A necrotic pulp should be suspected when the tooth
does not respond to pulp sensibility tests. However, this
will not always be the case since teeth with pulp canal
calcification, previous root fillings or pulpotomies will
also not respond to pulp sensibility tests. Likewise,
some teeth or patients just do not respond to such tests
for no apparent reason. When pulp necrosis is present,
the history may reveal past trauma, previous episodes
of pain or history of restorations and caries.
Radiographically, a tooth with a necrotic pulp may
have signs (such as untreated caries, an extensive
restoration, previous pulp capping) or there may be no
such signs (e.g., following trauma). Trauma to a tooth
may cause pulp necrosis as a result of severing the
apical blood supply if the tooth has been displaced
from its normal position (e.g., luxations, avulsion) or if
there has been significant damage and inflammation to
the apical periodontal ligament (e.g., subluxation).
No significant radiographic changes are evident at
the root apex unless there is also periapical involve-ment,
and this only occurs once the necrotic tissue
becomes infected. It is important to realize that a
necrotic pulp per se does not cause apical periodontitis
unless it is infected.
Pain usually does not present unless the periodontal ligament is affected. In this
situation, the canal is infected and leads to apical
periodontitis.
Occasionally, patients will complain of a dull
continuous ache that is exacerbated by heat but
relieved by cold water being held over the tooth. The
reason is unknown although it has been speculated that
micro-organisms producing gases may infect the
necrotic pulp and these gases contract with application
of the cold water which relieves pressure on the nerve
endings that may still be functioning, particularly in the
apical portion of the canal. However, the relief from the
cold water is only temporary and the pain returns as
soon as the tooth warms up again and the gases
expand. This situation occurs since the apical part of
the pulp nerves are the last part of the pulp to necrose.
It is likely that the apical nerves maintain some viability
through blood supply to their more medial portions for
a short time after the rest of the pulp has died.
Once a necrotic pulp is invaded by bacteria, then the
bacteria will spread throughout the entire root canal
system. The necrotic pulp acts as a source of nutrients
for the bacteria which ingest the necrotic tissue and
render the tooth pulpless. This may occur within 1–2
months of the initial invasion by the bacteria.