An extreme approach to an open root end

(This article is expected to be published in the Malaysian Dental Association (MDA) News)

Root canal treatment (RCT) on an immature permanent tooth with necrotic pulp and apical periodontitis remains a challenge to us, dental clinicians. Cases of traumatized immature upper incisors, immature lower premolars with fractured dens evaginatus and sometimes in deep caries lesions of immature first molars may lead to pulplal injuury and RCT. An immature tooth takes approximately three years after its eruption for apical closure. If the tooth is still in an early stage of root development, canal walls will be thin and fragile. The absence of an apical constriction poses challenges in standard cleaning and shaping procedures and it is difficult to obtain a good seal during obturation.

A procedure called apexification is currently the first line of treatment for immature necrotic permanent teeth (1). According to American Association of Endodontists Glossary of endodontic terms (2003), apexification is defined as a method of inducing a calcified barrier of a root with an open apex or continued apical development of an incomplete root in teeth with necrotic pulp. The canal is filled with calcium hydroxide (CaOH) to induce the formation of an apical hard tissue barrier, which composed of dentin, cementum, bone or osteodentin. This process usually took 6 to 18 months. Apexification with mineral trioxide (MTA) shortened the long duration of this mode of treatment to single or two visits and the aim was to provide an effective apical seal without any attempt for apical closure. Apexification, unlike apexogenesis, do not promote root lengthening and thickening of lateral walls. Therefore, immature teeth with thin canal wall are more susceptible to vertical fractures, either during or after apexification. Do you ever question if it is worthwhile saving immature teeth, especially those with thin walls, or replacing them with implants is a better option?

Apexogenesis refers to a vital pulp therapy procedure performed to encourage physiological development and formation of the root end, whereas apexification is only performed onto non-vital teeth. There are several clinical case reports that did not show a clear cut between these two clinical procedures. When an apexogenesis approach is performed on a non vital infected immature tooth, continued root development was observed (2). This stimulates new perceptive on how we treat immature teeth with necrotic pulp, favouring apexogenesis over apexification.

Revascularization is a new treatment protocol to generate tissues into pulp space of nonvital infected tooth (3). In order to create an environment for regeneration of infected necrotic teeth:

· Canal has to be effectively disinfected

· Matrix in the form of blood clot has to be created in the canal to allow new tissue to grow

· Coronal access has to be tightly sealed to prevent recontamination.

Banchs and Trope described the revascularization method of an immature necrotic permanent lower premolar with apical periodontitis and sinus tract (4). Infection was controlled by copious irrigation of sodium hypochlorite (NaOCl) and a triple antibiotic preparation, consisting of minocycline, ciprofloxacin and metronidazole, as the intra-canal medicament. No mechanical instrumentation was recommended as it might further weakened the root. When the canal was clean and free from inflammatory exudates, bleeding was intentionally created by irritating apical tissues gently, to form a blood clot below the cemento-enamel junction and the access cavity sealed with MTA and composite restoration. The tooth was asymptomatic, the sinus disappeared and radiolucency reduced in size after 26 days. Subsequent radiographic evaluation up to two years showed successful apexogenesis with root lengthening and lateral reinforcement of canal walls. Pulp space also returned to a vital state, with a positive response to cold test.

How does tissue regenerate and what is this new tissue in the pulp space? An immature open-apex tooth has a rich blood supply and contains stem cells with the capacity to regenerate. It is also possible that viable pulp cells at the apical part of the canal proliferate into the newly formed matrix. In the absence of intra-canal infection and presence of a matrix, these cells differentiate into odontoblast and deposit dentin, causing apexogenesis. Growth factors in the blood clot itself may also contribute to regeneration.

Revascularization is a new and promising topic in endodontics. In line with our general goal to preserve pulp vitality and conservative treatment, more research is looking into pulp regeneration for mature teeth. It is not impossible since there are vital pulp tissues in mature teeth with periradicular lesion and dental stem cells do exist on permanent teeth. In the era of stem cell technology, is pulp regeneration our new direction? RCT may be much simpler in future without mechanically instrumenting the intricate root canal system, instead, disinfection of the infected pulp and stimulation pulp regrowth will be the new protocol.

Having said all that, revascularization is still in its infancy as a routine endodontic procedure. There are still may uncertainties and we need more clinical studies to establish its guidelines and indications. We still do not know its long term outcome of this new procedure. Will there be mineralized tissues filling and obliterating the canal space and what is the impact of this occurrence? It will be a problem if the calcified canal is indicated for a conventional non-surgical RCT in future. For now, we can select cases carefully when attempting this new method. Duration of infection can be a determining factor. This can be worked out simply by checking the stage of root development on the periapical radiograph and age of the patient. Success will be less likely when an immature tooth has been necrotic and infected for more than five years. Gentle flushing of canal with NaOCl is cannot be overemphasized here to prevent injecting the solution into the soft tissues, which may cause a NaOCl accident. Minocycline, one of the three antibiotic mixture, should be used with caution in anterior teeth as it causes severe dentin staining. If there is no signs of regeneration after three months, the conventional method can be carried out.

If you would like to know more about revascularization and tissue regeneration, join us at the MES-SES Joint Meeting on 31st October, 2010. Two experts, Dr Jeeraphat Jantarat from Thailand and Dr Leung Siu Fai from Hong Kong, will share their clinical experiences and scientific knowledge in this topic. Hope to see you there.

References

1. Raftar M. Apexification: A Review. Dent Traumatol 2005; 21: 1-8

2. Chueh LH, Huang GT. Immature teeth with periradicular periodontitis or abscess undergoing apexogenesis: a paradigm shift. J Endod 2006; 32:1205-13

3. Iwaya S, Ikawa M, Kubota. Revascularization of an immature permanent tooth with apical periodontitis and sinus tract. Dent Traumatol 2001; 17:185-7

4. Banchs F, Trope M. Revascularization of Immature Permanent Teeth with apical periodontitis: New treatment protocol? J Endod 2004; 30 (4): 196-200