One of Supertooths innovative teaching aids is a simple glass model of a fissure inside chewing surfaces where over 80% of cavities occur from acid demineralisation where carbohydrate like sugar in food trapped at every meal or snack, is changed to acid demineralisation by resident plaque bacteria.
Two identical pieces of square glass with sharp edges removed by rubbing with a fine stone or old diamond drill from the dentist and each square are clamped together with a Celco fold back paper clip.
Place a drop of red or blue food dye on the groove and see how surface tension sucks the dye in under capillary action.
Brush with toothpaste showing that brushing and toothpaste have no access.
Push into chewing gum which has no access.
Push into half a grape, a slice fruit like an orange which will displace the red dye. A piece of celery will aso displace the dye after more chewing.
You can see the glass model on YouTube http://www.youtube.com/watch?v=nRca_whVI4Y