CEMENTUM
STRUCTURE • Cementum is the calcified avascular mesenchymal tissue that forms the outer covering of the anatomic root . • The inorganic content of cementum (hydroxyapatite;) (hydroxyapatite;) is 45% to 50%, which is less than that of bone (65%), enamel (97%), or dentin (70%).
composition Organic(50%-55%)
Inorganic(40%-45%)
• Type I Collagen fibers
• Calcium
• Protein polysaccharides
• Phosphorous • Traces of Magnesium • Fluoride • Water
Collagen Fibers • The two sources of collagen fibers in cementum are; • Sharpey's (extrinsic) fibers, which are the embedded portion of the principal fibers of the periodontal ligament and are formed by the fibroblasts, and • fibers that belong to the cementum matrix per se (intrinsic) and are produced by the cementoblasts.
Cells • Cementoblasts also form the noncollagenous components of the interfibrillar ground substance, such as proteoglycans, glycoproteins, and phosphoproteins.
Physical Properties • It is yellowish in color but lighter than dentin. • It is less harder than dentin.(70 KHN) • Cementum is permeable, but decreases as age advances
Types of Cementum Acc to location; a) Coronal Cementum. b) Radicular Cementum. Acc to Presence or absence of cells; a) Acellular (primary) cementum. b) Cellular (secondary) cementum. Both consist of a calcified interfibrillar matrix and collagen fibrils
Classification • Acc to content of fibrils; a) Fibrillar Cementum. b) Afibrillar Cementum. Acc to Schroeder et .al; • Acellular afibrillar cementum (AAC) • Acellular extrinsic fiber cementum (AEFC) • Cellular mixed stratified cementum (CMSC) • Cellular intrinsic fiber cementum (CIFC) • Intermediate cementum
Differences between Acellular & Cellular cementum Acellular (primary) cementum Cellular (secondary) cementum • First formed cementum Formed after acellular • Formed before reaches occlusal cementum surface. Formed after tooth reaches • Covers cervicle third or half of the occlusal surface. tooth. Covers apical third of root. • No cells. Contains cells (cementocyte). • More calcified. Less calcified. • Sharpeys fibers make up most of the structure. Sharpeys fibers occupy a smaller portion. I) Inserted perpendicular to tooth surface. I) Arranged parallel to root II)size,No.,distribution increases surface. with function. II) May be completely or partially III) Completely calcified. be calcified.
Acellular & Cellular cementum.
Afibrillar type of cementum • In addition, loss of the cervical part of the reduced enamel epithelium at the time of tooth eruption may place portions of mature enamel in contact with the connective tissue, which then will deposit over it an acellular afibrillar type of cementum
Acellular afibrillar cementum (AAC) • It contains neither cells nor extrinsic or intrinsic collagen fibers, apart from a mineralized ground substance. • It is a product of cementoblasts • It is found as coronal cementum in humans, with a thickness of 1 to 15μ.
Acellular extrinsic fiber cementum (AEFC) • It is composed almost entirely of densely packed bundles of Sharpey's fibers and lacks cells. • It is a product of fibroblasts and cementoblasts • It is found in the cervical third of roots. • Its thickness is between 30 and 230microns.
(AEFC)
Cellular mixed stratified cementum (CMSC) • It is composed of extrinsic (Sharpey's) and intrinsic fibers and may contain cells. • It is a co-product of fibroblasts and cementoblasts, • It appears primarily in the apical third of the roots and apices and in furcation areas. • Its thickness ranges from 100 to 1000 nm.
Cellular intrinsic fiber cementum (CIFC) • It contains cells but no extrinsic collagen fibers. • It is formed by cementoblasts, • It fills the resorption lacunae.
Intermediate cementum • It is an ill-defined zone near the cementodentinal junction of certain teeth that appears to contain cellular remnants of Hertwig's sheath embedded in calcified ground substance.
Permeability of Cementum • In very young animals, cellular and acellular cementum are very permeable and permit the diffusion of dyes from the pulp and external root surface. • In cellular cementum, the canaliculi in some areas are contiguous with the dentinal tubuli. • The permeability of cementum diminishes with age
Cementoenamel Junction
Cementoenamel Junction • Three types of relationships involving the cementum may exist at the cementoenarnel junction. • In about 60% to 65% of cases, cementum overlaps the enamel. • In about 30% an edge-to-edge butt joint exists; and • In 5% to 10% the cementum and enamel fail to meet. • In the last instance, gingival recession may result in accentuated sensitivity because the dentin is exposed.
Cementoenamel Junction
Thickness of Cementum • Cementum deposition is a continuous process that proceeds at varying rates throughout life. • Cementum formation is most rapid in the apical regions, where it compensates for tooth eruption, which itself compensates for attrition.
Thickness of Cementum • The thickness of cementum on the coronal half of the root varies from 16 to 60micron, or about the thickness of a hair. • It attains its greatest thickness (up to 150 to 200μ ) in the apical third and in the furcation areas. • It is thicker in distal surfaces than in mesial surfaces, probably because of functional stimulation from mesial drift over time.
