Microapical surgery of a periapical cyst caused by apical ramification: a case report and review of the literature

Abstract

Background

The destruction of tooth apical bone mainly comes from odontogenic apical cysts caused by pulp necrosis, chronic inflammation, or trauma. Some affected teeth can be cured by modern root canal treatment or non-surgical retreatment, but some affected teeth do not heal after treatment. Apical surgery should be considered when root canal therapy has failed, root canal retreatment through the crown channel is difficult, or true cysts are present. This article explores the use of microapical surgery to treat a periapical cyst caused by apical ramification, emphasizing a minimal surgical approach for this lesion.

Case presentation

A 47-year-old female (Han nationality) presented with a chief complaint of recurrent buccal mucosal fistula in their maxillary posterior teeth for 1 year. Clinical examination revealed a porcelain-fused-metal crown of the maxilla of the left second premolar (tooth 25) and buccal mucosa fistula. X-ray assessment showed a high-density shadow in the root canal and low-density transmission from the root apex to the middle third of distal root surface. Microscopic apical surgery was performed under local anesthesia. The apical ramification was exposed and a root apex of 3 mm was cut off. Then the apical foramen of buccal root canal, palatal root canal, and apical ramification were filled retrogradely with mineral trioxide aggregate, and finally sewn up. Follow-up X-ray at postoperative 12 months and 24 months showed that the bone density of the root apex and distal root surface was higher compared with the values measured immediately after operation. There were no clinical symptoms, and normal mucosa.

Conclusion

The patient presented with a recurrent buccal mucosal fistula in the maxillary left second premolar. Microscopic apical surgery was performed under local anesthesia. After minimally invasive surgery, apical resection, inverted preparation, and mineral trioxide aggregate treatment, at postoperative 24 months, the outcome was satisfactory, with recovered apical bone, normal mucosa, and no clinical symptoms. For periapical cysts, X-ray and cone-beam computed tomography images should be read carefully before the operation. The semicircular low-density transmission image around the apical sidewall indicates the apical ramification, and that root canal treatment or microapical surgery should be performed. The operating microscope enhances visibility and provides the surgeon with a better understanding of canal anatomy, a better surgical view, and the ability to undertake more complex but predictable apical resection techniques.

Introduction

Periapical cysts are the most common inflammatory odontogenic jaw cysts, and chronic inflammation stimulates the proliferation and secretion of the Malassez epithelium, resulting in fluid retention in the cystic cavity to form apical cysts [1, 2]. They are located in the three-dimensional pathological cavity of the periapical region of the infected tooth and are a common type of odontogenic inflammatory cyst of the jaw, mainly occurring in the upper jaw [3]. The apical cyst usually causes swelling, which may not be prominent initially. Still, if the treatment is neglected, it can gradually cause cortical expansion, devitalize the adjacent teeth, resulting in pathological migration of the teeth, causing absorption and thinning of the labial and buccal bone walls, and a ping-pong sensation during palpation [4].

The main disease of periapical cysts is the spread of bacterial infections within the root canal to the apex, resulting in a complex root canal system, including accessory root canals and apical bifurcations [5]. If the infectious substances are not cleaned up in a timely manner, apical cysts are prone to occur in the later stages of root canal treatment. The small branches that break out at the root tip are called apical bifurcations. At this time, the main root canal still exists, with an incidence rate of no more than 25%. The number of branches generally does not exceed 3 mm, which is more common in premolars and molars [6]. Because there is a certain angle between the apical bifurcation and the main root canal, it becomes a dead angle during root canal preparation and filling, and instruments or materials cannot reach it [7]. Therefore, this is also one of the main reasons for the occurrence of periapical cysts caused by apical bifurcation after root canal treatment.

The treatment of periapical cysts includes conventional nonsurgical root canal therapy when the lesion is localized, or root canal treatment combined with periapical surgery when the lesion is large [8]. Periapical surgery is an endodontic therapy through a surgical flap, which focuses on removing a portion of a root with anatomical complexities, and an undebrided canal when a complete seal cannot be achieved through an orthograde nonsurgical approach [9]. It is undertaken to confine microorganisms in the root canal(s) by sealing the root canal apically, eliminating the most apical and more complicated part of the root canal, and removing the periapical lesion for further histological evaluation. The rate of successful healing of periapical surgery has been reported to range from 60% to 91% [10, 11].

