ALVEOLAR BONE
Contents
Introduction
Bone Histology
Cells and Intercellular Matrix
Bone Development
Remodelling
Age Changes
Clinical Considerations
Conclusion
References
Introduction
Bone- used to designate both an organ and a tissue
Specialized mineralized connective tissue
Functions:
mineralised supporting tissue
act as a reservoir for ions
(especially calcium).
provide a framework for bone marrow
gives attachment to muscles
its "plasticity', allows it to remodel according to the functional demand placed upon it.
CLASSIFICATION (Ten Cate )
DEVELOPMENTALLY, Endochondral bone Intramembranous bone
HISTOLOGICALLY, according to its density, mature bone can be divided into; Compact (cortical) bone Cancellous (spongy) bone
MICROSCOPICALLY:
Lamellar bone
Fibrous bone
LAMELLAR BONE:
Most of the bones, whether compact or cancellous, are composed of thin
plates of bony tissues called lamellae.
These are arranged in piles in a cancellous bone, but in concentric
cylinders (Haversian system or secondary osteon) in a compact bone.
FIBROUS BONE (WOVEN BONE):
It is found in young fetal bone. Collagen fibers - more variable diameter Irregular orientation giving it matted appearance
DEVELOPMENT OF ALVEOLAR PROCESS
Alveolar process is dependent on the presence of teeth for its
development and maintenance.
At the late bell stage, bony septa and bony bridge start to form,
and separate the individual tooth germs from another, keeping
individual tooth germs in clearly outlined bony compartment.
(BERKOVITZ)
Initially, this bone forms a
thin egg shell of support,
termed as the ‘tooth crypt’,
around each tooth germ.
FIG. 9-5 A developing root shown by a divergent apex around the dental papilla (arrow), which is enclosed by an opaque bony crypt.
Relationship between
a deciduous tooth & its
accompanying
succedaneous tooth
detailing the formation
of the alveolar bone
- Scoh, Symonds 1974
12/85
AT BIRTH AT 7MONTHS
AT 2½ YRS 7 YRS
Bone
67 %
Inorganic
Hydroxyapatite
33% (organic)
28% 5 %
Collagen type Ӏ Non coll.proteins
(ca10{po4}6{oh}2)
Osteocalcin, Osteonectin, Bone morphogenic proteins, Phosphoproteins and Proteoglycans
Ground substance- Glycosaminoglycans, proteoglycans and water
Osteopontin, Bone Sialoprotein- cell adhesion proteins (Mackie et al, 2003)
Osteocalcin (bone GLA protein)
Found in bone matrix
Expressed only by fully differentiated cells
Specifically localized to developing bone
Produced by osteoblasts and odontoblasts
Role in bone formation
Osteopontin
Glycosylated phosphoprotein
Role in bone formation and resorption
Synthetized by osteoblasts, osteoclasts, osteocytes, smooth muscles and epithelial cells
Role in cell adhesion
Significant amounts at mineralizing front
Bone sialoprotein
Structural protein of bone
Restricted to mineralized tissues
Secreted by osteoblasts
Osteonectin
Glycoprotein bound to HA
Calcium binding glycoprotein
Synthesized by fibroblasts and role in wound healing
Inorganic material- calcium, phosphate ,hydroxyl, carbonate, citrate
Trace amounts of sodium, magnesium and fluorine (Glimcher 1990)
Hydroxyapetite crystals of ultramicroscopic size
Enzymes like alkaline phosphatase, ATP and pyrophosphatase
Parallel to collagen fibres and contribute to lamellar appearance of bone
Alveolar bone
Portion of maxilla and mandible that forms and supports the tooth sockets (alveoli)
Forms when tooth erupts to provide osseous attachment to PDL
Disappears gradually after tooth loss
‘Tooth dependent bony structure’ (Schroeder et al, 1991)
Transverse section
Longitudinal section
Morphology determined by size, shape, function and location of teeth
Formed during fetal growth by intramembraneous ossification
Cancellous Bone
Compact Bone
Shelf like bone
Holds the tooth firmly in position during mastication
Aids in movement
Adapts to occlusal loads
Helps to move the teeth for better occlusion.
