Gels of calcium phosphate, formed by mixing high concentrations of calcium and phosphate, have been used to desensitize teeth. Objectives: To study the viscoelastic properties of gel formation and conversion and to understand how these properties could best be used for clinical applications. Methods: A controlled stress rheometer with a cup and bob measuring system at an oscillation frequency of 0.1 Hertz and a target strain of 0.001 at 37 °C was used to study the effects of pH, fluoride, calcium and phosphate concentrations (Ca/P ratio at 1.5) and volume ratio of calcium and phosphate solutions. The viscoelasticity, G*, of the gel was continuously measured and the formation kinetics was expressed as gelation half-time (T1/2). Results: Gel formation, as indicated by the increase in G*, occurred in calcium chloride solutions of 0.1 mol/L and higher when combined with a K2HPO4 solution (pH 9.2). At 1.5 mol/L of calcium, a maximum G* of 105 Pascal was reached when mixed with a K2HPO4 solution at the Ca/P volume ratio of 0.5, P solutions with low concentration of F (0.01 mol/L) didn’t affect the G*, while a higher concentration (0.5 mol/L) decreased the G*. At a higher pH solution (K3PO4, pH 13)), G* decreased to 104 Pascal. At acidic KH2PO4 solution (pH 4.5), no gel formation was observed. Monovalent ions, H+, OH-, and F- weakened the gel. Conclusion: The viscoelasticity of calcium phosphate is a good measure of gel formation and is sensitive to pH, calcium and phosphate concentrations. These findings suggest two sets of conditions: one with highest G* and rapid viscous gel formation that may be better for topical desensitization, and the other with higher concentration of F and higher pH that may be better for treating a cavity preparation prior to restoration. Supported by ADAHF, NIST & NIH.