Alveolar bone

it is a lecture prepared by me for BDS students

1. Alveolar bone: Anatomy, Biology & Histology Dr. LB Kamait Department of Periodontology and Oral Implantology

2. Contents Introduction Histology of bone Components of bone Bone resorption Bone remodelling Factors responsible for bone resorption Factors responsible for bone formation Development of alveolar bone & Alveolar process Clinical implication

3. Introduction Alveolar process is defined as the parts of the maxilla and mandible that form and support the tooth sockets Forms with eruption of tooth to provide osseous attachment to forming pdl Disappears with loss of tooth

4. Because the alveolar processes develop and undergo remodeling with tooth formation and eruption, they are tooth-dependent bony structures

5. Gross histology of bone Characteristics of all bone are dense outer sheet of compact bone and central medullary cavity Medullary cavity filled with red or yellow bone marrow Trabecular /spongy bone present in extremities of long bone

6. Periosteum The tissue that covers the outer surface of bone 2 layers outer (fibrous) layer rich in blood vessels and nerves composed of collagen fibers and fibroblasts inner layer composed of osteoblasts surrounded by osteoprogenitor cells

7. Endosteum: tissue that lines the internal bone cavities The endosteum is composed of a single layer of osteoblasts and sometimes a small amount of connective tissue

8. Cellular components Osteoblast : Plump, cuboidal, mononuclear cell that synthesize collagenous and non collagenous bone matrix proteins Origin : Differentiated from pluripotent follicle cells

9. Osteoblast contains high level of alkaline phosphatase on the outer surface of their plasma membrane Cytoplasm is intensely basophilic Abundant and well developed protein synthetic organelles such as rough endoplasmic reticulum

10. Osteoblasts also secret number of cytokines, Growth factors (RANKL, osteoprotegerin (OPG), latent proteases and growth factors including bone morphogenetic protein)

11. Regulation of osteoblast activity PTH : PTH receptor present in osteoblast only not in osteoclast stimulate bone resorption and maintain Ca+ balance PTHrP (PTH related peptite ) are produced by osteoblast in very early stage of their differentiation and decreases with maturation Persistent increased level of PTHrP increase osteoclast formation by RANKL formation PTH and Vitamin D3 enhance bone resorption at pharmacological ph and support bone formation at low (physiological) concentration

12. Growth hormone and insulin stimulates bone matrix and mineralization by stimulation of IGF-1 from liver BMP migration, proliferation and aggregation of mesenchymal cells & differentiation in to osteogenic cells TGF – β , IGF I,II stimulates matrix production by osteoblast (by - - of matrix metalloproteinase expression and + + of tissue inhibitors of matrix metalloproteinases ) FGF, PDGF , promote osteogenesis Glucocorticoids :prolonged usedepletion of osteoprogenic precursor cells ++ PTH

13. Osteocytes As osteoblast form bone, some become entrapped within the matrix they secrete, these cell become osteocytes. The more rapid the bone formation, the more osteocytes are present per unit volume Embryonic ( woven ) and repair bone more osteocyte compared to lamellar bone.

14. Osteocytic lacunae Canaliculi Osteocyte maintain contact with adjacent osteocyte and osteoblast or bone lining cell with osteocytic processes

15. Canaliculi penetrate bone matrix and permit diffusion of nutrients, gases, waste products between osteocytes and blood vessels. Sense the change in the environment and send signals that affect the other cells involved in remodeling Failure of this interconnecting system between osteoblast and osteocytes leads to sclerosis and death of bone

16. Osteocytes posses an ellipsoid cell body with long axis parallel to surrounding bone lamellae Oval nucleus with narrow rim of faintly basophilic cytoplasm Few organelles but sufficient RER & golgi aparatus

17. Osteoclast Lie in Howship’s lacunae Large cell ( 40-100 um) 15 to 20 closely packed nuclei More the nuclei  the more resorbing capacity Shape variable due to motility Acid phosphatase containing vesicles & vacuole Mitochondria and golgi complex extensive RER sparse

18. Formation of osteoclast Derived from hematopoitic cells of monocyte- macrophage lineage Their proliferation and differentiation requires cell - cell interaction with osteoblast and stromal cells

19. Regulation of osteoclast activity Osteoprotegerin : RANKL antogonist Estrogen: suppresses the production of bone resorbing cytokines (IL -1, IL-6) production of TGF- β by osteoblast  apoptosis of osteoclast Vitamin D3, PTH: stimulate bone resorption by osteoclast Calcitonin : inhibit osteoclastic activity Cytokines ( IL-1,6,11) enhances osteoclastogenesis (IL-4,10,12,13,18) limit osteoclast formation

20. TNF- β differentiation of osteoclast OCIL ( osteoclast inhibitory lectin ) TGF- β , interferon – γ (inhibits proliferation and differentiation of committed precursors into mature osteoclasts Bisphosphonate ( carbon substituted pyrophosphate compounds) with high affinity for hydroxy apatite and ability to inhibit osteoclast bone resorption PGE 2 : powerful mediator of bone resorption .

