The various classifications of FOL proposed by different authors are listed below.^[4]

1985 — Charles Waldron^[5]

1987 — Working classification by Mico M. Malek

1990 – Peiter J. Slootweg & Hellmuth Muller

1992 — World health organization (WHO) classification

1993 — Modified classification by Waldron

2001 — Brannon & Fowler classification^[6]

2005 — WHO classification of FOL^[7]

2006 — Paul M. Speight & Roman Carlos classification

2008 - Eversole classification

2017 – No specific modification

Classification of fibro-osseous lesions — WHO classification of FOL (2005)^[7]

Ossifying fibroma (OF)

Fibrous dysplasia

Osseous dysplasia

Periapical osseous dysplasia

Focal osseous dysplasia

Florid osseous dysplasia

Familial gigantiform cementoma

Central giant cell granuloma

Cherubism

Aneurysmal bone cyst

Solitary bone cyst

Osseous dysplasia also called as Cemento-Osseous dysplasia, Cemental dysplasia these are non-neoplastic fibro-osseous lesions of the tooth-bearing regions of the gnathic bones.^[5] There is formation of cementum like mineralized component.2 ([Figure 1])

There are 4 distinct forms

Focal cemento-osseous dysplasia

Florid cemento-osseous dysplasia

Periapical cemento-osseous dysplasia

Familial gigantiform cementoma

Focal cemento-osseous dysplasia is seen in middle-aged females commonly in mandibular molar region as an asymptomatic lesion small in size7 ([Figure 2])

Florid cemento-osseous dysplasia was first reported by Melrose et al in 1976. It is asymptomatic and commonly presents as multifocal lesion in posterior maxilla and mandible region. Mostly often affects mandible (bilaterally) in middle aged or older black women. It presents as dull pain and draining sinus associated with exposure of sclerotic bone.1 ([Figure 3]) Periapical cemento-osseous dysplasia (Periapical Cemental Dysplasia) It is present in apical region of vital mandibular anterior teeth as a solitary or multiple small lesions and exceed 1cm. It is asymptomatic, self-limiting, seldom lesion that expand the bone. ([Figure 4]) Familial gigantiform cementoma (Gigantiform cementoma) is a rare lesion first reported by Norberg in 1930. The term gigantiform cementoma, in as much as it implies a solitary process, is misleading because the condition typically resents as slow-growing, multifocal/multiquadrant and expansile lesions involving both jaws.12 It may arise from remnants of cementum which remain after extraction and is commonly seen in black females. It clinically presents as swelling of jawbones which lead to facial deformity, deposition of excessive cementum impairs vascularity of affected area, bone becomes susceptible to infection and complications like osteomyelitis may develop. It is inherited as an autosomal dominant trait. Lesions arise during childhood and progressively expand to cause facial deformity during early adult years.1,2,3

Radiographically appears as a radiolucent lesion in early stages, as the lesion starts to mature it shows radiopaque sclerotic border and mixed radiolucency - radiopacity. Fully mature lesions are radiopaque. It is restricted to the jaws and may arise in two, three or all four quadrants. The roots of the associated teeth are not affected and the lesion does not extend beyond the inferior alveolar canal or ramus though it crosses the midline of the jaws.1([Figure 5]) Histopathological features show hypercellular fibroblastic stroma with monomorphic appearing spindle shaped fibroblasts and collagen fibers, immature bone trabeculae and cementum like tissue dispersed throughout the lesion. The latter is formed of hypocellular basophilic and curvilinear structures resembling cementicles that are normally seen in the periodontal ligament.1,3 ([Figure 6])

The distinguishing features of types of osseous dysplasia are mentioned in [Table 1] Cementifying fibroma, Ossifying fibroma, or Cemento-ossifying fibroma

It is fibro-osseous neoplasm, i.e. it is a benign bone-producing fibrous neoplasm of the skeleton. Ossifying fibroma is a well-demarcated lesion composed of fibrocellular tissue and mineralized material of varying appearances.^[1]

Ossifying fibroma of the craniofacial skeleton are separated into two main clinicopathologic entities:^[8]

Ossifying fibroma of Odontogenic origin (Cemento-ossifying fibroma), and Juvenile ossifying fibroma Cemento-ossifying fibroma (COF) synonymously called as Ossifying fibroma or Cementifying fibroma affects the tooth bearing areas of the mandible and maxilla. It is believed to be derived from the progenitor cells of the periodontal membrane which are capable of dual differentiation into fibroblasts, osteoblasts, and cementoblasts. Clinically it appears as a painless expansion of the jaws, particularly the mandible in individuals in the 3rd & 4th decades of life with a definite female predilection.^[1]

