Evolution & development of periodontium 22.08.14

PRESENTED BY;DR. CHERRY CHAMRIA

Evolution & Development Of Periodontium

Contents

Defination of Evolution. Theories Of Evolution-Darwin’s Theory Lamarck’s Theory Genetic Evidence of Evolution Evolution Of Periodontium: Process Of Evolution

Evolution of the Periodontium: Cementum Alveolar Bone Periodontal Ligament Gingiva. Defination of Development Developmental Theories Development Of the Periodontium: Cementum Alveolar Bone Periodontal Ligament Gingiva.

Evolution of the Periodontium

“Evolution is the change in the inherited characteristics of biological populations over successive generations”

Experienced by group of people

Darwin, Charles- “On the Origin of Species”

Theories of Evolution-Darwin’s Theory.

Darwin has defined evolution as “descent with modification” When members of a population die,

they are replaced by the progeny of parents better adapted to survive and reproduce in the enviorment in which natural selection takes place.

Past-Apes Present-Humans Future-Mutants.?


Darwin’s Theory

Descent with modification refers to the passing on of traits from parent organisms to their offspring.


Darwin’s Theory

Common descent is the scientific theory that all living organisms on Earth descended from a common ancestor.


Darwin’s Finches

1) thicker beak-feed on seeds, that r crushed between beaks

3) still narrower & sharper- called as “vampire “ finches, creeps on the sea birds & feeds itself.

2)narrower beaks- eat insects.

4)woodpecker finches that pick a twig, make them sharp and then poke it into dead branches to pry out grubs as meal.


Lamarck’s Theory of Evolution

The idea that an organism can pass on characteristics that is acquired during its lifetime to its offspring.

Lamarck said “Individuals lose characteristics they do not require (DISUSE)And develop characteristics that are useful(USE)

Ref: Invertebrate zoology and paleontology

Gene Mutation

A mutation is a change in DNA, the hereditary material of life.

Genetics in Dentistry, 2010. Author: Pal GP, Mahato Niladri Kumar

Gene Mutation & Evolution

MYH16 gene over the years became a pseudogene, lead to decrease in the size of jaw musculature & increase in brain size.

It caused narrower jaws, smaller teeth and space for the 3rd molar became less. 3rd molar is almost vestigeal now on account of the MYH-16

Mutation accounts for the graceful human jaw, in contrast to apes protruding facial ridges.

Evolution & Dentistry

Origin Of teeth In Vertebrates

The first occurence of tooth like structures was found in the posterior pharynx of jawless fishes about 500 million years ago.

It is still unclear whether oral teeth evolved with jaws for predation and mastication or first appeared as external dental armour as protection from predation.

Evolution & Dentistry

Reduction of size of teeth over 2000 years

Invention of stone tools for food preparationwidely reduced the teeth size.

Pottery furthur reduced teeth size- as food could be warmed & hence easy to consume.

However as man started walking, the hands had greater role in obtaining food. Longer jaws became short.

Sharper canines required to catch prey from the teeth

Emes et al.

REVIEW

On The Evolution of Human Jaws and Teeth: A Review

• Yusuf Emes (1), Buket Aybar (2), Serhat Yalcin (2) •

1 - Research Assistant, Istanbul University Faculty of Dentistry, Department of Oral and Maxillofacial Surgery,

Istanbul, Turkey

2 - Professor, Istanbul University Faculty of Dentistry, Department of Oral and Maxillofacial Surgery, Istanbul,

Turkey

Address for correspondence:

Dr. Yusuf EmesE- mail: emes @istanbul.edu.tr

Bull Int Assoc Paleodont. 2011;5(1):37-47.

Abstract

The jaws and teeth of Homo sapiens have evolved, from the last common ancestor of chimpanzee and men to their

current form. Many factors such as the foods eaten and the processing of foods by fire and tools have effected this

evolution course. The evolution of the masticatory complex is related to other anatomical features such as brain

size and bipedal posture, and leads to important proceedings like the formation of speech and language. In this

review, the evolution of human jaws and teeth and its impact on the general course of human evolution is

discussed.

