Updated Pellicle Cleaning Ratio Method for in vitro  Stain Removal

Objectives:

To improve the original pellicle cleaning ratio (PCR) method of Stookey et al. (J.Dent.Res.,1982).

Methods:

Bovine enamel specimens were prepared and embedded as per the original method, but to improve the uniformity of the stain uptake, etching was performed by mounting them onto a frame before exposure to 1% HCl, super-saturated Na₂CO₃ and 1% phytic acid.  For staining, specimens were mounted on a specially designed instrument containing 8 wires, each capable of holding 20 blocks, and rotated through a trough containing tea, coffee, mucin, tryptone soy broth and iron chloride.  The instrument is mounted in an incubator, with the temperature at 50C rather than the original 37C, as this was found to increase the rate of stain uptake.  Four toothpastes were evaluated (n=8), with cleaning performed using a Martindale Abrasion Tester, and residual stain removed using flour of pumice and a grinding wheel.  Tooth colour at each stage was measured using a chromameter.  No external standard was used, and PCR was calculated according to:

PCR = 100 x {L*(brushed) – L*(stained)}/{L*(pumiced) – L*(stained)}

Results:

Apart from allowing a higher throughput of blocks for staining, the modifications to the method result in smaller error bars as shown in the table (standard deviations in brackets), which relate to standard errors of approximately 3% compared to more than 10% for the original Stookey paper.  Based on the results shown, paste D is significantly poorer than pastes A, B and C, while paste A is also significantly better than paste B, which would not have been apparent with the original method.

Conclusions:

The modifications to the original PCR method result in higher throughput and more accurate results.