Bone functions and the requirements for bone grafts and substitutes in the orofacial region.
ABSTRACT Bone is the largest calcium storage, has distinctive plasticity and adaptability and is part of the supporting tissue. An adequate composition is thus necessary. The bone matrix consists of organic and anorganic structures. Osteoblasts, osteoclasts and osteocytes are responsible for bone formation, resorption and metabolism. The periosteum, endosteum and bone tissue are a functional unit and provide protection, nutrition and growth. Bone is subject to continuous remodelling.
Vol. 65, No. 1, pp. 56–58
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Bone functions and the requirements for bone
grafts and substitutes in the orofacial region
J. Fanghänel1, T. Bayerlein1, T. Gedrange1, E. Kauschke2, E. Rumpel2, W. Gerike3,
V. Bienengräber4, P. Proff1
1Clinic for Orthodontics and Preventive and Paediatric Dentistry, University of Greifswald Dental School,
2Institute of Anatomy and Cell Biology, Ernst Moritz Arndt University, Greifswald, Germany
3Artoss GmbH, Rostock, Germany
4Clinic for Cranio-Maxillofacial and Plastic Surgery, University of Rostock, Germany
[Received 21 December 2005; Accepted 8 February 2006]
Bone is the largest calcium storage, has distinctive plasticity and adaptability and
is part of the supporting tissue. An adequate composition is thus necessary. The
bone matrix consists of organic and anorganic structures. Osteoblasts, osteoclasts
and osteocytes are responsible for bone formation, resorption and metabolism.
The periosteum, endosteum and bone tissue are a functional unit and provide
protection, nutrition and growth. Bone is subject to continuous remodelling.
Key words: bone composition, function, metabolism, remodelling
The orofacial or stomatognathic system with its
components forms a functional circle representing
a biocybernetic system with bone playing a key role.
The structure of the osseous viscerocranium is target-
ed to withstand and divert the chewing pressure .
This requires a functional composition which is main-
tained even after osseointegration of bone graft sub-
stitutes. The periods of function and inactivity oc-
curring in the jaw bones are more clearly noticeable
than in any other bone of the body. Continuous re-
modelling guarantees adaptation to the forces that
The bones make up the skeleton which bears the
body’s weight. Additionally, the skeleton provides the
origin and attachment of the muscles. Owing to its bio-
logical plasticity, bone is capable of adaptation to stress.
The cranial bones protect the central nervous sys-
tem, the sense organs, and the bone marrow.
Development of masticatory pressure pillars
The development of masticatory pressure pillars
in the viscerocranium diverts the chewing pressure
and the trajectorial structure of the mandible (Fig. 1).
Figure 1. Functional structure of the viscerocranium .
J. Fanghänel et al., Bone functions and the requirements for bone grafts and substitutes in the orofacial region
About 99% of the body’s calcium is stored in the
skeleton, including the cranial bones. The stored
calcium is mobilised when blood calcium concen-
tration declines. Calcium is mainly released from
hydroxyapatite crystals in the spongy substance.
Hormone and vitamin metabolism
Bone is connected to hormone and vitamin me-
tabolism. The osteoblasts possess receptors for par-
athyroid hormone, vitamin D3, cytokines and growth
factors. They produce factors that increase osteo-
clast proliferation and differentiation. Calcitonin ex-
erts a receptor-mediated inhibiting effect on osteo-
clast activity. Androgens as well as oestrogens gen-
erally stimulate the building of bone substance and
accelerate epiphyseal gap and suture closure.
Bone is a specific connective tissue, which main-
ly consists of the extracellular substance/bone ma-
trix, cells, vessels, and nerves.
The bone matrix consists of anorganic and organic
material . The anorganic material, which determines
bone stiffness, constitutes about half of the matrix.
The major part (50%) is composed of calcium and phos-
phate in the form of hydroxyapatite crystals. Addition-
ally, non-crystalline calcium phosphate, citrate, bicar-
bonate and, further, magnesium, kalium and sodium
salts are found. The apatite crystals are surrounded
by matrix substance and lie along the collagen fibrils.
A “hydration cover” facilitates ion exchange between
crystal and body fluids. The non-calcified organic ma-
trix is referred to as osteoid and provides the body’s
elasticity. It consists mainly of collagen.
Cells are indispensable for osseointegration.
Osteoblasts are located exclusively at the sur-
face of spongious trabecles and synthesise and se-
crete Collagen I, proteoglycans and glycoproteins.
As their activity diminishes, the cells become increas-
ingly flatter and form processes. The matrix proteins
produced are released towards the surface of the
existing bone matrix. The organic material enabling
bone elasticity constitutes about 20%. Finally, water
amounts to about 10% of the matrix substance.
