Optimised microcomputer-guided quantitative microradiography on dental mineralised tissue slices.

It is well realised that the contact microradiographic method is the most direct method that gives position-dependent information on the mineral content of calcified tissue and its loss. We developed a microcomputer-guided microradiographic system which features fast operation by the experimenter with a low appearance of errors. Tooth tissue slices of 75 micron thickness are cut with a sawing machine. Images (Cu K alpha radiation) of the tooth slice and an aluminium step wedge (exposure 10-15 s) are made on film (Kodak SO-253). The images of step wedge and tooth slice are scanned in a densitometer (1 micron X 30 microns slit), which is fitted with an XY table (0.5 micron steps). A microcomputer (Apple IIe) is programmed to control the XY table and to record the optical film transmission. Scans of the images are plotted on the computer screen. The calibration step optical film transmission values are determined by the operator by adjusting a computer-generated bar onto the individual steps shown on the screen. The dose-density relation of the film is approximated by the program by a fourth-degree polynomial using the step-wedge data. The resulting curve is used to convert the tooth-slice data into a mineral volume percentage. To enable the calculation of total mineral loss (in kg m-2) (loss integrated over depth), the operator adds the assumed diagram for sound enamel onto the display. This is done by adjusting computer-generated bars to the scan of the tooth slice shown on the screen. The resolving power in the image made by the microradiographic system is 3 microns X 30 microns. On the basis of the analysis of random errors and a comparison with chemical analysis of tooth slices we claim that the error in mineral volume percentage amounts to 4% of its value. Starting with a microradiographic image of a tooth slice 5 min are required to obtain a microradiographic curve on paper and to obtain a value for mineral loss.