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Bacterial infections of the tooth and the surrounding tissues progress rather slowly,
but every step is so much more severe than the previous one.
Cariogenic bacteria will first tear enamel down.
Then they’ll bore through dentin.
When they or their toxic waste get into the pulp, pulpitis occurs.
Without immediate treatment, pulpitis can cause irreversible damage and require a root
canal.
If no treatment is performed, the pulp will eventually die off through necrosis.
At that point, the tooth is considered dead, and in essence, it becomes a staging area
for bacteria to spread further.
Our immune system will, at that point, try to stage a defense around the apices of the
dental root.
We call that “battlefield” apical periodontitis, which is one of the periapical lesions.
The primary form of defense our body has against infection is the polymorphonuclear leukocyte,
also known as the neutrophil.
It is the finest soldier serving our body, and its task is to locate and destroy microbes
that intrude into the body, wherever that might be.
This is usually a very effective force, and most of the times sufficient.
When an infection occurs, neutrophils will mobilize in huge numbers, head to the site
of infection, and leave the circulatory system, searching for bacteria to destroy.
They achieve this through three methods.
First is degranulation, where neutrophils release a bunch of granules containing various
enzymes, that hurt bacteria.
Then, they will use neutrophil extracellular traps, or NETs, to immobilize the wounded
bacteria.
These are actually nets, made out of neutrophil DNA!
Finally, neutrophils will then gobble up the bacteria through phagocytosis as a final means
of its destruction.
All of this works really well, most of the time.
But, fighting infection is a bloody affair and many of the neutrophils perish during
the fight.
Macroscopically, the battlefield, containing neutrophil remains, released enzymes, NETs
and dead bacteria, makes up pus.
And a lot of it can accumulate, given the severity of the infection.
Enzymes from the pus will irritate the surrounding tissues, creating an acute phase of apical
periodontitis.
The accumulation of pus is called a periapical abscess, as it surrounds the root.
This abscess can eventually form a sinus tract, which is a narrow passageway that extends
from the abscess to the mouth, through which the pus can drain out.
The periapical abscess can also progress into a periapical cyst, which is when fibrous tissue
and immune cells surround an area of chronic infection containing pus.
In less fortunate cases of periapical lesions on the maxillary teeth, the cyst can form
a fistula to the maxillary sinus, causing a severe case of sinusitis.
If the external drainage fails to happen, and the cyst or abscess continues to grow,
the lesion might progress to osteomyelitis, which is the inflammation of the underlying
bone, or cellulitis, which is the inflammation of the throat.
One severe form of cellulitis is called Ludwig’s angina, where the inflammation of soft tissues
is so severe, it may lead to death through suffocation.
Treatment of periapical lesions usually involves antibiotics to curb the infection.
Then, an endodontic therapy is performed where the decaying pulp is removed and the abscess
is drained.
The pulp space gets thoroughly cleaned and disinfected, while the tooth crown is repaired,
allowing the dead tooth to continue doing its mechanical function of chewing.
Endodontic therapy has a high success rate, however, the treated tooth can sometimes reinfect
and an extraction may be required.
All right, as a quick recap.
Periapical lesions are inflammatory in origin, and involve apical periodontitis, which may
evolve into periapical abscess or a periapical cyst.
Abscesses can drain into the mouth or cause cellulitis.
Treatment involves antibiotics, pus drainage, endodontic treatment of the tooth, and failing
all that, extraction of the affected tooth.