ALVEOLAR BONE STRUCTURE CLASSIFICATION BONE REMODELLING

1. BONE
BY
DR. KRITI TREHAN
1st MDS
12/9/17

2. 1. Introduction
2. Classification
3. Composition
4. Histology
5. Formation
6. Resorption
7. Remodeling
8. Alveolar process and Alveolar bone
9. Clinical implications
10. Systemic Disorders affecting Bone
11. References
CONTENTS

3. WHAT IS BONE
• Bone is essentially a highly vascular, living,
constantly changing mineralized connective
tissue.
• It is remarkable for its hardness, resilience and
regenerative capacity, as well as its
characteristic growth mechanisms.
• It is the basic unit of human skeleton.

4. FUNCTIONS

5. CLASSIFICATION
DEVELOPMENT
• ENDOCHONDRAL
• INTRAMEMBRANO
US
SHAPE
•LONG
•SHORT
•FLAT
•IRREGULAR
•SESAMOID
STRUCTURE
•MICROSCOPIC
WOVEN
LAMELLAR
•MACROSCOPIC
COMPACT
SPONGY

6. A TYPICAL LONG BONE

8. COMPOSITION
•Minerals- Hydroxyapatite crystals
•Amorphous Calcium phosphate
• Mg, Na, K ,Fl Zn,Cu – smaller quantity
INORGANIC CONTENT
•Collagen ( Type I >95% primarily),TYPE V
ORGANIC CONTENT
•Osteocalcin/ bone gla protein
•Osteopontin
•Bone sialoprotein
•Other proteins- osteonectin,
dermatopontin and proteoglycans
NON-COLLAGENOUS PROTEINS

9. HISTOLOGY

10. All bones consist of :
1.Outer compact bone
2.Inner medullary cavity
(cancellous/trabecular bone + red/yellow
marrow)
Periosteum
The outer surface of most
bone is covered by a layer of
condensed fibrous tissue, the
periosteum which contains cells
capable of converting into osteoprogenitor
cells and osteoblasts.
Endosteum
Is a thin vascular connective layer that
lines the inner surface of the bony tissue
that forms the medullary cavity of long
bones.

11. Compact Bone
• This type of bone is ivory-like and dense in texture without cavities.
• Forms the thick-walled tube of the shaft (or diaphysis) of long bones,
which surrounds the marrow cavity (or medullary cavity). A thin layer
of compact bone also covers the epiphyses of long bones.
• It consists mainly of haversian systems or secondary osteons
• Contains blood vessels, lymphatic vessels, nerves, and osteocytes
along with the calcified matrix.

12. •Haversian Systems
•The basic metabolic unit of compact bone also called osteons

13. •Volkmann's canals
•Are oblique canals running at right angles to the long axis of bone.
•Contain the neurovascular bundle and connect the haversian canals
with each other and also with the medullary cavity .
•Lamellae
•Concentric - surrounding each Haversian canal
•Interstitial - bony plates that fill in between the haversian systems.
•Circumferential – Circumferential lamellae are circular lamellae that
line the external surface of the cortex adjacent to the periosteum and
line the inner surface of the cortex next to the endosteum. There are
more outer than inner circumferential lamellae.
•Lacunae
These are small spaces between the lamellae , each containing a bone
cell called osteocyte.
•Canaliculli
These are fine radiating channels which
connect the lacunae with each other and central haversian canal

14. SPONGY BONE
• Spongy bone (anatomic term)/ Trabecular bone
(radiographic term)/ Cancellous bone (histologic term)
• They have the same cells and intercellular matrix but
differ in the arrangement of the components. These are
poorly organized tissue in contrast to compact bone and
contains more spaces as compared to compact bone.
• Trabeculae aligned in path of tensile and compressive
stresses to provide maximal resistance to occlusal forces
with minimum bone substance (Glickman et al 1970)

15. HEMOPOIETIC TISSUE IN BONES
•Red marrow is present in young bone.
•It contains stem cells of both fibroblast/mesenchymal and blood
lineage .
•It is found within cavities of spongy bone of long bones and diploe of
flat bones.
•Yellow marrow is present in old bone.
•Characterized by loss of hemopoietic potential and increased
accumulation of fat cells.

