Cementum & Alveolar Bone Lecture PDF

Cementum Dr. Nawal Khalifa Babikir Cementum Definition: Specialized calcified mesnchymal tissue that covers the root & said to be part of the hard tissue component of the periodontium. Avascularised tissue that is incapable of remodelling.  Characteristics H...

Cementum Dr. Nawal Khalifa Babikir Cementum Definition: Specialized calcified mesnchymal tissue that covers the root & said to be part of the hard tissue component of the periodontium. Avascularised tissue that is incapable of remodelling.  Characteristics Hardness is less than that of dentin. Light yellow in color. Can be distinguished from enamel by its lack of luster & its darker hue. Semi-permeable to a variety of materials.  Contains ……..inorganic substances …….organic material & water. Cementum has the highest fluoride content of all the mineralized tissues. Composition: It formed of: Cellular. Fibrillar. Ground substance  Composition: Organic Inorganic Collagen: Hydroxyapatite Type I 90% (Ca10[Po4]6[OH]2) Type III 5%. less than that of bone (65%), enamel (97%), or dentin (70%). 1. Cellular:- cementocyte (form the cementum during tooth formation). – cementoblast( found in lacuni , forms cementum in resorption foci). 2. Ground substance. 3. Fibrillar:. Extrinsic Intrinsic. Thickness Cementum deposition is a continuous process that proceeds at varying rates throughout life. It attains its greatest thickness in the apical third and in the furcation areas. It is thicker in distal surfaces than in mesial surfaces, Thickness vary: Coronally(16-60um). Apically (120-200um). Where a micrometer is equal to one millionth of a meter. Types : It has two types: 1. Acellular: i. Sharpey’s fibers make up most of its structure. ii. Thickness 30-230 μm. iii. First to be formed, and covers approximately the cervical third or half of the root. 2. Cellular: i. less calcified. ii. Formed after the tooth reaches the occlusal plane. iii. Is more irregular and contains cells (cementocytes). iv. Sharpey's fibers occupy a smaller portion of cellular cementum.  Classification According to that cementum is classified into: 1. Acellular Afibrillar: i. It is a product of cementoblasts. ii. most coronal. iii. Thickness is 1-15 μm. 2. A cellular extrinsic fibrillar: i. It is a product of fibroblasts and cementoblasts ii. Composed almost entirely of densely packed bundles of Sharpey’s fibers. iii. Cervical third of roots. iv. Thickness(30-230um) 3. Cellular mixed cementum: i. Classification Composed of extrinsic & intrinsic fibers & may contain cells. ii. Co-product of cementoblasts & fibroblasts. iii. Apical third of roots, apices & furcation areas. iv. Thickness (100-1000um) 4. Cellular intrinsic: i. Contains cells but no extrinsic collagen fibers. ii. Formed by cementoblasts. iii. It fills resorption lacunae. 5. Intermediate cementum: i. Poorly defined zone near the cementodentinal junction. ii. Contains cellular remnants of Hertwig's sheath embedded in calcified ground substance.  CEJ It is the borderline between cementum and enamel. Types: Three types of relationships involving the cementum may exist at the cementoenamel junction: 1. Intact: 30% , an edge-to-edge butt joint exists. 2. Deficient: enamel and cementum fail to contact in 5%-10%, that result in an area of exposed dentin. 3. Overlapping: cementum overlap the enamel(60%- 65%).  Functions of cementum 1. Cementum furnishes a medium for the incorporation of the principal periodontal fibers, thereby securing the binding of the tooth root to the alveolar bone proper. 2. Cementum serves as a reparative tissue in case of root fracture or resorption. 3. Functional adaptation : * When the superficial layer of cementum functionally ages, a subsequent layer is deposited thus restoring the integrity of the attachment apparatus. * Another feature of functional adaptation is the excessive formation of cementum on the apical root surface to compensate for the occlusal and incisal wear and restore the normal occlusion  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, cysts, and tumors; teeth without functional antagonists; embedded teeth; replanted and transplanted teeth; periapical disease; and periodontal disease. Among the systemic conditions mentioned as predisposing to or inducing cemental resorption are calcium deficiency, hypothyroidism, hereditary fibrous osteodystrophy, and Paget's disease.  Abnormalities Hypercementosis. is an abnormal thickening of cementum. It may be diffuse or circumscribed. Etiology: accelerated elongation of a tooth. inflammation about a tooth tooth repair and / Paget's disease of bone.. If the overgrowth improves the functional qualities of the cementum, it is termed Cementum hypertrophy. If the overgrowth occurs in non-functional teeth (or) if it is not correlated with increased function, it is termed hyperplasia.. Localized hypercementosis may sometimes be observed in areas in which enamel drops have developed on the dentin. The hyperplastic cementum covering the enamel drops occasionally is irregular and sometimes contains round bodies that may be calcified epithelial rests. Excementosis. The same type of embedded calcified round bodies frequently are found in localized areas of hyperplastic cementum & are designated as excementosis. Ankylosis.: Ankylosis is the union of tooth and bone with no intervening connective tissue. Etiology: Ankylosis may develop after chronic periapical inflammation, tooth replantation, and occlusal trauma and around embedded teeth. Aleolar Bone Alveolar process It is the part of the jaw that forms and supports the teeth socket. It forms when the teeth erupt to provide the osseous attachment to the forming PDL. It disappears gradually after the tooth is lost.  It is formed of several parts: 1. An external plate of cortical bone: formed by Haversian bone and compact bone lamellae. 2.Alveolar bone proper: inner socket wall formed of thin, compact bone and bundle bone. 3.Cancellous trabeculae: lie between the two compact bone acts as support for the alveolar bone.  Socket Wall The socket wall consists of dense, lamellated bone, some of which is arranged in haversian systems, and bundle bone. Bundle bone is the term given to bone adjacent to the periodontal ligament that contains a great number of Sharpey's fibers. Bundle bone is not unique to the jaws; it occurs throughout the skeletal system wherever ligaments and muscles are attached. Cells and intercellular matrix It is formed during fetal growth by intermembranous ossification. Consist of osteocytes. The bone consist of two thirds of inorganic matters. Mainly composed of minerals( calcium, phosphate, carbonate, citrate.....) The mineral salts are in the form of hydroxyaptite crystals (65%-70%).  The organic one third consist mainly of collagen type I. Remodeling is the major pathway of bony changes in shape, resistance to forces, repair of wounds, and calcium and phosphate homeostasis in the body.  Protection Functions of Alveolar bone Alveolar bone forms and protects the sockets for the teeth. Attachment It gives the attachment to the periodontal ligament fibers, which are the principle fibers. These fibers which enter the bone are regarded as Sharpey’s fibers. Support It supports the tooth roots on the facial and on the palatal/lingual sides. Shock-absorber It helps absorb the forces placed upon the tooth by disseminating the force to underlying tissues.  Alveolar bone anatomy varies from person to person and this depends on: 1. Prominence of root. 2. Alignment of the teeth. 3. Angulations of root. Anomalies of alveolar bone: Fenestration: it is a window in the external wall, it’s not connected to the alveolar margin. Dehiscence: it’s also an exposed root surface, but it is connect to the alveolar margin. Occur in 20%,common on lateral incisor ( facial, anterior). Thanks