Dentigerous cysts are a type of benign odontogenic cyst that results from fluid accumulation in the space between the crown of an unerupted tooth and the reduced enamel epithelium, resulting in the formation of a sac-like cyst in the tissue surrounding the crown (15,27,30). They are characterized by slow growth and expansion affecting the surrounding alveolar bone, leading to bone weakness or defects that can result in fractures, tooth loss, and infection (10). Dentigerous cysts often develop when skull conformation or significant dental crowding impedes normal tooth eruption (18). For this reason, they are commonly found in toy, small-breed, or brachycephalic dogs (28). These cysts have been associated with unerupted maxillary canine teeth, the mandibular first premolar, both mandibular canines, a single mandibular canine, and a supernumerary maxillary premolar (10,15,26,27,30). Although rare, dentigerous cysts can become neoplastic or lead to secondary infections (17,30). Large cysts can induce resorptive lesions in the roots of adjacent teeth or lead to osteolysis of the alveolar bone, thus increasing the risk of pathological fractures, with potential complications including nasal discharge, facial swelling, osteomyelitis, and the loss of adjacent teeth (10). Diagnosis is made by imaging examinations such as dental radiographs, computed tomography (CT), and histopathological examination with the removal of the cyst wall (5,10,19,30). Radiographically, these cysts feature distinct radiopaque margins and a radiolucent center attached to the cervix of an unerupted tooth (10,15,19,27).

Surgical intervention is the only way to treat an odontogenic cyst. The tooth that involved the cyst and those affected by the cyst have to be extracted. The epithelial lining of the cyst is also completely removed to prevent recurrence due to remnants of the cyst wall, and the surrounding tissue is curetted (5,27). However, this process often results in considerable loss of the dental hard tissue affected by the dentigerous cyst. Additionally, in small-breed dogs, due to their naturally higher tooth root-to-mandible size compared to large-breed dogs, there is a concern that tooth extraction may increase the risk of instability, including mandibular fractures (11,29). Therefore, guided bone regeneration (GBR) should be considered as a treatment option for dentigerous cysts in small-breed dogs.

Guided bone regeneration (GBR) is a surgical technique that involves the placement of biomaterials within the extraction socket, which are then covered with a barrier membrane to facilitate bone regeneration. These biomaterials offer structural stability by filling the physical gaps and are gradually resorbed by the cells of the body, ultimately being replaced by native bone tissue (29,31). Barrier membranes, which can be either non-absorbable or absorbable, support this process by creating separation between the internal bone defect and the external environment, thus preventing soft tissue invasion while the bone tissue regenerates within the defect (29). This method is likely to result in greater bone regeneration and alveolar ridge preservation compared to leaving the site unfilled and using only suturing because soft tissue invasion could impede new bone growth (2).

To date, there have been few case reports on the use of GBR to treat dentigerous cysts in small-breed dogs in Korea. This study thus presents case reports detailing the use of GBR in conjunction with conventional surgical methods on two small-breed dogs with dentigerous cysts associated with their mandibular canine teeth, which resulted in favorable clinical outcomes.

Case 1

A 2-year-old neutered male mixed-breed dog (weight: 3.6 kg) visited a local animal hospital due to gingival swelling around the left mandibular buccal canine tooth. A skull radiograph taken at the hospital revealed a horizontally unerupted left mandibular canine tooth and a thinned mandible surrounding the left mandibular canine due to significant alveolar bone loss (Fig. 1). Consequently, the dog was referred to the Veterinary Medical Teaching Hospital at Chonnam National University for the treatment of a dentigerous cyst associated with the left mandibular canine tooth.

Figure 1. Skull radiograph images from Case 1. (A) Left-right lateral radiograph. (B) Left ventral/right dorsal oblique radiograph. A skull radiograph taken at the local animal hospital revealed a horizontally unerupted left mandibular canine tooth and a thinned mandible surrounding the left mandibular canine due to significant alveolar bone loss (yellow solid arrow).

