This case report has been written according to Preferred Reporting Items for Case Reports in Endodontics (PRICE) 2020 guidelines. The PRICE 2020 flowchart was shown in Figure 1. Informed consent has been obtained from the patient for publication as a case report of the process of treatment for this ECR lesion. An overview of the treatment timeline is presented in Table 1. A 43-year-old non-smoking female was referred to our university hospital clinic by a private dental clinic for the management of an extensive ECR lesion. The patient complained of discomfort in the maxillary right lateral incisor and reported a history of a fall that happened 10 years ago. However, the patient had not paid particular attention at the time, as the patient was asymptomatic immediately after the trauma, and there was a lack of superficial damage. During the assessment of the initial trauma (10 years ago) at a private clinic, the affected tooth had undergone caries removal in the proximal and distal aspects of the tooth. Several years later, the patient was diagnosed with ECR at a private dental clinic. The discomfort at the affected tooth gradually increased, and the radiographic translucency of the ECR lesion became larger.
At the time of presentation, the patient was not on any medications and had no relevant general medical or family history. Furthermore, common causes of ECR, such as history of orthodontic treatment, parafunctional habit, or abnormal occlusal pattern, were not detected. Overall, oral hygiene was good, and plaque levels were well controlled. Bruxism or occlusal interference was not apparent. There was no pathological tooth mobility of either the affected or its adjacent teeth. No tenderness was noted on palpation, and slight pain was reported on vertical percussion. Pulp sensibility tests demonstrated a negative response to thermal stimulation (cold test; Pulper, GC, Tokyo, Japan) or the electrical pulp test (Digitest II, MORITA, Kyoto, Japan) in comparison with the responses to the adjacent teeth. The periodontal probing depth was less than 3 mm on the buccal side, but 4 mm deep, with bleeding and slight pus exudate from the distal aspect of the palatal surface. Root caries as a differential diagnosis were ruled out because no infected dentine was detected.
An intraoral radiograph (Figure 2(a)) revealed a large ECR lesion extending from the distal to the proximal side; however, no obvious radiolucency was evident at the root apex. No radiographic signs of swelling or sinus tract were observed at the right maxillary incisor. CBCT was performed to further explore the extent of the ECR (Figure 2). Horizontal and sagittal CBCT images showed that the ECR lesion had reached the pulp tissue in up to one-third to one-half of the root in the axial direction, and horizontally, the hard tissue defect extended by approximately 180  mainly on the palatal side. It was accordingly diagnosed as a Class III according to Heithersay's classification and Class 2Bp lesion according to Patel's classification (Figure 2(b)). After diagnosis and classification, a treatment plan (including options) was discussed with the patient. The patient was specifically informed that due to the extent of ECR, it would be difficult to perform root canal treatment (RCT) without accompanying periodontal surgery, which would also include debridement and restoration of the destructed hard tissue.
Owing to the patient's desire to retain the tooth after explanation, consent was obtained for intentional replantation after RCT. Extraction of the tooth followed by placement of a conventional bridge, adhesive bridge, or dental implant (immediate or delayed) was discussed as a potential alternative to intentional replantation. 'Ideal' rubber dam isolation clamping the tooth in question was not possible due to a lack of coronal tooth substance so a split dam technique was all that could be used if RCT and intentional replantation were selected. After presenting the advantages and disadvantages of each treatment method to the patient, the placement of an adhesive bridge after tooth extraction was considered only if intentional replantation was unsuccessful.
Based on the clinical examination, ECR treatment was carried out under magnification using a DOM (M320-D, Leica Microsystems, Wetzlar, Germany). Due to the nature and extent of the ECR lesion, as discussed previously the split dam isolation technique was performed under local anaesthesia, and the palatal gingival tissue adjacent to the ECR was removed using an electronic scalpel under dry conditions to facilitate coagulation. Thereafter, RCT was initiated using a diamond bur with a water-cooled high-speed handpiece. The root canal was narrowed due to ECR and required careful negotiation to access the root canal system. Apical patency was maintained with an H-file #10 (Dentsply Sirona, Ballaigues, Switzerland), and root canal length was measured electrically using an apex locator (Root ZX3, MORITA). Subsequently, a glide path was established, and the root canal was enlarged using a nickel-titanium (NiTi) file system (HyFlex EDM, Coltene, France) with an Endomotor (TriAuto ZX2, MORITA), which was capable of simultaneously measuring the electrical root canal length. The working length was further confirmed on a periapical radiograph image by placing a gutta-percha cone (Figure 3(a)). The root canal was profusely irrigated with 2.5% sodium hypochlorite (Neo Cleaner, NC, Neo Dental Chemical Products Co., Ltd., Tokyo, Japan) and 3% ethylenediaminetetraacetic acid solution (Smear Clean, Nishika, Yamaguchi, Japan) delivered using a 27-G root canal irrigation syringe (Neo Dental Chemical Products Co., Ltd.) with simultaneous agitation using a NiTi instrument (X-p Endo finisher, FKG Dentaire, La Chaux-de-Fonds, Switzerland). The root canal was then dried with sterile paper points. A calcium hydroxide dressing (Calcipex II, Nishika) was placed. The first-visit treatment was completed by carefully placing a temporary restoration of glass ionomer cement (GlassIonomer FX ULTARA, Shofu, Kyoto, Japan) up to the root canal orifice to avoid coronal leakage from the palatal side.