Osteoclasts are multi-nucleate, large mobile cells,
which resorb mineralised bone and stem from the
mononuclear phagocyte system. One surface of re-
sorbing osteoclasts faces the mineralised bone tis-
sue. The surface periphery is closely connected to
the matrix by a sealing zone. The area surrounded
by this zone displays numerous folds (a “ruffled bor-
der”). Between the “ruffled border” and the bone
matrix there is an extracellular space, the so-called
“resorption lacuna” where bone resorption occurs.
The osteoclast secretes H+ ions to the lacuna by
means of a vacuolar ATPase located in the folded
membrane, and the matrix minerals are dissolved in
the acid milieu. The release of lysosomal enzymes
leads to decomposition of the collagen fibrils.
Osteocytes develop from osteoblasts and repre-
sent the metabolic centres of the bone. Their cell
bodies are located in the lacunae. With their pro-
cesses they are interconnected by gap junctions com-
posed of arrays of small channels. The processes
permit intercellular substance transport. An exchange
of compounds between osteocytes, mineralised
matrix and blood vessel also occurs in the gap sys-
tem between cells and calcified bone matrix. The cells
respond to mechanical stress exerted on the bone
and sustain the extracellular matrix. After their death
the matrix undergoes resorption.
Periosteum and endosteum
The main functions of these are protection and
nutrition as well as the continuing supply of osteo-
blasts for thickness growth and successful defect
repair. The outer layer of the periosteum, the stra-
tum fibrosum, consists of fibroblasts, collagenous
and elastic fibres. Sharpey’s fibres are bundles of
collagenous fibres connecting the periosteum with
the bone substance. The inner layer, the stratum
germinativum, is formed by divisible cells (“lining
cells”) which can differentiate into osteoblasts. The
stem cells play an important role for bone growth
and repair. The endosteum fills the inner cavities of
the bone, is thinner than the periosteum, and con-
sists of progenitor cells and only a small amount of
According to the array of osteocytes and collagen
fibres, reticulated bone and lamellar bone are dis-
Reticulated bone (also “primary bone”) is found
only during bone development and repair processes,
and, therefore, also in osseointegration. Its mineral
content and radiodensity is lower. The collagen fibrils
run irregularly. This type of bone is replaced, except
in the suture and alveolar areas, by lamellary bone.
Folia Morphol., 2006, Vol. 65, No. 1
Within lamellary bone (Fig. 2) the collagen fi-
bres and the other matrix components form lamel-
lae of 3–7 µm thickness, which are arrayed in con-
centric layers around a central channel (the Haver-
sian canal). This structure is referred to as the “Hav-
ersian system” or “osteon”. The cell bodies of the
osteocytes are located between the lamellae. Each
channel contains nutritive vessels, nerve fibres, and
loose connective tissue. The canals communicate with
the bone marrow cavity, the periosteum and with
each other (by Volkmann’s canals, which also lead
outward). The channel system reflects a complex and
delicate microcirculation . Each osteon is surround-
ed by mineralised matrix with few collagen fibres
(cementum). Immediately beneath the periosteum
and around the marrow cavity lie general lamellae,
more outer and fewer inner. Between the outer and
inner general lamellae are located the so-called os-
teons and the often irregularly shaped intermediate
lamellae. The latter are residual lamellae of a Haver-
sian system which has been degraded during a re-
Substantia compacta, Substantia spongiosa of
the cranial bones. The outer compact bone layer is
referred to as the substantia compacta, the inner
layer, which possesses numerous interconnected
cavities, as the substantia spongiosa. The latter rep-
resents a spongy trabecular framework. However,
both structures show lamellary bone composition.
Figure 2. Bone lamellae .
Bone shape and composition are adjusted to its
mechanical function. The structure reflects trajectorial
architecture and conforms to tension and strain tra-
jectories. Bone substance is arranged in such a way
that the best possible absorption and transmission is
achieved with minimum expense of material in the
loaded area. The trajectorial construction, of the man-
dible for example, permits selective material usage in
the loaded area. This lightweight construction saves
muscular strength for motor activity. Bone morphol-
ogy is genetically determined and is modified by ex-
ternal influences through differentiation. Bone is sol-
id by its anorganic components and elastic by its or-
ganic components. Thus bone substance is in a dy-
namic equilibrium of adaptation . Figure 3 shows
the oscillation between atrophy and hypertrophy, re-
sorption and apposition.
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Figure 3. Functional structure of bone and dynamic equilibrium .