EVOLUTION OF THEORIES
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INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com
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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 www.indiandentalacademy.com
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.
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EVOLUTION OF PARADIGM’S www.indiandentalacademy.com
Various paradigms 1920-1940 • Development of the Genomic Paradigm • •
More emphasis on structure rather than function. (Krogman) Moss subdivided this period: 1. Preradiologic Phase-Emphasis placed on craniometry 2. Radiologic Phase
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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 www.indiandentalacademy.com
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. www.indiandentalacademy.com
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 www.indiandentalacademy.com
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. www.indiandentalacademy.com
--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. www.indiandentalacademy.com
MAINLY DOMINATED BY GENOMIC PARADIGM
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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. www.indiandentalacademy.com
DEVELOPMENT OF AN ALTERNATIVE PARADIGM www.indiandentalacademy.com
--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 www.indiandentalacademy.com “morphogenic primacy”
--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. www.indiandentalacademy.com
Significant developments: 1. Functional Matrix Revisited (Moss-1997) 2. Von Limborg’s Conceptual Theory.
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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. www.indiandentalacademy.com
FUNCTIONAL MATRIX REVISITED
PRESENT
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GROWTH CENTER vs GROWTH SITE • Cranial growth centers—facts or fallacies Kalevi Koski (1968)AJO
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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. www.indiandentalacademy.com
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. www.indiandentalacademy.com
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. www.indiandentalacademy.com
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