Objective:
To develop a simple and rapid in-vitro whitening model for evaluating bleaching performance of prototype hydrogen peroxide (HP) gel in pre-dosed flexible trays.
Method:
Bovine teeth were pre-brushed with standard toothpaste to remove loose extrinsic stain. Baseline L*a*b* was taken for each tooth using a Hunter LabScan XE spectrophotometer. Teeth were randomised and allocated to test groups (n=7). Prototype tray products (0-10.5%w/w HP) and Crest Whitestrips® (CWS 6%w/w HP) were applied to the teeth. Both products were held in place by a plastic ring. Phosphate buffered saline was gently lapped over the teeth at 37°C (45minutes/day for the prototype, 30minutes twice daily for CWS). Formulations were removed by brushing under running water. L*a*b* was re-measured and the change in L*a*b* calculated. A one-way ANOVA (95% LSD) test using StatGraphics Plus software was performed.
Results:
|
Study 1 |
Mean change in L*(± s.d.) |
||
|
|
Day 1 |
Day 3 |
Day 5 |
|
10.5%w/w |
6.00±1.88 |
9.01±2.82 |
10.23±3.21 |
|
5.25%w/w |
3.95±1.99 |
6.50±2.73 |
7.73±2.92 |
|
0%w/w |
1.57±1.14 |
2.85±1.54 |
3.82±1.93 |
|
CWS |
1.56±0.99 |
3.66±2.02 |
5.17±2.81 |
|
Water |
-0.08±0.26 |
-0.78±0.47 |
-0.63±0.55 |
|
Study 2 |
Mean change in L*(± s.d.) |
||
|
|
Day 1 |
Day 3 |
Day 5 |
|
5.5%w/w |
5.05±1.94 |
9.16±2.34 |
11.12±2.34 |
|
3.3%w/w |
4.05±1.48 |
7.57±2.54 |
9.34±2.89 |
|
1.0%w/w |
3.43±1.43 |
6.72±3.10 |
8.31±3.90 |
|
0%w/w |
1.71±0.52 |
2.97±1.14 |
3.79±1.32 |
|
CWS |
2.38±0.66 |
4.72±1.68 |
6.17±2.07 |
Both studies showed a clear dose-response for the HP gels. The model showed statistically significant differences between treatments within individual studies, despite the large standard deviations, due to using a natural substrate. By day 5 the bleaching capacity of the teeth was saturated and discrimination between treatments was reduced. The placebo effect may be due to dehydration of teeth. Appropriate use of internal controls allowed relative bleaching performance to be assessed. In both experiments the prototype 5%w/w HP gel directionally outperformed CWS 6%w/w HP at all time-points.
Conclusion:
The bovine model provides a good model for evaluating bleaching performance.