional appliance)
 There is full palatal coverage and fully
extended lingual flanges
 There is no buccalchannel
 300 gms of force/12 hours a day
b. Teuscher appliance
 Teuscher (1978)
 Basically it is an activator with two
significant design features - torquing spurs
on the upper incisors to prevent retroclination and headgear to produce
more vertical controland anterior restraint on the maxilla
 There advancement of 6mm maximum and minimal bite opening
 Indicated in high angle class II D1
Newportappliance: same as TB

Mandibular anterior repositioning appliance (MARA): New fixed functional
appliance (Rondeau 2002, Pangrazio-Kulbersh et al 2003) consists of metal
modules fixed to both first upper molars at right angles to the occlusal plane,
and pairs of abutments fixed to the lower molars, which make contact when the
jaw is closed, thus rendering it impossible for the patient to bring the dental
arches into contact in the distal bite position. Only through active protrusion of
the mandible can the modules and abutments be manoeuvred past each other to
allow complete jaw closure. The appliance is normally fixed by means of
orthodontic bands or temporary crowns, with the wires being guided into a
small, welded-on square profile
tube and slight reactivation being achieved by fitting spacers. Ligatures on the
metal bows prevent them from slipping out. This appliance can thus be regarded
overall as a training device aimed at encouraging the patient to adopt an anterior
mandibular position.( Kinzinger 2002)
Fig 1 Intra Oral view of MARA, Pangrazio-Kulbersh et al 2003
Pangrazio-Kulbersh et al (2003) MARA positions the mandible forward into a
Class I occlusion. The results of the study showed that the MARA produced
measurable treatment effects on the skeletal and dental elements of the
craniofacial complex. These effects included a considerable distalisation of the
maxillary molar, a measurable forward movement of the mandibular molar and
incisor, a significant increase in mandibular length, and an increase in posterior
face height (Fig 2). The effects of the MARA treatment were then compared
with those of the Herbst and Fränkel appliances. The treatment results of the
MARA were very similar to those produced by the Herbst appliance but with

less headgear effect on the maxilla and less mandibular incisor proclination than
observed in the Herbst treatment group
Fig 2 Skeletal and dental changes by MARA, Pangrazio-Kulbersh et al 2003
A fixed magnetic appliance
 Described by McNamara 1998,
 This appliance presents a promising mode of improving facial harmony in
patients with Class II, Division 1 malocclusion associated with mandibular
retrusion, increased lower facial height, and increased interlabial gap.
 Further research and development of the appliance are advocated.

 It is useful in high angle caseas the condyle is displaced inferiorly resulting
in increase in the PFH and improving of the MMPA angle.
 A fixed magnetic appliance was designed that hinged the mandible open and
exerted an intrusive force on the teeth. Treatment with this appliance resulted
in:
1. An increase in length of the mandible
2. Intrusion of teeth
3. Upward and forward autorotation of the mandible
4. Creation of temporary buccalcrossbitecaused by the shearing force of
repelling magnets
Miniblock appliance
A. Design:
Same as TB but with
1. Reduced height of block with 90 degree angulation of the step.
2. Gradual advancement 3mm
3. Incisor torque spurs.
B. Advantages:
1. The idea is that gradual advancement will activate lateral pterygoid
muscle, this will achieve better growth.
2. The reduced the visco-elastic force on the teeth by gradual advancement
will cause less teeth inclination.
3. Reduction in the block height will cause the reactive force vector to pass
close to the centre of resistance of maxilla so it cause less rotation of maxillary
plane and then less increase in the facial height.
4. The benefit of the incisor torque spur is controlling of incisor inclination
C. Evidences

