Microprobe and SEM analysis of surface coatings on caries-like lesions in enamel after metal ion mordanting and APF application

Protection of short-time enamel erosion by different tetrafluoride compounds

OBJECTIVE

This in vitro study aimed to analyse the protective effect of differently concentrated titanium (TiF(4)), zirconium (ZrF(4)) and hafnium (HfF(4)) tetrafluoride on enamel erosion.

METHODS

Polished enamel surfaces of 36 bovine crowns were covered with tape leaving 4 enamel windows each 3mm in diameter exposed. The crowns were randomly assigned to six groups (each n=6) and pretreated with 4% TiF(4), 10% TiF(4), 4% ZrF(4), 10% ZrF(4), 4% HfF(4) or 10% HfF(4) for 4 min (first window), 10 min (second window) or 15 min (third window). The fourth window of each crown was not pretreated and served as control. Erosion was performed stepwise with 1% HCl (pH 2) in five consecutive intervals of each 15 s (total 75 s). Enamel dissolution was quantified by colorimetric determination of phosphate release into the acid. For each tooth, cumulative phosphate loss of enamel pretreated with one of the tetrafluoride compounds was calculated as percentage of the respective control and statistically analysed using two-way ANOVA.

RESULTS

Enamel erosion was significantly reduced by TiF(4), ZrF(4) and HfF(4) application. Cumulative phosphate loss (mean % of control, 75s erosion) after 4-15 min application was significantly lower for 4% ZrF(4) (7-11%), 10% ZrF(4) (2-6%), 4% HfF(4) (11-9%) and 10% HfF(4) (12-16%) compared to 4% TiF(4) (42-27%) and 10% TiF(4) (54-33%). Only for 4% and 10% TiF(4), phosphate loss decreased with increasing duration of application, but also increased with increasing acid intervals.

CONCLUSION

TiF(4), ZrF(4) and HfF(4) might protect enamel against short-time erosion, but protection was more enhanced by ZrF(4) and HfF(4) compared to TiF(4) application overtime.

Mineral loss from bovine enamel by a 30% hydrogen peroxide solution

This study investigated the effect of a 30% hydrogen peroxide bleaching agent on bovine enamel in terms of mineral loss. Contents of mineral elements both in the teeth and bleaching agent were evaluated to estimate the effect of hydrogen peroxide on teeth. Finely polished non-carious bovine incisors (n = 5) were immersed in a 30% hydrogen peroxide solution for 120 h. The amounts of concentrated elements in the bleaching agent (5 mL) were measured using inductively coupled plasma-atomic emission spectrometer and ion chromatograph. The contents of mineral elements in the teeth were measured using an electron probe microanalyzer. The Ca/P ratio in the bleaching agent was approximately 1.99. The amount of Zn in the bleaching agent was below the detection limit. The total content of mineral elements of the unbleached enamel (90.75 +/- 1.58) was slightly greater than that of the bleached enamel (87.44 +/- 0.77). The Ca/P ratio of the bleached enamel was 2.06. The amount of Ca loss from the bleached enamels after 120 h was similar to the amount of Ca loss from teeth exposed to a soft drink or juice for a few minutes. Therefore, mineral loss caused by the bleaching process may not be a threatening factor to teeth.

Morphology of initial lesions of enamel treated with different commercial dentifrices using a pH cycling model: scanning electron microscopy observations

The aim of this study was to evaluate and compare the 'calcium fluoride-like reaction products' formed, both on the surface and in the subsurface caries-like lesions of enamel, from different commercial dentifrices manufactured locally from developed and developing countries. The experiment was conducted by using the in vitro single-section technique under the pH-cycling system used for 10 days. The tested dentifrices include; Maxam DFP Maxam Tartar Controls, First, Tianqui Medicated (China); Vicco Vajradenti (India); Colgate MFP2. Crest Tartar Control (USA); and a non-fluoride dentifrice, Jie Yin (China) used as control. The surface and subsurface of the lesions, before and after treatment, were examined using scanning electron microscopy. Varying degrees of fine globular patterns of calcium fluoride-like material were observed on the enamel surfaces of five out of eight groups and in the subsurface of four groups. Two treatment groups showed a 'similar appearance' compared with the control and untreated groups. This study suggests and supports that, when compared with 'multinational dentifrices', some Chinese and Indian dentifrices manufactured locally failed to induce the typical morphological appearance of globules as seen with fluoride dentifrices.

Electron probe microanalysis and transverse microradiography studies of artificial lesions in enamel and dentin: a comparative study

In cardiology and research involving the interactions between restorative materials and dental hard tissues, it is important for small changes in tooth mineral content to be measurable. Currently, transverse microradiography (TMR) is the most accepted tool for the above purpose. Electron Probe Microanalysis (EPMA) can yield both qualitative identification of elements and quantitative compositional information. The purpose of this study was to compare the mineral distribution in well-defined artificial lesions, in dentin and enamel, by the use of both TMR and EPMA on the same sample. The good correlation between the two sets of data validates EPMA as a technique and helps in the interpretation of its results. The data from TMR analysis are expressed as vol% of mineral, while EPMA gives the levels of Ca and phosphate in wt%. The conversion between the two sets of data is complicated by the fact that local density is, as yet, unknown.

