Strontium-releasing fluorapatite glass-ceramics: Crystallization behavior, microstructure, and solubility

The purpose of this work was to investigate the effect of strontium partial replacement for calcium on the crystallization behavior, microstructure and solubility of fluorapatite glass-ceramics. Four glass compositions were prepared with increasing amounts of strontium partially replacing calcium. The crystallization behavior was analyzed by differential scanning calorimetry and X-ray diffraction (XRD). The microstructure was investigated by scanning electron microscopy. The chemical solubility was quantified according to ISO standard 10993-14. The amount of strontium released in solution after incubation in TRIS-HCl or citric acid buffer was measured by atomic absorption spectroscopy. XRD analyses revealed that partially substituted strontium-fluorapatite and strontium-åkermanite crystallized after strontium additions. The lattice cell volume of both phases increased linearly with the amount of strontium in the composition. Strontium additions led to a reduction in crystal size and an increase in crystal number density. The chemical solubility and amount of strontium released in solution increased linearly with the amount of strontium present in the composition in both TRIS-HCl and citric acid buffers. Total amounts of strontium released reached a maximum of 547 ± 80 ppm in TRIS-HCl and 1252 ± 290 ppm in citric acid buffer for the glass composition with the highest amount of strontium. For all strontium-containing compositions, the amount released in TRIS-HCl continued to increase between 70 and 120 h, indicating sustained release rather than burst release. © 2017 Wiley Periodicals, Inc. J Biomater Res Part B: 106B: 1421-1430, 2018.

NaF rinse and dentifrice concentrations on enamel lesion demineralization

PURPOSE

To compare the in vitro effectiveness of two mouthrinses containing different concentrations of NaF to reduce enamel lesion demineralization.

METHODS

Nine extracted caries-free molars were selected and cleaned. The teeth were painted with acid resistant varnish, leaving a 1 mm × 4 mm window exposed. The teeth were cycled in a demineralizing solution at pH 4.5 for a total for 96 hours. The teeth were sectioned longitudinally through the unpainted window using a hard-tissue microtome, producing 96 sections. The sections were measured and photographed under polarized light microscopy using water and Thoulet's 1.47 as imbibing mediums. Six treatment groups were randomly created: (A) water control group, (B) 0.05% rinse group once a day (C) 0.02% rinse group twice a day, (D) 1,500 ppm paste group used twice a day, (E) combination group containing 0.05% rinse once a day, and 1,500 ppm paste twice a day, and (F) combination group containing 0.02% rinse and 1,500 ppm paste twice a day. A 10-day cycling protocol was carried out. All sections were then re-measured and re-photographed. A statistical analysis was performed to detect any differences between pre- and post-treatment groups.

RESULTS

There was a statistically significant difference in lesion depth between the water control group and the 1,500 ppm paste group as well as the 0.05% rinse in combination with 1,500 ppm paste group (P= 0.0184). No statistically significant differences were found between the control group and any other groups. A statistically significant difference was found in lesion area between the two rinse groups alone and the 1,500 ppm paste group, as well as the 0.05% rinse in combination with the 1,500 ppm paste group (P= 0.0002). An analysis of the results suggested that both rinse concentrations performed equally well in reducing lesion demineralization when used alone. However, only the 0.05% rinse used in combination with 1,500 ppm paste decreased lesion demineralization as compared to the water control group, and was equally as effective as the 1,500 ppm paste alone.

CLINICAL SIGNIFICANCE

Within the limitations of this in vitro study, it was found that a fluoride containing dentifrice (1,500 ppm) and a combination of a fluoride containing dentifrice (1,500 ppm) and a 0.05% (210 ppm) fluoride rinse were more effective at reducing demineralization of enamel lesions than sodium fluoride rinses at concentrations of 0.02% and 0.05% alone or the combination of 0.02% NaF rinse with fluoride toothpaste.

Erosive potentials of brewed teas

PURPOSE

To measure the pH, titratable acidity, fluoride concentration and erosive potential of brewed teas.

METHODS

Bag teas were purchased to represent black, green, citrus, fruity, and floral tea flavors from Tulsi, Bigelow, HyVee, Tazo, and Yogi brands and brewed (1 bag/240 ml) in boiling water for 3 minutes. The pH, titratable acidity, and fluoride concentrations were measured. Following these measurements, a representative tea from each flavor was selected for investigation of erosion potential. Six extracted human molars were randomly assigned to each tea. Teeth were painted with fingernail polish to expose a 1 x 4 mm window and then soaked in tea for a total of 25 hours with teas refreshed every 5 hours. Teeth were then sectioned using a microtome and photographed using a polarized light microscope. Lesion depths (i.e., eroded surfaces) were measured using Image Pro Plus software. Differences in physiochemical properties and lesion depths between beverages were investigated using one-way ANOVA with post-hoc Tukey's HSD test. Relationships among lesion depths and physiochemical properties were evaluated using the Pearson correlation test.

