Abstract: A system for treating teeth and associated tooth structure using a pressurized air propellant mixed with abrasive material includes a manifold which defines air passages leading from the pressurized air source to dispensing chambers which hold the abrasive material. The manifold further provides a convenient structure for mounting a number of the system components. The manifold simplifies assembly of the system and improves the integrity of air passages within the system. The air abrasion system also has a mixing block and continuous purge feature which eliminate crosstalk and backflow problems when switching between abrasive materials. Evacuation apparatus incorporating a cyclone separator is integrally provided with the system which requires minimal regular maintenance and maximizes suction flow through the apparatus.