Relative error (variability) associated with an improved instrument for measuring gingival crevicular fluid.

This investigation was undertaken to compare the variability in a new Periotron model 6000 to the variability in the previous Periotron model 600 and to the variability of the ninhydrin area method (NAM) for measuring quantities of fluid collected on filter paper strips. A Hamilton microliter syringe was used to deliver normal human serum to filter paper strips. Strips receiving varying quantities were randomly and blindly assigned to Periotron models 6000 and 600 until 10 strips containing each of 0.15, 0.30, 0.45, 0.60, 0.75, 0.90 and 1.05 microliter had been read using model 6000 and 10 strips containing each of 0.15, 0.30 and 0.45 microliter had been read using model 600. All strips were subsequently read using the NAM. The entire procedure was repeated using distilled water containing 0.1% methyl green. Coefficients of variation (CV) were computed for all sets of data. In all cases the CVs for the Periotron 6000 were significantly smaller than those for the Periotron 600 or the NAM. Pooled estimates of CVs (0.15-0.45 microliter) for the Periotron models 6000 and 600 were 0.054 and 0.116, respectively, (P less than or equal to 0.005) with serum and 0.059 and 0.095, respectively, (P less than or equal to 0.05) with distilled water containing 0.1% methyl green. Pooled estimates of CVs (0.15-1.05 microliter) for the Periotron model 6000 and the same strips subsequently measured with the NAM were 0.046 and 0.069, respectively, (P less than or equal to 0.005) with serum and 0.055 and 0.076, respectively, (P less than or equal to 0.001) with distilled water containing 0.1% methyl green.(ABSTRACT TRUNCATED AT 250 WORDS)