Alveolar Bone PDF

Alveolar bone Dr Sandeep Gupta Oral Pathologist ALVEOLAR PROCESS It is defined as the parts of the maxilla and mandible that form and support the sockets of the teeth. It forms when the tooth erupts to provide the osseous attachment to the forming periodontal ligament; It disappea...

Alveolar bone Dr Sandeep Gupta Oral Pathologist ALVEOLAR PROCESS It is defined as the parts of the maxilla and mandible that form and support the sockets of the teeth. It forms when the tooth erupts to provide the osseous attachment to the forming periodontal ligament; It disappears gradually after the tooth is lost. ALVEOLAR PROCESS Alveolar bone Spongy bone Cortical plate  ALVEOLAR BONE PROPER It surrounds the roots of the tooth & gives attachment to the principal fibers of the periodontal ligament. Histologically bundle bone & lamellaler bone  ALVEOLAR BONE PROPER (cont,d) A-BUNDLE BONE: The bone which lines the socket in which sharpey’s fibers are embedded is known as bundle bone. Is perforated with many small foramina for B.v and nerves , thus its also called cribriform plate. Contains more calcium salts per units area than other bone. It also known as lamina dura because of its radiopacity. b- Lamellated bone. Is also compact but with haversian system. Bundle bone Lamina Dura  SUPPORTING ALVEOLAR BONE It is the bone that surrounds the alveolar bone proper & gives support to the socket. Consists of cortical plates & spongy bone ( cancellous bone) A-CORTICAL PLATES Consists of compact bone & form the outer & inner plates of the alveolar process. Thinner in maxilla than in the mandible. Thickest in the premolar & molar region of the mandible. Buccal plates are thin but lingual are heavy. A-CORTICAL PLATES(cont,d) In maxilla the outer cortical plate is perforated by many small opening through which blood & lymph vessels pass, But is dense in lower jaw. In anterior region of both jaws the cortical plate is fused with the alveolar bone proper,no spongy bone is found. plates are covered by periosteum.  B-SPONGY BONE It is the bone which fills the space between the outer & inner plates &the alveolar bone proper. Consists of heavy trabeculae with bone marrow spaces. Trabeculae There are 2 main type: A-Type 1: *The interdental &interradicular trabeculae are regular&horizontal in a ladder like arrangment. *This type is seen most often in the mandibule. B-Type 2: *Shows irregularly arranged,numerous,delicate interdental &interradicular trabeculae. *This type is more common in the maxilla.  Bone marrow The bone marrow is red in young bone and yellow in old. -histologicalhy consists of: 1- blood forming elements 2- Osteogenic cells. 3- Adipose tissue.  THE INTERDENTAL SEPTUM Consists of cancellous bone bordered by the socket walls of approximating teeth & the facial & lingual cortical plates. If roots are too close together, an irregular window can appear in the bone adjacent roots.  EMBRYOLOGY OF ALVEOLAR BONE Near the end of the 2nd month of fetal life, mandible and maxilla form a groove that is opened toward the surface of the oral cavity As tooth germs start to develop, bony septa form gradually. Origin 0  OSTEOGENESIS The process of bone formation is called osteogenesis. A-Intra- membranous B-Endochondral bone formation bone formation 0  OSTEOGENESIS (cont,d) Alveolar bone is formed during fetal growth by intramembranous ossification and consists of a calcified matrix with osteocytes enclosed within spaces called lacunae. The osteocytes extend processes into canaliculi that radiate from the lacunae. The canaliculi form an anastomosing system through the intercellular matrix of the bone, which brings oxygen and nutrients to the osteocytes through the blood and removes metabolic waste products. Bone growth occurs by apposition of an organic matrix that is deposited by osteoblasts.  A-INTRA-MEMBRANOUS BONE FORMATION In this type of ossification, the formation of bone is not preceded by the formation of a cartilagenous model, Instead bone is laid down directly in a fibrous membrane. Loose mesemchymal tissue 0 Intra- membranous bone formation (cont,d) At the site of bone formation, mesenchymal cells become aggregated. Some mesenchymal cells lay down bundles of collagen fibres. Some mesenchymal cells differentiated into osteoblasts. 0 Intra- membranous bone formation (cont,d) These osteoblasts secrete a gelatinous matrix called osteoid around the collagen fibres. They deposit calcium salts into the osteoid leading to conversion of osteoid into bone lamellae. Now the osteoblasts move away from the lamellae & a new layer o osteoid is secreted which also gets calcified 0  B-ENDOCHONDRAL BONE FORMATION In this type, the bone formation of a cartilagenous model which is subsequently replaced by bone. Mesenchymal cells become condensed at the site of bone formation. Some mesenchymal cells differentiate into chondroblasts & lay down hyaline cartilage. The cartilage is surrounded by a membrane called perichondrium.This is highly vascular & contains osteogenic cells. 0 ENDOCHONDRAL BONE FORMATION (cont,d) The intercellular substance surrounding the cartilage cells becomes calcified due to the influence of enzyme alkaline phosphatase secreted by the cartilage cells. 0 ENDOCHONDRAL BONE FORMATION (cont,d) Thus the nutrition to the cartilage cells is cut off leading to their death which results in formation of empty spaces called primary areolae.  