Review on fluoride-releasing restorative materials--fluoride release and uptake characteristics, antibacterial activity and influence on caries formation

Fluoride release from restorative materials

The aim of this study was to evaluate in vitro fluoride (F) release from 4 restorative materials (3M ESPE): Ketak Molar Easymix [KME - conventional glass ionomer cement (GIC)]; Rely-X luting 2 [RL2 - resin-modified GIC (RMGIC)]; Vitremer (VIT- RMGIC); and Filtek Z250 [Z250 - negative control]. Disc-shaped specimens were fabricated according to the manufacturer's instructions and placed into 10 mL of reverse osmosis water at 37°C until the analyses were done using a liquid membrane for selective F ion electrode (Orion 710). F release was evaluated every 6 h in the first day and thereafter daily during 28 days (d). The results were analyzed statistically by two-way ANOVA and Tukey's test (α=0.05). Mean F release and standard deviation values (in ppm) were: KME: 6 h- 0.34 ± 0.04; 24 h- 1.22 ± 0.30; 7 d- 0.29 ± 0.09; 14 d- 0.20 ± 0.04; 28 d- 0.16 ± 0.01; RL2: 6 h- 2.46 ± 0.48; 24 h-12.33 ± 2.93; 7 d- 1.37 ± 0.38; 14 d- 0.80 ± 0.13; 28 d- 0.80 ± 0.21; VIT: 6 h- 0.98 ± 0.35; 24 h- 4.35 ± 1.22; 7 d- 0.66 ± 0.23; 14 d- 0.40 ± 0.07; 28 d- 0.39 ± 0.08; Z250: 6 h- 0.029 ± 0.001; 24 h- 0.024 ± 0.009; 7 d- 0.023 ± 0.004; 14 d- 0.025 ± 0.001; 28 d- 0.028 ± 0.001. RL2 RMGIC released more F than the other materials in all periods. The greatest release of F occurred in the first 24 h.

Remineralization of artificial dentinal caries lesions by biomimetically modified mineral trioxide aggregate

Fluoride-releasing restorative materials are available for remineralization of enamel and root caries. However, remineralization of dentin is more difficult than remineralization of enamel due to the paucity of apatite seed crystallites along the lesion surface for heterogeneous crystal growth. Extracellular matrix proteins play critical roles in controlling apatite nucleation/growth in collagenous tissues. This study examined the remineralization efficacy of mineral trioxide aggregate (MTA) in phosphate-containing simulated body fluid (SBF) by incorporating polyacrylic acid and sodium tripolyphosphate as biomimetic analogs of matrix proteins for remineralizing caries-like dentin. Artificial caries-like dentin lesions incubated in SBF were remineralized over a 6 week period using MTA alone or MTA containing biomimetic analogs in the absence or presence of dentin adhesive application. Lesion depths and integrated mineral loss were monitored with microcomputed tomography. The ultrastructure of baseline and remineralized lesions was examined by transmission electron microscopy. Dentin remineralization was best achieved using MTA containing biomimetic analogs regardless of whether an adhesive was applied; dentinal tubules within the remineralized dentin were occluded by apatite. It is concluded that the version of MTA employed in this study may be doped with biomimetic analogs for remineralization of unbonded and bonded artificial caries-like lesions in the presence of SBF.

Efficacy of a non-drilling approach to manage non-cavitated dentin occlusal caries in primary molars: a 12-month randomized controlled clinical trial

BACKGROUND. Despite the efficacy of non-drilling approaches to manage non-cavitated dentin occlusal lesions (NCDOL) in permanent teeth, there is no data validating this type of therapy in the primary dentition. AIM. To compare the efficacy of a traditional fissure sealant in managing NCDOL in primary molars. DESIGN. This study is a randomized controlled clinical trial with a split-mouth design. Thirty schoolchildren with two NCDOL were selected and divided into two groups. The experimental group received a resin-based fissure sealant, whereas the control group was treated with a conventional composite resin. Treatment efficacy was evaluated after 1 year by means of clinical and radiographic examinations. RESULTS. The two treatment modalities were found to be similarly effective in managing DONCL in primary molars. CONCLUSION. For the management of non-cavitated dentin occlusal caries in primary teeth, the invasive approach can be replaced with non-drilling fissure sealing techniques.