The owner had initially observed that the area of gingival swelling was becoming larger. In a conscious oral examination, the swollen gingiva was noted to be discolored, with a dark blue color around the unerupted left mandibular canine tooth area. A CT scan was performed to assess the mandibular stability and the extent of the cyst. The following pre-anesthetic medications were administered: famotidine 0.5 mg/kg IV (Dong-A Gaster Inj.^TM, Dong-A ST, Seoul, Korea), cefazolin 20 mg/kg IV (C.K.D. Cefazolin Inj. 1 g, Chongkundang Pharm. Co., Seoul, Korea), glycopyrrolate 5 μg/kg SC (Myungmoon Mobinul Inj. 1 mL, Myungmoon Pharm. Co., Seoul, Korea), and midazolam 0.3 mg/kg IV (Bukwang Midazolam Inj. 5 mL, Bukwang Pharm., Seoul, Korea). General anesthesia was induced with propofol 6.0 mg/kg IV (Freepol-MCT Inj. 12 mL, Daewon Pharm. Co., Seoul, Korea) and maintained with isoflurane (Ifran^®, Hana Pharm, Seoul, Korea) inhalation and 100% oxygen. The CT scan revealed a horizontally unerupted canine tooth, fluid accumulation in the space between the canine tooth and alveolar bone, and a thinned mandible with severe alveolar bone loss. The cyst size was measured to be 18.58 mm in length, 7.49 mm in width, and 9.33 mm in height (Fig. 2). After the CT scan, fine needle aspiration (FNA) of the cyst showed yellow serous exudate and cytology showed a few inflammatory cells including macrophages (Fig. 3). A few days later, no abnormalities were detected in the new pre-anesthetic examinations detailing dental examination and dental treatments, including thoracic X-rays and laboratory tests, so the patient was scheduled for surgery to address the dental issues.

Figure 2. Skull computed tomography (CT) scans from Case 1. (A) Sagittal plane. (B) Transverse plane. (C) Coronal plane. (D) 3D reconstruction image. The CT scan revealed a horizontally unerupted canine tooth, fluid accumulation in the space between the canine tooth and alveolar bone, and a thinned mandible with severe alveolar bone loss. It also indicated that the cyst size was 18.58 mm in length, 7.49 mm in width, and 9.33 mm in height (yellow dotted circle).

Figure 3. Images of the exudate from the dentigerous cyst from Case 1. (A) Yellow serous exudate produced via fine needle aspiration. (B) Inflammatory cells in the exudate via cytology (1,000× magnification, stained with hematoxylin-eosin). (C) Macrophages in the exudate via cytology (1,000× magnification, stained with hematoxylin-eosin).

Preoperatively, the dog was pre-anesthetized with maropitant citrate 1 mg/kg SC (Cerenia^® 10 mg/mL solution, Zoetis, Parsippany, NJ, USA), famotidine 0.5 mg/kg IV, cefazolin 20 mg/kg IV, glycopyrrolate 5 μg/kg SC, morphine 0.3 mg/kg IM (Hana Morphine HCl Inj., Hana Pharm), medetomidine 5 μg/kg IM (Tomidin, Provet, IST, Turkey), and ketamine (Yuhan Ketamine 50 Inj., Yuhan Co., Seoul, Korea) at a continuous rate infusion of 10 μg/kg/min. General anesthesia was induced with propofol 2.5 mg/kg IV and maintained with isoflurane inhalation and 100% oxygen. Local nerve blocks were administered into the bilateral infraorbital, middle mental, and mandibular foramina by injecting 0.5% bupivacaine (Myungmoon Bupivacaine HCl 0.5% Inj., Myungmoon Pharm. Co.) at 0.12 mL/site just before ultrasonic scaling. Intravenous fluid (Hartmann’s Sol. [500 mL/bag], JW pharm, Gwacheon, Korea) was infused at a rate of 4.5-5.5 mL/kg/h.

After ultrasonic scaling, a thorough oral examination with a dental explorer and probe revealed no specific abnormalities. However, intraoral full-mouth dental radiographs (iM3 CR 7 [Dental] Veterinary X-ray System, iM3, NSW, Australia) showed that the left mandibular canine tooth was horizontally unerupted into the left mandible. A large radiolucent cyst with distinct margins was observed around the left mandibular canine tooth, extending to affect the left mandibular 3rd incisor, canine, and 1st premolar tooth. Severe alveolar bone loss and a thinned mandible were observed. The size of the left mandibular cyst was 18.6 mm × 9.0 mm (Fig. 4A), which was consistent with the CT scan. Therefore, we planned the following treatment based on these examination results: teeth extraction (3rd incisor, canine, and 1st premolar tooth), complete cyst wall removal, curettage, and GBR, including bone grafting with xenograft materials that were subsequently covered with a collagen membrane.

