Root-like apical hard-tissue structure associated with apical periodontitis in an immature permanent tooth: a case report and literature review

Abstract

Background

Normal root formation depends on the developing apical complex (DAC), which coordinates root and periodontal tissue development. Root-like apical hard-tissue development is a rare odontogenic finding that has been reported in association with developmental disturbances, trauma, and inflammatory conditions.

Case presentation

This case report describes a 15-year-old male presented with pain in the lower right premolar (tooth 45). Cone-beam computed tomography and histopathological revealed chronic periapical periodontitis associated with a root-like apical hard-tissue structure containing a central radiolucent canal-like space. The lesion was managed with root canal therapy and endodontic microsurgery, resulting in a favorable outcome without complications during the 12-month follow-up period.

Conclusions

This case illustrates a rare root-like apical hard-tissue structure associated with chronic apical inflammation. Although the radiographic and histopathological findings were compatible with previously reported cases of segmental root development, the exact developmental origin of the lesion could not be determined. The findings contribute to the clinical characterization of a rare root-like apical hard-tissue anomalies and emphasize the importance of careful radiographic and histopathological evaluation. Combined root canal therapy and endodontic microsurgery resulted in a favourable clinical outcome in this case.

Background

A segmental root development is a radiographically identifiable apical-like structure that exists independently from the main root and may contain pulp-like tissue, with a bony or fibrous space between the two structures. This condition is often associated with trauma or abnormalities in tooth development. Normal root development relies on the developing apical complex (DAC), a functional unit composed of Hertwig’s epithelial root sheath (HERS), the dental papilla, and the dental follicle. The coordinated interactions among these tissues ensure synchronous formation and maturation of the root and periodontal structures [1]. Jiang X et al. have demonstrated that the DAC retains the intrinsic capacity to induce root–periodontium complex formation even after detachment from the main root, highlighting its pivotal role in apical morphogenesis [2]. Clinically, several hypotheses have been proposed to explain segmental root development formation, including displacement of the DAC or trauma-related apical injury. However, definitive biological evidence supporting these mechanisms remains limited [3, 4].

Dens evaginatus, a common developmental anomaly of the crown, may fracture and expose the pulp chamber, triggering inflammatory cascades that result in pulp necrosis and chronic periapical periodontitis. These complex pathological changes can hinder apical closure and may be accompanied by intraradicular calcifications, posing significant diagnostic and therapeutic challenges. For malformed immature permanent teeth with apical periodontitis, current treatment strategies include apexogenesis, apical barrier techniques, and pulp regeneration [5]. Revascularization, as a biologically based regenerative approach, depends on the residual apical tissues and DAC activity to induce vascularized, functional pulp-like tissue and promote continued root development [6]. However, when the DAC is damaged or detached, root formation is often arrested and the success rate of revascularization significantly decreases. Such conditions are particularly challenging in cases with complex apical morphology, including segmental root development, where precise removal of the pathological structure while preserving the remaining developmental tissues is critical.

Endodontic microsurgery provides an effective approach for managing complex apical lesions, such as segmentally developed roots. With the aid of dental operating microscopes, ultrasonic root-end preparation, and biocompatible retrograde filling materials, endodontic microsurgery enables precise localization and minimally invasive removal of pathological tissues or aberrant root structures. This approach minimizes mechanical and thermal injury, preserves critical apical regulatory tissues, and may improve the biological environment for subsequent revascularization or pulp regenerative procedures, thereby reducing the risk of secondary surgery and postoperative complications [7–9].

This report describes a rare case of segmental root development associated with extensive periapical inflammation. The clinical features, diagnosis, and management are described, and the possible pathogenic mechanisms and therapeutic considerations are discussed in the context of the existing literature.

Case presentation

A 15-year-old male patient presented with a chief complaint of pain in the lower right premolar tooth (tooth 45) for one week. The patient reported that he had undergone root canal treatment for the same tooth three years earlier at another hospital, but the treatment had not been completed. His medical history was noncontributory, with no systemic diseases or drug allergies. Tooth 45 exhibited an open access cavity on the occlusal surface. The tooth was sensitive to percussion but showed no mobility. Periodontal probing depths were 3–4 mm, and no gingival swelling was observed (Fig. 1a). Cone-beam computed tomography (CBCT) revealed an access open to the oral environment in tooth 45, with an open apical foramen. The root canal walls appeared smooth and continuous without evidence of fracture, and the tooth was classified as Nolla stage 8. In the periapical region, a well-defined hyperdense lesion measuring 4.9 × 3.9 × 4.5 mm was observed. The lesion displayed a flat coronal outline and a conical configuration apically, with a central cone-shaped radiolucency suggestive of a root canal structure (Fig. 1b-e). The clinical diagnosis was chronic periapical periodontitis of tooth 45, with a suspected supernumerary tooth. The patient and his parents were fully informed of the clinical condition, recommended treatment, and potential costs, and they provided written informed consent for root canal therapy of tooth 45 and endodontic microsurgery.

