Identification of light and heavy plaque formers using different methods

Objectives: Plaque formation rates differ significantly between persons in a population. To recruit suitable participants for clinical studies of oral hygiene products, the selection of light or heavy plaque formers is important. The aim of this investigation was to discover the method that best distinguishes between light and heavy plaque formers.

Methods: The study population of 47 participants consisted of dental students and staff of the dental and medical school. After dental prophylaxis, participants stopped oral hygiene measures for 72 hours. Afterwards, plaque growth in each individual was determined by the plaque index (PLI, Silness & Loe 1964), the plaque formation rate index (SIM, Simonsson et al. 1987), and a modified plaque formation rate index (PFRI, Axelsson 1990). Indices were recorded in a split-mouth approach. Light and heavy plaque formers were selected according to methods described by Simonsson et al. 1987 and Axelsson1990.

Spearman correlation coefficients were calculated to compare the methods.

Results: PFRI identified seven light plaque formers, only five were detected by SIM and PLI. Four heavy plaque formers were determined by PFRI and PLI, five by SIM. PLI and SIM highly correlated (r=0.840**), PLI and PFRI showed medium (r=0.563**), SIM and PFRI low (r=0.412**) correlations. While 21.7% light plaque formers and 4.3% heavy plaque formers were found among dental students, only 8.3% light and 12.5% heavy plaque formers were found among staff (PFRI).

Conclusions: The number of individuals with light and heavy plaque formation, within a given study population, differs depending on method selection. Methods relying on the same detection system (PLI, SIM) highly correlate while PFRI and SIM do not. Plaque formation rate should be determined before a study with preference for light plaque or heavy plaque formers is performed.