ANATOMY OF THE PERIODONTIUM

Department of Periodontics and Community Dentistry Prof. Fatin Awartani Department of Periodontics and Community Dentistry

Part II Cementum and Alveolar bone

Cementum

Calcified mesenchymal tissue that forms the outer covering of the anatomic root

Cementum: Provides a means of attachments for the periodontal ligament fibers to the tooth. Consists of calcified collagen fibers and interfibriller ground substance. Made up of 40-45%of inorganic material and 50- 55% organic matter and water.

Cementum Composition Organic matrix50%-55% Type I collagen (90%) Type III collagen (5%) Cementocytes Proteoglycans* Glycoprotiens Phosphoprotiens Inorganic content: Hydroxyapetites (45-50%)

Width varies from 16 to 60 microns in the coronal half of the root and 150 to 200 microns in the apical third of the root. Width increases with age, 95 microns at age 20 and 215 microns at age 60.

Cementum What are the sources of collagen fibers in cementum? Extrinsic sharpeys fibers formed by Fibroblasts. Intrinsic Fibers of the cementum matrix formed by cement oblasts.

The insertion of sharpy’s fibers into the cementum Extrinsic Fibers - Constitute a considerable proportion of the bulk of Cementum. - The embedded portion of the principal fibers of the periodontal ligament. - Formed by the fibroblasts - Composed of mainly collagen type I, coated by collagen type III. The insertion of sharpy’s fibers into the cementum

Intrinsic fibers cementocytes Belong to the cementum matrix Produced by cementoblasts

Types of cementum

Two types of cementum acellular and cellular acellular cementum is found on the coronal areas of the root. cellular cementum is found in the apical areas of the roots and in the furcation areas of multirooted teeth.

TWO MAIN FORMS OF CEMENTUM ACELLULAR - first to be formed covers approximately the cervical third of half of the root does not contain cells formed before the tooth reaches occlusal plane sharpey’s fibers make up most of the structure of acellular cmentum

CELLULAR(secondary cementum) formed after tooth reaches occlusal plane contains cells in lacunae less calcified than acellular more common on apical half of tooth greatest increase with age is cellular type in apical half of root

Acellular and cellular cementum are both arranged in lamellae separated by Incremental lines parallel to the long axis of the root.

Types of Cementum Schroeder's Classification Acellular Afibrillar Cementum Acellular Extrinsic Fiber Cellular intrinsic Fiber cementum. Cellular mixed stratified cementum Intermediate Cementum

Schroeder Acellular afibrilar cementum Acellular extrinsic fiber cementum Cellular mixed stratified cementum Cellular intrinsic fiber cementum Intermediate cementum contents Mineralized ground substance Densely packed bundles of sharpy’s fibers Extrinsic (sharpy’s f) Intrinsic fibers - celss - Intrinsic - cells Poorly defined zone near the cementodentinal junction of certain teeth. source cementoblasts Fibroblasts+ cementoblasts Fibroblasts + cementoblasts site Coronal cementum cervical third of roots Apical third of roots Apices furcation areas. Fills resorption lacunae. thickness 1-15μm 30-230μm 100-1000μm Schroeder

Cementoenamel junction: the area where enamel and cementum meet at the cervical region of the tooth. Three different relationships among the enamel and cementum: 60% to 65% of the cases the cementum overlaps the enamel 30% of the cases edge to edge 5% to 10% cementum fails to meet enamel resulting in exposed dentin

CEMENTOENAMEL JUNCTION In the last case, gingival recession may result in accentuated Sensitivity because of exposed dentin.

Abnormalities of cementum Cemental aplasia or hypoplasia: Absence or paucity of cellular cementum. Cemental hyperplasia or hypercementosis: Excessive deposition of cementum. An age related phenomenon.

Microscopic cementum resorption Extremely common 90.5% In the apical third of the root 76.8% 19% in the middle third 4%in the gingival third 70% confined to cementum( no dentin involvement) Henry Jl et al.

Ankylosis Fusion of the cementum and alveolar bone with obliteration Of the periodontal ligament

Recession :Exposure of cementum to oral environment

Alveolar Bone Osseous tissue is rigid connective tissue that is normally organized into definite structures termed bone. The alveolar process is defined as the parts of the maxilla and the mandible that form and support the sockets of the teeth

Alveolar Bone

The Alveolar Process Consist Of 1-Inner and outer cortical Plate (Compact Bone)

1-compact bone include : a-The Haversian canal b-Volk-manns canals(blood supply) c- Lamella and osteocyte in lacunae.

2- Cancellous bone (spongy): spongy Bone: -Between the two compact layers -Consist of trabeculae that enclose marrow spaces.

3-The alveolar bone proper : Bone lines the socket and extends over the alveolar crest often appears as a radiodense line, termed the lamina dura. -Other term Bundle bone.

Alveolar bone consist of Summary Alveolar bone consist of 1- alveolar bone proper (lamina dura in radiographs) 2- trabecular bone 3- compact bone

1)Alveoli: The space in the alveolar bone that accommodate the roots of the teeth (tooth socket).

2)Supporting alveolar bone: cancellous and cortical bone that surrounds the alveolar bone proper

3)Interproximal bone (interdental septum): bone located between the roots of adjacent teeth. 4)Interradicular bone: bone located between the roots of multirooted teeth

5)Radicular bone: alveolar process located on the facial or lingual surfaces of the roots of teeth

Composition of Alveolar Bone 1-The cells(osteoblast,osteoclast and osteocytes). 2-Extra-cellular matrix consists consists of two-thirds inorganic matter and one third organic matrix.

CELLS OF ALVEOLAR BONE Calcified matrix with osteocytes enclosed in lacunae Constantly changing Osteoblasts deposit Osteoclasts resorb Matrix deposited by osteoblasts is not mineralized and is termed osteoid. As new osteoid is deposited the old osteoid mineralizes. Osteoclasts are large multinucleated cells that are often on surface or in Howship’s lacunae. Main function is resorption of bone.

The inorganic matrix is composed of the minerals calcium and phosphate, The organic matrix consists mainly (90%) of collagen type I, with small amounts of non collagenous proteins

The cortical plates and the bone lining of the socket meet at the alveolar crest, usually 2mm below the cementoenamel junction.

Patterns of bone destruction in periodontal disease 1-Horizontal bone loss 2-Verticl or Angular defects. 3-Osseous craters. 4-Ledges

FENESTRATION - isolated areas which the root is denuded of bone and root surface is covered only by periosteum and overlying gingiva DEHISCENCE - denuded areas extend through the marginal bone

Fenestration: Dehiscence: some bone present in the bone coverage the most coronal portion is missing at the coronal portion of the roots

Differences Between Cementum and Bone Cementum is not vascularized. Cementum has minor ability to remodel. Cementum is more resistant to resorption compared to bone Cementum lacks neural component Cementum contains a unique proteoglycan interfibrillar substance. 70% of bone is made by inorganic salts Cementum contains 46% of inorganic salts

Summary: Periodontium consists of 4 different tissues: Gingiva Cementum PDL Alveolar bone They are anatomically separated, but functionally , they all depends on each other in maintaining a viable, healthy supporting structure for the tooth.

Have a nice future perio patient!