Fig. 1.

Clinical and radiographic examination. a Preoperative intraoral photograph, lateral view: the gingiva adjacent to the apex of tooth 45 showed no swelling or sinus tract. b CBCT revealed a radiopaque foreign body at the apical region of tooth 45. c Axial view demonstrated the cross-section of the apical radiopaque mass, with a low-density structure suspected to be the root canal indicated by the red arrow. d, e Coronal and sagittal views showed the apical radiopaque structure in both orientations. The blue arrows indicate the canal walls of tooth 45, while the red arrows point to the suspected root canal within the mass

Because the main root canal showed incomplete previous treatment and persistent infection, conventional root canal therapy was first performed to eliminate intracanal infection before surgical removal of the apical structure. After confirming no contraindications to local anesthesia, tooth 45 was isolated with a rubber dam (Fig. 2a). The root canal was prepared using EDTA and mechanical instrumentation up to a size 35/0.06, followed by copious irrigation with 1% sodium hypochlorite and saline, ultrasonic activation, and drying. The root canal was obturated under a dental operating microscope using iRoot-SP sealer combined with warm gutta-percha, and the access cavity was restored incrementally with nano-hybrid resin (Fig. 2b-d).

Fig. 2.

Root canal therapy and endodontic microsurgery procedure of tooth 45. a Preoperative intraoral photograph. b Root canal obturation with iRoot SP sealer and warm gutta-percha. c Flowable resin lining and layered nanocomposite restoration. d Occlusal adjustment of the restoration. e Triangular incision made at the surgical site. f Apical lesion of the alveolar bone associated with tooth 45. g Exposure of the periapical lesion under magnification. h Complete removal of the apical supernumerary tooth. i Hemostasis of the bone cavity. j Retro-grade filling of the apical root end. k Retro-grade filling with iRoot BP. l Placement of CGF in the bone cavity. m Coverage of the surgical site with CGF membrane. n Coronally repositioned flap with interrupted sutures. o Immediate postoperative radiograph showing dense root canal filling

Following routine disinfection and draping, infiltration anesthesia was administered to teeth 44–46 using articaine with epinephrine. A triangular mucoperiosteal flap was reflected at the surgical site (Fig. 2e). The buccal alveolar bone overlying the apex of tooth 45 appeared pale (Fig. 2f). Under the microscope, a turbine-assisted approach was used to expose the periapical lesion (Fig. 2g), and the supernumerary apical tooth was completely removed under direct vision (Fig. 2h). Granulation tissue was curetted from the periapical area, and hemostasis was achieved on the bone surface (Fig. 2i). The apex was smoothed and stained with methylene blue to check for cracks in the root section. Ultrasonic retro-grade filling of the canal to approximately 3 mm depth was performed, followed by cleaning, drying, and retro-grade filling with iRoot-BP (Fig. 2j, k). The bone cavity was irrigated with saline and filled with concentrated growth factor (CGF) and covered with a CGF membrane to guide bone regeneration (Fig. 2l, m). The flap was repositioned coronally and secured with interrupted 5 − 0 absorbable sutures (Fig. 2n). Postoperative instructions were provided, and immediate postoperative radiographs confirmed high-density filling within the canal (Fig. 2o).

The excised lesion was identified as a conical, white hard-tissue mass (Fig. 3a), with pink soft tissue observed at the coronal center, suggestive of pulp-like tissue (Fig. 3b). Histological analysis demonstrated typical dental architecture, characterized by a distinct odontoblast layer, dentin, predentin, and vital pulp tissue in the centre, no enamel was observed, confirming the odontogenic origin of the specimen. These features confirmed the odontogenic nature of the excised structure. However, histopathological findings alone could not determine whether the lesion represented a separated apical fragment, an independently developed segmental root structure, or another odontogenic developmental anomaly (Fig. 3c).

Fig. 3.

Postoperative specimen and histopathological findings. a Gross view of the excised supernumerary structure from the periapical region. b Coronal aspect of the excised specimen. c Histopathological section confirming odontogenic tissue

At 3-, 6-, and 12-month follow-ups, tooth 45 demonstrated normal gingival appearance, intact occlusal restoration, negative percussion response, and no mobility. Radiographic examination revealed a gradual reduction in the size of the periapical radiolucency (Fig. 4).

Fig. 4.

