Cementum and its development

Cementum is the calcified, avascular mesenchymal tissue that forms the outer covering of the anatomic root.
it describes the development of cementum and its various types.

1. Cementum Presented by- Dr. Anushri Gupta PG first year Department of Periodontology

2. Definition Cementum is the calcified, avascular mesenchymal tissue that forms the outer covering of the anatomic root .

3. Development of cementum The rupture of Hertwig root sheath allows the mesenchymal cells of the dental follicle to contact the dentin where they start forming a continuous layer of cementoblast . Cementum formation begins with the deposition of a meshwork of irregularly arranged collagen fibrils sparsely distributed in a ground substance of matrix called precementum or cementoid

4. This is followed by a phase of matrix maturation , which subsequently mineralizes to form a cementum . Cementoblasts , which are initially separated from the cementum by uncalcified cementoid , sometimes become enclosed within the matrix and are trapped. After they are enclosed they are called cementocytes .

5. Summary of (1) the differentiation of odontoblasts from ectomesenchymal cells in the radicular pulp, (2) the fragmentation of Hertwig's epithelial root sheath with residual portions forming the epithelial rests of Malassez , and (3) the ensuing differentiation of cementoblasts from Hertwig's epithelial root sheath cells or follicle cells, and the follicle contribution to the formation of the fiber bundles of the periodontal ligament (PDL) and, possibly, osteoblasts .

6. The two main source of collagen fibers in cementum are Sharpey fibers (extrinsic), which are the embedded portion of the principal fibers of the periodontal ligament and which are formed by the fibroblasts, fibers that belong to the cementum matrix (intrinsic), which are produced by the cementoblasts .

7. BIOCHEMICAL COMPOSITION : Inorganic : 45-50%, mainly hydroxy -apatite crystals . Organic: 50-55%, mainly Type I collagen (90%) and type III (About 5%) Non collagenous proteins like polysaccharides ( prteoglycans ), alkaline phosphatase bone sialoprotein fibronectin osteocalcin proteolipids osteopoetin and several growth factors

8. Classification Based on – Location. Presence or absence of cells. Origin of collagenous fibers of the matrix. According to schoreder .

9. A. Location – 1. Radicular cementum : It is the derivative of dental follicle, proper covers the entire dentin of the root from CEJ to the apex. It extends partially into apical foramen to line the apical walls of the root canal. 2. Coronal cmentum : In humans, it is restricted to areas of reduced enamel epithelium.  

10. B. Presence or absence of cells- Acellular cementum (primary) It is first formed cementum . Formed before the tooth reaches the occlusal plane It does not contains cells and covers approx. cervical third or half of the root. Cellular cementum (secondary) It is formed after the tooth reaches the occlusal plane. It is more irregular and contains cells called cementocytes in lacunae. less calcified than acellular cementum .

11. Thickness : 30-230 micrometers. Sharpey’s fibers make up most of the structure of acellular cementum and play a principle role in supporting the tooth. Sharpey’s fibers occupy a smaller portion and may be less calcified .

12. C. Based on origin of collagenous fibers - Intrinsic fibre cementum : Cementoblast secretes collagen fibres and ground substance. These fibres are parallel to root surface and do not extend into PDL. Extrinsic fibre cementum : When PDL fibres get attached to fibrous fringe of acellular cemenum , it is k/a Sharpey’s fibers . In permanent teeth, attachment occurs after teeth has erupted in oral cavity.

13. D- Schroeder classification- Acellular afibrillar cementum (AAC)- contains neither cells nor extrinsic or intrinsic collagen fibers, except for a mineralized ground substance. Acellular afibrillar cementum is a product of cementoblasts and found as coronal cementum in humans, with a thickness of 1-15µm.

14. Acellular extrinsic fiber cementum (AEFC)- It is composed entirely of densely packed bundles of sharpey fibers and lack cells. Acellular extrinsic fiber cementum is a product of fibroblasts and cementoblasts . It is found in the cervical third of roots in humans, but it may extend farther apically. Its thickness is between 30 and 230µm.

15. Cellular mixed stratified cementum (CMSC)- It is composed of extrinsic ( sharpey ) and intrinsic fibers, and it may contain cells. It is a co-product of fibroblasts and cementoblasts . In humans, it appears primarily in the apical third of the roots and in furcation areas. Its thickness ranges from 100 to 1000 µm.

16. Cellular intrinsic fiber cementum (CIFC)- Contains cells but no extrinsic collagen fibers. It is formed from cementoblast . In human it fills the resorption lacunae.(small concavities on the root surface)

17. INTERMEDIATE CEMENTUM It is poorly defined zone near the cementodentinal junction of certain teeth that appers to contain cellular remnants of the Hertwig’s sheath embedded in calcified ground substance. Generally present apical third region as a continuous layer or sometimes found in isolated areas.

18. Cementoenamel junction- It is the relation between the enamel and cementum edges at the cervix of the tooth. Three types of relationships involving the cementum may exist at the cementoenamel junction- 60-65% cementum overlaps enamel. 30% edge to edge butt joint. 5-10% cementum and enamel fail to meet.

