▪ Sample preparation:
1. The external root surfaces of the teeth will be cleaned with a curette to remove calculus and periodontal tissues, and then will be placed in 5.25% NaOCl for 30 minutes to remove soft tissue debris. The teeth will be stored in sterile saline till use.
2. Pre-operative radiographs will be taken from bucco-lingual and mesio-distal aspects to assess the presence of a single patent canal and the absence of internal resorption and confirm fulfilling eligibility criteria without any complexities or defects.
3. The teeth will be decoronated using a low-speed diamond saw under copious irrigation to obtain 16 mm uniform root lengths.
4. K-file size #10 will be inserted in the canal to check patency then working length will be adjusted using K-file #15 until showing from the apex and subtracting 1mm, so a standardized working length of 15 mm will be obtained.
5. The apices will be sealed by flowable composite Filtek Supreme[1] and impeded in epoxy resin blocks to prevent extrusion of the irrigation solution and simulate in-vivo conditions.
6. The root canals will be instrumented with FKG Race EVO rotary files up to RE4 (0.40 tip size and 4% taper)[2] then increase flaring with ( 0.35 tip size and 6% taper) according to the manufacturer’s specifications.
7. In all groups, the canals will be irrigated with 3 ml of freshly prepared 5.25 % sodium hypochlorite solution as an irrigation solution after each file using a 30-gauge max-i-Probe needle tips[3] placed 1mm shorter from the working length.
8. Apical patency will be retained by using#10 K-file between each rotary file.
9-Final irrigation 5ml of distilled water then drying with paper points
10-Obturation is done using Single cone technique #40 6% master cone to less than the full working length by 1 mm after injecting bioceramic sealer into the canal…the excess core is sheared off with a hot instrument.
11-All specimens are stored at 37 in 100% humidity for 2 weeks to enable a complete set of the sealer
12-After 2 weeks the root filling are removed with FKG Race EVO 40/0.4 (FKG Dentaire SA, Switzerland) at constant speed of 600 rpm , torque = 1-1.5 as suggested by the manufacturer
-After full removal of gutta percha, If full WL isn't reached, small hand files (C-files, C+files) are used.
13-The specimens will be randomly divided into 2 groups according to the type of solution used as follows:
-Group A: Formic acid 10% used for removing bioceramic sealer.
-Group B: HCL 20% used for removing bioceramic sealer.
14-Solutions are applied using plastic syringes in volume of 5 ml and left for 5 minutes.
15-Then investigate whether bioceramic sealer is removed or not and amount of removal.
16- A cotton pellet will be placed at the canal opening before cutting of the grooves
to prevent entrance of any debris formed during sectioning.
17- Two longitudinal grooves will be prepared on the buccal and lingual surfaces with
a diamond disk, to facilitate splitting of the roots.
18- The roots will be split longitudinally for SEM observation. The coronal, middle, and apical thirds of the root canal will be examined individually in each specimen