A composition and method of treatment for desensitizing hypersensitive dentin and cementum capable of effective results specially in one-treatment application. The essential ingredient or compound of the desensitizing composition is an alkali metal or ammonium oxalate where this salt may be mono- or di-substituted. The hydrogen or mono-substituted salts are preferred due to their lower pH which renders them more efficient in the protocol of this invention. These oxalates may be used effectively in the range 0.5% by weight to aqueous solution saturation. However, a range of 2.0% to solution saturation is much preferred due to the practice of the invention as a single-treatment agent. Furthermore, saturated solutions of the oxalates are most preferred also due to greater efficiency. The compositions may be used in aqueous solutions and as non-toxic paste with conventional fillers and excipients. In the paste form, the oxalate is preferred in a weight percent basis of 2-18%.