AGE AND FUNCTIONAL CHANGES OF DENTIN
AUTHOR: Dr. Vidya GS, MDS
VITALITY OF DENTIN
Dentin is considered as a vital tissue due to the following reasons.
- The odontoblast and its process are an integral part of the dentin.
- This tissue has the capacity to react to both physiologic and pathologic stimuli.
- Dentin is laid throughout life whose rate of formation may slow down with time.
- Certain stimuli like caries, attrition causes changes in the dentin.
Therefore, dentin is also susceptible to changes with age.
The dentin can undergo changes with time.
They can be subdivided into:
- Changes in physical and functional characteristics of dentin
- Tubular changes in dentin
- Formation of tertiary dentin
- Dead tracts
- Sclerotic dentin
CHANGES IN PHYSICAL AND FUNCTIONAL CHARACTERISTICS OF DENTIN
- With age, decreased sensitivity of dentin is noted.
- Increased brittleness and decreased permeability are the other ages changes noted with age.
TUBULAR CHANGES IN DENTIN
- Continued deposition of intratubular dentin leads to a reduction in the diameter of the dentinal tubule.
- It may even result in complete closure of the tubule.
- Also, continued dentin deposition is found to be responsible for the reduction or even obliteration of the pulp chamber in older individuals.
FORMATION OF TERTIARY DENTIN
- Various stimuli like caries, attrition, abrasion, operative procedures are responsible for certain changes in the dentin.
- During such processes, if the odontoblasts are either exposed or cut, then these cells may either die or survive.
- The factors which govern the status of the cell survival depends on the intensity of the injury.
TYPES OF TERTIARY DENTIN
Tertiary dentin may either be reactionary or reparative in nature.
FORMATION OF TERTIARYDENTIN
Formation of reactionary dentin
- If odontoblast cells survive on exposure to various stimuli, then the dentin produced is called as reactionary or regenerated dentin.
Formation of reparative dentin
- If the cells are killed on exposure to various stimuli, then they are replaced with new odontoblasts.
- These new odontoblasts are differentiated from either the cell rich zone of pulp or from the undifferentiated perivascular cells present deep in the pulp.
- The dentin formed from these replaced odontoblast is called as reparative dentin or response dentin.
Figure 1: Schematic representation of formation of reactionary and reparative dentin
FEATURES OF REPARATIVE DENTIN
- The main characteristic feature of reparative dentin is the presence of few twisted tubules when compared to normal dentin.
- Due to the irregular nature of the dentinal tubules, it is also termed as irregular secondary dentin.
- The process of dentinogenesis during tertiary dentin formation is less ordered.
- The size of the dentinal tubules varies and they have high mineral content.
- The dentinal tubules also present with irregular circumference with mineralized tissue projecting within them.
- Interglobular dentin may also be observed.
- Also, the incremental line with varying mineral content was noted.
- Absence of dentin phosphophoryn was also seen.
- Re-expression of Nestin and Notch protein during reparative dentin formation was observed.
Figure 2: Schematic representation of reparativedentin with few dentinal tubules
Figure 3: Schematic representation of formation of reparative dentin with twisteddentinal tubules
TYPES OF REPARATIVE DENTIN
This type of reparative dentin shows the inclusion of dentin forming cells within the rapidly produced intercellular substance. This type is commonly seen in dentin produced in response to rapidly progressing caries. BMP plays a role in the production of this type of dentin.
Figure 4: Schematic representation of Osteodentin
- In others, a combination of both the osteodentin and tubular dentin can be seen.
Figure 5: Schematic representation of combination of osteodentin and tubular dentin
- Loss of odontoblast process within the dentinal tubules may occur as a result of caries, attrition, abrasion, cavity preparation or even erosion which leads to empty tubules filled with air.
- In dried ground sections of normal dentin, these processes may disintegrate and leave behind only the empty tubules.
- Narrow pulp horns are the most affected sites of degeneration of odontoblast processes due to crowding.
- These empty tubules are filled with air and are called as the dead tracts.
- Dead tracts appear black in transmitted light and white in reflected light.
- They demonstrate decreased sensitivity of teeth and are common in older teeth.
- They are also considered as an initial step in formation of sclerotic dentin.
Figure 6: Schematic representation of dead tracts in transmitted light
Figure 7: Schematic representation of dead tracts in reflected light
SCLEROTIC/ TRANSPARENT DENTIN
- Various stimuli which are responsible for the formation of reparative dentin also bring about certain protective changes in the existing dentin.
- They are responsible for the appearance of collagen fibers and the apatite crystals within the dentinal tubules.
- Gradual deposition of the apatite crystals is responsible for the tubule to be filled with a meshwork, hence the tubule is blocked and this is considered as a protective mechanism.
- The deposition of the mineral obliterates the tubule lumen and the refractive indices of the dentin in them are equalized.
- Hence they appear similar to peritubular dentin and also become transparent due to equalized refractive indices.
FEATURES OF SCLEROTIC DENTIN
- They are commonly seen in the roots of older teeth and also under slowly progressing caries.
- Sclerotic dentin reduces dentin permeability and hence increases pulp vitality.
- Greater mineral density is observed in this type of dentin.
- It is harder than normal dentin, while its fracture toughness is reduced and elastic property is unaltered.
- Smaller crystals are present when compared to normal dentin.
Figure 8: Schematic representation of sclerotic dentin
1) Kumar GS. Orban’s Oral Histology and Embryology. 13 th ed. Elsevier; 2011.
2) Nanci A. Ten Cate’s Oral Histology. 8 th ed. Mosby; 2012.
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