Strontium uptake by powdered and intact human root dentine

The in vitro ability of strontium to exchange with calcium of root dentine and dentine in powder form was studied. Matched pairs of non-erupted and erupted third molar teeth were extracted from 12 individuals, aged 21-29 years. Each tooth was cut into 2 halves along its longitudinal axis, and the crown and pulp canal covered with wax. The root surfaces and powdered dentine were immersed in SrCl₂ solutions of various concentrations and for different time periods. Samples of the tooth specimens were re-immersed in distilled water, NaCl or CaCl₂ solutions for examination of released strontium. Strontium and calcium determinations were carried out by atomic absorption spectroscopy in the root surfaces, powdered dentine and in the immersion solutions. The mean strontium concentrations in the surface and subsurface root layers increased with the concentration of the SrCl₂ immersion and the period of exposure, but the displaced calcium was not proportional to the strontium uptake. On the other hand, increasing strontium uptake by dentine powder was related to an increasing release of calcium into the immersing solution at a ratio of about 1:1. The findings suggest that strontium adsorption takes place mainly at the crystal surfaces of the roots. In powdered dentine, diffusion into the crystal interior was probably the dominant process in strontium uptake.