Periodontics 4Th Grade/Lecture (4) Dr

Periodontics 4th Grade/Lecture (4) Dr. Basma F. Alanbari Cementum & alveolar bone

Cementum: The cementum is a specialized mineralized tissue covering the root surfaces and, occasionally, small portions of the crown of the teeth. It has many features in common with bone tissue. However, the cementum contains no blood or lymph vessels, has no innervation, does not undergo physiologic resorption or remodeling, but is characterized by continuing deposition throughout life.

Composition: 1) Inorganic: 40-50% – Hydroxyapatite which is less than that of bone (65%), enamel (97%), or dentin (70%). 2) Organic: 50% ,Collagen Type I (90%),The Sharpey's fibers constitute the extrinsic fiber system (E) of the cementum and are produced by fibroblasts in the periodontal ligament. The intrinsic fiber system is produced by cementoblasts and is composed of fibers oriented more or less parallel to the long axis of the root. 3) Cellular : a. Cemtoblast: responsible for cementum formation. b. Cementocyte: found within lacunae only in the cellular cementum, they communicate with each other by means of canalculi through which they get nourishment. c. PDL fibroblast: they belong to the PDL where they are responsible for synthesis of the principle fibers but since these fibers become imbedded in the cementum, PDL fibroblast indirectly participate in the cementum formation. d. Cementoclast: these cells are responsible extensive root resorption that lead to the primary teeth oxfolaition. since permenant teeth do not undergo physiologic resorption sometimes a localized cemental resorption may occur which appears as concavities in the root surface and may be caused by local or systemic causes.local conditions include periodontal diseases,trauma from occlusion, orthodontic movement, cyst & occur on the mesial surfaces in association with mesial drift among systemic conditions are calcium deficiency, hypothyroidism. 4) Ground substance: these are proteoglycans, glycoproteins and phosphoprotiens formed by Cementoblast & become mineralized by precipitation of hydroxyapatite crystals.

Function: 1. Cementum provides attachment to the collagen fibers of periodontal ligament to the root. 2. Cementum functions as a covering for the root surface, a seal for the open dentinal tubules thus, preventing dentinal sensitivity. 3. Cementum aids in maintaining the teeth in functional occlusion. 4. It contributes to the process of repair after damage to the root surface& compensate for attrition of teeth at their occlusal or incisal edge.

Types of cementum 1. Acellular cementum is the first cementum to be formed and covers approximately the cervical third or half of the root; it does not contain cells. It consists of only Sharpey’s fibers, which is a product of fibroblasts and cementoblasts. this cementum is formed before the tooth reaches the occlusal plane. 2. Cellular cementum, forms after the tooth has reached the occlusal plane. It contains cementocytes in individual spaces (lacunae) that communicate with each other through a system of anastomosing canaliculi.

Cementoenamel junction (CEJ): A. 60-65%—Cementum overlaps enamel. B. 30% - Edge to edge butt joint is there. C.10% - Space is present between cementum and enamel and there is no cementoenamel junction.

Significance of CEJ: It helps in determining the level of attachment and the amount of bone loss.

Thickness of cementum: Cementum deposition is a continuous process that proceeds at a varying rates throughout life .cementum formation is rapid in the apical regions where it compensates for tooth eruption.

External root resorption in permanent teeth: Classified into: 1. Surface Resorption 2. Inflammatory Resorption 3. Replacement Resorption

Surface Resorption: is a Self-limiting process, involving small outlining areas followed by spontaneous repair. -Stimulation is minimal and for a short period. -This defect is usually undetected radiographically and is repaired by a cementum-like tissue. -Commonly seen after orthodontic treatment.

Inflammatory Resorption: Where root resorption has reached dentinal tubules of an infected necrotic pulpal tissue or periodontal tissue, either Transient inflammatory resorption-common after Rx. Or Progressive inflammatory resorption: When stimulation is for a long period.

Replacement resorption, Bone replaces the resorbed tooth material that leads to ankylosis -rarely seen after orthodontic treatment.

Cementum anomalies

a. Hypercementosis refers to a prominent thickening of the cementum. It may be localized to one tooth or affect the entire dentition with nodular enlargement of the apical third of the root. Hypercementosis of the entire dentition may occur in Paget’s disease.

b. 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 also it may develop after chronic periapical inflammation & occlusal trauma.

c. Exposure of cementum to the oral environment: 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 which is accompanied later by cemental necrosis and subsequent dentin exposure directly to the various oral stimuli resulting in dentin hypersentivity.

