Regenerating lost pulp tissue as a result of trauma or disease is very interesting and exciting concept. Revascularization via blood clotting is considered to be a feasible and practical approach in this direction .Although studies have reported this method with promising results since long, yet consensus is lacking on treatment protocols as well as the nature of tissues formed inside the root canal space . The objective of this paper is to appraise various root canal revascularization methods via blood clotting procedures strived in endodontic practice and the contemporary recommendations for their successful outcome.
INTRODUCTION:
Regeneration of injured or lost tissues or organs as a result of trauma or disease has become a riddle in modern medicine. due to most of the materials/procedures still under experimental stages and lack of homogeny on treatment protocols. The origin of biologically compatible regenerative endodontic procedures that allow regrowth of damaged dentin and root structures including the cells of pulp-dentin complex dates back to around 1952, when Dr. B. W. Hermann first reported the application of Ca(OH)2 in vital pulp amputation .1 Many materials like platelet rich plasma (PRP), Emdogain , recombinant human bone morphogenic protein (rhBMP) , fibroblast growth factor 2 (FGF2) as well as procedures like guided tissue or bone regeneration (GTR, GBR) and
distraction osteogenesis have been tried since then to regenerate various dental tissues.2-6 Off late, the focus of research in regenerative endodontics is on using a combination of stem cells, scaffolds, growth factors engaged in tissue engineering and the future looks promising.7 How ever, none of these procedures could be actually transformed into realistic endodontic practice with predictable success rates.
Root canal revascularization via blood clotting has become a new norm in regenerative endodontic practice with successful clinical results reported though conventional techniques like partial pulpotomy , apexification and apexogenesis are not obsolete yet.8The notion that Root canal revascularization is a one stop solution to regenerate compromised pulp tissue is a misnomer since the lack of long term follow-up studies and consensus on treatment protocols makes it difficult to standardize the procedure and further debate is warranted on the modus operandi.
ROOT CANAL REVASCULARIZATION VIA BLOOD CLOTTING:
Conventionally, revascularization is believed to be achievable only for the root canal space of an avulsed, reimplanted tooth.9-12 However , studies prove that the same can be achieved for an immature or mature permanent tooth with periapical periodontitis or abscess by means of thoroughly disinfecting the canal followed by inducing bleeding and establishing blood clot into the root canal system via over instrumentation supplemented by a good coronal seal.13-16 Theoretically, it was presumed that the formation of a blood clot in the sterile root canal system creates a scaffold of fibrin that entraps stem cells capable of initiating new tissue development. 7
REVASCULARIZATION OF AVULSED TEETH:
Most of the case reports demonstrated successful revascularization of the pulp space after reimplantation of avulsed teeth with immature apices.9-12 Vital apical portion of the pulp that grow coronally to replace the necrotic tissue and intact crown of the tooth which offers a good seal against bacterial permeability are the reasons implicated for the same.16 Also, the short roots and open apices create a unique environment for the ingrowth of new tissues into the root canal space. 9-12
REVASCULARIZATION IN INFECTED IMMATURE TEETH:
Revascularization of the pulp space in infected immature teeth with apical periodontitis is impossible unless the canals are disinfected. From this, it can be interpreted that disinfection of the canals is a critical step for the success of revascularization.13-15 Much emphasis is laid on disinfection with intracanal irrigants like NAOCL or chlorhexidine as the thin dentinal walls preclude successful biomechanical preparation as well as to protect the viability of the cells of dental pulp stem cells.17-21 This is usually followed by a pack of tri-antibiotic paste (a mixture of ciprofloxacin,metronidazole, and minocycline paste) or ca(oh)2 for several weeks to further sterilize the canal .18,22-25 Discoloration of the dentin had been reported with minocycline containing mixture and either cefaclor can be substituted for it or it can be left out of the combination.26 Maintaining good coronal seal is one more imperative aspect for the success of the procedure and most of the studies used an MTA seal over blood clot followed by a composite restoration.15,27-28 However, at least one study had used calcium enriched mixture (CEM) cement placed over blood clot with good results.19
REVASCULARIZATION IN INFECTED MATURE TEETH:
Necrotic pulps with closed apices require over instrumentation of since it was demonstrated that apical diameters of 1.1mm have greater likelihood of revascularization.29 This is necessary to promote adequate nutrient diffusion and oxygen supply for the initial viability of the cells as the cells that are more than 200 μm (coronal portion of the root canal) away from the point of maximum oxygen diffusion are prone for anoxia and necrosis.30
FACTORS INFLUENCING REVASCULARIZATION:
The type of tooth injury, fracture type, presence of necrosis or infection, periodontal status, presence of periapical lesions, stage of tooth development, vitality status, patient age, and patient health status are some of the factors influencing revascularization.8 Thorough disinfective protocol and good quality coronal seal also influence revascularization.13-15,27-28 In addition, it was the blood clot irrespective of scaffold that is very important for revascularization.31 Some clinicians recommended the use of an anesthetic without a vasoconstrictor when trying to induce bleeding.28Also, young patients have shown considerable degree of success rates compared to older since the no. of circulating stem cell concentrations in older patients might be lower.32
MERITS OF REVACULARIZATION:
Root canal revascularization via blood clotting is a relatively simple and practical approach which can be accomplished with presently available instruments and materials. More over, the possibility of immune rejection and contamination can be averted since the root canal system is filled with patient’s own blood cells.7 Case reports revealed progressive thickening of dentinal walls , continued root development and positive response to thermal pulp testing.15 A 24 month follow up comparative study between revascularization induced maturogenesis and conventional apexification found the former to be advantageous .33
DRAWBACKS OF REVASCULARIZATION:
The reliance on patient’s compliance because of the multi appointment nature of the procedure and the lack of long term follow-up studies makes revascularization procedure a supplement but not a substitute to the already existing treatment protocols like apexogenesis, apexification, or partial pulpotomy.8 Also, the concentration and composition of the progenitor/stem cells entrapped in the fibrin clot is unpredictable particularly in older patients that may lead to disparity in the results.32
HISTOLOGICAL ASPECTS OF REVASCULARIZED TISSUE:
A successful regenerative endodontic procedure must redevelop damaged coronal, cervical or apical dentin and resorbed root in addition to producing pulp-like tissue, ideally, the pulp-dentin complex. HERS cells signal progenitor/stem cells of the periodontal ligament and apical papilla to differentiate into cementoblast and root primary odontoblast cells that contribute to cementum like tissue and root dentine respectively.34-35The survival of cells of HERS and apical papilla in apical periodontitis /abscess after revascularization procedure is vital to produce cementum-like tissue and root development.36
It was speculated that pulp tissue regeneration might occur after revascularization procedure but there was no convincing histological evidence indicating true pulp regeneration. 37 Several animal studies described the tissue inside the canal space as cementoid or osteoid and periodontal ligament- like fibrous connective tissue and it was theorized that the periodontal ligament tissue ingresses into the root canal space and might deposit cementum on the canal walls.31 On the other hand, one study revealed that there is about 30% possibility of the pulp tissue entering the pulp space instead of the periodontal tissue.11 However, human studies are not available till date so as to understand the exact nature of the hard tissue formation and root development.
CONCLUSIONS:
Based on the present studies, it is reasonable to conclude that revascularization is a reparative process instead of a regenerative process and further studies are warranted to substantiate the regenerative potential of the revascularization process inside the root canal space. Also, since long term studies are not available and the exact nature of the tissue formed inside the pulp canal in humans is not understood, it is better to consider revascularization therapy only when other conventional modalities of treatment like apexification, apexogenesis and partial pulpotomy fail.
