Histology - Alveolar Bone Flashcards
What are the supporting structures of periodontal ligament?
Cementum (Calcified)
Lamina propria (Non calcified)
Alveolar bone also called lamina dura (Calcified)
Periodontal ligament (Non calcified)
What is the composition of the alveolar bone?
Mineral contributes 65% of the weight of the tissue
Mineral is in form of HAP
Describe the bone structure of the alveolar bone
Bone can be Compact (outer parts of bone) or Cancellous/spongy/trabecular (inner parts)
Describe the bone structure of compact bone
Compact bone contains parallel plates found at endostial/ periosteal surfaces inner/outer
Harversian systems are observed and brought about by removal & remodelling of lamellae bone. When harversian systems mature, bone is laid down on inner surface which contradicts vascular canal & mineral becomes more dense.
Describe the bone structure of cancellous bone
Cancellous bone houses bone marrow
In anterior teeth alveolar process not much cancellous bone formed from interior/exterior cortical plates
In posterior teeth alveolar proves contains cancellous bone
Describe the region of periodontal ligament where it’s attached to bone
There is a junction between the periodontal ligament and the demineralised bone
The periodontal ligament projects fibres (Sharpey’s fibres) into the bone
Osteoblasts are found in the periodontal ligament (produce bone)
Osetocytes are found within the bone (trapped osteoblasts)
Osteoids is the unmineralised pre bone area
Describe sharpey’s fibres
Sharpey’s fibres pass from the periodontal ligament to the adjacent bone
Bone with multiple Sharpey’s fibres are termed bundle bone
Sharpey’s fibres may pass through the alveolar bone and inserts into the root of adj tooth
As Sharpey’s fibres do this become continuous with transalveolar fires
Cancellous bone does not contain no transalveolar fibres
Describe the process of bone degradation
Dependent upon presence of teeth as loading does not occur on teeth
Teeth may be lost/extracted leading to fracture of alveolar bone
Loss of teeth leads to alveolar crest reduces which leads to bone plasticity
Describe osteoblasts
Osteoblasts are responsible for secreting the bone matrix
Large amount of RER (production of proteins) + Form continuous layer (in a line)
Describe osteocytes
Osteoblasts that have become entombed in the bone matrix
Osteocytes can communicate with other osteoblasts/osteocytes though canaliculi
Canaliculi are the small side channels of osteocytes
Describe osteoclasts
Osteoclasts are responsible for the degradation of bone
Large multinucleated cells which is formed from fusion of many phagocytes
Found in a depression known as the Howship’s lacuna (HL)
HL forms due to degradative process of osteoclast which gives bone surface irregular outline
Describe osteoclast function
Osteoclasts have microvilli which contain brush like projections on microvilli
This increase surface area for degradative processes
H+ is pumped out of the osteoclast into the bone (dissolves mineral)
Lysosomal enzymes help break down bone and calcium & phosphate is absorbed
Annular zone is a area that keeps the low pH localised
Describe the bone lines
Resting line/mineralising line is smooth line of previous bone deposition.
Reversal line a irregular line where resorption has reversed to formation
Describe formation of reversal line
Area of bone is being resorbed. This is evident as osteoclasts can be observed in the Howships Lacunae.
A functional load is applied to the area of bone (loading) so bone resorption is no longer required so osteoclasts migrate away from the Howships Lacunae Osteoblasts then form on the surface where osteoclasts have just left so resorption line now trapped as a reversal line (as it becomes fossilised)
