Cementum Lecture Notes PDF - Fall 2024

Course Title: Oral Biology Course Code: BDS 123 Topic of Lecture: Cementum.. Lecturer: Prof Samah Mehanny Associate Prof Sara Mahmoud F A C U L T Y O F D e n t i s t r y T h e F u t u r e S t a r t s H e r...

Course Title: Oral Biology Course Code: BDS 123 Topic of Lecture: Cementum.. Lecturer: Prof Samah Mehanny Associate Prof Sara Mahmoud F A C U L T Y O F D e n t i s t r y T h e F u t u r e S t a r t s H e r e F A L L 2 0 2 4  Cementum Cementum is a specialized calcified dental tissue covering the anatomical root of human teeth. Cementum serves as a medium of attachment of the collagen fibers that bind the tooth to the surrounding structures.  Cementum Cementum resembles bone in some of its physical and chemical structures , however, it is : Avascular. Insensitive. Unnable to remodel.  Physical properties Color Light yellow Lighter in color than dentin, darker than enamel.  Physical properties Thickness Acellular cementum (20-50 m) Cellular cementum (150-200 m)  Physical properties Permeability Permeable from dentin and PDL sides. Cellular C is more permeable than Acellular C.  Chemical properties Inorganic 45-50% Organic 50- 55% Hydroxyapatite crystals Collagen Proteoglycans Less harder than dentin& much less harder than enamel Cementum contains the greatest amount of fluoride in all mineralized tissues.  Cementogenesis 1- Matrix formation 2- Maturation Collagen fiber Ground Hydroxy apatite type I substance crystals  Matrix formation Cementum is formed during root formation Cementoblasts D HER Future C E J Epith. Diaph. Cementoblast is a protein forming and secreting cell. Collagen fibers + ground substance. D Large nucleus with dispersed chromatin threads. Cementoblast RER Golgi apparatus Mitochondria Secretory granules Alkaline phosphatase Prepared by Samah Mehanny Maturation occur layer by layer for the collagen fibers Cementum Cementoblasts Cementoid layer Prepared by Samah Mehanny  Cementum Structure D D Acellular cementum Cellular cementum Prepared by Samah Mehanny  Cementocytes Epithelial rest of Malassez Cementoid layer Acellular cementum Cellular cementum Prepared by Samah Mehanny  Acellular Cementum Thickness : 20-50 µm. Cells: no cells. Ground section: It is clear and structureless; Incremental lines of Salter are parallel to the surface. Sharpay’s fibers space can be seen in it (extrinsic fibers). Formed slowly.  Cellular Cementum Thickness: increase gradually till root apex reaching 150- 200 µm. Location: at the apical third and the furcation area of premolars and molars. Rate of formation: It is formed faster than acellular cementum. It is more permeable than acellular cementum. Cells: It contains cementocytes ( Imprisoned cementoblasts). PDL side Cellular Cementum Lacunae of cementocytes Dentin side Incremental lines of Salter Cementocytes Prepared by Samah Mehanny  Cellular Cementum Viable Dentin side superficial cementocytes Degenerated deep layer’s cementocytes PDL side Prepared by Samah Mehanny  Alternating layers of a cellular and cellular cementum could be seen. Prepared by Samah Mehanny  Cementocyte & Osteocyte Dentin side Osteocyte Lacuna Canaliculi PDL side  Cementocyte & Osteocyte Dentin side Osteocyte Lacuna Canaliculi Periodontal side Prepared by Samah Mehanny  Feature Osteocytes Cementocytes Cellular cementum of the apical portion of the Location Bone tooth Differentiation from mesodermal or ectomesenchymal Differentiation from ectomesenchymal Origin osteoblasts embedded in the osteoid matrix cementoblasts embedded in the cementoid matrix Alteration of shape and size, development of dendritic Transition to mature cell type processes, and declining secretory activity indicated by The same reduction in secretory organelles Have dense network of dendritic cell processes (40– Have less dense network of dendritic cell processes Cell morphology 100 or more) (estimated at 8–20) A complex lacuno-canalicular network connects A less complex lacuno-canalicular network connects Communication osteocytes to each other, to vascular elements, and to cementocytes to each other and to surface cells surface cells such as osteoblasts. such as cementoblasts. Because cementum is not thought to remodel, cementocytes are embedded for life; more deeply Life span Dictated by the rate of bone turnover in the region buried cementocytes show signs of stress and degradation, and empty lacunae may indicate cell death Act as mechanosensors, regulate local bone Functions homeostasis and remodeling, and contribute to Unknown endocrine control of systemic mineral metabolism  Incremental Lines Of Salter They are hypermineralized faint lines run parallel to the root surface The distance between them in acellular is less than that in cellular cementum Cemento Dentinal Junction It is not distinctive, because the Fibers of dentin and C cementum intermingle at the D interface. Cemento Dentinal Junction Smooth in permanent teeth Scalloped in deciduous teeth  Cemento-Enamel Junction 10% cementum and enamel doesn’t meet because of delayed separation of epith root 60% cementum 30% cementum meets the sheath of Hertwig (area of dentin not overlaps E enamel in a sharp line covered by C). (afibrillar cementum) Cemento-Enamel Junction 30% cementum meets the enamel in a sharp line Edge to edge 30% Prepared by Samah Mehanny  10% cementum and enamel don’t meet because of delayed separation of epith root sheath of Hertwig (bared area of dentin). Cementum do not meet enamel 10% Prepared by Samah Mehanny 60% cementum overlaps E (afibrillar cementum) Before tooth eruption, the enamel at the cervical area lose its REE covering where the connective tissue of the dental sac lays down cementum on the exposed enamel (it contains non-collagenous proteins) Cementum overlaps enamel 60% Prepared by Samah Mehanny  Types Of Cementum 1- Acellular cementum. 2- Cellular cementum. 3- Afibirllar cementum. Prepared by Samah Mehanny  Functions Of Cementum 1- It occludes sensitive dentin. 2- Acts as a medium for attachment of collagen fibers of PDL (Sharpey’s fibers). 3- The continuous formation of cementum keeps the attachment apparatus intact. 4- Cementum deposition apically compensate for the attrition. 5- It is a major reparative tissue (as in case of fracture or resorption of root) Root resorption Reparative Cementum Age changes of cementum  1-Thickness Cementum formation is continuous throughout life in a very slow rate Especially in apically and in the furcation area. 2- Hypercementosis; abnormal thickening of cementum. May affect one tooth or all teeth Localized Generalized Hypercementosis Aetiology: 1-Aging. 2-Inflammation of the root. 3-Trauma repair. D D Generalized Prepared by Samah Mehanny  Types Of Hypercementosis Hypercementosis Hypercementosis hypertrophy hyperplasia In functional teeth In non-functional teeth Increase number of Decrease number of Sharpey’s fibers Sharpey’s fibers Prepared by Samah Mehanny Hypercementosis Hypercementosis hypertrophy hyperplasia Prepared by Samah Mehanny Hypercementosis  Cementicles Calcified oval or round nodules found in the PDL, single or in groups. The origin may be calcified epith. Cells (Rests of Mallasez). They may be: free attached impeded  Cementicles It has been postulated that cementicles originate from degenerating cells or epithelial cell rests of Malassez in the periodontal ligament.  Attached cementicle Prepared by Samah Mehanny  2- Permeability From periodontal From dentin side Decrease , side remains but remain at the at apical area superficial ONLY recently formed layers Group C