Ⅰ.INTRODUCTION

The dentigerous cyst is defined as a cyst that originates by the separation of the follicle from around the crown of an unerupted tooth. The dentigerous cyst encloses the crown of an unerupted tooth and is attached to the tooth at the cementoenamel junction. The pathogenesis of this cyst is uncertain. Although dentigerous cysts may occur in association with any unerupted tooth, most often they involved mandibular third molar. Other relatively frequent sites include maxillary canines, maxillary third molars, and mandibular second premolars¹⁾.

Although dentigerous cysts may be encountered in patients over a wide age range, they are discovered most frequently in patients between 10 and 30 years of age. There is a slight male predilection. Dentigerous cyst can grow to a considerable size. Many authors believe that dentigerous cyst continue to enlarge as a result of increased osmotic pressure within the lumen of the cyst. Large cysts may be associated with a painless expansion of the bone in involved area. Extensive lesions may result in facial asymmetry¹⁾.

The usual treatment for a dentigerous cyst is enucleation of the cyst together with removal of the unerupted tooth. Large dentigerous cysts also may be treated by decompression. This permits decompression of the cyst, with a resulting reduction in the size of the bone defect. The decompression by making a small opening into the cyst and inserting a stent, or drainage tube, can result in substantial reduction in the size of the cyst. This is recommended to decrease the size of the cyst to take it away from important structures such as teeth and the inferior alveolar nerve and to reduce the chance of a pathologic fracture or bony discontinuity with definitive treatment. With this decompression technique, subsequent enucleation of the smaller lesion is then usually performed²⁾.

These cases are large dentigerous cysts treated by decompression thereafter enucleation. Less extensive surgical procedures were used and some teeth were preserved.

Ⅱ.CASES REPORT

1.Case 1

A 35-years-old man visited in oral and maxillofacial surgery department in the different hospital. In past dental record and history he had a large cystic lesion in the right side of the mandible extending from the right third molar to first molar region with unerupted right mandibular third molar (Fig. 1). In the axial computed tomography (CT) scan, a well-defined intrabony cystic lesion was found with expanded and thinned buccal and lingual cortical bones (Fig. 2).

He had been treated by decompression with Penrose drain under local anesthesia in the hospital. Cyst enucleation was planned. But he moved in our city so he visited our oral and maxillofacial surgery department. The day of visit, in clinical examination there was a Penrose drain in the buccal gingiva of the right first molar. The diagnosis of cystic lesion was dentigerous cyst in histologic examination. In panoramic view the size of cyst was not changed but radiopacity was more increased compared with previous panorama (Fig. 3). Electric pulp test(EPT) for mandibular right first molar was positive at 5 scales and second molar was positive at 6 scales.

He wanted to be continued the treatment of decompression. That day, he was treated by drain change with 6mm Penrose drain under local anesthesia. After about 3 months, dental CT was taken. CT finding showed that bone healing was improved and cystic cavity was replaced with bony material (Fig. 4). We decided to continue the treatment of decompression for 2-3 months. Cystic lesion was more decreased and cystic cavity replaced by bony material. About 3 months later, cyst enucleation and extraction of #48 were done under local anesthesia. Healing was improved on operation site. After 4 months clinical result was good(Fig. 5). Electric pulp test for mandibular right first molar was positive at 2 scales and second molar was positive at 9 scales. Root canal treatment of #46, 47 was not required. Teeth of vitality of #46, 47 were retained.

2.Case 2

A 17-years-old man visited in our oral and maxillofacial surgery department. He complained of swelling on right middle face. The swelling was begun a week ago. There were pain, palpation and tenderness on right buccal area. The mobility of first and second right upper molar was three degrees. In panoramic view there was a large cystic lesion in right maxillary sinus and severe bone resorption on first and second right upper molar area. In the coronal CT scan there was a large cystic lesion in right maxillary sinus. The cystic lesion expended to lateral wall of right maxillary sinus and lateral nasal wall. Severe bone resorption was at lateral wall of right maxillary sinus, lateral nasal wall and apical area of right upper molar. Right upper 3^rd molar was displaced upwards (Fig. 6). Root resorptions of #16, 17 were found on the CT image.

A provisional diagnosis was dentigerous cyst as incisional biopsy and decompression were done with Penrose drain under local anesthesia. Dentigerous cyst was diagnosed by pathologic examination. Decompression on the cyst continued for three months. After three months follow-up CT was taken and in CT image the size of cystic lesion was decreased considerably and the right upper 3^rd molar was more displaced downwards than the previous location. Extraction of #17 tooth was planned because of insufficiency of supporting alveolar bone. Preoperative Electric pulp test of #15, 16 tooth were negative finding when endodontic treatments of #15,16 were done. Cyst enucleation and teeth extraction of #17, 18 were done under general anesthesia. At postoperative 8 months the lesion was completely healed on CT image(Fig. 7). Extraction of #16 tooth had been expected preoperatively but postoperative healing was good and regeneration of supporting alveolar bone was found and the tooth was preserved(Fig. 8).

Ⅲ.DISCUSSION

The usual treatment for a dentigerous cyst is enucleation of the cyst together with removal of the unerupted tooth. If eruption of the involved tooth is considered feasible, the tooth may be left in place after partial removal of the cyst wall. Patients may need orthodontic treatment to assist eruption¹⁾.