Functions of alveolar bone
Supplies vessels to the PDL.
Houses & protects developing permanent teeth while supporting primary teeth.
Organizes successive eruptions of primary & secondary teeth.
Bone Histology
Three parts
1) External plate of cortical bone
2) Inner socket wall
3) Cancellous trabeculae (between two compact layers)- function of support
Cortical bone
1) Circumferential lamellae (encloses entire adult bone and forms the outer perimeter
2) Concentric lamellae (make up bulk of compact bone and forms the basic metabolic unit of bone, the osteon)
3) Interstitial lamellae (inter-spread between adjacent concentric lamellae and fill the spaces between them..actually fragments of pre-existing concentric lamellae and can be of many shapes)
Osteon –cylinder of bone parallel to long axis of bone (structural and metabolic units)
Haversian canal –in centre of osteon, lined by single layer of bone cells
Each canal has a capillary
Haversian canals interconnected by Volkmann canals
System for dense bones like cortical plates and alveolar bone proper, where surface vessels are unable to supply blood
Socket wall
Dense , lamellated bone – alveolar bone proper (contains sharpeys fibers and circumferential lamellae)
Cribriform plate (anatomic term)
Lamina dura (radiographic term)
Bundle bone (histologic term)
Bundle bone
Bone adjacent to PDL that contain sharpeys fibers
Contains higher calcium than other areas
Many features in common with cementum layer on root surface
Collagen fibers larger in diameter, less numerous , less mature
Localized within alveolar bone proper
Sharpeys fibers completely calcified or partially calcified with uncalcified core
Not unique to jaw -occurs wherever ligaments and muscles are attached
Thickness of 100-200 microns
High turnover rate
FIBER ARRANGEMENT IN ABP
DOUBLE FIBRILLAR ORIENTATION:
Extrinsic fibers- Sharpey’s fibers
run perpendicular to bone surface
produced by PDL fibroblast
At their insertion in bone, they become mineralized, with their periphery
being hypermineralized than cores.
Intrinsic fibers
Laid down by osteoblasts between Sharpey’s fibers
Irregularly arranged & less dense.
Cancellous bone
Presence of trabeculae enclosing irregular marrow spaces lined with a layer of thin, flattened endosteal cells
Variation in trabeculae pattern depending upon occlusal forces and genetically
Matrix consists of irregularly arranged lamellae separated by incremental and resorption lines
Found in inter-radicular and inter-dental spaces
Maxilla>mandible
Trabeculae alligned in path of tensile and compressive stresses to provide maximal resistance to occlusal forces with minimum bone substance (Glickman et al 1970)
in thickness and number with force
Spongy bone (anatomic term)
Trabecular bone (radiographic term)
Cancellous bone (histologic term)
CANCELLOUS BONE:
Type 1: The interdental and interradicular trabeculae are regular
and horizontal in a ladder like arrangement.
Type 2: Shows irregularly arranged numerous delicate
interdental and interradicular trabeculae
CORTICAL BONE SPONGY BONE
About 85% of bone About 15% of bone
Lesser turnover than spongy Higher turnover
Remodel about 3% of its mass each year
remodel about 25% of its mass each year
Mechanical/protective role More metabolic function
Interdental septum
Consists of cancellous bone bordered by alveolar bone proper of approximating teeth and facial and lingual cortical plates
Narrow septa- only cribriform plate
Irregular window
Study by Heins et al 1986
Area Cribriform plate+cancellous bone
Only cribriform plate
Irregular window
Maxillary molars
66.6% 20.8% 12.5%
Mandibular premolar and molar
85% 15% 0%
Mesiodistal angulation of IDS is parallel to line drawn between CEJ of approximating teeth (Ritchey et al, 1953)
Shape and size of IDS depends on
1) Size and convexity of crowns of approximating teeth
2) Position of teeth
3) Degree of eruption
Crest of IDS located 1-2 mm apical to CEJ of adjacent teeth
Diagram of relation between CE junction of adjacent teeth shape of crest of alveolar septa
Bone marrow
• Embryo and newborn,
• Ribs, sternum, vertebrae, skull, humerus
• Hemopoiesis
Red hematopoieti
c marrow
• Adult
• Red marrow foci found sometimes in maxillary tuberosity, symphysis and angle of ramus
• Storage of energyYellow fatty
marrow
Cells
CELL TYPES IN BONE
Determined osteogenic precursor cells
Inducible osteogenic precursor cells
Muscles.
