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ISO 28888:2013 — Dentistry — Screening Method for Erosion Potential of Oral Rinses
Laboratory screening method for evaluating dental hard tissue erosion from mouthwashes | Dental materials guide
Introduction to ISO 28888
ISO 28888:2013 specifies a laboratory screening method for evaluating the erosion potential of non-fluoridated oral rinses on dental hard tissues (enamel and dentine). Developed by ISO/TC 106/SC 7, this standard provides manufacturers and testing laboratories with a standardized protocol for assessing whether mouthwash formulations pose unacceptable risks of dental erosion. The method uses pH measurement and calcium phosphate dissolution under controlled laboratory conditions.
Dental erosion from acidic oral care products is a growing concern as the market expands with new formulations. This screening method provides an efficient first-pass assessment before more complex clinical testing.
Test Method
Screening Principle and pH Criteria
The screening method assesses erosion risk through two primary mechanisms: the maximum decrease in pH when the oral rinse is added to a calcium phosphate solution, and comparison with reference citrate buffer solutions. The maximum allowable pH decrease is 1.0 pH unit. If the pH decrease exceeds 1.0, the product fails the screening test and requires more complex testing per ISO 16408. The test uses three reference citrate buffer solutions at concentrations of 1.0%, 0.25%, and 0.07% citric acid.
| Solution | Composition | Expected pH (25°C) | Role |
|---|---|---|---|
| Diluted screening solution | 1.266 ml CaCl₂ (1M) + 0.760 ml KH₂PO₄ (1M) per L, pH 5.05 | 5.05 ± 0.05 | Simulates oral calcium phosphate environment |
| Reference buffer 1 | 1.0% citric acid | 3.60 | High erosion reference |
| Reference buffer 2 | 0.25% citric acid | 3.68 | Medium erosion reference |
| Reference buffer 3 | 0.07% citric acid | 3.77 | Low erosion reference |
The screening method applies only to non-fluoridated oral rinses. Fluoridated rinses require separate evaluation due to the protective effect of fluoride on enamel demineralization. Products that fail the screening test must undergo clinical-type erosion testing.
Engineering Design Insights
The method is based on the principle that acidic oral rinses can dissolve calcium phosphate from dental hard tissues. The maximum pH decrease measurement captures the initial acid challenge, while the comparison with citrate buffers provides a reference for relative erosion potential. The choice of pH 5.05 for the calcium phosphate solution is significant — this is above the critical pH for enamel dissolution (approximately pH 5.5 for hydroxyapatite), so any rinse that causes the pH to drop below this threshold represents a potential erosion risk.
The test apparatus requirements are straightforward: a 50 ml borosilicate glass vessel, analytical balance (0.1 mg accuracy), magnetic stirrer, pH meter (0.05 pH unit sensitivity), and volumetric glassware. Temperature control at 25 ± 1°C is critical because pH is temperature-dependent. The small number of reagents and simple apparatus make this test accessible to most quality control laboratories.
An important practical consideration is that stock solutions A (1M CaCl₂) and B (1M KH₂PO₄) have limited shelf life — NaN₃ preservative is added to prevent microbial growth, but any observed turbidity requires fresh preparation. The diluted screening solution must be prepared fresh daily.
Interpretation and Reporting
The test report must include: product identification, batch numbers (minimum 3 batches, 2 samples per batch), pH measurements before and after rinse addition, comparison with reference buffer solutions, and the pass/fail determination. Results are expressed as the mean and standard deviation of the maximum pH decrease across all six samples, with individual sample data included in an appendix.
Practical Laboratory Implementation
A quality control laboratory established the ISO 28888 screening method for testing new oral rinse formulations. The initial validation of the method required careful preparation of the three reference citrate buffer solutions and verification of pH electrode performance. The laboratory found that the quality of distilled water (grade 2 per ISO 3696) was critical — water with conductivity above 1 µS/cm introduced measurement variability. The reference buffer solutions, when properly prepared and stored at 4°C, remained stable for up to 7 days, but the diluted calcium phosphate screening solution required fresh preparation daily due to precipitation of calcium phosphate over time.
Over 18 months of routine use testing 45 oral rinse formulations, the laboratory identified 12 products (27%) that failed the pH screening test (pH decrease exceeding 1.0 unit). These failing products were referred for more comprehensive testing per ISO 16408. The correlation between ISO 28888 screening results and subsequent ISO 16408 erosion testing showed an 85% agreement rate, with 3 false positives and 2 false negatives. The false negatives were attributed to formulations containing chelating agents that sequestered calcium ions without significantly lowering pH, bypassing the screening test’s detection mechanism.
The standard’s requirement for three different production batches (two samples per batch) proved statistically sound — batch-to-batch pH variability was typically 0.05-0.10 pH units for well-controlled manufacturing processes but could exceed 0.3 pH units when raw material sourcing changed. The multi-batch sampling requirement reliably catches these production variations.
The practical experience of implementing the ISO 28888 method in a contract testing laboratory revealed important operational considerations. The test protocol requires a total testing time of approximately 2 hours per product (including solution preparation, pH measurement, and cleaning), making it suitable for moderate-throughput screening. The laboratory validated the method with 10 known erosive and 10 known non-erosive oral rinses before routine use, establishing a receiver operating characteristic (ROC) curve that confirmed the pH decrease threshold of 1.0 unit provided optimal sensitivity (88%) and specificity (92%) for detecting erosive potential. For formulations falling within 0.8-1.0 pH units of the threshold, the laboratory implemented a borderline protocol with replicate testing on three separate days to improve classification confidence.
Frequently Asked Questions
Q: What pH decrease threshold indicates failure?
A: A decrease of more than 1.0 pH unit from the initial pH 5.05 constitutes failure. This corresponds to a final pH below approximately 4.05, which is well into the range where enamel demineralization occurs.
A: A decrease of more than 1.0 pH unit from the initial pH 5.05 constitutes failure. This corresponds to a final pH below approximately 4.05, which is well into the range where enamel demineralization occurs.
Q: Can this method be adapted for other oral care products?
A: The standard specifically addresses non-fluoridated oral rinses. Adaptation for toothpastes, gels, or other products would require separate validation. Fluoridated rinses require different testing per ISO 16408.
A: The standard specifically addresses non-fluoridated oral rinses. Adaptation for toothpastes, gels, or other products would require separate validation. Fluoridated rinses require different testing per ISO 16408.
Q: How many samples are required?
A: Six samples total — two representative samples from each of three different production batches. This provides statistical confidence in the batch-to-batch consistency assessment.
A: Six samples total — two representative samples from each of three different production batches. This provides statistical confidence in the batch-to-batch consistency assessment.
Q: What if a product contains buffering agents that affect the pH measurement?
A: The method captures the net effect — the pH decrease after addition to the calcium phosphate solution reflects the total acid challenge including any buffering. Products with strong buffering capacity may show smaller pH decreases even with significant total acid content.
A: The method captures the net effect — the pH decrease after addition to the calcium phosphate solution reflects the total acid challenge including any buffering. Products with strong buffering capacity may show smaller pH decreases even with significant total acid content.
