A method for determining the available treatment dosage of stabilized chlorine dioxide in the prevention and the treatment of plaque accumulation, volatile sulfur compound production, gingivitis and periodontitis, and for differentiating the treatment dosage from other chlorine-containing compounds that may not have such beneficial effects is disclosed. When in solution as stabilized chlorine dioxide, the presence of other ions such as chlorate and chloride may not only obscure results as to the concentration of stabilized ClO.sub.2, but also reduce the predicted effectiveness. The present invention uses validated analytical methods to predict the effectiveness of stabilized ClO.sub.2 by more precisely measuring its concentration in solution. Such measurement renders precision at a level required of food-grade and pharmacy-grade chemotherapeutic agents in the oral cavity. Preferred concentrations are within the range of about 0.005 to about 2% (w/v) stabilized chlorine dioxide. The solution may be in the form of wash, rinse, soak, paste, gel, aerosol spray, or other suitable delivery system.