 Two reports of a RCT study (Shrarme and Le, 2002, Gill & Lee 2002)
compared the hard and soft tissue effects of a conventional twin-block with a
single large advancement and a modified twin-block named the Mini block.
The only differences of significance were that the conventional Twin-block
retroclined the upper incisors a little more and advanced hard and soft tissue
Pogonion approximately 2mm more on average. Lower incisor proclination
was very similar.
Fixed twin block
A. History: Developed by Mike Read (2001).
B. Advantages
 Robustness and possibly patient comfort
 Because the two halves of the appliance are not permanently linked together,
the problems of leverage on the fixation points does not arise during
mandibular excursion in contrast to Herbest appliance.
 Integration of FA is easy from the start
 No lateral open bite.
C. Disadvantages
• OH problems and decalcification
• Need for lower premolar bands to remain securely cemented.
• Not quick and easy for all clinicians to make, fit and adjust as well as
robustness.
• Need technical development and extra experience are continually bringing
improvements.
Twin-block appliances

a. History of TB
• These appliances were originally described by William Clark (1982).
• Survey in UK by Chadwick 1998, 75% of orthodontist are using TB.
b. Indications of TB
1. Cooperative
2. Good OH
3. Class 2 with deep OB with minimal dental compensation
4. Growing patient. Recent prospectivestudies have found that stage of maturity
of the cervical spine did not influence outcome, O’Brien 2003. The same
result by Trenouth and Desmond 2012 who showed that there is no
correlation between the age and the skeletal effect of TB.
c. Advantage of TB
Harradine and Gale (2000) and Morris et al. (1998)
1. Robust
2. Easy to repair
3. Easy to activate.
4. Relatively well tolerated by the patient becauseit is two pieces that is not
interfering with function.
5. Expansion is easy by a midline screw
6. Incorporation of auxiliary and headgear is easy.
7. Suitable for mixed or permanent dentition.
d. Disadvantage ofTB
1. Require skilled technician
2. Failure rate of 33% (O’Brien)

3. Poorretention of LRA because of shallow inter-proximal dental
undercut in a younger age group.
4. AP change too rapid: This would result in posterior open bites.
5. Teeth tilt excessively: lower incisor proclination and upper incisor
Retroclination
6. It increase the VH which make it worse in high angle cases
7. Short term skeletal effect
e. Design
A. The original design
1. U6s, U4s & L4s delta clasps.
2. labial bow,
3. Ball end clap between lower incisors.
4. 45 degree blocks it made from hot acrylic.
5. HG tube.
6. Anchorage
The anchorage component of the TB comes from
 AP from reciprocal anchorage of the block as well as HG if it is added
 Transversely from reciprocal anchorage around the screw
B. The modified design by Clark in 2010
1. Delta clasps on U4, U6,L4 (Delta clasp is preferable becauseit will not
open by insertion and removal)
2. No labial arch because the ULS will retraction by the effect of lower lip.
3. Ball end clasp mesial to L3s
4. Midline screw
5. Inclined bite plane of 70-75 with 7-8mm thickness the cover up to half
of lower 5. The reason for this is to prevent interference with clasping of

lower premolars and to allow potential grinding of upper block with
sufficient acrylic remaining as a ramp to supportposturing.
6. Interincisal opening in deep bite case should be 2mm and in high angle
case should be 5mm to controllower posterior teeth eruption.
7. Lowe lingual flange extend posteriorly to L6 and L7 for better
anchorage
C. Currently favoured designfeatures
A national UK survey in 2000 by Spicer in Bristol discovered that the
following was the most popular.
1. URA: Cribs on the 4&6, A labial bow, Midline screw, Blocks on
4,5,6,
2. LRA: cribs on 4&6, incisor capping, blocks on 4,5. at a steep angle
of 70 degrees to the occlusal plane and should be mesial to the lower 6,
permitting removal of the lower molar crib and grinding of the upper
block if accelerated eruption of these teeth is required.
D. Labial arch
1. In order to maximize the TB effects it is better to include the
upper buccal teeth only (without labial bow) and to involve all lower
postteeth. So, the result would be distalising the upper postteeth while
the ULS will be moved by the effect of lower lip and the traction of the
transeptal fibres following U buccalteeth movement (Lee et al 2005).
2. Qureshi 2007 found that the use of labial bow increase LLS
proclination and more mandibular growth.
3. A recent RCT had shown that the presence or absence of a labial
bow had no effect on maxillary incisor retraction or skeletal change.
Yaqoob O, DiBiase 2011 . Compliance may well be improved by an
absence of upper labial wirework.

