Genetics in orthodontics

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Gregor Johann Mendel

www.indiandentalacademy.com

Genetics in orthodonticswww.indiandentalacademy.com

Content 2.Principle of genetic

transmission3. Aetiological heterogenecity 4 .population genetics5.Hereditory in craniofacial

complex . a) general

principle. b)

dentition c)

skeleton6. Syndrome7. Twins study

1. Terminology


Terminology GENE : The term gene was introduced by Johannsen in 1909

Gen = Being born, producing, coming to be.

Gene is the structural and functional unit of hereditary which occupies a specific place (locus) on a chromosome). It is capable

of reproducing itself exactly at each cell division and ducts formation of enzyme or protein.

Homozygote : If alleles are like, and is homozygous for that gene concern. Heterozygote : If alleles are dissimilar. Genotype : the genetic make up of an individual.

Phenotype : External manifestation which genes produce. observable properties, measurable feature Congenital : Present at time of birth.

MUTATION : Mutation is defined as a change in genetic construction from one stable form

to another stable form. The first mutation was recognized by T.H. Morgan in

Drosophila Melanogaster or fruit fly in1910. Genome : the genome contain entire genetic content of a set of choromosome present with in a cell or in organism.


You may have had a very illustrious great great grand Father ; but by the law of chance you have received Only about 1/16 of your gene from him. You received as just as many gene from the horse thieves , gamblers And other undesirable who may have been in that Generation of your family tree. A.M.WINCHESTER


GENE (DNA)

RNA FORMATION

PROTEIN FORMATION

CELL STRUCTURE CELL ENZYME

CELL FUNCTION


Dominant inheritance

A dominant can be recognized from the following characteristics:

1)Every diseased person has a parent who manifests the disease2)The disease appears in every generation.3)Unaffected persons cannot transmit the disease. 4)When a diseased person marries a normal individual the chance of the children being normal or diseased are equal.

In higher form of life inheritance does not occur in such mathematical ratio as Mendel found in peas by T.H. MORGAN.www.indiandentalacademy.com

Recessive inheritanceRecessive can be recognized from the following characteristics1.More than one brother and sister may be affected .

2.The abnormality is more commonly seen in children resulting 3.Diseased individuals generally have parents who are normal from marriage between close relatives.4. Diseased person who marry normal individuals usually have normal children 5. If two diseased person marry ,all their children affected


Aetiological heterogeneity

Etiology may have a variation .it may have a multifactorial basis so that different patient are not necessarily affected for the same reason. eg: no single cause can be identified in cleft lip pt or vander woude syndrome. It may be associated with environment teratogen such as alcohol , cigarette smoke and anticonvulsant drugs .


Population geneticsAs each chromosome carries hundred or thousand of genetics in a linear Order , and there is intra species specificity in the gene order. The same Chromosome contain same gene , chromosome map can be constructedThis enable studies of genetic linkage and association .

Two term mostly used in population genetics. 1)penetrance 2) expessivity


Twins study

a) Dizygotic twins b) monozygotic twins


Facial development in the embryo is demarcated by the appearance of the pre-chordal plate (the cranial end of the embryo) on the fourteenth day of development. One of the most unusual features of vertebrate facial development is the origin of the facial mesenchyme which arises from nural crest cells. Migration and division Of neural crest cells are extremely important in facial develop-ment .the derivatives of cephalic neural crest cells are the maxilla, mandible, zygomatic, nasal bones, and bones of the cranial vault .Although the cessation of neural crest cell migration and the factors that cause neural crest cells to localize in particular regions are notyet completely understood, their migration into the branchial arches occurs in a highly regulated manner. This process is presumed to be under the control of genes known as homeobox genes, which endowneural crest cells (NCC) with a positional identity, which mediates aspects of craniofacial morphogenesis and patterning.

Craniofacial development in embryo


Muscle specific homeobox genesMsx-1 and Msx-2 appear to be involved in epithelial- mesenchymal interactions, and are implicated in cranio -facial development, and in particular in the initiation, developmental position (Msx-1) and further development(Msx-2) of the tooth buds

Control of tooth development

Amelogenesis imperfecta (AI): this is a group of genetically heterogeneous disorders affecting enamel formation .It is clinically heterogeneous in that hypoplastic, hypo calcified And hypomaturation ; and genetically heterogeneous with familie sex exhibiting autosomal dominant,autosomal recessiveand X-linked inheritance . Also, the prevalenceappears to vary quite significantly between 1:14,000 and 1:700 (Backman and Holm,1986). In humans, two amelogenes, AMGX and AMGY,have been cloned and mapped to the X and Y chromosomes,respectively (Lau et al., 1989) and in 1997MacDougall et al. mapped the ameloblastin gene within thecritical region for autosomal dominant AI at chromosome4q21. It is likely, however, that mutations in several genes may be involved in the aetiology of different forms ofautosomally inherited AI.


Dentinogenesis imperfecta (DI): this is autosomaldominant and occurs in approximately 1:8000 live births. Itpresents with brownish discolouration of the teeth, crownssusceptible to rapid attrition, fragile roots and pulp chamber obliteration due to abnormal continuous productionof dentine matrix . DI also Presents a number of sub-types, one of which is coupled withosteogenesis imperfecta in which there is an alteration intype 1 collagen genes. Most patients with this type Of dentinogenesis imperfecta have mutations and deletions for amino acid substitutions in genes with encode forsub-units of type 1 collage. The structural defects in the collagen type 1 molecules affects the extra cellular matrix formation.


malocclusionStudy of craniofacial relationship in twin’s has provided much use full Information consering the role of hereditory in maloclusion

Class 11 division 1: extensive cephalometric studies have been carried out to Determine the heritability of this trait. It show that in the class 11 div 1 pt. the mandible is significantlymore retrudedThan in class 1 pt., with the body of the mandible smaller and over all mandibularLength reduced. Environmental factor can also contribute to the etiology of class 11 div 1 Malocclution.