Figure 4. Intra-oral left mandibular radiographs from Case 1. (A) Preoperative dental radiograph. (B) Dental radiograph 7 months after the operation. Yellow dotted line area: left mandibular dentigerous cyst. Blue area: alveolar bone loss area. Red solid arrows: 3rd incisor tooth and 1st premolar tooth. Yellow solid arrow: unerupted canine tooth. Yellow dotted arrow: extraction socket filled with bone graft materials. The dental X-ray showed that the left mandibular canine tooth was unerupted horizontally into the left mandible. A large radiolucent cyst with distinct margins was observed around the left mandibular canine tooth, extending to affect the left mandibular 3rd incisor, canine, and 1st premolar tooth. Severe alveolar bone loss and a thinned mandible were evident. The size of the left mandibular cyst was 18.6 mm × 9.0 mm. Seven months after surgery, dental radiographs under general anesthesia revealed that the extraction socket of the canine tooth had filled well with newly formed bone that had a density similar to the existing and surrounding alveolar bone. No unstable conditions such as mandibular fractures were visible.

After checking the status of the lesion site (Fig. 5A), the oral cavity was rinsed with a 0.12% chlorhexidine solution. The surgical area was draped and prepared for dental treatment. An incision was made horizontally along the buccal gingiva where the cyst was located (Fig. 5B), and a periosteal elevator was used to create a gingival flap to approach the cyst wall and the unerupted canine tooth (Fig. 5C). Following alveoplasty with a high-speed handpiece and a dental #1 round diamond bur, the left mandibular canine was extracted with dental hand instruments (Fig. 5D). The extraction socket was flushed with 0.9% normal saline (N/S) (JW NS Inj. [100 mL/bag], JW pharm) several times before and after complete cyst wall removal with non-toothed Adson forceps and curettage with a periosteal elevator (Fig. 5E). After thoroughly soaking the powdered xenograft bone material (Medpark Bone XP, Medpark, Busan, Korea) in normal saline or the patient's blood, the remaining alveolar cavity was then slowly filled up to the root area with an appropriate amount of the graft material (Fig. 5F). It was ensured that the graft material remained within the extracted socket and conformed to the contours of the alveolar bone. Care was taken not to apply excessive force because this could crush the granular structure, damaging the graft material and reducing its effectiveness for bone regeneration. After filling the socket with the graft material, an absorbable collagen membrane (Lyoplant^® Aesculap, B. Braun, Melsungen, Germany) was placed between the bone graft materials and gingival flap in the extraction socket (Fig. 5G) without any fixation device to prevent displacement of the graft. Finally, the flap was sutured using a simple interrupted pattern with poliglecaprone 25 sutures (MONOCRYL 5-0, Ethicon, Raritan, NJ, USA) to secure both the graft and the barrier membrane in place (Fig. 5H).

Figure 5. Photographs of the left mandibular canine tooth and dentigerous cyst before treatment and intraoperative procedures from Case 1. (A) Preoperative view. (B) The incision along the buccal aspect of the cyst for extraction. (C) Exposure of the left mandibular canine. (D) Extraction socket for the left mandibular canine. (E) Flushing the extraction socket with 0.9% normal saline (N/S) after complete removal of the cyst wall and curettage. (F) Filling the extraction socket with bone graft materials. (G) Covering the bone graft with a collagen membrane. (H) Surgery site after gingival flap suturing.

The patient was discharged on the day of surgery and prescribed the following medications to take orally twice daily (PO, BID) for 7 days: carprofen 2.2 mg/kg (RIMADYL^® Chewable Tablets, Zoetis), misoprostol 3 μg/kg (Misoprostol Tab. Nelson, Nelson Korea, Eumseong, Korea), amoxicillin/clavulanate 12.5 mg/kg (Amocla Tab., Kuhnil Pharm., Seoul, Korea), ursodeoxycholic acid (UDCA) 7.5 mg/kg (Ursa Tab. 100 mg, Dae Woong Pharm. Co., Seoul, Korea), and silymarin 2.5 mg/kg (Legalon Cap. 140, Bukwang Pharm.). In addition, the patient was prescribed oral cleansing gel containing neutralized zinc (MAXI/GUARD^® OraZn^®, Addison Biological Laboratory, Fayette, MO, USA) to apply to all teeth 1 or 2 times a day. The owner was instructed to clean the patient’s mouth and to provide soft food.

