In vitro root caries progression measured by 125I absorptiometry: comparison with chemical analysis

Effects of salicylic-lactic acid conditioner on the shear bond strength of brackets and enamel surfaces

The purpose of this study was to evaluate the effects of salicylic-lactic (SL) acid conditioner on the shear bond strength of brackets. Fluoride releasing (Light-bond) and non-fluoride releasing (Enlight) composite adhesives were used after conditioning with 0.22% salicylic + 9% lactic acid or 34% phosphoric acid. Composite adhesives were light cured with either a halogen light curing (HLC) unit for 30-50 s or a plasma arc curing (PAC) unit for 4 s. The shear bond strength was measured with an Instron. Failure modes of debonded brackets were identified based on adhesive remnants on the bracket and tooth. Salicylic-lactic acid conditioning was found to provide adequate shear bond strength. Groups conditioned with SL acid were debonded mainly at the enamel-resin interface and comparatively clean enamel surface after debonding was observed than those conditioned with phosphoric acid. Using confocal laser scanning microscopic examinations, it was found that demineralization patterns between SL acid and phosphoric acid conditioned groups were not different when the same adhesive was used. The SL acid conditioner did not reduce the demineralization. Light-bond adhesive showed less demineralization than Enlight adhesive. The PAC unit can be recommended as an alterative to the HLC unit because it significantly reduces the irradiation time.

Effect of intermittent delivery of fluoride to solution on root hard-tissue de- and remineralization measured by 125I absorptiometry

The effect of intermittent fluoride levels on root hard-tissue de- and remineralization was studied once daily for 21 days in a pH-cycling caries model with simulated fluoride clearance curves. Four root hard-tissue blocks, from each of 12 human teeth, were cut out parallel to the cementum surface. During a daily 15-hour period, the blocks were subjected 12 times to pH changes similar to those which occur in plaque after a carbohydrate intake. The fluoride was delivered immediately before a daily nine-hour remineralization period. Four experiments were independently carried out: One block from each tooth was subjected to pH-cycling without and with fluoride delivery, simulating a rinse with 0.025, 0.2, and 1.0% sodium fluoride (NaF), respectively. The mineral change in the blocks was monitored by 125I absorptiometry and expressed as the change in transmission (delta T). The surface between the data points (delta T values) and the x axis (time points) was used as a summary measure, i.e., the area under the curve (AUC). When no fluoride was delivered, the delta T increased over 21 days, indicating loss of mineral. The AUC was, on average, 5.85 +/- 0.68 (mean +/- S.E.) %.day. In the 0.025% NaF-rinse experiment, there was a marked reduction in mineral loss, indicated by an average AUC of 1.66 +/- 0.59%.day. In both the 0.2 and 1.0% NaF-rinse experiments, a decrease in delta T, indicating gain of mineral, was observed from day 2. Negative delta T values occurred after 7 and 3 days, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Demineralization and remineralization evaluation techniques

This paper compares the experimental techniques utilized to assess the de- or remineralization of enamel or dentin in intra-oral studies. In in situ studies, it is important for one to know how much mineral has been lost or gained, and where the loss or gain occurred. The main emphasis in this paper is on techniques suitable for direct or indirect mineral quantification. The measuring techniques considered are microradiography, iodine absorptiometry, various microhardness tests, polarized light, light-scattering, iodide permeability, and wet chemical analysis. The various techniques are compared concerning suitability for the determination of mineral content in vol% (or wt%), mineral changes in vol% micron (or kg.m-2), and mineral distributions. Furthermore, sample preparation, the importance of protein penetration, nominal mineral loss range, the estimated mineral loss threshold, and the applicability to dentin are compared and considered. It is concluded that, although more than ten techniques are available for the measurement of changes after de- or remineralization in situ, transverse microradiography is the most practical technique for the direct and quantitative measurement of mineral content, mineral changes, and mineral distributions. Cross-sectional microhardness testing and light-scattering are also practical indirect techniques for quantitative mineral loss (or gain) determination in intra-oral studies.

