1. BONE
Chapter 10
A narrative report
Submitted by:
Bautista, Louis Clyde C.
Gatdula, Dave Joseph B.
Ong, Charles Adrian P.
Santos, Pauleen Ashley R.
Torres, Jhoana Marie O.
Tria Tirona, Rafaelle Jeanna E.
Submitted to:
Dr. Marie Antoniette R. Veluz

2. CHAPTER 10: BONE
What is a bone?
A bone is a specialized connective tissue, which consists of intercellular substances and
osteocytes. Systematically, it is finally controlled by hormonal factors. Locally it is controlled
by mechanical forces including tooth movement, growth factors, cytokines, and
piezoelectric conditions. It consists of 67% of inorganic matrix which is a poorly crystallized
calcium-deficient Hydroxyapatite crystals (Ca10(PO4)6(OH)2), while 33% is made up of
Organic matrix which contains 28% collagen and 5% noncollagenous protein (Osteonectin,
osteocalcin, bone morphogenetic protein, bone proteoglycan, bone sialoprotein). The ratio
between hard and soft components is sufficient to ensure a degree of elasticity. Bone
resists compressive forces best and tensile forces least.
There are plenty of functions a bone can perform, and these are the following:
Mechanical function includes protection of the internal organs of the body, provides
structural framework to keep the body supported, and it provides movement of the body.
Synthetic function includes blood production in the bone marrow. This process is called
hematopoiesis. Metabolic functions of bone include the storage of important minerals in
the body like calcium and phosphorus, storage of important growth factors, and for the
storage reserve of fatty acids.
The Structural Elements of the bone are the bone cells, bone matrix, sharpey’s fibers,
blood vessels, nerves, lymphatic vessels. Bone cells are primarily responsible for the
formation, resorption, and maintenance of osteoarchitechture.
There are 3 types of bone cells are described with each specific function:
Osteoblasts are uninucleated cells that synthesize
both collagenous and noncollagenous bone proteins.
They are located on the surface of bone or osteoid.
Osteoblasts also synthesize the enzyme alkaline
phosphatase, which is needed locally for the
mineralization of osteoid. When the bone is no longer
forming, the surfaces of the osteoblasts become
inactive and are called Lining cells. These lining cells
retain their gap junctions with osteocytes, creating a
syncytium that functions to control mineral
hemostasis and ensure bone vitality. Osteoblasts do
not divide. They give rise to osteocytes, remain as
osteoblasts, or return to the state of osteoprogenitor
cells from which they derived. They secrete type I and
type V collagen and small amounts of several
noncollagenous proteins, and a variety of cytokines. Parathyroid hormone & vitamin D
enhance bone resorption at high concentrations but supporting bone formation at

3. lower concentrations, while Calcitonin & estrogen inhibit bone resorption. On the other
hand, Glucocorticoids inhibit both resorption and formation of the bone, but primarily
formation. Osteoblasts also synthesize a variety of cytokines and growth factors such as Bone
morphogenetic protein (BMP), Transforming growth factor beta (TGF-BETA), Insulin-like
growth factor, Platelet-derived growth factor (PDGF-AH) and Fibroblastic growth factor
beta (FGF-BETA) that help in regulating cell metabolism.
Osteocytes are osteoblasts secreted in the
bone matrixes that are entrapped in lacunae. An
osteocyte lies in its own lacuna and contacts its
neighboring osteocytes cytoplasmically through
canaliculi. The processes of adjacent cells make
contact via gap junctions, maintaining the vitality
of osteocytes by passing nutrients and
metabolites between blood vessels and distant
osteocytes, regulating ion homeostasis, and
transmitting electrical signals in bone. Osteocytes
are responsible for osteolysis or limited
resorption of bone materials at the walls of the
osteolytic lacunae and canals, and osteoplasia,
the secondary rebuilding of perilacunar bone
mineral. They are known to be as the “housekeepers” of the bone since they are actively
involved in the maintenance of the bony matrix.
Osteoclasts are probably derived from a
monocytic-macrophage system, which are
responsible for bone resorption. They are large,
multinucleated cells with fine, fingerlike cytoplasmic
processes and are rich in lysosomes that contain
tartrate-resistant acid phosphatase (TRAP).
Osteoclasts lie in resorption craters known as
Howship’s lacunae on bone surfaces or in deep
resorption cavities called cutting cones. They possess
an organelle-poor, brush-like cytoplasmic border
known as ruffled border which demarcates the zone
of resorption. The osteoclasts resorbs the bone by
first attaching themselves to the mineralized tissue
and create a sealed environment that is acidified to demineralize the hard tissue. After the
exposure to the acidic environment, the organic matrix is broken down by the secretion of
proteolytic enzymes.