16. BONE CELLS
OSTEOBLASTS
Osteoblasts are mononucleated cells
responsible for the secretion and synthesis
of the organic constituents of bone matrix.
These cells are derived from
osteoprogenitor cells of mesenchymal
origin.
• Basophilic, plump cuboidal / slightly
elongated cells.
• These cells are found on the forming
surfaces of growing or remodelling bone.
• The most active secretory cells in
bone.

17. Produce--
• Type I collagen
• Noncollagenous bone proteins like Sialoprotein, Osteopontin,
Osteonectin
• Growth factors –BMP, Transforming growth factor, insulin like growth
factor, platelet derived growth factor, fibroblastic growth factor.
•Express and release alkaline phosphatase, which has been shown to be
closely associated with new bone formation and has been recognized
as a reliable indicator of osteoblast function.
• In addition, it has a controlling influence in activating Osteoclasts. It
contains receptors for the parathyroid hormone,vitamin D3,estrogen
and regulates the osteoclastic response to these hormones.

18. OSTEOCYTES
• Osteocytes are ‘entrapped’ osteoblasts within bone .
•Osteocytes occupy spaces (lacunae) in bone called
osteocytic lacuane.
•No. of osteocytes depends on the rapidity of bone
formation. More the rapidity more the cells per unit
volume.
•Osteocytes have an extensive network of cell
processes or extensions and through these channels
osteocytes maintain contact with adjacent osteocytes
and osteoblasts .

19. OSTEOCLASTS
•Osteoclast is a type of bone cell that removes bone tissue by removing the
mineralized matrix of bone.
•These are large cells with 15-20 closely packed nuclei and acidophilic
cytoplasm.
•Lie in Howship’s lacunae.
• Osteoclasts produce a number of
enzymes, chief among them acid
phosphatase, that dissolve both
the organic collagen and the
inorganic calcium and phosphorus
of the bone.

20. • The side of the cell closest to the bone contains many small projections
(microvilli) that extend into the bone’s surface, forming a ruffled, or
brush, border that is the cell’s active region. .

21. MICROSCOPIC ORGANIZATION
OF BONE
With regard to matrix arrangement, bone tissue
can be divided into the following categories:
Woven bone (primary bone tissue) - This is
immature bone, in which collagen fibers are
arranged in irregular random arrays and
contain smaller amounts of mineral
substance and a higher proportion of
osteocytes than lamellar bone; woven bone is
temporary and is eventually converted to
lamellar bone.
Lamellar bone (secondary bone tissue) - This
is mature bone with collagen fibers that are
arranged in lamellae. Lamellae in compact
bone are concentrically organized around a
vascular canal, termed a haversian canals.

22. BONE FORMATION
• The process of bone formation is called osteogenesis .
1. Endochondral bone formation
2. Intramembranous bone formation

23. INTRAMEMBRANOUS FORMATION

24. ALVEOLAR PROCESS
• The alveolar process is that portion of the maxilla and
mandible that forms and supports the sockets of the
teeth.
• Proper development of the alveolar process is
dependent on tooth eruption and its maintenance on
tooth retention. When teeth fail to develop (e.g.
anodontia), the alveolar process fails to form.
• When all teeth are extracted, most of the alveolar
process becomes involuted, leaving basal bone as the
major constituent of the jawbone. The remaining
jawbone, therefore, is much reduced in height.
• It is composed of an outer and inner cortical plate of
compact bone that enclose the spongiosa, a
compartment composed of spongy bone .

25. GROSS MORPHOLOGY
MAXILLA/
MANDIBLE
ALVEOLAR
PROCESS
ALVEOLAR
BONE PROPER
BUNDLE
BONE
LAMELLAR
BONE
SUPPORTING
ALVEOLAR
BONE
BASAL BONE
INNER &
OUTER
CORTICAL
PLATES
SPONGY
BONE

26. ALVEOLAR BONE PROPER
• The alveolar bone proper consists partly of lamellated bone and partly of
bundle bone and is about 0.1 - 0.4 mm thick.
• It surrounds the root of the tooth and gives attachment to principal fibres of
the pdl.
LAMELLATED BONE
o The deeper portion of the alveolar bone proper is made of haversian system
(osteons).
o Each osteons has a blood vessel in a haversian canal and is surrounded by
concentric lamellae .
o Some lamellae of this bone are arranged roughly prallel to the surface of the
adjacent marrow spaces, whereas others form haversian systems.