4. Sometime lower labial arch can be added if the LLS are spaced.
E. Posteriorattachments
Additional headgear produced more maxillary restraint and less rebound force
on the lower teeth which lead to reduce lower incisor proclination. Parkin et al
(2001).
The purposeof this study was to compare the skeletal and dental changes
contributing to Class II correction with 2 modifications of the Twin-block
appliance: Twin-block appliances that use a labial bow (TB1) and Twin-block
appliances that incorporate high-pull headgear and torquing spurs on the
maxillary central incisors (TB2). After pretreatment equivalence was established,
a total of 36 consecutively treated patients with the TB1 modification were
compared with 27 patients treated with the TB2 modification. Both samples
were treated in the same hospital department and the same technician made all
the appliances. The cephalostat, digitizing package, and statistical methods were
common to both groups. The results demonstrated that the addition of headgear
to the appliance resulted in effective vertical and sagittal controlof the maxillary
complex and thus maximized the Class II skeletal correction in the TB2 sample.
Use of the torquing springs resulted in less retroclination of the maxillary
incisors in the TB2 sample when compared with the TB1 sample; however, this
difference did not reach the level of statistical significance
Indications for concurrent headgearwith functional appliances:-
1. Maxilla is very prominent
2. Proclined LLS.
3. Long face/'high angle' case
F. Anterior attachments

1. Addition of double cantilever Z spring or anterior screw with
torqueing spring to deal with class II D2. The bite registration is taken
with the buccal segment relationship in an over corrected position, this
may result in an edge-to-edge incisor position or a slight reversed
overjet. However, by ensuring that there is 7–8 mm of separation in the
buccalsegments, there should be no incisal interference as the upper
labial segment is proclined. It is also essential to have sufficient height
of the blocks to ensure that the patient is more comfortable posturing
forwards than closing in centric relation (Dyer and Sandler 2002). The
advantages of this technique are:
 As advancement of the upper labial segment occurs simultaneously with
sagittal correction the patient should never have an increased overjet
placing them at risk of trauma due to prominent upper incisors.
 This technique also prevents patients being left with an increased overjet
if they fail to comply with the functional phase following upper incisor
proclination.
 Theoretically increase the upper posterior teeth distalization and reduce
the LLS proclination because of the altered anchorage balance.
2. Addition of southern end clasp to the upper and lower incisors
will enhance the skeletal effect and reduce upper incisor retroclination
and lower incisor proclination (Trenouth and Desmond, 2012). The
Southern end clasp was originated by DiBiase and Leavis. It locks the
tooth surface against the acrylic base plate providing greater control
over the axial inclinations of the incisors. The design is similar to the
original Jackson clasp. But it has a problem when expansion by midline
screw is wanted.
3. Acrylic capping of the lower incisors is commonly practiced, but
this has been shown to be ineffectual in preventing proclination Young
& Harrisson 2005 but it might cause demineralization (Dixon, 2005).

4. Flapper spring can be added similar to Southern end clasp and
result in resulted in less retroclination of the maxillary incisors, Parkin
2001
5. Torquing spring: the claimed advantages are to control
retroclination of ULS. The positive effect of the torquing spring had
been proved by Harridine and Gale in 2000.
f. Advancement
 It can be activated in asymmetrical way to correct ML deviation
 One go or incremental advancement of functional appliances?
This was recommended by Petrovic 1975 and Rabie et al 2003. The
theoretical purposes of incremental advancement:
1. Repeated stimulation of lateral pterygoid resulting in more mandibular growth.
If the appliance is stretched as one go then the advantages of lateral pterygoid
will be lost.
2. Less dentoalveolar effect.
3. Better patient compliance.
 RCT compared the effects of twin-block treatment with a single advancement
to an edge-to-edge bite and the incremental advancement (Banks et al 2004).
This excellent paper by the developer of this particular incremental mechanism
clearly showed no advantage for the incremental method in terms of process or
outcome of the treatment.