In vitro study of the effects of fluoride-releasing dental materials on remineralization in an enamel erosion model

OBJECTIVES

This study was conducted to compare the remineralization effects of five regimens on the loss of fluorescence intensity, surface microhardness, roughness and microstructure of bovine enamel after remineralization. We hope that these results can provide some basis for the clinical application of these materials.

METHODS

One hundred bovine incisors were prepared and divided into the following five groups, which were treated with distinct dental materials: (1) Clinpro™ XT varnish (CV), (2) F-varnish (FV), (3) Tooth Mousse (TM), (4) Fuji III LC(®) light-cured glass ionomer pit and fissure sealant (FJ) and (5) Base Cement(®) glass polyalkenoate cement (BC). Subsequently, they were detected using four different methods: quantitative light-induced fluorescence, microhardness, surface 3D topography and scanning electron microscopy (SEM).

RESULTS

The loss of fluorescence intensity of CV, BC and FJ groups showed significant decreases after remineralization (p<0.05). The microhardness values of the BC group were significantly higher than those of the other groups (p<0.05) after 6 weeks of remineralization. The CV group's surface roughness was significantly lower than those of the other groups after 6 weeks of remineralization (p<0.05). Regarding microstructure values, the FV group showed many round particles deposited in the bovine enamel after remineralization. However, the other four groups mainly showed needle-like crystals.

CONCLUSIONS

Glass ionomer cement (GIC)-based dental materials can promote more remineralization of the artificial enamel lesions than can NaF-based dental materials. Resin-modified GIC materials (e.g., CV and FJ) have the potential for more controlled and sustained release of remineralized agents. The effect of TM requires further study.

An in-vitro assessment of weekly cumulative fluoride release from three glass ionomer cements used for orthodontic banding

OBJECTIVES

To compare the in-vitro Weekly Cumulative Fluoride Release (WCFR) of three Glass Ionomer Cements (GICs) used for orthodontic banding.

MATERIALS AND METHODS

The GICs tested were Granitec (Confi-Dental, Louisville, CO, USA), Bandtite (American Orthodontics, Sheboygan, WI, USA) and Ariadent (Apadana Tak Co, Tehran, Iran). Fifteen discs of each GIC were constructed (6mm diameter and 1.5mm depth). Specimens were immersed in 5 ml of deionised water and the WCFR was measured at weekly intervals, on days 1, 8, 15, 22 and 29 after immersion in deonised water, using the potentiometery device and single junction saturated calomel electrode technique (Jenway, England, UK). To compare the WCFR profile of 3 GICS, data were subjected to the one-way analysis of variance (ANOVA), and were appropriate, the Scheffe or Tamhane multiple comparison tests (post-hoc). For assessing the longitudinal changes of average WCFRs in 3 GICs, the repeated measures ANOVA were used. Post hoc tests using the Bonferroni correction was also used to compare the average WCFRs at different time-points.

RESULTS

One-way ANOVA and post-hoc multiple comparison tests revealed significant differences in WCFR among 3 GICs at five time-points (p<0.05). The post-hoc multiple comparison test revealed Bandtite cement had consistently higher WCFR at all time-points, compared to Granitec and Ariadent cements (p<0.05). The one-way ANOVA test revealed significant differences in WCFR at different time-points for all GIC groups (p<0.05). The day 8 exhibited the highest WCFR for all GICs. The repeated measures ANOVA test revealed significant differences in WCFR at different time-points for all GIC groups (p<0.0005). Reviewing average WCFR on days 22 and 29, these values for Granitec, Bandtite and Ariadent GICs, were higher (p<0.05), not different (p>0.05), and significantly lower (p<0.05) than the day 1 values, respectively.

CONCLUSIONS

Bandtite followed by Granitec showed higher WCFR compared to Ariadent.

Novel dental composites reinforced with zirconia-silica ceramic nanofibers

OBJECTIVE

To fabricate and characterize dental composites reinforced with various amounts of zirconia-silica (ZS) or zirconia-yttria-silica (ZYS) ceramic nanofibers.

