Statistical analysis
To compare the enzymatic activities among subjects
without periodontal disease, subjects with gingivitis and
subjects with periodontal disease, one-way analysis of
variance (ANOVA) was used. To determine the significance
of differences among groups, the P values were adjusted
by the Bonferroni method for multiple comparisons.
To set the cut-off points for the biochemical markers,
receiver operating characteristic curves (ROC curves)
were constructed and the points showing minimum
difference between sensitivity and specificity were decided
for gingivitis or periodontitis. The chi-squared test was
carried out to confirm the statistical significance, and
positive or negative predictive values were calculated for
the biochemical markers. These analyses were conducted
using SPSS ver. 14.0 (SPSS, Tokyo, Japan).