g. Clinical tips
1. It is recommended to trim the acrylic palatal to ULS to allow spontaneous
alignment by the lower lip and the stretch of transeptal fiber.
2. Always check the difference between OJ and reverse OJ since the difference
is fixed and this is a good landmark of the treatment progress
h. Effectiveness ofthe Twin-block appliance comparedto normal
1. Lund & Sandler 1998: This prospective controlled study investigated the
net effects of the Twin Block functional appliance taking into account
the effects of normal growth in an untreated controlgroup. statistically
significant restraint in the maxillary growth was observed. Forward
growth of the mandible. Dentoalveolar effect as usual.
2. O’Brien 2003 9TB, CG, OJ 7mm, 8-10years) 73% dentoalveolar and 27%
skeletal)
i. Profile changes:
O’ Brien 2009 did a study to compare the effect of TB on the facial profile using
silhounte tracing for treated and untreated patient who had been rated by their
peers and teachers and found that children with Class II malocclusion, treated
with Twin-blocks in the mixed dentition, had profiles that were generally
perceived as more attractive than those of an untreated cohort, by bothpeers and
teachers. However, these differences were small.
j. Psychosocialbenefits of early orthodontic treatment with the Twin-
block appliance
O’Brien 2003 RCT study Results showed that early treatment with Twin-
block appliances resulted in an increase in self-concept and a reduction of
negative social experiences.

FAQ about functional appliance
I. Treatment duration
Treatment should continue for at least 12 months to allow intermediate collage
fibres (type 3) to change to more stable one (type 1) (McNamara 1990 &
Voudouris 2003)
II. Advantages of two stage treatment with the functional appliance
King 1990
1. Better cooperation. (True, O’Brien 2003, 2009 with regard to TB treatment
early treatment 18% failure but late 33%)
2. Psychosocialadvantages (true O’Brien 2003)
3. Elimination of gingival/palatal trauma. Questionable?
4. High trauma with increased overjets >9mm (Todd & Dodd 1983) (45% 10 yr
olds with OJ more than 9mm have traumatised incisors compared to 27% if the
OJ was less than 9mm especially if the lip is incompetent) however RCT
comparing early versus late treatment concluded:
 all groups experienced trauma
 very early treatment may prevent trauma but not costeffective (Koroluk et al
2003)
 So that, the provision of a mouthguard is recommended to try to prevent
trauma for patients with an increased risk of trauma (contact sports, large OJ).
 Latest Cochrane review confirm the trauma prevention benefit.
5. Eliminate growth/local disturbances before they have had time to act fully.
Questionable?
6. Craniofacial tissues more malleable so more favourable changes in skeletal
and dental relationship achieved but may not be clinically significant. (true for
short term, Tulloch, 2004, Kelling, 2008, O’Brien 2003)
7. Less root resorption than one phase (Brin 2003 use the data of UNC and prove
that)

III. Advantages of one stage treatment with the functional appliance
1. Better teeth clasping
2. Little cost
3. Growth still present
4. Less risk of burning patient co-operation. Patient has time expiry
approximately 3yrs which can be lost in the first phase leaving no compliance
in the second phase.
5. Soft tissues do not mature until 12-14yrs with vertical growth of lips this might
affects stability of corrected OJ
6. Extraction decision is easy and less 50% less than two phase treatment
(Tulloch 2004)
7. Better final occlusion (O’Brien, 2009)
8. No difference from early treatment in term of skeletal, dental and
psychological results (Tulloch 2004, O’Brien 2009, Dolce 2007, Harrison,
2007)
IV. Stability of myofunctional appliances results
• Maxillary changes more stable than mandibular changes.(Weislander, 1993)
• Mandibular skeletal changes all lost after 2 years. Tulloch et al 2004
• 58% dental relapse (Pancherz, 1991)
• Good buccal interdigitation reduces dental relapse (Pancherz and Fackel, 1990)
and (Tulloch et al., 1990)
V. SAQs
How long TB should be?
At least 1 year to allow remodelling of fossaand
the intermediate fiber to be be changed to type 10
stable fiber (Lee 2013) because in the beginning
the dominant fiber are type II (Rabie 1979) which