METHODS

Control composites (70 wt% glass particle filler, no nanofibers) and experimental composites (2.5, 5.0, and 7.5 wt% ZS or ZYS nanofibers replacing glass particle filler) were prepared by blending 29 wt% dental resin monomers, 70 wt% filler, and 1.0 wt% initiator, and polymerized by either heat or dental curing light. Flexural strength (FS), flexural modulus (FM), energy at break (EAB), and fracture toughness (FT) were tested after the specimens were stored in 37°C deionized water for 24h, 3 months, or 6 months. Degree of conversion (DC) of monomers in composites was measured using Fourier transformed near-infrared (FT-NIR) spectroscopy. Fractured surfaces were observed by field-emission scanning electron microscope (FE-SEM). The data were analyzed using ANOVA with Tukey's Honestly Significant Differences test used for post hoc analysis.

RESULTS

Reinforcement of dental composites with ZS or ZYS nanofibers (2.5% or 5.0%) can significantly increase the FS, FM and EAB of dental composites over the control. Further increase the content of ZS nanofiber (7.5%), however, decreases these properties (although they are still higher than those of the control). Addition of nanofibers did not decrease the long-term mechanical properties of these composites. All ZS reinforced composites (containing 2.5%, 5.0% and 7.5% ZS nanofibers) exhibit significantly higher fracture toughness than the control. The DC of the composites decreases with ZS nanofiber content.

SIGNIFICANCE

Incorporation of ceramic nanofibers in dental composites can significantly improve their mechanical properties and fracture toughness and thus may extend their service life.

Drinking water fluoride and blood pressure? An environmental study

The relationship between intakes of fluoride (F) from drinking water and blood pressure has not yet been reported. We examined the relationship of F in ground water resources (GWRs) of Iran with the blood pressure of Iranian population in an ecologic study. The mean F data of the GWRs (as a surrogate for F levels in drinking water) were derived from a previously conducted study. The hypertension prevalence and the mean of systolic and diastolic blood pressures (SBP & DBP) of Iranian population by different provinces and genders were also derived from the provincial report of non-communicable disease risk factor surveillance of Iran. Statistically significant positive correlations were found between the mean concentrations of F in the GWRs and the hypertension prevalence of males (r = 0.48, p = 0.007), females (r = 0.36, p = 0.048), and overall (r = 0.495, p = 0.005). Also, statistically significant positive correlations between the mean concentrations of F in the GWRs and the mean SBP of males (r = 0.431, p = 0.018), and a borderline correlation with females (r = 0.352, p = 0.057) were found. In conclusion, we found the increase of hypertension prevalence and the SBP mean with the increase of F level in the GWRs of Iranian population.

Influence of the curing mode on fluoride ion release of self-adhesive resin luting cements in water or during pH-cycling regimen

This study evaluated the effects of curing modes and storage conditions on fluoride release of resin cements. In phase 1, the cumulative fluoride release rate from samples of the resin cements (Panavia F 2.0, RelyX Unicem, MaxCem, and BisCem) was quantified after 15 days storage in water (n=4). In phase 2, the fluoride release profiles from the same materials were analyzed during pH cycling (n=4). In this second phase, fluoride was measured at specific times (one, two, three, five, eight, and 15 days). Disk-shaped specimens were prepared (10 mm × 0.5 mm), and the materials were either light activated or allowed to autopolymerize. For both phases, the fluoride release was measured using a fluoride ion-specific electrode. The fluoride release in water was not affected by the curing mode of RelyX Unicem and Maxcem resin cements. Panavia F. 2.0 and BisCem resin cements, either light cured or autopolymerized modes, released higher amounts of fluoride in water than the other self-adhesive cements. In phase 2, the concentration of fluoride released decreased from the first day of pH cycling until the 15th day for all resin cements, for both curing modes, regardless of the storage solution used (demineralizing/remineralizing). The fluoride release rate during pH cycling by Panavia F 2.0 and MaxCem was not affected by the curing mode. The effect of the curing mode on fluoride ion release in water or during pH cycling was product dependent.

Effects of periodic fluoride treatment on fluoride ion release from fresh orthodontic adhesives

OBJECTIVE

Periodic fluoride treatment may contribute to the ability of fresh orthodontic adhesives to provide long-term F(-) release. The effects of periodic fluoride treatment on the amount of F(-) release from fresh orthodontic adhesives was investigated.

