Theoretically, you could create a series of graphics, each showing a different combination of highlighted teeth. You could store these graphics in separate records in a related table and link to them in response to user selections on your main layout. For 28 teeth, that's something like 28 x 28 = 784 combinations. Thus, you might not want to put in that much effort.
If you choose the check box route, you could do this:
Define a value list with a single space as it's custom value.
Format each "tooth checkbox field" with this custom value.
Place each check box formatted field in place and size it so that the field is nearly the same size as the check box.
Set a conditional format on all these check boxes:
Not IsEmpty ( Self )
and select a solid fill color such as black for the check box field.