Dentin Sensitivity (Note)

• Not all, but few dentinal tubules have nerve endings in the inner dentin or the pre-dentin-pulp junction.

• These nerve endings are in a close association with the odontoblast process.

• Nerve endings in dentinal tubules are mostly found coronally, usually near the pulp horns.

• With this in mind let’s explore some theories explaining dentin sensitivity.

POSSIBLE CAUSES OF DENTIN SENSITIVITY

• Thermal factors like heat and cold.

• Air desiccation or air drying.

• Mechanical factors like probing or using a bur.

THEORIES OF DENTIN SENSITIVITY

There are 3 theories explaining the possible cause for dentin sensitivity, them being:

1. Theory of direct neural transmission – this implicates that the nerves in the dentinal tubules are directly stimulated by external factors causing dentin sensitivity.

2. The odontoblast process possibly acting as a receptor permitting transduction of signals – this theory implicates the odontoblast process of possibly being a receptor that transmits signals to the closely associated nerve endings in the inner dentin.

3. Hydrodynamic theory – external stimuli like heat, cold, air drying etc. could affect the flow of the dentinal fluid in the tubules that could in turn cause mechanical disturbance of the nerve endings, stimulating them to cause sensitivity.

DIRECT NEURAL TRANSMISSION

• This theory of direct neural transmission does not hold good and is not accepted.

• The reason being that

  • Nerve endings are not present in all dentinal tubules. They are relatively scarce.

  • Nerve endings if present, are present in the inner dentin/ predentin-pulp junction. They do not extend upto the DEJ (outer dentin). Dentin sensitivity does not solely depend on direct stimulation of nerve endings.

  • Application of local anesthetic on the dentin does not decrease or nullify dentin sensitivity.

  • It is also shown that chemical mediators of inflammation like histamine and bradykinin (these are mediators that can cause pain) do not cause pain in the dentin.

ODONTOBLAST TRANSDUCTION THEORY

• This theory was proposed keeping in mind that odontoblasts are neural crest in origin.

• However, this theory also does not hold good and is not accepted for the following reasons.

  • The odontoblasts cannot transmit signals to the nerve endings as they lack neurotransmitter vesicles capable of doing so. There is no evidence to state that odontoblasts could behave like nerves.

  • The odontoblasts do not have a synaptic relationship with the nerve endings.

  • Application of local anesthetics does not put an end to dentin sensitivity.

HYDRODYNAMIC THEORY

• This has been the most accepted theory till date.

• The dentinal fluid movement causes mechanical disturbances in the micro-environment and depolarizes nerve endings in the inner dentin.

• This theory explains why external stimuli like heat or cold, air drying, mechanical factors etc cause sensitivity. These external factors induce dentinal fluid movement in the dentinal tubules.

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REFERENCES AND FURTHER READING

1. Berkovitz BKB, Hollan GR, Moxham BJ. Oral Anatomy, Histology and Embryology. 4^th ed. Mosby Elsevier; 2009.

2. Nanci A. Tencate’s Oral Histology. Development, Structure and Function. 8^th ed. Elsevier; 2013.

3. Kumar GS. Orban’s Oral Histology and Embryology.13^th ed. Elsevier; 2011.

4. Avery JK. Oral development and Histology. 3^rd ed. Thieme Medical Publishers; 2002.

5. Miglani S, Aggarwal V, Ahuja B. Dentin hypersensitivity: Recent trends in management. J Conserv Dent. 2010;13(4):218-224. doi:10.4103/0972-0707.73385

6. Liu, XX., Tenenbaum, H.C., Wilder, R.S. et al. Pathogenesis, diagnosis and management of dentin hypersensitivity: an evidence-based overview for dental practitioners. BMC Oral Health 20, 220 (2020). https://doi.org/10.1186/s12903-020-01199-z