Friedenstein (1973) divided osteoprogenitor cells into:
Osteoblast
Produce organic matrix of bone
Differentiated from pluripotent follicle cells
No decrease with age
Uninuclear cells
Secrets collagen as well as non collagenous proteins
Present on outer bone surface
Have high levels of alkaline phosphatase (this feature distinguishes it from fibroblasts)
Alkaline phosphatase believed to cleave organically bound phosphate and help in bone growth
Active-plump, cuboidal
Inactive-flattened
Secrete type Ӏ and V collagen, variety of cytokines and several members of BMP such as BMP-2, BMP-7, TGF-ß, IGF-1, IGF-2
BMP family helps in bone formation and repair
Under physiologic condition which support resorption- release of IL-6 and hydrolytic enzymes
Osteocyte
Enclosed within spaces called lacunae within calcified matrix
Entrapped Osteoblasts
Reduction in size and loss of matrix synthesizing ability after being entrapped
Excess space-lacunae
Extend processes into canaliculi that radiate from lacunae
Anastomosing system
Bring O2 and nutrients to osteocytes through blood and remove metabolic waste products
More rapid the bone formation-more osteoblasts get entrapped – more osteocytes (eg- bone formed during repair)
Osteolytic osteolysis- osteocytes capable of resorption
Three functional states of osteocytes
Quiescent osteocytes:
paucity of rER, diminished golgi apparatus
An osmiophilic lamina representing mature calcified matrix is seen in close apposition to cell
membrane.
Formative osteocyte:
abundant rER & golgi apparatus
evidence of osteoid in pericellular space within the lacuna.
Resorptive osteocyte:
Numerous ER & well developed golgi apparatus.
The pericellular space is devoid of collagen fibrils & may contain a flocculent material suggestive
of breakdown product.
‘Osteocytic osteolysis’.
Osteoclast
Originate from hematopoietic tissue
Fusion of mononuclear cells (blood derived monocytes) to form a multinucleated cell
Very large, 5-50 nuclei
Active on less than 1% of bone surface
Mobile and capable of migrating
Lie in Howships lacunae
Acidophilic cytoplasm
Active osteoclasts- ruffled border facing bone (hydrolytic enzymes are secreted)
Increases surface area
Clear zone devoid of organelles but rich in actin filament, vinculin, talin (site of adhesion of osteoclast to bone)
Sealing zone
Ruffled border-enzymes like tartarate resistant acid phosphatase, carbonic anhydrase, proton pump ATP’s
Cathepsin containing cytoplasmic vesicles near ruffled border
OSTEOCLASTIC FUNCTION IN BONE RESORPTION
1. Attachment of the osteoclast to mineralized bone surface
2. Creation of sealed acidic environment through action of proton pump which demineralizes bone & exposes the organic matrix
3. Degradation of the exposed organic matrix to its constituent amino acids by the action of released enzymes like acid phosphatase & cathepsin
4. Sequestering of the mineral ions & amino acids within the osteoclasts.
Tencate 1994- Described sequence of events of resorptive process:
Bone Lining Cells
- When bone is no longer forming…..surface
osteoblasts become inactive ….. Lining cells.
- Thin flat nucleus, few cytoplasmic organelles
- Retain gap junctions with osteocytes….functions
to control mineral homeostasis & endure bone
vitality.
