Help with dental caries detector project

I need to build a simple circuit to detect dental caries. The employed technique is through measurement of electrical resistance of the tooth, which is approximately somewhere in the range of 0-4.4 M ohm for a caried tooth, and higher than 4.4 M ohm for normal teeth. An AC ohmeter circuit needs to be built to measure the resistance of tooth and this has to be interfaced with 3 LEDs to indicate the extent of cavities based on electrical resistance values. How do I build the circuit? How do I connect the LEDs with the AC ohmmeter? should I programme a micrcoontroller? How can I do it?
Please help

This sounds very much like the way a pH meter operates. To calibrate, you have to adjust the magnitude of the current and the mechanical dimensions of the electrode pair (or do you measure the resistance between the carrie probe and a armband?

One thing you should probably think about is whether you can make the thing battery powered so you don't have to worry about leakage currents from the AC mains, which would make the subject uncomfortable or dead.

Here is a Google search that might put you on the right track. Check out the "images for..."
https://bit.ly/1A087kt

Thank You !
It is the resistance that has to be measured.
Can a pH meter circuit be used in this case, by measuring the pH levels of normal and carious tooth?

These devices are currently available to buy so can I ask why you have to design one?

A dentist simply SEES (money, that all your teeth need repairs of $250 each or more) a carie in a tooth. This electronic ohm-meter is not used but instead is used during a root canal to measure that all of the root has been removed. Frequently an expensive Xray is used to see (more money) a carie in a tooth.

It is for a project

The form factor of a PH meter probe probably would not be compatible with your intended use, but the circuitry might be if the ranges are comparable.