The ossifying fibroma (OF) was firstly named by Montgomery in 1927. In 1972, WHO classified the ossifying fibroma as a bone derived tumor, while the cementifying fibroma as a subtype of cementoma, however, both of them were then reclassified by WHO in 1992 as one type of bone derived tumor, the cemento-ossifying fibroma. But in 2005, WHO had renamed the cemento-ossifying fibroma as ossifying fibroma (OF) again, and which was reclassified as three subtypes: the COF, the JTOF and the JPOF. In this study, the 55 cases of OF included: OF 70.9%, JPOF 20.0%, JTOF 5.5%. JTOF was relatively rare.
There are different mean age between the three subtypes. The mean age of the occurrence of COF is 35, while the age is younger in JPOF. The age of onset of JTOF is younger, the mean age of JTOF is 8.5–12. The range of age of JTOF is relatively wide, 62.8% patients of JTOF is diagnosed between 5–15, but there still reports about JTOF patient at the age of 80. The latest research showed that the mean age of the patients with JPOF (18. 9 ± 12.0 years) was significantly higher than that of the patients with JTOF (11.5 ± 6.0 years). In this study, of the COF patients, the female between 30 and 40 also took up a relatively high proportion, it was almost consistent with previous reports. However, in JPOF patients, the female patients were a little more than the males. It was a little different from the previous reports that some researches showed that male patients was a little more than the females[8, 9]. The real adolescent OF is the JTOF, varied between 11 ~ 17, the male (2/3,66.7%) inclination made it different with the two other subtypes.
The three subtypes of OF also have characteristics of the sites.COF always occurred in the posterior of mandible supporting teeth and frequently in females. According to previous studies, JPOF occurred more frequently in the fronto-naso-orbitoethmoidal region than OF, which predominantly affected the jaws, with a slight predilection for the maxilla. Some cases that mainly affected the maxillary sinuses also affected the ipsilateral nasal cavity or the orbit. It was reported in the literature that the paranasal sinuses (70% in the paranasal sinuses, followed by 20% in the maxilla and 10% in the mandible) were the most common sites. In this study of JPOF, 55.5% patients in the maxillaries, and 36.4% patients involved the para-nasal sinus. JTOF almost occurred in the jaw bone only, 50% in the maxilla, 44% in the mandible and 6% involved the para-nasal sinus[8, 9, 12]. However, in this study, 66.7% JTOF occurred in the mandible. In addition, we found 2 cases of multi-lesion (2/55,3.6%), one involved both the maxilla and mandible, and the other one involved the two sides of mandible.
The imaging features of OF present different imaging findings according to its stage of development. The OF display X-ray transparent shadow with low density, the mixed shadow containing both the transparent and opaque region or the X-ray opaque high density changes. Consistently, most cases in this study exihibited the sclerotic fringe surrounding mixed shadow with definitely borderline, but the lesion in the maxilla displayed confused borderline because of the neighbouring bones. 1(1/55,1.8%) cases exhibited the cortical destruction in the mandible, it can be identified from the FD which rarely display the cortical destruction. The growth of OF always results in the impede of tooth eruption, displacement and loss, but the root absorption is relatively rare[14, 15]. It was consistent with previous studies in which 17%-33% of OF occurred displacement and 10%-44% occurred root absorption[1, 15, 16]. In this study, 10 cases (10/55,18.2%) of OF displayed tooth displacement, 5 cases (5/55,9.1%) exhibited absorption in amputated type. However, in our experience, there was no report showed that root absorption in amputated type in FD. Whether root absorption in amputated type can be differentiated from the diagnosis of OF and FD requires further investigation. The mechanism of the root absoption of OF perhaps is similar to the ameloblastoma, as a real tumor, cause the tooth displacement, absorption and the destruction of canales mandibulae.
The clinical treatment of OF always has been controversial, the surgery of OF is determined by its size and region, mainly includes conservative curettage and extended resection. The completed resection is necessary to prevent relapse, while the bone transplant help to restore aesthetics and function. Slootweg et al. investigated no difference between conserved and radical treatment[19, 20]. When the patient was young, the majority of scholars suggested conservative treatment instead of radical resection until the complete development of the maxillofacial region[1, 3, 21, 22]. In this study, 10 cases (10/32,31.3%) of OF suffered relapse after curettage, for relatively younger age and large size of tumor. There was significant difference between the two surgical methods (P༜0.05).The first surgery of extended resection seemed important to prevent the relapse of OF.