Periosteum and endosteum Both are layers of differentiated osteogenic connective tissue
Periosteum covers outer surface of bone and endosteum lines the internal bone cavities
Bundles of collagen fibres from outer layer penetrate bone and bind periosteum to bone
Endosteum composed of a single layer of osteoblasts with some connective tissue
Periosteum
• Rich in blood vessels, nerves• Contains collagen fibres and
fibroblasts• Fibrous periosteum
Outer layer(fibrou
s)
• Composed of osteoblasts and osteoprogenitor cells
• Cellular periosteumInner layer (osteogenic
)
Functions of periosteum
Medium through which muscles, tendons and ligaments are attached to bone
Nutritive function to the bone
Osteoprogenitor cells – Important role during development and repair after fracture
Fibrous layer- acts as limiting membrane (exostoses in cases of periosteal tear)
Bone Development
1) Endochondral bone formation
2) Intramembranous bone formation
3) Sutural bone formation
Endochondral bone formation Cartilage replaced by bone
Shape of cartilage resembles miniature version of bone to be formed
At end of long bones, vertebrae, ribs, head of mandible and base of skull
Condensation of mesenchymal cells
Perichondrium at the periphery
Rapid growth of cartilage
Cartilage replaced by bone gradually by osteoblasts at periphery
Intramembranous bone formation
Occurs directly within mesenchyme
Bone develops directly within the soft connective tissue
Vascularity increases and osteoblasts differentiate and lay down bone
Occurs at multiple sites (primary ossification center)
Ossification centers grow radially
Cranial vault, maxilla, body of mandible and mid shafts of long bones
Proceeds at extremely rapid rate
Woven bone formed first in form of radiating spikules which ultimately fuse to form plates
Transition of woven bone to lamellar bone
Mesenchymal condensation followed by increase in vascularity
Some mesenchymal cells lay down collagen fibre bundles forming a membrane
Some differentiate into osteoblasts and lay down osteoid Which then gets calcified
Mineralization always lags behind the production of bone matrix
Sutural bone growth
Bone forms along suture margins
Found in skull
Fibrous joints between bones
Allow only limited movement
Helps skull and face to accommodate growing organs like eyes and brain
Vascular supply
Derived from inferior and superior alveolar arteries of maxilla and mandible
Lymphatic drainage
Submandibular lymph nodes
Nerve supply
Branches from anterior, middle and posterior superior alveolar nerves for maxilla and branches from inferior alveolar nerve for mandible
Osseous topography
Bone contour follows root prominence
Intervening vertical depressions that taper towards margin
Height of facial/lingual plates affected by 1) Allignment of teeth 2) Angulation of root to bone 3) Occlusal force
Osseus topography:
Normally: prominence of the roots with the intervening vertical depressions that taper toward the margin.
On the labial version: the margins of the labial bone is thinned to a knife edge & presents an accentuated arc in the direction of the apex.
On the lingual version: the margins of the labial bone is blunt & rounded & horizontal rather than arcuate.
Buttressing bone- adaptive mechanism against occlusal force (thickened cervical portion of alveolar plate)
Fenestration and Dehiscence
Fenestration- Isolated areas in which root is denuded of bone and root surface covered only by periosteum and overlying gingiva
Dehiscence- Denuded area extends through marginal bone
Facial > lingual
Anteriors > posteriors
Frequently bilateral
20% of all teeth affected
Caused due to malposition, root prominence, labial protrusion and a thin cortical plate
Can complicate procedure and outcome of periodontal surgery
Remodelling
Remodeling of alveolar bone Least stable of periodontal tissues Structure in a constant state of flux
• Functional requirements• Age related changes in bone
cells
Local influence
s• Hormones (PTH, vit D,
calcitonin)Systemic influence
s
Remodeling is the major pathway of bone changes in shape, resistance to forces, repair of wounds, and calcium and phosphate homeostasis in the body.
