The purpose of this study was to obtain information about the detailed histopathology of naturally occurring root caries. Fifty extracted human teeth exhibiting some degree of root caries were sectioned longitudinally and examined with transmitted light, polarized light and microradiography. The occurrence of the histological zones of dentinal caries was tabulated and revealed a lesion body in all eases Light microscopy showed the same basic features as microradiography and was most useful when the sections were imbibed in quinoline. A structureless area below the main body of the lesion was observed in 77% of the cases when using quinoline. This fluid more clearly defined the extent of the lesion and may show a “phenolic reaction” when using polarized light microscopy. Partial radiopaque surface layers were observed in almost 80% of the sections. This study has described the detailed histopathology of root caries, and aids in the development of model systems to evaluate this emerging dental health problem.

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.

Exposure of both small carious lesions and artificial caries-like lesions to a synthetic calcifying fluid in vitro produced a significant degree of ‘healing’ or remineralization of the lesion. Changing the calcium concentration of the calcifying fluid had a marked effect on the degree of remineralization produced. When a low calcium concentration of 1 mM was employed, remineralization occurred throughout the entire depth of a lesion. Under these conditions, there was a mean reduction of 69% in area of the body of the lesion and a mean increase of 40% in orientated mineral. The dark zone at the advancing front of the lesion showed a dramatic increase in area of 526% and was much closer to the enamel surface relative to the control. When higher calcium ion concentrations of 3 mM were used, remineralization occurred but was limited to the surface of the lesion. Under these conditions, the mean reduction in area of the body of the lesion was 20%, brought about by a mean increase in orientated mineral of 17%. Although changes were found in relation to the dark zone, these were much smaller than those found for the 1-mM fluid, the increase in area being 38%. With respect to exposure times, results obtained using ten consecutive 24-hour exposures to the synthetic calcifying fluid were similar to those obtained after ten consecutive 1-hour exposures. Remineralization, therefore, occurred within each 1-hour exposure increment. Scanning electron microscopy showed that crystal diameters for sound enamel were in the range 35–40 nm. In the body of the lesion crystal diameters were reduced and found to be in the range 10–30 nm. In lesions remineralized with the high calcium-calcifying fluid containing 3 mM calcium, crystal diameters were larger than those found in either control lesions or in sound enamel, being in the range 50–75 nm. When the low calcium-calcifying fluid was used, remineralized lesions showed crystal diameters in the range 50–150 nm with a small number of crystals having diameters of 200 nm. Calculation of the supersaturation of the calcifying fluids revealed that the low calcium-calcifying fluid having 1 mM calcium favors crystal growth as opposed to nucleation.

The beneficial effects of fluoride on enamel have been well documented. However, limited data are available concerning the amount of fluoride required for beneficial effects on tooth root. Although studies have shown that fluoride inhibits root demineralization, the aim of this study was to investigate the location, extent and amount of remineralization on root dentin substrates after demineralization has occurred. The root surfaces of extracted human teeth were demineralized in a pure chemical buffer containing varying concentrations of sodium fluoride. After this lesion initiation, the same root sections were then placed into a remineralizing solution. The root sections were characterized after demineralization, and again after remineralization, by polarized light microscopy (PLM) and microradiography (MRG). Lesion depths after the demineralization phase were found to be inversely proportional to the fluoride concentration. When fluoride was present, bands or lines within the body of the lesion were observed with PLM and MRG. Using quantitative MRG, variations in mineral content and distribution were recorded. Examination of the root sections after the remineralization phase showed remineralization to have occurred on the remaining mineral and not on organic matrix devoid of mineral. The amount and location of mineral deposition may be of great significance in the arrestment and treatment of in vivo root surface caries.

This study suggests that, when compared to 'multinational dentifrices', Chinese and Indian dentifrices manufactured locally failed to show 'healing' efficacy even though they claimed to contain varying levels of fluoride.