COMPARABILITY AND DISCRIMINATING POWER OF 4 PLAQUE QUANTIFICATIONS

This study was designed for analysis of the discriminating power of 4 different quantifications of supragingival plaque: (1) plaque wet weight (PWW); (2) the plaque index (PlI); (3) the PLQ index measuring the coronal extension of plaque; (4) the area % of stained plaque. Different quantities of plaque were produced by adding chlorhexidine acetate (CHX), hydrogen peroxide (H2O2), or sucrose to experimental chewing gums. Total mean scores of 12 subjects in each of 3 test groups revealed that chewing of CHX gum resulted in the lowest plaque scores with all 4 quantifications and that the highest scores were recorded for the PWW or PlI of the sucrose gum users. Chewing of the H2O2 gum produced as much plaque as the sucrose gum when evaluated according to the PLQ index and exceeded the sucrose gum scores when evaluated according to the area % index. The PWW discriminated best between low, medium and high plaque scores after chewing of both CHX, H2O2 and sucrose gums. PlI scores 1 and 3 remained stable whereas the frequency of PlI score 0 strongly decreased and that of score 2 strongly increased when going from gums producing low (CHX) and medium (H2O2) to large (sucrose) amounts of plaque. The PLQ index discriminated well between low and medium but poorly between medium and large amounts of plaque. The area % index functioned well when subjects with low (CHX) and medium (H2O2) plaque scores were subgrouped into those with < 30%, 30-70% or > 70% of their tooth surfaces covered with stained plaque. After use of the sucrose gum, none of the 12 subjects exhibited area % scores in excess of 70%. Calculation of correlation coefficients between the 4 plaque quantifications revealed a strong correlation between PWW and PlI, PWW and PLQ, and PlI and PLQ recordings, whereas no significant correlation was found between PWW and area % recordings. It was concluded that the choice of a plaque quantification method is important for meaningful evaluation of clinical trials.