1. Introduction

Odontogenic keratocyst (OKC) is a developmental odontogenic cystic lesion with aggressive growth potential and a high recurrence rate, which is derived from odontogenic epithelium [1]. OKC was first described by Phillipsen in 1956 [2]. Until 2005, OKC was classified by World Health Organization (WHO) as Odontogenic keratocyst tumor (KCOT) [3]. However, it was later changed to odontogenic keratocyst again in 2017 [4]. In addition, OKC has a certain malignant potential, so the nomenclature and treatment of OKC remain still controversial [5]. Odontogenic cysts have similar characteristics in clinical and radiological examination. Because the envelopmental type of Odontogenic keratocyst (OKC) contains adjacent unerupted teeth and radiographs may reveal a radiolucent cystic lesion around the crown, it is often misdiagnosed as a dentigerous cyst [6]. Histological examination is the gold standard for diagnosis [7].

The postoperative recurrence rate of odontogenic keratocysts ranges from 14.8%–21.1% [8, 9, 10]. Cystectomy and decompression are both effective for the treatment of jaw cysts. Compared to cystectomy and decompression separately, the combination of cystectomy after decompression has a significantly lower recurrence rate [9, 10]. Younger patients treated with decompression for longer would get a better treatment effect [11]. This paper reports on a large odontogenic keratocyst in the left mandible that was treated by decompression and secondary enucleation.

2. Case report

A 13-year-old male patient came to the oral and maxillofacial surgery clinic with a chief complaint of progressive swelling in the left face for more than a week. The patient denied systemic disease and a history of drug allergies.

Extraoral examination revealed an asymmetric face with a bulging left mandible. The color and texture of facial skin are normal (Fig. 1). The left lower lip was hypoesthesia, but pain can still be perceived.

Fig. 1.Extraoral photos of patient. (A) Extraoral photo showing an asymmetric face in first visit. (B) Extraoral photo eighteen months after enucleation.

Intraoral examination demonstrated mandible expansion from the vestibular sulcus of the left mandibular second premolar to the buccal side of the retromolar pad (Fig. 2). The overlying mucosa was hard and tender on palpation. Teeth 37 (left mandibular second molar) and 38 (left mandibular third molar) were absent in the dentition.

Fig. 2.Intraoral photo in first visit showing the bulge at buccal side of retromolar pad (the area indicated by the black arrows).

Cone beam computerized tomography (CBCT) examination showed a unilocular radiolucent area with a clear boundary at the angle of left mandible and the mandibular ramus (Fig. 3). Tooth 37 is affected in a lower position close to the apex of tooth 36. Moreover, ectopic tooth 38 impacted near the mandibular notch. The shaded area contained teeth 37 and 38, measured approximately 70 × 50 × 27 mm. The mandibular outline was signally expanded, and the bone cortical was partially defective at the anterior lesion edge. There was no obvious resorption of the adjacent tooth root, and the mandibular canal was invisible in the CT image (Fig. 4).

Fig. 3.Reconstructed CBCT images in different periods. (A) Preoperative reconstructed CT images of the mandibular lesion. (B) Reconstructed CT images of the mandibular lesion three months after the decompression. (C) Reconstructed CT images of the mandibular lesion ten months after the decompression (before the secondary enucleation). (D) Reconstructed CT images of the mandibular lesion eighteen months after the enucleation.

Fig. 4.CBCT sagittal view of the left mandible. (A) Sagittal view of CT image at the first visit. (B) Sagittal view of CT image three months after the decompression showing the reappearance of mandibular canal. (C) Sagittal view of CT image ten months after the decompression (before the enucleation). (D) Sagittal view of CT image eighteen months after the enucleation.

3. Treatment

3.1 First stage: decompression

Decompression was performed under general anesthesia, and the impacted third molar was extracted. During the operation, we first made an incision to create a bony fenestration of about 20 × 20 mm at the distal of tooth 36. After the incision, the cholesterol crystal overflowed, and white keratin was found in the cyst cavity. The cyst tissue was thick and tough. However, teeth 37 and 38 were undetected in the cystic cavity because the crowns were covered by cyst tissue. The biopsy defined a diagnosis of odontogenic keratocyst (Fig. 5A,B). One week after the operation, an obturator was manufactured (Fig. 6A) and inserted into the fenestrae to maintain the surgical window during decompression (Fig. 6B). The patient was instructed to irrigate the cavity with a sterile saline solution twice a day to avoid infection.

