External cervical resorption (ECR) is also called “invasive” cervical resorption because of its progressive nature. ECR has been increasingly reported in recent years because in most cases, it progresses asymptomatically; in the worst case, it warrants immediate intervention. The exact cause remains to be elucidated, but orthodontic treatment, trauma, bleaching of non-vital teeth, periodontal treatment [1], bisphosphonate therapy [2], and varicella-zoster virus infections [3] are cited as etiological factors. Pathologically, cementum damage or loss in the cervical region is often cited as an association [4,5]. Although non-bacterial inflammation has ample supporting evidence for its implications in the inflammatory process [6], bacterial invasion can modify secondary progression [7]. Two-dimensional stage classification by Heithersay [1] has been cited for a long time in the literature, but the activity of CBCT in recent years is well known, ECR was also classified three-dimensionally by Patel [8]-height (four stages), circumferential direction (four stages), and proximity to the root canal (two stages). Treatment strategies for external cervical resorption depend on whether it is invasive or not and necessitates restorative procedures with periodontal surgery and nonsurgical endodontic treatment. Tooth extraction may be required in excessively advanced cases [9]. Therefore, early diagnosis and appropriate treatment are essential. However, in advanced cases, pulpitis may develop 1 or crown discoloration may be evident, with few subjective symptoms [10]. Moreover, ECR is often found in advanced medical conditions [5,11]. In this paper, we report ECR affecting submerged central incisors with low eruption rates. Since it is in a low position, it can be said that it is in an advanced state from the viewpoint that the defect extends below the bone margin; however, preservation may be possible if it is guided to the occlusal plane.

However, when considering infection control, mechanical strength, and aesthetics, simply practicing these methods may not sufficient. No similar studies have been conducted. Here, we report the case of a 10-year-old girl who underwent orthodontic treatment, nonsurgical endodontic treatment, and direct composite resin adhesive restoration, with successful outcomes.

A 10-year-old girl visited the Nihon University Matsudo Hospital with a chief concern of poor esthetics of the maxillary right anterior teeth. We planned to perform traction of the impacted maxillary right lateral incisor (#12) and prepared the patient for orthodontic treatment (Fig. 1). When she visited the Orthodontics Department to understand the treatment plan, discoloration of her central incisors (#11) was noted; therefore, cone-beam CT (KaVo 3D eXam +, KaVo Dental Systems Co., Ltd.) was performed for differential diagnosis with caries and internal resorption (Fig. 2) followed by a detailed endodontic examination. According to Patel’s classification, the #11 had class 3Dp ECR (Height; 3: extending to the middle-third of root / Circumferential; D, > 270° / Proximity to the root canal; p, probable pulpal involvement.) with a low eruption rate. Although the cause of the submerged state of the tooth was unknown, physiological tooth mobility was observed, and there was no concomitant bone replacement or external resorption; therefore, orthodontic treatment was considered possible.

Fig. 1: Preoperative Intraoral Photography and Two-Dimensional Radiographs of The External Cervical Resorption (#11).

(A) Pink Discoloration Observed Inside #11, Which Has Finished Sprouting at A Low Level. The Formation of Tooth Root #11 Is Completed.

(B) On Two-Dimensional Radiographs, The External Cervical Resorption Cannot Be Clearly Observed Because #12 Is Projected Overlapping.

Fig. 2: Cone-Beam CT Images Obtained at The Time of The First Visit.

(A)–(O) Axial CBCT Image From the Crown to The Middle Third.

(P) – (U) Sagittal CBCT Section Distal to The Mesial.

(C) And (D) Pericanal Resorption-Resistant Sheet Could Not Be Confirmed Between the Resorbing Part and Pulp.

(E) A Defect That Appears To Be The Onset Of Absorption (Portal Of Entry) Is Observed On The Palatal Side (Yellow Arrow).

(G) The External Cervical Resorption Surrounds the Pulp by Approximately 300°.

(S) Pericanal Resorption-Resistant Sheet Is Observed Around the Pulp Along with The Portal of Entry (Yellow Arrow).