4. Bone Matrix
Bone matrix is the intercellular substances of bone and consists of organic and inorganic
components. The association of these substances gives bone its hardness and resistance.
The organic component is composed of:
 collagen fibers with predominately type I collagen (95%) which provides tensile
strength
 proteoglycans that are responsible for compressive strength
 matrix proteins
 osteocalcin that functions to promote mineralization and bone formation
 osteonectin that plays a role in regulating collagen attachment, and
 osteopontin, a cell binding protein that is similar to an integrin
 Cytokine and growth factors that aid in bone cell differentiation, activation,
growth, and turnover.
The inorganic component is made up of Hydroxyapatite crystals (Ca10(PO4)6(OH)2) which
provides the compressive strength of the bone.
Sharpey’s Fibers are lateral fibrous elements extended into the bone matrix.
Blood Vessels, Nerves, Lymphatic vessels (Haversian canals)
Structure of a bone
Bone tissue of which bones are composed of may be
described as compact bone or trabecular bone. The compact bone
forms the outer layer of the bone itself. It is ivory-like and dense in
structure and has no cavities. It is the shell of many bones and
surrounds the trabecular bone in the center. The trabecular bone may
also be reffered to as the spongy or cancellous bone. It has numerous
cavities and contains the bone marrow. Complete osteons are usually
absent here due to the thinness of the trabeculae.
It consists of three layers namely: circumferential lamella
(subperiosteal bone), concentric lamella and the interstitial lamella.
The circumferential lamella makes up the outside surface of the
bones. It is not made up of small concentric circles and follows the
surface of circumference of the bone. The next one is the concentric
lamella which contains the basic unit of the bone called the osteon.

5. The osteon contains the Haversian canals which provide a pathway so that nutrients from the blood
vessels may reach the osteocytes. The Volkmann’s canals interconnect the Haversian canals forming a
network of blood vessels. The third one is the interstitial lamella which is said to be the incomplete or
fragmented osteons that are located between the secondary osteons. They represent the remnant
osteons left from partial resorption of old osteons during bone remodeling.
circumferential lamella concentric lamella
Growth of bone
It is also known as ossification or the formation of the bone. It includes both bone formation and
bone resorption or the removal of mineral materials and organic matrix of bone. There are three types
of ossification. These are the endochondral formation, intramembranous formation and the sutural
bone growth.
Endochondral formation is the formation of bone tissue that is preceded by the formation of
cartilage model that resembles the shape of the bone that is to be formed. The cartilage predecessor of
the bone mineralizes and is gradually removed by resorption. The bone tissue formed replaces it. The
examples of bones formed through this method are the long bones of the arms and legs.
The second one is the intramembranous formation wherein the bone tissue is formed without
preceding cartilage pattern. It is formed by fibrous connective tissue. Osteoblasts secrete bone matrix
called the osteoid and the matrix then mineralizes to form the bone proper. Some of the osteoblasts
become trapped in the forming bone and become osteocytes. Examples of bones formed through this
method are the mandible and maxilla.
Lastly, the sutural bone growth. Sutures are fibrous joints between the bones which permit the skull
and face to accommodate growing organs. It has the same osteogenic potential as the periosteum and it
connects 2 periosteal surfaces, namely: the cambium which is the osteogenic layer and the capsule
which is the inner layer.
Alveolar process
As such develops in the conection with the growth of the jaw and erruption of the of teeth.
These are parts of the maxilla and mandible that are especially designed to provide sockets and support
of teeth. It is called processus alveolaris in maxila and pars alveolaris in the mandible bone.

