Biomechanics of fixed functional appliances

BiomechanicsOf Fixed
Functional Appliances
www.indiandentalacademy.com

• Introduction
• Classification
• Indications
• Contraindications
• Design of Appliances
• Fixed v/s Removable: The Biology Of Functional Appliances
• Mechanics
• Conclusion
• Bibliography
CONTENTS

Intro ductio n
• Fixed functional appliances first appeared in the
early 1900s, when Emil Herbst in 1905 presented his
system at the Berlin International Dental Congress.
• This device was one of the early attempts to produce
mechanically a “jumping of the bite”; an idea that
had earlier been advocated by Kingsley, among others.

• Since then and up to the seventies, very little was
published on this appliance. It was at that time that
Hans Pancherz brought the subject back into
discussion with the publication of several articles on
the Herbst.
• It was only in the eighties that several systems
derived from Herbst’s work started to appear.

• A number of fixed functional appliances have gained
popularity in recent years to help achieve better
results.
• Talking about good results, it should be remembered
that successful treatment always begins with good
diagnosis for which an appropriate treatment plan is
formulated . This is followed by mechanotherapy in
order to attain the desired treatment objectives.

• In order that the latter part, viz. mechanotherapy
can be executed without any hitches it is essential
that a clinician be well versed with the biomechanics
of the appliance that he/she chooses to employ.
• Without this knowledge a clinician is akin to a
person who is ‘lost in a maze’. He knows the
‘entrance’ and the ‘exit’ but he just does not know
how to get there!

Classification

a) Removable functional appliances – Activator,
Frankel
b) Semi-fixed functional appliances - Denholtz,
Bass
c) Fixed functional appliances – Jasper Jumper,
Herbst,
MPAwww.indiandentalacademy.com

According to the force produced
(Jasperand McNamara, Am JOrthod 1995)
1) Appliances producing pushing force.
a) Temporarily fixed functional
appliances
Twin block.
b) Permanently fixed functional
appliances.
Herbst & its family.
Rick-a- nator.
MPA
Jasper jumper
Churro jumper
2) Appliances
producing pull
force
eg. Severable
Adjustable
Intermaxillary
Force (SAIF)
spring

Classification Of Fixed Functional
Appliances
1) Flexible fixed functional appliances.
eg. Jasper jumper
Churro jumper
2) Rigid fixed functional appliances
eg. Herbst appliance
3) Hybrid fixed functional appliances
eg. Eureka spring.

1. Herbst Appliance
2. Jasper Jumper
3. Mandibular Protraction Appliance (MPA)
4. Mandibular Advancing Repositioning Splint
(MARS) Appliance
5. Adjustable Bite Corrector
6. Churro Jumper
7. Eureka Spring
8. Rick-e –Nator
9. The Klapper Super Spring

10. Bite Fixer
11. Magnetic Telescopic Device
12. Amoric Torsion Coils
13. Scandee Tubular Jumper
14. Universal Bite Jumper
15. BioPedic Appliance
16. Mandibular Anterior Repositioning Appliance
17. Intraoral Snoring-Therapy (IST) Appliance
18. Ritto Appliance
19. Twin Force Bite Corrector

Indicatio ns
• It is used primarily in actively growing individuals
with favorable facial growth patterns.
• Cl . II skeletal pattern with mandibular deficiency
• Lack of vertical development in lower face height

• Cl. II molar relationship
• True deep over bite, with infraocclusion of the
posterior segments
• The mandibular incisor teeth should be positioned
upright over basal bone structures
• The maxillary and mandibular teeth should be well
aligned

Co ntraindicatio ns
• Non-growing individuals
• Cl . II skeletal pattern with maxillary excess
• Increased lower anterior face height

• Cl. I molar relationship
• Shallow over bite
• Pseudo deep bite due to supra eruption of the anterior
teeth (“Gummy” smile)
• Proclined mandibular anterior teeth
• Decreased overjet/ Retroclined maxillary anterior
teeth

Design Of TheAppliances
• Herbst Appliance
• Jasper Jumper
• Mandibular Protraction Appliance

Herbst Appliance
• The appliance can be compared to an artificial joint
working between the maxilla and the mandible.
• A bilateral telescope mechanism attached to
orthodontic bands keeps the mandible mechanically in
a continuous anterior jumped position

Each telescopic device consists of
1. A tube ( upper)
2. A plunger ( lower)
3. Two pivots
4. Two screws.
Plunger
Tube
Pivots
Screws

• The pivot for the tube is usually soldered to the
maxillary permanent first molar band, and the pivot
for the plunger to the mandibular first premolar band.
• The screws prevent the telescoping parts from slipping
off the pivots.

