L10 Flashcards
A. Bone Structure and Composition
Cortical (compact) bone
Trabecular (cancellous or spongy) bone
Periosteum
Endosteum
Neurovascular supply
Marrow space
The Haversion System (Secondary Osteon):
Main Functional Unit of Cortical Bone
The wall: concentric lamellae
The central canal: Haversian canal, nerve and blood supply
Main cell component: Osteocytes
Separation between osteons: Interstitial lamellae
Connection between osteons: Volkmann’s canals
Osteons, Lamellae and Lacunae/Canaliculi
Primary osteon
Secondary osteon
Concentric lamellae Circumferential lamellae Interstitial lamellae
Lacunae
Canaliculi
Bone Matrix
Inorganic matrix: mainly in the form of hydroxyapatite
Organic matrix: mainly collagen I
Bone Cells 2 lineages
Mesenchymal lineage
Hematopoietic lineage
- Mesenchyme Stem Cells (MSC)
Also referred as colony-forming fibroblast (CFU-F), or marrow stromal cells
Potential to differentiate into multiple cell types
Morphological features: small cell body, few cell processes
Confirmation of MSC Identity
Ability of osteogenic, chondrogenic and adipogenic differentiation
Our findings are consistent with reports from many others and support that
local delivery of MSCs can enhance bone regeneration.
MSCs info
- Derived from pigs
- Have been used in human surgeries to stop bleeding
- Recently have been used in a few in-vivo animal studies and showed promising results in carrying cells for bone regeneration
- Commercially available and sterile
- Easy to fit into a mandibular distraction site and fast biodegradable
- Our preliminary experiments have shown good cell integration and infiltration with this material and all procedures can be handled in strictly sterile environment
A Commonly Held Mechanism:
Empower local bone regeneration by providing a large source of MSCs, hence boosting or bypassing the slow MSC recruitment process
- Osteoblasts: Bone-forming Cells
Basic characteristics:
- Located on bone surface - Generally cuboidal shape - Mononucleated - HE staining: basophilic cytoplasm (large quantity of rough endoplasmic reticulum)
Major Functions of Osteoblasts
1.Synhesize and secret extracellular matrix
Collagen related proteins:
Collagen type I, III, V
Glycoproteins:
Alkaline phosphatase
Osteonectin
Glycoaminoglycan-containing proteins:
Aggrecan
Versican
Decorin
Biglycan
Hyaluran(MEPE):
Matrix extracellular phosphoglycoprotein
RGD-containing glycoproteins:
Thrombospondins
Fibronectin,
Vitronectin
Fibrillin 1 and 2
Small insulin-binding N-linked glycoproteins (SIBLING):
Osteopontin
Bone sialoproteins
gamma-Carboxy glutamic acid-containing proteins:
Matrix Gla protein
Osteocalcin
- Regulate matrix mineralization
Inside the vesicles, calcium and phosphorous can reach high concentrations without being saturated.
TNAP:
Tissue non-specific alkaline
phosphatase
NPP1:
Nucleotide pyrophosphatase
phosphodiesterase
NTP:
Nucleoside triphosphates
ANK:
Ankylosis protein
BSP:
Bone sialoprotein
- Regulate Osteoclasts through Molecular Interactions
The OPG/RANKL/RANK system:
RANKL: stimulate osteoclast differentiation and maturation
OPG: bind to RANKL and indirectly inhibit osteoclast differentiation
- Osteocytes:
Bone-maintaining Cells
Osteocyte Basic characteristics
- Derived from osteoblasts when buried in the matrix
- Located in laculae inside the matrix
- Most abundant cell type in bone
- Mononucleated
- Multiple dendritic processes
Main Functions of Osteocytes
Regulate osteoblasts & osteoclasts through cell processes
- Maintain bone vitality and function - Sense mechanical loading
After sensing loading, osteocytes regulate bone formation/resorption mainly through the
sclerostin-OPG/RNAKL system
Sclerostin (SOST) is only expressed in
osteocytes, not in any other bone cells
- Osteoclasts: Bone-resorption Cells
Basic characteristics
- Largest of all bone cell types - Often located on bone surface (Howship’s lacunae) - Multinucleated - Tartrate resistant acid phosphatase (TRAP) positive cytoplasm
Characteristics of osteoclasts
Abundant mitochondria
- Vesicles: acid phosphatase - Sealing zone: attachment and sealing - Ruffled border: pump H+ (for demineralization), release enzymes (for organic matrix degradation)
Main Functions of Osteoclasts
Demineralize bone
- Degrade organic matrix - Endocytosis of degraded products
- Bone Lining Cells: Inactive Osteoblasts (?)