Follow-ups at 3-, 6-, and 12-month. a, b Intraoral views at 3 months postoperatively showing healthy gingiva without swelling or sinus tract. c Periapical radiograph at 3 months demonstrating reduction in the periapical radiolucency. d, e Intraoral views at 6 months postoperatively showing stable occlusal restoration, no mobility, and negative percussion response. f CBCT at 6 months demonstrating further reduction of the periapical lesion. g, h Intraoral views at 12 months. i Periapical radiograph at 12 months

Discussion

Root development begins when the crown formation is nearly complete and progresses gradually toward the apex, accompanied by the development and maturation of the periodontal tissues [10]. HERS originates from the proliferation of the inner and outer enamel epithelia at the cervical loop and forms a bilayered structure, in which the inner layer surrounds the dental papilla and the outer layer interfaces with the dental follicle [11]. These components interact in a highly coordinated manner and function collectively as an integrated biological unit, termed the DAC [10]. Notably, previous experimental studies have demonstrated that even when physically separated from the main root, the DAC retains its intrinsic capacity to induce the formation of root and periodontal tissues both in vitro and in vivo, highlighting its independent developmental potential [12–15]. In the present case, the radiographic and histopathological findings demonstrated a root-like hard-tissue structure with a root-like morphology and a central pulp-like space. These findings were compatible with previously reported cases of segmental root development. However, because no previous radiographic records documenting the developmental process were available, the precise developmental origin of the lesion could not be established. Therefore, it could not be determined conclusively whether the lesion represented a separated apical fragment, an independently developed segmental root structure, or another odontogenic developmental anomaly.

Independent development of root-like apical structures has been described in a limited number of clinical reports, particularly in immature teeth affected by trauma or developmental disturbances during root formation [3, 16, 17]. Several hypotheses have been proposed to explain these findings, including separation of the developing apical complex (DAC) from the main root and subsequent autonomous development of the detached tissues. Experimental studies demonstrating the developmental potential of DAC provide biological support for such interpretations. However, direct evidence confirming these mechanisms in human clinical cases remains limited. In the present case, the excised lesion exhibited a root-like morphology with a central pulp-like space on radiographic and histopathological examination, findings that were compatible with previously reported cases of segmental root development or separated apical structures. Nevertheless, because no radiographic records documenting the developmental process were available, the lesion could not be definitively classified as a separated apical fragment, an autonomously developed segmental root structure, or another odontogenic developmental anomaly. Therefore, the developmental origin of the lesion should be regarded as indeterminate.

Several reports have described root-like apical structures in association with developmental anomalies such as dens evaginatus. These teeth are susceptible to early pulp exposure, pulp necrosis, and chronic apical inflammation, which may interfere with normal root development [18–20]. Although inflammatory and developmental factors have both been proposed as potential contributors to the formation of unusual apical hard-tissue structures, the available evidence remains insufficient to establish a definitive causal relationship. In the present case, chronic apical periodontitis and a distinct ectopic apical hard-tissue structure were observed concurrently; however, whether these findings were developmentally or pathogenetically related could not be determined.

The differential diagnosis of radiopaque apical lesions includes idiopathic osteosclerosis(IO) and compound odontoma(CO). IO typically lacks an internal pulp-like space and consists of dense bone-like tissue, whereas CO is characterized by enamel-containing tooth-like structures. In the present case, histopathological examination demonstrated dentin, predentin, odontoblast-like cells, and vital pulp tissue without enamel formation, supporting the diagnosis of a root-like structure and excluding these entities [21, 22]. One of the most distinctive features of the present lesion was the combination of radiographic and histopathological findings. CBCT demonstrated a well-defined radiopaque structure with a central canal-like radiolucency, closely resembling root morphology. Histopathological examination further revealed dentin, predentin, odontoblast-like cells, and vital pulp-like tissue, confirming its odontogenic nature. The correlation between imaging and histological findings was critical for excluding other radiopaque apical lesions and for characterizing the lesion as a root-like odontogenic structure.

Current clinical management of pulpal disease includes vital pulp therapy, root canal therapy, and regenerative endodontic procedures, with treatment selection depending on root development stage and pulpal infection severity [23]. In immature permanent teeth with chronic apical periodontitis, treatment aims to promote apical closure through apexogenesis, apical barrier techniques, or regenerative procedures [24]. Regenerative approaches include pulp revascularization and tissue engineering. Revascularization relies on residual viable periapical tissues and can be enhanced by platelet-rich plasma or platelet-rich fibrin, promoting root maturation and periapical healing [25]. Tissue engineering involves exogenous stem cell transplantation to regenerate the pulp–dentin complex [26]. Clinical studies report a 60% success rate and 90% periapical healing following revascularization in immature teeth [27]. Continued root development depends on the survival of Hertwig’s epithelial root sheath under inflammatory conditions [28]. However, persistent apical infection remains a major limitation and a key cause of regenerative failure despite canal disinfection [29].