However, nonsurgical retreatment can be questionable or impractical, such as in cases with an extensive coronal restoration that should be sacrificed [12]. Because new restorative rehabilitation is required after successful retreatment, it creates a further financial burden for the patient. Periapical surgery may be the most practical treatment option for managing these cases. In this study, we report a case of a periapical cyst caused by apical ramification treated by microapical surgery.

Case report

Patient information

A 47-year-old female (Han nationality) presented to the department of stomatology of our hospital with a chief complaint of recurrent buccal mucosal fistula in the maxillary left second premolar for 1 year. The patient provided a history of root canal therapy and porcelain fused metal (PFM) crown restoration because of apical periodontitis in the maxillary left second premolar. There was no obvious pain and discomfort after treatment. However, she suffered from repeated fistula of the buccal mucosa in the maxillary left second premolar 2 years later. There was a history of pus growth and decline.

The patient denied any history of cardiovascular disease, hypertension, diabetes, or other systemic diseases, as well as infectious diseases such as hepatitis and AIDS. She reported no allergy to penicillin. Personal and family history were not mentioned.

Clinic findings

Patient was missing the maxillary left canine. The maxillary left canine, first premolar, and second premolar were repaired with single-ended fixed bridges without tooth mobility. The buccal mucosa and gingiva of the maxillary left second premolar showed no redness, swelling, or bleeding, but there was a fistula (the center of the red circle in Fig. 1A). There was no obvious swelling or fistula in the palatal mucosa and gums (Fig. 1B), with no abnormality in periodontal probing. Teeth were not sensitive to percussion and probing.

Fig. 1.

Intraoral images of maxillary left second premolar before treatment. A buccal view red circle: the fistula; B palatal view

Imaging examinations

The red gutta-percha point (02 taper) was inserted into the buccal fistula and a radiograph was taken. Radiograph findings revealed the high-density restoration at the crown of the second premolar and high-density filling in the root canal, but it did not reach the apex. At the same time, the low-density transmission of the distal root surface from the root tip to the middle third can also be seen. The tracer gutta-percha pointed to the middle third of the 25th tooth (the curved high-density area in Fig. 2A). The cone-beam computed tomography (CBCT) examination showed double root canals of tooth 25, apical low-density transmission shadow, and the surrounding bone white lines (Fig. 2B–D).

Fig. 2.

Radiographic image of the tooth before retreatment. A Gutta percha point (indicated by red arrow). B coronal plane of cone-beam computed tomography. C sagittal plane of cone-beam computed tomography. D cross-sectional plane of cone-beam computed tomography

Final diagnosis

She was diagnosed with a radicular (periapical) cyst at the maxillary left second premolar.

Treatment scheme

Plan A: Microapical surgical exploration for maxillary left second premolar. If root fissure is observed during the operation, remove the affected tooth; otherwise, conventional microapical surgery should be performed.

Plan B: Removal of PFM on the maxillary left canine, first premolar, and second premolar, and root canal retreatment for second premolar. Diagnosis and treatment of first premolars based on pulp viability testing, and single crown restoration should be taken into consideration. Implant restoration for left canine.

After communicating with the patient, the patient chose the former treatment scheme after weighing the pros and cons. Oral hygiene education and regular follow-ups were conducted through the entire treatment process.

Therapeutic intervention

Preoperative evaluation of surgery

(1) Difficulty evaluation: the affected tooth was in the maxillary posterior area, with a small operating space and a small mouth opening. The maxillary left second premolar had double root canals and long crown roots, making it difficult for root canal inversion preparation and retrograde filling with mineral trioxide aggregate (MTA), especially at the palatal root. Affected tooth had full crown restorations, so the flap should be designed to avoid exposure of the crown edge leading to second restoration. (2) Location evaluation: based on X-ray and CBCT images, measure the length of the root canal and locate the apical foramen and bone destruction area.

