PHP offers a way to do this quite easily.
Depending on the complexity of your plans, you might have to expand this, but for your simple example above, here's the deal:
Assume your url is http://.../index.php?selected=tooth (<<note varied syntax, slightly)
PHP Code:
<form ...>
<input type="dropdown" value="<?php //initiates php
$sel = $_GET['selected']; //assigns the 'tooth' (etc) value to the $sel variable.
echo $sel; //prints to html the value of $sel, in this case 'tooth'.
?>">
<more form stuff...>
</form>
the above should simplify down to
PHP Code:
<form ...>
<input type="dropdown" value="tooth">
<more form stuff...>
</form>
If it needs to be more complex, then get more into php. It can do if statements, loops, and other things that might help you out. Really depends what you need.
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