27. BUNDLE BONE
oThe lamellated bone is
covered by areas of bundle
bone .
oIt is that bone in which the
principal fibres of the
periodontal ligament are
anchored.
oIt is characterized by
scarcity of fibrils in the
intercellular substance.
o Bundle bone is formed in
areas of recent bone
apposition. Lines of rest are
seen in bundle bone.

28. oRadiographically, it is also referred to as the lamina dura because of
increased radiopacity,which is due to the presence of thick bone without
trabeculations.
• The alveolar bone proper , which forms the inner wall of the socket is
perforated by many openings that carry branches of the interalveolar
nerves and blood vessels into the pdl and is therefore called the
cribiform plate.
•Bone between the teeth is called interdental septum and is composed
entirely of cribiform plate.

29. SUPPORTING ALVEOLAR
BONE
Cortical plate
• It consists of compact bone and form the outer and inner plates of the
alveolar processes.
• Bone underlying the gingiva is the cortical plate, both cribiform plate
and cortical plate are compact bone separated by spongy bone.
Spongy bone
• It fills the area between the cortical plates and the alveolar bone
proper.

30. • The trabeculae of the spongy bone butress the functionl forces to which the
alveolar bone proper is exposed.
• Radiographically, spongiosa can be classified into two main types.
 Type 1: The interdental and interradicular trabeculae are regular and
horizontal in a ladder like arrangement. (more often in mandible)
 Type2: Shows irregularly arranged numerous delicate interdental and
interradicular trabeculae. (more often in maxilla)
AGE CHANGES IN BONE
• Alveolar sockets appear jagged and uneven.
• The marrow spaces have fatty infiltration
• The alveolar process in edentulous jaws decrease in size.
• The distance between crest of the alveolar bone and CEJ increases with
age.
• Internal trabecular arrangement is more open, which indicate bone loss.

31. • Houses the roots of teeth.
• Anchors the roots of teeth to the alveoli, which is achieved by
insertion of sharpey’s fibres into the alveolar bone proper.
• Helps to move the teeth for better occlusion.
• Helps to absorb and distribute occlusal forces generated during tooth
contact.
• Supplies vessels to periodontal ligament.
• Houses and protects developing permanent teeth.
FUNCTIONS OF ALVEOLAR
BONE

32. BLOOD SUPPLY
•Derived from inferior and superior alveolar arteries of maxilla and
mandible, venous drainage accompanies the arterial supply
NERVE SUPPLY
•Branches from anterior, middle and posterior superior alveolar nerves
for maxilla and branches from inferior alveolar nerve for mandible
LYMPHATIC DRAINAGE
•Submandibular lymph nodes

33. BONE RESORPTION
•Bone resorption is removal of mineral and organic components of bone
under the action of osteolytic cells, of which the most important is the
osteoclast.
SEQUENCE OF EVENTS OF BONE RESORPTION
First phase - Formation of osteoclast progenitors in the hematopoietic
tissues.
Second phase - Activation of osteoclasts at the surface of mineralized
bone.
Third phase – Involves Activated osteoclasts resorbing the bone.

34. ALTERATIONS IN THE OSTEOCLAST
Immediately before the resorption event, the osteoclasts undergo changes which
faciliate bone resorption. The two distinct altertions are
1. Ruffled border
2. Sealing zone at the plasma membrane.
 These changes occur only in the region of the cell that is next to the bone surface.
 Sealing zone serves to attach the osteoclasts very closely to the surafce of bone and
creates an islolated microenviroment for the resorption to take place.
 The attachment of osteoclasts to the
sealing zone is due to the presence of
cell membrane proteins
integrins,especially αVβ3 which binds
to specific amino acids sequences
present in proteins of the bone matrix,
namely, RGD.