Following examinations 3 days, 7 days, 1 month, and 7 months after surgery, there was no redness, laceration, inflammation, pain, or swelling at the surgical site. Dental radiographs taken 7 months later revealed that the extraction socket of the canine tooth had filled with newly formed bone with a density similar to the existing and surrounding alveolar bone. No unstable conditions such as mandibular fractures were identified (Fig. 4B). The oral condition of the patient has been checked at each visit and the prognosis is good.

Case 2

A 3-year-old spayed female Pomeranian dog (weight: 4.4 kg) was referred to the Veterinary Medical Teaching Hospital at Chonnam National University by a local animal hospital for the treatment of a dentigerous cyst associated with the left mandibular canine tooth. The owner of the patient had noticed a gingival mass in the left mandible two months earlier. The patient exhibited hypersalivation and difficulty in chewing hard food. During a conscious oral examination, the cyst was observed to be discolored, with a dark blue color around the left mandibular canine area (Fig. 6A). No abnormalities were detected in the pre-anesthetic examination. Therefore, the patient was scheduled for surgery to address the dental issues. Preoperatively, the dog was pre-anesthetized in the same manner as in Case 1, except that midazolam 0.2 mg/kg IV was used instead of 5.0 μg/kg IM medetomidine for sedation. General anesthesia was induced with propofol 5.0 mg/kg IV and maintained with isoflurane inhalation and 100% oxygen. Local nerve blocks were used on the bilateral infraorbital, middle mental, and mandibular foramina by injecting 0.15 mL of 0.5% bupivacaine just before ultrasonic scaling. Fluids were infused at a rate of 2.5-5.5 mL/kg/h.

Figure 6. Photographs of the left mandibular canine and dentigerous cyst before treatment and intraoperative procedures from Case 2. (A) Discolored cyst with a dark blue color around the unerupted left mandibular canine area. (B) The incision along the buccal aspect of the cyst for extraction. (C) Exposure of the left mandibular canine. (D) Extraction socket for the left mandibular canine. (E) Flushing the extraction socket with 0.9% N/S after complete removal of the cyst wall and curettage. (F) Filling the extraction socket with bone graft materials. (G) Covering the bone graft with a collagen membrane. (H) Surgery site after gingival flap suturing.

Intraoral full-mouth dental radiographs revealed that the left mandibular canine tooth was horizontally unerupted into the left mandible, with severe alveolar bone loss similar to that observed in Case 1. A large radiolucent cyst with distinct margins was present around the left mandibular canine, with cystic infiltration into the alveolar bone of the left mandibular 3rd incisor, canine, and 1st premolar tooth. The size of the left mandibular cyst was 17.4 mm × 12.5 mm (Fig. 7A, B). Therefore, dental treatment was the same as in Case 1: rinsing the oral cavity with 0.12% chlorhexidine solution, teeth extraction, flushing the extraction socket with 0.9% N/S, complete cyst removal, curettage, GBR in the extraction socket, and gingival flap sutures (Fig. 6B-H). Post-operative dental X-rays confirmed that the teeth were completely extracted and the bone graft material was well positioned within the extraction socket (Fig. 7C).

Figure 7. Dental radiographs from Case 2. (A) Preoperative, extra-oral mandibular radiograph. (B) Preoperative, intra-oral left mandibular radiograph. (C) Postoperative, intra-oral mandibular radiograph. (D) Extraoral radiograph taken two weeks after surgery. Yellow dotted line area and white solid arrow: left mandibular dentigerous cyst. Blue area: alveolar bone loss area. Red solid arrows: 3rd incisor tooth and 1st premolar tooth. Yellow solid arrow: unerupted canine tooth. Yellow dotted arrow: extraction socket filled with bone graft materials. A preoperative dental X-ray revealed that the left mandibular canine tooth was horizontally unerupted into the left mandible, with severe alveolar bone loss. A large radiolucent cyst with distinct margins was present around the left mandibular canine, with cystic infiltration into the alveolar bone of the left mandibular 3rd incisor, canine, and 1st premolar tooth. The size of the left mandibular cyst was 17.4 mm × 12.5 mm. Post-operative dental X-rays confirmed that the teeth were completely extracted and the bone graft material was well positioned within the extraction socket. Two weeks after surgery, an extra-oral dental X-ray taken without general anesthesia confirmed that the bone graft material had filled and was maintained within the extraction socket.