At the second RCT visit, the tenderness on percussion had significantly subsided. The glass ionomer cement and calcium hydroxide dressing was removed after isolation using a split dam rubber dam technique, and the root canal was re-irrigated and dried. Then, the root canal was filled with a methacrylate resin sealer (MetaSEAL soft paste, Sun Medical Co. Ltd., Shiga, Japan) and a single-matched taper gutta-percha cone (Figure 3(b)). As the tooth was asymptomatic after RCT, an orthodontic hook device was placed for extrusion before intentional replantation (Figures 4(a), 4(b), and 4(c)). A video illustrating these processes is provided as video information (refer to https://doi.org/10.6084/m9.figshare.20787508.v1). After administering local anaesthesia, the temporary sealing material was removed, and the gingival tissue on the palatal side of the ECR was kept dry by removal and coagulation using an electrical scalpel. A 0.7-mm in diameter cobalt-chromium (Co-Cr) hook device was affixed in the root canal using carboxylate cement (HY-BOND Carbo Cement, Shofu), and then a custom-made wire was bridged to the adjacent teeth and fixed with 4-methacryloxyethyl trimellitate anhydride/methyl methacrylate tributylborane (4META-MMA/TBB) resin (Superbond, Sun Medical Co. Ltd., Shiga, Japan). One orthodontic thread was used to tie the wires to provide a sustained extrusion force. Follow-up procedures involved changing the orthodontic threads once per week for three weeks.
The orthodontic device used to extrude the tooth was removed under local anaesthesia before intentional replantation. Intentional replantation was performed by one operator and two assistants in an operating room under magnification (Figures 4(d), 4(e), 4(f), 4(g), 4(h), and 4(i), refer to videos https://doi.org/10.6084/m9.figshare.20787613.v1). The mobility of the tooth increased after device removal, and gentle extraction was performed using forceps (Claw, YDM, Tokyo, Japan). Next, the crown was rotated 180  to confirm that it fits into the extraction socket. This permitted the ECR lesion observed under magnification, and a dye detection solution (usually used for caries detection, Caries detector, Kuraray Noritake Dental Inc., Tokyo, Japan) was utilised to identify the extent of the ECR. The lesion was then meticulously curetted to ensure that no resorptive tissue remained. A resin-based composite restoration was placed and cured using blue light irradiation (Pen cure 2000, MORITA) before the tooth morphology was adjusted. Finally, the tooth was replanted in the extraction socket. A sterile saline solution was used to minimise dryness and contamination of the dentine debris, except during ECR removal and morphological modification of composite restorations using a high-speed handpiece. The crown was sutured to the gingiva to promote initial wound healing and stability and fixed to the adjacent tooth with composite resin for reinforcement. The extraoral work time for the intentional replantation procedure was approximately six minutes. These treatments were performed by an endodontist with >10 years of experience.
Follow-up appointments were scheduled at various time points (Figures 5(a), 5(b), 5(c), 5(d), and 5(e)). After one week, the sutures and resin cement were removed. Three months after intentional replantation, a provisional restoration was fabricated. RCT was performed with the split dam isolation due to the risk of periodontal exudate contaminating the canal. The tooth was observed for a prolonged period after obturation, with no subsequent symptoms or abnormal findings evident clinically or radiographically. After determining that additional root canal retreatment was not necessary based on a 6-month follow-up, a composite resin crown (Kuraray Noritake Dental Inc.) was constructed using computer-aided design/computer-aided manufacturing as the final step in the restoration process. There were no clinical symptoms during this period, and radiographs showed no detrimental effect of intentional replantation. Furthermore, no clinical symptoms or abnormal findings were observed 18 months after intentional replantation. These results demonstrate the success of ECR treatment with RCT and intentional replantation (Figure 6).