Oral

• Alveolar process


  Parts of the maxilla and mandible that form and support the tooth sockets

  
• Alveolar socket


  Cavity within the alveolar bone in which the root of the tooth is held by the periodontal ligament

  
• Disappears with loss of tooth
• Interdental septum


  Alveolar bone between the roots of adjacent teeth

  
• Inter-radicular septum


  Alveolar bone between the roots of multi-rooted teeth

  
• Alveolar bone is subjected to continual and rapid remodeling associated with tooth eruption and subsequently the functional demands of mastication

  
• Anatomically, no distinct boundary exists between the body of maxilla or the mandible and their respective alveolar bone

  
• Alveolar crest


  Found 1.5-2.0 mm below the level of the CEJ
• If you draw a line connecting the CE junctions of adjacent teeth


  This line should be parallel to the alveolar crest. If the line is not parallel, then there is high probability of periodontal disease

  
• Chemical composition of alveolar bone

  • 67% inorganic: hydroxyapatite crystals
  • 33% organic materials, mainly collagen fibers (28%) which lies in a ground substance of glycoproteins and proteoglycans with small amount of noncollagenous proteins (5%)

  
• Hydroxyapatite


  Deposited in between the molecules of collagen as well as in the ground substance of bone
• Enzymes that participate in the precipitation of hydroxyapatite crystals


  Alkaline phosphatase and pyrophasphatase
• Functions of alveolar bone


  • Houses the roots of teeth
  • Anchors the roots of teeth to the alveoli
  • Helps to move the teeth for better occlusion
  • Absorbs and distribute occlusal forces (tooth contact)
  • Supplies vessels to pdl
  • Houses & protect developing permanent teeth while supporting primary teeth
  • Organizes eruption of primary and permanent teeth

  
• Development of alveolar process


  1. At the end of 2nd month of fetal life, the maxilla as well as mandible forms a groove that open to surface of oral cavity

  2. Tooth germs develop within the bony structures at late bell stage

  3. Bony septa and bony bridge begin to form and separate the individual tooth germs from one another, keeping individual tooth germs in clearly outlined bony compartments

  
• Along with tooth germs, alveolar nerves and vessels are also present
• The dental follicle surrounds each tooth germ, which is located between tooth germs and its bony compartment

  
• Changes in the alveolar process with development of roots and tooth eruption


  1. As roots develop, the alveolar process increases in height

  2. The cells in the dental follicle start to differentiate into periodontal ligament and cementum

  3. Some cells in the dental follicle differentiate into osteoblasts and form alveolar bone proper

  
• Alveolar bone proper


  Consists of bundle bone and lamellated bone

  
• Supporting alveolar bone


  Consists of cortical bone and spongy bone

  
• The cortical plate and alveolar bone proper meet at the alveolar crest (usually 1.5-2 mm below the level of the C.E.J. on the tooth it surrounds)

  
• Cortical bone


  The outer (labial or buccal) and inner (lingual) plates of the alveolar process, consisting of compact bone

  
• Alveolar bone proper


  The inner wall of the sockets, providing attachment for the fibers of the periodontal ligament (Sharpey's fibers), developed from the dental follicle

  
• Alveolar bone proper


  • Perforated by many foramina transmitting nerves and blood vessels, also called the cribriform plate
  • Increased radiodensity due to thick bone without trabeculae, also called the lamina dura

  
• Bundle bone


  • Coarse fibered bone with fibers running parallel to the socket wall and arranged in lamellae
  • Bundles of Sharpey's fibers embedded at right angles to the fibers

  
• Lamellated bone


  • Thicker layer of lamellar bone formed of longitudinal lamellae, lying between the bundle bone and the supporting spongiosa

  
• Supporting alveolar bone


  Bone that forms the labial and lingual covering of the alveolar bone proper

  
• Cortical plate


  • Consists of longitudinal lamellae and Haversian systems, dense and continuous with the compact bone of the jaw bodies
  • In the maxilla, perforated by openings for blood and lymph vessels
  • In the anterior teeth region, very thin with no spongy bone, fused with the alveolar bone proper