Treatment Plan and Progression

Consent was obtained from the patient and her guardian to write a paper describing the disease state, specific treatment details, troubleshooting, and treatment progress. Pulpectomy and root canal filling are necessary to seal off the communication with the periodontal tissues for appropriate management of ECR [9], which can be achieved by using a moisture-proof rubber dam. Moreover, the progression of external resorption was assumed to be an indication for tooth extraction. Therefore, along with provisional root canal treatment, the ECR treatment was prioritized. Subsequently, orthodontic force was applied to improve the tooth malposition as much as possible, and then root canal filling and crown restoration were performed. The patient was asymptomatic. Local anesthesia was administered using 0.9 mL lidocaine with 1/80000 adrenaline bitartrate (ORA injection; Showa Yakuhin Kako, Tokyo, Japan).

Procedures Followed in the Conservative Dentistry Department from 1st Visit to 3rd Visit

An air turbine was used to excavate the labial surface of the maxillary right central incisor to the site of resorption and the pulp chamber. Using a microscope (OPMI pico; Carl Zeiss, Jena, Germany), the granulation tissue filling the root resorption area was mechanically and chemically debrided using an ultrasonic tip (diamond-coated or non-coated; J Morita MFG Corp., Kyoto, Japan)?(Fig. 3A, B). Chemical irrigation was performed using 2.5% sodium hypochlorite. Because the debridement of the affected areas could not be completed in one sitting, intracanal medicament calcium hydroxide (Calcipex; Nippon Shika-Yakuhin, Shimonoseki, Japan) was used as an interappontment dressing. Temporary sealing of the access hole for each treatment was performed using composite resin (Clearfil Majesty Es-2 Premium, Kuraray Noritake, Okayama, Japan), considering the esthetic requirements. After performing minimum necessary expansion pulpectomy without rubber dam isolation, and the root canal was temporary filled with Ca(OH)₂ paste (Vitapex; Neo Dental Chemical Products Co., Tokyo, Japan) throughout the orthodontic period. The entire resorption site, including the site perforating the periodontal tissue (portal of entry; Fig. 2 arrow; Fig. 3C Black arrow, perforation; Fig. 3D) was filled with glass ionomer cement to isolate the root canals, and the orthodontic treatment was initiated.

Fourth and Fifth Treatment Visits

After the orthodontic treatment had progressed to the point where it was possible to install the clamps used for rubberdam application, Vitapex was thoroughly removed and the working length of the root canal was measured (DENTA PORT; J Morita MFG Corp., Kyoto, Japan); the canal was instrumented with ProTaper Gold (Dentsply Sirona, York, PA) to size F4 (#40). The smear layer was removed with a 15% EDTA solution, and the canal was irrigated with physiological saline and obturated by lateral condensation of gutta-percha and zinc oxide-eugenol sealer (Canals, Showa Yakuhin Kako, Tokyo, Japan) (Fig. 3E, F). After most of the orthodontic treatment was completed, the cement was removed from the resorption site; the site and access cavity were restored with a composite resin (Clearfil Majesty Es-2 Premium, Kuraray Noritake, Okayama, Japan) using a fiber post (GC Fiber Post, GC, Tokyo, Japan) (Fig. 4A–C). Most of the resorption sites were on the bony margin, and restoration was performed following gingival reshaping using electrocautery.

Fig. 3: Intraoral Photograph During External Cervical Resorption Treatment and Radiograph at The Time of Root Canal Filling.

(A) And (B) Removal of Granulation Tissue After Ultrasonic Cleaning with Sodium Hypochlorite.

(C) Portal Of Entry (Black Arrow) And Pericanal Resorption-Resistant Sheet (Yellow Arrow) After Removal of Granulation Tissue.

(D) Although There Is a Perforation (Black Arrow) In the Distal Region, It Is Not Thought to Be a Portal of Entry Because It Is Not Located at The Bone Edge.

(E) After Orthodontic Treatment, A Rubber Dam Is Used Immediately Before the Root Canal Filling.

Sixth Treatment Visit

Six months after the root canal filling, progress was observed at the end of the orthodontic treatment. No pathological findings were observed in #11, but the gingiva had receded compared to that on the central incisor (#21) on the opposite side. In addition to a slight morphological correction of #11, a direct veneer restoration of #12, which was a dwarf tooth, was performed using the same composite resin as in #11. (Fig. 4D).

Fig. 4: Intraoral Photographs of The Composite Resin Restoration of The External Cervical Resorption and Crown Using Fiber Posts Intraoperatively, Immediately Postoperatively, And 6 Months Later.

(A) And (B) After Removing the Glass Ionomer Cement, A Metal Matrix Is Installed to Cover the External Cervical Resorption Site.

(C) #11 Immediately After Filling.

(D) Six Months After Root Canal Filling, Immediately After #12 Composite Resin Filling And #11 Morphology Correction.

