Objective: Periotron 8000^® is an electronic instrument that quantifies the volume of gingival crevicular fluid and saliva. Previous literature has proposed use of different fluids for calibration of the instrument, including human serum. The objectives were to compare different fluids used for instrument calibration, determine the correlations, and the most appropriate conversion equation for the model.

Materials and Methods: The fluids evaluated were physiological saline, human serum, fetal bovine serum, and saliva.The Periotron 8000^® instrument was calibrated with each fluid, and the correlation between these substances was analyzed. The calibration data were adjusted to a straight line, a second-, third-, and fourth-degree polynomial. R²(goodness-of-fit) values and the root mean square error (RMSE) were calculated for each regression model.

Results: All the correlations were significant. However, saliva correlated more strongly with physiological saline solution. The fourth-degree polynomial was the most accurate as a conversion equation because it presented higher R²and lower RMSE.

Conclusions: The four fluids evaluated are useful to calibrate the Periotron 8000^® instrument because they produce accurate regression models. Using saliva as a reference, the best fluid for calibration is physiological saline solution.