21. Osteogenesis / ossification The process of bone formation is called osteogenesis Two type of bone formation 1. Intramembranous ossification 2. Endochondral bone formation

22. Sequence of event in bone resorption (Ten Cate) Ten cate , 1. 2. 3. 4.

23. Factors regulating bone resorption IL-1: powerful and potent bone-resorbing cytokine Mechanism: by stimulating the production and release of PG E2 Direct action of IL-1 , through an 80 kDa receptor IL-6 : resorption formation of cells with an osteoclastic phenotype TNF: resorption mediated by IL-1, IL-6 inhibits differentiation of osteoblast phenoptype

24. 4. Colony-stimulating factors  stimulate differentiation of osteoclast precursors into mature osteoclasts indirectly through IL-1 & PGE2 5. Prostaglandins and other arachidonic acid metabolites: slow-acting, but powerful, mediators of bone resorption and affect both active mature osteoclasts as well as differentiated osteoclast precursors. 6. Androgen & sex steroids: inbibits IL-1

25. Factors regulating bone formation Platelet derived growth factors : platelets, oseoblast , serum, stimulates DNA synthesis & cell replication in osteoblasts increases collagen synthesis & bone matrix apposition 2 Heparin-binding growth factors: members of family of 7 related heparin binding proteins well known acidic & basic FGF Both factors: mitogenic for bone cells and to enhance collagen and noncollagen protein synthesis

26. 3. Insulin-like growth factors: IGF I & IGF II liver increases preosteoblastic cell replication & have a stimulatory effect on osteoblastic collagen synthesis and bone matrix apposition also decrease the degradation of collagen. tranforming growth factor β : stimulate pre- osteoblastic cell replication, osteoblastic collagen synthesis bone matrix apposition and alkaline phosphatase activity

27. 5. Bone morphogenetic proteins: induces chondrocyte differentiation & matrix mineralization activates osteoblast precursor cells  mature osteoblasts stimulate collagen production by mature osteoblasts

28. Development of alveolar process At the end of 2 nd month of fetal life ,the maxilla as well as mandible forms a groove that open to surface of oral cavity tooth germs contained in these groove (alveolar vessels & nerve) Gradually bone septa develops between this germs

29. Later primitive mandibular canal is separated from dental crypts by horizontal plate of bone Alveolar process in strict sense , develops only during eruption of the teeth and diminishes in height after the loss of teeth

30. Functions of alveolar bone Houses the roots of teeth Anchors the roots of teeth to the alveoli, which is achieved by the insertion of Sharpey’s fibers into the alveolar bone proper 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

31. The alveolar process consists of the following: 1 . An external plate of cortical bone is formed by haversian bone and compacted bone lamellae .

32. 2. The inner socket wall of thin, compact bone called the alveolar bone proper It is seen as the lamina dura in radiographs Histologically, it contains a series of openings (i.e., the cribriform plate )

33. 3. Cancellous trabeculae between these two compact layers act as supporting alveolar bone The interdental septum consists of cancellous supporting bone enclosed within a compact border

34. Bundle characterized by thin lamellae arranged in layers parallel to root with intervening apposition line. Some area Sharpy’s fiber ; completely mineralized most area , it contains uncalcified core within calcified outer layer

35. Supporting alveolar bone It is that bone which surrounds the alveolar bone proper and support the alveolus. consists of 1.Cortical plates 2. Spongy bone

36. a. Cortical plate Buccal and lingual cortex Compact bone thinner in in maxilla Thicker mand . premolar & molar Buccal thinner In ant. Region of both jaw , labial cortical plate and alveolar bone proper fuses—so no spongy bone in between

37. b. Spongy bone Fills the space between cortical plate and alveolar bone proper consists heavy traveculae and bone marrow space types: type 1: the interdental and interradicular trabeculae are regular & horizontal (ladder like) . Present in Manbible type 2: the interdental and inter radicular trabeculae are numerous & irregular present in maxilla Zuckerkandl and hirschfeld (nutrient canals)

38. Bone marrow In embryo and new born , the bone carry red hematopoietic marrow Gradually replaced by fatty or yellow inactive marrow Red marrow in adult : Ribs, Sternum, vertebra and skull Maxillary tuberosity , maxillary and mandibular premolar and molar area, mandibular symphysis , ramus angle

39. Interdental Septum The interdental septum consists of cancellous bone that is bordered by the socket wall cribriform plates of approximating teeth the facial and lingual cortical plates (Figure 1-56). If the interdental space is narrow, the septum may consist of only the cribriform plate

40. Shape of alveolar crest Alveolar bone proper and cortical plate meet each other at 1.5 to 2mm below the CEJ Constant in health If neighbouring teeth are inclined  oblique Most common: between premolar & molar

41. Osseous Topography The bone contour normally conforms to the prominence of the roots , with intervening vertical depressions that taper toward the margin

42. The height and thickness of the facial and lingual bony plates are ffected by the alignment of the teeth angulation of the root to the bone occlusal forces

43. Fenestration and Dehiscence Isolated areas in which the root is denuded of bone and the root surface is covered only by periosteum and overlying gingiva are termed fenestrations Marginal bone intact When the denuded areas extend through the marginal bone, the defect is called a dehiscence

44. Clinical implications Physiologic mesial migration By age 40, loss of 0.5cm by physiologic mesial migration

45. Effect of non functioning tooth Loss of bone volume between cortical plate the bone trabeculae are less numerous and thin Alveolus shows pronouned rarefaction

46. Effect of orthodontic forces Bone resorbs at the site of pressure and apposed on the side of tension At the site of tension, osteoblast are activated & deposit osteoid

47. Effect of tooth loss Labial aspect of alveolar crest is principal site of resorption In maxilla , Residual alv . Ridge upward & inward In mandible, downward and outward Reasons of bone loss after is disuse atrophy decreased blood supply unfavorable prosthesis pressure

48. Thank you