ECR begins with the loss of cementum below the attachment of the gingival epithelia. In the early stages, the periodontal ligament, cementum, and dentin are affected in that order. As it progresses further, it spreads toward the crown and apex of the tooth and simultaneously involves the pulp. The maxillary central incisor is the most common type of tooth affected by ECR [12], which is caused by trauma, bleaching, and the resulting hypoxic conditions [10]. Additionally, while bacterial contamination and hypoxia promote inflammation [13], mechanical stimulation exacerbates external resorption [14]. There have also been reports of cases of ECR occurring due to genetic mutations in the DCDC1, which are involved in the multinucleation process of cell fusion and osteoclast differentiation gene or the antimicrobial peptide DEFB 114 [15] and cases of FLNA mutations [16]. Both cases occur over multiple teeth. The progression is divided into three stages: resorption initiation, resorption, and repair phase [9]. The site of resorption initiation is called the portal of entry (POE) and osteoclast-like multinucleated cells are observed at this site [5]. As resorption progresses, it progresses toward the pulp cavity; however, in most cases, the surrounding layer of the pulp is protected by a layer of hard tissue called a pericanal resorption-resistant sheet (PRRS), which does not usually harm the pulp [5]. However, according to Patel’s classification, there are also cases in which the pulp cavity is perforated [8]. In a recent study, 74% of ECRs examined with CBCT were assessed as being in close proximity to or reaching the pulp cavity [17]. In the repair phase, just as resorption begins from the POE, remodeled bone-like tissue enters the resorption site and fuses with the bone [5,9]. This was the most common maxillary central incisor, and CBCT findings at the time of treatment showed that the resorption had reached the pulp at the crown of the tooth (Fig. 2A–D). Although there was no history of trauma, the eruptive force of the ectopically erupted lateral incisor may have caused the central incisor to complete its roots at a low level, resulting in external resorption. Horizontally impacted wisdom teeth can cause resorption and eruption failure of adjacent teeth. Furthermore, because no bone infiltration was observed in the resorption area, it was inferred that resorption occurred during the resorption phase. During the repair phase, the tooth fuses with the alveolar bone; thus, in some cases, ECR that had developed in an impacted mandibular second premolar was corrected after surgical dislocation [18]. Since physiological agitation was observed in the mobility test, we learned that the patient was not in the repair phase and that repair was possible. For treatment at the 3Dp stage, repairing the root canal from inside during root canal treatment is recommended [9,19]. In this case, we determined that nonsurgical restorative treatment was possible after orthodontic treatment. The issues in implementing this procedure were the pros and cons of root canal treatment in situations in which rubber dams are difficult to place, the need to balance the timing of intervention to suppress the progression of resorption early, and concerns about periodontal infection during the orthodontic period. This is because the resorption site may have communication with the gingival sulcus and get further exposed to oral bacteria after orthodontic treatment than at the initial consultation. In contrast, we believe that performing temporary glass-ionomer cement filling, traction correction, use of conventional lateral condensation technique, and composite resin filling, in this order, will best prevent infection and at the same time allow appropriate repair. In fact, glass ionomer cement showed the best results as a restorative material for ECR cases localized to the dentin [20]. MTA fillings cause tooth discoloration and affect adhesion of restorative materials to the tooth. Mechanical cleaning or chemical debridement and removal using trichloroacetic acid are recommended for the resorptive tissues [18], but in this case, mechanical cleaning was mainly used, and 2.5% sodium hypochlorite was used as a supplement. This is because almost all sites of resorption can be visually confirmed using a microscope. PRRS was visible under a microscope near the cervical region of the tooth (Fig. 3C, yellow arrow), and the degree of mineralization was higher than that of normal dentin. It has also been reported that when PRRS is destroyed, excessive calcification causes changes in the oxygen partial pressure within the pulp, affecting the progress of resorption [5]. Lateral condensation technique was used to fill the root canal because apical bone healing is delayed immediately after traction, and the vertical pressure may harm the healing tissues [21]. The incisal edges of the left and right teeth were aligned; however, the heights of the cervical lines were different, probably because the heights of the bones were different. Periodontal orthopedic treatment may be considered once the patient’s growth and development are completed. Rubber dam isolation is essential when performing root canal treatment, and American Association of Endodontists (AAE)'s Guide to Clinical Endodontics is also described as following; '' Tooth isolation using the dental dam is the standard of care; it is integral and essential for any nonsurgical endodontic treatment.” However, in this case, it was necessary to treat the ECR area and the root canal treatment at the same time, so the treatment was performed first in consideration of the characteristics of ECR, resulting in the satisfaction of the patient. Therefore, it was assumed that a good prognosis could be obtained by treating the resorption site and timing the traction in cooperation with the orthodontist.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Declaration of Interests

The authors deny any conflicts of interest related to this study.

