Laboratory Testing Core & Facility

Abrasion-Cleaning Unit experimental models

This method is used to determine the abrasive level of dentifrices and abrasives in human root dentin. The RDA value is calculated in relation to the abrasive level of a standard material (Ca2P2O7, Odontex Inc.), which is given the empirical value of 100. It involves the laboratorial procedure developed by Hefferren (1976) and recommended by the ADA and ISO 11609.

This method is used to determine the abrasive level of dentifrices and abrasives in human enamel. The REA value is calculated in relation to the abrasive level of a standard material (Ca2P2O7, Odontex Inc.), which is given the empirical value of 10. It is based on the laboratorial procedure developed by Hefferren (1976) and recommended by the ADA and ISO 11609.

This test was developed in order to assess the ability of dentifrices to remove stained pellicle artificially created on enamel surfaces; that is, to determine the cleaning ability of dentifrice formulations. The results of this test have shown to be comparable to those obtained in a clinical trial. Thus, they may be considered for the prediction of clinical findings with a reasonable degree of confidence. The PCR value is calculated relatively to a standard material (Ca2P2O7, Odontex Inc.), which is given the empirical value of 100.

This method is based on the work previously published by Bailey and Phillips (1950), on the study of abrasive prophylactic agents and techniques on enamel surfaces. Toothbrushing provides several benefits, including the polishing of enamel surfaces. Different toothpastes/abrasives may provide different polishing potential for enamel surfaces, and this can be determined by light reflection analysis. The outcome for this test is the difference in enamel gloss (or light reflection) between the pre- and post-treatment measurements.

pH, titration

Hara and Zero (Eur J Oral Sci. 2008; 116:1–6)

pH-stat

Scaramucci et al. (J Dent. 2011; 39:841­–8)

Static models (demin and remin)

Hara et al. (Caries Res.2005; 39:134­–8); Hara et al. (Caries Res.2008; 42:51–6)

Erosion-abrasion cycling model

Hara et al. (Caries Res. 2005; 39:134­–8); Hara et al. (Caries Res. 2008; 42:51–6)

Fluoride Unit experimental models

This method is used for the analysis of water and oral care products. It is conducted using a combination fluoride ion-specific electrode and a pH/ion meter. Samples are mixed 1:1 with TISAB II to adjust ionic strength. Readings are obtained directly from the ion-selective electrode.

This method is used for the analysis of environmental and biological samples (i.e., saliva, food, soil, serum). It is conducted using a modification of the hexamethyldisiloxane microdiffusion method of Taves (1968).

This method directly measures the activity of fluoride ions in samples of minimal fluid volume (usually less than 0.005 µL). This method is used primarily for determining fluoride content of dental biofilm fluids/solids and plasma from human and animal models (mice, zebra fish). Samples are placed under mineral oil directly on the electrode surface and numerous samples can be measured in rapid succession.

This method can evaluate the effect of treatment time and dilution on the ability of oral care products to promote fluoride uptake. The test procedure is a modification of Test Method #40 in the FDA Monograph, which includes the formation of a caries-like (subsurface) lesion that is formed using a solution of 0.1M lactic acid and 0.2% Carbopol 907, 50% saturated with HAP at a pH of 5.0. Enamel microbiopsies are conducted using modification of the microdrill enamel biopsy technique as described by Sakkab et al. to analyze the fluoride content of partially demineralized enamel.

Remineralization Unit experimental models

pH cycling models were designed to simulate the dynamic variations in mineral saturation and pH associated with the natural caries process (White, 1995). They reproduce specific events of the caries process under controlled conditions, allowing the investigation of individual mechanistic variables that would not be possible to do or would be extremely difficult to do under in vivo conditions. At the same time, it is important to recognize that because of not being able to reproduce the whole complexity of caries dynamics, in vitro experiments provide only limited information on the effects of different variables on the caries process.

While there are several pH cycling models commonly used, the one developed by White (1987, 1988) has been shown to be an excellent model to evaluate the remineralization potential of fluoride dentifrices. This model is able to demonstrate a dose-response (0, 250 ppm and 1100 ppm F) in both enamel and dentin (Dunipace et al., 1992; Faller, 1992; Schemehorn et al., 1994) and can be used with either bovine or human enamel (Schemehorn et al., 1992).

The Indiana Oral Health Research Institute has also the capabilities and experience to conduct other pH cycling models, such as the one developed by Featherstone et al. (1986).

The main difference between these two models is the net outcome—the model developed by White (1987, 1988) is a net remineralization model, whereas the one developed by Featherstone et al. (1986) is a net demineralization model. Thus, both aspects of in vitro caries lesion remineralization and prevention can be studied at the Indiana Oral Health Research Institute.

The Indiana Oral Health Research Institute employs the following techniques to characterize caries lesions:

  • Surface microhardness (SMH)
  • Cross-sectional microhardness (CSMH)
  • Transverse microradiography (TMR)
  • Quantitative light-induced fluorescence (QLF)
  • Enamel fluoride uptake (EFU)

The procedure used in this model is FDA Test #33 for the determination of the enamel solubility reduction of different products. Extracted human teeth are cleaned and exposed to a lactic acid buffer. The amount of phosphate dissolved from the teeth is quantified. The teeth are then exposed to the treatment and demineralized again. Again, the amount of phosphate in the lactic acid buffer is determined. Finally, teeth are exposed to the lactic acid buffer, and the amount of phosphate dissolved from the teeth is quantified once again. The percent of enamel solubility reduction is then computed as the difference between the amount of phosphorus in the pre- and post-treatment lactic acid solutions, divided by the amount of phosphorus in the pre-treatment solution and multiplied by 100.

Microhardness analysis

Our Tukon 2100B microhardness tester measures surface hardness of flattened and polished dental substrates or composite materials. Systems are equipped with Knoop and Vickers diamonds and connected to a Clemex CMT HD computer image analysis system (ASTM E 384 and DIN/ISO 6507 compliant) for measurement of indents. A Märzhäuser automated stage is utilized for indent placement, with 2 stage micro-stepper motors accurate to <1 µm movements. Microhardness tester load cells are capable to delivering test loads from 5 grams to 1 kg.

Tooth processing unit

Our labs have multiple grinding and polishing machines used for grinding and polishing bovine and human enamel and root dentin, or dental composites and ceramics for studies of caries, erosion, and abrasion, and surface microhardness testing.

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