OKC is a typical developmental cyst with a recurrence rate of 12 to 58.3% [2, 4, 14, 15]. The reasons for this wide range could be differences in the number of cases and the duration of observation, whether lesions with ortho- or para-keratinized epithelium were included, and whether lesions associated with basal cell nevus syndrome were included. The recurrence rate of 28.8% observed in this study was similar to the 30% observed in previous reports using more than 300 cases [16, 17]. Although, the exact reason for the high recurrence rate of OKC has not been established, it is thought to be due to incomplete removal of primary lesion with thin epithelial lining, the presence of satellite cysts, and epithelial remnants.
The average age at initial diagnosis was 33.1 years. While the range was wide (7 to 84 years), patients in the third and fourth decades accounted for almost 53% of all the cases. These results are similar to the results from previous reports of peak incidence between the second and fourth decades of life [18, 19]. In this study, the ratio of rate of incidence in male to female patients was 1.33:1.00. The rate of recurrence in male and female patients was 30.9% and 27.2%, respectively. However, there was no statistically significant difference in the incidence and recurrence rate by sex. Previously, various authors have reported male preponderance [20], no sex difference [21], and female preponderance [22] with reference to occurrence of OKC. Thus, sex-related incidence is controversial.
The primary lesion of OKC occurred in the maxilla in 34% of the cases, and in the mandible in 66% of the cases. A total of 63.2% of lesions occurred in the mandibular ramus and posterior region. Myoung and Hong reported that the recurrence rate in the mandible was higher than in the maxillary lesion [4]. In this study, the recurrence in the mandible was 30.9%, which was higher than the recurrence in the maxilla (24.7%), but there was no statistical significance (p = 0.283). The highest recurrence rate was observed in the posterior mandible (39.7%), and the lowest in the posterior maxilla (24.6%). The differences of recurrence rate between posterior mandible and posterior maxilla were more than 10%, but they were not statistically significant (p = 0.464). The reason for the highest recurrence rate in the posterior mandible is thought to be due to the incomplete resection of the tooth root and the presence of inferior alveolar nerve.
Among the 274 lesions, the size of 3 to 6 crowns was most common (111 lesions), followed by less than 3 crowns (109 lesions), and larger than 6 crowns (54 lesions). In previous reports, the rate of recurrence in relation to size has been controversial. Some researchers reported no correlation [4, 20]. However, in this study, the rate of recurrence increased as the size increased, and this was statistically significant. In addition to the size of the lesion, the rate of recurrence was higher in the multilocular lesions than in the unilocular lesions, which is similar to a previous report [21]. Therefore, if the lesion is multilocular or has a size larger than 6 crowns, a higher rate of recurrence can be predicted, and thus, a long-term follow-up is indicated.
In this study, it was observed that as the size of the lesion increased, the maxillofacial surgeon attempted decompression, followed by enucleation rather than immediately performing enucleation. No recurrence was observed in the cases when en bloc excision was performed. However, in 27.1% of the cases of enucleation and 35.8% of the cases of enucleation after decompression, recurrence was observed. When decompression is performed, the size of the cystic mass decreases, but the surrounding satellite cysts remains. The growth of these satellite cysts is thought to be the reason for higher recurrence [22].
It has been reported that recurrence of OKC occurred after a few decades [3], but many reports have reported that most recurrence occurs within an average of 5 years [2, 19, 23]. In this study, recurrence occurred at 57.5 months on an average. The median was 32.5 months postoperatively, which is similar with the previous study results. In this study, the fastest recurrence was observed about 7 months postoperatively, and the longest recurrence was 21 years after the initial operation. Of all recurring lesions, 74.3% occurred within 5 years after the first operation, and 94.8% occurred within 10 years after surgery. Since about 20% of recurring lesions occurred between 5 years and 10 years postoperatively, periodic follow-up of at least 10 years is indicated following enucleation of OKC. In particular, in the case of a recurrence, there is a tendency for repeated recurrence, so the authors think it is important to build a close follow-up plan.
Many treatment methods have been attempted to reduce this recurrence, such as the Carnoy’s solution [24], cryotherap y[25], and peripheral ostectomy, but no treatment modality, except en bloc excision, has led to a significant reduction in terms of rate of recurrence [16, 17, 26]. Research on target therapy and gene therapy in the future may develop new treatment methods to reduce the occurrence, growth, and recurrence of OKC. Until then, the maxillofacial surgeon should be aware that small-sized OKC is asymptomatic, thus most patients recognize the lesion only when swelling, facial deformation, and infection-related pain occurring due to increased lesion size. In addition, the patient’s tissue deficiency increases as the size of the lesion increases, and consequently, the rate of recurrence increases. Therefore, a regular periodic radiographic examination is necessary to identify the lesion before symptoms occur. The periodic follow-up is important to observe recurrence of OKC, but only few studies have been conducted to prevent recurrence itself. New treatment modalities, which can suppress recurrence, are indicated, such as gene therapy for the PTCH gene, smooth end receptors.