Conclusion The evolution of human masticatory complex is strongly related to diet, the use of tools and fire, and has a more important part in the evolution of mankind more than the dentists know.

mailto:[email protected]

PERIODONTIUM

Periodontium refers to the specialised tissues that both surround and support the teeth, maintaining them in the maxillary and mandibular bones.

Parts of the Periodontium Cementum. Alveolar Bone. Periodontal Ligament. Gingiva.

Ten Cate‘s oral histology 7th edition

Evolution of Cementum

Evolution: There is a replacement of the ankylosis of the tooth & bone to a ligamentous suspension of the tooth. Because of this, movement of the mammalian teeth is made possible, resulting in continual repositioning as required by the jaw growth & also tooth-wear.

Evolution of Alveolar Socket/Bone.

This evolution was explained by Simpson which is referred to as “Chance Similarity”Bones grown in shape & size in response to frequent and habitual strains & loose mass in the absence of forceThis explains the epigenetic trait in size of alveolar process. In early man, the teeth were big, and alveolar sockets were large to hold on to the teeth, but as the forces for chewing reduced, the teeth size decreased hence the size of the alveloi also decreased.

There is a fundamental difference in the manner of attachment of early man and teeth. In the ancesters the teeth are ankylosed to the bone. In the mammals, they are suspended in their sockets by ligaments. In the early man-the teeth “move” with the bones to which they are fused , whereas now they move as independent units. This movement is made possible by the remodeling of the periodontium.

The evolutionary change replaces the ankylosis of tooth and bone to a ligamentous suspension of the tooth. This change permits movement of mammalian teeth and the continued repositioning necessitated by jaw growth or tooth wear.

Evolution of the Periodontal Ligament

3 Types of teeth implantation are recognized:

Acrodonta tooth is attached to the apex of the jaw.

Pleurodont a tooth is attached to the lingual surface of the jaw.

Thecodont- a tooth is set into a deep socket in the jaw.

Evolution And History Of The Periodontal Ligament - A Review. The Internet Journal of Medical Technology. 2012 Volume 6

By a Hinge

By Ankylosis

By implantation in bony sockets(Gomphosis)

Attachment of Gingiva by means of Fibrous Membrane

Evolution And History Of The Periodontal Ligament - A Review. The Internet Journal of Medical Technology. 2012 Volume 6

Development is the specified state of growth or advancement in a short period of time.

Experienced by individuals.

Development of the Periodontium

Development of Jaws

The most anterior of the brachial arches undergoes tranformation to form the upper & lower jaws.

Ref: Human Embroyology by Dr. Bruce M. Carlson

The primitive oral cavity, or stomodeum is lined by stratified squamous epithelium called oral ectoderm, which contacts the endoderm of the foregut to form the bucco-pharyngeal membrane, which ruptures in about the 27th day(1st month) of gestation.

Surrounding the stomodeum are several tissue prominences that constitute the building blocks of the face.

Most of the cells lining this are neural crestal /ectomesenchymal in origin


At 4-5 weeks, the primordia consists of 5 major prominences-1) Unpaired frontonasal2) Paired naso Medial 3) Paired naso-Lateral4) Paired maxillary &5) Mandibular prominence.



Development Of the Periodontium

Oral Epithelium Forms Enamel Organ-which forms the Gingival epithelium.

Ectomesenchyme forms the Dental papilla- which forms PDL, Alveolar bone, Cementum

Ref: Oral Cells & Tissue by P.R Garant, DMD

Periodontium is defined as those tissues which support & invest the tooth.

It provides the support necessary to maintain the teeth in function.

Parts:CementumAlveolar BonePeriodontal LigamentGingiva

Carranza’s Clinical Periodontology-11th Edition

Cementum

Also called “The other bone”

It is a hard avascular connective tissue that covers the roots of teeth

It is the mineralised dental tissue covering the anatomic roots of human teeth.