METHODS

F(-) release was measured from a nonfluoride-releasing composite, a fluoride-releasing composite, a polyacid-modified composite (compomer), and two resin-modified glass-ionomer cements (RMGICs) at 1, 2, and 5 days after one of the following treatments: 225 ppm F(-) solution, 900 ppm F(-) solution, acidulated phosphate fluoride gel (APF), fluoridated dentifrice, and deionised water (control). F(-) release was measured in a 5-day cycle, which was repeated 9 consecutive times. The amount of F(-) release for each group was analysed using the repeated measures analysis of variance. Statistical significance was set at a level of α=0.05.

RESULTS

Periodic fluoride treatment temporarily increased F(-) release in fresh fluoride-releasing orthodontic adhesives, but not in fresh nonfluoride-releasing composite. The order of effective fluoride-release was RMGICs>compomer>fluoride-releasing composite>nonfluoride-releasing composite. The application of APF or 900 ppm F(-) solution was the most effective way to maintain F(-) release from fresh orthodontic adhesives. However, the amount of F(-) release gradually decreased with increasing specimen age.

CONCLUSION

Given the difficulty of routine use of APF at home, the results of this study show that a combination of RMGICs and high-dose fluoride mouth rinse is the most effective protocol to maintain F(-) release from fresh orthodontic adhesives.

CLINICAL SIGNIFICANCE

Most studies have investigated fluoride-uptake abilities using aged materials in which fluoride had been lost for at least 1 month. This study has found that periodic fluoride treatment altered the conventional F(-) release pattern of fresh fluoride-releasing materials and type of fluoride-containing medium plays a more critical role in fluoride recharging of the materials than fluoride concentration. This study will help clinicians to find the most effective fluoride treatment protocol of fresh materials.

Glass-ionomer cement restorative materials: a sticky subject?

Glass-ionomer cement (GIC) materials have been in clinical use since their inception 40 years ago. They have undergone several permutations to yield different categories of these materials. Although all GICs share the same generic properties, subtle differences between commercial products may occur. They have a wide range of uses such as lining, bonding, sealing, luting or restoring a tooth. In general, GICs are useful for reasons of adhesion to tooth structure, fluoride release and being tooth-coloured although their sensitivity to moisture, inherent opacity, long-term wear and strength are not as adequate as desired. They are useful in situations where they are not disadvantaged by their comparatively lower physical properties, such as where there is adequate remaining tooth structure to support the material and where they are not subject to heavy occlusal loading. The last decade has seen the use of these materials being extended. However, they are likely to retain their specific niches of clinical application.

Preparation and evaluation of a novel glass-ionomer cement with antibacterial functions

OBJECTIVE

The objective of this study was to use the newly synthesized poly(quaternary ammonium salt) (PQAS)-containing polyacid to formulate the light-curable glass-ionomer cements and study the effect of the PQAS on the compressive strength and antibacterial activity of the formed cements.

MATERIALS AND METHODS

The functional QAS and their constructed PQAS were synthesized, characterized and formulated into the experimental high-strength cements. Compressive strength (CS) and Streptococcus mutans viability were used to evaluate the mechanical strength and antibacterial activity of the cements. Fuji II LC cement was used as control. The specimens were conditioned in distilled water at 37°C for 24 h prior to testing. The effects of the substitute chain length, loading as well as grafting ratio of the QAS and aging on CS and S. mutans viability were investigated.

RESULTS

All the PQAS-containing cements showed a significant antibacterial activity, accompanying with an initial CS reduction. The effects of the chain length, loading and grafting ratio of the QAS were significant. Increasing chain length, loading, grafting ratio significantly enhanced antibacterial activity but reduced the initial CS. Under the same substitute chain length, the cements containing QAS bromide were found to be more antibacterial than those containing QAS chloride although the CS values of the cements were not statistically different from each other, suggesting that we can use QAS bromide directly without converting bromide to chloride. The experimental cement showed less CS reduction and higher antibacterial activity than Fuji II LC. The long-term aging study suggests that the cements may have a long-lasting antibacterial function.

