What Is Ossifying Fibroma

Overview

Benign tumours of the bones aren’t often discussed as their malignant counterparts. Many of them can be rare, and have a slow growth that makes them go unnoticed for a long time, and one example of this is ossifying fibroma.¹ This type of benign tumour arises from bone tissue, commonly affecting the jaws, and often causes a hard mass to grow over months or years.¹ There are a few conditions that have been associated with the development of ossifying fibromas, such as hyperparathyroidism². But what actually causes this condition? And how can you treat this tumour?

Types of ossifying fibroma

There are two types of ossifying fibroma: the central ossifying fibroma (COF) and the peripheral ossifying fibroma (POF). But what are the differences between them?

Firsty, the central variant is considered a fibro-osseous lesion by the World Health Organization (WHO), that is, a disease that affects bone and fibrous tissue, even though it very much behaves like a tumour.³ The COF arises from cells of the periodontal ligament: the periodontal ligament is a joining of fibres that connect the tooth’s roots to the alveolar bone.¹ These tumours can be further classified into three types, depending on the microscopic aspect:

• Ossifying fibroma: when the tumour is rich in osteoid (bone-like) calcification.¹
• Cemento-ossifying fibroma: when the tumour contains both bone-like and cement-like calcifications.¹ Cement is a type of hard mineralized tissue that covers the root of the teeth.
• Cementifying fibroma: when it is rich in cement-like calcifications.¹

Most cases of COF affect the mandible: it is estimated that 70-90% of tumours arise from the mandible.³ However, other cranial and facial bones can be affected, such as the maxilla, and the periorbital, frontal, ethmoid, sphenoid, and temporal bones.¹

The peripheral variant, however, is not a tumour but a reactive lesion: it occurs as a response to chronic inflammation and an irritant stimulus.⁴ This means that, once the stimulus is removed, the lesion tends to shrink or disappear completely, unlike a true tumour, which keeps growing regardless. Common known stimuli are plaque and dental calculus, maladapted fillings and crowns, and poorly adapted prosthetics or orthodontic devices.⁴ As the name suggests, it is a peripheral lesion, meaning that it arises from the growth and proliferation of peripheral cells from the gums.⁴ Most of the time, POF affects the anterior regions of the maxilla, near the incisors and canines.⁴

Causes

The true origins of COF are uncertain when it occurs sporadically: it is known that it forms through the proliferation of cells of the periodontal ligament.² However, some cases are not sporadic and are actually related to syndromes and genetic conditions:

• Hyperparathyroidism jaw tumour syndrome: this is a rare genetic disorder that causes a mutation of the CDC73 gene; this gene is known to be a tumour suppressor gene, meaning that it controls the cell cycle.² Losing control of the cycle means that cells can keep growing without being kept in check, even if they have been damaged; this syndrome can cause multiple COF tumours, and it also increases the risk of cancer of the parathyroid glands.²
• Familial gigantiform cementoma: is another condition that increases risk of multiple ossifying fibromas; although it isn’t clear which gene is affected, it is known that this disease is a genetic dominant condition that has variable expression, so different people can be affected in variable severity by it.² This disease causes multiple giant COFs that can cause severe facial deformity and it affects only the bones of the face.²
• Gnathodiaphysial dysplasia: is a disease caused by a mutation of the GDD1 gene; this gene regulates musculoskeletal growth, and it is present in normal cardiac and skeletal muscles, as well as in chondrocytes (cartilagenous tissue cells) and osteoblasts (cells that produce bone).² Besides causing multiple COF lesions in the jaws, this disease also makes bones all over the body more fragile and brittle, and more prone to fracture.²

POF lesions are usually associated with the presence of an irritant stimuli.⁴ This chronic stimulus creates an area of inflammation and the growth of bone tissue can be a response to the trauma, as hard mineralized tissues are more resistant than the normal gingival tissue.⁴ As previously stated, POF is not a real tumour, and removing the cause of inflammation can regress or even completely resolve the lesion.⁴ It can be quite similar to other reactive disorders, and differential diagnosis might be hard without a biopsy.⁴

Signs and symptoms

Most of the time, ossifying fibromas, especially central ones, can remain asymptomatic for months or even years.¹ Sometimes a tumour can be found accidentally when doing an X-ray for unrelated reasons.¹ COF is often noticed when there is:

• Swelling³
• Facial asymmetry³
• Paresthesia (loss of sensation or motor control of parts of the face)³
• Pain³
• Tooth mobility or exfoliation (loss)³
• Pus discharge, if infected³

As for peripheral ossifying fibroma, it is generally diagnosed much earlier: as it appears on the gum, it is hard for a patient not to notice it.⁴ It commonly presents as an asymptomatic hard mass, usually pink or reddish in colour, similar to the gum.⁴ However, this lesion can become ulcerated and cause the patient to feel pain.⁴