It covers and protects the root dentin (covers the opening of dentinal tubules)

It provides attachment to the periodontal fibers

It compensates for tooth resorption

Histology of oral tissue – Ten Cate , 7th editionOrbans Oral Histology & Embryology-12th edition

Development of Cementum

Subdivided into:

Pre-funtional –formed during root formation

3.75-7.75 years

Functional- occurs when tooth is about to reach occlusion

Throughout life

Periodontology 2000. Vol. 13, 1997, 41-75

Cementum formation occurs along theentire tooth

Development of Cementum

Outer & inner enamel epithelium forms the bilayer of cells and proliferate downward and form Hertwig’s epithelial root sheath.

Orbans Oral Histology & Embryology-12th edition

HERS sends inductive signal to ectomesenchymal pulp cells to secrete predentin by differentiating into odontoblasts. These odontoblasts secrete the organic matrix of the first formed root predentin.


HERS becomes interrupted, this break allows, the newly formed predentin to come in contact with the dental follicle and the cells derived from them are cementoblasts.

Cementoblasts lay down cementum

These cells 1st form compartments with cellular processes that demarcate intrinsic collagen fibers that are parallel to the long axis of the root surface . Extrinsic fibers are formed later

Image from cell


The HERS-epithelial cells never completely disappear & they persist in small clusters called Epithelial cell rests of malassez


First layer of cementum is actually formed by the inner cells of the HERS and is deposited on the

root’s surface is called intermediate cementum or Hyaline layer of

Hopewell-Smith

Deposition occurs before the HERS disintegrates which seals of the

dentinal tubules

Intermediate cementum is situated between the granular dentin layer

of Tomes and the secondary cementum that is formed by the cementoblasts (which arise from

the dental follicle)


Types of cementum

Acellular cementum: covers the rootadjacent to dentin.

Cellular cementum:covers the apical area and overlying acellular cementum. Also common in interradicular areas

Cementum is more cellular as thethickness increases in order to maintainViability.


Role of the epithelial cell rests of Malassez in the development, maintenance and regeneration of periodontal ligament tissuesJimin Xiong, Stan Gronthos, P. Mark BartoldAbstractPeriodontitis is a highly prevalent inflammatory disease that results in damage to the tooth-supporting tissues, potentially leading to tooth loss. Periodontal tissue regeneration is a complex process that involves the collaboration of two hard tissues (cementum and alveolar bone) and two soft tissues (gingiva and periodontal ligament). To date, no periodontal-regenerative procedures provide predictable clinical outcomes. To understand the rational basi. An important structure during tooth root development, the Hertwig's epithelial root sheath is not only a barrier between the dental follicle and dental papilla cells but is also involved in determining the shape, size and number of roots and in the development of dentin and cementum, and may act as a source of mesenchymal progenitor cells for cementoblasts. In adulthood, the epithelial cell rests of Malassez are the only odontogenic epithelial population in the periodontal ligament. Although there is no general agreement s of regenerative procedures, a better understanding of the events associated with the formation of periodontal components will help to establish reliable strategies for clinical practice. An important aspect of this is the role of the Hertwig's epithelial root sheath in periodontal development and that of its descendants, the epithelial cell rests of Malassez, in the maintenance of the periodontiumon the functions of the epithelial cell rests of Malassez, accumulating evidence suggests that the putative roles of the epithelial cell rests of Malassez in adult periodontal ligament include maintaining periodontal ligament homeostasis to prevent ankylosis and maintain periodontal ligament space, to prevent root resorption, to serve as a target during periodontal ligament innervation and to contribute to cementum repair. Recently, ovine epithelial cell rests of Malassez cells have been shown to harbor clonogenic epithelial stem-cell populations that demonstrate similar properties to mesenchymal stromal/stem cells, both functionally and phenotypically. Therefore, the epithelial cell rests of Malassez, rather than being ‘cell rests’, as indicated by their name, are an important source of stem cells that might play a pivotal role in periodontal regeneration.

Periodontology 2000 Volume 63, Issue 1, pages 217–233, October 2013

http://onlinelibrary.wiley.com/doi/10.1111/prd.2013.63.issue-1/issuetoc




J Periodontal Res. 2008 Aug;43(4):478-81.

Cell death and quantitative reduction of Rests of Malassez according to age.Gonçalves JS, Sasso-Cerri E, Cerri PS.Department of Morphology, Laboratory of Histology and Embryology, Dental School, São Paulo State University (UNESP), Araraquara, SP, Brazil.