A quantitative analysis of mineral loss and shrinkage of in vitro demineralized human root surfaces

Demineralization of dentin specimens proceeds at a faster rate than that of enamel. Although this is generally accepted, a quantification of the rate of formation of root lesions is hampered by the shrinkage of the lesions when these are dried prior to microradiographic analysis. This leads to a significant underestimation of the lesion depth and total mineral loss. The aim of this paper was to quantitate the rate of mineral loss during root lesion formation in vitro and to determine the shrinkage of root specimens as a result of drying. Unerupted roots of human teeth were subjected to a demineralizing system of 0.1 mol/L lactate buffer (pH = 4.8) with 0.2 mmol/L methanehydroxydiphosphonate during four, 11, 22, and 44 days. The root lesions were assessed by quantitative microradiography. The demineralizing solutions were analyzed to determine the amounts of root tissue dissolved. A comparison of these two sets of data showed that, with the demineralizing system used, root lesions may shrink up to 62%. Fixation of the specimens in fixative did not affect this shrinkage. Chemical analysis showed that mineral loss proceeded linearly with time. From the data-sets of this study, a model was developed to compensate for the shrinkage in the dentin specimens. In this way, it was possible to calculate the lesion depth at four demineralization times as being 130, 220, 320, and 530 microns, respectively. These values were in agreement with a microscopic determination of the lesion depth.

A review of quantitative methods for studies of mineral content of intra-oral caries lesions

Modern prospective caries studies require the measurement of small changes in tooth mineral content. Quantitative measurements of changes in mineral content in a single caries lesion is desirable. Quantitative methods can be either destructive or non-destructive. The latter type permits longitudinal studies to be conducted. Various methods available for the analysis of lesion parameters are reviewed. The basic principle of each method is summarized, and its characteristics are discussed. For each method, the correlation between the measured parameter and mineral loss, the useful range of mineral loss, the discrimination threshold, and the repeatability, are presented. Where such quantities were not available in the original papers, they were calculated from literature data. A comprehensive table of specifications of all methods is given.

Root hard-tissue demineralization rate measured by 125I absorptiometry: comparison with lesion-depth measurements

The aim of the present study was to compare demineralization of root hard tissue, monitored by 125I absorptiometry, with lesion-depth measurements under polarized light microscopy. The intact roots of ten human molars, which had not been exposed to the oral environment, were divided into 39 cementum/dentin blocks and exposed to a buffer solution of pH 4.5 containing 2.2 mmol/L calcium and inorganic phosphate. After demineralization for 3.5, 7, 14, and 21 days, transmission measurements by 125I absorptiometry were performed, and one block from each tooth was taken out of the solution for lesion-depth measurement. The results showed a high degree of correlation (r = 0.952) between lesion depth and change in transmission, with a more rapid increase initially in both variables. A linear relationship with the square root of time was found. Conversion of transmission data to lesion-depth data was possible when this caries model system was used on cementum dentin blocks.

Effects of fluoride on caries development and progression using intra-oral models

This paper reviews the use of intra-oral model systems to help elucidate the role of fluoride and its mechanism of action in caries prevention. The intra-oral models currently in use were found to be of three general types. The most widely used system has consisted of a removable appliance that relies on the use of dacron gauze or a recessed sample to enhance plaque formation. Similarly, the banding model of Ogaard requires the presence of orthodontic band material to produce a plaque accumulation niche for demineralization, while the crown single-section technique relies mainly on placement of the sections in plaque-retentive areas (below contact points). In general, the models may be used for the assessment of food cariogenicity, an evaluation of de- and re-mineralization, and measurement of fluoride incorporation into enamel or root substrates. On evaluation of lesion initiation and progression in vivo, it is apparent that few non-destructive in vivo techniques are available that offer the sensitivity of laboratory-based analysis. Thus, the use of intra-oral models that allow lesion formation and progression to occur in the oral environment, but can be measured with the sensitivity of in vitro techniques, has been extremely important. Although the magnitude of the fluoride dose, the longevity of fluoride in the oral environment, and the time required for remineralization are different from those found in vitro, it is apparent that the presence of fluoride in the aqueous phase is now thought to be of primary importance. Mechanistically, the presence of fluoride will both inhibit demineralization by acid and promote remineralization under more neutral conditions. Thus, one of fluoride's major contributions is to affect the rates of lesion formation and progression. It was concluded that low-concentration fluoride agents with a high frequency of application would best fulfill the above needs.

In vitro studies on the effects of fluoride on de- and remineralization

The recent literature extensively describes the role of ambient fluoride in the de- and remineralization of dental enamel. Fluoride in sub-ppm concentrations is effective in promoting mineral deposition and inhibiting mineral dissolution. The latter phenomenon is most likely attributable to the concomitant precipitation of a fluoride-rich mineral phase which inhibits further dissolution. These fundamental processes result in an inhibition of enamel demineralization and an enhancement of enamel lesion remineralization. Alternatively, fluoride may also induce the 'arrestment' of enamel lesions. For the in vivo patterns and the effects of caries-preventive substances to be studied, de- and remineralization can best be examined with a pH-cycling system in which the pH depressions occurring in the oral environment are mimicked in a laboratory model. Such an approach has proved useful in developing optimal fluoride schemes which can be tested in animal, intraoral, and clinical studies.