resulted from activation of lateral pterygoid
muscle.
What factor which
normally influences
extraction decisions
should not apply at the
end of functional
appliance treatment?
The overjet should be fully reduced and no longer a
factor.
What additional factors
will probably be present
which were not present
at the start of functional
treatment?
a) Upper incisor retroclination
b) Lower incisor proclination
c) Distal tipping of other upper teeth
d) Differential growth of the jaws during the
functional phase
How exactly would you
assess the factors in
question 3?
A cephalometric radiograph to measure all these
factors.
How are these factors in
question 3 likely to
influence your treatment
from the end of the
functional phase?
2a,b,c, will influence towards extraction or a more
anchorage-providing extraction pattern or
headgear. 2d is related and may reveal that overjet
correction has been largely due to favourable
growth as opposed to lower incisor proclination
and that extractions are less indicated.
What twin-block design
features would you
specificallychoose in a
patient with an anterior
open bite?
Avoid any acrylic or wirework which prevented
eruption of the incisors. no torquing spurs on the
upper incisors and no acrylic or ball-clasps on the
lowers
High-pull headgear.
Spinner or passive tongue thrust breaker

NB: As Tulloch 1998 points out, there is a
widespread belief that children who grow vertically
will respond less well to class 2 treatment, but this
is not well documented or understood. The study
by Ruf and Pancherz (1997) found no evidence to
supportthis view. The “hyperdivergent” cases in
fact showed 1 mm. better mandibular responsethan
the “hypodivergent” cases although this was not
statistically significant. This evidence suggests that
‘high angle’ cases are no reason to avoid functional
appliances because of the potential effects on
growth
features would you
patient with upright
upper incisors (not
proclined)?
You would probably opt for torquing spurs to
minimise further retroclination of the upper
incisors.
features would you
patient in the early
mixed dentition?
In the absenceof premolars to crib, you might well
opt for features giving more retention on the
incisors such as upper torquing spurs or even
Southend clasps and lower ball-clasps +/- acrylic
capping.
features would you
patient with a very deep
overbite?
Wirework to impede further eruption of the upper
incisors would be sensible such as torquing spurs
and in the lower appliance, incisor capping
An absence or early removal of molar cribs in
order to permit eruption of the molars to level the

curve of Spee at an earlier stage.
Aust Orthod J. 2012 Nov;28(2):190-6.
An investigation of cephalometric and morphological
predictors of successful twin block therapy.
Fleming PS1
, Qureshi U, Pandis N, DiBiase A, Lee RT.
Author information
Abstract
OBJECTIVE:
To identify predictors of overjet reduction, changes in mandibular length (Co-Me) and antero-posterior
changes in mandibular position (Pog-Vert) during Twin Block therapy.
METHODS:
Pre- and post-treatment cephalograms of 131 participants were analysed (Mean age 12.73 years +/-
1) following Twin Block therapy.
RESULTS:
Mean annualised overjet reduction was 7.29 mm (+/- 2.99) with chin projection improving by 2.66 mm
(+/- 5.37). The magnitude of the initial overjet was a strong predictor (95% CI: 0.30, 0.77, p < 0.01) of
overjet reduction and change in chin position (95% CI: 0.08, 0.77, p = 0.02). Greater forward
movement of Pogonion occurred if there was greater retrusion of Pogonion at the outset (95% CI:
0.15, 0.45, p < 0.01). No prognostic relationship was noted for other potential cephalometric
predictors including pretreatment mandibular lower border morphology and Co-Go-Me angle.
CONCLUSION:
No relationship between mandibular morphology, vertical skeletal pattern and favourable
dentoalveolar and skeletal responses to Twin Block therapy could be found. These results require
confirmation on an external sample.
Eur J Orthod. 2013 Jan 4. [Epub ahead of print]
An extended period of functional appliance therapy: a
controlled clinical trial comparing the Twin Block and
Dynamax appliances.
Lee RT1
, Barnes E, Dibiase A, Govender R, Qureshi U.