• The length of the tube determines the amount of bite
jumping.
• Usually the mandible is retained in an incisal end-to-
end relationship.

• The length of the plunger is kept at a maximum in
order to prevent it from slipping out of the tube when
the mouth is opened wide.
• If the plunger is too long, however, it may protrude
far behind the tube and injure the buccal mucosa
distal to the maxillary permanent first molar.

• The mechanism permits vertical opening movements
and, when properly constructed, also lateral
movements of the mandible.
• The pivot openings for the tube and plunger should be
wide enough to provide a loose fit of the telescoping
parts at their points of attachment. This increases the
lateral movement capacity of the lower jaw.

There are a number of modifications/ variations to the
original Herbst design, which would include the
following:
• Cast splint Herbst
• Stainless steel crown Herbst
• Acrylic splint herbst
• Cantilevered Bite Jumper
• MALU – Mandibular Advancement Locking Unit
• Flip-Lock Herbst Appliance
• Ventral Telescope

Jasper Jumper
The system is composed of two parts
• The Force Module and
• The Anchor Units.

The force module is constructed of a stainless
steel coil or spring that is attached at both ends to
stainless steel endcaps, in which holes have been
drilled in the flanges to accommodate the anchoring
unit.

• This module is surrounded by an opaque polyurethane
covering for hygiene and comfort. The modules are
available in seven lengths, ranging from 26 mm to 38
mm in 2 mm increments.

Anchor Units

Attachment to themain arch wire

Attachment To Auxiliary Arch Wires:
TheUseOf ''Outriggers''

•When the force module is straight, it remains
passive. As the teeth come into occlusion, the
spring of the force module is curved axially as
the muscles of mastication elevate the mandible,
producing a range of forces from 1 to 16 ounces.

Mandibular Protraction ApplianceNo.
2
(CarlosMartinsCoelho Filho, JCO 1995 )
• The MPA No. 2 is fabricated by making right-angle circles in
two pieces of 0.032" (0.8mm) stainless steel wire

• A small piece of rigid coil, from 0.024" (0.6mm)
stainless steel wire, or a stainless steel tubing is
slipped over one of the wires.

• One end of each wire is inserted through the other
wire's loop, so that each wire passes through the other
up to the limit of the wire coil .
• The coil prevents the two wires from interfering with
each other and ensures their correct relationship.

• The maxillary archwire is made with occlusally
directed circles against the molar tubes.
• The mandibular archwire should have occlusally
directed circles placed about 2-3mm distal to each
cuspid.

Fixed v/s Remo vable: The Bio lo gy Of
Functio nalAppliances

• Fixed functional appliances are normally known as
"non-compliance Class II correctors" giving a false
idea about the co-operation necessary during
treatment.

• When we compare them to removable appliances, we
can clearly recognize fixed appliances as non-
compliance devices.
• However, for treatment to be successful, good co-
operation is always necessary, especially if skeletal
modifications instead of dentoalveolar compensations
are desired.

• According to Proffit, there are two mechanisms to
protrusion: Active & Passive.
• In PASSIVE protrusion, the mandible is held
forward by the orthodontic appliance. This the case
with fixed functional appliances.

• In ACTIVE protrusion, the patient ‘responds’ to the
appliance by using his or her muscles, especially the
lateral pterygoid to hold the mandible forward.
• Stimulating the muscles was thought to be important
from the beginning of functional appliance therapy,
hence both the generic functional name and the
specific term activator.

• Whether the patient actively uses his musculature to
posture the mandible forward or passively rests
against the appliance may or may not affect the
amount of mandibular growth.
• But this definitely affects the amount of tooth
movement that occurs and may determine the effect
on the maxilla.

