Mechanisms of Bone Loss Flashcards
Key functions of alveolar bone:
- Houses the roots of the teeth
- Anchors the roots of the teeth to the bone with the help of insertion of terminal periodontal ligament fibres known as Sharpey’s fibres
- Helps to absorb and distribute occlusal forces generated during mastication /tooth to tooth contact
- Provides blood supply to the periodontal ligament
Gingival cuff:
Role?
Contains in healthy status?
- The area of the gingival cuff is critical in maintaining the correct relationship between the gingiva and the tooth.
- Protects the deeper tissues of the periodontal ligament and alveolar bone.
- Number of cell types in this region which, in normal healthy conditions, coordinate together to maintain the status quo in terms of connective tissue and alveolar bone integrity.
Composition of Bone:
Inorganic 67% – Hydroxyapatite
– form of small plates mostly interspersed between collagen fibrils.
Organic 33%
- 28% Collagen
- 5% non-collagenous proteins such as bone sialoprotein, osteocalcin, osteopontin, growth factors and other proteins.
Osteoblasts:
- BONE SYNTHESIS- Synthesise the organic matrix of the bone
- Mononucleated cells
- Produce and are rich in alkaline phosphatase.
- The secretory products of osteoblasts are; type I collagen, the dominant component of the organic matrix, small amounts of type V collagen and proteoglycans and several non collagenous proteins.
Osteoclasts:
- Resorption of the bone
- Multinucleated and larger in size
- Rich in acid phosphatase and other lysosomal enzymes.
- Has a proton pump associated with ruffled border and pumps hydrogen ion into the sealed compartment adjacent to the bone surface where active resorption is taking place.
- The osteoclasts are usually situated in resorption pits called Howship’s lacunae
Osteocytes/ osteoblast relationship:
- Are osteoblasts trapped in the matrix they secrete.
- The number of osteoblasts that become osteocytes depends on the rapidity of bone formation.
Bone remodelling:
- The process by which the size and shape of the bones are maintained.
- Bone turnover occurs in focal, discrete areas involving group of cells called BMUs = Basic multi-cellular units.
- The hormones most important in bone metabolism are parathyroid hormone (PTH), 1,25-dihydroxyvitamin D, calcitonin, Oestrogen and the glucocorticoids.
Parathyroid hormone, Vit D and bone remodelling:
- Parathyroid hormone and Vit D actions are dual.
- PTh enhances bone resorption at high (Pharmacologic) concentrations
- PTh supports bone formation at lower (Physiologic) concentrations.
Calcitonin and oestrogen effects on bone resorption?
inhibitors of bone resorption
Name 2 inhibitors of bone resorption?
Calcitonin and Oestrogen
Inhibitor of primary matrix formation?
Glucocorticoids
Role of Glucocorticoids and bone remodelling?
Acts as an inhibitor for primary matrix formation
Calcium Metabolism and Parathyroid hormone relationship:
- Decreased concentration of Ca2+ in the brain results in an increase in the production of Parathyroid hormone.
- Increased PTH affects bones and the kidney and inadvertently the intestines.
Bone - PTH inhibits osteoblasts and stimulates osteoclast‐mediated bone resorption, leading to an increase in alkaline phosphatase
Kidney
(i) Increased extraction of Ca2+ from the glomerular filtrate.
(i) Increased excretion of Po4-
GI
- PTH does not directly affect gastrointestinal absorption of Ca2+. Its effects are mediated indirectly through regulation of synthesis of 1,25(OH)2D3 in the kidney.
Factors regulating bone RESORPTION:
- Interleukin – 1 (IL-1)
- Interleukin – 6 (IL-6)
- Tumour necrosis factor (TNF- α)
- PGE -2 (Prostaglandins E – 2) and arachidonic acid metabolites.
- Glucocorticoids / sex steroids such as androgens
Factors regulating bone FORMATION:
- Platelet derived growth factor (PDGF)
- Transforming growth factor (TGF-β)
- Heparin binding growth factors
- Insulin-like growth factor
- Bone morphogenetic proteins