Diagnosis

Diagnosis of ossifying fibroma is done through a combination of factors. Clinical evaluation of the lesion and patient’s history, including family history (that can point to genetic syndromes related to ossifying fibromas or not), is important when formulating a diagnostic hypothesis.² Complementary exams like X-rays, CT scans and MRI scans are also extremely important, especially when dealing with central lesions, in order to determine the size, extension and precise localization of the tumour.¹

Ossifying fibromas usually present as well-defined, homogeneous lesions with a clear radiopaque (white) border.⁵ However, it is known that depending on the stage of the lesion, its aspect can differ: some of them can be entirely radiolucent (black) in an X-ray while others can present with a mixture of radiolucent and radiopaque areas as it mature, and some lesions can be entirely radiopaque (white)³. Unlike a malignant tumour that mostly destroys surrounding tissue, ossifying fibromas tend to expand the bone².

A biopsy is indicated to confirm the diagnosis.² Central ossifying fibroma is often encapsulated and there is a clear separation of the tumour from normal bone tissue.² Microscopically, COF usually has a mineralized matrix that can resemble either bone tissue or cementum tissue, with calcification patterns that resemble either one or both of these tissues.² There is also a fibrous component, the stroma, that serves to support and bring nutrients and oxygen to the tumour: this stroma is often rich in fibroblasts (cells that produce collagen fibres), and it permeates between the calcified areas.²

Peripheral ossifying fibromas can also present with areas of calcification.⁴ However, it also has a significant presence of inflammatory cells, indicating its reactive nature.⁴ Unlike other reactive lesions, there are no giant cells, epithelial cells, or odontogenic cells, and this helps differentiate between numerous other lesions.⁴

There are a number of conditions that can be similar to ossifying fibroma. A few differential diagnosis for COF are:

• Fibrous dysplasia⁵
• Adamantimoma⁵
• Osteoid osteoma⁵
• Osteofibrous dysplasia⁵
• Osteoblastoma²
• Juvenile ossifying fibroma²
• Osteosarcoma²
• Chronic osteomyelitis²

As for POF, other lesions should be considered:

• Peripheral odontogenic fibroma⁴
• Peripheral giant cell granuloma⁴
• Pyogenic granuloma⁴
• Irritation fibroma⁴

Management and treatment

Treatment usually consists of surgery for complete removal of the lesion.² Central ossifying fibromas usually need a larger clear margin, even though it is a benign tumour, to avoid recurrence: recurrence without clear margins has been reported to be as high as 80%, while with a larger margin this rate drops to something between 0 to 4%.³ This can happen because small lesions tend to have a well-defined capsule that separates the tumour from healthy tissue, while larger lesions usually lose the integrity of the capsule as the tumour grows and the cells infiltrate the surrounding tissue.³ In some cases, reconstruction of the bone with bone grafts is needed if the tumour is large.³

Peripheral ossifying fibroma is usually smaller than its central counterpart, but in some cases, it can grow quite large and be called giant POF; when this happens, it can start to push the teeth apart and even cause tooth mobility.⁴ It’s important to remove the trauma factor that caused the lesion to appear in the first place: scaling to remove plaque and dental calculus (tartar), satisfactory crowns and fillings, and prosthetic and orthodontic devices that fit well, among other measures.⁴ The treatment for larger lesions is also surgical, with complete removal of the lesion.⁴ Recurrence rates are usually up to 20%.⁴ 

Epidemiology

Ossifying fibroma most often affects patients between the ages of 20 and 40, but cases involving children and the elderly have been reported.¹ There is slight predilection from individuals assigned female at birth (AFAB).²

Summary

Ossifying fibromas are disorders that affect bone and fibrous tissues; there are two types, central ossifying fibromas (COF) and peripheral ossifying fibromas (POF). COF is a true tumour that arises from cells of the periodontal ligament (a conjunct of fibres that connect the tooth’s root to the alveolar bone), while POF is a reactive disorder that arises from inflammation due to chronic trauma to the gingiva, caused by poorly fitting prosthetics or orthodontic devices. 

COF can also be related to genetic disorders if there are multiple of them, and examples of diseases that can cause multiple ossifying fibromas are hyperparathyroidism jaw tumour syndrome, familial gigantiform cementoma and gnathodiaphysial dysplasia. Common signs and symptoms include swelling, pain, facial asymmetry, and loss of sensation (paresthesia). Diagnosis is made through a combination of clinical evaluation, complementary exams like X-rays and CT scans, and a biopsy. 

Possible differential diagnoses include other fibro-osseous disorders like osteofibrous dysplasia, bone tumours like osteoblastoma, osteoid osteoma and osteosarcoma, and osteomyelitis. For POF, other reactive disorders like pyogenic granuloma should be considered. Treatment consists of surgical removal of the lesion and removal of traumatic factors. Ossifying fibroma usually affects people between the ages of 20 to 40, with a slight preference for AFAB individuals.