RESULTS

pH, titratable acidity and fluoride concentrations differed between tea flavors (P < 0.05) and between brands (P < 0.05). Lesion depths produced by the citrus tea (83.1 +/- 10.3 microm) were greater than those produced by the fruity tea (56.5 +/- 6.1 microm); both teas produced greater depths than black (30.1 +/- 7.4 microm), floral (25.0 +/- 3.2 microm) or green (22.3 +/- 6.3 microm) teas (P < 0.05). pH (r = -0.96; P = 0.009) was inversely and titratable acidity (r = 0.97; P = 0.006) was positively associated with lesion depths.

The effect of surface defects in early caries assessment using quantitative light-induced fluorescence (QLF) and micro-digital-photography (MDP)

OBJECTIVES

The purpose of this study was to consider the impact of surface defects on quantitative light-induced fluorescence (QLF) and micro-digital-photography (MDP) measures, in relationship to lesion depth.

METHODS

Simulated enamel carious lesions were developed on 45 extracted human teeth. Images of each tooth were captured with both QLF and MDP. The teeth were sectioned and lesion depth was measured with polarized light microscopy (PLM). Pearson correlations were computed using data from the 27 lesions which did not have surface loss, and then separately based upon the 18 lesions which did display surface loss. MDP variables ΔR and ΔX measure reflected light, whereas QLF variables ΔF and ΔQ measure fluorescence.

RESULTS

A strong correlation was identified between lesion depth and ΔF (r=-0.765, p<0.0001), and ΔQ (r=-0.827, p<0.0001) on intact lesions while a weak but suggestive, although non-significant, correlation was identified between average lesion depth and ΔR (r=0.369, p=0.059) and ΔX (r=0.595, p=0.0011). However, the corresponding correlation was not statistically significant, when lesions with surface loss were considered for QLF and MDP measures.

CONCLUSIONS

QLF measures ΔF and ΔQ were strongly correlated with lesion depth in lab-simulated lesions with no surface loss, but not among lesions with surface defects. The two MDP-associated measures, ΔR and ΔX, could not be said to differ significantly when lesions with and without surface defects were compared with lesion depth. Because intact lesions can be remineralized, accurate assessment of their status is imperative for caries treatment.

CLINICAL SIGNIFICANCE

Dental caries is still widely prevalent today. We now know that with early stage detection, remineralization can be accomplished. Being able to identify dental caries in its reversible stage (before physical surface loss) is paramount for the clinician to be able to treat the disease non-invasively.

Fluorescence changes in remineralized and nonremineralized enamel adjacent to glass ionomer ART restorations: an in vitro study

PURPOSE

The purpose of this study was to evaluate fluorescence changes of remineralized and nonremineralized enamel margins adjacent to glass ionomer restorations during a pH cycling sequence.

METHODS

One hundred permanent molar and premolar teeth were placed in a demineralizing solution for 3 days and restored with a glass ionomer restoration (simulating Atraumatic Restorative Treatment [ART]). Half were placed in a remin solution for 7 days to create a remineralization (remin) group. Specimens were randomly divided into 4 groups (N=25): (a) 2 remin groups; and (b) 2 nonremin groups. One half of the remin and nonremin group specimens were treated with a 5,000-ppm sodium fluoride solution during pH cycling with remin fluid and an acidic beverage over 20 days. Fluorescence changes were recorded with quantitative light fluorescence (QLF). Higher fluorescence values indicated less lesion porosity. Statistical comparisons between the groups over the 5 measurement sessions of cycling were performed using repeated measures of analysis of variance with a post-hoc test, paired-sample t test and 2-sample t tests (alpha=0.05).

RESULTS

The remin groups experienced significantly less lesion porosity than the nonremin groups. Fluoride groups experienced less lesion porosity than the nonfluoride groups.

CONCLUSIONS

A brief period of remineralization and use of a prescription strength fluoridated rinse improved the enamel substrate surrounding glass ionomer restorations, resulting in less lesion porosity.

