The follicular odontoma, also known as a dentigerous cyst, is derived from the distension of a tooth follicle.  It constitutes a cyst containing a viscid fluid, and an imperfectly formed tooth is often found embedded in its wall.  The cyst usually forms in relation to one of the permanent molars, and may attain considerable dimensions.

The fibrous odontoma is the result of an overgrowth of fibrous tissue surrounding the tooth sac, which encapsulates the tooth and prevents its eruption.  The thickened tooth sac is usually mistaken for a fibrous tumour, until, after removal, the tooth is recognised in its interior.

Composite Odontoma.—­This is a convenient term to apply to certain hard dental tumours which are met with in the jaws, and consist of enamel, dentine, and cement.  The tumour is to be regarded as being derived from an abnormal growth of all the elements of a tooth germ, or of two or more tooth germs, indiscriminately fused with one another.  It may appear in childhood, and form a smooth unyielding tumour, often of considerable size, replacing the corresponding permanent tooth.  It may cause a purulent discharge, and in some cases it has been extruded after sloughing of the overlying soft parts.  Many examples of this variety of odontoma, growing in the nasal cavity or in the maxillary sinus, have been erroneously regarded as osteomas even after removal.

On section, the tumour is usually laminated, and is seen to consist mainly of dentine with a partial covering of enamel and cement.

Diagnosis.—­Odontomas are often only diagnosed after removal.  When attended with suppuration, the condition has been mistaken for disease of the jaw.  Fibrous odontomas have been mistaken for sarcoma, and portions of the maxilla removed unnecessarily.  Any circumscribed tumour of the jaw, particularly when met with in a young adult, should suggest the possibility of an odontoma.  Skiagrams often give useful information both for diagnosis and for treatment.

Treatment.—­The solid varieties of odontoma can usually be shelled out after dividing the overlying soft parts.  In the follicular variety, it is usually sufficient to excise a portion of the wall, scrape out the interior, and remove any tooth that may be present.  The cavity is then packed and allowed to heal from the bottom.

#Fibroma.#—­A fibroma is a tumour composed of fibrous connective tissue.  A distinction may be made between the soft fibroma, which is comparatively rich in cells and blood vessels, and in which the fibres are arranged loosely; and the hard fibroma, which is composed of closely packed bundles of fibres often arranged in a concentric fashion around the blood vessels.  The cut surface of the soft fibroma presents a pinkish-white, fleshy appearance, resembling the slowly growing forms of sarcoma; that of a hard fibroma presents a dry, glistening appearance, aptly compared to watered silk.  The