pH measurements with an ion sensitive field effect transistor in the mouth of patients with xerostomia

A transistor pH electrode (ion-sensitive field-effect transistor), placed in the upper dentures of xerostomia patients and five healthy volunteers, was used to register pH changes in five-, six-, and seven-day-old dental plaque. A mouth rinse with a 10% sucrose solution caused a pH fall of about three-decades. A significant difference in the duration of critical plaque pH was observed; in xerostomia patients, a 10% longer period of pH <5.7 was registered during 60 min following a sucrose rinse. Normal oral functions were not influenced by the denture containing the integrated electrode. Both in vitro and in vivo tests showed remarkable electrode stability. Materials and measurement methods are described.