The patient was discharged on the day of surgery and prescribed the same oral medications and oral cleaning gel as for Case 1, except that famotidine 0.5 mg/kg (Famotidine Tab. 20 mg Nelson, Nelson Korea) was used instead of misoprostol 3 μg/kg. The owner was also given the same instructions regarding the diet and cleaning of the mouth as in Case 1.

Two weeks after surgery, the patient showed no signs of dehiscence, redness, bleeding, or pain. An extra-oral dental X-ray taken without general anesthesia confirmed that the bone graft material had successfully filled and been maintained within the extraction socket (Fig. 7D). Six months after surgery, a gross oral examination revealed that the site where the cyst had been removed was found to be completely healed.

Conventional treatment for dentigerous cysts involves the extraction of the tooth associated with the cyst, complete removal of the cyst wall, curettage, and/or cyst marsupialization (10,27). There are two primary methods to regenerate the extraction socket with new bone after tooth extraction and cyst removal: spontaneous bone healing and GBR. Typically, the tooth extraction socket will heal naturally without the need for bone grafting (5,30). The blood clot left in the socket after suturing can serve as a natural scaffold or support. For this reason, some studies have suggested that bone grafting might not be necessary for tooth extraction sockets (5). However, the natural filling of the extraction socket can result in the irregular filling of bone within the cavity, a lack of support for adequate bone regeneration, and delayed bone filling (5,30). As such, if the surrounding alveolar bone has already been resorbed by the cyst, the natural healing process after tooth extraction can increase the risk of mandibular instability and fracture (11). In veterinary dentistry, the use of bone grafting is controversial because bone grafting for extraction sockets is either not considered essential (5) or its application has not been established (11). However, recent research in human dentistry has established that bone grafting accelerates bone healing and improves bone regeneration quality (29).

In the present study, both cases 1 and 2 were presented with gingival dark blue swelling on gross oral examination. They showed a cyst with fluid accumulation around the embedded canine tooth and significant buccal and lingual alveolar bone loss on dental radiographs. The cytology for Case 1 revealed no significant findings other than the presence of a small number of inflammatory cells. The findings on the skull radiographs and CT images for Case 1 were similar to those in the dental radiographs. Based on these examinations, both cases were diagnosed as dentigerous cysts.

On the dental radiographs, the dentigerous cysts measured 18.6 mm × 9.0 mm in Case 1 and 17.4 mm × 12.5 mm in Case 2. They had a higher tooth root-to-mandible size ratio. This case report led us to hypothesize that using GBR for two small-breed dogs could effectively reconstruct mandibular morphology and function in cases where there has been some degree of mandibular bone loss, and we considered applying GBR to two small-breed dogs. Compared to large-breed dogs, small-breed dogs have a congenitally higher tooth root-to-mandible size ratio (9,13), and when teeth in the mandible are extracted, the amount of alveolar bone remaining after extraction is low. Natural healing of large extraction sockets in small-breed dogs can thus be challenging due to a lack of structural support, leading to mandibular fractures or instability and limited or decreased bone regeneration due to patient aging or underlying disease. The case reported by Okuda (20), in which cystic cavities resulting from extensive bone resorption were filled with Perioglass^® in a dog, demonstrated a favorable prognosis. Therefore, using GBR appeared to be a suitable approach given the congenital characteristics of small dogs (9) and was expected to improve the prognosis for treating dentigerous cysts.