6. Functions
It supports the tooth roots on the facial and on the palatal/lingual sides. It is the one responsible
for the separation of teeth from mesial to distal. And also contributes to absorption and distribution of
oclussal pressure produced in tooth to tooth contact.
Structures of the alveolar bone
Cortical plate
It provides strength and protection for the supporting bone (maxilla and mandible also acts as a
site for attachment for skeletal muscles. It is covered by periosteum. In labial sections cortical plate is
attached directly to the alveolar bone proper. This arrangement causes the bone overlying the roots of
the anterior teeth brittle in nature. Cortical plate in mandible is more dense and has fewer perforations
for passage of vessels and nerves than in the maxilla.
Alveolar Crest
The alveolar crest is the highest point of the alveolar ridge and joins the facial and lingual
cortical plates.

7. Trabecular Bone
Trabecular or spongy bone lies within the central portion of the alveolar process, and is the less
dense, cancellous bone. When viewed by a radiograph, trabecular bone has a web-like appearance.
Alveolar bone proper
The alveolar bone proper is a thin layer of compact bone, which is a specialized continuation of
the cortical plate and forms the tooth socket. The lamina dura is a horseshoe shape white line on a
dental radiograph that roughly corresponds to the alveolar bone proper.
Development of the alveolar process
The alveolar bone starts to develop near the end of the second month of fetal life. Both the
maxilla and mandible form a groove at their free surface (towards the oral cavity). The tooth germs of

8. the deciduous teeth are contained in this groove. Gradually, bony septa develop between the adjacent
tooth germs.
In fetal life, the developing bone is a non-lamellar type of bone surrounded by a thick
periosteum. Areas of secondary cartilages may appear at the growing alveolar margins during the rapid
growth of alveolar bone.
After eruption of teeth, the alveolar bone gradually takes its adult form. The alveolar process
starts developing strictly during tooth eruption.
During the bell stage, the dental follicle migrates away from the tooth germ in preparation for
the formation of periodontium. Histodifferentiation happens. Fibers from outside of the dental follicle
will form a membrane containing network of fibers which contain cells. This develops into osteogenic
tissue where cells differentiate into osteoblasts.
As the tooth erupts, the membranous bone in the body of mandible and maxilla extends
occlusally. It serves as an attachment of the periodontal ligament to hold the tooth in place.

9. Reorganization of the spongiosa or the cancellous bone also determines the development of the
alveolar process. In non-functional arches, the traberculae becomes thinner and therefore lessens the
size of the alveolar bone. in functional arches, the traberculae of the alveolar bone thickens to function
well in mastication and therefore makes the alveolar process longer or larger.
Vascular Supply of Alveolar Bone
The alveolar processes of the maxilla are supplied with oxyhemoglobinated blood from the
posterior superor alveolar artery, middle superior alveolar artery and anterior superior alveolar artery
which are all branches of maxillary artery. The Alveolar processes of the mandible are supplied with
oxyhemoglobinated blood by the inferior alveolar nerve which is also a branch of maxillary artery. The
maxillary artery is a branch of the external carotid artery.
Age Changes
Mesial drifting
It is a gradual movement of all the posterior teeth in a mesial direction. It occurs only if there
has been interproximal wear between the teeth. The drift is not a passive one however, as it has been
shown that during chewing, the bite force has a mesial component. Bone will be resorbed in the tense
area of the periodontal ligament and bone formation in the pressured area.
Masticatory Forces
The alveolar bone will adapt and bone marrow spaces will become smaller and the trabecula
becomes thicker for increase in masticatory function.

10. Loss of function
As a result of loss of function, the bone marrow spaces become wider and the trabecula
becomes thinner.
Tooth extraction/exfoliation
Alveolar process disappears because of bone resorption by osteoclasts. There will be an
apposition of embryonic bone. There will be a formation of residual or alveolar ridge. The residual ridge
will appear more radiolucent in radiographs because of its lesser calcification.
The Mandible
The mandible is the largest and strongest bone of the face, serves for the reception of the lower teeth. It
consists of a curved, horizontal portion, the body, and two perpendicular portions, the rami, which unite
with the ends of the body nearly at right angles.
Development of the Mandible: The Body of the Mandible