CONCLUSIONS

This study developed a novel antibacterial glass-ionomer cement. Within the limitations of this study, it appears that the experimental cement is a clinically attractive dental restorative due to its high mechanical strength and antibacterial function.

Fluoride release, recharge and mechanical property stability of various fluoride-containing resin composites

AIM

To determine the fluoride release and recharge of three fluoride-containing resin composites when aged in deionized water (pH 6.5) and lactic acid (pH 4.0) and to assess mechanical properties of these composites following aging.

METHODS

Three fluoride-containing resin composites were analyzed in this study; a new giomer material named Beautifil II, Gradia Direct X, and Tetric EvoCeram. A glass ionomer cement, Fuji IX Extra, was also analyzed for comparison. Specimens were fabricated for two test groups: group 1 included 10 disc specimens initially aged 43 days in deionized water (five specimens) and lactic acid (five specimens). The fluoride release from these specimens was measured using a fluoride-specific electrode on nine specific test days during the aging period. Following 49 days of aging, each specimen was recharged in 5000 ppm neutral sodium fluoride solution for 5 minutes. Specimen recharge was then repeated on a weekly basis for 3 weeks. The subsequent fluoride rerelease was measured at 1, 3, and 7 days after each recharge episode. Group 2 included six disc specimens aged for 3 months in deionized water (three specimens) and lactic acid (three specimens). The hardness and elastic modulus of each specimen was measured using nano-indentation at intervals of 24 hours, 1 month, and 3 months after fabrication. Two-way factorial analysis of variance (ANOVA) and post-hoc (Tukey) testing was used to assess the influence of storage media (two levels) and composite type (three levels) on the fluoride release, fluoride rerelease, hardness, and elastic modulus of the assessed materials. The level of significance was set at p=0.05.

RESULTS

All three composites demonstrated fluoride release and recharge when aged in both deionized water and lactic acid. The cumulative fluoride released from Beautifil II into both media was substantially greater than the fluoride released from Gradia Direct X and Tetric EvoCeram after 43 days aging and was significantly (p<0.05, ANOVA, Tukey test) greater during several analysis periods. Beautifil II demonstrated the greatest recharge ability of the three composites over the 3-week recharge period in both media. Fuji IX Extra demonstrated a significantly (p<0.05) greater fluoride release and recharge compared with the three resin composites. The elastic modulus and hardness of the three composites did not decrease significantly (p<0.05) with fluoride release or fluid uptake over the 3-month aging period, in either media.

CONCLUSION

The three composites in the present study demonstrated fluoride release (Beautiful II > Gradia Direct X > Tetric EvoCeram) and fluoride recharge (Beautiful II > Gradia Direct X > Tetric EvoCeram). This capability raises the possibility of fluoride-containing composites exhibiting a lower incidence of recurrent caries than non fluoride–containing composites. The mechanical properties of each composite did not diminish with aging and fluoride release over the testing period.

Characterization of an antimicrobial dental resin adhesive containing zinc methacrylate

This study evaluates the effect of zinc methacrylate (ZM) on the degree of conversion (DC), cytotoxicity and antimicrobial activity (AA) of an experimental resin. Tetraethyleneglycol dimethacrylate was used as the experimental resin and it was photo activated using camphoroquinone and ethyl 4-dimethylamine benzoate. Additionally, 1.0, 2.5, 5.0, 10, 20 and 30 wt% of ZM was added to the various experimental resins. The DC was accessed by Fourier Transform infrared spectroscopy. For cytotoxicity, immortalized mouse fibroblasts were exposed to the experimental resin extracts. An MTT assay was used to access the cytotoxicity. The AA against Streptococcus mutans UA159 was accessed by the agar diffusion method. An improvement in the DC in all concentrations of ZM was observed. The greater the amount of ZM on the experimental resin, the less the cytotoxicity was provoked. Three ZM concentrations showed AA that exhibited various inhibition growth zones with 10, 20 (10 mm) and 30 wt% (15 mm).

Caries-preventive effect of resin-modified glass-ionomer cement (RM-GIC) versus composite resin: a quantitative systematic review

AIM

To determine whether resin-modified glass-ionomer cement (RM-GIC), when compared with composite resins (CR), offers a significant caries-preventive effect.

