The Effect of Using Different Scaffolds in Retreated Teeth on The Clinical and Radiological Success of Regenerative Endodontic Treatment

This study was designed as a prospective, controlled clinical trial to compare the clinical and radiographic outcomes of four regenerative endodontic approaches applied to permanent teeth requiring single-root retreatment. The sample size was calculated using G*Power v3.1 (Heinrich Heine University, Düsseldorf, Germany) based on an effect size of 0.50, a significance level of 0.05, and a power of 0.80; a total of 60 patients, with 15 patients per group, were planned to be included in the study. The null hypothesis (H0) of this study is that there will be no difference in the clinical and radiographic success of four different regenerative approaches (apically induced blood clot, injected i-PRF, A-PRF, and A-PRF+) applied to necrotic permanent teeth requiring single-root retreatment. The necessary institutional approval and ethics committee approval have been obtained for this study. Patient participation will be voluntary; patients will be informed about the study, and informed consent forms will be obtained from those who wish to participate. Following the application of local anesthesia and a rubber dam, the relevant teeth will be disinfected with 2.5% NaOCl, and the general shape of the cavity will be formed using a sterile diamond bur with a high-speed, water-cooled air turbine. If caries is present, sterile steel burs attached to a low-speed micromotor and an angle piece will be used to remove it. Once the access cavity is complete, the root canal filling material will be removed with retreatment files without chemical agents. The working length will be determined, and mechanical preparation will be kept to a minimum. The apical opening will be enlarged to a diameter equal to the tip diameter of a #40 file. For root canal irrigation, 20 mL of 1.5% sodium hypochlorite, 20 mL of normal saline, and 10 mL of 17% EDTA will be used. After calcium hydroxide is placed in the root canal, the tooth will be sealed with a temporary filling material. Second Session (3 weeks later): If there are no symptoms, the temporary filling material and calcium hydroxide will be removed. A final irrigation will be performed with 20 mL of 17% EDTA. The volunteer patients included in the study will be divided into four groups according to the random assignment determined on the www.randomizer.org website.

Group 1: (Blood Clot Group) Bleeding will be induced by exiting the apical foramen with sterile Type K files to ensure the canal is filled with blood.

Group 2: (i-PRF Group) 10 cc of venous blood drawn from the patient's antecubital vein will be centrifuged at 700 rpm for 3 minutes. The upper yellow layer will be drawn up with a syringe and injected into the root canal.

Group 3: (A-PRF group) The 10 cc of venous blood obtained as in Group 2 will be centrifuged at 1500 rpm for 14 minutes. The upper yellow layer will be removed from the tube and applied to the root canal using sterile pluggers.

Group 4: (A-PRF+ group) The 10 cc of venous blood obtained as in Group 2 will be centrifuged at 1300 rpm for 8 minutes. The yellow layer on top will be removed from the tube and applied to the canal using sterile applicators.

In all groups, after a bioceramic-based covering material is placed over the scaffold, a glass ionomer base material will be applied, and the teeth will be restored with a bonding agent and composite. Post-treatment, periapical X-rays will be taken of all patients, and a KIBT scan will be performed. Patients will be evaluated clinically and radiographically at 3-, 6-, and 12-month follow-up visits. The clinical evaluation will assess spontaneous pain, percussion sensitivity, palpation sensitivity, the presence of a fistula, and mobility. Vitality tests will be performed using a cold test and an electrical pulp test. At the 12-month follow-up, a KIBT scan will be performed to examine changes in lesion size, root wall thickness, or hard tissue formation.

Measurement of Dentin Thickness KIBT images will be acquired using an I-CAT (Imaging Sciences, Hatfield, PA, USA) tomography device in accordance with the standard imaging protocol. During imaging, the Frankfurt horizontal plane will be positioned parallel to the floor. In contrast, the midsagittal plane will be positioned perpendicular to the floor using the jaw support unit and laser alignment beams. Images will be acquired using standard parameters: an 8x8 cm field of view (FOV) of the relevant jaw, 120 kVp, 8 mA, a voxel size of 0.25 mm³, and a scan time of 14.7 seconds. Dentin thickness measurements for the relevant tooth will be performed on axial sections. Measurements will be determined in millimeters at three regions-4, 6, and 8 mm from the radiographic apex-based on the distance between the root canal wall and the external root surface.

Root Canal Volume Measurement Root canal volume measurements for the teeth will be performed using the ITK-SNAP software. KIBT images will be imported into the program in DICOM format. The region of interest will be delineated as a rectangular area using a semi-automatic segmentation method. During segmentation of all images, the minimum and maximum threshold values will be optimized based on the gray density distribution. Minimal manual adjustments will be made for each tooth as necessary. A region-growing algorithm will be applied, and a manual spread point will be placed at the root canal midpoint. The segmentation process will spread outward from the selected spread point and automatically terminate when it exceeds the predefined threshold boundaries. Segmentation areas extending beyond the anatomical boundaries will be manually corrected. The resulting volume values will be recorded in mm³ via the software's "Volume and Statistics" tab.

Measurement of Periapical Lesion Dimensions Periapical lesion dimensions will be assessed in millimeters along three axes. The bucco-lingual and mesio-distal widths of the lesion will be measured on the axial section where the lesion appears widest. The vertical dimension will be determined from the sagittal section at which the lesion appears widest.

Statistical Analysis All data will be analyzed using SPSS Statistics 17.0 for Windows (SPSS Inc., Chicago, IL), and a P-value of < 0.05 will be considered statistically significant. Lesion size and dentin thickness will be analyzed using a t-test. Volumetric changes in the root canal before and after regenerative endodontic treatment will be tested using the Wilcoxon signed-rank test.