Four variables affecting magnitude of dentrifice abrasiveness.

A five-factor study was done on human dentin abrasion that involved two abrasives, either alone or in dentifrice form, two brush brands, two brush hardnesses, two concentrations, and two temperatures of testing. The hard brushes caused 3.6 times as much wear as the soft brushes, a greater influence than the abrasives compared. A brush X hardness interaction indicated that there is a wide variation among the stiffness gradings of toothbrushes. Tests run at 37 C were 28% less abrasive than those at room temperature, suggesting a softening of bristles because of the warmer temperature. A highly significant abrasive X concentration interaction showed that dentifrices became more than twice as abrasive on dilution form 100 to 50%, but that abrasives alone did not show such changes on dilution. The second study included two hardnesses, two abrasives, three diluents, four concentrations, and two replicates. An interaction was found between abrasive and diluent, showing that glycerine inhibited abrasion by 88% in comparison with saliva and CMC. A hardness X concentration interaction showed that wear varied widely with concentration for the hard brush but scarcely at all for the soft brush. These findings suggest that abrasiveness of dentifrices depends strongly on testing conditions and that no single set of conditions is suitable for evaluating dentifrice abrasiveness.