Once pulp necrosis and infection has been
established, apexification procedures need to be
initiated. The access cavity preparation should be made
large enough to encompass the larger than normal
underlying pulp and to allow access of endodontic
instruments to the divergent walls. Cleaning should be
carried out with great care using copious amounts of
irrigant, such as sodium hypochlorite. Reliance on
irrigation to remove debris rather than filing is
important, as the canal walls in the apical region are
thin and fragile. Over-zealous use of files may damage
the walls. An endodontic ultrasonic device operated in
a canal full of sodium hypochlorite can help remove
debris, but care should be taken to ensure that the
ultrasonic instrument does not compromise the walls of
the canal.
Teeth with infected root canals and open apices are
now routinely treated with calcium hydroxide root
induction techniques followed by orthograde gutta-percha or
MTA root filling techniques. The use of
propriety corticosteroid/antibiotic pastes can have a
role in initial management to control the apical
periodontitis and then once the canal has been fully
debrided and the tooth is symptom-free, calcium
hydroxide can be placed into the canal using a spiral
filler or a proprietary injection syringe. It is imperative
that the access cavity then be sealed adequately while
apexification takes place. A “double seal” with Cavit®
and a stronger restorative dental material is
recommended in order to prevent breakdown of the
temporary restoration which can lead to re-infection of
the canal and subsequently to further apical
periodontitis.
Apexification can take from six to 24 months. The
role of the medicament is uncertain and apexification
has been reported to occur with a number of different
paste formulations including tricalcium phosphate, zinc
oxide and antibiotic pastes. Continued root develop-ment and
apical doming can also occur when the canal
has been instrumented and left empty or, occasionally,
if no treatment at all has been performed.
Regular radiographic assessment is necessary to
monitor progress of apexification. The calcium
hydroxide should be replaced if apexification is not
proceeding, or if the material has resorbed more than
one-quarter of the way into the canal space. If the
calcium hydroxide is left in the canal for too long with-out replacement,
then apexification may not occur.
As the apical portion of the canal is often larger than
the coronal portion and since the cross-section of the
canal is much wider in the labio-lingual (or labio-palatal)
direction than mesio-distally, a softened gutta
percha root filling technique should be used to fill the
canal. Care should be taken not to apply too much
pressure during root filling since this may dislodge the
apical dome. In addition, the amount of heat used
should be limited since the root walls are thin and the
heat may be transmitted to the periodontal ligament
with potential for adverse effects.
Restoration of an immature tooth that has under-gone
apexification is difficult as the pulp space is large and divergent,
and the remaining root structure will be
weak. Subsequent fracture of the root is a possible
sequel to apexification procedures, especially if there
is any further trauma to the tooth although it can also
occur during normal function. The patient, and his/her
parents, should be warned of this possibility before
treatment is commenced. It has been recommended that
these teeth should be strengthened by the use of an
intracanal acid-etched composite resin restoration.