Cement
- Definition :
Cementum is a specialized calcified tissue covering the root surfaces from the enamel-cementum junction to the apex
- It allows the tooth to be anchored in its socket.
- Cementum forms throughout life.
- Cementogenesis
The cementum begins to be deposited when the crown formation is complete. After the crown formation, the external and internal epithelial layers join together, which will give rise to the HERTWIG epithelial sheath. This sheath will trigger the formation of dentin on the one hand, and conditions the formation of the root on the other hand.
The epithelial tissue is subsequently invaded by the vascular layer of connective tissue which dislocates it, giving rise to MALASSER epithelial remains.
The dentin-connective tissue contact leads to the formation of cementum which occurs in 03 stages:
- 1st stage: differentiation of fibroblasts into cementoblasts
- 2nd stage: secretion of the cementoid matrix; the cementoblasts develop the first elements of the pre-cementary organic matrix composed of fundamental substance and fine collagen fibrils
- 3rd stage: mineralization of the cementoid matrix; the 1st layer of pre-cementum becomes mineralized while the cementoblasts retreat and begin to develop a new layer of organic matrix mineralized by hydroxyapatite crystals from the underlying dentin
Once the acellular cementum is deposited, the development of cellular cementum begins. The cementoblasts are walled up in lacunae called cementoplasts and become cementocytes.
** On the edge; we find a pre-cementary layer with an alignment of cementoblasts and cementocytes
The mineralization of cellular cement occurs in foci which end up forming lamellae.
- Anatomy:
- Thickness: the cementum covers the root surface, its thickness is variable, it depends on the root region and the age of the patient.
This thickness is maximum at the apex (150 to 200µ) and thins in the neck region. These values can triple at the age of 70 years.
- Enamel-cement ratio : 03 types of relationships can occur:
- Cement covers cervical enamel in 65% of cases
- The cementum and enamel are end-to-end, in 30% of cases
- Cementum and enamel do not join in 0.5% of cases
- Cement-dentine ratio
– The C/D junction appears as a thin line that corresponds to the granular layer of tomes; consisting of a narrow zone of small interglobular spaces and a hyaline layer.
- Physicochemical properties:
- Physical properties:
- Color : Its color is light yellow, slightly more colorful than dentin; and clearly different from enamel and it is easily distinguished from the latter by its lack of shine and its more opaque appearance.
- Hardness: it is the 3rd calcified tissue after enamel and dentin and the least resistant to abrasion
- Density: lower than that of enamel and dentin
- X-ray absorption: it is 02 to 06 times weaker than that of dentin
- Permeability : it varies according to pulp vitality and age
- Chemical properties:
Cementum being the least mineralized of the hard tissues, consisting of approximately 65% of materials
minerals (calcium, phosphorus in the form of hydroxyapatite, and fluorine); and 23% of organic matter formed essentially of collagen, and mucopolysaccharides and 12% of water
- Histology
Cementum is a tissue containing:
- cells: cementoblasts, cementocytes and cementoclasts
- and a fundamental substance: composed of an organic framework (formed essentially of type 1 collagen associated with glycoprotein complexes and muccopolysaccharides); and mineral materials essentially calcium phosphate of the hydroxyapatite type
There are 02 essential types of cement:
- Acellular cementum (primary, fibrillar) covers the entire root
- Cellular cementum (secondary, osteocement) covers the apical 1/3 of the root
A recent classification takes into account the origin of the collagen fibers of the matrix. We distinguish intrinsic fibers due to the synthetic activity of cementoblasts and extrinsic fibers produced by fibroblasts of the desmodont and subsequently incorporated into the cementoid matrix (Scharpey fibers)
- Primary acellular cementum:
- Appears first during embryonic root development
- Contains no cellular elements
- Its presence at the apical 1/3 may be missing
- It is a lamellar tissue, made up of a calcified cementum substance and a large number of collagen fibers, hence its name “fibrillar cementum”; there are 2 types of collagen fibers:
Intrinsic fibers: formed by cementoblasts; they are parallel to each other and parallel to the surface of the dentin
Extrinsic fibers: represented by the “SHARPEY” fibers of the periodontal ligament
- Cellular cementum:
- Cellular secondary cement with intrinsic fibers
It differs from primary cementum by several characteristics: its secretion begins well before the organization of the LAD, in the form of a matrix and collagen fibers. (The mineralization of this matrix is not instantaneous: as in bone tissue and dentin, there is an intermediate non-mineralized substance, called Cementoid, equivalent to osteoid and predentin)
It is located in the apical third of the root and in the inter-radicular regions. Its role in dental attachment appears minor, since it is missing in certain teeth (canines and incisors). It is characterized by the presence of cementoblasts incorporated in the matrix
- Mixed fiber cellular secondary cement
After organization of the periodontal ligament, its fibers are incorporated into the continuous secretion of cementum produced by the cementoblasts. In ME this tissue is hollowed out with cavities encompassing cementocytes with numerous cytoplasmic extensions. The fully mineralized intrinsic fibers are grouped in dense bundles parallel to the surface. The larger extrinsic fibers are perpendicular to the root and often have a non-mineralized center.
- Vascularization and innervation:
- The cementum is neither vascularized nor innervated
- It is nourished by diffusion from the desmodontal connective tissue
- Physiology
& – fixation function : from the tooth to the alveolar bone via the desmodontal fibers
The cementum deposit increases throughout life; it allows the fixation of the “SHARPEY” fibers; the number, diameter, and distribution of the fibers in the cementum are always linked to the functional stimulations of the tooth
&- apposition function : cement deposition occurs throughout life, it increases with age and at the apex.
This apposition is a phenomenon of compensation for the abrasion of the proximal and occlusal faces.
This apposition allows the maintenance of the physiological width of the desmodontal space and a sufficient length of the root to maintain the occlusal function and preserve the crown-root relationship during active eruption.
&- resorption function : cementum differs from bone by the rarity of its resorption, either in the form of true areas or in the form of small lacunae.
&- repair function : we see repairs of dentin substance losses and root fractures. It is the root cement that fills these resorptions
&- permeability function : the study of permeability was carried out using dyes; these pass from the cement surface to the dentin and from the pulp to the cement (young teeth)
Permeability decreases with age
VX- Cementum pathology :
- Hypercementosis (senescence):
Called cementum hyperplasia, it is a prominent thickening of the cementum, it can affect one or more teeth or the entire set of teeth.
It is sometimes difficult to distinguish between hypercementosis and a physiological thickening of the cementum.
Hypercementosis is a generalized thickening of the cementum accompanied by a nodular enlargement of the apical third of the root
- Cementicles:
They are rounded (globular) masses of cementum arranged in concentric lamellae and devoid of cells.
They are sometimes attached to the root cementum or to the alveolar bone, sometimes free in the ligament, their number increases with age
Conclusion :
Cementum holds an important place among the constituents of the deep periodontium.
Cement
Early cavities in children need to be treated promptly.
Dental veneers cover imperfections such as stains or cracks.
Misaligned teeth can cause difficulty chewing.
Dental implants provide a stable solution to replace missing teeth.
Antiseptic mouthwashes reduce bacteria that cause bad breath.
Decayed baby teeth can affect the health of permanent teeth.
A soft-bristled toothbrush preserves enamel and gums.