BACKGROUND AND OBJECTIVE: Rests of Malassez are clusters of epithelial cells that remain in the periodontal ligament throughout life. However, it has been reported that the number of these structures decreases with age, and some epithelial cells undergo apoptosis in rests of Malassez of young and adult rats. Therefore, the purpose of the present study was to investigate the incidence of epithelial cell death and the quantitative changes in the rests of Malassez in rat molars of different ages.

MATERIAL AND METHODS: Fragments containing the upper molars of rats aged 29, 45 and 120 d were fixed, decalcified and embedded for analysis by light microscopy. In the sections stained by hematoxylin and eosin, the number of rests of Malassez and the number of nuclei of these epithelial structures were obtained. Moreover, the nuclei exhibiting typical features of cell death were also counted in each rest of Malassez. The terminal deoxynucleotidyl transferase-mediated dUTP nickend labeling (TUNEL) method for detection of cell death was also carried out.

RESULTS: In all groups examined, some rests of Malassez exhibited epithelial cell nuclei with typical features of apoptosis and some of them were also TUNEL positive. From 29 to 120 d of age in rats, the quantitative analysis showed a significant decrease in the total number of rests of Malassez in the cervical, middle and furcation regions of the periodontal ligament. Moreover, a significant decrease of epithelial cell nuclei was concomitant to an increase in the frequency of cell death in the oldest rats.

CONCLUSION: These results suggest that epithelial cell death by apoptosis may be, at least in part, responsible for the reduction in the number of rests of Malassez according to age.

Alveolar Process

Alveolar Process/Bone

The specialised bone, that contains the alveoli or sockets of the teeth & supports the teeth

If teeth are lost, alveolar process disappears.

Mainly comprised ofBuccal surfaceOuter cortical boneAlveloar bone properSupporting bone

Jaw Bones mainly comprise of Alveolar Bone & Basal Bone

Alveloar bone dissapers (resorbed ) in edentulous cases and gets down to basal bone.

Basal bone houses the major nerves and blood vessels, and functions as a site of muscle attachment.

Ref: Oral Cells and tissues: P.R Garant DMD

Intramembraneous ossification is the direct formation of the bone within highly vascular sheets of the mesenchyme.

Near the end of the 2nd month of fetal life, in late bell stage, the mandible and maxilla form a groove that is opened toward the surface of the oral cavity known as bony crypt. This contains loose mesenchyme with cytoplasmic processes.

Development of Alveolar Process

Ref: Oral Cells and tissues: P.R Garant DMD

A centre of osteogenesis develops that is in association with capillaries & they adhere to the cytoplasmic processes of the mesenchyme.

These cells differenciate into osteoblasts and secrete bone matrix. Once surrounded by bone matrix they are called osteocytes.

The deposition of this gradually reduces the space between the crypt wall & the tooth, to the dimentions of the PDL.

As tooth germs start to develop, bony septa forms gradually. The alveolar process starts developing during tooth eruption.

Orban’s Oral Histology & Embryology 13th editionBy G.S Kumar.

The development of the periodontium: The origin of alveolar bone

Faculty of Dentistry, University of Toronto, 124 Edward Street, Toronto, CanadaThe Anatomical Record 01/2005; 173(1):69 - 77. DOI: 10.1002/ar.1091730106

ABSTRACT: First molar tooth germs consisting of dental organ, dental papilla and dental follicle were dissected from one-day old mice and transplanted subcutaneously into young adult animals of the same strain. Three to four weeks after implantation the host animals were sacrificed and the transplants harvested. The transplants were prepared for either routine histological examination or for electron microscopy. Forty tooth germs continued development with the formation of a periodontium consisting of cement, periodontal ligament and bone. Electron microscopical examination of this material demonstrated the presence of lymphocytes in association with the subcutaneous bone and thereby suggested the origin of the bone from donor tissue.

Development of PDL

The PDL is derived from the dental sac tissue investing the tooth germ.

The PDL is derived embryonically from the ectomesenchymal tissues.

Development of PDL begins with root formation.


