Growth Relativity Hypothesis: Viscoelastic Forces Affect Condyle & Fossa

Growth relativity hypothesis
www.indiandentalacademy.com

Hypothesis presented for the
mechanism of condylar-fossa growth
modification with propulsive
mandibular appliances, such as the
Herbst & Twin-block

Introduction
Extensive use of orthopaedic
appliances – Herbst, Twin-block &
other auxiliaries
“Why” & “How”

 Normal C-GF growth
 Condylar remodelling
 Pathosis at the condyle …. adaptation

Condylar modification
Genetic theory– Genetic control
 pre-natal
 Effectivenessof orthopaedic applianceson
condylar growth ?- Brodie

cybernetic theory – hyperactivity of LPM
 anatomic research – no significant
attachment of LPM to thecondyle
 other muscle& tendon attachments– deep
masseter , temporalis- Rees

 LPM tendon – anterior border of fibrous
capsule

Whetten & johnston – LPM traction .. Little
effect on condylar growth
Permanently implanted longitudinal muscle
monitoring techniques –
postural & functional LPM activity
Studies on humans-
-Auf der maur
-Pancherz
-Anchus pancherz

Functional matrix hypothesis –
influenceof non-skeletal tissues
Exact method of condylar growth
stimulation?

Increased vertical dimension & decreased LPM activity
Condylar pull “stress” – mandibular growth
Condylar compression - C-GF modification
– Graber & Joho
vertical dimension - postural masticatory muscle
activity – EMG records by Storey et al

 Evidenceof decreased muscleactivity – use
of propulsiveorthopaedic appliances
 Causefor growth modulation?

Mandibular growth is a composite
of regional forces & functional agents
of growth control that interact in
response to specific extracondylar
activating signals – Endow & Hans
Extrinsic signals – basis of “Growth
relativity theory”

 Growth relativity – growth that isrelative
to thedisplaced condylesfrom actively
relocating glenoid fossa
 Growth – long term retention results
short term treatment outcomes

Extension of Wolff’s law
 Growth relativity states that –
“with orthopaedically displaced condyle , the bone
architecture is influenced by the neuromusculature & the
contiguous, non – muscular , viscoelastic tissues anchored
to the glenoid fossa & the altered dynamics of the fluids
enveloping bone”

3 main foundations
Displacement
Viscoelasticity
Referred force (transduction)

 Viscoelasticity
-applied to elastic tissues – muscles
In G R it applies to all non – calcified tissues
Elasticity of --retrodiskal tissues
--fibrous capsule
-- Synovial fluid flow
-- LPM perimycium
-- TMJ tendons & ligaments
-- Other soft tissues
-- Body fluids

Mandibular advancement(displacement)
Stretch of non – muscular viscoelastic tissues
New bone formation
transduction
Synovial fluid dynamics
Engorged blood vessels
Influx of nutrients

Growth restriction-glenoid fossa
 GF - posteroinferiorgrowth – Bjork, Popovich&
Thompson
 posteriorly directed viscoelastic tissues – effect
condyle and GF
 Reverse growth– relocation anteroinferiorly
 Class IIcorrection

Growth restriction-glenoid fossa

Light bulb analogy of condylar
growth & retention

Discussion
Epiphysis Vs condyle
Tissue separating forces
Ephiphyseal cartilages - little
short term adaptation potential
No fibrocartilagenous cap
No significant tissue separating
forces
Significant short term adaptation
potential
Presence of fibrocartilagenous
cap

 Condyle dissimilar to epiphysis
…functionally
…anatomically
…immunologically
…chemically &
…ontogenetically
 condyle does not act like an
epiphysis during orthopaedic
treatment

Retention relapse
 Deactivation of modification due to
compression of retrodiskal tissues
 Hence long term adaptation is not
clinically significant

Retention relapse

conclusion
No measurable long-term benefits for the
mandible are derived from the first phase of
“functional” appliance therapy in a two phase
treatment.

Future studies
 Synovial fluid dynamics
 Study conducted on primates – using
full occlusal coverage herbst block &
twin block appliances – hence
oppurtunity to use
cephalometric
histomorphometric
electromyographic methods
to investigate observed changes

Clinical implications of
viscoelasticity
 Dentoalveolar changes
 AP & vertical changes – differential
eruption
 Transverse changes
 Buccal segment intrusion & extrusion

Bibliography
1. Contemporary orthodontics –
william R.Proffit ; 3rd
edn
2. Orthodontics – Principles and practice
-T.M.Graber ; 3rd
edn
3. The primary role of functional matrices in
facial growth – AJO-DO 1969 jun :(20-31)
4. The doctrine of functional matrices-
AJO-DO 1969 july; 56:no.1

Bibliography
5. Twenty years of functional cranial
analysis – AJO-DO 1972 may;61:no.5
6. The role of functional matrix in
mandibular growth – AJO-DO 1968
apr;38:no.2
7. The capsular matrix –AJO-DO 1969
nov;56:no.5
8. Genetics , epigenetics and causation-
AJO-DO 1981 oct;(366-75)

Bibliography
The functional matrix hypothesis revisited
9. The role of mechanotransduction – AJO-DO
1997 July;112:8-11
10.The role of an osseous connected cellular
network- AJO-DO 1997 Aug;112;221-26
11.The genomic thesis – AJO –DO 1997
Sep;112:338-42
12.The epigenetic antithesis and the resolving
synthesis – AJO-DO 1997 oct;112:410-7

Bibliography
13.Factors affecting the growth of the midface
–The functional matrix hypothesis :
reflections in a jaundiced eye – Lysle
E.Johnston Jr
GROWTH RELATIVITY HYPOTHESIS
14. Improved clinical use of Twin-block and
Herbst as a result of viscoelastic tissue
forces on the condyle and fossa in
treatment and long – term retention :
Growth relativity
AJO-DO 2000 Mar;117:247-66

Growth Relativity Hypothesis: Viscoelastic Forces Affect Condyle & Fossa

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