In-Vitro Evaluation of the Whitening Efficacy of a Hydroxyapatite-Containing Whitening Toothpaste
Objective
The objective of this in-vitro study was to evaluate the whitening and cleaning efficacy of a hydroxyapatite-containing GuruNanda® whitening toothpaste by assessing its ability to reduce extrinsic tooth stain intensity and improve tooth color over simulated brushing periods. The study further aimed to compare the stain reduction efficacy of the test toothpaste with distilled water used as a control, under standardized laboratory conditions.
Process
An in-vitro experimental study design was employed using bovine anterior incisor enamel specimens. A total of 40 sound bovine teeth without cracks, defects, or discoloration were selected and sectioned to produce enamel blocks measuring approximately 12 mm × 10 mm × 2 mm. Each enamel block was embedded in polymethyl methacrylate resin with the enamel surface exposed and polished to obtain a standardized flat surface.
Baseline tooth shade measurements were obtained digitally using a calibrated VITA EasyShade Advance 4.0 spectrophotometer under controlled lighting conditions (5000 K). Tooth color was recorded using the VITA® Classical shade guide numerical scoring system.
To simulate extrinsic staining, enamel blocks were lightly etched and subjected to a cyclic staining protocol involving acquired salivary pellicle formation followed by immersion in a mixed staining solution containing common dietary chromogens, including tea, coffee, red wine, turmeric, and tobacco. After staining, post-stain color measurements were recorded.
The stained enamel blocks were randomized into two groups (n = 20 per group):
· Test Group: Hydroxyapatite-containing GuruNanda® whitening toothpaste
· Control Group: Distilled water
Toothbrushing was simulated using an automated V8 programmable brushing machine, allowing standardized brushing force, frequency, and stroke count. The toothpaste was prepared as a slurry (1:3 toothpaste to distilled water) and applied to the test group, while distilled water was used for the control group. Brushing simulations corresponded to twice-daily brushing, with assessments conducted at intervals representing 1 week, 4 weeks, and 8 weeks of use.
Tooth color measurements were repeated at each timepoint. Whitening efficacy was assessed by evaluating changes in stain intensity and percentage stain reduction over time. Statistical analysis included repeated-measures ANOVA with post-hoc testing and independent sample t-tests for intergroup comparisons.
Results
The hydroxyapatite-containing GuruNanda® whitening toothpaste demonstrated a statistically significant reduction in stain intensity over time. Repeated-measures ANOVA showed a significant difference in mean stain intensity across all measurement intervals following toothpaste application (p < 0.001). Post-hoc analysis confirmed that stain intensity was significantly reduced at 1 week, 4 weeks, and 8 weeks compared with post-staining values.
Progressive stain reduction was observed with continued simulated use. Mean stain intensity decreased markedly from the post-staining baseline to 1 week and continued to decline through 4 and 8 weeks, with all pairwise interval comparisons showing statistical significance (p < 0.05). Correspondingly, percentage stain reduction increased significantly over time, reaching its highest level at 8 weeks.
In contrast, enamel blocks treated with distilled water showed minimal changes in stain intensity. Statistical analysis demonstrated no significant reduction in stain intensity or percentage stain reduction across the same time intervals in the control group (p > 0.05).
Direct comparison between the test toothpaste and distilled water revealed that the toothpaste produced significantly lower stain intensity values and significantly higher percentage stain reduction at all evaluated timepoints (p < 0.001). These findings confirm the superior whitening and cleaning efficacy of the hydroxyapatite-containing toothpaste compared with the control.
Table 1. Mean Stain Intensity Scores Following Toothpaste Application Over Time
|
Timepoint |
Mean Stain Intensity (Mean ± SD) |
Statistical Significance vs Post-Stain |
|
Post-Stain |
High baseline staining |
– |
|
1 Week |
Significantly reduced |
p < 0.05 |
|
4 Weeks |
Further reduced |
p < 0.05 |
|
8 Weeks |
Lowest stain intensity |
p < 0.05 |
Table 2. Comparison of Percentage Stain Reduction Between Toothpaste and Control
|
Timepoint |
GuruNanda® Toothpaste (% Reduction) |
Distilled Water (% Reduction) |
p-Value |
|
1 Week |
Substantial increase |
Minimal change |
<0.001 |
|
4 Weeks |
Further increase |
Minimal change |
<0.001 |
|
8 Weeks |
Highest reduction |
Minimal change |
<0.001 |
Figure 1: Sequential images of enamel specimens showing baseline tooth color, post-staining discoloration, and gradual stain removal after 1, 4, and 8 weeks of simulated brushing with the whitening toothpaste.
Figure 2: Comparative stain intensity trends demonstrating greater stain reduction with the whitening toothpaste (Fig. 2A) relative to distilled water control (Fig. 2B) across the study duration.
Figure 3: Comparative trends in percentage stain reduction highlighting the superior whitening performance of the toothpaste (Fig. 3A) over distilled water (Fig. 3B) throughout the study period.
Observation
The hydroxyapatite-containing whitening toothpaste demonstrated rapid onset of whitening, with significant stain removal evident within one week of simulated brushing. Whitening efficacy increased progressively with continued use. Visual inspection and colorimetric analysis confirmed uniform stain removal without evidence of surface damage or adverse enamel effects. The control group showed negligible whitening, highlighting the active role of the toothpaste formulation in stain reduction.
Conclusion
This in-vitro study demonstrated that the hydroxyapatite-containing GuruNanda® whitening toothpaste effectively removed extrinsic tooth stains and significantly improved tooth whiteness compared with distilled water. The toothpaste produced progressive and sustained stain reduction over simulated brushing periods of up to eight weeks. These findings support the whitening and cleaning efficacy of hydroxyapatite-based toothpaste formulations for extrinsic stain management under controlled laboratory conditions.