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Fig. 4.21. Higher magnification of Fig. 4.20 shows the continuity between the root forming tubular dentin (right side) and the ce-mental masses of the cementoblastoma

Pain is the most common presenting symptom and the posterior jaw areas are the predilection site. Sometimes, the lesion is attached to multiple neighbouring teeth [156]. Radiographically, the lesion is demarcated with a mixed lucent and dense appearance and is continuous with the partially resorbed root of a tooth. As recurrence and continued growth are possible, treatment should consist of removal of the lesion along with the affected tooth or teeth, and should also include some adjacent jaw bone [14].

4.4.3. Odontogenic Tumours -Mixed Epithelial and Mesenchymal

Mixed odontogenic tumours are composed of both epithelial-derived and mesenchymal-derived tissues. These tumours recapitulate proliferation and differentiation as seen in the developing teeth. Deposition of the dental hard tissues - enamel and dentin - may also occur [73, 174, 181]. Lesions with an identical histology can show neoplastic as well as hamartomatous behaviour [118, 153].

It is one of the less common lesions [34, 109, 127]. Mean age of occurrence is 14.8 years, but cases may be seen from as young as only 7 weeks up to as old as 62 years. Most cases are seen in the posterior mandible [96, 118].

The epithelial part of ameloblastic fibroma consists of branching and anastomosing epithelial strands that form knots of varying size. These knots have a peripheral rim of columnar cells that embraces a loosely arranged spindle-shaped epithelium. These epithelial strands lie in a myxoid cell-rich mesenchyme. The amount of epithelium may vary among cases and regionally within an individual case. There is no formation of dental hard tissues. Mitotic figures, either in epithelium or mesenchyme, are extremely rare; when easily found, they should raise concern about the benign nature of the case.

Ameloblastic fibroma may contain granular cells. Whether these lesions should be called granular cell ameloblastic fibroma or granular cell odontogenic fibroma is controversial (see also Sect. 4.4.2.2) [118, 170].

The epithelial component of ameloblastic fibroma closely resembles that of ameloblastoma. The stro-mal component, however, is entirely different: in ame-loblastoma it is mature fibrous connective tissue whereas in the ameloblastic fibroma it is immature, embryonic, cell-rich myxoid tissue. Areas similar to ameloblastic fibroma may also be observed in the hyperplastic dental follicle [71, 165]. The radiographic appearance makes the distinction; a radiolucent rim surrounding an un-erupted tooth in the case of a dental follicle and an expansive radiolucent jaw lesion in the case of an ameloblastic fibroma.

Most cases of ameloblastic fibroma present as painless swellings or are discovered due to disturbances in tooth eruption. Radiographically, the tumour presents as a well-demarcated expansive radiolucency, often in connection with a malpositioned tooth.

Treatment consists of enucleation and curettage. In some cases, recurrence may occur [118]. Sometimes, ameloblastic fibroma may progress to malignancy. These lesions are characterised by increased cellulari-ty and mitotic activity of the mesenchymal component and therefore known as ameloblastic fibrosarcoma (see Sect. 4.4.4.6) [96].

4.4.3.2 Ameloblastic

Fibro-Odontoma

4.4.3.1 Ameloblastic Fibroma

ICD-O:9330/0

Ameloblastic fibroma lacks a hard tissue component, only displaying soft tissues similar to those found in the immature tooth germ.

ICD-O:9290/0

Ameloblastic fibro-odontomas are lesions that combine a soft tissue component, similar to ameloblastic fibroma, with the presence of dentin and enamel. In rare cases, only dentin is formed; those tumours are called amelo-blasticfibro-dentinoma (ICD-O:9271/0) [73, 181].

Fig. 4.22. Ameloblastic fibro-odontoma combines the soft tissue elements of an ameloblastic fibroma with the deposition of the dental hard tissues enamel and dentin. Cavities in the homogeneous eosinophilic dentin contain high-columnar ameloblasts lying down enamel matrix (deep purple)
Fig. 4.23. Panoramic radiograph showing radiodense mass in connection with a tooth germ, a picture typical of complex odon-toma

Ameloblastic fibro-odontomas are rare [34, 127]. They occur primarily within the first two decades and have the posterior jaw areas as sites of predilection, the mandible more often involved than the maxilla [118, 153].

The soft tissue component is identical to that of am-eloblastic fibroma. Dentin may be formed either as eo-sinophilic mineralised material containing tubuli, just as in normal teeth, but it may also form as an homogeneous eosinophilic mass with sparse cells included. It always lies in close association with adjacent epithelium and forms the scaffold for the deposition of enamel matrix that is laid down at the epithelial-dentin interface by columnar epithelial cells that have reached their terminal differentiation as ameloblasts. The dental hard tissues are arranged haphazardly without any reminiscence of the orderly structure characterising normal teeth (Fig. 4.22).

Hyperplastic dental follicles may also show focal areas with the appearance of ameloblastic fibro-odonto-ma. Differential diagnostic considerations are the same as those as already mentioned (see Sect. 4.4.3.1). Ameloblastic fibro-odontomas can be distinguished from ameloblastomas by the presence of cellular myxoid tissue and of dentin and enamel.

Most cases of ameloblastic fibro-odontoma present as painless swelling or are discovered due to disturbances in tooth eruption. Radiographically, the tumour presents as a well-demarcated expansive radio-lucency with a radiopaque centre. Treatment consists of enucleation and curettage. Recurrence is rarely seen [46].

4.4.3.3 Odontoma -Complex Type

ICD-O:9282/0

Complex odontoma is a lesion composed of a haphazard conglomerate of dental hard tissues. This hamartoma is one of the more common odontogenic lesions [34, 127]. The posterior mandible is the favoured site (Fig. 4.23). Ages at which this lesion occurs are difficult to determine as lesions may be present unnoticed for a long time, the age distribution mentioned reflecting the age when the lesion was found rather than the age at which it formed. This explains the enormous range in age distribution reported: 2-74 years [118].

Complex odontomas consist of a usually well-delineated mass of dental hard tissues in a haphazard arrangement. The bulk of the lesion consists of dentin recognisable by the presence of tubuli. Enamel plays a minor role, usually confined to small rims in cavities in the dentin mass. The stroma consists of mature fibrous connective tissue.

Sometimes, odontomas may contain areas identical to the calcifying odontogenic cyst including ghost cells [22, 61, 80]. Odontoma-like structures may also occur in the hyperplastic dental follicle (see Sect. 4.4.2.1).

Complex odontomas may reveal their existence by disturbances in tooth eruption, missing teeth or jaw expansion. Quite often, they are incidental findings on radiographs taken for other purposes. In those cases, an amorphous calcified mass is seen that may be connected with the crown of an unerupted tooth. Treatment consists of conservative removal. Recurrences are not seen.

Compound Type

ICD-O:9281/0

Compound odontoma is a malformation consisting of tiny teeth that may vary in number from only a few to numerous. These teeth do not resemble the normal

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