Fluorescein Chemistry and Measurement of Dental Plaque

Objectives: Fluorescence of fluorescein was proposed by Bogari and Wright in the 1904 Journal of the American Chemical Society. Biochemical communities have regularly used fluorescein to tag cells and molecular entities. Dental use of fluorescein was first described in a 1970 patent for the self-diagnosis of dental plaque using the Plak Lite^™ lamp and fluorescein solution. In 1972, Löe and coworkers used this system for the systematic study of dental plaque using high-speed film photography. The Objective of this presentation is to define some of the chemical characteristics of fluorescein  relevant to the clinical determination of dental plaque since those earlier studies.

Methods: Dental plaque was disclosed with buffered mildly acidic and alkaline solutions of sodium fluorescein, USP, and photographed with a digital camera, computer and software system. Plaque with buffered fluorescein solutions was collected to determine the interactions between oral fluids, plaque and fluorescein using a Hitachi F7000 spectrofluorimeter to determine the frequency and intensity of the energizing illumination and the emitted fluorescence.

Results: Very high fluorescence was obtained with 490nM excitation. Excitation at 365nM was 1/10^th this level with 265nM excitation producing an intermediate fluorescence. The disclosed plaque fluorescent area at alkaline pH was reduced ~40% with 285nM, but the disclosed plaque area with 365 and 490nM excitation was reduced 10%. At mild acidic pH, reduction in disclosed plaque area was 30% with 265nM, 20% with 365nM and 40% with 490nm excitation.

Conclusions: The fluorescence of disclosed plaque was quenched thus reducing  both intensity and area with frequency of excitation, pH of the disclosing solution and characteristics of the pH buffering . Method specifics and  interaction with oral fluids and products being assessed are fundamental to the definitive clinical study design.

Partial support for studies was provided by Colgate Palmolive Company and Odontex, Inc.