Dental anatomy
Padraic M. Dixon MVB, PhD, MRCVS, Nicole du Toit BVSc, MSc, PhD, MRCVS, in Equine
Dentistry (Third Edition), 2011
Alveolar bone
Alveolar bone is very flexible and constantly remodels to accommodate the changing shape and
size of the dental structures it contains. Alveolar bone can be divided into two main parts: a thin
layer of compact (radiodense) bone (the ‘cortex’ of alveolus) that lines the alveolus proper, in
which Sharpey's fibers insert, that is radiographically termed the lamina dura (lamina dura
denta). This area is radiographically detectable (but not on computed tomography) as a thin
radiodense line in brachydont teeth but due to irregularities of the periphery of some normal
equine cheek teeth, this feature is not always obvious on lateral radiographs of equine teeth (Fig.
5.37). Secondly, the main alveolar bone surrounding the lamina dura denta cannot be
morphologically differentiated from the main bone of the mandible or maxilla in adult
brachydont teeth.1 However, recent studies have shown that in horses, the alveolar bone beneath
the lamina dura remains spongy and porous throughout life – similar to the alveolar bone of
developing children's teeth – probably a reflection of its constant remodeling as the equine teeth
constantly erupt.2 This presents an area of anatomical weakness, which may explain why
sequestration of the alveolar cortical bone can occur following oral extraction of cheek teeth. The
most prominent aspect of the alveolar bone beneath the gingival margin (occlusally) is termed
the alveolar crest.
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Anatomy of the teeth and periodontium
Cecilia Gorrel BSc MA VetMB DDS MRCVS HonFAVD DipEVDC, ... Leen Verhaert DVM
Dipl. EVDC, in Veterinary Dentistry for the General Practitioner (Second Edition), 2013
Alveolar bone
The alveolar bone is composed of the ridges of the jaw that support the teeth. The roots of the
teeth are contained in deep depressions, the alveolar sockets in the bone. The alveolar bone
develops during tooth eruption and undergoes atrophy with tooth loss. It responds readily to
external and systemic influences. The usual response to stimuli results in resorption, but this may
be accompanied by deposition in some situations.
Alveolar bone consists of four layers. In addition to the three layers found in all bones,
namely periosteum, dense compact bone and cancellous bone, there is a fourth layer called
the cribriform plate, which lines the alveolar sockets. Radiographically, this appears as a fine
radiodense line called the lamina dura. The crest of the alveolar bone is normally located around
1 mm below the cemento-enamel junction. Blood vessels and nerves run through the alveolar
bone and perforate the cribriform plate. The majority of these blood vessels and nerves supply
the periodontal ligament.
Summary
⧫
Cats and dogs (like humans) are diphyodont, i.e. primary (deciduous) teeth are shed to
make way for the permanent dentition.
⧫
The bulk of the mature tooth is composed of dentine, covered by enamel on the crown
and cementum on the roots.
⧫
Enamel is the hardest tissue in the body, consisting mainly of calcium hydroxyapatite. Its
formation is complete by the time of tooth eruption. Regeneration is not possible, only
repair by surface mineralization.
⧫
The endodontic system (pulp) makes up the center of the tooth and contains odontoblasts,
which produce dentine throughout the life of the animal.
⧫
The periodontium serves to support the tooth and absorb functional forces. It consists of
the gingiva, periodontal ligament, cementum and alveolar bone.
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Tooth organogenesis, morphology and physiology
K Gulabivala, Y-L Ng, in Endodontics (Fourth Edition), 2014
Alveolar bone
Alveolar bone is that part of the maxilla and mandible which supports the teeth by forming the
“other” attachment for fibres of the periodontal ligament (Fig. 1.148). It consists of two plates
of cortical bone separated by spongy bone (Fig. 1.149). In some areas, the alveolar bone is thin
with no spongy bone (Fig. 1.148). The alveolar bone and the cortical plates are thickest in the
mandible. The spaces between the trabeculae of the spongy bone are filled with marrow, which
consists of haematopoietic tissue in early life and of fatty tissue later (Fig. 1.149). The shape and
structure of the trabeculae reflect the stress-bearing requirements of the particular site. The
surfaces of the inorganic parts of the bone are lined by osteoblasts, which are responsible for
bone formation: those which become incorporated within the mineral tissue are
called osteocytes and maintain contact with each other via canaliculi; osteoclasts are responsible
for bone resorption and may be seen in the Howship's lacunae (Fig. 1.150). Cortical bone
adjacent to the ligament gives the radiographic appearance of a dense white line next to the dark
line of the ligament (see Figs 1.144, 1.145). Bone is a dynamic tissue, continually forming and
resorbing in response to functional requirements. In addition to such local response to
needs, bone metabolism is under hormonal control. It is easily resorbed under the influence
of inflammatory mediators at either the periapex or the marginal attachment. In health, the crest
of the alveolus lies about 2 mm apical to the cemento–enamel junction (Fig. 1.151) but,
in periodontal disease, it may lie much more towards the apex of the root.
