GB/T 40002-2021Oral hard tissue safety evaluation of toothpastes (English PDF)

5.1 General

This method is based on the use of a microhardness meter to measure the changes in the surface hardness of the oral hard tissues treated by oral care products, thereby evaluating the oral hardness. Whether the cavity care products are safe for the oral hard tissues.

This method selects very strict test conditions. In special circumstances, more complicated test methods that are closer to clinical conditions can also be used.

5.2 Device

5.2.1 Micro hardness tester

The requirements of the microhardness tester are implemented in accordance with GB/T 4340.2, and the test load range in this method should meet 0.05kg~ 0.5kg.

5.2.2 Grinding and polishing equipment

Silicon carbide grinding discs with continuous particle size changes (the finest can reach P1200), which can use diamond slurry for sample polishing and/or etc. Effective automatic grinding and polishing device.

Note: Other enamel and dentin polishing methods that meet the baseline requirements of the specimen can also be used, such as the diamond powder method.

5.2.3 Electric heating constant temperature drying oven

The temperature can be controlled to be constant at 37°C±2°C.

5.3 Preparation of enamel and dentin specimens

Use caries-free, erupted or non-erupted human permanent teeth, or bovine teeth. The size of these teeth needs to meet the following test requirements. Make Use suitable utensils (such as curettes, scalpels, etc.) to remove all soft tissue residues, sterilize and store teeth with 0.1% thymol.

Note 1. 1000mL 0.1% (mass fraction) thymol preparation method. Weigh 1g of thymol, dissolve in 1mL of absolute ethanol, and then add water to make the volume up to 1000mL.

Note 2. If it is known that the physical and chemical properties of tooth enamel and dentin will not be changed, other antibacterial and storage solutions can also be used.

Use a dental drill or a cutting disc to cut the enamel-dentin junction into two parts. Use the crown part to prepare the tooth enamel specimen, and use the tooth root part To prepare dentin specimens, the size of the specimen should not be less than 3mm×3mm×3mm.

Note 3. According to the size and shape of the crown and root, a tooth can prepare up to two specimens.

Put the enamel and dentin blocks upside down in the mold for embedding, and the outer surface of the specimen needs to be facing down. Embed the specimen in In epoxy resin, make sure that the specimen is placed flat and parallel to the resin surface. The dentin and enamel specimens that have been embedded, using a series of particle sizes Silicon carbide sandpaper grinding and polishing paste and diamond grinding and polishing paste polished until the tooth surface is smooth and uniform, without visible cracks and blemishes. The use of grinding and polishing reagents does not It can affect the physical and chemical properties of the tooth surface.

Note 4. It is recommended to use P320, P600, P800, 9µm, 3µm and 1µm grinding and polishing conditions in sequence.

The Vickers hardness was measured by a microhardness tester, and the specimens were screened by the hardness value. The measurement conditions are. load 300g, last 15s.

Each sample is measured at four points, and the measurement position needs to be shown in Figure 1. The distance between the measuring point and the edge of the tooth block should not be less than 0.5mm. Also need to be evenly distributed For the four measuring points, the distance a and b between each measuring point shall not be less than 1mm. The hardness of the sample is the average of the measured values at four points.

The initial Vickers surface hardness of bovine dentin specimens that can be included in the test ranges from 30HV to 50HV, and the initial Vickers surface hardness of human dentin specimens The degree range is 30HV~70HV. The Vickers surface hardness of enamel specimens of bovine and human teeth ranges from 250HV to 350HV. whether Tooth enamel or dentin, both need to be randomly grouped according to the surface hardness value, each group has 8 tooth blocks.

The specimens should be kept in deionized water until they are used. Deionized water at least meets the requirements of Grade III water in GB/T 6682 Claim.

5.4 Preparation of control samples

5.4.1 Positive control

Use deionized water as a positive control for the test.

5.4.2 Negative control

Prepare 1% citric acid as the negative control of the experiment.

5.5 Preparation of test samples

5.5.1 Preparation of toothpaste slurry

Toothpaste and deionized water are weighed according to the mass ratio of 1.3, stirred and mixed to avoid foam. Each specimen needs At least 5mL toothpaste slurry.

5.5.2 Preparation of mouthwash sample

Use mouthwash samples directly to process the specimens, and each specimen needs at least 5mL mouthwash.

5.6 Preparation of saliva

Human saliva or artificial saliva can be used. If artificial saliva is used, its preparation and requirements are as follows.

a) Preparation of 1L artificial saliva. accurately weigh 0.246g (accurate to ±0.0005g) calcium nitrate (or 0.354g tetrahydrate Calcium acid), 0.1225g (accurate to ±0.0005g) potassium dihydrogen phosphate, 9.685g (accurate to ±0.0005g) potassium chloride and 4.184g (accurate to ±0.0005g) bis(2-hydroxyethyl)aminotris(hydroxymethyl)methane in a 1L beaker, add 800mL Deionized water. Stir well to dissolve. Adjust the pH value to 7.0±0.05 with 1mol/L HCl. Transfer this solution to 1L In the volumetric flask, make the volume up to the mark with deionized water;

b) The final concentration of each component in artificial saliva is. 1.5mmol/L calcium nitrate, 0.9mmol/L potassium dihydrogen phosphate, 130mmol/L Potassium chloride, 20mmol/L bis(2-hydroxyethyl)aminotris(hydroxymethyl)methane.

5.7 Test cycle

Soak the specimen in toothpaste slurry or mouthwash for 5 minutes, control the temperature at 37°C±2°C, then wash the specimen thoroughly with deionized water, and then use it Soak the specimen with human saliva or artificial saliva for 55 minutes, and the temperature is controlled at 37°C±2°C. Repeat the above operation for a total of 6 cycles. Finally use The human saliva or artificial saliva immersed the specimen for no less than 12h, and the temperature was controlled at 37°C±2°C.

5.8 Detection

After the cycle treatment, the tooth block sample was rinsed with deionized water and stored in deionized water for later hardness testing.

A Vickers hardness tester was used to measure the surface microhardness of the cyclically processed tooth block samples. For the distribution of measuring points, see (Figure 1) Vickers Hardness measurement location map. Before measuring, make sure that the surface of the sample is dry. The measuring condition of the hardness tester is 0.3kg load, lasting 15s, and the measuring operation Work in accordance with QB/T 4780.

5.9 Data processing

The hardness value change deltaHV before and after the cycle treatment of each tooth is calculated in formula (1). deltaHV=HVpost-HVpre (1) Where. deltaHV ---The change in hardness value of each tooth piece, in kilograms per square millimeter (kg/mm2);

HVpost---The hardness value measured after cyclic processing, in kilograms per square millimeter (kg/mm2);

HVpre --- The hardness value measured before the cycle treatment, in kilograms per square millimeter (kg/mm2).

Note: All subsequent statistical analyses are based on deltaHV.

5.10 Statistical analysis methods

According to the definition of validity test and non-inferiority test in GB/T 3358.1, the analysis of deltaHV is as follows.

a) Validity test. A bilateral test is carried out at the 95% confidence level, and the average value of the positive control group is significantly better than the average value of the negative control group.

b) Non-inferiority test. A one-sided test is performed at the 95% confidence level, and the difference between the test product group and the positive control group is statistically significant Significance is less than the minimum effective difference, where the minimum effective difference is equal to half of the average difference between the positive control group and the negative control group. change In other words, a one-sided test is performed at the 95% confidence level, and the average value of the test product group is significantly better than that of the positive control group and the negative control group. average value.

c) The above two requirements should be met at the same time, and the tested product can be judged as non-inferior to the positive control.