Effect of an alcohol-free, 1% chlorhexidine gel as an adjunct to a fluoridated dentifrice using an intraoral crown model

BACKGROUND/AIMS

The use of chlorhexidine as a topically applied oral antiseptic is well documented; however, clinical studies examining the effects of chlorhexidine gel on in situ dental caries are limited. This study utilized an in situ caries model and a modified crossover design to examine whether the addition of a biweekly topical, alcohol-free, 1% chlorhexidine digluconate gel to a daily fluoridated dentifrice inhibited artificial caries in dental tissues better than the fluoridated dentifrice alone when compared to a nonfluoridated placebo dentifrice.

METHODS

Thirty patients were recruited based on their need for a mandibular, full crown. Artificial caries lesions were created in extracted human teeth and enamel and root tissue sections 100 mum in thickness were characterized using polarized light microscopy. The sections were fixed in the crown and placed on the prepared tooth. The participants were assigned a placebo toothpaste, a toothpaste with 1,100 ppm F or a 1,100 ppm F toothpaste followed by 1 ml of 1% chlorhexidine gel at day 1 and day 14 (chlorhexidine+). Patients were instructed to brush twice daily for 4 weeks. Following each round, the sections in the crown were replaced with new sections. The sections were recharacterized and the mean changes were compared using ANOVA at alpha = 0.05.

RESULTS

The chlorhexidine + Fdentifrice and the F dentifrice alone significantly reduced lesion area in enamel tissue when compared to the placebo dentifrice. Both treatments also inhibited lesion progression and initiation in root tissue better than control in this model system. Although the chlorhexidine+ group enhanced remineralization and inhibited lesion progression better than the F(-) dentifrice alone for all outcomes measured, the differences were not significant.

CONCLUSIONS

The chlorhexidine, in conjunction with a fluoride dentifrice, was no more effective than the fluoride dentifrice alone. Further study is needed before this 1% alcohol-free chlorhexidine gel should be recommended as an adjunct to a fluoride dentifrice in the treatment of dental caries.

Effect of 2% plain and fluoridated milk on root surface caries in vitro

The caries-protective effect of milk and fluoridated milk on enamel has been reported; however, few data are available concerning the role of milk and/or fluoridated milk on root surfaces. The aim of this study was to compare the effect of plain and fluoridated milk on root surface caries. Artificial root surface lesions were created, sectioned and analyzed using polarized light microscopy (PLM) and microradiography (MRG). The sections were covered except for the original surface and assigned to a treatment group. The samples were immersed in 2% plain milk or fluoridated milk for 40 hours and re-evaluated. Changes were measured and mean differences were compared with an unpaired t-test. Both techniques revealed a reduction in lesion depth for each milk group; however, a significantly greater reduction (p<0.05) was observed with the fluoridated milk. These results suggest that fluoridated milk may have a beneficial effect on the remineralization of root surface caries.

Effect of fluoridated milk on progression of root surface lesions in vitro under pH cycling conditions

The aim of this study was to assess the effect of milk with 0, 2.5 or 5 ppm F on progression and remineralization of caries-like root surface lesions using a pH cycling model. The root surface lesions were created utilizing a partially saturated lactic acid buffer at pH 4.6. Longitudinal sections were cut through the lesion and analyzed using polarized light microscopy (PLM) and microradiography (MRG). The sections were then coated with an acid resistant varnish, except the outer natural surface that would be exposed to water, milk or fluoridated milk and cycled in a de- and remineralizing system for 2 weeks. The lesions were characterized again by PLM and MRG after treatment. A significant reduction in lesion progression was found by PLM and MRG after treatment with either non-fluoridated or fluoridated milk when compared to the control group. Using quantitative MRG, mineral change and distribution in the lesions were recorded. A possible protective effect of fluoridated milk on root surface caries was supported by a reduction in the progression of the lesions and an increase in the mineral within the lesion.

In situ evaluation of sodium hexametaphosphate-containing dentifrices

The purpose of this investigator-blinded, five-treatment, crossover human intraoral study was to evaluate the effects of two experimental dentifrice formulations containing either stannous fluoride (SnF(2)) or sodium fluoride (NaF) packaged with sodium hexametaphosphate in a dual-phase delivery system on demineralization-remineralization using an in situ model system. The experimental dentifrice formulations' ability to alter demineralization-remineralization was compared to a series of three controls: SnF(2)-positive control, NaF-positive control and no-fluoride placebo-negative control. The single-section crown model, developed at the University of Iowa, was used to assess the fluoride efficacy of two experimental products versus the placebo containing no fluoride and positive controls. The results of the current in situ study suggest a clinical level of anticaries activity for the experimental SnF(2) and NaF dentifrice formulations that was as good as either of the positive controls, when evaluated using polarized light microscopy. This supports the conclusion that the use of the sodium hexametaphosphate ingredient does not interfere with the normal fluoride activity of these toothpastes. In addition, the experimental SnF(2) product was numerically better than both the NaF and placebo controls at preventing demineralization of sound root surfaces.