REMODELING
Regulation of bone remodelling is a complex process involving hormones and local factors acting in a autocrine and paracrine manner on the generation and activity of differentiated bone cells – Sodek et al 2000
Bone-99% of body calcium ions
Major source of calcium release when blood Ca
Monitored by parathyroid gland
Bone coupling
Decrease in blood Ca
Detected by receptors on chief cells of parathyroid gland
Release of PTH
Stimulate osteoblasts to release IL-1 and IL-6
Stimulates monocytes to migrate to area
Monocytes coalesces to form multinucleated osteoclasts in presence of LIF-
Leukemia inhibiting factor released by osteoblasts
Bone resorption
Release of Ca ions from hydroxyapetite crystals
Normal blood calcium levels
PTH secretion stopped by feedback mechanism
Organic matrix resorbed with hydroxyapetite
Collagen breakdown
Release of organic substrate which are covalently bound to collagen
Stimulates differentiation of osteoblasts
Bone deposition
‘COUPLING’ refers to interdependency of osteoclasts and osteoblasts in remodelling
Bone multicellular unit (BMU)
Reversal line
MEDIATORS OF BONE RESORPTION
STIMULI FACTORS REGULATING OSTEOCLAST FORMATION & FUNCTION
POTENTIAL THERAPEUTIC STRATEGIES TO TREAT BONE RESORPTION
Age changes
Similar to those occurring in remainder of skeletal system
Osteoporosis with ageing
Decreased vascularity
Reduction in metabolic rate and healing capacity(implants, extraction sockets, bone grafts)
Bone resorption may be increased or decreased
More irregular periodontal surface
Thinning of cortical plates
Rarification of bone
Reduction in no of trabeculae
Lacunar resorption more prominent
Susceptibility to fracture
Thickening of collagen fibers
Decrease in water content
Clinical and implant considerations
- Gingival margins …follows the contour of alveolar process.
Abnormalities such as ledges, exostosis & tori…reflect on
gingiva.
- Areas of fenestrations & dehiscence - partial thickness flap.
Clinical Considerations
- Process of bone remodeling - in orthodontic treatment.
- Knowledge of the various factors regulating bone formation
has resulted in their use for regeneration of bone.
Buccal-lingual/palatal ridge resorption during first 3 months after extraction about 30%... Reaching 50% at the end of 1 year (Schropp et al , 2003)
Resorption more pronounced at buccal than lingual/palatal aspect of ridge leading to shift of center of ridge towards lingual/palatal side
Socket preservation
Classification (Lekhom and Zarb- 1985)
4 bone qualities for the anterior regions of the jaw bone:
Quality1, Quality 2, Quality 3, Quality 4
Misch Bone Density Classification
D1-dense cortical
D2-porus cortical and coarse trabecular
D3-porus cortical and fine trabecular
D4-fine trabecular
Regional Acceleratory Phenomena
Local response to a noxious stimulus.
A process by which tissue forms faster than the normal regional
regeneration process.
- Frost et al, 1983
By enhancing the various healing stages, this phenomena makes the
healing process occur 2 – 10 times faster than normal physiologic
healing.
RAP begins within a few days of injury, typically peaks at 1 - 2
months, usually lasts 4 months in bone, & may take 6 - >24 months
to subside.
Duration & intensity of RAP α type & amount of stimulus & the
site where it was produced.
Noxious stimuli of sufficient magnitude: can evoke RAP.
Fractures
Mechanical abuses
Noninfectious inflammatory injuries: dental implant procedures
Bone grafting surgeries
Internal fixation procedures
Mucoperiosteal surgery
Injury to bone: Pathologic process
Arthrofibrosis
Neuropathic soft tissue problems
Rheumatoid phenomena
Secondary osteoporosis
Excessice heat
RAP is delayed / not initiated.
Formation of biologically delayed union / nonunion.
RAP does not result in a change in bone volume.
Restricted to bone remodelling.
More evident in cortical bone.
Usually accompanied by a systemic response: Systemic
Acceleratory Phenomena
Biochemical agents also appear to facilitate the RAP.
PG E1
Bisphosphonate
Inadequate RAP is associated with:
DM
Peripheral neuropathies
Regional sensory denervation
Severe radiation damage
Severe malnutrition
Conclusion
Thus a sound knowledge of bone anatomy, histology and physiology, will help the clinician in diagnosing and treatment planning, and lead to a favorable outcome of surgical procedures performed
References
Carranza’s Clinical Periodontology- 10th edition
Clinical Periodontology and Implant Dentistry- Jan Lindhe- 5th edition
Contemporary Implant Dentistry- Carl Misch- 3rd edition
Orban’s Oral Histology and Embryology- 11th edition
Structure of Periodontal Tissues in Health and Disease- Periodontology 2000, vol 40, 2006, 11-28
Thank you
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