Basic characteristics
- Flattened spindle shape - Located on bone surface - Ovoid mono-nucleus - Few organelles
Function
- Uncertain
- May be induced to proliferate and differentiate into osteoblasts
- May be involved in smoothening
osteoclast lacunae
C. Bone Modelling and Remodelling
There are two processes for bone formation:
A. Endochondral ossification: form cartilage first
B. Intramembranous ossification: directly from periosteum
C. Sutural bone formation: a special intramembranous process through sutural matrix
Bone Formation Processes underlying
Jaw Bone Growth
Mx
intramembranous (surface and sutures)
Bone Formation Processes underlying
Jaw Bone Growth
Mn
Mn – endochondral (condyle) & intramembranous (surface)
Modeling:
change of overall bone size and shape; bone
formation and resorption happen at different locations
Remodeling:
Replacement of existing bone; bone
formation and resorption at the same location but at
different times
Secondary Osteons Are Important for
Cortical Bone Remodeling
Trabecular bone remodelling
starts at
bone surfaces
General Characteristics of Bone Remodeling
Cycle duration: formation > resorption
Remodeling rate: children > adults, trabecular bone > cortical bone
Osteoporosis: unbalanced formation/resorption net bone loss
Regulation: Multiple factors (gene, hormone, mechanical loading, metabolism, etc.)
Mesial-distal section:
Interdental septum has two layers: bundle bone and supporting bone
Bundle bone: Sharpey’s fiber
inserted to this layer
Other names: Alveolar bone proper, cribiform plate, lamina dura
Bundle bone-PDL fibers-Cementum
Cells between Sharpey’s fibers:
- Fibroblasts
- Mesenchymal stem cells and osteoprogenitors
- vascular cells
Cell on bone surfaces:
- Osteoblasts
- Bone lining cells
Embryonically, most craniofacial bones have
a different
tissue origin than long bones
Jaw bone mesenchyme is developed from
neural crest
(1st branchial arch) and mesoderm
Postnatal growth of the
alveolar process is highly correlated with tooth eruption
- Tooth agenesis –>
- Tooth agenesis poor development of alveolar bone
Modeling takes place during alveolar bone growth
Bone formation: Vertically at crests along with tooth eruption; transversely at buccal surface and lingual bundle bone along with buccal expansion
Bone resorption: Lingual surface and buccal bundle bone
Alveolar Bone Loss: Risk Factors
Periodontal disease
- Tooth loss - Pathology - Systemic disease - Side effects of medication - Trauma, parafunction, excessive orthodontic force
Techniques for alveolar bone preservation or augmentation
Guided bone regeneration with bioabsorbable membranes
- Bovine-derived bone graft - Mineralized human allograft - Bioactive glass material - Synthetic alloplast - Autogenous bone graft - Decoronation and submergence of roots - Immediate implants - Orthodontic tooth movement - Distraction osteogenesis - Stem cell assisted treatment
Alveolar Bone Changes In Response to Loading:
Orthodontic Tooth Movement
Tooth movement —- a modeling process of the alveolar bone
Due to resorption on one side, formation on the other, the
interdental septum is relocated, but not removed during tooth movement
PDL fiber attachment adapts to
bone modeling during orthodontic tooth movement
PDL Bone resorption side:
Detachment → → → → attachment reconstitution
Bone formation side:
Thickening of bundle bone → → → → remodeling of bundle bone from the endosteum (the opposite side of the PDL)
Source of osteoclasts on the resorption (compression) side:
- Normally, osteoclasts are not present in the PDL.
- Upon receiving compressive force, they are recruited from the blood flow (light pressure) and/or the bone marrow of the adjacent alveolar process (heavy pressure)
Heavy pressure
occludes blood vessels
In response to heavy pressure, osteoclasts were recruited from
bone marrow, the opposite side of the PDL undermining resorption
Source of osteoblasts on the formation (tension) side:
Possible sources of osteoblasts:
Osteoblasts already present at the bone surface
MSCs in the PDL
MSCs in the bone marrow
Bone lining cells
