An ameloblastic fibroma is a

fibroma Fibromas are benign tumors that are composed of fibrous or connective tissue. They can grow in all organs, arising from mesenchyme tissue. The term "fibroblastic" or "fibromatous" is used to describe tumors of the fibrous connective tissue. Wh ...

of the

ameloblast Ameloblasts are cells present only during tooth development that deposit tooth enamel, which is the hard outermost layer of the tooth forming the surface of the crown. Structure Each ameloblast is a columnar cell approximately 4 micrometers in ...

ic tissue, that is, an odontogenic

tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

arising from the

enamel organ The enamel organ, also known as the dental organ, is a cellular aggregation seen in a developing tooth and it lies above the dental papilla. The enamel organ which is differentiated from the primitive oral epithelium lining the stomodeum. The en ...

dental lamina The dental lamina is a band of epithelial tissue seen in histologic sections of a developing tooth. The dental lamina is first evidence of tooth development and begins (in humans) at the sixth week in utero or three weeks after the rupture of t ...

. It may be either truly

neoplastic A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

or merely

hamartoma A hamartoma is a mostly benign, local malformation of cells that resembles a neoplasm of local tissue but is usually due to an overgrowth of multiple aberrant cells, with a basis in a systemic genetic condition, rather than a growth descended fr ...

tous (an

odontoma An odontoma, also known as an odontome, is a benign tumour linked to tooth development. Specifically, it is a dental hamartoma, meaning that it is composed of normal dental tissue that has grown in an irregular way. It includes both odontogenic ...

). In neoplastic cases, it may be labeled an ameloblastic fibrosarcoma in accord with the terminological distinction that reserves the word ''

'' for benign tumors and assigns the word ''

fibrosarcoma Fibrosarcoma (fibroblastic sarcoma) is a malignant mesenchymal tumour derived from fibrous connective tissue and characterized by the presence of immature proliferating fibroblasts or undifferentiated anaplastic spindle cells in a storiform ...

'' to malignant ones. It is more common in the first and second decades of life, when odontogenesis is ongoing, than in later decades. In 50% of cases an unerupted tooth is involved.

Histopathology Histopathology (compound of three Greek words: 'tissue', 'suffering', and '' -logia'' 'study of') is the microscopic examination of tissue in order to study the manifestations of disease. Specifically, in clinical medicine, histopatholog ...

alone is usually not enough to differentiate neoplastic cases from

tous ones, because the

histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology that studies the microscopic anatomy of biological tissue (biology), tissues. Histology is the microscopic counterpart to gross anatomy, which looks at large ...

is very similar. Other clinical and radiographic clues are used to narrow the diagnosis.

Clinical Features

Ameloblastic fibroma is a rare benign mixed

epithelial Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...

and

mesenchymal Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood, or bone. The interactions between mesenchyme and epithelium help to form nearly ever ...

odontogenic tumour as it contributes to approximately 2% of all odontogenic tumours. It often occurs in the first or second decade of life. Ameloblastic fibroma usually appears as painless swelling of the jaw in the posterior region of the

mandible In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

. It can be associated with an impacted tooth and it might impede eruption of other teeth. The lesion can be asymptomatic when it is small and most are incidental findings of routine dental radiographic imaging, etc.

Diagnosis

Radiographic Features

Radiographically, ameloblastic fibroma has a variable appearance. It can appear as a unilocular lesion with smooth, well-defined margin when smaller. However, it can be multilocular when it is enlarged. It can be mistaken as

dentigerous cyst A dentigerous cyst, also known as a follicular cyst, is an epithelial-lined developmental cyst formed by accumulation of fluid between the reduced enamel epithelium and the crown of an unerupted tooth. It is formed when there is an alteration in ...

as the lesion is often associated with an impacted tooth.

Histopathology

The histopathology of ameloblastic fibromas resembles the stages of normal tooth development. These mixed lesions consist of histologically distinct epithelial and mesenchymal tissues. The epithelial tissue resembles dental lamina and enamel organ tissues, while the

mesenchyme Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood, or bone. The interactions between mesenchyme and epithelium help to form nearly ever ...

resembles the

dental papilla In embryology and prenatal development, the dental papilla is a condensation of ectomesenchymal cells called odontoblasts, seen in histologic sections of a developing tooth. It lies below a cellular aggregation known as the enamel organ. The ...

. The

component features strands which branch and join, or

anastomose An anastomosis (, : anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf veins, or streams. Such a connection may be normal (su ...

. This results in knots of differing mass, resembling islands in a loose stroma. Cells in the strands tend to be cuboidal, but where budding occurs from the strands the knots resemble tooth caps. The bud-cap stage of normal development shows

s forming palisades of

columnar cells Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...

adjacent to a starry-like, loosely formed layer known as

stellate reticulum In animal tooth development, the stellate reticulum is a group of cells located in the center of the enamel organ of a developing tooth. These cells are star-shaped (hence ''stellate'') and synthesize glycosaminoglycans. As glycosaminoglycans ...