Surgery procedure

The informed consent was obtained from the patient before operation. Location of apical foramen and bone destruction area were performed as aforementioned. All surgical procedures were performed using a surgical microscope (Carl Zeiss Meditec). Under local anesthesia, after disinfection and draping, A triangular incision was made on the membranous gingiva (red line in Fig. 3A) and the scar tissue of the fistula on the inner wall of the gingival flap was removed (Fig. 3B), and a full thickness buccal flap was elevated to reveal the apical lesion (Fig. 3C).The soft tissue of the root cyst was curetted (blue circle in Fig. 3D, removed soft tissue is indicated in the bottom-left of Fig. 3D). The weak bone on the peripheral wall of buccal bone was removed to expose the root apex (Fig. 3E, F). No longitudinal cracks in the lateral wall of the root canal were demonstrated by methylene blue staining, and the distal root surface, about 4 mm from the root apex, was stained (Fig. 3G), i.e., the apical foramen of the buccal root canal. The root apex was undercut (Fig. 3H) and retropreparation was performed (Fig. 3I) and the canal was retrofitted with MTA for 3 mm (Fig. 3J).

Fig. 3.

Surgical procedure. Yellow arrow: the apical foramen of the buccal root; blue arrow: the apical foramen of the palatal root; and green arrow: apical ramification foramen. A Schematic diagram of the mucosal incision (indicated by the red line). B Sticky scar tissue at the bone destruction point (scar tissue was indicated in the bottom-left). C Full thickness buccal flap was elevated to reveal the apical lesion. D Removal of the soft tissue of the root cyst (soft tissue indicated by blue circle, removed soft tissue is indicated in the bottom-left). E Removal of the weak bone on peripheral wall of the buccal bone destruction area. F Exposing the root apex. G Methylene blue staining showed the apical foramen (yellow arrow: the apical foramen of the buccal root; blue arrow: the apical foramen of the palatal root; green arrow: apical ramification foramen). H Undercutting the root apex by 3 mm (yellow arrow: the apical foramen of the buccal root, green arrow: apical ramification foramen.). I Retro-preparation of the root apex (yellow arrow: the apical foramen of the buccal root; blue arrow: the apical foramen of the palatal root; green arrow: apical ramification foramen). J Retrograde filling with MTA (yellow arrow: the apical foramen of the buccal root; blue arrow: the apical foramen of the palatal root; green arrow: apical ramification foramen). K Packing the gel sponge in the cyst cavity. L Suture of the mucosal flap

Gel sponge was filled up to support the valve soft tissue and prevent MTA slippage (Fig. 3K), and finally stitched up (Fig. 3L).

The X-ray after operation showed that the apical area was far from the low-density transmission shadow, with a lower density and a larger range compared with preoperative images (Fig. 6A), because the buccal peripheral wall bone was partially removed during the operation to expose the apex. After the operation, cefuroxime axetil, metronidazole, and dexamethasone tablets were taken orally as prescribed. The removed soft tissue of the periapical cyst was sent for pathological examination in the Department of Pathology, Daping Hospital of Army Medical University.

Fig. 6.

X-ray image after treatment. A Immediately taken after operation (the apical ramification foramen and the palatal root was overly filled with MTA). B Postoperative 12 months. C Postoperative 24 months

Pathological results showed discontinuous epithelium of the cyst wall, nesting of many lymphocytes and plasma cells locally, infiltration of a few neutrophils and eosinophils (Fig. 4), proliferation of small blood vessels, an increase of fibroblasts, and reactive proliferation of fibrous tissue to form a pseudocapsule-like structure enveloping inflammatory granulation tissue (Fig. 4).

Fig. 4.

Hematoxylin and eosin staining of periapical cyst soft tissue. Scale bar represents 500 μm

Follow-up and outcomes

The patient missed the follow-up at postoperative 3 months. The buccal view of tooth 25 at postoperative 6 months (Fig. 5A) showed scar formation, but no obvious redness, swelling, and fistulas in the gum and mucosa. The images at postoperative 12 months (Fig. 5B) showed no obvious clinical symptoms. The X-ray images at postoperative 12 months (Fig. 6B) and 24 months (Fig. 6c) showed that the bone density of the root apex and distal root surface was higher compared with the value measured immediately after operation. No obvious transmission shadow was observed and new bone was generated.

Fig. 5.

