Odontogenic tumors are a group of neoplastic growths that originate from the tissues responsible for tooth formation and the periodontal apparatus of the jaw. Odontogenic tumors usually present as radiolucent defect, which makes diagnosis somewhat confusing while differentiating them from cysts. Although cystic lesions are surrounded by sclerotic borders, few odontogenic tumors share similar features. This article reviews clinical concepts of several odontogenic tumors that occur in the proximity or in association with teeth and not merely focusing on relatively common conditions.
Early stages of odontogenic tumors are usually asymptomatic and slow-growing swelling.
Late stages of odontogenic tumors can cause facial asymmetry, symptomatic progressive swelling, pain, or bicortical plate expansion.
Odontomas and ameloblastomas are the most frequently reported odontogenic tumors across the globe.
Most odontogenic tumors are associated with unerupted/impacted tooth. Thus, exploring the cause of impaction through radiographic investigation may unravel odontogenic pathologies when detected.
Surgical approach is recommended in the management of odontogenic tumors.
Odontogenic tumors are pathologic outcomes from tissue elements that are part of the tooth-forming apparatus, that is, odontogenic tissues. These tumors occur exclusively in the bones of the jaw particularly around the teeth-bearing segments. Patients with odontogenic tumors usually present with symptomatic or asymptomatic swelling in the oral and maxillofacial region. Most of these swellings have either tooth-associated symptoms or tooth-associated radiological changes. The general dentist possesses a unique opportunity to be the first health care professional to see anatomic or radiographic changes in the maxillofacial region due to proximity of the neighboring structures that they routinely treat. Because general dentists serve as the preliminary point of patient contact and see patients on a regular basis, it is imperative that they become familiar with the recognition and diagnosis of odontogenic tumors. Although dentists have the examination skills and the knowledge regarding swelling and ulcerative conditions, the art of examination skills and the knowledge of differential diagnosis may have faded due to the relatively low prevalence of such conditions in general dental practice. Peter Morgan stated that “one reason that the field of odontogenic tumors appear so esoteric to the non-expert clinician or pathologist is that new entities appear and apparently standard well understood names are jettisoned, as if on a whim. ” This adds another layer of complexity while diagnosing such conditions in dental practice.
Odontogenic tumors comprise neoplastic growths of benign, malignant, or tumorlike malformations originating from odontogenic tissues. The interactions between ectodermal and mesenchymal elements from odontogenic tissues can initiate tumor formation due to disturbance in signaling mechanism for their growth and proliferation. This article presents relevant knowledge on clinical presentation, diagnostic criteria, and management details on commonly encountered odontogenic tumors. The correlation of the history, clinical presentation, radiographic presentation, and histological details are important factors in achieving an accurate diagnosis. The list of the odontogenic tumors is shown in Box 1 . Although there are many published classifications of odontogenic tumors, the have purposefully omitted them because their intention is to provide the general dentist with useful information on the conditions that will be discussed as aid to memory and understanding commonly encountered odontogenic tumors.
Keratocystic odontogenic tumor
Malignant ameloblastoma, ameloblastic carcinoma
Adenomatoid odontogenic tumor
Calcifying epithelial odontogenic tumor (Pindborg tumor)
Central odontogenic fibroma
Peripheral odontogenic fibroma
Calcifying cystic odontogenic tumor (calcifying odontogenic cyst, Gorlin cyst)
Odontoma is a benign tumor of mixed odontogenic origins consisting of both odontogenic hard and soft tissue. It is thought to be the most frequently encountered odontogenic tumor. Odontomas are composed of both epithelial and ectomesenchymal components that contribute to enamel- and dentinlike structures within the lesion. Although odontomas may consist of normal-appearing enamel/dentin structures, they have defects in their structural arrangement and hence they are considered as hamartomas, or tumorlike malformations, rather than true neoplasms.
The odontoma is seen predominantly in the second and third decade of life and has a slight female predilection. There are 2 main types: compound and complex. The lesion is easily recognized in radiographic examinations and appears as a radiopaque mass with thin radiolucent rim. Odontomas are usually managed by conservative enucleation but more extensive surgical procedures may be necessary for larger, more extensive lesions.
Odontomas are slow-growing, expanding, and painless intrabony lesions. Pain and inflammation may, however, result from secondary infection. The 2 types of odontomas are complex and compound odontoma. The distinction between these 2 types is based on either the appearance of toothlike structures or disorganized mass of dental tissue. The complex type is unrecognizable as dental structures, appearing as a radiopaque mass with varying densities. The compound odontoma has recognizable enamel, dentin, and cementum and consists of individual recognizable small teeth. The complex odontomas are located in the posterior mandible and identified based on disorganized mass of dental tissues, that is, enamel and/or dentine ( Fig. 1 A). Compound odontomas are located in the anterior maxillae and identified based on well-organized, multiple toothlike structures ( Fig. 1 B, C). Odontomas can also be associated with other odontogenic tumors such as calcifying odontogenic cyst, ameloblastic fibroodontoma (AFO), and odontogenic fibromas. The association of odontoma with Gardner syndrome and coronoid hypoplasia has also been reported.