STUDY DESIGN

Quantitative systematic review.

METHODS

Five databases were searched until 29 July 2010. Inclusion criteria were: relevant to review question related to orthodontic or restorative treatment; published in English; prospective clinical 2-arm study. Exclusion criteria were: no computable data reported; study groups not followed up in the same way. References of included articles were checked. The outcome measure was absence of carious lesions. Dichotomous datasets for both groups were extracted from accepted trials. Trials were assessed for selection-, detection/performance, attrition and publication bias.

RESULTS

Of the 11 trials included, 6 were accepted and 24 datasets extracted; 17 datasets showed no difference after 4 weeks to >25 months. There were 7 datasets that favoured (p < 0.05) RM-GIC after 12 - 24 months. The results are limited by risk of selection-, detection-/performance bias and attrition bias. Risk of publication bias was identified.

CONCLUSIONS

The overall results showed either no difference between the materials, or indicated that RM-GIC has a superior caries-preventive effect. The clinical meaning of this result remains uncertain due to risk of bias. High-quality randomised control trials are needed in order to answer the review question conclusively.

A novel hyperbranched poly(acrylic acid) for improved resin-modified glass-ionomer restoratives

OBJECTIVE

The objective of this study was to synthesize and characterize novel hyperbranched poly(acrylic acid)s via atom-transfer radical polymerization (ATRP) technique and tether the photo-curable methacrylate onto the poly(acrylic acid), use these polymers to formulate the resin-modified glass-ionomer cements, and evaluate the mechanical strengths of the formed cements.

MATERIALS AND METHODS

The hyperbranched poly(acrylic acid)s were synthesized using a self-condensing vinyl polymerization initiator via ATRP. The effects of the concentrations of both catalyst and initiator on molecular weight (MW) and degree of branching (DB) were studied. Compressive, diametral tensile as well as flexural strengths, fracture toughness, hardness and wear-resistance of the experimental cement were evaluated and compared to those of Fuji II LC cement. The specimens were conditioned in distilled water at 37°C for 24h prior to testing.

RESULTS

The concentrations of both catalyst and initiator had significant effects on MW and DB of the synthesized polymers. The concentration of the initiator also significantly affected both CS and DTS values of the cement. The experimental cement showed significantly higher mechanical properties, i.e., 53% in CS, 50% in compressive modulus, 125% in DTS, 95% in FS, 21% in FT and 96% in KHN, higher than Fuji II LC. The experimental cement was only 5.4% of abrasive and 6.4% attritional wear depths of Fuji II LC.

CONCLUSIONS

This study developed a novel resin-modified glass-ionomer cement system composed of newly synthesized hyperbranched poly(acrylic acid)s. It appears that this novel experimental cement is a clinically attractive dental restorative and may potentially be used for high-wear and high-stress-bearing site restorations.

A new approach to influence contact angle and surface free energy of resin-based dental restorative materials

The purpose of the present study was to identify novel delivery systems and active agents which increase the water contact angle and reduce the surface free energy when added to resin-based dental restorative materials. Two delivery systems based on zeolite or novel polymeric hollow beads (Poly-Pore), loaded with two low surface tension active agents (hydroxy functional polydimethylsiloxane and polydimethylsiloxane) or a polymerizable active agent (silicone polyether acrylate) were used to modify commonly formulated experimental dental resin composites. The non-modified resin was used as a standard (ST). Flexural strength, flexural modulus, water sorption, solubility, polymerization shrinkage, surface roughness Ra, contact angle θ, total surface free energy γS, and the apolar γSLW, polar γSAB, Lewis acid γS+ and base γS- components, and the active agents surface tensions γL were determined (P<0.05). The active agents did not differ in γL. The modified materials had significantly higher θ but significantly lower γS, γSAB and γS- than the ST. A Poly-Pore/polydimethyl siloxane delivery system yielded the highest θ (110.9±3.5°) acceptable physical properties and the lowest values for γSLW and γS-. Among the modified materials the polymerizable materials containing active agents had the lowest γAB and the highest γS+ and γS-. Although not significant, both of the zeolite delivery systems yielded higher γSLW, γS+ and γS- but lower γSAB than the Poly-Pore delivery systems. Poly-Pore based delivery systems highly loaded with low surface tension active agents were found not to influence the physical properties but to significantly increase the water contact angle and thus reduce surface free energy of dental resin composites.