Angle’s class II division 2Angel’s class 11 division 2 malocclusion , recognizes a unique combination of overbite, incisor Retroclination and sagittal discrepancy. A very severe 11/2 phenotype characterized by concealment of the mandibular incisor’s in malocclusion , has been called deskbiss in German or cover bite.x ray cephalometric and odontometric measurement were recorded for subject and data were compared from the control sample .which indicate the presence of strong genetic influence in the formation of angle’s class 11 division 2 deep bite discrepancy.Deckbiss or coverbite : At least one maxillary central incisor had to exhibit complete vertical

coverage to the corresponding mandibular incisor’s clinical crown in centric occlusion .www.indiandentalacademy.com

Class III.malocclusion.

Relative contribution of genetic and environmenal factor to class111 has been the subject of the Number of previous studies. A class 111 malocclusion resulting from a skeletal imbalance betweenthe maxilary and mandibular bases may result from deficiency in maxillary growth ,excessive Mandibular growth or a combination of both. A wide range of environmental factor have also been suggested as contributory to the development of mandibular prognathism1. Enlarge tonsil2. Nasal blockage3. Congenital anatomical defects .4. Hormonal disturbance.5. Endocrinal imbalance.6. Posture7. trauma


Hapsburg jaw(mandibular prognathism)

(contemporary treatment of dentofacial deformity by proffit white and sarver,2) The development of dentofacial deformity ; influence and etiologic factor, page 55.)


BUTLER’S FIELD THEORY

Mammalian dentition can be divided into several developmental fields . The development fields include the molar / premolar field the canine $ the incisor Field .Dental variability manifest itself strongly itself in distal region than in the Mesial direction .

Eg : . lateral incisor is more prone to variation than the central incisor.


Genetic and Non Genetic Diseases which are Potentially be treated by gene therapy :

1.Immune deficiency 2.Hypercholestrolamia 3. Haemophilia 4.Gaucher's disease 5.Mucopolysaccharidosis 6.Emphysema

7.Cystic fibrosis 8.Cancer 9.AIDS 10. CVS 11.Rheuamtoid arthritis and many other


Methods of Gene Therapy :

1.Viral Agents – A number of different virus can be used to transport foreign genetic material.

a) Retroviruses b) Herpes viruses

2. 2.Physical Agents a) Liposome mediated DNA transfer b) Receptor mediated endocytosis

c) Oligonucleotides


Syndrome

Syndrome of dentofacial disturbance of genetic origin can briefly can be listed .1)Micrognathia 2)Macrognathia 3)Cleft palate and cleft lip 4)Down’s syndrome ( 21 Trisomy) 5)Gardner’s syndrome 6)Marfan’s syndrome 7)Cherubism 8)Cleido cranial dysplasia 9)Mandibulo facial dyostosis 10)Osteogenesis imperfecta11)Bimaxillary protrusion. www.indiandentalacademy.com

12.Bimaxillary atresia 13.Retarded eruption of teeth 14. Hypodontia ,anodontia ,and oligodontia.15. Abnormal over jet and overbite.16. Open bite 17.High arched palate18.Abnormal occlusion and arrangement of teeth


Syndrome on the basis of inheritance

Dominant 1. vander woude syndrome 2. treacher collin syndrome 3. clido cranial dysplasia 4. ecto dermal dysplasia 5. sticklens syndromeRecessive 1. robert syndrome 2. appelt’s syndrome 3. christian syndrome 4. meckel syndrome


The changing concept : the genetic concept.The assumption was made that the cartilages and facial suture Were under genetic control. and that the brain determine the vault Dimension.in1960 moss formulated functional matrix hypothesis.Which provide logical frame work for an emerging concept.



CONCLUSION :

Genetics, always fascinated mankind. The first thinking ancestors of humans were curious about the matters of inheritance. Early attempts to unravel the mystery of genetics were simply hamper by lack of knowledge and understand of basic processes. Today, it is a known fact that every process of growth from multiplication to cell death is ultimately controlled by genes .The quest for understanding of how genetic factor contribute to disease, is gathering speed unraveling this network of events will undoubtfully be challenge for sometime. A large number of genetic disorders have oral manifestation and we as dental practitioner should be able to recognize them.


references1.(contemporary treatment of dentofacial deformity by proffit white and sarver, 2) The development of dentofacial deformity ; influence and etiologic factor, page 55.)2. AJO-DO Volume 1957 Dec (891 - 918):

A critical analysis of orthodontic concept and objectives - Wilson 3. The complex genetics of cleft lip and palate (Martyn T. Cobourne) Division of Orthodontics and Craniofacial Development,

GKT Dental Institute, London,UK 4.The Heritability of Malocclusion: Part 2. The Influence of Genetics in Malocclusion

P. A. Mossey, B.D.S., Ph.D., D.Orth. (R.C.S. Ed.), M. Orth. (R.C.S. Eng.), F.F.D. (R.C.S.I.) 5.Hand book of orthodontics by robert e moyers, dds, phd

6. The angle’s orthodontics vol 68 no1 1998 , page 9.

Thank you

7. Bjo march 1999 vol 26 no1 , 21 -288. Bjo /vol26/ 1999/195-203 9.Bjo /vol26/1999/103-113




Bjo march 1999 vol 26 no1 , 21 -28


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Genetics in orthodontics

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