Thickness of Cementum • Between the ages of 11 and 70, the average thickness of the cementum increases threefold, with the greatest increase in the apical region. • Average thicknesses of 95μ at age 20 and 215μ at age 60 have been reported.
Thickness of Cementum •
• Thickest at the apex • Thin at the cervical part.
Functions of Cementum. • Primary function is to furnish a medium for attachment of collagen fibers that bind to alveolar bone. • Continuous deposition helps to keep the attachment apparatus intact. • Root fracture or resorption can be repaired by new cementum deposition • Make functional adaptation of tooth possible. (i,edeposition of cementum apically can compensate for loss of tooth substance from occlusal wear&help maintain vertical dimension.)
Develpmental Anomalies with Cementum. Enamel Projections; If amelogenesis does not stop before the start of root formation,enamel may continue to form overportions normally covered by cementum. Enamel Pearls; This consists of globules of enamel on the root surface in cervical region.(act as plaque retentive areas)
Enamel Projections Enamel Pearls
Hypercementosis • The term hypercementosis (cementum hyperplasia) refers to a prominent thickening of the cementum. • It may be localized to one tooth or affect the entire dentition. • Hypercementosis occurs as a generalized thickening of the cementum, with nodular enlargement of the apical third of the root.
Hypercementosis The etiology of hypercementosis • The spikelike type of hypercementosis generally results from excessive tension from orthodontic appliances or occlusal forces. • The generalized type occurs in a variety of circumstances. In teeth without antagonists, hypercementosis is interpreted as an effort to keep pace with excessive tooth eruption.
Hypercementosis • In teeth subject to low-grade periapical irritation arising from pulp disease, it is considered compensation for the destroyed fibrous attachment to the tooth. • The cementum is deposited adjacent to the inflamed periapical tissue. • Hypercementosis of the entire dentition may occur in patients with Paget's disease.
Hypercementosis
Cementicle • Cementicle Globular masses of acellular cementum which form with in the periodontal ligament Types; Free-Lies within the PDL space. Attached-Lies fused to radicular cementum. Interstitial-Incorporated in the cementum.
Cementicle
Attached
Interstitial
Free
Cementoma Cementoma These are masses of cementum generally situated apical to the teeth, to which they may or may not be attached. They are regarded as either odontogenic neoplasms or developmental malformations.
Cementum Resorption and Repair • Permanent teeth do not undergo physiologic resorption as do primary teeth. However, the cementum of erupted as well as unerupted teeth is subject to resorptive changes that may be of microscopic proportion or sufficiently extensive to present a radiographically detectable alteration in the root contour.
Cementum Resorption and Repair • Cementum resorption may be caused by local or systemic causes or may occur without apparent etiology (i.e., idiopathic). • Among the local conditions in which it occurs are trauma from occlusion. orthodontic movement pressure from malaligned erupting teeth,
Cementum Resorption • cysts, and tumors;‘ • teeth without functional antagonists; • embedded teeth; replanted and transplanted teeth; • periapical disease; and periodontal disease.
Cementum Resorption • Among the systemic conditions mentioned as predisposing to or inducing cemental resorption are • calcium deficiency, • hypothyroidism, • hereditary fibrous osteodystrophy, and • Paget's disease.
Cementum Resorption and Repair • Cementum resorption appears microscopically as baylike concavities in the root surface (Fig. 2-16). • Multi-nucleated giant cells and large mononuclear macrophages are generally found adjacent to cementum undergoing active resorption (Fig. 2-17). • Several sites of resorption may coalesce to form a large area of destruction. • The resorptive process may extend into the underlying dentin and even into the pulp, but it is usually painless
Cementum Resorption and Repair • 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 a reversal line, which delineates the border of the previous resorption
Cementum Resorption and Repair • Embedded fibers of the periodontal ligament reestablish a functional relationship in the new cementum. • Cementum repair requires the presence of viable connective tissue. • If epithelium proliferates into an area of resorption, repair will not take place. Cementum repair can occur in devitalized as well as in vital teeth.
Cementum Resorption and Repair
Cementum Resorption and Repair • Anatomical repair. • Functional repair.
Ankylosis • Fusion of the cementum and alveolar bone with obliteration of the periodontal ligament is termed ankylosis. • Ankylosis occurs in teeth with cemental resorption, which suggests that it may represent a form of abnormal repair. • Ankylosis also may develop after chronic periapical inflammation, tooth replantation, and occlusal trauma and around embedded teeth.
Ankylosis • Ankylosis results in resorption of the root and its gradual replacement by bone tissue. • For this reason, reimplanted teeth that ankylose will lose their roots after 4 to 5 years and exfoliate
Exposure of Cementum to the Oral Environment • CLINICAL SIGNIFICANCE • Cementum becomes exposed to the oral environment in cases of gingival recession and as a consequence of loss of attachment in pocket formation. • The cementum is sufficiently permeable to be penetrated in these cases by organic substances, inorganic ions, and bacteria. • Bacterial invasion of the cementum occurs commonly in periodontal disease . • Caries of the cementum also can develop