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Managing Traumatic Injuries in the Young Permanent
Dentition
Dennis J. McTigue, ... Janice G. Jackson, in Pediatric Dentistry (Sixth Edition), 2019
Lateral Luxation
Alveolar bone fractures frequently occur in lateral luxation injuries and can complicate their
management (see Fig. 35.16B). In the most severe cases, PDL and marginal bone loss occur.
Treatment is to reposition the teeth and alveolar fragments as soon as possible. A splint should
then be applied for 3 to 6 weeks, depending on the degree of bone involvement. The author's
current protocol includes prescribing a 0.12% chlorhexidine mouthrinse. If the apices are closed,
the pulps will likely become necrotic; therefore endodontic therapy should be instituted soon
after the teeth are splinted. Again, teeth with open apices should be monitored until signs of
necrosis are evident.
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Development of Tooth and Associated Structures
Eva Matalová, ... Paul Sharpe, in Stem Cell Biology and Tissue Engineering in Dental Sciences,
2015
26.2.2 Alveolar and Jaw Bone Development
Alveolar bone development starts prenatally (at E13 for the mouse M1) and is based on
molecular signaling, as well as mechanical forces. Two major types of cells participate in the
process—osteoblasts and osteoclasts.
Osteoblasts in the alveolar bone originate directly from the
dental mesenchyme (intramembranous ossification). After realizing their function in bone matrix
production and mineralization, osteoblasts may undergo programed cell death, become bone
lining cells (inactive osteoblasts), or become osteocytes, cells encased in the mineralized bone.
Osteoclasts are multinuclear cells that differentiate from the monocyte-macrophage
haematopoietic progenitors recruited from the blood. The differentiation of mononuclear
osteoclast progenitor cells to mature osteoclasts involves fusion to form multinuclear cells, and
their polarization results in the development of the sealing zone and the ruffled border required
for the attachment to the extracellular bone matrix and bone resorption.
Several genes participating in odontogenesis can be found during osteogenesis, particularly Msx-
1 and Msx-2, Dlx family members (Dlx-1/2, Dlx-5/6), and Runx-2 (Figure 26.5).
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Figure 26.5. Illustration of tooth-bone complex development. Formation of alveolar bone is influenced by
mechanical pressure and particularly molecular signaling. Key molecules accompanying integration of the tooth
germ with the surrounding bone are shown in the epithelium (cream), mesenchyme (red), and bone (yellow).
Dlx family members regulate skeletal patterning within the jaw, and in the absence of Dlx-1/2
(downstream of Fgf-8) upper molar mesenchyme loses its odontogenic potential and becomes
chondrogenic [16]. Mice deficient in single Dlx genes or their combinations show various
skeletal defects. DLX-5 regulates expression of osteocalcin, a marker of osteoblasts, RUNX-2
activates expression of collagen type I, bone sialoprotein, osteocalcin, and osteopontin [17]. Dlx-
5, together with Runx-2, also represents differentiation genes of osteoblasts and osteoclasts
(Figure 26.6) [18].
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Figure 26.6. Differentiation of osteoblasts. Osteoblasts originate from pluripotent mesenchymal progenitors shared
with adipocytes and chondrocytes. Individual lineages are governed by specific gene expression, Runx2, Dlx5, Msx,
and Osx, and key molecules for osteoblast differentiation, Wnt, Runx2, Dlx5, Mxs, and Osx for following bone
mineralization.
Alveolar bone is missing or abnormally formed in mice deficient in Runx-2, Dlx-5/6, and Msx-1
genes. Moreover, application of BMP-4 inhibitors ex vivo causes absence of alveolar bone
formation [19]. Rescue experiments revealed a network of these genes where MSX-1 seems to
act upstream of Bmp-4 to activate expression of osteoblast differentiation genes Runx-2 and Dlx-
5.