11. 1. The mandible is ossified in the fibrous membrane covering the outer surfaces of Meckel's
cartilages. These cartilages form the cartilaginous bar of the mandibular arch and are two in
number, a right and a left.
2. Their proximal or cranial ends are connected with the ear capsules, and their distal extremities
are joined to one another at the symphysis by mesodermal tissue.
3. Meckel’s cartilage has a close, relationship to the mandibular nerve, at the junction between
posterior and middle thirds, where the mandibular nerve divides into the lingual and inferior
dental nerve. The lingual nerve passes forward, on the medial side of the cartilage, while the
inferior dental lies lateral to its upper margins & runs forward parallel to it and terminates by
dividing into the mental and incisive branches. From the proximal end of each cartilage the
malleus and incus, two of the bones of the middle ear, are developed; the next succeeding
portion, as far as the lingula, is replaced by fibrous tissue, which persists to form the
sphenomandibular ligament & the perichondrium of the cartilage persist as sphenomallular
ligament.
4. Between the lingula and the canine tooth the cartilage disappears, while the portion of it below
and behind the incisor teeth becomes ossified and incorporated with this part of the mandible.
The mandible first appears as a band of dense fibrocellular tissue which lies on the lateral side of
the inferior dental and incisive nerves. For each half of the mandible,

12. 5. Ossification takes place in the membrane covering the outer surface of Meckel's cartilage and
each half of the bone is formed from a single center which appears, in the region of the
bifurcation of the mental and incisive branches, about the sixth week of fetal life.
6. REMNANT’S OF MECKEL’S CARTILAGE
a. Ossification grows medially below the incisive nerve and then spread upwards between
this nerve and Meckel’s cartilage and so the incisive nerve is contained in a trough or a
groove of bone formed by the lateral and medial plates which are united beneath the
nerve. At the same stage the notch containing the incisive nerve extends ventrally
around the mental nerve to form the mental foramen. Also the bony trough grow
rapidly forwards towards the middle line where it comes into close relationship with the
similar bone of the opposite side, but from which it is separated by connective tissue.
b. A similar spread of ossification in the backward direction produces at first a trough of
bone in which lies the inferior dental nerve and much later the mandibular canal is
formed. The ossification stops at the site of future lingula. By these processes of growth
the original primary center ossification produces the body of the mandible.

13. Development of the Mandible: The Ramus of the Mandible
1. The ramus of the mandible develops by a rapid spread of ossification backwards into the
mesenchyme of the first branchial arch diverging away from Meckel’s cartilage. This point of
divergence is marked by the mandibular foramen.
2. Somewhat later, accessory nuclei of cartilage make their appearance:
a. a wedge-shaped nucleus in the condyloid process and extending downward through the
ramus.
b. a small strip along the anterior border of the coronoid process.
3. The condylar cartilage:
a. Carrot shaped cartilage appears in the region of the condyle and occupies most of the
developing ramus. It is rapidly converted to bone by endochondral ossification (14th.
WIU) it gives rise to:
b. Condyle head and neck of the mandible.
c. The posterior half of the ramus to the level of inferior dental foramen
4. The coronoid cartilage:
a. It is relatively transient growth cartilage center ( 4th. - 6th. MIU). it gives rise to:
i. Coronoid process.
ii. The anterior half of the ramus to the level of inferior dental foramen
5. These accessory nuclei possess no separate ossific centers, but are invaded by the surrounding
membrane bone and undergo absorption.
The Maxilla
The maxillæ are the largest bones of the face, excepting the mandible, and form, by their union,
the whole of the upper jaw. Each assists in forming the boundaries of three cavities, the roof of the
mouth, the floor and lateral wall of the nose and the floor of the orbit; it also enters into the formation
of two fossæ, the infratemporal and pterygopalatine, and two fissures, the inferior orbital and
pterygomaxillary. Each bone consists of a body and four processes—zygomatic, frontal, alveolar, and
palatine.
Development of the Maxilla: The Maxilla Proper
1. It develops in the mesenchyme of the maxillary process of the mandibular arch as
intramembranous ossification. It has one center of ossification which appears in a band of
fibrocellular tissue immediately lateral to and slightly below the infra orbital where it gives off
its anterior superior dental branch. The ossification center lies above that part of the dental
lamina from which develop the enamel organ of the canine.