Author information
Abstract
SUMMARYThe aim of this clinical trial was to compare the hard- and soft-tissue effects of 15 month
full-time functional appliance therapy with Twin Block (TB) and Dynamax (Dx) appliances. The effects
on both hard and soft tissue were analysed using cephalograms and three-dimensional optical
surface laser scans. One hundred and three subjects with a class II division 1 malocclusion, and a
minimum overjet of 7mm were available for analysis following stratified randomization according to
gender and age. Data was collected at the start of treatment, 15 month therapy, and after 3 month
post-treatment observation. Statistical analysis was conducted using analysis of covariance. The
results demonstrated both appliances corrected the overjet with significantly increased skeletal
dimensional changes with the TB compared with the Dx with forward movement of pogonion of
5.2mm (TB) and 0.7mm (Dx) P = 0.003. In addition, significant changes occurred particularly in the
vertical dimension where there was also an increase in total anterior face height in both groups (TB =
6.4mm, Dx = 5.5mm) and significant (P = 0.003) mandibular length changes were also observed (TB
= 7.2mm, Dx = 3.8mm). The cephalometric soft-tissue changes were significantly different between
the two appliances at soft-tissue pogonion (TB = 9.8mm, Dx = 4.6mm, P = 0.001). Laser scan three-
dimansional changes showed significant difference in the lower labial sulcus region where forward
movements were observed (TB = 8.2mm, Dx = 6.2mm; P = 0.04). Overall these changes appear to be
greater and more stable than those achieved in a previous 9 month study.
Review/ Effects as determined by clinical studies
Jakobsson (1967). Cephalometricevaluationof treatmenteffectonClassII,Division1malocclusions.
The purpose of the study was to evaluate the treatment effect on Class II, Division 1 malocclusions
when the patients were treated with either activator or headgear therapy and to compare the two
methods. The sample consisted of 33 boys and 27 girls, aged 8 to 9 years (mean 8.5 years). All
children had Class II div 1 malocclusions. Patients were divided into 20 triples according to dental
developmental age and morphology of malocclusion. It was decided by lot which patients in the
triple were to receive treatment and which were to serve as a control. All patients were reassessed
at 18 months. Cephalogram superimpositions of pre- and post-treatment were used to assess
treatment changes within each triple. Both activator and headgear treatment had, in a posterior
direction, a definite influence on the basal parts of the maxilla. During treatment there was an
increase in the anterior facial height and, to a lesser extent, a descent of the condyle. It was
concluded that the findings do not agree with the hypotheses that condylar growth and a forward
positionof the mandible canbe obtainedwithactivatortreatment.
Tulloch, Phillips and Proffit (1998). Benefit of early Class II treatment: progress report of a
two-phase randomized clinical trial:

Preadolescent children (OJ> 7 mm) were randomly assigned to observation only, headgear
(combination), or functional appliance (modified bionator) and were monitored for 15
months. 166 patients completed the first phase of the trial, 147 continued to a second
phase of treatment. The data from the first 107 patients to complete phase 2 form the basis
of this progress report. During phase 1, on average there was no change in the jaw
relationship of untreated children, but 5% showed considerable improvement and 15%
demonstrated worsening. Both early-treatment groups had a significant average reduction
in ANB angle, more by change in maxillary dimensions in the headgear group and
mandibular growth in the functional appliance group. There were wide variations in
response, however, with only 75% of the treated children showing favorable skeletal
response. Failure to respond favorably could not be explained by lack of cooperation alone.
On average, time in fixed appliances was shorter for children who underwent early
treatment, but the total treatment time was considerably longer if the early phase of
treatment was included. Only small differences were noted in anteroposterior jaw position
between the groups at the completion of treatment, and the changes in dental occlusion,
judged on the basis of Peer Assessment Rating scores, were similar between groups. Neither
the severity of the initial problem nor the duration of treatment was correlated with the
occlusal result. The number of patients who required extraction of permanent teeth was
greater in the early functional appliance group than in the headgear or control group. The
option of orthognathic surgery was presented more often in the cases of children who did
not undergo early treatment, but surgery was accepted or was still being considered almost
as frequently in the previous headgear group as in the controls, less often in the patients
previously treated with functional appliances.
Ghafari, Shofer, Jacobsson, Markowitz and Laster (1998). Headgear versus function
regulator in the early treatment of Class II, division 1 malocclusion: a randomized clinical
trial:
A prospective randomised clinical trial was conducted to evaluate the early treatment of
Class II, Division 1 malocclusion in prepubertal children. Facial and occlusal changes after
treatment with either a headgear or a Frankel function regulator are reported. Molar and
canine relationships, overjet, intermolar and intercanine distances were measured from
casts taken every 2 months, and mounted on a SAM II articulator. Cephalometric
radiographs were taken annually. The results indicate that both the headgear and function
regulator were effective in correcting the malocclusion. A common mode of action of these
appliances is the possibility to generate differential growth between the jaws. The extent
and nature of this effect, as well as other skeletal and occlusal responses differ. Treatment
in late childhood was as effective as that in midchildhood. This finding suggests that timing
of treatment in developing malocclusions may be optimal in the late mixed dentition, thus