BMP family members are critical for bone development, and in general support bone apposition.
In the tooth-bone complex, bone is the one which has a high capacity for remodeling and
becomes adapted to the growth of the tooth. RANK/RANKL/OPG are the best known players in
the remodeling interplay (Figure 26.7).
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Figure 26.7. Coordination of RANK/RANKL/OPG signaling in osteoclastogenesis. Initiation (left) and inhibition
(right) of osteoclastogenesis. Osteoblasts produce RANKL, osteoclasts have receptors for this ligand (RANK). After
RANK-RANKL interaction, osteoclast precursors proliferate, merge in multicellular structures, and differentiate into
matured osteoclasts. Cytokines (and hormones) play important roles in osteoclast differentiation. Decreased RANKL
or increased OPG (decoy receptor) production suppresses osteoclast differentiation.
After activation of RANK upon binding of its ligand (RANKL), precursors of osteoclasts
undergo differentiation. Whereas increase of OPG, a decoy receptor of RANKL, causes
inhibition of osteoclasts, it supports increase of bone mass leading to delayed tooth development
and hypomineralization. The RANK/RANKL/OPG team participates in accommodation of the
growing tooth in the mineralized bone up to eruption, whereas BMP members, particularly
BMP-2, support new bone formation, particularly in the basal part of the alveolus (Figure 26.8)
[20].
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Figure 26.8. Coordination of RANKL/BMP2 in tooth eruption. Osteoclastogenesis along the alveolus decreases
(decrease of RANKL) whereas, at the bottom of the alveolus bone, apposition proceeds induced by BMP2 (produced
by periodontal cells). The interaction results in bone apposition and movement of the tooth toward the oral cavity.
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Esthetics and oral and maxillofacial surgery
Daniel Buchbinder, in Esthetic Dentistry (Third Edition), 2015
Alveolar distraction
Alveolar bone distraction recently was introduced as an alternative to bone grafting for ridge
augmentation of traumatically induced, limited alveolar defects (Fig. 18-3A,B). Specially
designed expansion devices are used to slowly “distract” an osteotomized bone segment to
restore the lost alveolar height.
Once this has been achieved and the regenerate has been allowed to consolidate, the distractors
are replaced with endosteal fixtures that will osseointegrate and support a cosmetic prosthesis,
which will then have a more acceptable crown to root (fixture) ratio.14 A similar technique is
now used to distract the anterior mandibular alveolus in patients with atrophic mandibles to
create a more favorable site for the placement of endosteal fixtures.15 Changes in the design of
alveolar distractors will allow these devices to play a dual role of distractor/implant fixture
without having to change the hardware at the completion of the distraction (Fig. 18-3C,D).
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Periodontium and Periodontal Disease
Francis J. Hughes, in Stem Cell Biology and Tissue Engineering in Dental Sciences, 2015
34.2.3 Alveolar Bone
The alveolar bone is that part of the mandibular and maxillary bone which surrounds the teeth
and forms the tooth sockets. The bone of the tooth socket is a dense cortical plate into which the
principal fibers of the periodontal ligament are inserted, referred to as Sharpey’s fibers. As noted
above, this dense “Bundle Bone” is penetrated by many vascular channels which communicate
between the trabecular bone and the PDL. These vascular channels may also provide a route
whereby cycling mesenchymal transit progenitor cells from bone marrow may migrate into the
PDL during normal tissue homeostasis and wound healing.
Alveolar bone undergoes physiological turnover as is seen with other bones, and as discussed
further below may undergo more extensive remodeling during tooth movement and other
external stimuli. The presence and maintenance of the alveolar bone is tooth-dependent, such
that following tooth extraction it is slowly resorbed down to the body of the jaw bones. In the
case of complete tooth loss there is progressive bone resorption which can result in extensive
atrophy of the jaw bones which can present major clinical problems for implant placement and
construction of dental prostheses.
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Mechanotransduction of Orthodontic Forces
Sunil Wadhwa, ... Carol Pilbeam, in Current Therapy in Orthodontics, 2010
For alveolar bone tissue subjected to mechanical loading, orthodontic forces must be converted
into intracellular signals in mechanosensitive cells. This information must then be communicated
to other nonmechanosensitive cells to produce a coordinated response. For this to occur, the
following events must take place:
1.
