Primary epithelial tumours of the jaw.

Primary epithelial tumours in the jaw are an interesting group in that they may be derived from the lining epithelium of the mouth or from that which has invaded the jaw during' the embryonic development of the teeth. The exact origin of these tumours is often debatable, their diagnosis radiologically and histologically not always easy, and their prognosis therefore in doubt. The morphological possibilities of epithelial tumours of the jaw can only be appreciated if the details of the embryology of the teeth are borne in mind. It will be remembered that the ectodermal lining of the mouth grows into the primitive gum in the form of a solid dental lamina in the seventh week of development. At intervals along this lamina thickenings of the epithelium appear and constitute the enamel organs. At a later stage, as in the 16 weeks' embtyo illustrated in Fig .1, the enamel organ comes to lie over the mesenchymal dental papilla and has a central core of so-called stellate reticulum, which is a further differentiation of the epithelium, and a marginal layer of columnar enamel-forming ameloblasts. Ordinarily the stellate reticulum, the outer layer of ameloblasts, and the dental lamina disappear by the time the deciduous and permanent teeth are formed, but remnants of this epithelium may occasionally remain and give rise to neoplastic growth at a later date. It is important to remember that the adult oral mucosa, composed of squamous epithelium, of ectodermal or entodermal origin, has a capacity at least as great as that of the epithelium of the body surface to produce the whole range of epithelial tumours: simple inclusion and retention cysts, squamous cell carcinoma, basal cell tumours of " rodent" type, and adamantinomas. Any of these may invade the jaw and on occasion it is difficult to decide whether the tumour arose from an intraalveolar site or from the mucous surface. Most tumours in the jaw declare their presence by causing a swelling, and on radiological examination an area of absorption of bone is generally detected. It is not the purpose of this paper to discuss the diagnostic radiological features. Our experience in the Bristol Bone Tumour Register has been that one cannot always rely upon radiological appearances, and unfortunately a histological examination of a biopsy specimen may be misleading. Taken together the two methods generally enable one to make an accurate diagnosis, but only if the limitations of both are borne in mind. In a study over a period of six years of 10 examples of simple dental cysts, 12 adamantinomas, and five intra-alveolar carcinomas, and various carcinomas of the mouth cavity invading the jaw, we have been impressed particularly by the frequency with which a wrong clinical diagnosis has been made and by the hazards of histological diagnosis on small biopsy specimens. A few examples of these different types of epithelial tumour, some benign and some malignant, will serve to illustrate these features.