Dental Silicate Cements. II. Preparation and Durability

¹ Dental Materials Section, Laboratory of the Government Chemist, Minister of Technology, Cornwall House, Stamford Street, London, S.E.1, England

The variables associated with cement preparation can greatly affect cement durability, making technic at least as important as material selection. The amount of phosphate, silicate, and sodium eluted from the cement into water and the setting time of the paste increase as the P/L ratio decrease. This effect is critical at low values of this ratio. The effect on durability is permanent. The close correlation between phosphate eluted and setting time suggests that durability is dependent on reaction rate. Although compressive strength also decreases with the P/L ratio, the effect is less pronounced.

Increase of the period of temporary protection of the hardening cement from contact with the aqueous media for 24 to 48 hours greatly reduces the solution of material, because the cement-forming reaction is allowed to go to completion. For temporary protection, a number of commercial and experimental varnishes are satisfactory; for example, those based on nitrocellulose, methacrylate, vinyl, and amide polymers. Greases, which are easily removed, are unsatisfactory.