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Background/aim:  Alkali generation by oral bacteria plays a key role in plaque pH homeostasis and may be a major impediment to the development of dental caries. To determine if the capacity of oral samples to produce ammonia from arginine or urea was related to caries experience, the arginine deiminase system (ADS) and urease activity in saliva and dental plaque samples were measured in 45 adult subjects.

Methods:  The subjects were divided into three groups according to caries status; 13 caries‐free (CF) individuals (decayed, missing, and filled teeth = 0); 21 caries‐active (CA) individuals (decayed teeth ≥ 4); and 11 caries‐experienced (CE) individuals (decayed teeth = 0; missing and filled teeth > 0). Real‐time polymerase chain reaction was used to quantify the proportion of certain acid‐ or alkali‐producing organisms in the samples.

Results:  The amount of ammonia generated from the test …