In most cases odontomas can be diagnosed based on their radiographic appearance alone. The radiologic appearance depends on the stage of the lesion. The first stage is characterized by a radiolucent appearance due to lack of calcification. Partial calcification or radiopacity are seen in second or intermediate stage. The third stage is characterized by predominance of radiopaque masses of dental hard tissues with a thin radiolucent zone. Resorption or adjacent tooth or roots are uncommon. Association with unerupted teeth may be seen. Radiographically compound odontomas seem as collection of multiple toothlike structures of varying size and shape with periphery of narrow radiolucent zone, whereas complex odontomas seem as calcified mass with radiodensity of tooth structures with periphery of narrow radiolucent zone ( Fig. 2 ).
Microscopically odontomas are observed with multiple mineralized structures resembling small, single-rooted teeth with loose fibrous matrix. Pulp tissue may be seen in coronal and radicular zone of toothlike structures.
Differential diagnosis may include supernumerary tooth, AFO, and osteomas. Based on formation and the number of toothlike structures present, a supernumerary tooth can be easily differentiated from odontomas. Distinguishing AFO from odontoma can be challenging. Radiographically, the radiopacity seen in AFO is usually scattered, whereas the odontomas will have a central area of radiopacity. Radiographic appearance of complex odontoma may be confused with osteoma due to mineralized mass of tissue. However, the radiolucent zone at the periphery of the odontoma, which represents the dental follicle along with the radiodensity of the mass having a density similar to teeth, will differentiate odontomas from osteomas.
Odontomas are managed with conservative surgical excision and special surgical considerations are given for large odontomas. The prognosis of the condition is usually excellent with minimal to no recurrence.
Keratocystic Odontogenic Tumor (Formally Known as the Odontogenic Keratocyst)
Keratocystic odontogenic tumor (KCOT) is a controversial benign intraosseous cystic neoplasm of the jaw, which was formerly called odontogenic keratocyst but was reclassified under a new designation in order to better convey its neoplastic nature due to its aggressive and recurrence nature. KCOT is radiographically recognized as a unilocular radiolucent area with scalloped borders or multilocular radiolucent lesion in the posterior jaw. KCOT tend to grow more in anteroposterior direction rather than in buccal-lingual expansion ( Fig. 3 ). Because of its aggressive clinical behavior and high recurrence rate, the odontogenic keratocyst was considered to be a neoplasm. However, in 2018 both a World Health Organization and International Agency for Research on Cancer consensus concluded that further research is needed to explore the genetic changes in the KCOT/OKC for it to be classified as a neoplasm. Because of insufficient evidence to support neoplastic origins of keratocystic odontogenic tumor, the condition was again reclassified as a cyst, and in 2019 the appropriate name is again odontogenic keratocyst and it has been removed from the classification of odontogenic tumors. The clinical and diagnostic details of keratocystic odontogenic tumor are discussed in Arvind Babu Rajendra Santosh’s article, “ Odontogenic Cysts ,” in this issue.
Ameloblastomas are the second most common benign odontogenic tumor. They are potentially aggressive, locally invasive, slow-growing benign tumors that may originate from cell rests of dental lamina, epithelium from the enamel organ, epithelial lining of odontogenic cyst (ie, dentigerous cyst), and basal cell layer of oral mucosa. Based on clinical, radiologic, histologic, and prognosis aspects, ameloblastomas are classified as (1) classic/solid/multicystic ameloblastomas, (2) unicystic type, (3) peripheral, and (4) desmoplastic ameloblastoma. Histopathologic examination is mandatory for confirmation of diagnosis. Ameloblastomas are managed by wide surgical resection, and recurrences have been reported.
Ameloblastomas are uncommon among children and is predominantly seen in third and fourth decades of life with a male predilection. The posterior mandible is the most commonly affected site, although one of the authors (OEO) have noted that the parasymphysis/symphysial area is the most common sites in patients seen in Central and East Africa. Ameloblastoma is a slow-growing, painless swelling of the jaw. The clinical signs such as pain and disfigurement may be seen as the lesion advances in the size. The pain occurs due to pressure effects from the mass size on peripheral nerves and secondary infection. Ameloblastomas that present with large expansile mass of the jaw can cause thinning of cortical plate, and crepitation or egg shell crackling may be elicited while palpating jaw. Rarely the lesion can perforate jaw bone leading to ulcerated growth in oral cavity and sometimes the skin. Peripheral ameloblastomas present as painless, slow-growing gingival swelling that may produce shallow depression in the underlying bone rather than infiltration.