Development of PeriodontalLigament.

The fibre bundles rich in fibroblasts originate at the root dentin.

These nasant fibroblasts are tightly packed by the action of cementoblasts.

During tooth development , as PDL matures, the width of the ligament merge & form the principal fiber bundles(laid down coronally).

During development of the fringe fibres, fibroblasts exhibit cytoplasmic polarity which causes attachement to the cementum.


Initially , the fibers become embedded in the cementum as Sharpey’s fibers and are laid down in a coronal direction within the region identified as the developing PDL , giving them an orientation almost parallel to the root surface.

Fiber formation and deposition occur sequentially from newly forming cemento-enamel junction(CEJ) to the tooth root.


Then, fibers deposited become: Dentogingival and Transseptal fibers of gingiva .

By the time 1/3rd of root formation is complete fibers are inserted within the cementum matrix from the CEJ and traverse coronally following the outline of the newly formed crown.

Ref: Orban’s Oral Histology & Embryology-13th Edition

5 types of fibre attachment: Trans-septal, Oblique, Horizontal, Apical & Interradicular.

Eruptive movement & establishment of occlusion then modify the attachment of PDL.

Periodontal Ligaments Attachements.

Ref: Orban’s Oral Histology & Embryology-13th Edition

The gingival tissues are composed of a superficial epithelium of ectodermal origin(oral mucosa) & underlying connective tissue of mesodermal origin(developing tooth germ)

Development of the Gingiva

Ref -P. Mark Bartold ,A Sampath Narayan- Biology of the Periodontal connective tissue

Development of GingivaAs an erupting tooth approaches the oral epithelium, the enamel epithelium rapidly proliferates, forming the thick reduced enamel epithelium

- Periodontology 2000, Vol. 24, 2000, 9–27

As the crown erupts further, the reduced enamel epithelium ( ameloblast +cells of stratum intermedium ) overlying the enamel fuses with the oral epithelium, undergoes transformation whereby the reduced enamel epithelium gradually becomes junctional epithelium(enamel cuff) and establishes the dentogingival junction


The JE maintains a direct attachment to the tooth surface.During eruption, contact is established between the reduced enamel epithelium and the oral gingival epithelium.


Key Molecules In Periodontium DevelopmentMolecules in periodontium Function

A) GROWTH FACTORS

I. Transforming growth factor beta(including BMP)

Promote cell differentiation & subsequently cementogenesis

II. Pletelet derived growth factor & insulin like growth factor

Promote cementogenesis by altering cell cycle activities

III. Fibroblast growth factor All key events for formation & regeneration of periodontal tissues.

B) ADHESION MOLECULES

I. Bone sialoprotein Promote adhesion of selected cell to newly form root & also involved in promoting mineralization

II. osteopontin Regulate the extent of crystal growth in cementum

C) EPITHELIAL / ENAMEL PROTEIN Epithelial – mescenchymal interaction & may promote periodontal repair directly or indirectly

D) COLLAGENS TYP I & III play key role in Periodontal tissues development & regeneration Typ XII may assist in maintaining PDL space Vs continuous cementum formation

Histology of oral tissue – Ten Cate , 7th edition

Thesleff et al (1995), suggested roles of growth factors in reciprocal epithelial-mesenchymal tissues signaling during advancing tooth morphogenesis.

International Journal of Oral Science (2012) 4, 177–181; doi:10.1038/ijos.2012.61; published online 7 Dec 2012 REVIEW ARTICAL

Molecular regulatory mechanism of tooth root developmentXiao-Feng Huang1 and Yang Chai2AbstractThe root is crucial for the physiological function of the tooth, and a healthy root allows an artificial crown to function as required clinically. Tooth crown development has been studied intensively during the last few decades, but root development remains not wellunderstood. Here we review the root development processes, including cell fate determination, induction of odontoblast and cementoblast differentiation, interaction of root epithelium and mesenchyme, and other molecular mechanisms. This review summarizes our current understanding of the signaling cascades and mechanisms involved in root development. It also sets the stage for de novo tooth regeneration.CONCLUSIONWe have made important great progress in studies of tooth root development in the last 10 years. Development of ectodermal organs involves similar processes and, in some cases, the same genes as those used earlier in development. Like the tooth crown, tooth root development involves the interaction of the dental epithelium and the cranial neural crest-derived mesenchyme. These reciprocal interactions are mediated by a series of signals, including from TGF-B, BMP, FGF and other molecules. By the function of homebox genes, such as NfIc and Msx1/2. This review provides an overview of root development and highlights the developmental biology of the tooth root. We hope that knowledge about the cell fate of the HERS, interaction of dental epithelial and mesenchymal cells, and other molecular mechanisms during tooth root development will facilitate tooth regeneration studies in the future.