Fluoride release from a new glass-ionomer cement

This study compared the amount and pattern of fluoride release from a new glass-ionomer-based material (nano-ionomer) with other restorative materials and correlated the surface area to volume of nano-sized filler with its capacity to release fluoride in the powder, more quickly increasing the fluoride. The materials evaluated were a nano-ionomer (Ketac N 100), a conventional glass-ionomer cement (GC Fuji II), a resin-modified glass ionomer cement (GC Fuji II LC), a compomer (Dyract F) and a fluoride-releasing resin composite (Tetric N Flow). A resin composite (Synergy Flow) served as the control. Ten specimens were fabricated from each of these materials using a customized metal mold. The fluoride release was measured every 24 hours for the first seven days, and on days 14, 21 and 28, a combination fluoride ion—selective electrode connected to an ion analyzer. The data was analyzed by one-way ANOVA and Tukey HSD test (p=0.05). An initial fluoride “burst effect” was seen with all of the materials, except for the control and compomer. The conventional glass-ionomer cement showed the highest fluoride release on the first three days. The nano-ionomer showed the maximum release of fluoride for the remaining days. A low constant level of fluoride release was seen from the compomer and fluoride-releasing resin composite throughout the study period.

Fluoride release profile of a nanofilled resin-modified glass ionomer cement

The present study aimed to compare the fluoride (F-) release pattern of a nanofilled resin-modified glass ionomer cement (GIC) (Ketac N100 - KN) with available GICs used in dental practice (resin-modified GIC - Vitremer - V; conventional GIC - Ketac Molar - KM) and a nanofilled resin composite (Filtek Supreme - RC). Discs of each material (n=6) were placed into 4 mL of deionized water in sealed polyethylene vials and shaken, for 15 days. F- release (μg F-/cm²) was measured each day using a fluoride-ion specific electrode. Cumulative F- release means were statistically analyzed by linear regression analysis. In order to analyze the differences among materials and the influence of time in the daily F- release, 2-way ANOVA test was performed (α=0.05). The linear fits between the cumulative F- release profiles of RC and KM and time were weak. KN and V presented a strong relationship between cumulative F- release and time. There were significant differences between the daily F- release overtime up to the third day only for GICs materials. The daily F- release means for RC were similar overtime. The results indicate that the F- release profile of the nanofilled resin-modified GIC is comparable to the resin-modified GIC.

Cariostatic effect of fluoride-containing restorative materials associated with fluoride gels on root dentin

Secondary caries is still the main cause of restoration replacement, especially on the root surface

Dental caries: A complete changeover, PART III: Changeover in the treatment decisions and treatments

Comprehensive management of dental caries should involve the management of disease as well as the lesion. Current decision making process in cariology is influenced by numerous factors such as the size/ depth/ activity of the carious lesion and age/ the caries risk status of the patient. Treatment decisions should involve planning the non-operative/ preventive treatment for non-cavitated or early cavitated lesions and also formulating operative treatment for cavitated lesions. Apart from these two responsibilities, a clinician should also be knowledgeable enough to decide when not to interfere in the caries dynamics and how frequently to recall the patient for follow-ups. The non-operative treatment prescriptions vary in dose, intensity and mode of delivery according to the caries risk status. Minimal invasion and maximal conservation of tooth structure has become the essence of current operative treatments. This part of the series elaborates on the paradigm shift in the management of dental caries.

On the assessment of hydroxyapatite fluoridation by means of Raman scattering

Hydroxyapatite is the main mineral component of bones and teeth. Fluorapatite, a bioceramic that can be obtained from hydroxyapatite by chemical substitution of the hydroxide ions with fluoride, exhibits lower mineral solubility and larger mechanical strength. Despite the widespread use of fluoride against caries, a reliable technique for unambiguous assessment of fluoridation in in vitro tests is still lacking. Here we present a method to probe fluorapatite formation in fluoridated hydroxyapatite by combining Raman scattering with thermal annealing. In synthetic minerals, we found that effectively fluoride substituted hydroxyapatite transforms into fluorapatite only after heat treatment, due to the high activation energy for this first order phase transition.