Radiographic examination can greatly assist in the diagnosis of ameloblastomas. The frequent presentation type of ameloblastoma is solid/multicystic type, which appears as multilocular radiolucent destruction of bone. A well-defined, small or large radiolucent area in the bone gives the appearance of honeycomb or soap bubble appearance. The destructive changes of the jaw bone may be either confined to alveolar bone or half the mandible. Buccal and lingual cortical plate expansions are observed. Cortical plate expansions can be well recognized in occlusal radiographs. Resorption of adjacent roots of teeth is frequently observed. Association of unerupted tooth is common and adds a layer of complexity in differentiating ameloblastoma with circumferential type of dentigerous cyst. Although ameloblastoma frequently shows irregular scalloping border, this is not a consistent finding in all the cases. Mixed radiographic appearance is due to osseous septa in the lesion but not a true mineralized content in the lesion. Unicystic ameloblastoma shows a large unilocular radiolucent destruction of the involved jaw bone ( Fig. 4 ).
Microscopic examination shows ameloblast-like cells and stellate reticulum–like cells with fibrous stroma. Histologic variants of ameloblastomas include follicular, plexiform, acanthomatous, granular cell, desmoplastic, clear cell, basal cell, keratoameloblastoma, papilliferous type, mucous cell, hemangiomatous, and extragnathic types.
Differential diagnosis of ameloblastoma can be categorized into radiolucency with and without mineralization changes. Differential diagnosis of uni-/multilocular radiolucency without mineralization includes odontogenic keratocyst, central giant cell granuloma, and dentigerous cyst, whereas differential diagnosis panel of uni-/multilocular radiolucency with mineralization includes odontogenic myxoma, calcifying odontogenic cyst, and calcifying epithelial odontogenic tumor. One must look for size, location, and presence/absence of mineralization while formulating differential diagnosis. Central giant cell granulomas are commonly reported in anterior mandible, whereas ameloblastomas are seen in posterior region. Odontogenic keratocyst has a tendency to expand in anteroposterior region, whereas ameloblastomas tend to expand in a buccal-lingual direction. Dentigerous cyst tends to show pericoronal radiolucency, whereas ameloblastomas show impacted tooth in the lesion, not necessarily pericoronal radiolucency. Mineralization density is greatly appreciated in calcifying epithelial odontogenic tumor and calcifying odontogenic cyst.
Multicystic ameloblastomas are treated by wide range of surgical options ranging from simple enucleation to en-bloc resection. Peripheral ameloblastomas are managed by surgical excision and curettage of the bone at the base. Ameloblastomas have a tendency to recur, hence careful postsurgical follow-up visits are necessary.
Malignant Ameloblastoma and Ameloblastic Carcinoma
Ameloblastoma sometimes exhibit behavior of metastases that are most often found in the lungs. The diagnosis of malignant ameloblastoma should be made when a tumor in both primary and metastatic locations demonstrate histopathologic features of ameloblastoma.
The diagnosis of ameloblastic carcinoma should be made when microscopic examination of ameloblastoma cases shows cytologic features of malignancy in the primary tumor. Ameloblastic carcinomas show local aggressive behavior but do not demonstrate the character of metastasis.
Adenomatoid Odontogenic Tumor
Adenomatoid odontogenic tumor (AOT) is a benign odontogenic tumor arising from odontogenic apparatus showing odontogenic epithelium with mature fibrous stroma and without ectomesenchyme. AOT was formerly considered to be a variant of ameloblastoma. However, because of clinical and biological behavior, AOT is considered as a separate entity from ameloblastoma. Based on radiological features, 3 variants of AOT are recognized: (1) follicular/pericoronal, (2) extrafollicular/extracoronal, and (3) peripheral types. Microscopic examination is mandatory for confirmation of diagnosis. AOT usually responds well to surgical excision due to encapsulation of the lesion that can be enucleated from the adjacent bone. Aggressive behavior and recurrences are rarely reported.
AOTs are uncommon, benign, slow-growing, painless swelling of the jaw bone. Adenomatoid odontogenic tumors are sometimes referred as “two-thirds tumors,” because two-thirds of AOTS occur before second decade of life, two-thirds of cases are in anterior maxillae, two-thirds of cases are reported in women, two-thirds of AOTs surround an impacted tooth, and two-thirds of the time that impacted tooth is canine. Peripheral variant of AOT appears as small, sessile, exophytic mass over the labial gingiva of the maxillae.
AOTs are frequently recognized during radiographic examination of unerupted maxillary canine tooth. Radiolucent defect with mandible canine impaction is also observed ( Fig. 5 ). The lesion is predominantly intraosseous and shows variation in radiographic location. Based on the location of the lesion, it can be extrafollicular type (no relation to tooth structures); interradicular; adjacent to roots; superimposed on the root apex (periapical type); superimposed at midroot level; or peripheral type (extraosseous/gingival) with slight erosion of alveolar crest of bone. The follicular type is the most common type of AOT presentation. Radiographically, follicular type presents as well-defined, unilocular (oval or round) radiolucency associated with the crown of an unerupted tooth mimicking dentigerous cyst. Radiographic examination can greatly assist in the diagnosis of AOT. The intraoral periapical radiograph is the best radiograph to show radiopacities in AOT. Cone beam computed tomography seems to possess the best potential for diagnosing AOT.