Cementum Important Question And Answers

Cementum Question And Answers

Question 1: Define cementum.
Answer:

Cementum is the mineralized avascular mesenchymal tissue that covers the anatomic roots of teeth and provides attachment or anchorage for the periodontal ligament fibers.

• Cementum is characterized by continuous deposition throughout life and has a very slow rate of continuous synthesis and thereby irregularities on its surface are attended to.
• Cementum shares some physical, chemical, and structural characteristics with compact bone but differs from it in that it is avascular and more resistant to resorption and remodeling.

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Question 2: What is the thickness of the cementum?
Answer:

The cementum is thinnest at the cementoenamel junction (20–50 micrometers) and thickest at the apex of the root and furcation (200–300 micrometers). It is thicker on the distal surface than on the mesial surface, probably due to functional stimulation.

Question 3: What is the composition of cementum?
Answer:

Cementum Chemical Composition

Cementum being a mineralized connective tissue has both an organic and an inorganic phase. On a dry weight basis, 40–50% is inorganic substances mainly in the form of calcium phosphate as hydroxyapatite (Ca₁₀[Po₄]₆ [OH]₂). The other 50–55% is organic substance which is primarily collagen type-I and proteoglycans/glycoproteins.

Question 4: Describe the development of cementum.
Answer:

Cementum develops from the dental sac in particular from an area within it called the dental follicle. Undifferentiated mesenchymal cells of the follicle transform to cementum forming cells, cementoblast under the influence or enamel matrix proteins possibly secreted by the cells of the Hertwig’s epithelial root sheath.

Cells of Cementum

The primary cell is the cementoblast, which is responsible for laying down the acellular cementum.

• This cell may be distinct in origin from the cementoblasts giving rise to the cellular cementum.
• Cellular cementum is formed by cementoblasts that may originate in the perivascular space of the periodontal ligament. This is possibly one reason why acellular is not predictably regenerated as yet.

Fibers of Cementum

Extrinsic Fibers of Cementum

These fibers are portions of the principal fibers of the periodontal ligament (Sharpey’s fibers), which are embedded in the cementum. They are usually oriented perpendicular to the root surface. These fibers are also inserted into the alveolar bone.

Intrinsic Fibers of Cementum

These fiers belong to the cementum matrix and are formed by the cementoblast. They are oriented more or less parallel to the long axis of the root surface. They reinforce the insertion of extrinsic fiers.

Question 5: Classify and describe the various subtypes of cementum.
Answer:

There are two main types of cementum: Acellular (primary) and cellular (secondary).

Acellular Cementum

Acellular cementum usually forms at the time of root formation and tooth eruption. It covers the cervical third of the root and contains no cells in the matrix (no cementocytes). It is usually lamellated and has incremental lines (Salter) suggesting periods of synthesis followed by periods of rest.

Cellular Cementum

Cellular cementum is present at the apical third of the root and is characterized by the presence of embedded cells (cementocytes).

Schroeder has classified cementum as follows:

1. Acellular afirillar cementum
2. Acellular extrinsic fiber cementum
3. Cellular mixed stratified cementum
4. Cellular intrinsic fier cementum
5. Acellular intrinsic fiber cementum.

1. Acellular fibrillar cementum (AAC): It is found generally on mature enamel surfaces close to the CEJ.
2. It is thought to form when the reduced enamel epithelium disintegrates and the dental follicle interacts with the exposed enamel matrix leading to cementum deposition.
3. Acellular extrinsic fiber cementum (AEFC): It is the most important support apparatus on the root surface.
4. It consists of densely arranged collagen fiber bundles placed perpendicularly to the long axis of the tooth root projecting into the periodontal ligament.
5. Acellular extrinsic fiber cementum (AEFC) formation proceeds at a rate of 5 to 7 µm per day during the development of the tooth root.
6. Cellular mixed stratified cementum (CMSC): It is formed when the root development is about two-thirds completed.
7. This type of cementum contains a mixture of collagen fibers including the intrinsic fibers running parallel to the root surface and some extrinsic fibers running perpendicular to the root surface.
8. Cellular mixed stratified cementum is usually deposited on the root surfaces lining furcations and apical portions.
9. Cellular intrinsic fier cementum (CIFC): Cellular intrinsic fiber formation occurs when cementoblasts secrete the matrix rapidly and become entrapped in the matrix as cementocytes.
10. CIFC attaches to the still non-mineralized dentin through the intermingling of collagen fails and subsequent mineralization.
11. In addition, being a component of cellular mixed stratified cementum, the CIFC is also considered to be a form of reparative cementum.
12. Acellular intrinsic fier cementum (AIFC): AIFC is an acellular variant of cellular intrinsic fier cementum that is deposited during adaptive responses to external forces and forms without leaving cells behind.

Question 6: Differences between cellular and acellular cementum.
Answer:

Question 7: What are the types of cementoenamel junctions?
Answer:

The junction where cementum and enamel meet at the cervix of the tooth is referred to as the cementoenamel junction or (CEJ). There are three possible types of CEJ.

1. Cementum meets enamel at the cervical end of enamel (30% of all teeth)
2. Cementum and enamel do not meet (10% of all teeth)
3. Cementum overlaps enamel (60% of all teeth).

Question 8: Write briefly on the various changes observed in cementum following disease.
Answer:

Cementum resorption: It may be caused by both local and systemic conditions.

• Local conditions include trauma from occlusion, orthodontic movement, pressure from malaligned erupting teeth, cysts, periapical disease, transplanted teeth, and occasionally periodontal disease.
• Systemic conditions include calcium deficiency, hypothyroidism, hereditary fibrous osteodystrophy, and Paget’s disease.
• Cemental spurs (tears) occur as excrescences of cementum usually in teeth subjected to heavy functional or parafunctional forces.
• seen at the apical areas of the roots, sometimes to the extent that root morphology may be altered. Low-grade persistent periapical infection is thought to be one of the most common reasons for its occurrence.
• Repair and regeneration—cementum has a limited capacity to regenerate. Reparative capacity is largely a result of the continuous deposition of cementum. There is very little evidence of regeneration of AEFC.