Alveolar bone

Alveolar Bone Alveolar bone is part of the mandible and maxilla but its existence depends on the presence of teeth and, in the absence of teeth, it gradually resorbs. There is, however, no identifiable boundary between the alveolar bone and the bones of the jaws.

It is the portion of maxilla and mandible that forms and supports the tooth sockets (alveoli). Alveolar bone is a specialized connective tissue that is mainly characterized by its mineralized organic matrix. Together with the root cementum and periodontal ligament, the alveolar bone constitutes the attachment apparatus of the teeth. The main function is to distribute and reabsorb forces generated by mastication and other tooth contact.

Parts The alveolar process is divisible into separate areas on an anatomic basis, but it functions as a unit, with all parts interrelated in the support of the teeth. 1. Alveolar bone proper: Thin lamella of bone that surrounds the root of the tooth and gives attachment to principal fibers of the periodontal ligament is called as alveolar bone proper. The alveolar bone proper forms the inner wall of the socket. It is perforated by many openings that carry branches of the interalveolar blood vessels and nerves into the periodontal ligament and is called as Cribriform plate.The bone in which principal fibers called Sharpey’s fibers of periodontal ligament are anchored is known as bundle bone. Radiographically, this bundle bone appears as a thin radiopaque line surrounding the roots of teeth and is called as lamina dura.The lamina dura is evaluated clinically for periapical or periodontal pathology. 2. Supporting alveolar bone: Bone that surrounds the alveolar bone proper and gives support to the socket is called as supporting alveolar bone. It consists of 2 parts: i. Cortical plates: Which consists of compact bone and form the outer and inner plates of the alveolar bone. ii. Spongy bone: Which fills the area between these plates and alveolar bone proper. It is also called as trabecular bone or cancellous bone.

Components 1. Inorganic: 65% Hydroxyapatite 2. Organic: 33%• Collagen – 28% Type I – (Mainly), Type III, V, XII and XIV& Non- collagenous protein – 5%. The various noncollagenous proteins are osteonectin, osteopontin, bone sialoprotein, osteocalcin, bone proteoglycans, bone morphogenetic proteins . 3.cellular components a. Osteoblast: Osteoblasts are uninucleated cells that synthesize both collagenous and noncollagenous bone proteins and are thought to be derived from multipotent mesenchymal cells.

4 b. Osteocyte: As osteoblasts secretes bone matrix, some of them become entrapped in lacunae and are then called osteocytes. The number of osteoblasts that become osteocytes varies depending on their rapidity of bone formation, the more rapid the formation; the more osteocytes are present per unit volume. c. Osteoclast These are multinucleated derived from circulating blood cell monocytes. Osteoclasts are foundn in baylike depressions in the bone called Howship’s lacunae. d. Osteoprogenitor cells: They are long, thin stem cell population to generate osteoblast.

Periosteum consists of an inner layer of osteoblasts surrounded by osteoprogenitor cells, which have the potential to differentiate into osteoblasts, and an outer layer rich in blood vessels and nerves and composed of collagen fibers which penetrate the bone, binding the periosteum to the bone. Endosteum is composed of a single layer of osteoblasts and a small amount of connective tissue.

Fenestration and Dehiscence Since The anatomy of the alveolar processes depends upon the alignment and position of the teeth. When the teeth are in extreme buccal or lingual version combined with the alveolar process is extremely thin or missing on that side of the teeth, teeth malposition and prominent root contours all are predisposing factors for

fenestration& dehiscence. Fenestrations are the isolated areas in which root is denuded of bone and marginal bone is intact. Dehiscences are the denuded areas that extend through the marginal bone. Fenestration is window like circumscribed defect where as dehiscence is cleft like split defect. Dehiscence and fenestration are both associated with extreme buccal or lingual version of teeth. It occurs in 20% of all teeth. The defects are very important clinically because where they occur the root is covered only by the periosteum and overlying gingiva, which may atrophy under irritation and expose the root.

Bone remodeling Bone remodeling or bone turnover occur in order to allow the replacement of old bone by new bone. It does not stop when adulthood is reached, although its rate slows down, which is cyclical and usually covers a small area. It involves two processes - bone resportion and bone apposition. Thus, modeling and remodeling occur throughout life to allow bone to adapt to the external and internal demands

Resistance to resorption: Cementum is more resistant to resorption than the alveolar bone this due to the avascular nature of the cementum that protects it from the action of the inflammatory mediators hormones and hormones carried by blood having the capacity to activate the Resorptive cells. This explain the resorption of the alveolar bone prior to cementum during periodontal disease.