Plaque Glycolysis and Regrowth Model (PGRM)

Plaque Glycolysis and Regrowth Model (PGRM)

The Plaque Glycolysis and Regrowth Model (PGRM), a predictive ex vivo  model, evaluates the clinical effectiveness of antimicrobial (anti-plaque and anti-gingivitis) agents on plaque biofilms in the oral cavity. The model is designed so that treatments can be topically applied in vivo to dental plaque in separate oral quadrants. Plaque samples are taken from treated dental quadrants and compared to samples taken from untreated quadrants in the same individual. Samples are then placed in an appropriate growth medium, incubated at 37 0C for a specified time, and analyzed under standardized conditions in vitro, using two simple and sensitive endpoints: (1) glycolysis and (2) regrowth inhibition. 

Sampling can be done at time intervals to evaluate the retained activity of the antimicrobial agent and control products can be used in different quadrants as comparator products. 

This model is used to evaluate products such as devices (toothbrushes and other mechanical plaque removal methods) and products with antimicrobial activity (toothpaste and oral rinses). The PGRM is recommended in the FDA’s 21 CFR Part 356, Part III for testing of anti-gingivitis and anti-plaque product claims.

The Endpoints:

Glycolysis, a metabolic pathway involved in the extraction of energy from sugars, is widely used by microorganisms found in dental plaque.  The microorganisms metabolize dietary sugars into acids, resulting in a reduction in pH (more acidic), which can be easily measured in a solution of growth medium.  A plaque sample taken from a quadrant which has been treated with an effective antimicrobial formulation will exhibit a higher pH value (less acidic) of the post-incubation growth medium,  as compared to the pH  of post-incubation growth medium from  an untreated plaque sample.  This higher pH value is a result of inhibition of glycolysis.  

Regrowth inhibition, is evaluated by measuring the turbidity of plaque suspensions using spectrophotometry.  A plaque sample taken from a quadrant which has been treated with an effective antimicrobial agent will show a reduction in absorbance (less turbid),  as compared to the absorbance of an untreated plaque sample.  This reduction in absorbance is a result of inhibition of bacterial regrowth. Absorbance values used in this assessment are derived by subtracting the pre-incubated plaque suspension absorbance from the post-incubated plaque suspension absorbance, for both treated and untreated quadrants.

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