Fig. 5.The histopathologic image of lesion. (A) The histopathologic image of the cystic wall (Hematoxylin and Eosin stain; scale bar, 100 µm). (B) The histopathologic image of the cystic wall (Hematoxylin and Eosin stain; scale bar, 50 µm).

Fig. 6.A resin obturator. (A) The obturator like a removable partial denture. (B) The obturator retained in lower dentition.

Regular clinical and radiological examinations were arranged throughout the decompression period. Tooth 37 moved to bone fenestration at six weeks of follow-up (Fig. 7). A CT scan three months after the first stage operation indicated that cyst volume decreased significantly (Fig. 3). The mandibular canal could be clearly identified in a normal position (Fig. 4).

Fig. 7.Intraoral photographs showing the tooth 37 (red arrow) at the surgical window.

Ten months after decompression, a new CBCT examination showed that the radiolucent lesion size was reduced to 33 × 11 × 15 mm (Figs. 3,4). In the oral cavity, we found that the second molar spontaneously erupted with a lingual tilt and almost reached the occlusal plane (Fig. 8). Because the fenestration closed (Fig. 8) and the decompression achieved remarkable results, the enucleation was scheduled.

Fig. 8.Intro-oral photography in different period. (A) Intro-oral photography ten months after the decompression (before the enucleation). (B) Intro-oral photography six months after the enucleation. (C) Intro-oral photography eighteen months after the enucleation.

3.2 Second stage: enucleation

Ten months after the first stage operation, the second stage operation, the residual cyst was performed under general anesthesia. After enucleation, the residual bone cavity is filled with bone graft materials (Bio-Oss Collagen® 100 mg × 4, Geistlich Pharma AG, Wolhusen, Switzerland). Pathological examination confirmed the final diagnosis of OKC again. One and a half years after enucleation, a radiograph showed an ideal osteogenesis effect in the entire cavity (Figs. 3,4). The crown of tooth 37 moved about 11.6 mm compared to the preoperative CBCT. In clinical examination, the contour of mandible and face gradually changed into symmetry.

Additionally, tooth 37 spontaneously erupted to the occlusal plane with a slight lingual inclination (Fig. 8), and the buccal cusp of tooth 37 contacted the central fossa of the second molar maxillary (Fig. 9). Extraoral examination showed that the facial appearance was symmetrical (Fig. 1) and the sensory function of inferior alveolar nerve recovered to normal. There are no signs of recurrence in clinical and radiographical examinations.

Fig. 9.Buccal view of occlusion showing the functional occlusal contact of the tooth 37.

3.3 Analysis of tooth eruption

The patient underwent several CBCT scans during the entire treatment period. We exported the CBCT data (pre-operation, three and six months after decompression, before enucleation, and eighteen months after enucleation) in DICOM format. We imported them to Mimics Research 21.0 (Materialize, Leuven, Belgium) to reconstruct the 3D models of jawbone and teeth of the left lower jaw. Finally, the 3D models in STL format were imported in 3-Matic 11.0 (Materialize, Leuven, Belgium) to analyze the eruption of impacted second molar. After aligning multiple models in the 3-Matic, we can see the eruption pathway of impacted tooth 37 during the entire treatment process (Fig. 10A–D). After measurement, we found that the angle of impacted tooth 37 changed by approximately 70°.

Fig. 10.Views of the matched reconstructed models at different times showing the eruption pathway of the impacted second molar during the entire treatment period. (pink: first visit, blue: three months after decompression; green: six months after decompression; yellow: before secondary enucleation; red: eighteen months after enucleation). (A) Buccal view (B) Lingual view (C) Bottom view (D) Top view.

4. Discussion

Enlargement of the jawbone cyst cavity is mainly affected by hyperplasia of the cyst lining epithelium, the increase of hydrostatic pressure and osmotic pressure in the cavity, and various factors related to bone resorption in cyst fluid [11, 12]. The bony wall and the involved teeth in odontogenic keratocysts are under pressure from the outward expansion of cyst, resulting in bone resorption, tooth impaction and distant displacement.