The radiographic appearance shows well-defined and unilocular radiolucency which may be completely radiolucent or may show various degrees of opacification depending on the amount of calcified tissue present. In the mandible, larger lesions tend to expand inferiorly producing a characteristic downward bowing and thinning of the inferior border. Displacement of surrounding teeth and root resorption may be seen.2

Histopathologically the lesion is well-defined and may be encapsulated, showing hypercellular fibroblastic stroma with sparse collagen fibers and blood vessels, and containing variable amounts of calcified structures. Stromal fibroblastic cells show hyperchromatic nuclei. Calcified structures are composed of variable amounts of osteoid or bone and lobulated basophilic masses of cementum-like tissue resembling the cementicles that are normally found in the periodontal membrane. These structures may coalesce and form curvilinear trabeculae which may be acellular. Osteoblastic rimming of the bone trabeculae is evident. The cementum-like tissue is often woven and may show a characteristic quilted pattern.1,2 ([Figure 7])

Juvenile ossifying fibroma ([Table 2])

Its 2 forms are

Juvenile trabecular ossifying fibroma (JTOF)

Juvenile psammomatoid ossifying fibroma (JPOF)

Ossifying Fibromas Associated with Systemic Genetic Disorders

A group of benign fibro-osseous lesions affecting the jaws and microscopically described as ossifying fibromas or cemento-ossifying fibromas are manifestations of systemic genetic disorders. These are rare and not very well defined conditions.

Ossifying Fibromas Associated with Systemic Genetic Disorders are — 8

Hyperparathyroidism-jaw tumor syndrome

Familial gigantiform cementoma

Gnathodiaphysial dysplasia/fragile bone syndrome with fibro-osseous jaw lesions Hyperparathyroidism — Jaw Tumor Syndrome (HPT-JT) is an autosomal dominant syndrome with high but incomplete penetrance and variable expression, characterized by primary hyperparathyroidism (PHPT) with multiple parathyroid adenomas occurring at an early age with increased risk for parathyroid carcinoma, fibro-osseous jaw lesions and renal cysts or tumors. Jaw tumors occur during adolescence or early adulthood and they persist and may grow after parathyroidectomy and restoration of a normal serum parathyroid hormone level. Mutations in the HRPT2 gene have been reported to be associated with the occurrence of these lesions. The lesions are more common in mandible, occurring bilaterally and affecting the tooth bearing areas and may extend into the mandibular ramus. It is expansive, lytic lesions that may be unilocular or multilocular. It may be radiolucent, radio-opaque or a combination. Resorption of roots of the affected teeth is noted.

Histopathological features shows well-defined but unencapsulated and it is identical to COF. It composed of hypercellular fibroblastic stroma containing variable amounts of calcifying structures that may form woven bone trabeculae or cementum-like structures. Treatment is surgical.^[8]

Familial Gigantiform Cementoma (FGC): FGC is a rare form of ossifying fibroma. Gigantiform cementoma is a rare, benign fibro-cemento-osseous disease of the jaws, seen most frequently in young girls. It is also included in this type of lesion.^[5]

Gnathodiaphysial Dysplasia (GDD): It was first coined by Riminucci et al. Described as cemento-ossifying fibromas of the jaws associated with multiple fractures, bowing and cortical thickening of the tubular bone. It is a gigantiform cementomas associated with extragnathic skeletal abnormalities. Bone abnormalities are variably described as osteopenia, osteogenesis imperfecta, fragile and brittle bone. It is an autosomal dominant generalized skeletal syndrome. GDD1 gene, also known as TMEM16E or anoctamin 5 (ANO5) is mapped to a locus on chromosome 11p14.3–15.1. Two missense mutations (C356R and C356G) in GDD1. Radiographic features are expansive radiolucent with radiopaque areas. It affect both maxilla and mandible bilaterally. It shows multiple sclerotic areas of the tooth- bearing areas of the jaws or as a unilateral expansive multilocular lesion. The extragnathic bone shows osteopenia, demineralization, trabecular coarsening, diaphysial cortical thickening and bowing of the femora and tibiae. Histopathological features shows. Cemento- ossifying fibromas with immature bone and lobulated calcified masses in cell rich fibroblastic stroma. Treatment is surgical.^[8], ^[9], ^[10], ^[11], ^[12], ^[13], ^[14], ^[15], ^[16], ^[17]