الفهرس 
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Abstract
The aim of the present investigation was to histopathological assessment of the regenerative potential of permeant mature teeth with necrotic pulp and apical periodontitis with different apical diameters in comparing to conventional endodontic treatment.
72 premolars in six health dogs (12 premolars in each dog) to sum 72 teeth and 144 root canals were collected for this study. Teeth were distributed into sex groups: root canal obturation (RCT) with continuous wave compaction for root canals prepared up to #F3 ProTaper file, Regenerative endodontic therapy for root canals prepared up to #F3 ProTaper file (RET-F3), RET for root canals prepared up to a #F4 ProTaper file (RET-F4), RET for root canals prepared up to a #F4 ProTaper file (RET-F5), positive (P) and negative (N) controls included infected and healthy teeth respectively. Each group was further subdivided into two subgroups according to evaluation periods (one and three months).
Induction of infection was done followed by canal disinfection using the Ca(OH)2 paste. Treatment protocols were performed according to the previous classification and samples were left for follow up according to the period for each sup-group.
Histological evaluation included inflammatory reaction, bone/resorption, tissue in-growth, hard tissue formation, quantitatively results were evaluated using appropriate scoring system. Data were collected, tabulated and statistically analyzed.
Histological evaluation of inflammatory cell count showed that the RCT group had the highest count comparing to RET groups and increasing the apical size diameter among RET groups resulted in decrease in inflammatory cell count in both evaluation period. At three-month evaluation period there was no statistical significance difference between RET-F4 and RET-F5 groups.
Regarding percentage of bone resorption, RCT group showed less percentage of sample that had bone/root resorption than the rest of experimental groups. At three-month evaluation period there were no statistical significance difference among all experimental groups.
Concerning tissue in-growth inside root canal space; increasing the apical diameter was associated with more tissue in-growth inside root canal space with no statistical significance difference between RET-F4 and RET-F5 groups at the two evaluation periods. The nature of this tissue resembles periodontal connective tissue with variable amounts of inflammatory cell infiltration and low to moderate number of blood vessels at central portion that were engorged by red blood cells (RBCs).
When hard tissue formation was investigated, results showed variety of hard tissue formation inside root canal space, there were no statistical significance difference among all experimental groups regarding scores of new hard tissue formation.
There was no statistical significance difference between 1st and 2nd evaluation period for all tested parameters except inflammatory cell counts that showed significate reduction after the 2nd evaluation period.
Conclusions:
Under the circumstances of this study, it can be concluded that:
1- Regenerative endodontic therapy was successfully decreasing the inflammatory cell count for mature teeth with necrotic pulp and apical periodontitis.
2- Revascularization procedure induced tissue resembling pulp-like tissue and not true pulp tissue inside the root canal space.
3- Increasing the apical size diameter during RET resulted in decrease in inflammatory cell count.
4- The minimum apical diameter for tissue ingrowth to coronal one third of the root canal space during RET was 0.40mm.
Recommendations:
1- Longer follow up period is needed for monitoring of the repair process.
2- Further studies are recommended for using different irrigates to disinfect the canal space and release growth factors found in dentin.
3- Further studies are recommended for using tissue engineering protocol (cell-based approach).