Declaration of Generative AI in Scientific Writing

None

1. Heithersay GS. Invasive cervical resorption: an analysis of potential predisposing factors. Quintessence Int. 1999; 30: 83-95.
2. Patel S, Saberi N. External cervical resorption associated with the use of bisphosphonates: a case series. J Endod. 2015; 41: 742-748.
3. Patel K, Schirru E, Niazi S, Mitchell P, Mannocci F. Multiple apical radiolucencies and external cervical resorption associated with varicella zoster virus: a case report. J Endod. 2016; 42: 978-983.
4. Heithersay GS. Clinical, radiologic, and histopathologic features of invasive cervical resorption. Quintessence Int. 1999; 30: 27-37.
5. Mavridou AM, Hauben E, Wevers M, Schepers E, Bergmans L, Lambrechts P. Understanding external cervical resorption in vital teeth. J Endod. 2016; 42: 1737-1751.
6. Goon WW, Cohen S, Borer RF. External cervical root resorption following bleaching. J Endod. 1986; 12: 414-418.
7. Fuss Z, Tsesis I, Lin S. Root resorption--diagnosis, classification and treatment choices based on stimulation factors. Dent Traumatol. 2003; 19: 175-182.
8. Patel S, Foschi F, Mannocci F, Patel K. External cervical resorption: a three-dimensional classification. Int Endod J. 2018; 51: 206-214.
9. European Society of Endodontology (ESE) developed by; Patel S, Lambrechts P, Shemesh H, Mavridou A. European Society of Endodontology position statement: external cervical resorption. Int Endod J. 2018; 51: 1323-326.
10. Patel S, Mavridou AM, Lambrechts P, Saberi N. External cervical resorption-part 1: histopathology, distribution and presentation. Int Endod J. 2018; 51: 1205-1223.
11. Libonati A, Montella D, Montemurro E, Campanella V. External Cervical Resorption: a case report. Eur J Paediatr Dent. 2017; 18: 296-298.
12. Mavridou AM, Bergmans L, Barendregt D, Lambrechts P. Descriptive analysis of factors associated with external cervical resorption. J Endod. 2017; 43: 1602-610.
13. Gold SI, Hasselgren G. Peripheral inflammatory root resorption. A review of the literature with case reports. J Clin Periodontol. 1992; 19: 523-534.
14. Clement AW, Willemsen WL. Cervical external root resorption. Ned Tijdschr Tandheelkd. 2000; 107: 46-49.
15. Muromachi K, Hosomichi K, Park H, Yamaguchi T, Tani-Ishii N. Identification of Candidate Genes of Familial Multiple Idiopathic Cervical Root Resorption. J Endod. 2023; 49: 1537-1547.
16. Qin W, Gao J, Ma S, Wang Y, Li DM, Jiang WK, et al. Multiple Cervical Root Resorption Involving 22 Teeth: A Case with Potential Genetic Predisposition. J Endod. 2022; 48: 1526-1532.
17. Patel S, Abella F, Patel K, Lambrechts P, Al-Nuaimi N. Clinical and radiographic features of external cervical resorption – An observational study. Int Endod J 2023; 56: 1475-1487.
18. Zasciurinskiene E, Rastokaite L, Hosseinzadehfard P, Lodiene G. Idiopathic External Cervical Resorption of the Impacted Second Premolar: A Case Report. Appl. Sci. 2023; 13: 11383.
19. Patel S, Foschi F, Condon R, Pimentel T, Bhuva B. External cervical resorption: part 2 - management. Int Endod J. 2018; 51: 1224-1238.
20. Askerbeyli Ors S, Kucukkaya Eren S. Effects of different treatment modalities on biomechanical behavior of maxillary incisors with external invasive cervical resorption at different progression levels. Dent Traumatol. 2023; 39: 605-615.
21. van Zyl SP, Gulabivala K, Ng YL. Effect of customization of master gutta-percha cone on apical control of root filling using different techniques: an ex vivo study. Int Endod J. 2005; 38: 658-666.