From molecules to mastication: the development and evolution of teeth.

Department of Orofacial Sciences and Program in Craniofacial and Mesenchymal Biology, University of California San Francisco, San Francisco, CA, USA.Wiley interdisciplinary reviews. Developmental biology 03/2013; 2(2):165-82. DOI: 10.1002/wdev.63Source: PubMedABSTRACT: Teeth are unique to vertebrates and have played a central role in their evolution. The molecular pathways and morphogenetic processes involved in tooth development have been the focus of intense investigation over the past few decades, and the tooth is an important model system for many areas of research. Developmental biologists have exploited the clear distinction between the epithelium and the underlying mesenchyme during tooth development to elucidate reciprocal epithelial/mesenchymal interactions during organogenesis. The preservation of teeth in the fossil record makes these organs invaluable for the work of paleontologists, anthropologists, and evolutionary biologists. In addition, with the recent identification and characterization of dental stem cells, teeth have become of interest to the field of regenerative medicine. Here, we review the major research areas and studies in the development and evolution of teeth, including morphogenesis, genetics and signaling, evolution of tooth development, and dental stem cells.

Conclusion: Important advances have been made in our understanding of the development and evolution of the teeth. The tooth provides valuable model for the elucidation of major biological questions and the identification. The rapid increase in our understanding of dental development in extant & extinct vertebrate species using techniques including 3D imaging, genetic manipulations, omics analyses and genome wide association studies make this an exciting time to study development and evolution of teeth.

International Journal of Oral Science (2013) 5, 75–84; doi:10.1038/ijos.2013.41; published online 28 June 2013

Bone morphogenetic protein-2 gene controls tooth root development in coordination with formation of the periodontiumAudrey Rakian, Wu-Chen Yang, Jelica Gluhak-Heinrich, Yong Cui, Marie A Harris, Demitri Villarreal,Jerry Q Feng, Mary MacDougall and Stephen E HarrisAbstractFormation of the periodontium begins following onset of tooth-root formation in a coordinated manner after birth. Dental follicle progenitor cells are thought to form the cementum, alveolar bone and Sharpey’s fibers of the periodontal ligament (PDL). However, little is known about the regulatory morphogens that control differentiation and function of these progenitor cells, as well as the progenitor cells involved in crown and root formation. We investigated the role of bone morphogenetic protein-2 (Bmp2) in these processes by the conditional removal of the Bmp2 gene using the Sp7-Cre-EGFP mouse model. Sp7-Cre-EGFP first becomes active at E18 in the first molar, with robust Cre activity at postnatal day 0 (P0), followed by Cre activity in the second molar, which occurs after P0. There is robust Cre activity in the periodontium and third molars by 2 weeks of age. When the Bmp2 gene is removed, major defects are noted in root, cellular cementum and periodontium formation. First, there are major cell autonomous defects in root-odontoblast terminal differentiation. Second, there are major alterations in formation of the PDLs and cellular cementum, correlated with decreased nuclear factor IC (Nfic), periostin and α-SMA+ cells. Third, there is a failure to produce vascular endothelial growth factor A (VEGF-A) in the periodontium and the pulp leading to decreased formation of the microvascular and associated candidate stem cells in the Bmp2-cKOSp7-Cre-EGFP. Fourth, ameloblast function and enamel formation are indirectly altered in the Bmp2-cKOSp7-Cre-EGFP. These data demonstrate that the Bmp2 gene has complex roles in postnatal tooth development and periodontium formation.

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Evolution & development of periodontium 22.08.14