ENDOCHONDRAL BONE FORMATION (cont,d) The blood vessels & osteogenic cells from the perichondrium invade the calcified matrix which is now reduced to bars or walls due to eating away. of the calcified matrix. this leaves large empty spaces between the walls called secondary areolae  ENDOCHONDRAL BONE FORMATION (cont,d) The osteogenic cells from the perichondrium become osteoblasts & arrange themselves along the surface of there bars of calcified matrix. The osteobleasts lay down osteoid which later becomes calcified to form a lamella of bone. 0 MICROSCOPIC STRUCTURE OF BONE 0  PERIOSTEUM The outside of all compact bone is covered by a thin connective tissue membrane called the periosteum. Is rich in blood vessels and nerves. Is composed of collagen fibers and fibroblasts. Bundles of periosteal collagen fibers penetrate the bone, binding the periosteum to the bone.  OSTEON It is the structural & metabolic unit of the lamellar bone. It consists of haversian canal in the center which harbors a blood vessels. This is surrounded by concentric, mineralized lamellae to form the osteon; known as concentric lamellae. Spaces between the different osteon is filled with interstitial lamellae. 0  HAVERSIAN SYSTEM Consists of the haversian canal & the volkmann’s canal. Haversian canal located in the center of the osteon. Volkmann’s canal are the connecting vessels which connect the haversian canal. FUNCTION: provides nutrition to the bone. 0  LAMELLAE Made up of osteocytes found within empty spaces called lacunae. Mainly 3 types: 0  LAMELLA E 1-CIRCUMFERENTIAL LAMELLAE : They are bony lamellae that surround the entire bone, forming its outer surface. 2-CONCENTRIC LAMELLAE : They form the bulk of the bone & osteon. 3-INTERSTITIAL LAMELLAE : They are lamellae that found between adjacent concentric lamellae. they fill the space between the concentric lamellae.  BONE MARROW RED BONE MARROW : Mainly found in the embryo & newborn. They help in formation on RBCs & WBCs. In the oral cavity, it is found in the maxillary tuberocity, the maxillary molars, the mandibular molars, the mandibular premolar areas, the mandibular symphysis & the ramus angle. Radiographically seen as a zones of radiolucency YELLOW BONE MARROW : It is a fatty marrow that does not produces red &white blood cells. 0  Bone cells Osteoblasts , osteocytes , and osteoclasts  OSTEOBLASTS These are bone forming cells Origin: stem cells These are mononucleated cells that synthesize collagenous & non - collagenous bone matrix proteins. It exhibits a high level of alkaline phosphatase on their outer plasma membrane. When active……. They are plump, cuboidal in shape. When non-active……. They becomes slight flattened. 0  OSTEOBLASTS (cont,d) Function:- - Synthesize collagen (type I and V) and non-collagen pt. - Mineralization - Rich in alkaline phosphate enzyme. - Its maturation stage lining cells that they maintain transport and glycopt synthesis.  OSTEOCYTES As the osteoblasts secrete the bone matrix, some of the osteoblasts get entrapped in lacunae; they are called osteocytes. The space in the matrix occupied by an osteocyte is called the osteocytic lacuna. 0  OSTEOCYTES (cont,d); Function – Maintain bone as living tissue because of their metabolic activity Maintain exchange of calcium between bone & ECF  OSTEOCLASTS These are bone resorbing cell that are multinucleated , large & generally found in cluster. Origin: circulating monocytes & local mesenchymal cells. The osteoclasts are found against the one surface occupying shallow depressions called howship’s lacunae. 0  OSTEOCLASTS (cont,d) -function : -Is degradation of bone causing resorption Upon arrival, active enzymes, such as tartrate resistant acid phosphatase, are secreted against the mineral substrate.  BONE COMPOSITION 67% 33% Inorganic Organic Hydroxyapetite crystals Non collagenous Collagen proteins calcium type I phosphates Osteocalcin hydroxyl Osteonectin carbonate Phosphoproteins sodium proteoglycans magnesium Sioloprotein fluorine Bone morphologic protein 0  FENESTRATIONS & DEHISCENCES Isolated areas in which the root is denuded of bone & the root surface is covered only by periosteum & overlying gingiva are termed fenestrations. When the denuded areas extends through the marginal bone then defect is called a dehiscence. 0  FENESTRATIONS & DEHISCENCES (cout,d) Etiology… unknown Predisposing Factors : Prominent root contour. Malposition. Labial portion of the root combined with a thin bony plate. Seen more often on facial bone than on lingual bone More common on anteriorly than posteriorly Occurs bilaterally BONE TURNOVER (REMODELLING) It's the replacement of old bone by new bone it Occurs in physiologic growth movements. It's rapid during childhood It's slow in young but continuous throughout life Influencing factors local systemic Functional requirements on Parathyroid hormone the tooth Calcitonin Age related changes in the Vitamin D3 bone cells  BONE TURNOVER (REMODELLING) (cout,d) Remodeled alv.b. when stained shows incremental lines called Resting lines and Reversal lines:  Resting lines : are hypocalcified lines represent phasic formation of bone. Reversal lines : are hypocalcified lines , mark the change from bone resorption to bone deposition.  Sequences of resorptive events Attachment of osteoclasts to the mineralized surface of bone. Creation of a sealed acidic microenvironment through the action of the proton pump, which demineralizes bone &exposes the organic matrix. Degradation of the exposed matrix by the action of released enzymes such as acid phosphatase & cathespin B. 0 Thank You