  
• Spongy/cancellous bone (Supporting spongiosa)


  • Fills the space between the alveolar bone proper and cortical plates
  • In the anterior teeth and alveolar crest regions, very thin or absent

  
• Types of spongy bone


  • Type I: Trabeculae arranged horizontally in a regular ladder-like manner, more common in the mandible and more resistant to masticatory forces
  • Type II: Trabeculae show irregular arrangement, more numerous and delicate, common in the maxilla

  
• Spongy bone


  • Consists of trabeculae of various sizes and shapes, enclosing irregular medullary cavities containing bone marrow
  • Marrow spaces contain mainly fatty tissue with infrequent islands of red blood cells
  • Red marrow transforms to fatty marrow with age, persisting only in the distal part of the upper third molar, condyle head, and mandibular angle

  
• Bone cells include osteoprogenitor cells, osteoblasts, osteocytes, and osteoclasts

  
• Spongy bone


  • Irregular arrangement of bone trabeculae enclosing irregular medullary cavities containing bone marrow
  • Marrow contains mainly fatty tissue with infrequent islets of red blood cells
  • Red bone marrow transforms into fatty marrow by age, persisting only in distal part of last upper molar, head of condyle, and mandibular angle

  
• Type 2 bone


  • Bone trabeculae show irregular arrangement, more sensitive
  • Common in maxilla

  
• Bone cells


  • 1. Osteoprogenitor cells: Undifferentiated mesenchymal cells in deepest layer of periosteum and lining Haversian canals, capable of dividing and giving rise to other bone cell types, morphologically resemble mesenchymal cells
  • 2. Osteoblasts: Responsible for bone formation, found on bone surface when bone matrix is being deposited, secrete osteoid tissue later mineralized by osteoblasts to form bone, elongated cells with basophilic cytoplasm, high alkaline phosphatase activity, contain well-developed rough endoplasmic reticulum and Golgi apparatus
  • 3. Osteocytes: Principal cells of bone tissue, trapped in bone, cell bodies in lacunae and processes in canaliculi, metabolically active in maintaining and storing minerals in bone
  • 4. Osteoclasts: Located on bone surface where resorption occurs, large multinucleated cells in Howship's lacunae, derived from circulating monocytes or osteoprogenitor cells, phagocytic cells with foamy eosinophilic cytoplasm and numerous lysosomes, plasma membrane adjacent to bone has ruffled borders

  
• Bone formation and growth


  1. Bones grow until age 25

  2. Ossification is the process of bone formation

  3. Two main forms of ossification: 1) Endochondral ossification - occurs within cartilage (long bones, fracture healing): Formation of cartilage template, chondrocyte hypertrophy, apoptosis, vascularization, invasion of osteoblast precursors, osteoblasts differentiate and replace cartilage with bone

  4. Intramembranous ossification - occurs in flat bones mainly in skull: Mesenchymal cells form clusters of osteoprogenitors that differentiate in place into osteoblasts which form bone

  
• Bone resorption


  1. Occurs through 3 processes by osteoclasts: 1) Decalcification of inorganic material - secretion of organic acids like citric and lactic acid that chelate bone and increase hydroxyapatite solubility

  2. Degradation of organic matrix - by lysosomal acid proteases and collagenase enzymes secreted by osteoclasts, breaking down collagen extracellularly

  3. Transport of soluble products to extracellular fluid or blood

  
• Decalcification of inorganic material


  1. Secretion of organic acids (mainly citric and lactic acid) by osteoclasts at the ruffled border

  2. Chelation of bone

  3. Increase solubility of hydroxyapatite
• Degradation of organic matrix


  1. Activity of lysosomal acid protease and collagenase enzymes secreted by osteoclasts

  2. Breakdown of collagen extracellularly
• Transport of soluble products


  Soluble products transported to extracellular fluid or blood vascular system
• Bone remodeling


  Bone deposition by osteoblasts after bone resorption by osteoclasts