The slope of the material dispersion dM/dλ at λ0, the material dispersion zero where d2n/dλ2=0, can be calculated to yield values applicable to crystals and glasses. The results, in units of ps/nm km μm, range from 217 for B2O3 and 105 for SiO2 to 9 for TI2O and 0.40 for TlI. The key parameters affecting the material dispersion slope at λ0 are the chemical valence of the anion, the reduced mass and the density.