19. Three configurations of the cementoenamel junction in ground sections. A, Cementum overlaps the enamel. B, A deficiency of cementum ( bracket ) leaves root dentin exposed. C, A butt joint is visible ( arrow ).  

20. Dentino-cemental junction- The terminal apical area of the cementum where it joins the internal root canal dentin is known as cementodentinal junction . When root canal treatment is performed, the obturating material should be at the cementodentinal junction. There is no increase or decrease in the width of the cementodentinal junction with age. cementodentinal junction is 2-3µm wide.

21. Thickness of cementum - Cementum formation is most rapid in apical regions where it compensates for tooth eruption. The thickness of cementum on the coronal half of the root varies from 16-60µm. Greatest thickness (≤150 - 200µm) in the apical third and in the furcation area. Thicker in distal surface than in mesial surface.

22. Between the age of 11 and 70 years, the average thickness of cementum increases. Average thickness of 95µm at the age of 20 yrs and 215µm at the age of 60 yrs.

23. FUNCTIONS: ANCHORAGE Cementum serves as a medium for the attachment of collagen fibers that bind the tooth to alveolar bone ADAPTATION Continuous Deposition of cementum in apical area compensates for loss of tooth substance from occlusal wear. This process also serves to maintain the width of the periodontal ligament space at the apex of the root.

24. REPAIR Major reparative tissue for root surfaces in case of fractures and resorptions . In this process cellular cementum is formed . It repair of root fractures, Seals off necrotic pulps (apical occlusion) protection of the subjacent dentinal tubules . Cementogenic activity contributes to periodontal ligament fiber reattachment and relocation that occurs as a consequence of mesial drifting of teeth

25. Hypercementosis - Abnormal thickening of cementum with nodular enlargement of the apical third of the root. May be localized to one tooth or affect the entire dentition. It also appears in the form of spikelike growth. The spikelike type of hypercementosis generally results from excessive tension caused by orthodontic appliances or occlusal forces.

26. Hypercementosis of the entire dentition may occur in patients with paget disease. Other systemic disturbances that may lead to or may associated with hypercementosis include acromegaly , arthritis, calcinosis , rheumatic fever and thyroid goiter.

27. Cementum resorption and repair- Permanent teeth do not undergo physiologic resorption as primary teeth do. Cementum resorption may be caused by local or systemic factors. Local condition – trauma from occlusion orthodontic movement pressure from malaligned erupting teeth. Cyst and tumors.

28. Embedded teeth Replanted and transplanted teeth Periapical disease Periodontal disease Systemic condition- Calcium deficiency Hypothyroidism Hereditary fibrous osteodystrophy Paget disease

29. Cementum resorption appears microscopically as baylike concavities in the root surface. Multinucleated giant cells and large mononuclear macrophages are generally found adjacent to the cementum that is undergoing active resorption . Cementum resorption is not necessarily continuous and may alternate with periods of repair and the deposition of new cementum . The newly formed cementum is demarcated from the root by a deeply staining irregular line termed as reversal lines.

30. Age Changes in Cementum Cementum grows appositionally throughout life at a linear rate, although the variations in width of i ncremental lines indicate that the rate of cementum deposition varies from period to period . Generally , cementum increases in thickness by different growth patterns among types of cementum being formed . Its thickness varies greatly with tooth group, tooth surface area, and cervical/apical root positions.

31. Cementum , like bone, is a dynamic tissue, capable of responding to occlusal forces and physiological tooth movement. The greatest amount of cementum is deposited apically, constricting the apical foramen, and in the furcations of multi-rooted teeth. According to Schroeder , cementum is thicker in areas exposed to tensional forces, whereas Dastmalchi et al. found that cementum thickness is increased more rapidly at the distal than the mesial parts of root surface.

32. Ankylosis - Fusion of cementum and alveolar bone with obliteration of periodontal ligament . Ankylosis occurs when partial root resorption  is followed by repair with either   cementum  or  dentin  that unites the tooth root with the alveolar bone, usually after trauma. It occur due to- Cemental resorption Chronic periapical inflammation Tooth replantation Occlusal trauma

33. Ankylosis results in the resorption of the root and its gradual replacement by bone tissue. Clinically ankylosed teeth lack the physiologic mobility of normal teeth, which is one diagnostic sign for ankylotic resorption .

34. Exposure of cementum to the oral environment- Exposure of cementum to the oral environment in cases of gingival recession and as a result of the loss of attachment in the pocket formation . Cariogenic plaque, rather than periodontitis or gingival inflammation, is the essential factor responsible for root caries development .

35. The different forms of root surface caries, ranging from minor undemineralized and discolored areas to extensive yellow-brown soft areas, are rarely associated with cavitation below the affected cementum . Active root surface lesion presents a well-defined area of softening and yellowish discoloration while Inactive root surface lesion appears hard on probing with dark discoloration.

36. CONCLUSION As the patterns of oral disease continue to evolve, restorative strategies in future research will include the root-calcified tissue system . A complete understanding of tissue microstructure and chemical composition and the basic reaction patterns of root dentin and cementum to restorative techniques and materials must be pursued. It always must be remembered that the cervical margin of restorations located below the cemento -enamel junction is primarily an area of vital tissue therapy.

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