Effects of copper, iron and fluoride co-crystallized with sugar on caries development and acid formation in deslivated rats

The purpose was to explore the effects of combinations of copper, iron and fluoride (Cu, Fe and F) incorporated in sucrose by co-crystallization on caries development in the deslivated rat model and to examine acid formation by bacteria in the rat mouth. Ninety-six Sprague-Dawley rats were infected with Streptococcus sobrinus 6715 and desalivated when aged 26 days. Eight groups were placed in a König-Höfer programmed feeder and received 17 meals daily at hourly intervals, and essential nutrition (NCP No. 2) by gavage twice daily for 21 days. The groups received (1) plain sucrose, (2) F (8 parts/10(6)) co-crystallized with sucrose, (3) Fe (88 parts/10(6)) sucrose, (4) Cu (75 parts/10(6)) sucrose, (5) Cu + F sucrose, (6) Cu + L Fe sucrose, (7) F + Fe sucrose, and (8) Cu + Fe + F sucrose. At death the jaws were removed and sonicated in 0.9% saline solution for microbial assessment. In addition, organic acid assays were performed for each animal. Keyes smooth-surface and sulcal caries scores were lowest in the Cu + Fe + F sucrose group, but not statistically significantly different from those of the other Cu groups. The numbers of Strep. sobrinus found in the groups that received Cu, Cu + Fe, Cu + F, F + Fe and Cu + Fe + F sugar were lower than in the control group. Lactic acid was found in lower concentrations in Fe, Cu, Cu + F, Cu + Fe and F + Fe groups than in the other groups. It appears that combinations of Cu; Fe and F co-crystallized with sugar may have an additive effect in reducing the cariogenic potential of sugar by affecting lactic acid formation and reducing bacterial colonization.

Physical examination of caffeine's effects on the enamel surface of first molar in new-born rats

Samples of the first molars of offspring whose dams were fed a diet supplemented with caffeine were examined by scanning electron microscopy, X-ray diffractometry and electron microprobe analysis. Scanning microscopy of the enamel surface of the caffeine group revealed a consistently rougher surface than in the non-caffeine controls, both before and after acid exposure. X-ray diffraction analysis of the pulverized whole tooth in the caffeine group showed broader diffraction peaks for the lattice plane reflections (202) and (300), indicating smaller crystallites. Pure enamel samples of the caffeine group examined with a Gandolfi X-ray camera also revealed more diffuse diffraction lines than in the non-caffeine controls, further indicating smaller crystallites in the enamel. The calcium and phosphorus contents of the acid-exposed samples in both control and caffeine groups were lower than the non-acid exposed control and caffeine groups by electron microprobe analysis. After exposure to acid, the calcium and phosphorus contents of the outer surface of the enamel in the caffeine group were greatly reduced as compared to that of the non-caffeine controls. Thus various methods consistently indicate that caffeine ingestion during early growth affects the enamel surface of the first molars, resulting in impaired mineralization. Caffeine intake may therefore have a negative effect on amelogenesis and possibly increases susceptibility to dental caries.

A comparison of the influence of lanthanum and fluoride on de- and remineralization of bovine enamel in vitro

The influence of fluoride and lanthanum on enamel softening was compared by hardness measurements and by determination of the calcium content in the solution. The addition of lanthanum to an acetate buffer solution (0.05 mol/L, pH = 5.0) had no significant influence on the change of the indentation length and on the calcium release, compared with those of the control group. In the fluoride group, a moderate increase of the indentation length and a reduced calcium loss were observed. In a second experiment, surface-softened bovine enamel was treated with calcifying solutions (Ca/P ratio = 1.67). Differences in treatment were created by the addition of traces (2 ppm) of lanthanum, fluoride, or both. The acid resistance of the treated enamel was evaluated by two successive softening steps (0.1 mol/L acetate buffer, pH = 5.5). Alterations of the enamel surface were longitudinally followed with a hardness tester. The addition of fluoride, lanthanum, or both significantly improved the rehardening of surface-softened enamel, compared with that of the control group. A 2 x 2 factorial analysis of variance showed that lanthanum and fluoride had a highly significant main effect and a significant negative interaction effect on the rehardening of surface-softened enamel. Subsequent acid treatments revealed that only samples treated with a fluoride-containing solution were adequately protected from further dissolution. The enamel surfaces treated with a solution containing both lanthanum and fluoride were covered with an acid-resistant surface coating. SEM observation of this surface layer revealed the presence of globular and spherulite structures.

Electron probe micro-analysis for subsurface demineralization and remineralization of dental enamel

A quantitative study of fluoride distribution profile changes in dental enamel was conducted by means of electron probe micro-analysis (EPMA). Fluoride-deposited hydroxyapatite powders were chosen as fluoride standards, and analytical conditions were optimized. The lower limit of detection for fluoride was estimated to be 270 ppm, with an accelerating voltage of 5 kV, a specimen current of 40 nA, and a counting time of 40 seconds. Fluoride profiles in fluoride-treated dental enamel, which exhibited intact surface layers and subsurface demineralization, were determined. The results were also compared with those of an acid-abrasion method, and reasonable consistency was found between these two methods, although the acid-abrasion procedure yielded a slightly lower fluoride content in the initial layers, followed by a higher content of fluoride in the deeper layers. The precision of fluoride profile data obtained from EPMA permits further studies to be conducted on the kinetics of subsurface demineralization and intact surface layer formation ("white spot" formation) which is observed during the acid challenge of dental enamel.