Alveolar Bone Flashcards
What are the 3 layers of alveolar bone. Describe them.
Outer layer corticol plate is compact bone extending from alveolar crest to lower border of socket. Compact bone hollows in bone matrix. Middle layer is trabecular bone which encloses vessels and adipose rich yellow marrow. Bars and sheets intersect to form sponge like network. Continuous remodelling due to masticatory forces. Trabeculation aligned along lines of stress. Innermost layer that lines tooth socket is alveolar bone/bundle bone/cribriform. Sharpey’s fibres from PDL insert perpendicularly into adjacent cementum and alveolar bone
Explain the sieve like appearance of alveolar bone proper
Cribriform plate. Numerous holes as perforated by neurovascular network. Numerous vascular canals called Volksmann’s canals connect Haversian canals and medullary spaces to PDL
What is the composition of alveolar bone
60% inorganic material, mainly uncarbonated hydroxyapatite (strength). 25% organic material — 90% type 1 collagen (intrinsic and extrinsic fibres), 10% ground substances (proteoglycans, glycoproteins) (plasticity). 15% water
Function of alveolar bone
Protection. Attachment to muscles. Framework for bone marrow. Reservoir for calcium and phosphate.
Describe the blood supply of alveolar bone
Inner 2/3 of compact bone receives blood supply from bone marrow via Volkmann’s canals. Outer 1/3 receives blood supply from periosteal vessels. Trabecular bone receives from blood marrow. At bone marrow, nutrient arteries flow through marrow sinusoids.
Functions of osteoblast (Rich in alkaline phosphatase with extensive RER)
Form and mineralise ECM
Synthesise proteoglycans and other bone proteins
Synthesise osteoid matrix on mineralisation front
Deposit type 1 collagen in concentric or parallel layers to form lamellar bone
Features of osteoclast
Derived from haemapoietic cells of macrophage lineage. Ruffled border to increase surface area for enzymes to work on. Organelle free region/clear zone that attaches cell to bone surface via integrins, forming tight seal at ruffled border, to isolate microenvironment where hydrolytic enzymes can be deposited. Lie in Howship’s lacunae. Multinucleated so that more template DNA to increase transcription to make more necessary enzymes.
What is the layering in compact bone
Circumferential lamella: parallel layers surround external and internal bony surface ie periosteum and endosteum
Concentric lamella: bulk of compact bone, deep to circumferential lamella. Layers surround Haversian canals
Interstital lamella: fragments of pre existing lamella interspersed between osteons
What is the reversal line
Site of change from bone resorption to bone deposition. Scalloped outline reflecting position of howship’s lacunae. Rich in sialoprotein and osteopontin
Reversal line vs resting line
Reversal line marks change from resorption to deposition of bone. Resting line marks rhythmic deposition of bone with periods of rest.
Reversal line scalloped while resting line parallel and vertical
Why is there bone loss with aging
Fenestration: apical root penetrates bone
Dehiscence: bone loss in coronal root zone
Osteoporosis: resorption greater than deposition
