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 (PII); (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 (H 2 O 2 ), 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 PII of the sucrose gum users. Chewing of the H 2 O 2 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, H 2 O 2 and sucrose gums. PII scores 1 and 3 remained stable whereas the frequency of PII score 0 strongly decreased and that of score 2 strongly increased when going from gums producing low (CHX) and medium (H 2 O 2 ) 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 (H 2 O 2 ) 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 PII, PWW and PLQ, and PII 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.