35. REMOVAL OF HYDROXYAPATITE
• Dissolution of mineral phase by the action of HCl.
• The protons for the acid arise from the activity of cytoplasmic carbonic anhydrase II which is
synthesised in the osteoclast.
•Protons are released by an ATP consuming proton pump which is an absolute must for normal
bone resorption.
DEGRADATION OF ORGANIC MATRIX
•Next step involves the digestion of organic components of matrix by proteolytic enzymes which
are synthesized in ostoclasts,namely, CATHEPSIN –K and MMP-9. As a result visbile
depression or Howship’s lacunae is excavated into the bone.

36. REMOVAL OF DEGRADATION PRODUCTS FROM LACUNAE
•Once liberated from bone , free organic and inorganic particles of bone matrix
are packed in membrane bound vesicles within cytoplasm of osteoclast.
•These vesicles and their contents pass across the cell and fuse with FSD
(Function secretory domain) a specialized region of basal membrane.
•The vesicles are released by
exocytosis into the
extracellular space away
from bone.
•Following resoprtion
osteoclasts undergo
apoptosis , which provides a
mechanism for limiting
resorptive activity.

37. During this phase bone is formed along the periosteal surface and
destroyed along the endosteal surface
.
BONE REMODELLING
• Bone remodelling is performed by clusters of osteoclasts and
osteoblasts arranged within temporary anatomical structures called
Basic Multicellular Units (BMUs).
• Traversing and casing the BMU is a canopy of cells that creates a
bone-remodelling compartment.
The status of bone represents the net result of a balance between the two
processes.
‘Coupling’ of bone resorption and formation.

39. An active BMU consists of a leading front of osteoclasts and
osteoblasts occupy the tail portion of the BMU
–
• The leading edge
of resorption
Cutting
cone
• Osteoblasts
secrete osteoid
Filling
cone

40. The main functions of remodeling are-
To prevent the accumulation of damaged and fatigued bone by regenerating new
bone.
To allow bone to respond to changes in mechanical forces.
To facilitate mineral homeostasis.
STRUCTURAL LINES IN BONE
Reversal line or cementing line-
-The site of change from bone resorption to bone
deposition is represented by a scalloped outline.
-Rich in sialoprotein & osteopontin.
Resting line –
Rhythmic deposition of bone with periods of
relative quiescence seen as parallel vertical
lines.

41. Mediators of bone remodelling
Parathyroid Hormone
Calcitonin
• Estrogen
• Vitamin D3
• Growth hormones
• IL -1
• TNF α and β
• Prostaglandins
• BMPs
• Bacterial products

42. Clinical implications of Alveolar bone in
Complete dentures
EDENTULOUS INTRAORAL BONY CHANGES
•Anatomic changes will invariably take place within the alveolar
processes of the jaws following dental extractions.
• When the teeth are present, the pressures exerted are transmitted in the
form of tension to the bone by the periodontal membrane. This type of
stress is acceptable for the alveolar bone.
•Once the teeth are extracted, the load is not directed to the entire bone,
but is applied only its surface. Alveolar bone can only tolerate this
compression to a certain extent.
• The long-term effect of dentures over bone is the atrophy of the
residual alveolar ridge or what Atwood calls reduction of residual ridges
(RRR).

43. Residual alveolar ridge is the portion of the alveolar ridge and its soft
tissue covering which remains following the removal of or loss of teeth.
[GPT-8]
•The residual bony architecture of the maxilla and mandible undergoes a
life-long catabolic remodelling.
•The rate of reduction in size of the residual ridge following extractions
is maximum in the first 3-6 months and then gradually tapers off.

44. According to Atwood’s :
(JPD 1971 Vol.26)
Order 1 : Pre-extraction
Order 2 : Post-extraction
Order 3 : High, well rounded
Order 4 : Knife-edge
Order 5 : Low, well rounded
Order 6 : Depressed
ORDER 1 ORDER 2 ORDER 3
ORDER 4 ORDER 5 ORDER 6
CLASSIFICATION

45. TREATMENT AND
PREVENTION
•A thorough knowledge will provide the clinician with the additional
piece of information required for the selection of an adequate plan of
treatment.
• For certain types of atrophy, a combination of surgery and prosthetics is
required to provide a rapid solution for patients severely handicapped by
dentures.
•It will permit the selection of a technique of choice for the treatment,
based on knowledge about the condition of the remaining hard and soft
tissues.
•Most ideal is a high ridge with flat crest with parallel or nearly parallel
sides.
•Knife edge ridge or a ridge with multiple bony spicules offer the poorest
prognosis.