Postoperative intraoral images. A Postoperative 6 months. B Postoperative 12 months

Discussion

Periapical cysts are the most common cyst of the jaw and are caused by inflammatory processes [13]. Periapical cysts are divided into pocket cysts (with connection to the root canal system) and true cysts (with no connection to the root canal system), accounting for 6% and 9% of chronic periapical diseases, respectively [14]. True cysts represent a disease entity not dependent on root canal infection, and cannot heal following nonsurgical root canal treatment [15, 16]. Pulp testing, radiographs, and histopathologic evaluations are helpful in achieving an accurate diagnosis. The gold standard of diagnosis is pathological examination of tissue sections. The symptoms of the periapical cysts depend on the status of inflammation. A tooth with acute inflammatory exacerbation is symptomatic and presents with pain or discomfort. Clinically, a large cyst can cause jaw swelling, leading to absorption and thinning of the buccal and labial bone walls, manifested as a ping-pong sound during palpation over the mucosa at the periapical zone of the offending tooth [16]. A periapical cyst is identified radiologically by a well-defined, well-circumscribed, single-chamber radiolucency closely associated with the apex of the affected tooth. An abscess of lamina dura and a faint or thin radiopaque line (sclerotic border) that encircles the cystic region are also important radiographic markers for securing a diagnosis. In some cases, a thin layer of blocking projection shadow is observed in the periphery of the transmission area, which is related to declined cyst growth and the repair of the surrounding bone tissues.

Most cases are managed either by root canal treatment and periapical surgery, or by extractions [17]. The affected teeth of periapical cysts should be monitored at 3, 6, and 12 months after conventional root canal treatment. If the periapical transmission area disappears, with normal periodontal cavity, increased bone density, and intact hard bone plate, all suggest a good prognosis and a pocket cyst is highly suspected. In that case, crown repair is adequate, instead of microapical surgery [18]. The existence of a fistula and an unchanged or enlarged periapical transmission zone indicates a high risk of a true cyst. In that case, microapical surgery is necessary. In our study, although X-ray examination of the affected tooth showed that the root canal treatment was insufficient, considering that the crown had been repaired (a continuous crown), microapical surgery was adopted rather than root canal retreatment after crown removal. Retreatment might be time-consuming and costly if replacement of an extensive restoration is required. Periapical surgery may be the most practical treatment option for managing these cases.

Clinically, premolars have a higher incidence of pulp and periapical disease. In addition, there are also many anatomical morphological variations such as lateral canal and root apical ramification [19]. Therefore, it is more difficult to carry out perfect root canal treatment, and root canal omission is prone to lead to treatment failure. In the complicated root canal system, the small branches originating from the root apex are called apical ramifications, while the main root canal still exists. The incidence of apical ramification is ≤ 25%, with no more than three branches usually in premolars and molars. There is a small region between the apical ramification and the main root canal, where devices or materials find it hard to reach during the preparation and filling of the root canal. Apical ramifications have been implicated in endodontic treatment failure and are one of causative factors in developing periapical cysts after root canal therapy [7, 20]. Kim and Kratchman suggested that at least 3 mm of the root-end must be removed in root-end resection because 98% of the apical ramifications exist within 3 mm of the root-end [21]. In our study, the distance between the apical ramification and the root apex was 4 mm, but only 3 mm root apex was removed considering the consistency of the crown:root ratio after the root resection. The buccal root foramen, palatal root foramen, and apical ramification foramen are retroprepared and retrogradely filled with MTA to seal the canal and prevent bacterial infection inside and outside the root canal [22, 23].

The buccolingual X-ray examination used in clinic often only finds one root canal, so X-ray projections from different angles are needed to show the buccal-lingual root canals that overlap each other due to vertical projection. However, the type of root canal cannot be determined only by the results of X-ray observations and CBCT imaging is required [24]. If the preoperative X-ray shows blurred root canal images or abnormal root canal images, the possibility of root canal variation should be considered and a CBCT should be taken. CBCT imaging plays an important role in the early detection of the existence of variant root canals to guide treatment [25]. CBCT layered reconstruction technology facilitates the discovery of the existence of small root canals, and provides a reliable basis for the feasibility of treatment and the accuracy of treatment. For teeth with periapical infection, based on the apical transmission area confirmed by X-ray and CBCT images, the doctor can locate the infection center of lesion and explore the source of infection. If the root apex point is the center, main root canal infection is suspected; if the center deviates from the root apex point, apical ramification or root fissure is suspected. In our study, the apical transmission area of the affected tooth was located at one-third of the distal apex; therefore, during apical surgery, the doctor can focus on the specific area of the distal apex to explore apical ramification or root fissure, which improves the efficiency.

