Abstract: An improved method of treating periodontitis includes the steps of: creating a formulation containing a lanthanide-containing protease inhibitor; and applying the formulation to a periodontal area. The lanthanide may be cerium chloride, samarium chloride, lutetium chloride, cerium chloride heptahydrate, lutetium chloride hexahydrate, samarium chloride hexahydrate, gadolinium, gadolinium nitrate, gadolinium chloride, gadolinium chloride hexahydrate and gadolinium nitrate hexahydrate. The invention also provides an improved method of reducing dentinal sensitivity, including the steps of: creating a formulation containing at least one of gadolinium and a gadolinium-containing compound; and applying the formulation to a sensitive dentinal area. The formulation may be a paste, a solution or a powder.