THE EFFECTS OF UREA AND SALTS OF AMMONIUM PHOSPHATE ON SALIVARY AMYLASE

¹ Dental Department, Montefiore Hospital, New York, N. Y.

Urea in a concentration of from 5 to 9 per cent (0.83 to 1.45 M) is without inhibitory effect on salivary amylase at 37 to 39° C. and pH 7 in the presence of 10^–2 N sodium chloride.

At high temperatures (above 50° C.) and at low temperatures in the absence of NaCl, amylase undergoes spontaneous, progressive inactivation or denaturation. Under these conditions, 5 to 9 per cent urea markedly inhibits amylase, apparently by an effect on the denaturation process.

The inhibitory effect of urea is counteracted by 0.1 per cent (.007 M) ammonium phosphate.

It is unlikely that urea in concentrations resulting from the use of commercially available dentifrices affects the caries process in vivo by means of a denaturing action on amylase.