The postoperative recurrence rate of OKC is related to surgical methods. Aggressive surgical approaches might have a lower recurrence rate than conservative strategy [10]. But Mohanty et al. [13] suggested that conservative procedures are effective in most cases of OKC. Stanbouly et al. [14] concluded that 2-stage conservative treatment (decompression followed by enucleation) has a lower recurrence rate compared to single-stage conservative treatment. Hyun et al. [15] described the successful treatment of recurrent OKC involving erupting teeth in a 7-year-old boy. He concluded that conservative surgery should be considered first for children who suffer from OKC involves unerupted permanent teeth. Zhang et al. [16] reported the satisfactory effect of recompression in a case of recurrent OKC after decompression with adjunctive enucleation. ÖZKAN et al. [17] reported a 10-year-old boy with OKC treated by decompression, the cyst healed and the impacted teeth erupted spontaneously after treatment. In conclusion, conservative treatment (decompression and marsupialization) should be the first choice for children with OKC even if recurrent OKC.

When choosing a treatment strategy, many factors should be considered, such as cyst size, relation to important anatomical structures, and the position of involved teeth [18]. Retention of impacted teeth involved in cysts is a key point. It has been pointed out that the extraction indications for cysts involving impacted teeth are the following: impacted third molars; inverted impacted teeth; supernumerary teeth; deformed teeth [19]. However, tooth extraction should be suspended if the impacted teeth are adjacent to an important anatomical structure, such as the mandibular canal and maxillary sinus. Furthermore, premolars, canines, and other teeth that may affect the integrity of the dental arch and cause aesthetic and psychological problems after extraction should not be removed [18, 19]. In this case, the inverted impacted third molar was suitable for extraction, and the second molar was preserved.

Eruption of normal teeth requires two conditions. First is the eruption pathway formed by bone resorption over the crown. The second is bone formation at the root. The dental follicle regulates these two procedures of bone remodeling [20]. A previous article believes that dental follicle tissue can be used as a stress sensor to mediate bone tissue remodeling, which plays a crucial role during intraosseous eruption [21]. Sarrafpour et al. [22] reported that cystic soft tissue may also have the same effect as dental follicle tissue. Additionally, during the extra-bony eruption stage, the position of the teeth will be affected by bone remodeling and muscle force [21].

In the present case, the pressure in the cystic cavity is released after decompression. And the eruption channel of impacted second molar was created. At the same time, concentric osteogenesis occurred in the bone wall around the cyst due to the outflow of internal fluid and the release of pressure. Therefore, impacted teeth can spontaneously erupt after decompression. Some studies show that nearly 70% of impacted teeth treated by fenestration and decompression can spontaneously erupt. Most remaining impacted teeth that do not completely erupt can also be treated with orthodontic traction to erupt in a normal position and establish stabile occlusion [19].

According to the literature, the angle of impacted teeth might change the fastest during the first three months after decompression [23, 24]. Surgically, it has been reported that if the impacted teeth cannot erupt in three months, they will eventually not spontaneously erupt to the occlusal plane [24]. However, Farshidfar et al. [25] reported a case of a 9-year-old patient whose right lower first premolar fully erupted spontaneously one year after decompression. In our case, a first-time radiological examination indicated that the second molar horizontally impacted the buccal side of first molar apex. Eighteen months after enucleation, tooth 37 had to stabilize occlusal function. Due to the outcomes of this patient, we believe that although the bone remodeling and tooth eruption are active within three months after decompression, the period of postoperative observation can also be appropriately extended.

5. Conclusion

We showed this case with a large odontogenic keratocyst in the left mandible. In this young patient, decompression and secondary enucleation were performed because the lesion affected the left mandibular second molar, third molar, and even the mandibular canal. These two combined surgical techniques can effectively reduce the risk of injury to the inferior alveolar nerve and seek more autogenous repair of bone defects. Eighteen months after the operation, the second molar erupted on the lingual tilt in the dentition, and it has played stabilized occlusal function. However, orthodontic treatment remains considered a necessary way for molar uprighting. The treatment effect of this case showed that decompression is an effective therapy for large cystic lesions in adolescents.

Availability of data and materials

The data presented in this study are available on reasonable request from the corresponding author.

Author contributions

LBZ and HJW—designed and performed the research study. JZ and JFH—analyzed the data. JFH—wrote the manuscript. All authors read and approved the final manuscript.

Ethics approval and consent to participate

This study was approved and exempted by the Medical Ethics Committee of the Hospital (LCYJ2022017). Informed consent of this report was obtained from the patient and family.

Acknowledgment

None.

Funding

This work was supported by Special Fund for High-Level University Construction Talents of Guangzhou Medical University (Guangzhou, Guangdong Province, China. B185006003006).

Conflict of interest

The authors declare no conflict of interests.