Dentinal tubules are a potential pathway for the diffusion of noxious chemicals or microorganisms to the pulp. The dentin has a limited capacity for its own defense – by the complete or partial closure (obliteration) of the tubules via the following processes:
Histologically, sclerosed dentin appears as “Transparent dentin”.
|Narrowing of the dentinal tubules by the formation of dense calcific material (peritubular dentin).||(Primary) Odontoblasts||Pathological – Sclerosis progresses rapidly;
Occurs beneath advancing carious lesion or dentin exposed by attrition/ abrasion/ erosion.
Sclerosis occurs more slowly;
Natural part of ageing.
|Calcium Phosphate deposition||Crystals of calcium phosphate are deposited deep within the dentinal tubules.||(Primary) Odontoblasts||Occurs beneath slowly advancing carious lesion.|
|Salivary precipitation||When processes leading to demineralization (low pH associated with erosion, caries) are arrested, remineralization occurs.||Ca2+ and PO43- ions in saliva||Precipitation of salivary calcium and phosphate can occlude dentinal tubules exposed to saliva, and effectively desensitize hypersensitive dentin.|
|Reactionary dentin||Tertiary dentin laid down by surviving odontoblasts.||(Primary) Odontoblasts|
|Reparative dentin||Tertiary dentin laid down by newly-differentiated odontoblasts.||Secondary odontoblasts differentiated from pulp mesenchymal cells||Pulp mesenchymal cells undego varying degrees of differentiation, and lay down tertiary reparative dentin.|
|MAGNITUDE OF INJURY||RESPONSE|
|Mild injury (due to attrition or shallow cavity preparation)||Regular Reparative dentin (“REACTIONARY DENTIN”)* containing relatively normal dentinal tubules are laid down by the (primary) odontoblasts at the pulp-dentin interface in the area of damage, as a continuation of the main body of dentin.|
|Moderate to severe injury||In case of more severe injury or injury of longer duration, the primary odontoblasts die. The pulp mesenchymal cells differentiate into secondary odontoblasts and lay down REPARATIVE DENTIN that shows varying degrees of tubular morphology (irregular dentin to atubular dentin) and mineralization (poor). This varied morphology is due to the stage of differentiation of the newly formed odontoblast.|
|Chronic injury||In chronically inflamed pulp, diffuse calcification occurs due to deposition of calcific matrix by mesenchymal cells. When the calcified material is laid down in the form of well-organized dentin, it forms “pulp stones”. Pulp stones may also form in an otherwise normal pulp for no apparent reason.|
- The textbook of Mount & Hume describes Reactionary and Reparative dentin as the same entity, both being laid down by (primary, pre-existing) odontoblasts.
- The textbook of Seltzer & Bender’s Dental Pulp describes Reactionary dentin as the tertiary dentin laid down in mild-moderate injury by the (primary) odontoblasts.
When injury is severe, leading to death of the odontoblasts, the mesenchymal cells of pulp differentiate into new (secondary) odontoblasts and lay down reparative dentin. Depending on the state of differentiation of the newly-formed odontoblasts, lay down irregular dentin to atubular dentin. This distinction between reactionary and reparative dentin is followed by other textbooks like: Orban’s Oral Histology, Cohen’s Pathways of the Pulp, 10th ed.