The purpose of the present study is to analyze the oral environment of patients with squamous cell carcinomas of the oral cavity and to look for a key to a primary prevention method for such squamous cell carcinomas.
From 1968 through 1990, a total of 454 patients with squamous cell carcinomas of the oral cavity (lower gingiva: 223, tongue: 155, floor of the mouth: 76) were reviewed at the Department of Oral Radiology, Osaka Dental University Hospital, to evaluate their oral environment. The oral environment in these patients (carcinoma groups) was examined with the aid of an orthopantomogram and evaluated with modified DMF (D: decay, M: missing, F: filling) values and the loss of alveolar bone ridge. A control group of 390 patients (30 years of age or over) without abnormal findings (remarkable bone change caused by tumor, cyst or infection) in the teeth and jaws were also evaluated at the same hospital, in May and June, and in November and December, 1992.
Statistical significance was tested by means of analysis of variance (ANOVA) and t-test.
The following is a summary of the results:
1) The tooth decay rate (number of decayed teeth/number of remaining teeth) of the carcinoma groups was higher than that of the control group. But there was no statistically significant correlation between the carcinoma groups and the control group.
2) The degree of loss of the alveolar bone ridge of the carcinoma groups was advanced.
In particular, this degree of loss in the patients with carcinomas of the floor of the mouth was significantly more advanced than that of the control group (49 years or less: P<0.01, 50-59 years: P<0.001, 60-69 years: P<0.05, 70 years or more: P<0.005).
3) The degree of loss of the alveolar bone ridge of the control group and that of the tongue group were nearly the same.
It is suspected that the weight of the factors stimulating carcinogenesis in the oral cavity depends on the tumor location. However, the progress of alveolar bone loss can be considered a high risk factor for carcinogenesis in the floor of the mouth and the lower gingiva. Therefore, the control of periodontal disease is seen as the first step in the primary prevention of squamous cell carcinomas of the oral cavity.

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In implant treatment, we use computed tomography (CT) with a radiographic measurement stent to decide the accurate position of fixtures preoperatively. In order to show the position and direction of fixtures on CT images, alminium pipes, which are the same in diameter as fixtures, are placed on the stent. Hydroxyapatite phantom is used for the measurement of bone mineral content.
This CT examination provides the following useful information:
1) A series of axial CT images were obtained in a short time without patient's movement. These images, 2-mm thick slices, were able to give enough information about the bucco-lingual width, shape and density of the bone.
2) Multiplanar reformation (MPR) images were reconstructed from a series of axial images. Alminium indicators of the stent were useful to decide the optimum position and direction of fixtures, because MPR images could show the anatomical structures where implants were to be placed.
3) Three-dimensional (3D) images reconstructed from a series of axial images were useful in showing the bone surface and the adjacent inclined roots.
4) Bone mineral content in the jaw bone was measured using hydroxyapatite phantom.

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