You Must Know about Two Nerve Fibers in the Pulp of A Tooth

The following nerve fibers are responsible for pain of pulpal origin:


A Delta Fibers:

  • Largest diameter 3 to 20 mm
  • Myelinated
  • Faster conducting up to 100 m/s
  • Responsible for localized, sharp dentinal pain

Electric pulp tester stimulates A delta fibres first because of their lower threshold.
C  Fibres:

  • Smallest diameter 0.5 to 1 mm
  • Unmylinated
  • Polymodal
  • Slow conducting 0.5 to 2 m/s
  • Responsible for dull and throbbing pain


Thermal, chemical or mechanical stimuli stimulate “C” fibers resulting in dull, poorly, localized and throbbing pain.
NOTE: As the intensity of stimulus is increased along with A delta fibres , some of the C fibres also get stimulated resulting in strong unpleasant sensation.

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