External orthodontic forces must be converted into a signal detectable by the cell
(transduction mechanism).
2.
The periodontal ligament (PDL) and alveolar bone must have cells that are able to detect
mechanical loading–induced signals (mechanosensitive cells).
3.
Mechanosensitive cells must have a mechanism to sense the signal (mechanoreceptor).
4.
Mechanoreceptors must transduce loading information to intracellular signals.
5.
Intracellular signals within mechanosensitive cells must lead to the production and
release of cellular mediators to communicate mechanical loading information to other
cells.
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Alveolar reconstruction in cleft for implant rehabilitation
J.-B. Seigneuric, M.-P. Vazquez, in Preprosthetic and Maxillofacial Surgery, 2011
State of the art17
Previously described in 1908, surgical techniques of gingivoperiosteoplasty became more
popular after 1950. Every patient with CLP involving alveolar process can be proposed for
gingivoperiosteoplasty and bone graft. Chronology and decision of alveolar bone graft is still a
matter of debate. Facial growth and dental age are two factors affecting choices of surgeons.
Before two years of age: early or early primary bone grafting
The aim of this early procedure is to prevent segmental collapse and constriction of the maxilla.
The benefit of early closure of the oronasal fistula can also be pointed out, suppressing nasal
leakings. Surgical closure with early alveolar bone graft is known to have a significant effect on
early facial growth, but results have been debated. Early stabilization may prevent the amount of
transversal expansion of the maxilla required by orthodontic treatment,18 but there remain few
advocates of primary bone grafting.19 Even though authors propose early gingivoperiosteoplasty
without bone graft,20 this procedure is known to produce insufficient alveolar bone for late
stability and dental eruption.7 Free periosteum graft21 can also be proposed for early closure of
the alveolar process from the 5th to 7th month of life.
Between two and five years of age: early secondary bone graft
Secondary alveolar bone grafts were first described by Boyne,22 and Abylhom and
Enemark.5, 7 This protocol seems to be well accepted, according to the amount of publications
and results. The purpose of this chronology points out several anatomical and functional benefits:
•
strengthening of the alveolar ridge in the area of the cleft;
•
support of transversal dimension of the maxilla after orthodontic expansion;
•
proper bony surroundings for dental eruption;
•
support for the alar base.
Orthodontic management achieves the correction of transversal collapse of the maxilla with
segmental alignment of the two sides of the cleft. A fundamental precondition for success of this
procedure is to provide sufficient periosteum, using lateral translation of the muco-periosteum
flap. Failure of the surgery or insufficient results can be promoted by poor parodontal trophicity
and prevent dental eruption or implant surgery in optimal conditions. Thus, the choice of leaving
the alveolar cleft free of parodontal scars before bone graft can be pointed out. Better results can
be observed in a virgin clefted alveolus.
This surgical chronology takes place before permanent dentition, promoting dental eruption
through bone graft. The graft can be performed before lateral incisor eruption or cuspid eruption
in the case of a missing lateral incisor. Cuspid and lateral incisor promote graft healing and
stimulate bone.23 Some authors propose to perform early alveolar bone graft at the age of 18 to
36 months.16 Resorption of grafted bone can reach 50% of initial gain in the case of
missing lateral incisors or lack of cuspid stimulation.
After five years of age: late secondary bone graft
Purpose is similar to early secondary bone graft (support to the alar base and closure of the
residual oronasal fistula). Alveolar bone graft and strengthening of the maxillary arch allows
further osteotomies to correct maxillo-mandibular discrepancies.7, 10 Interest of grafting before
cuspid eruption is all the more warranted as osteogenic activity is optimal at this age. The
lateral incisor can be maintained in the grafted cleft even though it would not help for terminal
rehabilitation (due to crown or radicular malformations). We know that teeth located in the
grafted area as well as adjacent teeth tilted into the direction of the graft clearly stimulate the
graft, so that progressive resorption can be prevented.6 In case of hypodontia (missing lateral
incisor and/or cuspid), missing occlusal stress accelerates bone graft resorption. In addition, graft
can be stressed by orthodontic treatments (for tooth spacing, alignment or expansion) leading
to bone loss and resorption.23
For all these reasons, it seems to be difficult to define the perfect age for alveolar grafting. Age
before eruption of the cuspid is commonly proposed, but according to other authors, age between
8 and 11 years is proposed.6, 24−26 In our protocol, we propose alveolar bone graft associated with
gingivoperiosteoplasty as soon as possible from 5 years old. Of course, child cooperation must
be effective and orthodontic preparation completed. At this age, before mixed dentition, surgical
management offers excellent rates of success.
