Lec. 9 Dr. Ali H. Murad CEMENTUM Bone Like Connective Tissue Assisting in Tooth Support

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Lec. 9 Dr. Ali H. Murad CEMENTUM Bone like connective tissue assisting in tooth support. that covers the tooth root from the cementoenamel junction to & surrounding the apical foramen.

The cementum carry out 2 important functions: 1-It seals the surface of the root dentin & cover the ends of the open dental tubules. 2-Serves as an attachment for PdL fibers, these fibers function as an attachment for the Pd ligament fibers to the tooth root & aid in maintaining the tooth in it’s socket.

Physical properties 1-less hardness than that of dentin & enamel. 2-Is light yellow in colour , & somewhat lighter in colour than dentin . And can be distinguished from enamel by its lack of luster & its darker colour. 3-permeable to a variety of materials.

Chemical composition 1-in the fully formed permanent teeth the cementum contains about 45% - 50% inorganic substance & 50% - 55% organic materials & water. 2-the inorganic portion consists mainly of Ca & phosphate in the form of hydroxyapatite. 3-also contain highest fluoride of all the mineralized tissue 4-the organic portion of cementum consists of collagen & protein polysaccharides.

Structures of cementum Under the light microscope, two kinds of cementum can be differentiated A- Acellular B- Cellular Acellular cementum: that part of the cementum covering 1/3 – 1/2 of the root of a tooth adjacent to the CEJ. It consists of collagen fibers & ground substance. Cellular cementum: that part of the cementum covering the apical 1/2 - 2/3 of the root of a tooth. This cementum is most abundant on the root tip.

Acellular cellular cementum is thinnest at the CEJ.(20-50 micron) & thickest toward the apex (150-200 micron). collagen fibrils of both acellular & cellular cementum are arranged in a very complex fashion. In some areas, discrete bundles of collagen fibrils can be seen. These bundles known as Sharpey’s fibers, which make up a substantial portion of the cementum.

the cells incorporated into cellular cementum called cementocytes, are similar to osteocytes. They lie in spaces known as lacunae. A typical cementocyte has numerous cell processes, or canaliculi, radiating from cementocyte cell body. These processes may branch, & they frequently 2

anastomose with those of a neighbouring cell, & most of the processes are directed toward the periodontal surface of the cementum.

Lacunae in the deeper layers of cementum appear to be empty, due to degeneration of cementocytes, because the cementocyte become faraway from the origin of nutrition. Both of acellular & cellular cementum are separated by incremental lines into layers, which indicate periodic formation. Acellular cementum may occasionally be found on the surface of cellular cementum, but cellular is frequently formed on the surface of acellular cementum.

Cementogenesis cementum formation is preceded by the deposition of dentin along the inner aspect of Hertwig’s epith. Root sheath. once dentin formation is under way, breaks occur in epith. Root sheath ,allowing newly formed dentin to come in direct contact with C.T cells of dental follicle & differentiated it to cementoblast. The cementoblast synthesize collagen & protein polysaccharides, which make up the organic matrix of cementum & known as cementoid (uncalcified cementum matrix).

After some cementum matrix has been laid down, it’s mineralization begins by Ca & phosphate ions which present in tissue fluids & deposited into the matrix & are arranged as unit of hydroxyapatite. the growth of cementum is a rhythmic process, & as a new layer of cementoid is formed, the old one calcified. However, a thin layer of cementoid usually observed on the cementum surface, & this cementoid tissue is lined by cementoblasts. N.B: when the Hertwig’s epith. Root sheath degenerate some sheath cells migrate away from the dentin toward the dental sac & become the epith. Rests of Malassez which remain in PdL.