Discussion

Clinicians frequently encounter the sequlae of trauma and are rarely present when the trauma actually occurs. It is important to be aware of possible healing responses. In this case we report the spontaneous closure of an open apex in an infected immature tooth with arrested root development. AP was controlled solely by irrigation and without instrumentation of the canal. The HTB was maintained and incorporated in the root canal filling.

Root development of the treated tooth was arrested when ¾ of the root was formed and the foramen is fully open. It can be estimated (4) that the offending event occurred between the ages 8-11. This coincides with the patient’s vague recollection of a dental trauma when he was very young. Apical periodontitis eventually developed after bacteria gained access to the root canal system (RCS) possibly through the lingual invagination. It could also be that infection at that age was the initiating event that interrupted root formation and not the early facial trauma. Hard tissue deposition can occur in the presence of infection (5-7) and a HTB can be formed even before the AP has been resolved. (8, 9) Interestingly, the tooth had been asymptomatic for years and AP was only noticed on a routine oral hygiene exam.

Disinfection of the RCS in the immature tooth is challenging. Copious irrigation with minimal instrumentation is now recommended for disinfection of the infected immature tooth in regenerative procedures,(10) and was the treatment of choice for this case. An alcohol rinse was done before the irrigation with CHX to prevent interaction with sodium hypochlorite and potential discoloration.(11) EndoVac was included in our irrigation protocol as it was shown to be able to produce a sterile environment in vivo. (12, 13) The HTB was complete. The foramen was not patent nor was patency forcibly attempted. The goal was to reduce the microbial insult causing the AP and maintain the HTB and use it as a barrier for containing the disinfectants and obturating material within the canal space. Furthermore, the naturally formed barrier has the potential to maintain itself as a protective barrier against the ingress of irritants.

The CBCT and the 3D imaging showed that the HTB contained porosities which were not seen in the periapical radiograph (Fig 2, 3). A 5mm layer of MTA was used placed on the HTB to seal the porosities and to augment the existing barrier (14, 15). MTA has also been successfully used in one visit apexification treatments MTA has mild antibacterial properties, is biocompatible with the apical tissue. (16) Intracanal MTA causes an increase in pH across dentin and has potential anti-resorptive properties.(17) Exposure of dentin to MTA can also bring about the release of fossilized bioactive molecules such as TGF β1. (18) These could activate dental cells to form mineralized tissue which could contribute to the maintenance of the HTB.

The nature of the HTB formed in apexification has been investigated and the calcified tissue has been found to contain a mixture of cementum, bone, and dentin with inclusions of soft connective tissue islands giving the barrier a “Swiss Cheese” histological appearance.(3) These inclusions could be the voids seen in the CBCT image.

Hard tissue, cementum, dentin and bone can be formed in the presence of infection (5-7) and a HTB can be formed before the AP has been resolved. (8, 9) The wide diameter of the open apex and possible remnants of dental pulp cells could have contributed to the hard tissue deposition. (19, 20)

Restoration of the tooth was done with a fiber post and resin material which can bond to dentin and make the tooth less susceptible to tooth fracture as has been suggested. (16, 21, 22)

The naturally occurring HTB demonstrates the regenerative potential of the apical area. In the future, regenerative treatment of immature tooth may enable hard tissue to be formed all along the canal walls including the cervical area which would make these immature teeth less susceptible to root fracture.