Sometimes, adult patients have not been taken charge of: they present an alveolar oro-nasal
fistula with bone lack. Full gingivoperiosteoplasty must be performed with complete dissection
and closure of the fistula before iliac cancellous bone graft, performed at the same surgical time.
Onlay tertiary bone graft is performed in a secondary operation. Early resorption of the bone
graft seems to be more important in these cases (Fig. 13.3).
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13.3. (a) Right CLP with persistent oronasal fistula and bone defect. (b) 3D scanner view of the alveolar bone defect.
(c) Control six months after iliac cancellous bone graft. (d) 3D scanner control at the same time showing good bone
healing but insufficient crestal bone level. (e) Tertiary onlay bone graft with early resorption (six months after bone
graft).
Tertiary bone graft: implant surgery (see Chapter 2)
This surgery is stressed by poor trophicity of scared gingiva. Cosmetic results should be
completed by connective mucogingival graft.
Some authors choose to eliminate implant choice, according to disability of a single endosseous
implant to support transversal maxillary arch contention. They prefer the use of a fixed or
bonded bridge supported by adjacent teeth.7
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Craniofacial Biology, Orthodontics, and Implants
Tien-Min Gabriel Chu, ... William J. Babler, in Basic and Applied Bone Biology, 2014
Alveolar Bone Proper
The formation of alveolar bone proper is initiated with the eruption of the developing tooth.
Once the crown of a tooth has been formed, root formation begins. Formation of the root
involves a complex interaction between the mesenchyme of the dental follicle and the
Hertwig root sheath. The dental follicle gives rise to cementoblasts that begin to deposit
the cementum that lines the external surface of the root. Concurrently, other mesenchymal cells
in the dental follicle differentiate into fibroblasts, forming the periodontal ligament (PDL), and
still other mesenchymal cells differentiate into osteoblasts adjacent to the bone, forming the
sockets within the alveolar process. This relationship between cementum deposition, connective
tissue fiber formation, and bone deposition facilitates the embedding of PDL fibers into the
cementum of the tooth and the alveolar bone proper.
As the root continues to form, the PDL continues to increase in length as the new root portion
provides attachment to new fibers of the PDL. Similarly, the alveolar bone lining the socket
continues to be remodeled. Bone deposition occurs vertically, thus increasing the depth of the
socket. The alveolar bone continues to remodel, filling in around the root as it erupts and
lengthens. It is during this process that the true alveolar bone is created to provide support for the
tooth. Ultimately, the crown of the tooth emerges from the bony jaw, pierces the
overlying gingiva, and moves toward occlusion. As the tooth comes into functional occlusion,
the PDL absorbs and then distributes the force placed on the tooth during mastication or other
events and distributes it to the surrounding alveolar process via the alveolar bone proper.
Alveolar bone proper appears on a radiograph as a thick radiopaque line adjacent to the alveolar
socket, termed the lamina dura.
The alveolar bone proper provides the attachment site for Sharpey fibers from the PDL.
These collagen fibers are organized into bundles and calcified within the bone to provide a
strong attachment between tooth and bone. This portion of alveolar bone is sometimes referred to
as bundle bone due to the presence of the fiber bundles. Bundle bone, in turn, merges with
adjacent lamellar bone that comprises the alveolar process. Bundle bone is the most important
to tooth movement and disease processes involving the periodontium. The remaining portion of
the alveolar bone proper is lamellar bone. It is perforated by numerous small foramina that allow
the nerves and vessels within the alveolar process to reach the PDL tissues. This perforated bone
is often referred to as the cribriform plate. The bone lining the socket is closely contoured with
the tooth, and its coronal margin becomes the alveolar crest. The composition of alveolar bone
proper is similar to that of other bone. There is some evidence, however, that the alveolar crest is
more mineralized than the bone adjacent to the apex of the tooth. Under functional occlusion, the
thickness of the alveolar bone also increases. This is unsurprising, since the tension of the PDL is
increased with functional occlusion and this in turn stimulates bone deposition.
