Alveolar bone
I-Definition of the alveolar bone or alveolar process.
The alveolar bone is an element of the periodontium, consisting of the extension of the maxillary and mandibular bones which forms and supports the dental alveoli.
It is the main supporting tissue of the dental organ.
It is a bone that is born and disappears with the teeth and perfectly matches the shape of the teeth.
II-anatomical structure
The anatomical structure of the alveolar bone is closely related to various factors.
-dental anatomy
-the position of the teeth
-occlusal functional stimulation
– local physicochemical conditions.
– vascular anatomy
The alveolar bone is made up of:
-two bone tables: *vestibular
* Lingual for the lower arch; palatal for the upper arch
-dental alveoli
-the inter-alveolar septa (inter-dental and inter-radicular).
1-The bone tables.
Each bony table consists of an external and internal bony cortex.
These cortices are made up of compact bone tissue of variable thickness.
The thickness is more reduced at the level of the maxilla than at the level of the mandible, at the anterior level than at the posterior level of the alveolar arches.
2-The dental alveoli
These are the sockets in which the dental roots are inserted and they are located between the two cortices.
Their shape and depth are conditioned by:
-the shape and length of the root
-the position of the tooth on the arch
-the occlusal function
The dental alveoli are surrounded by an alveolar wall which is a thin layer of bony tissue called: cribriform plate.
At the level of the maxillary and mandibular anterior teeth, this wall generally fuses with the cortices without interposition of spongy bone tissue.
On the other hand, at the level of the molar and premolar sector, spongy bone tissue can be interposed between the alveolar wall and the cortices.
On X-ray, this bony wall appears as a radiographic line called the lamina dura.
A discontinuity of this line can be considered a sign of bone pathology.
Dental alveoli
3-inter-radicular septa and inter-dental septa
The interdental septa are located between each alveolus and the interradicular septa partition the alveoli of multirooted teeth.
The septa are made of spongy bone tissue that is interposed between the alveolar walls and the internal and external cortices.
These septa are dug with channels through which the blood vessels, lymphatics and interradicular nerves pass.
Interdental and interradicular septa
4-the marginal crest of the alveolus or alveolar crest
This is the point where the bony tables and the bone of the alveolar wall meet.
This ridge is located 1.5 to 2 mm below the level of the enamel-cementum junction.
The appearance and anatomical position of the crest depends on various factors
-the buccal-lingual width of the tooth
-the position of the tooth on the arch
– The cervical contour of the enamel-cement junction
The alveolar ridge is normally slightly rounded into a rim but can be very sharp like a knife blade if the bone is thin.
Dental malpositions lead to changes in the profile of the alveolar ridge.
The alveolar ridge
III histological structure
Bone tissue (compact or spongy) is made up of a mineralized extracellular matrix; cells included inside spaces called lacunae.
1 – extracellular matrix is composed of an organic fraction and a mineral fraction.
*organic fraction .
Represents approximately 21% of the dry weight of bone tissue
It is composed mainly of collagen fibers, non-collagenous proteins and lipids.
*mineral fraction
It represents 70% of the weight of bone tissue, consisting of phosphate, calcium, magnesium, carbonate, sodium and water.
2-Bone cells
*. Osteoblasts
They are cells of mesenchymal origin, roughly prismatic, with a nucleus
bulky, eccentric, opposite osteoid tissue.
The main function of the osteoblast is to synthesize and mineralize osteoid tissue during bone growth, its renewal in adults, and bone repair throughout life.
.*Osteocytes
Osteocytes are called osteoblasts incorporated into the calcified substance that they themselves have built. Each osteocyte is enclosed in a lacuna, called: osteoplast.
Osteocytes have a role in matrix signaling and communication. They are sensitive to mechanical stimuli and detect the need for increased or decreased bone formation in the process of functional adaptation and bone healing.
*Osteoclasts
They are giant, multinucleated cells of varying sizes, with numerous
mitochondria, exhibiting a brush border arrangement in contact with the bone.
Their main role is bone resorption within the HOWSHIP lacunae, particularly in the remodeling process.
3-Histological organization
3-1–the cortices
They consist of a thin layer of periosteal lamellar bone tissue and Haversian bone tissue.
*-periosteal lamellar bone tissue
It consists of only a few lamellae separated by apposition lines and osteocytes arranged regularly in each lamella.
The periosteum which covers the external surface of this tissue is made up of:
-an internal layer composed of osteoprogenitor cells and functional bone cells, mainly osteoblasts.
-a dense fibrous outer layer
*-Haversian bone tissue
It presents: * haversian canals widened by osteoclastic resorptions
* Plus or complete osteones.
3-2-the spongy bone tissue of the septa
It is made up of thin trabeculae composed of lamellae of bone tissue.
These trabeculae delimit more or less important medullary spaces containing bone marrow, generally of the yellow type.
3-3-the alveolar wall
It consists of a thin layer of fasciculated bone tissue.
These are periodontal ligament fibers included in the alveolar wall in the form of Sharpey fibers which give it this appearance of fasciculated bone tissue.
IV-Anatomical anomaly
The vestibular table is often very reduced in thickness compared to the palatal or lingual table.
Bone resorption can cause fenestrations and dehiscences.
*Fenestrations: are isolated areas where the root is exposed or its surface is covered only by the periosteum surrounded by the gum.
*Dehiscences: this is the absence of the bony marginal edge, they are areas without bone tissue in the shape of a more or less wide and irregular V extending up to the apical half or third of the root
V-vascularization and innervation
vascularization is ensured by:
- superior and inferior alveolar branches and arteries
- the arteries of the inter-radicular septa
- periosteal arterioles of the corticals
- ligamentous arterioles
Innervation is provided by the terminal branches of the trigeminal nerve, coming from the anterior, middle and posterior dental nerves for the maxilla and from the inferior dental and buccal nerve for the mandible.
VI-physiology
The alveolar bone is a supporting tissue but a plastic tissue capable of adapting to tooth movement.
1-Histophysiological aspect of bone tissue changes
Tissue remodeling is mainly ensured by the succession of osteoclastic resorption phases and osteoblastic apposition phases.
Under the influence of a stimulus, the bone is resorbed by osteoclasts, then after an inversion phase, newly formed bone tissue is deposited by osteoblasts in the resorption focus.
2-regulation of bone tissue remodeling
It is ensured by endocrine, vitamin, ionic and mechanical factors.
, functional, capable of acting on the activity of bone cells .
3-occlusion and alveolar bone
There is a close relationship between the forces of occlusion and alveolar bone:
-on the one hand alveolar bone must support the teeth during occlusal function
-on the other hand, its structure and its very existence depend on the functional stimulation it receives.
Alveolar bone
Deep cavities may require root canal treatment.
Dental veneers correct chipped or discolored teeth.
Misaligned teeth can cause uneven wear.
Dental implants preserve the bone structure of the jaw.
Fluoride mouthwashes help prevent cavities.
Decayed baby teeth can affect the position of permanent teeth.
An electric toothbrush cleans hard-to-reach areas more effectively.