. However, the pattern of budding strands is distinctive from normal development. The Ameloblastic Fibroma epithelial tissue could be confused with the most common odontogenic tumour, the

Ameloblastoma Ameloblastoma is a rare, benign or cancerous tumor of odontogenic epithelium ( ameloblasts, or outside portion, of the teeth during development) much more commonly appearing in the lower jaw than the upper jaw. It was recognized in 1827 by Cusa ...

. Therefore the mesenchymal component is histologically important in differential diagnosis. The mesenchymal stroma in normal development is a rich myxoid connective tissue. It gives rise to the

dental follicle Dental may refer to: * Dental consonant, in phonetics * Dental Records, an independent UK record label * Dentistry, oral medicine * Teeth See also * * Dental care (disambiguation) * Dentist (disambiguation) * Tooth (disambiguation) A tooth (: t ...

which encapsulates the developing tooth. In Ameloblastoma the stroma is mature, often fibrous. This is distinct from the mesenchymal element of Ameloblastic Fibroma which is devoid of

collagen Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...

. The Ameloblastic Fibroma stroma remains primitive, undifferentiated, cell-rich and myxoid. Rarely, it may contain granular cells. However, this may also be observed in a hyperplastic dental follicle, and therefore other histological and radiological diagnostic features should be observed. The malignant ameloblastic fibroma will have features of malignant transformation such as mitotic figures in either

tissue. There is a resemblance to

. The malignant Ameloblastic Fibroma histologically shows transformation in the mesenchymal component with increased cellularity, accompanied by a progressive reduction in epithelial tissue.

Classification

An ameloblastic fibroma is classified by The World Health Organisation as a benign mixed odontogenic tumour. It develops from the dental tissues that grow into teeth. During human development, embryonic cells of

ectoderm The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from the o ...

and

produce

and

ectomesenchyme Ectomesenchyme has properties similar to mesenchyme. The origin of the ectomesenchyme is disputed. It is either like the mesenchyme, arising from mesodermic cells, or conversely arising from neural crest cells. The neural crest is a critical grou ...

tissues. These proliferate and mature into

s and fibrous

connective tissue Connective tissue is one of the four primary types of animal tissue, a group of cells that are similar in structure, along with epithelial tissue, muscle tissue, and nervous tissue. It develops mostly from the mesenchyme, derived from the mesod ...

, and ultimately teeth. Ameloblastic fibromas contain both of these tissues, and its name is derived from them. It is a

neoplasm A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

, meaning it is a mass of abnormal growth of cells or tissue. If the mass contains hard dental tissues they are known as

, which are not true neoplasm, but classified as

tous lesions.

Treatments

As ameloblastic fibromas are rare and the literature regarding treatment is limited there is controversy regarding treatment approach. A conservative treatment strategy, such as enucleation and curettage, is usually sufficient for small ameloblastic fibromas. However, extensive and aggressive lesions may require radical treatment such as in older patients who have likely high recurrence tendency. If the ameloblastic fibroma is small, ‘reconstruction’ will not be required. Conservative treatment usually involves enucleation and thorough curettage of the affected area alongside extraction of the affected teeth. Enucleation is the removal of an organ or tumor in such a way that it comes out clean and whole. Thorough enucleation is important as there are reports of a high recurrence rate (Trodahl reported a 36.4% recurrence rate). Immediate reconstruction is required post enucleation and curettage of the affected area. Some patients may require reconstruction which can include a full thickness bone graft. This treatment allows the patient to retain oral function and as much facial structure as possible. Occasionally, more radical treatment is required with excision of the tumour with a margin of healthy tissue. This kind of treatment also requires reconstruction of the affected area, with bone grafts often being the preferred choice for remodelling. This is done when the tumour is large or is deemed to have a high chance of malignant transformation. In some cases the fibroma may envelop a nerve and may have to be removed too. Implants in compromised areas filled with a bone graft can prove useful for functional and aesthetic stability. Implant retained prosthesis can be placed and can make a vital overall functional and masticatory difference. Close radiographic and clinical follow up is important to identify recurrence and malignant transformation.

Epidemiology

Odontogenic tumours are uncommon, with a prevalence of around 2% and only 1-2% of these are ameloblastic fibromas. As they are rare, there is limited evidence available, mostly case studies. There is a slight male predilection, developing most commonly within the first two decades of life. They are often identified when tooth development is complete with the posterior mandible being the most common site. Although benign, ameloblastic fibromas that occur in later decades as well as a third of treated ameloblastic fibromas can recur and around 11% may undergo malignant transformation, though this figure is questioned. Odontoma are the most prevalent of the odontogenic tumours in the early decades.