14. 2. The ossified tissue appears as a thin strip of bone. It spread in different directions as:
a. Backward: Below the orbit toward the developing zygomatic bone.
b. Forward: Toward the future incisor region
c. Upward: To form the frontal process of the maxilla.
3. As a result of this pattren of bone deposition, a bony trough is formed (infraorbital groove)
where the infraorbital nerves lies. The inner and outer edges of this groove grow up, meet and
fuse forming a canal that encloses the nerve & open anteriorly at the infraorbital foramen
4. The ossified tissue appears as a thin strip of bone. It spread in different directions as:
a. downward: To form the outer alveolar plate for the maxillary tooth germs
b. Toward the midline: Ossification spreads with the development of the palatal process in
the substance of the united palatal folds to form the hard palate. At the union between
the palatal process and the main part of the developing maxilla, a large mass of bone
produced. From this region & on the inner side of the dental lamina & tooth germs, the
inner alveolar plate of deciduous canines and molars develops.
5. Development of the maxillary sinus: At 4 MIU as a small depression of the mucosa of the lateral
wall of the nasal cavity. In its gradual extension the sinus comes into relation with the maxilla
above the level of the palatal process & hallows out the interior of the bone, so separating its
upper or orbital surface from its lower or dental region.

15. Development of the Maxilla: The Premaxilla
Two centers of ossification for the premaxilla:
A. The palato-ficial center:
Appear at the end of 6 WIU. It starts close to the external surface of the nasal capsule, in
front of the anterior superior dental nerve and above the germ of the lateral deciduous incisor.
From this center bone formation spreads:
1. Above the teeth germ of the incisors.
2. Then downward behind them.
To form the inner wall of their alveoli & palatal part of the premaxilla.
B. The prevomerine center (paraseptal center):
It begins at about 8-9 WIU along the outer alveolar wall. It is situated beneath the anterior
part of the vomer bone and it forms that part of the bone lies mesial to the nasal paraseptal
cartilage.
Accessory Cartilages
1. Accessory cartilagenous center appears in the region of the future zygomatic or molar process
and this undergoes rapid ossification & adds considerable thickness to the bulk of this part.
2. Also small areas of secondary cartilagenous center appears along the growing margin of the
alveolar plate.
3. In the middle line of the developing hard palate between the two palatine processes.

16. Lines in Bones
There are four lines that can be seen in bone tissues: reversal,
cementing, aplastic and resting lines. Reversal line shows the evidence
of previous remodeling activity and it is formed by filling of new bone in
a previously resorbed cavity. The relative amount of reversal lines
indicates the amount of remodeling that has occurred. Cementing lines
separates adjacent lamellae of bone from each other. It is also refered
RL as the incremental lines in bone . Aplastic line is a layer of basophilic
AL
substance which laid down on the surface of the bone that has been
AL inactive for a long period of time. While resting line is a line which
separates the new layer of bone from the old bone which has been
inactive.
CL
AL
Clinical Consideration
Although bone is one of the hardest tissues in the human body, bone is also is biologically a
highly plastic tissue. It is also exceedingly sensitive to pressure. Bone resorbs on the side of pressure
and apposes on the side of tension. On sites where bone receives pressure, high amounts of cyclic
adenosine monophosphate can also be observed. Bone also gives response to its functionality. A
highly functional bone is denser than a bone that does not receive any functional forces at all. When
bones are fractured or a tooth was extracted from it, embryonic type of bone or coarse fibrillar bone
is formed on the site.
Bone is continuously remodels and is being replaced by a newer bone tissue from embryonic
period until death is termed as bone turnover. Bone turnover rate of 30% to 100% per year is
common to rapidly growing children. In adults, it is decreased to 5% per year. Periodontal diseases
gives the most frequent and harmful change in the alveolar process. Progressive loss of alveolar
bone in periodontal disease is difficult to control and even more difficult to regenerate or repair
when damaged. This situation is one of the greatest challenges to periodontics. Studies and
experiments on implanting artificial roots on the alveolar bone gave promising results in decreasing
the speed of bone resorption. Acromegaly is an overgrowth of the jaw bone.
Acromegaly
Periodontitis

17. BIBLIOGRAPHY
Oral Histology – Development, Structure and Function, 4th Edition by Ten Cate, A. R.
Orban’s Oral Histology and Embryology, 11th Edition by Bhaskar, S. N.
Permar’s Oral Histology and Microscopic Anatomy, 10th Edition by Melfy, R. C.
Northern Illinois University:Department of Biological Sciences Website
Medscap Website
Oral Biology by Berkovitz, Moxham, Linden, and Sloan