The wide application of dental microscopes during apical surgery has greatly improved the surgical field of view [21, 26, 27], and the success rate of microapical surgery has reached 91.5–96.8% [23, 28]. The methylene blue staining plays an important role in microapical surgery. Methylene blue can stain soft tissues such as periodontal ligaments, but cannot stain hard tissues such as dentin. After methylene blue staining, under a high-powered microscope, we can determine whether the root surface is intact, whether missing root canals, collateral root canals, apical ramifications, and root fissures are ignored, and whether the root filling is tight, which can provide useful information during the surgery. If root fissures are found, intraoperative extraction (single-root tooth) or root splitting (multiple-root tooth) is performed. If the apical ramification is observed within 3 mm from the anatomical root apex, it can be resected together with the root apex. If the apical ramification is more than 3 mm from the anatomical root apex, the apical ramification foremen can be reserved and retropreparation and retrograde filling are performed, with close follow-up.

Incision design is of critical importance in microapical surgery. It affects access, visibility, anatomical structures, repositioning, and suturing [29]. Factors such as the location and extent of periapical lesions, the biological width of the gums, and aesthetic requirement of the patient, mitigation of postoperative gingival recession, and scar formation should be considered. The triangular full-thickness flap with an intrasulcular incision has been widely used in periapical surgery for the mandibular molar area. However, this incision results in recession and shrinkage of the papilla [30]. In this respect, currently, the papilla base incision and membranous gingival incision are recommended to prevent loss of interdental papilla height. The former can completely expose the surgical field, but is prone to gingival recession [10, 31]. The latter can maintain gingival morphology, but the disadvantage is that the surgical field exposure is incomplete and there is a risk of mucosal scarring. In our study, the patient was reluctant to replace the crown, so we opted for a membranous gingival incision to avoid postoperative gingival recession leading to exposure of the restoration margins.

In this case, minimally invasive surgery was used to remove the apical cyst tissue, with the advantage of a minimally invasive membranous gingival triangular flap incision according to the localization of the lesion at the apex, protecting the biological width of the gingiva of the tooth, avoiding looseness between the edge of the crown restoration and the tooth caused by postoperative gingival recession, and not requiring the cost of a subsequent crown replacement. The disadvantage is incomplete removal of cyst tissue due to mucosal scarring and possible incomplete exposure of the surgical area. However, this case has a crown from tooth 23 to tooth 25, which is not suitable for single tooth intention replantation of tooth 25, so the best option is microapical surgery. The other limitation of this article is that the guided surgery could have been used, which would have improved the accuracy of the resection process.

Conclusion

The patient presented with a recurrent buccal mucosal fistula in the maxillary left second premolar, and her radiographic examination revealed bone destruction.

A membrane gingival triangular flap incision was used to flap and scrape off granulation tissue, revealing the presence of apical bifurcation. It is clear that the apex cyst in the maxillary left second premolar was caused by residual bacteria in the apical bifurcation, resulting in a series of clinical symptoms. After minimally invasive surgery, apical resection, inverted preparation, and MTA treatment were performed. The operating microscope enhances visibility and provides the surgeon with a better understanding of canal anatomy, a better surgical view, and the ability to undertake more complex but predictable apical resection techniques.

The patient was continuously followed up after surgery. At postoperative 24 months, the outcome was satisfactory, with recovered apical bone, normal mucosa, and no clinical symptoms.

Author contributions

Liyun Bai and Na Hu participated in the collection of cases, composed the draft, and wrote the case presentation of the manuscript. Qin Yang and Dongquan Pu wrote the introduction. Xiaoqian Feng and Yiyun Yue made the picture. Weiwei Xiao performed the hematoxylin and eosin staining. Rui Liu wrote the discussion of the manuscript and reviewed the manuscript. Li Liu and Xia Zhou performed the surgery and greatly contributed to the writing of the manuscript. All authors read and approved the final manuscript.

Funding

The study was supported by the Natural Science Foundation of Xizang Autonomous Region (XZ202501ZR0050), the Natural Science Foundation of Shigatse Region (RKZ2025ZR-002), the Postgraduate Education Research Project of Army Medical University (2023yjsB15), and the Micro-course Project of Postgraduate Education of Army Medical University (Y2025W17).

Availability of data and materials

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study was reviewed and approved by the Army Characteristic Medical Center. Informed consent was obtained from the patient so that case records could be made available for scientific publication.

Consent for publication

Written informed consent was obtained from the patient for publication of this case report and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.

Competing interests

The authors declare that there is no conflict of interest regarding the publication of this paper.