The prerequisites essential for root maturation include the presence of wide open apex for tissue ingrowth, young aged individuals where high stem cell regeneration potential is present, cautious use of sodium hypochlorite as an irrigant for effective disinfection and the use of triple antibiotic paste as intra canal medicament3. Another major factor is the initiation and/or placement of a scaffold that creates a platform for regeneration to occur. An appropriate scaffolding must yield a correct spatial location of stem cells and regulate its differentiation, proliferation and metabolism by inducing growth factors9. The growth factors present in PRP and PRF such as platelet derived growth factor, transforming growth factor, insulin like growth factor etc stimulate mitogenic response leading to proliferation and differentiation of the Stem Cells of Apical Papilla (SCAP) into odontoblasts which are influenced by the cells of the Hertwig’s epithelial root sheath (HERS)4. These odontoblasts deposit atubular dentin at the apical and lateral walls of the root canal leading to continued root maturation12.
Simonpieri et al13 stated that PRF acts as a biological connector between bone particles thereby maintaining and protecting grafted biomaterials, facilitates cell migration for neoangiogenesis, promotes healing by release of cytokines, up regulates the inflammatory process and acts as an anti-infectious agent. Ulusoy et al14 compared the use of a blood clot, PRP, PRF and platelet pellets as scaffolds for RE therapy and concluded that the platelet derivatives yielded a higher rate and prolonged exposure to the growth factors with less chances of obliteration of the canal space.
Studies have proven the effectiveness of revascularisation procedures in adolescent age group because of increase in the differentiating ability of the stem cells in terms of quantity, quality and mobilization capacity unlike in aged individuals. On the contrary, there is growing evidence that mesenchymal stem cells recruited in the RE procedure are either less prone to ageing or elude ageing indefinitely7. Therefore a wide range of patients between the age group of 9 to 25 years was chosen in the study. Avoiding mechanical debridement of canal walls and use of lower concentration of NaOCl, further ensures the vitality of SCAP15. NaOCl at concentrations greater than 3% is found to be cytotoxic to periodontal ligament cells and SCAP cells16. Martin et al17 stated that 17% EDTA when used as the final irrigant partially reverses the detrimental effects of high concentrations of sodium hypochlorite solution and has a positive effect on the survival and differentiation of SCAP. The modified version of TAP suggested by Thomson et al18, where minocycline was replaced with amoxicillin and used in combination with ciprofloxacin and metronidazole to prevent discoloration was employed in our study. An optimal coronal seal is essential to prevent the ingress of bacteria. Therefore a tight coronal seal was established with 3-4mm thickness of MTA placed coronally over the PRF scaffold19.
The primary objective of RE was achieved at 6 months follow up period, in all the cases with complete resolution of symptoms and periapical radiolucencies, where existed. Literature reveals few studies on quantitative analysis in RE20-22. Hence our study also focussed on the quantitative radiographic assessment of the secondary objectives such as root length, apical diameter and thickness of dentinal walls. A significant overall mean decrease of 88.40% in apical diameter and an increase of 16.92% in root length were observed. Since the coronal thirds of all the teeth were fully developed, we analysed the changes in the dimensions of the middle and apical thirds of the mesial and distal dentinal walls. There was a significant increase in the thickness of both the walls in the middle and apical thirds. When compared with the preoperative values, significant difference in all the parameters was observed from the 12th month onwards.
Chen et al23 reported five types of responses in the regeneration of immature teeth : type I – increased thickening of the canal walls and continued root maturation, type II- no significant continuation of root development with blunt and closed root apex, type III- continued root development with open apical foramen, type IV- severe calcification (obliteration) of the canal space and type V- formation of a hard tissue barrier between the coronal MTA plug and the root apex. In our study at 2 years, Type III was observed in all the teeth except one, suggesting complete root maturation (Fig. 1,2). In only one case, a type V response was noticed (Fig. 3). The probable reason could have been the MTA placement upto the middle third which induced the hard tissue barrier formation.
Based on the literature evidence put forth the following mechanisms for root maturogenesis can be considered:
- Few vital pulp cells remain at the apical canal end which has the ability to resist destruction even in the presence of inflammation and has the ability to proliferate and differentiate into odontoblasts .
- The periodontal ligament stem cells have the ability to proliferate and grow within the apical end of the canal lumen through the open apex in cases where there is destruction of HERS and SCAP.
- The PRF acts as a reservoir of growth factors which stimulates the differentiation, growth and maturation of fibroblasts, odontoblasts and cementoblasts from their undifferentiated precursors24.
Although controversies exists on the clinical vitality status of the teeth treated with RE, the pulp sensibility assessment – cold test carried out during the follow up period was found to be negative, probably due to the thick coronal seal of 3-4mm with MTA and composite resin diminishing the chances to know the exact vitality status.
According to Ritter et al25, in the study conducted on dog teeth, it was reported that the ingrowth of tissue is more likely to originate from periodontal ligament consisting of bone, cementum and dentin like material rather than pulp tissue. As there is limited literature evidence substantiating the type and nature of newly formed tissue, further studies have to be undertaken in this aspect.
Limitations: Grey MTA used in the study resulted in discolouration of all teeth.