Evolution of theories 4

EVOLUTION OF THEORIES
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Craniofacial biology as
“Normal Science”
David S. Carlson
• According to Kuhn(1970)
Normal science
Research firmly based upon one or
more past scientific achievements that
Some particular scientific community
acknowledges as supplying the
foundation for its further practice

Paradigm
It is a conceptual scheme that
encompasses individual theories and
is accepted by a scientific
community as a model and
foundation for further research.

EVOLUTION OF PARADIGM’S

Various paradigmsVarious paradigms 1920-1940
More emphasis on structure rather than function.
(Krogman)
Moss subdivided this period:
1. Preradiologic Phase-Emphasis placed
on craniometry
2. Radiologic Phase
• Development of the Genomic Paradigm

Bookstein/Moyers
--The development and early use of
Radiographic cephalometry initiated a more
energetic period of data acquisition and
Quantification of growth and form.
Moss- “Classic Triad”
1. Sutures are primary growth sites
2. Growth of the cranial vault occurs
only by periosteal deposition and
endosteal resorption.
3. All cephalic cartilages are primary
growth centers under direct genetic
control

1940-1960
• Craniofacial biology saw an increased emphasis on
experimental animal research in an effort to account
for the actual mechanism of facial growth.
• Studies were more methodological and conceptual.
• Investigators began to recognize that there is much
more variation within the facial region and that this
variation could be the result of modifying influences
during Ontogeny.

Technological developments:-
• Use of Radioopaque Implants.
• Vital Dyes.
• Autoradiography.
• In-vivo and In-vitro transplantations.
By the end of 1950’s two similar approaches were seen
within the single Genomic Paradigm:
• Comprehensive Approach
• Structurofuntional Approach

Comprehensive Approach:
-Continued with craniometrics but with more
Sophisticated hardware including radiographs,
cephalostats and software in the form of statistical
models.
Structurofunctional Approach:
-Concentrated more on “cause and effect
relationships” Within and among the biologic
systems of the Craniofacial complex.

--By the end of 1950’s the genomic paradigm was put
into question
--Periosteal and Sutural bone growth were removed
from the genomic paradigm and given the status of
secondary, compensatory or adaptive phenomena
--But due to lack of evidence the genomic paradigm
remained dominant and the alternative view that
“Function” plays a major role continued to gather
momentum.

MAINLY DOMINATED
BY
GENOMIC PARADIGM

1960-1980
--Formulation of an Alternative paradigm.
--Termed as the “Functional Paradigm” stated that the
Craniofacial complex is highly adaptable to the
functional demands placed on it and its developmental
environment.
--Melvin Moss’s “Functional Matrix Hypothesis” is
believed by most craniofacial biologists to be the
alternative paradigm (1960,American Journal Of
Anthropology)
--His second paper on Functional hypothesis was
included in the Ist Vistas in Orthodontics in 1962.

DEVELOPMENT OF AN ALTERNATIVE PARADIGM

--Moss 10 yrs later released a third paper on the same.
--From then on the “Functional” hypothesis became a topic
of theoretical debate involving people like:-
• Moorrees(1972)
• Johnston(1976)
• Koski(1977)
• Wayne Watson(1982)
Debate focused on:
• That cephalic cartilages have no intrinsic
growth properties.
• The mechanisms by which the capsular
matrices(oral,nasal,pharyngeal)assert
“morphogenic primacy”www.indiandentalacademy.com

--Alexander Petrovic and Associates(1975)
•Proposed the cybernetic models of
mandibular growth.
1980-2000
• This period saw a confluence of both the genomic
and the functional paradigms.
• A more focused view was developed and merits
and demerits of each theory were considered.

Significant developments:
1. Functional Matrix Revisited (Moss-1997)
2. Von Limborg’s Conceptual Theory.

Conclusion:
The 2 Paradigms present:
1.Genomic--Exists primarily on the strength of the
belief that facial growth and form should
be encoded genetically.
2.Functional--Includes the Functional Matrix Hypothesis
and its extension-The epigenetic hypothesis
-- At the present time a confluence of these two
paradigms is seen until a new one is proposed.

FUNCTIONAL
MATRIX
REVISITED
PRESENT

GROWTH CENTER vs GROWTH
SITE
• Cranial growth centers—facts or fallacies
Kalevi Koski (1968)AJO

According to BAUME:
Growth Center:
Is a site of endochondral ossification with
tissue separating force,contributing to the
increase of skeletal mass.
Growth Site:
Regions of Periosteal or suture bone
formation and modeling resorption adaptive
to environmental influences.

SUTURES
• On the basis of definition sutures cannot be called
growth centers.
• Histologically it is evident that sutures are not
similar to Epiphyseal growth plate.
• The question remains.
--whether there is an expansive force.
--Is the growth in the sutural area of primary
nature,that is does it have an independent growth
potential OR is it of secondary nature,that is in
response to some factor or factors.

Evidence in favor of the dependent role
of the sutural growth appears to be
accumulating
• Subcutaneous auto transplants of the
zygomatico-maxillary suture area in the guinea
pig have not been found to grow.
• An extripation of facial sutures appears to have
no appreciable effect on the dimensional
growth of the skeleton.
• The shape of the sutures has been found to
depend on functional stimuli,the closure of
sutures appears extrinsically determined and it
is possible to bring the sutural growth to halt
by mechanical forces.

Evolution of theories 4

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