The effect of baseline lesion mineral loss on the remineralization of enamel lesions by a sodium fluoride dentifrice was studied in situ by means of an appliance carrying enamel sections. Artificial lesions of various sizes were created, by means of acidified gelatin, and were then mounted on the appliances of five volunteers. Each brushed twice daily for two min with a 1000 ppm F sodium fluoride dentifrice. Measurements of mineral content were made at baseline and at weekly intervals by microradiographic/microdensitometric techniques. Data from all five volunteers showed a linear increase in remineralization rate with increasing lesion size. Thus, in studies which compare the effects of different remineralizing formulations, care must be taken to ensure that initial lesion sizes are matched, or that the results are expressed as a percentage change in mineral content.

Transversal microradiography is the most widely accepted method used to study changes in mineral content profiles. In spite of its widespread use, relatively little information is available on its validity and reproducibility. Following the recommendation of the Consensus Conference on Intraoral Model Systems, this study was designed to explore reproducibility of lesion analysis within a laboratory and comparability of analysis among various laboratories. Incipient enamel lesions were produced by four research groups using both a common (‘standard’) and a local (‘preferred’) protocol. Sections were produced by each group and allocated to ‘mixed’ bags of specimens, which were analysed by the groups. With the chosen scheme some sections were analysed six times by the same group (as an internal reference standard) while others were analysed by all four groups. The data for the mineral content profiles were expressed as the integrated mineral loss (IML) value and lesion depth. The results showed the lesions produced with the standard protocol to be in the range 2,000–3,000 vol% mineral × μm for IML. The IML of the lesions produced with the preferred protocol varied between 1,800 and 6,300 vol% mineral × μm. Variation in IML values could be attributed to the biological variation between lesions, but also to time (of microradiograph production) and measurement effects, calibration of the magnification of the specimens, and the parameters used in the algorithm to calculate IML. Some of these parameters also affected the lesion depth. It is advised to standardise (or at least report) the method of calculation of IML, and to include a reference lesion between analyses in a longitudinal study as an internal standard. With the data produced, it was calculated that the number of lesions required to differentiate between preventive treatments varied substantially among laboratories. The recommendations given will improve the power of the screening methods for caries-preventive agents for which microradiography is an essential analytical method.

An in vitro pH-cycling experiment was carried out to investigate the effect of fluoride concentration on enamel demineralization and remineralization. Artificial caries lesions were formed in an acid-buffered solution and subjected daily to a 3-hour acid attack, a 5-min immersion in the test NaF solution (0, 1,250, 500, 1,000, 1,750 and 2,500 ppm F), and to 21 h in an artificial saliva. Changes in mineral content were assessed weekly for 5 weeks using microradiography/microdensitometry. The lesions in the control group (0 ppm F) and the 1-ppm F group demineralized. Remineralization was significantly higher in the 500-ppm F group compared to the 250-ppm F group. However, higher fluoride concentrations did not produce any further significant increase in remineralization. Laminations were apparent in lesions subjected to the 250- and 500-ppm F solutions.

A variety of methods has been employed to produce artificial caries-like enamel lesions. The aim of this paper was to use a pH-cycling regime to compare the de-/remineralization behavior of lesions prepared by two methods. Lesions were produced by use of either an acidified undialyzed gelatin system or a buffered solution. Enamel sections, each containing four lesions, were allocated to four groups (A, B, C, D) and subjected to a daily pH-cycling regime of 16-hour demineralization and eight-hour remineralization. Groups A & B contained gelatin-prepared lesions, whereas Groups C & D contained solution-prepared lesions. To the remineralizing solutions used in Groups B & D, 2 ppm fluoride was added. The mineral content in the lesions was assessed, by means of microradiography/microdensitometry, at baseline and at intervals for six weeks. The lesions in all four groups exhibited net demineralization. In terms of the total mineral lost from the lesion (the delta z parameter), the demineralization rates of the solution-prepared lesions were significantly greater than those of the corresponding gelatin-prepared lesions. All sections in the non-fluoride groups showed subsurface demineralization in initially sound enamel, whereas only one section in the fluoride groups showed an area of mineral loss. Laminations in the mineral content profiles were apparent only in Group D. The results of this study indicate that the method of lesion preparation affects the subsequent behavior of lesions when exposed to de- and remineralizing protocols.

An enamel-section-carrying intra-oral appliance to predict the results of double-blind anti-caries studies has been developed. Initial validation was against the F concentration effect attained in a clinical trial where three sodium monofluorophosphate (SMFP) dentifrices were used. Original appliance-based work showed significant differences in remineralization between non-F and F dentifrices, but not between different F dentifrices. However, it was shown later that acidified gel-prepared lesions were not as responsive as solution-prepared lesions to de- and remineralizing processes, and lesion remineralization rates were found to be dependent on initial lesion size. An in situ cross-over study was then repeated with use of acid-solution-created lesions, and seven volunteers completed the project. Each brushed twice daily x 2 min with either 0, 1000, or 2500 ppm F, as SMFP dentifrice. After a two-week wash-out, subjects wore the appliances for four weeks. Enamel mineral content was assessed at 0, two, and four weeks via microradiography/microdensitometry, and a statistically significant dose-response was obtained between non-F and F as well as between 1000 and 2500 ppm F pastes, i.e., as per the three-year clinical trial data. Hence, the model's suitability for pre-clinical screening was confirmed. It has also been used in caries microbiological studies, in root caries investigations, and currently in chewing gum cariogenicity experiments.

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The in situ dental caries model developed in Glasgow was evaluated by determining whether it could demonstrate a fluoride dose response in a crossover study using 0, 250, and 1,000 ppm F from sodium fluoride dentifrices. In situ appliances, each carrying four enamel sections with multiple artifícal carious lesions, were worn by 12 dentate subjects for three 5-week experimental runs, during which they brushed twice daily with a test paste. Mineral changes in the lesions were measured by analyzing microradiographs, using an image analysis system, after 0, 2, 4, and 5 weeks and the rate of change calculated. Two-way analysis of variance showed no significant intersubject effects (for any of the parameters), but demonstrated strong evidence of a linear fluoride dose effect: total mineral loss (▵z) p = 0.0596; lesion body p = 0.0423; surface zone p = 0.0081. However, the exclusion of the data from 1 low-caries (DMFS = 1), high-calculus-forming subject produced even stronger evidence as to the efficacy of this model (▵z p = 0.0226; lesion body p = 0.0164; surface zone p = 0.0081). Hence, these results suggest this model is useful for studying fluoride products according to guidelines of American Dental Association.

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