OB P7- Bone and calcium Flashcards
what are the functions of bone?
> Skeletal : – Protects organs – Provides rigidity – Allows attachment of muscles and teeth – Movements > Container for marrow > Ca2+ pool
why understand bone?
- Regional differences in the mouth (Local anaesthesia)
- Bone changes in the mouth (e.g. to extraction of teeth)
- Orthodontic tooth movements - Osseointegration – implants
- Bisphosphonates
what is the bone composition?
60% mineral : - Largely hydroxyapatite 25% organic : -90% Type I collagen - 10% grounds substance 15% water
what does collagen do to bone?
collagen is a fibrous structural protein which gives elasticity to bone
what are the 2 types of bone in the jaw?
- Alveolar bone - contains the tooth
- Basal bone - basic structure of the jaw
why is fitting a lower denture difficult?
there is no ridge to fit the lower denture over as the bone resorbs away once teeth are removed
what makes a lower denture fit better/
2 implants inserted that the denture clips into
what are the two different types of bone around the tooth?
- Cortical bone (compact bone - dense)
- Trabecular bone ( spongy , cancellous bone)
why does the density and porosity affect local anaesthesia?
cortical bone is thin around the upper teeth and porous so anaesthetic will diffuse through
what layer of bone surrounds the tooth?
lamina dura (bundle bone - cribriform plate)
why is it called lamina dura?
Due to radiographic appearmace - white ridge around teeth
what is the intraligamentary anaesthesia technique?
stick needle down PDL space between bone and tooth
inject small amount of anaesthetic -allows us to apply high pressure
(passes out of the holes and diffuses through trabecular bone and reaches apex
what are the 3 types of lamellae?
Circumferential -Outside of most cortical bone Concentric -Organised in Haversian systems / osteons Interstitial - Remnants of old lamellae
What is found in the middle of the lamellae?
blood vessels
what lines are found in the lamellae?
cementing lines
what is important about osteocytes in lamellae that is different to cementocytes?
osteocytes have processes that go in both directions whereas cementocytes only have one process that points outwards
what are the two types of bone formation?
- endochondral
- intramembranous
Describe endochondral ossification.
Cartilage -> calcified cartilage -> bone
Describe intramembranous ossification.
- Condensation of mesenchymal cells
- Osteoblasts – produce osteoid matrix
- Woven bone
- Primary osteon formation
what is woven bone?
when collagen is randomly organised
Describe the formation of primary osteons.
- connective tissue condensation around Blood vessels + advancing layer of osteoblasts laying down woven bone
- as osteocytes advance, some surround the edge of the condensation and some advance still laying down woven bone
- forms lamellae around the dental vessel
- primary osteons surrounded by woven bone
Describe osteoblasts.
– Mesenchymal or ectomesenchymal derived
– On bone surface (periostuem , endosteum )
– Produce osteoid matrix
Describe osteocytes.
– Trapped osteoblasts – (cf cementocytes) – Cell processes – Linked by gap junctions – Cells vital
what are osteoclasts.
– Derived from haemopoietic source
• Macrophage/monocyte line
– Large multinucleate cells
where are osteoclasts found and what is their role?
– In Howships Lacunae:
• Dissolve bone mineral – acid
• Breakdown organic matrix - enzymes
How often is bone remodelled?
continuous
what occurs during the turnover of bone?
resorption and deposition
how often is bone completely replaced?
every 10 years:
– Keeps skeleton effectively engineered for its use – Helps maintain plasma Ca2+ levels
How is bone remodelled?
– Cutting cone - osteoclasts
– Filling cone – osteoblasts
what does bone turnover result in?
secondary osteons
How much calcium is in the Body?
> 1Kg Ca2+ in body
99% in bones and teeth
– Only 0.4% exchangeable
1% in body fluids
Can calcium be taken out of bone and teeth?
calcium can be taken out of bone in small amounts but NOT teeth
what can remove calcium from bone?
osteocytes and osteoclasts
what are the roles of Ca2+?
-Membrane permeability: > Decreases membrane permeability (esp PNa) > Decreases cell excitability > Low Ca2+ -> spontaneous APs - results in tetany - Excitation – contraction coupling - Excitation – secretion coupling - Hard tissue formation - Blood clotting - Enzyme reactions - Secretions – e.g. milk
what is quick Ca2+ regulation?
Rapid exchanges between bone and ECF
What is slow Ca2+ regulation?
– Intestinal absorption
– Renal excretion
what does the parathyroid hormone do?
- Essential for life
- Release in response to falling [Ca2+]plasma
- increases [Ca2+]plasma
- Prevents hypocalaemia
- Withdraws [Ca2+] from the bone bank
Describe the fast Ca2+ efflux to plasma.
– Small labile pool of Ca2+ in bone
– Involves osteocytes - osteocytic osteolysis
Describe the slow Ca2+ efflux to plasma.
– Bone dissolution
– Shift remodelling to favour resorption
– Involves osteoclasts
what effect does the parathyroid hormone have on the kidney?
Reduced excretion of Ca2+
what is caused by deficiency in the parathyroid hormone?
- Iatrogenic parathyroid gland damage
- Tetany
- Asphyxiation
what is caused by excess of the parathyroid hormone?
- Hyperplasia of PT gland
- Tumours
- Weak bones
- Ectopic mineralisation
what are “C” cells on thyroid gland?
calcitonin
what is the role of calcitonin?
Prevents [Ca2+] plasma becoming high
what is the action of calcitonin?
- Reduce osteocyte activity
- Reduce osteoclast activity
- Reduce osteoclast numbers
what is essential for Ca2+ absorption In the intestine?
Vitamin D - Cholecalciferol
when is Vitamin D - Cholecalciferol produced?
Produced in skin in response to sunlight on a precursor
what is the action of vitamin D?
Increase Ca2+ absorption in the intestine
what does BRONJI stand for?
Bisphosphonate Related Osteonecrosis of the Jaws
what does MRONJ stand for?
Medication related osteonecrosis of the jaws (used now)
what are biphosphates used for?
– Osteoporosis – reduce fracture rates
– Bone metastases
how do biphosphates work?
Reduce osteoclast activity – reduce bone breakdown
How is MRONJ caused?
– Impaired bone turnover -> exposed bone after extraction
