3. Discussion
Gardner described POdF in comparison with central odontogenic fibroma and histopathologically separated it into peripheral ossifying fibroma.5 POdF is a rare odontogenic tumor with gradual growth consisting of a hard, elastic, smooth gingival mass.1,3,4
The onset age of POdF is 5 months to 84 years, and there is seemingly a predominant peak in middle age, specifically, during patients’ forties.1,2,6,7 The most common sites to develop POdF are known to be the anterior maxilla and mandible in adults, while some reports show that POdF also occurs frequently in the mandibular canine to premolar region.7,8 A total of 25 reports of POdF occurring in patients younger than 19 have been published, of which, 12 reported POdF development in the mandible (Table 1).6,7,9–18 Among those, two cases, including the present case, reported POdF occurring in the mandibular premolar region of teenagers.10
Histopathologically, POdF is characterized by odontogenic epithelium scattered to various degrees in the fibrous substrate.3,5,7 Moreover, bone-like, dentin-like, or cementum-like hard tissue formation is observed, and it is classified into epithelium-poor or epithelium-rich type according to the degree of content of the dentin epithelium.19 Regarding the hard tissue inside the lesion, bone-like and cementum-like hard tissue formation have a reported frequency of 28.3% and 15.2%, respectively.6 In the present case, a region was described histopathologically as rich in cellular components as well as a mixture of small mass and cord-like epithelial components similar to Marasse’s epithelial remnants and Hertwig epithelial sheath. Moreover, bone-like calcification was observed in the deep areas of the tumor.
In this sense, there are so far only four reports of POdF with hard tissue inside the lesion among teenagers.17 Although few reports have been published on hard tissue formation in POdF, it has been suggested that the odontogenic epithelium inside the lesion may induce hard-tissue formation, which requires a lengthy time to develop in teenagers.17 Thus, it has been speculated that the frequency of calcification in POdF might be low.
Some reports of CK-positive cells in the odontogenic epithelium of POdF exist.20 In the present case, CK19-positive epithelial components resembled Marasse’s epithelial remnants and Hertwig epithelial sheath.
POdF was hypothesized to originate from the periodontal ligament, tooth sac, and dental papilla.17 Central odontogenic fibroma originates from the periodontal ligament or tooth sac according to the 2005 World Health Organization classification, while other authors have reported the possibility of periodontal ligament origin as well.19 We considered periodontal ligament or tooth sac as the origin of the tumor described here for the following reasons: the tumor was observed during the tooth-replacement period, tumor growth was observed from the neck of the adjacent tooth, fibroblast growth around the tumor did not resemble that of dental papilla, and Marasse’s epithelial remnants and Hertwig epithelial sheath-like cells were observed.
The rate of POdF recurrence after surgery is reportedly low.17,21 However, some studies have reported an early recurrence rate of 50% (29/58 cases).2,22,23