Lecture 7- Periodontium (Part 1).pdf

The Periodontium (Part 1) Intro to the Periodontium and Cementum By the end of this lecture, you should be able to: Identify the three main periodontal tissues Distinguish between the main types of cementum (structure, distribution, cellular content, function) Identify the main cell types involved i...

The Periodontium (Part 1) Intro to the Periodontium and Cementum By the end of this lecture, you should be able to: Identify the three main periodontal tissues Distinguish between the main types of cementum (structure, distribution, cellular content, function) Identify the main cell types involved in cementum development and maintenance Enamel “The Tooth” Up to now we have discussed “the tooth” as being composed of enamel, dentine, and the pulp. However, “the tooth” is more than these three components… Dentine Pulp “The Tooth” It also consists of the periodontal (“around the tooth”) tissues that support it and anchor it into the jaws: cementum, the periodontal ligament (PDL), and alveolar bone. Enamel Dentine Pulp PDL Alveolar bone Cementum “The Tooth” Adding the periodontal tissues to ”the tooth” is not arbitrary: their developmental origins are from the teeth, not from the jaw (more on that in the “alveolar bone” and “development of the periodontium lectures”) Enamel Dentine Pulp PDL Alveolar bone Cementum Cementum- the basics Cementum is the bone-like material that coats the roots of our teeth and grows slowly throughout life. It is avascular (no blood vessels in it). Limited ability to remodel or repair itself. Cementum Yellowish in external appearance. About 45-50% mineral (hydroxyapatite), the rest is mostly type I collagen (90% of the organic material). Cementum- the basics Why is it called cementum? It doesn’t “cement” anything… :s Cementum Cementum- the basics Cementum was the last of the hard tissues on the tooth to be discovered and named (after enamel and dentine). In the 1700-1800’s, teeth were widely thought to be made only of two tissues, but a third structure was appearing in comparative dental anatomy texts… Tenton, 1797 Robert Blake, 1798 Cementum was not discovered first in human teeth, hence the strange name. John Hunter, 1778 (he completely missed it) Detective work by Foster (2017) J. Perio. Res. 52: 666-685 Cementum- the basics The world “cementum” comes from the tissue found on elephant molars! Georges Cuvier Named “cement” by famous French naturalist and palaeontologist Georges Cuvier. He was describing the tissue in between the plate-like cusps of elephant molars as the “cementing” tissue that holds them togetherhence the name! Detective work by Foster (2017) J. Perio. Res. 52: 666-685 Cement Cementum- the basics In the 1840’s, Sir Richard Owen would discover Cuvier’s “cement” in other animals, showing that it coats the tooth roots in humans and other mammals, as well as in reptiles. He decided to keep the name “cementum” in honour of fellow palaeontologist Georges Cuvier. Detective work by Foster (2017) J. Perio. Res. 52: 666-685 Sir Richard Owen Cementum- types There are two main types of cementum: acellular (primary) and cellular (secondary) cementum. Acellular cementum develops first prior to tooth eruption, and is the principal cementum type along the cervical 2/3 (or more) of the tooth root. Deposition is slow, but continuous throughout life. Cellular cementum coats the apical 1/3 of the tooth root and is often thicker than the acellular cementum. Acellular cementum Acellular cementum Acellular cementum is often a thin, clear tissue (no cells inside) in ground thin sections covering and protecting the dentine. May contain incremental growth lines as well as Sharpey’s fibers. Sharpey’s fibers are partially mineralised collagen fiber bundles, in this case, they are the mineralised ends of the periodontal ligament. Acellular cementum Dentine Acellular cementum Acellular cementum is often a thin, clear tissue (no cell spaces inside) in ground thin sections. May contain incremental growth lines as well as Sharpey’s fibers. Sharpey’s fibers are partially mineralised collagen fiber bundles, in this case, they are the mineralised ends of the periodontal ligament. Dentine Acellular cementum Acellular cementum The main function of acellular cementum in humans is to provide the site of attachment for the fibers of the periodontal ligament. This form of acellular cementum is therefore crucial for anchoring a tooth into its socket. Dentine PDL Acellular