avoiding a retention phase before a later stage of orthodontic treatment with fixed
appliances.
Keeling, Wheeler, King, Garvan, Cohen, Cabassa, McGorray and Taylor (1998).
Anteroposterior skeletal and dental changes after early Class II treatment with bionators
and headgear:
Anteroposterior cephalometric changes in children enrolled in a randomized controlled trial
of early treatment for Class II malocclusion were studied. Children, aged 9.6 +/- 0.8 years at
the start of study, were randomly assigned to control (n = 81), bionator (n = 78), and
headgear/biteplane (n = 90) treatments. Cephalograms were obtained initially, after Class I
molars were obtained or 2 years had elapsed, after an additional 6 months during which
treated subjects were randomized to retention or no retention and after a final 6 months
without appliances. Calibrated examiners, blinded to group, used Johnston's analysis to
measure anteroposterior cephalometric changes. Annual skeletal and dental changes during
treatment, retention, and follow-up, and overall, were determined. They found that both
bionator and head-gear treatments corrected Class II molar relationships, reduced overjets
and apical base discrepancies, and caused posterior maxillary tooth movement. The skeletal
changes, largely attributable to enhanced mandibular growth in both headgear and bionator
subjects, were stable a year after the end of treatment, but dental movements relapsed.
Cura and Sarac (1997). The effect of treatment with the Bass appliance on skeletal Class II
malocclusions: a cephalometric investigation:
The short-term effects of treatment with the Bass appliance by comparative evaluation of
treated and untreated skeletal Class II malocclusions were studied. 47 Class II, division 1
malocclusion cases were observed. Twenty-seven (14 girls, 13 boys) were treated with the
Bass appliance for an average of 6 months. The remaining 20 cases (6 girls, 14 boys) served
as a control. At the end of the 6 month treatment period the statistically significant
treatment changes could be summarized as follows: the sagittal skeletal relationship was
improved as a result of favourable growth responses in both the maxilla and the mandible.
The overjet was reduced and the molar relationship was corrected as a result of the
extended skeletal changes. Distal movement of the upper dentition was evident, with
unchanged inclination of the maxillary incisors. Both anterior and posterior facial heights
were increased without changes in the inclinations of the palatal and mandibular planes. No
significant dental movement was observed in the mandible.

Tulloch, Proffit and Phillips (1997). Influences on the outcome of early treatment for Class II
malocclusion:
In the first phase of a randomized clinical trial of early versus late Class II treatment,
statistically significant differences were observed between the treatment and observation
groups. However, there were wide variations in response. The change in jaw relationship
(categorized as the annualized reduction in ANB angle) was favorable or highly favorable in
76% of the headgear, 83% of the functional appliance, and 31% of control (observation only)
groups. The patient's initial skeletal severity, age/maturity at the outset of treatment,
growth pattern, and cooperation with treatment were examined as possible influences on
early growth modification treatment. Correlations between the annualized change in the
ANB angle and any of the possible influences were close to zero and not statistically
significant. It was concluded that there is little to be gained from precisely timing early
treatment to specific age/maturity markers and that a favorable reduction in Class II skeletal
problems can occur for patients in a broad range of skeletal severity and growth patterns.
Cooperation, measured as the number of hours of reported wear, or the clinical assessment
of compliance, explained little of the variation in treatment response. The wide variation in
growth seen in the untreated patients highlights the importance of well-controlled studies if
clinicians are to improve their ability to select children with the greatest chances of a
favorable treatment response.
Tulloch, Phillips, Koch and Proffit (1997). The effect of early intervention on skeletal pattern
in Class II malocclusion: a randomized clinical trial:
In this controlled clinical trial, patients in the mixed dentition with overjet > or = 7 mm were
randomly assigned to either early treatment with headgear, or modified bionator, or to
observation. All patients were observed for 15 months with no other appliances used during
this phase of the trial. The three groups, who were equivalent initially, experienced
statistically significant differences (p < 0.01) in skeletal change. There was considerable
variation in the pattern of change within all three groups, with about 80% of the treated
children responding favorably. Although patients in both early treatment groups had
approximately the same reduction in Class II severity, as reflected by change in the ANB
angle, the mechanism of this change was different. The headgear group showed restricted
forward movement of the maxilla, and the functional appliance group showed a greater
increase in mandibular length. The permanence of these skeletal changes and their impact
on the subsequent treatment remains to be evaluated.