Large dentigerous cysts also may be treated by decompression. This permits decompression of the cyst, with a resulting reduction in the size of the bone defect¹⁾. The decompression by making a small opening into the cyst and inserting a stent, or drainage tube, can result in substantial reduction in the size of the cyst. This is recommended to decrease the size of the cyst to take it away from important structures such as teeth and the inferior alveolar nerve and to reduce the chance of a pathologic fracture or bony discontinuity with definitive treatment. With this decompression technique, subsequent enucleation of the smaller lesion is then usually performed²⁾. These cases were large dentigerous cysts treated by decompression before enucleation. Less extensive surgical procedures were used and some teeth were preserved.

The decompression of odontogenic cystic lesions has been widely used as a more conservative treatment, which requires a much smaller window, by creating an opening into the cystic cavity and by suturing a device (ie, tube, stent) to its periphery^2-4), compared with marsupialization. The cyst can then be enucleated at a later date with a less extensive surgical procedure and important structures such as teeth and the inferior alveolar nerve can be preserved. This procedure can release the intramural pressure, favor the formation of new bone tissue, and develop fewer complications than enucleation, curettage, and resection, but there is the necessity for more frequent follow-up.^5-7) sometimes patients complain about more frequent follow up which bother patients and physician. But the Advantages which are less extensive surgical procedure and the preservation of the important structures such as teeth and the inferior alveolar nerve are more valuable. In case 1 the teeth of #46, 47 were preserved without root canal treatment. Teeth of vitality of #46, 47 were retained. It was excellent outcome and the cost was saved.

In case 2 if cyst enucleation was treated first #16 tooth was removed because of the poor prognosis. But decompression was treated first and then regeneration of supporting alveolar bone was found and the tooth was preserved. In children the loss of the permanent molar teeth is a severe complication. This situation can lead to many problems which are a difficulty of mastication and a growth disturbance of alveolar bone and jaw. And the cost which is for rehabilitation will be expensive. In this case the result was excellent and the cost was more saved.

A cyst is a pathologic cavity in the soft tissue or bone with an outer wall composed of connective tissue and an inner wall composed of epithelium. The cavity has a watery, semisolid, or colloidal content. Cysts gradually enlarge owing to a combination of osmotic pressure and release of growth factors and prostaglandins^8,9). This persistent pressure exerted on the bony walls coupled with biomolecules cause bone resorption while the entity expands. Therefore, mitigating the pressure by making a small window into the cyst and keeping it open guarantees permanent drainage, thus preventing its enlargement. Eventually, bone growth will reduce the space¹⁰⁾. This applied physical principle was the rationale that Polish professor Carl Franz Maria Partsch used to introduce the concept of cystostomy in 1892 and cystectomy in 1910. Today, cystostomy is known as Partsch I or marsupialization, a term from the modern Latin marsupialis, from the Latin for the Greek marsupion, meaning ‘‘pouch.’’ Cystectomy(Partsch II) is enucleation and primary closure¹⁰⁾. Expanding on Partsch’s concept, Thomas¹¹⁾ described decompression in 1947. Thomas pointed out its benefits, which were maintenance of pulp vitality, preservation of the inferior alveolar nerve or maxillary sinus, prevention of fracture of the jaw, and low risk of recurrence¹⁰⁾. In 1991 an article by Brøndum and Jensen¹²⁾ paved the way for the reintroduction of marsupialization and decompression. In 1996 Marker et al⁷⁾ successfully decompressed 23 odontogenic keratocysts using small polyethylene tubes. They concluded that decompression resulted in new bone formation, thickening of the cyst wall, and conservation of bone and anatomic structures. Despite such optimistic results, from the literature review it seems that it was not until the early 2000s that marsupialization and decompression regained the attention of surgeons and pathologists, much at the urging of Pogrel^12,13).

Decompression has been considered an effective treatment for odontogenic cystic lesions to minimize cyst size^7,14). Some materials which are tube such as Penrose drain or plastic stent are used for decompression procedure. The decompression which requires a small window creates an opening into the cystic cavity and devices such as tube or stent are sutured to its periphery^2-4). In 2007 Huang et al¹⁵⁾ described a decompression plug for ameloblastomas. This plug, which is basically the same as that described by Marker et al7 was effective in decreasing tumor volume and minimizing the extent of surgery. The following year, Tolstunov¹⁶⁾ used a catheter for the same purpose. One of the drawbacks of decompression is the size of the tube, which could be dislodged over time. A stent fixation method, using 1.2-mm screws was proposed in 2012 by Swantek et al.¹⁷⁾ If retention is gotten by adjacent tooth plastic stent can be used. In 2014 Gao L et al reported decompression as a treatment for odontogenic cystic lesion of the Jaw¹⁸⁾. In the study a total of 32 patients with odontogenic cystic lesion of Jaw underwent decompression with customized thermoplastic resin stents. They concluded that the decompression was effective in reducing odontogenic cystic lesions of the Jaw and increasing bone density. In a case of lack retention elastic tube such as Penrose drain are usually used with suturing. Penrose drain was used with suturing in present cases.

In conclusion decompression can be considered an effective treatment for large odontogenic cyst to minimize cyst size. And then the cyst can be enucleated at a later date with a less extensive surgical procedure and important structures such as teeth and the inferior alveolar nerve can be preserved. The benefits of the method have been described and proved over the years, and as patients and surgeons become less aggressive. Decompression will become more popular when indicated. Cases must be carefully selected and the surgeon should consider many factors, such as patient age, type of lesion and time of evolution, and the patient’s cooperation.