Ameloblastic fibroma

{{Infobox medical condition

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| image = Enamelmineralization11-17-05.jpg

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| caption = Histology of developing tooth with enamel, dentin, ameloblasts, and odontoblasts labeled. Tooth bud is in maturation/crown stage.

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|symptoms = Painless swelling of the jaw.

|complications = Impacted tooth.

|onset = Childhood or adolescence.

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|diagnosis = Dental radiograph.

|differential = Ameloblastic fibro-odontoma or odontoma.

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|treatment = Surgical excision or curettage and removal of the effected teeth.

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|frequency = 2% of odontogenic tumors.

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An ameloblastic fibroma is a fibroma of the ameloblastic tissue, that is, an odontogenic tumor arising from the enamel organ or dental lamina. It may be either truly neoplastic or merely hamartomatous (an odontoma). In neoplastic cases, it may be labeled an ameloblastic fibrosarcoma in accord with the terminological distinction that reserves the word fibroma for benign tumors and assigns the word fibrosarcoma 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 alone is usually not enough to differentiate neoplastic cases from hamartomatous ones, because the histology is very similar. Other clinical and radiographic clues are used to narrow the diagnosis.

Clinical Features

Ameloblastic fibroma is a rare benign mixed epithelial and mesenchymal 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.{{Cite journal|last1=Ponnam|first1=SrinivasRao|last2=Srivastava|first2=Gautam|last3=Smitha|first3=B|year=2012|title=Ameloblastic fibroma|journal=Journal of Oral and Maxillofacial Pathology|language=en|volume=16|issue=3|pages=444–5|doi=10.4103/0973-029X.102515|issn=0973-029X|pmc=3519228|pmid=23248485 |doi-access=free }} It can be associated with an impacted tooth{{Cite journal|title=Ameloblastic Fibroma of the Maxilla with Bilateral Presentation: Report of a Rare Case with Review of the Literature|last1=Ealla|first1=Kranti Kiran Reddy|last2=Basavanapalli|first2=Vijayabaskar Reddy|year=2015|journal=Case Reports in Pediatrics|language=en|doi=10.1155/2015/250713|pmc=4299785|pmid=25628911|last3=Velidandla|first3=Surekha Reddy|last4=Manikya|first4=Sangameshwar|last5=Ragulakollu|first5=Rajesh|last6=Danappanavar|first6=Prasanna M.|last7=Vennila|first7=Vijayasree|volume=2015|pages=250713|doi-access=free}} 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.{{Cite book|last=Odell, E. W.|title=Cawson's essentials of oral pathology and oral medicine|others=Preceded by (work): Cawson, R. A.|isbn=978-0-7020-4982-8|edition=Ninth|location=[Edinburgh]|oclc=960030340|year=2017}}

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 as the lesion is often associated with an impacted tooth.{{Cite journal|last1=Nelson|first1=Brenda L.|last2=Folk|first2=Gretchen S.|date=March 2009|title=Ameloblastic Fibroma|journal=Head and Neck Pathology|language=en|volume=3|issue=1|pages=51–53|doi=10.1007/s12105-008-0091-0|issn=1936-055X|pmc=2807540|pmid=20596990}}

=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 resembles the dental papilla.

The epithelial component features strands which branch and join, or anastomose. 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 ameloblasts forming palisades of columnar cells adjacent to a starry-like, loosely formed layer known as stellate reticulum. 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. 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 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. 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 epithelial or mesenchymal tissue. There is a resemblance to fibrosarcoma. 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 and mesenchyme produce epithelial and ectomesenchyme tissues. These proliferate and mature into ameloblasts and fibrous connective tissue, and ultimately teeth. Ameloblastic fibromas contain both of these tissues, and its name is derived from them. It is a neoplasm, meaning it is a mass of abnormal growth of cells or tissue. If the mass contains hard dental tissues they are known as odontoma, which are not true neoplasm, but classified as hamartomatous 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.{{Cite web|url=https://www.cancer.gov/publications/dictionaries/cancer-terms|title=NCI Dictionary of Cancer Terms|date=2011-02-02|website=National Cancer Institute|language=en|access-date=2020-03-05}} Thorough enucleation is important as there are reports of a high recurrence rate (Trodahl reported a 36.4% recurrence rate).{{Cite journal|title=Europe PMC|journal=European Journal of Dentistry|year=2016|pmid=27011753|last1=Tozoglu|first1=S.|last2=Hatipoglu|first2=M.|last3=Aytekin|first3=Z.|last4=Gurer|first4=E. I.|volume=10|issue=1|pages=139–143|doi=10.4103/1305-7456.175700|pmc=4784144 |doi-access=free }} Immediate reconstruction is required post enucleation and curettage of the affected area.{{Cite journal|last1=Vasconcelos|first1=Belmiro C. E.|last2=Andrade|first2=Emanuel S. S.|last3=Rocha|first3=Nelson S.|last4=Morais|first4=Hécio H. A.|last5=Carvalho|first5=Ricardo W. F.|date=June 2009|title=Treatment of large ameloblastic fibroma: a case report|journal=Journal of Oral Science|volume=51|issue=2|pages=293–296|doi=10.2334/josnusd.51.293|issn=1880-4926|pmid=19550100|doi-access=free}} 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.{{Cite journal|last1=Chrcanovic|first1=Bruno Ramos|last2=Brennan|first2=Peter A.|last3=Rahimi|first3=Siavash|last4=Gomez|first4=Ricardo Santiago|date=April 2018|title=Ameloblastic fibroma and ameloblastic fibrosarcoma: A systematic review|journal=Journal of Oral Pathology & Medicine|volume=47|issue=4|pages=315–325|doi=10.1111/jop.12622|issn=1600-0714|pmid=28776760|hdl=2043/23318|s2cid=4873133|url=http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-16187 |hdl-access=free}}

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.{{citation | last=Baris Bingül | first=Kenan | title=Review of 101 benign epithelial, mesencymal and mixed odontogenic tumours | date=2017-08-24 | doi=10.26226/morressier.596dfd58d462b80292387c8c | page=}} In some cases the fibroma may envelop a nerve and may have to be removed too.{{Cite journal|title=Ameloblastic Fibroma of the Mandible Reconstructed with Autogenous Parietal Bone: Report of a Case and Literature Review|last1=Carroll|first1=Conor|last2=Gill|first2=Mishaal|year=2019|journal=Case Reports in Dentistry|language=en|doi=10.1155/2019/5149219|pmc=6604494|pmid=31316839|last3=Bowden|first3=Eleanor|last4=O’Connell|first4=John Ed|last5=Shukla|first5=Rajeev|last6=Sweet|first6=Chris|volume=2019|pages=5149219|doi-access=free}}

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.{{Cite journal|last1=Mishra|first1=Niraj|last2=Pal|first2=Umashankar|year=2012|title=Placement of implants in an ossifying fibroma defect obliterated with demineralized, freeze-dried bone allograft and Plasma-rich growth factor|journal=Contemporary Clinical Dentistry|language=en|volume=3|issue=4|pages=471–4|doi=10.4103/0976-237X.107444|issn=0976-237X|pmc=3636830|pmid=23633812 |doi-access=free }}

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.{{citation needed|date=November 2024}}