HISTOLOGY OF THE DENTAL ORGAN
Introduction: Dental histology aims to study dental tissues, from a morphological and physiological point of view.
Definition: Histology is an integrative science since it allows us to recognize the fundamental link that exists between the molecular architecture of organelles and cellular organization.
Histology of enamel:
Morphology of enamel: enamel is formed by the juxtaposition of mineralized prisms or rods which are stretched from the enamel-dentin junction to the surface of the crown and by an interprismatic substance which is also mineralized.
There are two types of striae; Retzius striae and Hunter-Schreger bands.
Each prism measures 4Ym in diameter, are perpendicular to the surface of the crown
Chemical structure: Enamel is made up of 96% minerals in the form of hydroxyapatite, 4% organic matter and water sitting between the crystals.
Minerals: are mainly hydroxyapatites (Ca10PO46H2O), calcium and phosphorus salts, various ions (strontium, magnesium, lead, fluorine) Water: either arranged around the crystals or incorporated into the proteins.
The organic matrix: made up of degradation products of enamel proteins. After tooth eruption, part of the matrix would be eliminated to the outside
Physical characteristics:
hard but brittle substance
adult enamel is translucent, bluish white
more radiopaque than other mineralized tissues
its thickness vulnerable to acid attack
varies according to the topography, more important in relation to the cusps and the incisal edge, decreases at the level of the neck
has a number of folds
Histology of cementum; hard, avascular connective tissue that lines the dental root. Although it is one of the three mineralized tissues of the tooth, it belongs to the periodontium since it is, with the alveolar bone, an essential attachment point of the periodontal ligament.
It contains 65% calcium and phosphate, mainly in the form of hydroxyapatite, 23% organic substances, especially collagen, and 12% water. Less mineralized than enamel and dentine, it has the same mineralization rate as bone.
Histology of cementum:
Classification: There are two types of cementum:
Acellular cementum: primary or fibrillar cementum
It is the first one that comes into contact with the root dentin.
Secondary or cellular cementum, it has a lamellar appearance and is formed after the primary cementum which covers it, it is thicker than the primary cementum especially in the apical region.
2/ENDODONT:
histology of the pulp-dentin complex;
a- Histology of dentin: dentin is a mineralized tissue, formed by specialized pulp cells; odontoblasts, whose extensions are housed in dentinal tubules extending to the dentin-enamel junction.
At a short distance from the pulp, each canaliculus is occupied by an odontoblastic extension,
separated from the intracanalicular dentin by a space probably occupied by a pericanalicular matrix
Chemical Composition:
It is made up of 70% mineral substance, 20% organic matter and 10% water.
The mineral matter is composed of hydroxyapatite crystals, which are sometimes joined by calcium carbonates, sulfates and phosphates as well as traces of Fe, Cu, Pb, Zn, Mg, Na, Cl, and F.
The organic portion contains 90% collagen as well as citrates, lactates, phosphoproteins,
Proteoglycans, glycoproteins, plasma proteins, phospholipids, glycol, cholesterol and free fatty acids.
Physicochemical property: dentin is an avascular mineralized tissue in permanent connection with the pulp by odontoblasts
The dentin has a slightly yellowish tint.
Dentin is harder than cementum.
Dentin is permeable in both directions, from the pulp and from the JED, this permeability decreases with age
Mineralization of dentin; globular appearance of calcified nodules which are separated by non-mineralized areas
b-pulp histology
The dental pulp is a loose, specialized connective tissue of gelatinous consistency; from the histological point of view the pulp is divided into a peripheral zone that includes elements located in the vicinity of the dentin, and a central zone that includes all the rest of the connective tissue of the pulp, composed mainly of the glucoproteins of the water and several metabolites transported from the blood to the cells; and finally by fibers mainly collagen fibers and other non-specific fibers
The peripheral zone, directly responsible for the formation of dentin, is itself divided into three zones:
The odontoblastic layer located at the pulp periphery; includes odontoblasts.
The acellular layer of Weill, particularly visible in the coronal pulp, contains the fibers and vessels.
The inner layer is rich in cells and is sometimes called Hohl’s zone.
Central zone contains cells, fibers, vessels and ground substance.
The odontoblastic layer located at the pulp periphery is composed of specific cells, the odontoblasts aligned in a regular palisade of a single layer, each odontoblast connected to neighboring odontoblasts by intercellular contacts, mainly of the desmodontal type;
Each functional odontoblast emits at least one extension towards the dentin and each extension can have lateral branches.
The odontoblast plays an essential role in the synthesis of collagen in the predentin matrix.
The empty Weill acellular layer on ordinary histological preparations, it is only poor in cells, contains numerous fibers:
Collagen fibers of odontoblastic origin;
Von Korff fibers.
The Hohl cell layer contains young cells, fibroblasts, this layer is very rich in arteriovenous elements
The central pulp mass is formed of connective tissue rich in cellular elements, and poorer in fibers than normal loose connective tissue, which gives an appearance reminiscent of young connective tissue.
The cells observed are mainly fibroblasts, and a few rare cells such as macrophages and histiocytes.
These cells bathe in a fundamental substance of specific composition accompanied by collagen fibers whose number increases with age, and a very important vascular-nervous and lymphatic plexus.
1-Histology of the desmodontium: dense connective tissue that surrounds the dental roots and mainly connects the teeth to the alveolar processes.
In the elderly it can disappear, which creates dental ankylosis.
a- the fundamental substance has a consistency and fluidity of a gel.
b- cells: we find fibroblasts, fibrocytes of bone and cement cells and defense cells. As well as epithelial cells represented by remnants of the Hertwing epithelial sheath.
c- fibers: mainly collagen fibers which have a diameter of 0.55 mm distributed in alveolo-dental bundles classified into 5 groups
The alveolar ridge group
The horizontal group
The oblique group (this is the most important)
The apical group arranged between the apex
And the base of the alveolus.
The inter-radicular group
As well as the oxytalline fibers which are parallel to the surface of the roots perpendicular to the axis of the collagen bundles.
d- vascularization occurs via vessels originating from branches of dental and mandibular arteriovenous trunks.
e- innervation: constituted by a plexus whose path overlaps that of the vascular network.
2- histology of alveolar bone:
Composition of bone tissue: the fundamental substance is made up of an organic and an inorganic framework.
The radiographic appearance of the alveolar wall is called the “lamina dura”
Histological structure: bone trabeculations have a convoluted path, they are formed by the juxtaposition of parallel lamellae
between them; the trabecular spaces are occupied by a richly vascularized cellular-fibrillar parenchyma
Conclusion
A perfect knowledge of the structures and ultra structures of dental tissues would be useful to practitioners by reminding them of the basic data necessary for the implementation of their therapies, the latter are constantly evolving and progressing.
The effectiveness of their treatments , the reactive behavior of the tooth and the biocompatibility of the materials is conditioned by the histological structure of the dental tissues on which they are applied.
HISTOLOGY OF THE DENTAL ORGAN
Misplaced wisdom teeth can damage adjacent teeth.
Ceramic dental crowns provide a natural-looking result.
Receding gums can expose tooth roots.
Clear aligners are a discreet alternative to braces.
Composite fillings are less visible than amalgam.
Interdental brushes prevent gum problems.
A diet rich in calcium strengthens teeth and bones.