Webster, Harkness and Herbison (1996). Associations between changes in selected facial
dimensions and the outcome of orthodontic treatment:
In children with Class II, Division I malocclusion who were treated with functional appliances,
the strength of the associations between the changes over 18 months in selected facial
dimensions and the success of orthodontic treatment as determined by the weighted Peer
Assessment Rating (PAR) were determined. Forty-two children, between 10 and 13 years of
age (mean age 11.6 years), were randomly assigned to either an untreated group (control)
or a group treated with either a Frankel function regulator or Harvold activator (treatment).
The outcome of treatment was assessed on study models and the craniofacial changes were
measured on lateral cephalometric radiographs. Correlation coefficients were then
calculated between the differences in the cephalometric variables over 18 months and the
differences in the PAR scores. In the treatment group, the effects of normal growth were
held constant by partial correlation. The partial used was the change in both stature and
weight. Significant positive partial correlations were found between the increases in total
anterior face height, posterior face height, S-Pg, and treatment success. Significant negative
partial correlations were found between downward movement of the maxilla and
mandibular body and lower anterior face height and treatment success. It is postulated that
these associations occurred mainly in response to the bite opening by the appliances.
Treatment success was also significantly associated with maxillary restriction, an increase in
the SNB angle and a reduction in the ANB angle. Changes in B point due to proclination of
the mandibular incisors were considered to be responsible for the two latter significant
associations. Although mandibular length increased significantly in the treatment group, as
compared with the control group, it was not significantly associated with treatment success.
Courtney, Harkness and Herbison (1996). Maxillary and cranial base changes during
treatment with functional appliances:
The purpose of this prospective study was to investigate the maxillary and the cranial base
changes after treatment with the Harvold activator and the Frankel function regulator
appliances. Forty-two children, who are 10 to 13 years old, with Class II, Division 1
malocclusions were matched in triads according to age and sex and randomly assigned to
either the control, Harvold activator, or Frankel function regulator group. Lateral
cephalometric radiographs were taken at the start of the study and 18 months later. Both
appliances reduced the overjet by tipping the maxillary incisors palatally and, as a
consequence, the length of the maxillary arch was reduced. The appliances had no effect on
either the horizontal or vertical position of the maxillary molars. Small, but statistically
significant, changes in the cranial base angle in the Frankel function regulator group were
attributed to relatively large changes at basion in several children, influencing the results
because of the small size of the sample. The appliances had no effect on the position of the
maxilla.

Nelson, Harkness and Herbison (1993). Mandibular changes during functional appliance
treatment:
The purpose of this prospective trial was to determine the changes in position and size of
the mandible in children treated with either the Frankel function regulator or Harvold
activator. Forty-two 10- to 13-year-old children with Class II, Division 1 malocclusions were
matched in triads according to age and sex and randomly assigned to either control, Frankel
function regulator, or Harvold activator groups. There were no statistically significant
differences between the groups at the beginning of the study. After 18 months, significant
increases in gonial angle and articulare-pogonion length in the Harvold group were
attributed to a change in the location of articulare because the condyles were positioned
downward and forward at the end of treatment. The main effects of both appliances were
to allow vertical development of the mandibular molars and increase the height of the face.
The Harvold appliance also proclined the lower incisors and increased mandibular arch
length. No evidence was found to support the view that either appliance was capable of
altering the size of the mandible.

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