In Vitro Simulation of pH Changes in the Oral Cavity

Objectives: Test the hypothesis that a shorter duration (one-day) of pH cycling, simulating pH changes intraorally, will cause significant surface degradation as a result of greater ion release compared with a longer duration (3-day) of pH cycling.
Methods: Twelve disks of glass-ceramic veneer (IPS Eris; Ivoclar Vivadent) were fabricated according to manufacturer instructions and grouped into either test sequence: I (pH 7, 10, 2); II (pH 10, 2, 7); and III (pH 2, 7, 10). Each specimen was placed in a polypropylene jar within a shaker bath containing deionized distilled water at 80 °C at a vibrating speed of 50 oscillations per min. Specimens were exposed to the first buffer solution in the sequence for 1 day rinsed in distilled water, dried in the air, and immersed in the next pH solution for another 1 day. Si⁴⁺ in the corrosion solutions were analyzed by means of an inductively coupled plasma atomic emission spectrometer for each 3, 15, and 27 days cycle. Ion concentrations were compared with ion release concentrations from a previous study where disks were exposed to the first buffer solution in the sequence for each 3 days, 30 days totaling 10 cycles, and analyzed for each 3 day cycle. R statistical software package (V.3.0.2) was used to create mixed-effects linear models.
Results: There was no significant difference in the Si release between 3day cycling and 1day cycling for any time period (p=0.82).
Conclusions: The results suggest that there is a no advantage to shortening the duration between 1day and 3day cycles to simulate changes in pH in the oral environment.