• For example, with the Herbst appliance, the condyle
is displaced anteriorly at all times.
• Therefore this appliance should be considered,
potentially, the most effective of the functional
appliances in altering jaw growth.
• But such is not the case!

• Though with the Herbst appliance, the condyle is
displaced anteriorly at all times, the amount of force
against the teeth is very much under the patients
control.
• The patient can use his/her own muscles to hold the
jaw forwards with the Herbst appliance serving only
as a stimulus to do so.
• Or the appliance can passively hold the jaw forward,
with little or no contribution from the muscles.

• When there is no contribution from the muscles, i.e.
when the muscles relax, the reaction force is
distributed to the maxilla and also to the maxillary
and mandibular teeth.
• Thus, if the muscles hold the jaw forward, there is
little or no reactive force against the teeth and
minimal tooth movement occurs.
• If the jaw repositioning is entirely passive, force
against the teeth can displace the teeth quite
significantly.

The “metabolic pump”

Biomechanics

Mf = F x d
= F x 10
= 10 F
Mc should be equal to
the Mf in order to get
bodily movement
i.e. Mc = Mf
Mc = 10F
Mc : F = 10F: F
= 10 : 1
d=10mm

Mf = F x d
= F x 10
= 5 F
Mc should be equal to
the Mf in order to get
bodily movement
i.e. Mc = Mf
Mc = 5F
Mc : F = 5F: F
= 5 : 1
d=5mm

Mc > Mf
Mc : F > 10 : 1
approx. 12 : 1

Static Equilibrium

Anchorage
• “Resistance to unwanted tooth movement”
• Reinforced anchorage eg. adding second molar to the
anchor unit
• Stationary anchorage eg. Pitting bodily movement of
one tooth v/s tipping movement of another.

Mechanicsof Fixed
Functional Appliances

• In terms of appliances and appliance design, there are
numerous fixed functional appliances.
• The mode of attachment does vary to a great extent.
• However, the forces that they exert are very similar,
i.e. a ‘push’ type of force to the maxillary and
mandibular dentition and to their respective jaw
bases.

First Order View

Mandibular Arch

2nd
Order

3rd Order View

Conclusion
Fixed functional appliances are, and will remain, an
invaluable tool for every orthodontist.
Having said so, it would not be inappropriate to say
that knowing the mechanics of the same would be
mandatory for every clinician.
By knowing this the clinician can not only minimize the
unwanted side effects but also optimise his treatment
results.

In addition, ignoring the biology and the biological
bases of these appliances would be an enormous error.
Just keep both of these in mind, add just a little bit of
common sense, and I assure you that you will get a
sound Bio+Mechanical finish.

Bibliography
1. Filho Carlos Martins Coelho. Mandibular Protraction
Appliances for Class II Treatment .J Clin Orthod; 29:319 –
336, 1995.
2. Graber T M, Rakosi T, Petrovic A G. Dentofacial
Orthopedics with Functional Appliances. St. Louis: Mosby;
2000.
3. Graber T M, Vanarsdall R L. Orthodontics Current
Principles and Techniques. St. Louis: Mosby; 2000.
4. McNamara J A Jr., Orthodontics and Dentofacial
Orthopedics. Ann Arbor: Needham Press; 2001. Jasper J J,
McNamaraJ A Jr. The correction of interarch malocclusions
using a fixed force module. Am J Orthod 108:6,641 – 650,
1995.

5. Pancherz H. The Herbst appliance— its biological effects
and clinical use. Am J Orthod 1985;87:1-20.
6. Proffit W R, Contemporary Orthodontics. St. Loius: Mosby;
2000.
7. Ritto K A , The Orthodontic CYBERjournal Fixed
Functional Appliances Classification.
8. Sachdeva R C L. Orthodontics for the next millenium.
Dallas: Ormco; 1997.
9. Schwindling F P. Jasper Junper Colour atlas. Merzig:
Edition Schwindling; 1997.
10. Williams P L. Gray’s Anatomy. Edinburgh: Churchill
Livingstone; 1995.

Thank
You

Biomechanics of fixed functional appliances

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