The supersaturated solutions of the present invention remain stable at least for the length of time and under normal conditions of their use. By this is meant that the supersaturated solution remains substantially supersaturated with respect to calcium and orthophosphate ions for the normal time the solution is rinsed or washed around the oral cavity. After this time, the solution may begin to contain some precipitate of calcium phosphates which would reduce its therapeutic effectiveness. Therefore, conveniently, the solution may remain supersaturated in the oral cavity for up to about five minutes, especially up to 2-3 minutes and necessarily up to about 1 minute, all measurements therefore taken at body temperature. It will be understood that, at lower temperatures such as room or ambient temperature, the supersaturated e solution will remain so for significantly longer periods such as of the order of up to 2 hours, especially up to 1 hour and necessarily for the length of time taken to use the supersaturated solution just mixed as a dental rinse or mouthwash which may be in the range of from about 3 minutes to about 15 minutes.