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Growth relativity hypothesis -John voudouris, 2000

INDIAN DENTAL ACADEMY Leader in continuing dental education

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

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

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

Growth relativity hypothesis Condylar modification Genetic theory– Genetic control 


Effectiveness of orthopaedic appliances on condylar growth ?- Brodie

Growth relativity hypothesis cybernetic theory – hyperactivity of LPM 

anatomic research – no significant attachment of LPM to the condyle

other muscle & tendon attachments – deep masseter , temporalis - Rees

Growth relativity hypothesis

Growth relativity hypothesis

Growth relativity hypothesis ď Ż LPM tendon – anterior border of fibrous capsule

Growth relativity hypothesis 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

Growth relativity hypothesis Functional matrix hypothesis – influence of non-skeletal tissues Exact method of condylar growth stimulation?

Growth relativity hypothesis 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

Growth relativity hypothesis 

Evidence of decreased muscle activity – use of propulsive orthopaedic appliances

 Cause for growth modulation?

Growth relativity hypothesis 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 hypothesis  Growth relativity – growth that is relative to the displaced condyles from 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”

Growth relativity hypothesis 3 main foundations Displacement Viscoelasticity Referred force (transduction)

Growth relativity hypothesis  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

Growth relativity hypothesis

Growth relativity hypothesis Mandibular advancement(displacement) Synovial fluid dynamics Influx of nutrients

Engorged blood vessels

Stretch of non – muscular viscoelastic tissues transduction

New bone formation

Growth restriction-glenoid fossa  GF - posteroinferior growth – Bjork, Popovich & Thompson  posteriorly directed viscoelastictissues– effect condyleand GF  Reversegrowth– relocation anteroinferiorly  ClassII correction

Growth restriction-glenoid fossa

Light bulb analogy of condylar growth & retention

Discussion Epiphysis


Tissue separating forces


No significant tissue separating forces

Ephiphyseal cartilages - little Significant short term adaptation short term adaptation potential potential

No fibrocartilagenous cap

Presence of fibrocartilagenous cap

Epiphysis Vs condyle

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

Retention relapse ď Ż Deactivation of modification due to compression of retrodiskal tissues

ď Ż Hence long term adaptation is not clinically significant

Retention relapse

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

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 matricesAJO-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 causationAJO-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 Leader in continuing dental education

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