The GBR process employed both xenograft materials and collagen-absorbable membranes in these cases. Absorbable collagen membranes were used as barrier membranes to separate proliferative soft tissue from the slower-growing bone tissue, thus helping to maintain space for bone regeneration (21). Collagen membranes can also offer several advantages, including high biocompatibility, biodegradation, hemostatic function, wound stabilization and healing, and ease of manipulation and adaptation. Unlike non-absorbable materials, it does not require secondary surgery (14,25). For these reasons, we used an absorbable collagen membrane among the various barrier membranes. As a result, based on the results of several studies (2) and our previous experience, using a barrier membrane preserved the alveolar ridge more effectively than simple suturing. Normally specific suturing or screws can be used to secure the membrane, but in these cases, there was not enough remaining tissue to secure the membrane due to the large amount of tissue removed. Therefore, the bone graft was covered with the membrane and the flap was sutured as tightly as possible to minimize membrane movement. This method prevented the bone graft from migrating to other areas after surgery, supporting successful bone regeneration.

Bone graft materials in the surgical site help to maintain mandibular structure, promoting new alveolar bone formation, preventing volume loss and surface recession, and providing structural stability (31). When using GBR, it is important to choose the appropriate bone graft material; therefore, we used a porcine-derived bone graft. Xenograft materials that use sterilized bone derived from other animals such as cattle or pigs are more osteoconductive than allografts because they are absorbed more slowly, which promotes bone healing (1,8,11,12). Unlike autografts and allografts, xenografts do not require additional surgery to obtain bone materials from the patient's body, and they can be produced and used in large quantities at a low cost (12). Following recent research findings, we used porcine-derived materials instead of bovine-derived materials. Compared to bovine-derived bone graft materials, porcine-derived bone graft materials have most of the key physiochemical characteristics such as greater porosity, rougher granule surface, and higher wettability (3,7,12,24). As a result, porcine-derived materials were utilized, resulting in easier surgical manipulation, well-filled graft materials into the roots, and positive clinical outcomes.

Bone grafting may be limited in cases of preoperative active infection, severe periodontal disease (6,9,13,16,22), malignancy or osteosclerosis around the lesion (13), and certain systemic conditions, such as diabetes, thyroid disorders, bone metabolism diseases (23), or autoimmune diseases (4). In Case 1, there was no evidence of severe periodontal disease during an oral examination or in dental radiographs. The FNA showed no bacteria but did reveal yellow serous exudate and a small number of inflammatory cells. The patient in Case 2 also had no evidence of severe periodontal disease during an oral examination or in dental radiographs. Generally, bone grafting is complicated by infection or inflammation. However, in two cases, the inflammation was not severe enough to restrict bone grafting. Therefore, the surgical sites in both cases were irrigated with normal saline several times before and after cyst wall removal and curettage before bone grafting was applied. Antibiotics and anti-inflammatory drugs were also prescribed to prevent further infection or inflammation at the bone graft site. Both patients were followed up for at least 6 months to evaluate the treated area, which healed successfully without complications such as additional infection, fractures, or cyst recurrence. This suggests that patients can be considered for GBR if cytology shows only mildly inflammatory cells or if periodontal disease progression is not severe.

The application of GBR for large bone defects caused by dentigerous cysts has rarely been reported. In this case series, positive clinical outcomes were obtained with GBR for large bone defects caused by dentigerous cysts; however, the small sample size, which affects the reliability of the results, precludes a detailed prognostic evaluation. Therefore, further studies are needed to compare the clinical outcomes of dentigerous cyst treatment with and without the application of GBR. Additional studies are also required to establish criteria for using GBR in defects due to dentigerous cysts in the following patient conditions: breed, skull/oral/tooth anatomy, the remaining alveolar bone status, mandibular stability, the size ratio of the root to the mandible, existing oral issues, and preoperative cytology results of the cystic fluid (especially in the inflammatory and infectious conditions).

This case report presents dentigerous cysts associated with the left mandibular canine tooth in two small-breed dogs. There have been very few case reports of GBR used in the treatment of dentigerous cysts in dogs in Korea. However, we used bone xenograft materials and absorbable collagen membranes for GBR. In both cases, the clinical prognosis was very good. In conclusion, these case reports are useful because they confirm that the proposed method represents an effective potential treatment for dentigerous cysts in small-breed dogs.

This study was financially supported by Chonnam National University (grant number: 2024-0172-01).

The authors have no conflicting interests.