46. PROSTHETIC IMPLICATIONS OF
ALVEOLAR BONE IN FPD
•The contour of edentulous ridge should be carefully evaluated before a
fixed partial denture is undertaken.
•The ideal ridge height and width allows placement of a natural looking
pontic which facilitates maintenance of plaque-free environment.
•Loss of residual ridge contour may lead to unasthetic open gingival
embrasures, food impaction and percolation of saliva during speech.

47. Role of alveolar bone in implantology
ROLE OF ALVEOLAR BONE IN IMPLANTOLOGY
•Dental implants have become a predictable treatment option for
restoring missing teeth.
•The term bone quality is commonly used in implant treatment and
reports on implant success and failure. Bone quality encompasses factors
other than bone density such as skeletal size, the architecture and 3-
dimensional orientation of the trabeculea, and matrix properties
.
•Bone quality is not only a matter of mineral content, but also of
structure. It has been shown that the quality and quantity of bone
available at the implant site are very important local patient factors in
determining the success of dental implants (Drage et al., 2007; Lindh et
al., 2004). Therefore, it is important to know the bone quantity and
quality of the jaws when planning implant treatment.

48. MISCH BONE DENSITY CLASSIFICATION
• D1: Dense
cortical bone
• D2: Thick
dense to porous
cortical bone on
the crest and
coarse
trabecular bone
within.
D3: Thin
porous cortical
bone on crest
and fine
trabecular bone
within.
D4: Fine
trabecular bone
D5:Immature,
non-mineralized
bone
Bone classification schemes
related to implant dentistry

49. LEKHOLM AND ZARB IN 1985
QUALITY 1
• HOMOGENOUS
COMPACT BONE
QUALITY 2
• THICK LAYER
OF COMPACT
BONE
SURROUNDING
A COREOF
DENSE
TRABECULAR
BONE
QUALITY 3
• THIN LAYER OF
CORTICAL BONE
SURROUNDING
DENSE
TRABECULAR
BONE
QUALITY 4
• THIN LAYER OF
CORTICAL BONE
SURROUNDING
A CORE OF LOW
DENSITY
TABECULAR
BONE

50. •In the jaws, an implant placed in poor-quality bone with thin cortex and
low-density trabeculae (Quality IV by Lekholm and Zarb (1985)) has a
higher chance of failure compared with the other types of bones. This
low density bone is often found in the posterior maxilla and several
studies report higher implant failure rates in this region (Bryant, 1998;
Drage et al., 2007; Penarrocha et al., 2004).
•When compared to the maxilla, clinical reports have indicated a higher
survival rate for dental implants in the mandible, particularly in the
anterior region of the mandible, which has been associated with better
volume and density of the bone (Turkyilmaz et al., 2008).

51. OSSEOINTEGRATION
•American Academy of Implant Dentistry
defined it as “contact established without
interposition of non bone tissue between
normal remodeled bone and on implant
entailing a sustained transfer and distribution
of load from the implant to and within bone
tissue”.
•Osseointegration requires new bone
formation around the fixture. A process
resulting from remodeling within bone tissue.
•Osteoblastic and osteoclastic activity helps
maintain blood calcium without change in
quantity of bone.

52. SYSTEMIC DISORDERS
AFFECTING ALVEOLAR BONE
• Systemic disorders affect the entire body , so the
radiographic changes manifested in the jaws are generlized .
The general changes include :
1. A change in size and shape of the bone.
2. A change in the number ,size and shape of the trabeculae.
3. Altered thickness and density of cortical structures.
4. An increase or decrease in overall bone density.