cementum Acellular cementum The main function of acellular cementum in humans is to provide the site of attachment for the fibers of the periodontal ligament. This form of acellular cementum is therefore crucial for anchoring a tooth into its socket. PDL PDL Shapey’s fiber Acellular cementum Dentine Acellular cementum Acellular cementum Because this form of acellular cementum contains the Sharpey’s fiber bundles from the periodontal ligament, this form of cementum is called: Dentine AEFC Acellular Extrinsic Fiber Cementum (“Fibers from outside”) Periodontal ligament Acellular cementum A second, rarer form of acellular cementum occurs along the cervical margin of the tooth and sometimes along the cervical most region of the crown: AAC Acellular Afibrillar Cementum (“No fibers”) Cementum configurations at the cervical margin 60% of people 10% of people 30% of people Ten Cate’s Oral Histology (8th Edition); Fig. 9-16 Cementum configurations at the cervical margin 60% of people Aaron’s tooth! 10% of people 30% of people Ten Cate’s Oral Histology (8th Edition); Fig. 9-16 Cementum- types There are two main types of cementum: acellular (primary) and cellular (secondary) cementum. Cellular cementum begins forming after ~half of the tooth root has begun to form. Cellular cementum is deposited more rapidly than acellular forms, and it is less mineralized. Not found in all teeth! May be absent in incisors and canines. Cellular cementum Ten Cate’s Oral Histology (8th Edition); Fig. 9-15 Cellular cementum Cellular cementum is unique in having cementocytes throughout (these are former cementoblasts that are now entombed in the cementum matrix à more on that in the development lecture). Cementocytes reside in spaces within the cementum, called lacunae (singular: lacuna). Cellular cementum often contains numerous incremental growth lines as well. Cellular cementum Dentine Ten Cate’s Oral Histology (8th Edition); Fig. 9-15 Cellular cementum Note: cementocytes have tiny projections called canaliculi, which are mostly pointing towards the outer surface of the cementum. (Blood vessels are over here) Cellular cementum The primary function of cellular cementum appears to be adaptive: Continuous deposition along the root apex as a tooth slowly erupts and moves within its socket. Minor role in attachment and re-attachment of the PDL fiber bundles. PDL Cellular cementum Cellular cementum The primary function of cellular cementum appears to be adaptive: Dentine Continuous deposition along the root apex as a tooth slowly erupts and moves within its socket. Minor role in attachment and re-attachment of the PDL fiber bundles. Cellular cementum Cellular cementum Because of this adaptive role, the rates of cementum deposition can change over time, and so can its matrix (lots of Sharpey’s fibers vs. none). It can also have acellular regions within it. Cellular cementum Dentine Cellular cementum Cellular Cementum (CMSC) This leads to a mixture of cementum layers within these regions, so we call it: CMSC Cellular Mixed Stratified Cementum (“Layers of different kinds of cementum”) Dentine Cellular cementum Cellular Cementum (CIFC) In layers of cellular cementum where there are no Sharpey’s fibers from the PDL: CIFC Cellular Intrinsic Fiber Cementum (“Fibers are from cementum itself”) Dentine Cementum types: Acellular (primary) cementum: Acellular Afibrillar Cementum Acellular Extrinsic Fiber Cementum Cellular (secondary) cementum: Cellular Intrinsic Fiber Cementum Cellular Mixed Stratified Cementum The cementoblast: An osteoblast-like cell responsible for deposition of collagenous cementum matrix (cementoid). Cementoblasts are derived from the dental follicle (will cover in the “Development of the periodontium” lecture. Cementoblasts deposit cementum matrix centrifugally (outwards from the tooth) and will migrate with the thickening cementum to avoid being entombed in the matrix (acellular cementum) Cementoblasts The cementoblast: Cementoblasts may also become entombed in the matrix to form cellular cementum. In this case, cementoblasts undergo a differentiation process to become cementocytes (cells responsible for maintaining the cellular cementum). Cementocyte Cementoblast By the end of this lecture, you should be able to: Identify the three main periodontal tissues Distinguish between the main types of cementum (structure, distribution, cellular content, function) Identify the main cell types involved in cementum development and maintenance