## 2 Materials and Methods
### Clinical Procedure  
History, examination, and investigation were performed to ascertain the presence of certain preoperative factors. Preoperative digital radiographs using the parallel technique were taken with a cone indicator and reference marker placed on the radiographic sensor Written informed consent was obtained from the patients.  
**Conventional re-root canal treatment:** Local anesthesia 1:80,000 lidocaine with epinephrine was administered and a rubber dam was used for isolation. Access to the root was gained by removing the coronal restoration, followed by application of GP solvent (Carvene, PREVESTDenPro Prevest Denpro Limited, Jammu, India) and 25 or 30 # H file (Mani, Utsunomiya, Tochigi, Japan) for the removal of articular filling. Working length was established by 35 or 40 # K file (Mani, Tochigi, Japan). Canal cleaning and shaping was performed by modified crown-down technique along with copious irrigation by 3.0% sodium hypochlorite (CanalPro NaOCl, Coltene/Whaledent, Alstatten, St. Gallen, Altsatten, Switzerland). Calcium hydroxide (Metapaste, Meta Biomed, Cheongju-si, Chungcheongbuk-do, Korea) was used as an intracanal medicament in between appointments. Finally, obturation was performed by cold lateral condensation technique followed by composite coronal restoration.  
All patients were recalled after 3 to 6 months for clinical and radiographic evaluation of the periapical healing after conventional re-root canal treatment. Periapical healing was observed in seven patients and five patients failed to appear on follow-up visit, therefore 12 patients were excluded from the study. Finally, 40 patients underwent periapical surgery due to nonhealing periapical lesions (Figure 1).  
**Periapical Surgery:** To begin with, local anesthesia 1:80,000 lidocaine with epinephrine was administered and a full thickness mucoperiosteal flap was elevated. After identifying the lesion site, access to the lesion was achieved by performing window preparation in cortical bone with small round bur No. 2 (Mani, Tochigi, Japan) in a slow-speed handpiece (Figure 2). The periapical lesion was identified and surgically removed by a surgical curette (Hibro Int, Tokyo, Japan). Zirconia-coated ultrasonic tip (Pro ultra, Maillefer DENTSPLY, Ballaigues, Switzerland) was used for apicoectomy and retrograde cavity preparation (Figure 3). The 3 mm apical fragment of the root was resected perpendicular to the long axis of the root with minimum or no bevel. Finally, MTA (Pro-root MTA, DENTSPLY Tulsa Dental Specialties, Johnson city, TX, USA) was used for retrograde filling (Figure 4). The flap was then repositioned and sutured with a 3/0 silk suture (ETHICON, Johnson & Johnsons, New Brunswick, NJ, USA). A periapical radiograph was taken after surgery. Analgesics and antibiotics were prescribed. These patients were recalled after 12 months for a follow-up visit. Both clinical and radiographic examination was performed at each follow-up visit (Figure 5). The parameters studied for clinical examination were pain, swelling, sinus tract, tenderness to palpation, tenderness to percussion, mobility, and discoloration. Radiographic healing was assessed using Periapical Index (PAI). The radiographic interpretation was carried out by two blinded endodontists. The interexaminer reliability in evaluating the postoperative radiographs was calculated and presented.  
Figure 1: Flowchart of Methodology.  
Figure 4: The retrograde filling was performed by MTA.  
Figure 3: Retrograde cavity preparation was performed by zirconia-coated ultrasonic tip used for periapical surgery.  
Figure 2: A full-thickness mucoperiosteal flap was reflected and the window was created around the periapical area of teeth 11 and 21.