With the onset of OF, there are also some changes in the serum level of ALP. The bone metastasis of tumor would result in the imbalance of bone absorption and formation. Correspondingly, the serum level of ALP, Ca and IP change. The bone alkaline phosphatase (BALP) is a glycoprotein secreted by mature osteoblasts, BALP could be hydrolyzed and connected with Phosphatidylinositol and polysaccharide then embed into cell membrane before being released into blood as ALP. As the osteoblast developing into osteocytes, the ALP decomposes organophosphorus compound into phosphate, which combines the Ca2+ form hydroxylapatite and then result in the bone mineralization with the help of osteocalcin(OCN). The up-regulation of serum ALP always suggests the attenuation of bone mineralization as a result of the stasis of osteoblasts. We investigated 7 cases (7/55,12.7%) of OF exhibited increased ALP, which concentrated in childhood and adolescent. Chi-square Test for ALP level showed that there was significance between the age groups(P < 0.05). The younger the patients were, the higher increased rate of ALP. It suggested the osteoblasts differentiation actively in the adolescent OF patients.
OF needs to be differentiated from FD, OD and HPT-JT. As the Benign Fibro-Osseous Lesions (BFOL), the OF, FD and OD exhibit similar pathological, imageological and clinical characteristics, but different treatment. Comparing with FD, first of all, the OF displays clear or sclerotic fringe, while the FD exhibits inconspicuous lesion which fuses with normal bone; secondly, the OF containing bone trabecula is surrounded by osteoblasts, but the FD containing immature trabecula surrounded by fibrous tissue without osteoblasts; finally, the OF always causes the tooth displacement, distortion of dental arch as well as the bulge of the jaw bone; however, the FD patient could maintain the shape of dental arch despite of thin cortical bone, and there is little tooth absorption. In addition, the mutation of GNAS gene in FD is frequent, as a cause of FD, the GNAS mutation could be used as an identification for FD and other fibrous-osseous diseases.OF also requires differential diagnosis with OD. OD is one type of non-tumorous fibrous-osseous disease, it always appeared in mandibles and associated with the root of tooth. Summerlin et al. described it as X-ray transparent-opaque mixed image with amorphous and wide range; the surgery sample was difficult to be separated from the bone and easily to be bleeding. The classical imageological exhibition of OD is that the high density fringe surrounds the mass of relatively low density, which is associated with the root of tooth; the connective tissue contains irregular bone like or cementum like masses, sparse collagen fiber scatters within the cementum mass and trabecula.The Hyperparathyroidism-jaw tumor syndrome (HPT-JT) is a autosomal dominant inherited disease, the patient displays hypercalcemia and high parathyroid hormone, the parathyroid adenoma, the lesion in the jaw and the cyst of kidney are common clinical symptoms. 25–50% HPT-JT patients have the ossifying fibroma[28–30], but the high level blood calcium and parathyroid hormone are the main identification of the syndrome and sporadic OF. Once the patient has been diagnosed as HPT-JT, it would better to excise the parathyroid to avoid parathyroid adenoma[31, 32].
The majority of sporadic OF are single lesions, multi-lesions are rare. The ratio of multiple lesions of OF cases is unclear, but we have found only 2 cases (3.6%) in 55 cases (Fig. 2–3). Also we have reported another two multiple cases in previous research. Sporadic multiple OF need to be differentiated from HPT-JT. In this study, the level blood calcium (2.51 mmol/L,2.29 mmol/L,2.15–2.55 mmol/L) and parathyroid hormone (21.53 pg/ml,49.70 pg/ml,15–65 pg/ml) of the two multiple cases were normal. Recently, the candidate tumor suppressor gene HRPT2 then as CDC73 have been identified in chromosome 1q24-q32, enconding a novel protein of 531 amionacids named parafibromin. Some studies show that Germline mutations and somatic inactivation of CDC73 are associated with HPT-JT and sporadic carcinoma and adenomas of parathyroid[4, 34]. Alterations in the tumor suppressor gene CDC73 in ossifying fibroma have recently been reported. In one series, which included four cases with OFs, mutations in CDC73 were found in two of the cases, suggested that CDC73 might be a key factor in the etiology of OFs. Howerver,Yan Chen et al. found that two somatic mutations were identified in 40 cases of OF (5%). The mutations of CDC73 of sporadic OF previously reported in the literatures were reviewed, and only 4 cases were identified the mutations of CDC73 (Table 7).These findings indicate that the CDC73 mutation is not common in the development of sporadic ossifying fibroma, and therefore may not be used as a marker for diagnosis. The effect of mutated CDC73 on sporadic OF needs to be studied further.