In the present case, the pulp chamber had remained open to the oral environment for approximately three years, and severe apical infection was evident, suggesting long-term microbial contamination and persistent inflammation. Such conditions are unfavorable for the survival and function of DAC and significantly reduce the likelihood of achieving true pulp regeneration. Furthermore, the presence of ectopic apical hard tissue acted as a physical barrier, which may have further impeded tissue ingrowth and revascularization, preventing continued root maturation and contributing to the poor regenerative prognosis [30]. Previous reports have described cases of chronic apical periodontitis associated with dens evaginatus and segmental root development managed using regenerative endodontic procedures without surgical removal of the apical segment. Although symptom resolution and functional retention were achieved, radiographic evidence of continued root maturation was limited in these cases [31]. In contrast, regenerative therapy was not considered an appropriate treatment option in the present case. The pulp had been exposed to the oral environment for approximately three years, accompanied by persistent infection and extensive apical structural alteration. Such long-standing inflammatory conditions are known to compromise the biological integrity of the dental apical complex and reduce the predictability of regenerative outcomes. Moreover, the presence of an ectopic apical hard tissue structure constituted a mechanical barrier that could hinder tissue ingrowth and revascularization.

In cases involving complex apical anatomical abnormalities such as ectopic apical hard tissue or segmental root development structures, conventional nonsurgical approaches may fail to remove pathological tissue or eradicate infection reliably. Endodontic microsurgery provides direct access to the apical region under high magnification and illumination, improving visualization and permitting precise removal of diseased tissues while preserving adjacent structures [32, 33]. Ultrasonic root-end preparation combined with biocompatible retrograde filling materials has been associated with favourable surgical outcomes and high healing rates across a range of case types [34, 35]. A recent retrospective study reported very high short-term success (>90%) for endodontic microsurgery with proper case selection and surgical execution, highlighting the clinical value of this approach when nonsurgical treatment is unlikely to achieve predictable results [33]. Therefore, given the anatomical complexity and persistent apical infection in the present case, microsurgical intervention was considered the most appropriate treatment strategy [9]. From a clinical perspective, the successful management of this rare lesion represents an important aspect of the present report. The lesion was associated with persistent apical infection, complex apical anatomy, and long-term exposure of the root canal system to the oral environment, all of which reduced the likelihood of predictable regenerative outcomes. Endodontic microsurgery enabled direct visualization and complete removal of the apical hard-tissue structure and associated inflammatory tissue while allowing precise root-end preparation and filling. The favorable clinical and radiographic healing observed during the 12-month follow-up period supports the effectiveness of this treatment strategy in managing similar rare and anatomically complex cases.As a single case report, causal inference regarding etiopathogenesis remains inherently limited. The biological interpretations discussed herein are intended primarily to provide context from the existing literature and should be regarded as hypothesis-generating rather than evidence of a specific developmental mechanism.

Conclusion

This report describes a rare root-like apical hard-tissue structure associated with chronic apical periodontitis in an immature permanent tooth. The lesion was comprehensively characterized through the integration of CBCT imaging and histopathological examination, which confirmed its odontogenic nature while not allowing definitive determination of its developmental origin. The successful outcome achieved through root canal therapy combined with endodontic microsurgery highlights a practical management approach for similar rare and diagnostically challenging cases.

Abbreviations

DAC

Developing apical complex

CBCT

Cone-beam computed tomography

CGF

Concentrated growth factor

CO

Compound odontoma

HERS

Hertwig’s epithelial root sheath

IO

Idiopathic osteosclerosis

Authors' contributions

YL and JS performed the data analysis and drafted the manuscript. XC, LL, and JL acquired the data. YY provided the radiographic examination report. DL, YT, HZ, and BW contributed to supervision, visualization, and project administration. JZ and ZG conceived and designed the study and revised the manuscript. All authors read and approved the final manuscript.

Funding

This work was supported by the Natural Science Research Project of the Guizhou Department of Education (No. [2024]128), Guizhou Science and Technology Plan (Basic of Guizhou Science and Technology -[2024] Youth 331), CSA West China Clinical Research Fund (CSA-W2025-08), Zunyi Science and Technology and Big Data Bureau HZ Zi (No. [2024]345) and Zunshi Kehe HZ Word (No. [2025]305).

Data availability

All data analyzed during this study are included in this published article.

Declarations

Ethics approval and consent to participate

Ethical approval for this study was obtained from the Ethics Committee of the Stomatology Hospital Affiliated to Zunyi Medical University (Approval No. ZYKQYLLS-2026-003).

Consent for publication

Written informed consent for publication of this case report and any accompanying images was obtained from the patient’s parents.

Competing interests

The authors declare no competing interests.