The use of saturated DCPD in remineralization of artificial caries lesions in vitro

Dicalcium phosphate dihydrate (DCPD) may play a significant role in the caries lesion since it is a stable calcium phosphate phase under acidic conditions. The reaction of DCPD and fluoride, forming fluorapatite (FAP), may provide a potentially promising treatment regimen for remineralization of caries lesions in vivo. The purpose of this study was to determine whether a two-step DCPD and inorganic wash with fluoride can remineralize artificial caries-like lesions in vitro. We used the single-section technique to facilitate quantitation of the same tissue before and after the experimental regimen. The two-step remineralizing treatment was repeated three times and consisted of a two-minute saturated DCPD treatment (pH 2.1) followed by a 24-hour inorganic wash. Lesion parameters were recorded before and after treatment by the taking of polarized light photomicrographs of each section after imbibition in several media. The changes in the tissue following treatment were expressed as a percent change in the area of the initial pre-treatment lesion. Significant reductions (p < 0.02) in lesion pore volume were observed in all aqueous media examined. In the lesions after imbibition in quinoline, remineralization was also apparent from the significant increase in the area of the dark zone following treatment. This two-step DCPD treatment appears to remineralize artificial caries-like lesions effectively, but additional work is needed to determine whether it affords any protection against subsequent cariogenic challenges.

Development of an intra-oral single-section remineralization model

An intra-oral model system has been developed which uses a single-section technique for before-and-after measurements on the same tissue. This model allows for placement of sections of enamel at both buccal and approximal sites. These sections may be sound or possess white-spot lesions. This allows for the evaluation of lesion initiation, lesion progression, and/or lesion remineralization. The sections are appropriate for measurement by polarized light microscopy, and, although not included in this study, they are also suitable for microradiographic evaluation. With ten human volunteers, the model system was evaluated by means of three rinse regimens in a cross-over design. The distilled water rinse showed the whole range of possible changes (e.g., demineralization, no change, and remineralization). More consistent remineralization was observed when a fluoride rinse or a remineralizing fluid was used. This model system should prove to be quite useful in evaluation of demineralization and remineralization phenomena in the oral environment.

Topical fluoride application and lesion progression in vitro

The objectives of this investigation were to study the effects of topical fluoride application on white spot enamel and the effect that this application would have on a second acid exposure (lesion progression). Artificial white spot lesions of approximately 200 micron were created with an acidified gel technique, central control sections were removed, and the remaining tooth halves were randomly paired, with one half serving as an untreated control while the other received a single four-minute application of 1.23% (w/v) fluoride solution of either NH4F, Na2SnF6, APF, or TiF4. Both tooth halves were sectioned following progression and examined with polarized light microscopy. Lesion depth, internal pore volume, and presence, size and shape of dark zones were determined. The considerable variation among progressed lesions revealed no significant benefit from any topical fluoride treatment.

Comparison of artificial white spots by microradiography and polarized light microscopy

This work compared lesions produced by three artificial caries systems with natural white spot lesions using both polarized light microscopy and microradiography. The three systems employed were the acidified gelatin gel, diphosphonate surface dissolution inhibitor, and a partially saturated buffer system. When we compared the natural white spot lesions with the artificial caries-like lesions, we found that the acidified gel system reproduced the classical histological zones most frequently. All systems showed a radiopaque surface layer overlying a radiolucent body of the lesion. This radiopaque layer could not be equated with the negatively birefringent surface zone seen in polarized light.

The effect of several topical fluoride agents on artificial lesion formation

NH4F, Na2SnF6, and TiF 4 were applied to human molars before in vitro lesion formation. Polarized light microscopy was used to evaluate the lesions formed; it showed that only the TiF4 treatment resulted in a reduction in lesion size when compared to APF test halves.

The effect of topical fluoride agents on fluoride uptake and surface morphology

Four topical fluoride agents were evaluated in vitro for their ability to form permanently bound fluoride. APF, NH4F, and Na2SnF6 formed soluble reaction products, while TiF4 did not. Surface coatings were present on those samples that showed higher levels of fluoride after washing.