53. •Metabolic disorders
• Osteoporosis
• Rickets and osteomalacia
• Osteopetrosis
• Hypophosphatasia
• Hypophosphatemia
• Renal osteodystrophy
Endocrine disorders:
•Hypo/Hyperparathyroidism
•Hyperpitutarism
•Hypo/Hyperthyroidism
•Diabetes mellitus
•Cushings syndrome

54. OSTEOPOROSIS
•Generalized decrease of bone mass and density.
•Imbalance occurs between bone formation and resorption.
•Decrease in bone formation result in changes in trabecular
architecture ,volume of trabecular bone, size and thickness of
individual trabeculae.
•Trabeculae are thin and indistinct
•(Diffuse granularity)
•Thinning of cortical boundaries
such as inferior mandibular cortex.
•Lamina dura may appear thinner.

55. RICKETS AND OSTEOMALACIA
•Inadequate serum calcium and phosphorus levels
• both abnormalities result from a defect in the normal activity of the
metabolites of Vitamin D, required for resorption of calcium in the
intestine. .
•Accumulation of osteoid in place of mineralized bone.
•RICKETS
oInferior mandibular border or the mandibular canal walls may be
thinned.
oCancellous bone trabeculae beco-
mes reduced in density, number,
thickness.
oLamina dura may be thinned
•OSTEOMALACIA
oGeneralized rarefaction of jaws
oCortical thinning
oSparse trabeculae
oLamina dura is thinned or lost

56. HYPOPHOSPHATASIA
•Due to defective production or function of alkaline phosphatase.
•Jaws: generalized radiolucency of maxilla and mandible.
• both cortical bone and lamina dura are thin.
•Alveolar bone is poorly calcified and may appear deficient.
•Both primary and permanent tooth have thin enamel, large pulp
chambers.
•Tooth is hypoplastic.

57. RENAL OSTEODYSTROPHY
•Renal rickets: bone changes result from chronic renal failure
•General: generalized decreased bone density and thinning of bony
cortices.
•Jaws: decrease in no of trabeculae, pattern is granular
•Loss of distinct lamina dura.
•Of interest is the occassional finding of an increase in bone density.

58. OSTEOPETROSIS
•Synonyms: albers –schonberg and marble bone disease
•Disorder of bone results from a defect in the differentiation and
function of osteoclasts
•Increased density bilaterally
•Internal aspect of bone is radio-opaque and lamina dura is lost.
•Entire bone is enlarged.
•Increased radio-opacity of jaws .
•Delayed eruption, loose tooth, malformed roots, missing tooth,
poorly calcified, more prone to caries.
•Lamina dura is thicker than normal

59. HYPERPARATHYROIDISM
•It is an endocrine abnormality in which there is an excess of
circulating PTH due to which there is increased bone remodelling and
serum calcium levels.
•Osteitis fibrosa generalisata(cystica): refers to pattern of generalised
rarefaction of bone.
•Bones appear quite radiolucent with thin cortices and hazy indistinct
trabeculae.
•Thinning of the cortical boundaries
•Density of the jaws is decreased
•The teeth stand out in contrast
to the radiolucent jaws,
•Normal trabecular pattern to
ground glass appearance.
•Trabeculae are numerous small
randomly oriented.
•Loss of lamina dura

60. HYPERPITUTARISM
• Results from hyperfunction of the anterior lobe of the pituitary
gland,which increases the production of the growth hormone.
• Enlargement of the jaws , most notably the mandible.
•Increase in the length of the dental
arches.
•The most profound growth occurs
in the condyle and ramus , often
resulting in class III skeletal
relationship.Thickness and height
of the alveolar process may
increase.
•Hypercementosis may be seen.

61. HYPERTHYROIDISM
•Excessive production of thyroid hormo
ne and increased level of thyroxine.
•Generalized decrease in bone density.
•Early eruption and premature loss of
primary teeth.
HYPOTHYROIDISM
•Synonyms; myxedema, cretinism
•In sufficient secretion of thyroxin
•Delayed eruption and short roots
•Thinning of lamina dura
•Maxilla and mandible are relatively
small
•External root resorption

62. REFERENCES
• Orban’s oral histology and embryology
• Contemporary Implant Dentistry, Carl E. Misch
• Prosthodontic Treatment for Edentulous
Patients, Boucher
• Oral Radiology: Principles and Interpretation, Stuart C.
White, Michael J. Pharoah
• Bone Quality Assessment for Dental Implants Ayse Gulsahi
Baskent University Faculty of Dentistry, Ankara, Turkey

63. Thank you