Remineralization Unit experimental models
OHRI pH cycling 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)
Microhardness Testing
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.
Enamel solubility reduction model
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.
