الفهرس 
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Abstract
The aim of this study was to assess the regenerative potential of mature teeth with chronic apical periodontitis histomorphometrically and immunologically. Alternative combinations of ciprofloxacin, DAP and TAP with and without collagen membrane and gelfoam scaffolds were used. Eighteen dogs aged 10 months were selected. Three lower premolars were chosen from each one of them. This corresponded to a total of 96 roots. Groups were allocated as into six experimental groups and two control groups, each group included 12 roots as follows:
1. Ciprofloxacin/Collagen
2. DAP/Collagen
3. TAP/Collagen
4. Ciprofloxacin/Gelfoam
5. DAP/ Gelfoam
6. TAP/Gelfoam
Controls included a positive group and a negative one where infected untreated and normal untouched teeth were respectively allocated.
Teeth were accessed and infection induced into root canals for one month, lesions were radiographically confirmed. Canal disinfection with antibiotics was carried out for one more month, then bleeding induction and scaffold placement with an MTA orifice plug and glass ionomer coronal seal were done for an extra month. Surgical extraction of teeth with the surrounding periapical bone was performed. Samples were decalcified and processed for histological and immunofluorescent analysis. Histological evaluation was qualitative based on the following criteria : corono-apical extent of neo-formed tissues, vascularity and inflammatory extents and nature of hard tissues (if any).
Immunofluorescent evaluation was based on quantification of the following markers:
1. Vimentin (intracellular cytoskeletal component in mesenchymal cells).
2. TGFb1 pleiotropic cytokine with context dependant functionality (pro and anti-inflammatory effects).
3. MMP13, main collagenase in pulp tissue with wide proteolytic spectrum over many substrates.
4. IL-17, a main pro-inflammatory cytokine released in chronic inflammatory conditions and linked to tissue destruction.
Images were captured using Axioplan microscope under 20 X magnification then images were stored as 12 bit for subsequent signal quantification using ZEN software. Intensity threshold was selected and pixels with higher signals represented regions of interest. Average intensity for each image was calculated by dividing the total intensity value by the total area of positive regions. The seven values were averaged to generate an overall intensity ratio per sample. An extra step was applied for MMP13 and TGFb1 for which slides were co-stained. MMP-13, TGFb1 and IL-17 were assessed to provide an index whether constructive or destructive remodeling were prevalent in the canals. Two-way ANOVA was used for statistical analysis of quantitative immunofluorescence data and Kruskal-Wallis test for qualitative H & E scores.
Histomorphometry results showed a significant correlation between revascularization protocol and each one of the tested parameters, corono-apical extent of neoformed tissues, vascularity, inflammatory extents and hard tissue nature (if any), (p<0.0001). Immunofluorescent intensities showed a significant interaction effect between antibiotic regimens and scaffold types.
DAP-based revascularization and ciprofloxacin-collagen protocols showed the best outcomes, vimentin intensities were comparable to negative control of normal pulps. IL-17 and MMP-13 were reduced. TGFb1 levels were high. Histologically they scored new tissues growing up to cervical and middle thirds, tissue nature was pdl-like in DAP-based protocols and Ciprofloxacin/Collagen. No to Minimal inflammation were scored in the three protocols. A layer of stellate shaped MSCs-like layer was observed along the dentinal border in DAP/Collagen group.
Conclusions
Under the conditions of the present study:
1. The attempted protocols variably yielded connective tissue with bone and cementum-like structures.
2. They reduced inflammation in necrotic mature teeth with chronic apical periodontitis.
3. DAP and CIP-based revascularization with collagen membrane and DAP/ gelfoam provided the best outcomes of constructive remodeling and reduction of inflammatory extents.
Future Recommendations
Implementation of scaffolding materials that actively stimulate an immune response besides the mechanical support to dental pulp based on the fact that the process takes place in the context of pulpal damage by microbial incursion and the resulting inflammatory response. Therefore, it will be crucial to combine these materials with treatment modalities that address the underlying pathologies associated with irreversible damage to dental pulp tissues (e. g. the rapid attenuation of pulpal inflammation and the clearance of microbes). This can be in the form of:
1. Slow release antibiotic-loaded scaffolds or drug delivery carriers that can be used to allow for a sustained leaching out of antibacterial, cell-friendly antibiotic doses to the necessary site, at a suitable concentration, within the therapeutic range, and in the suitable time period.
2. Bioactive scaffolds incorporated with growth-factor carrying inserts.