Fluoride releasing restorative materials: Effects of pH on mechanical properties and ion release

OBJECTIVES

Secondary caries and restorative fracture are the two main reasons for restoration failures. Fluoride ion (F) release can help inhibit caries. Plaque pH after a sucrose rinse can decrease to a cariogenic pH of 4-4.5. The objective of this study was to investigate the effects of solution pH and immersion time on the mechanical properties and F release of restorative materials.

METHODS

Three resin-modified glass ionomers (Viremer, Fuji II LC, Ketac Nano), one compomer (Dyract Flow), and one composite (Heliomolar), were tested. Flexural strength and elastic modulus were measured before and after 84d of immersion in solutions of pH 4, 5.5, and 7. F release was measured as a function of pH and immersion time.

RESULTS

Immersion and material type had significant effects on mechanical properties. Vitremer had a flexural strength (mean±sd; n=6) of 99±25MPa before immersion; it decreased to 32±9MPa after 84d of immersion (p<0.05). In comparison, Heliomolar had a smaller strength loss, decreasing from 99±9MPa to 65±7MPa (p<0.05). Solution pH had little effect on mechanical properties. For example, Fuji II LC had a strength of 63±15MPa at pH 4, similar to 61±30MPa at pH 5.5, and 56±22MPa at pH 7 (p>0.1). In contrast, solution pH had a significant effect on F release. F release at 84d for Fuji was 609±25μg/cm(2) at pH 4, much higher than 258±36μg/cm(2) at pH 5.5, and 188±9μg/cm(2) at pH 7.

SIGNIFICANCE

The restoratives tested were able to greatly increase the F release at acidic, cariogenic pH, when these ions are most needed to inhibit caries. However, mechanical properties of these F-releasing restoratives degraded significantly in immersion. Efforts are needed to develop F-releasing restoratives with high levels of sustained F release, as well as improved durability of mechanical properties for large stress-bearing restorations.

Detection of ions released from S-PRG fillers and their modulation effect

The purpose of this study was to analyze the ions released from a surface pre-reacted glass ionomer (S-PRG) filler in distilled water or lactic acid solution. S-PRG filler was mixed with either solution at 1000:1, 100:1, 10:1, and 1:1 ratios by weight. By means of inductively coupled plasma atomic emission spectroscopy and a fluoride electrode, elements released from S-PRG filler were identified to be Al, B, Na, Si, Sr, and F. To investigate the effect of solution pH on ion release, the pH values of the solutions before mixing and after 24 hours' mixing with S-PRG were measured. After 24 hours' mixing, the pH values of solutions at all ratios became more neutral or weakly alkaline regardless of their initial pH levels before mixing. In conclusion, results showed that S-PRG filler released several types of ions, and that ion release was influenced by the mixing ratio of the solution rather than the initial pH of the solution.

Neutralizing effect by resin-based materials containing silane-coated glass fillers

The aim of this study was to evaluate the fluoride release, neutralizing ability and inhibitory effect on secondary caries of resin-based materials containing a silane-coated glass filler. Resin-based materials containing fluoro-boro-alumino-silicate glass coated by 3-methacryloxypropyltrimethoxysilane or 3-aminopropyltrimethoxysilane were used and resin material containing glass filler without coating was used as a control. The fluoride release and pH value after immersion were measured for 10 weeks. The inhibitory effect was also evaluated. During the initial period, the material with 3-aminopropyltrimethoxysilane gave the greater amount of fluoride release and produced a higher pH value compared with the other materials. However, the neutralizing ability of the material with 3-aminopropyltrimethoxysilane filler became weaker with ageing of the specimens. The mean depth of outer lesions was similar among the three materials. Within the limitations of this study, secondary caries around restorations could not be inhibited even for products showing high fluoride releasing and neutralizing ability.

Fluoride and chlorhexidine release from filled resins

Resin-based materials that release either fluoride or chlorhexidine have been formulated for inhibiting caries activity. It is not known if the two agents, when incorporated into one material, would interact and affect their release potential. We hypothesized that the ratio of fluoride to chlorhexidine incorporated into a resin, and the pH of the storage medium, will affect their releases from the material. The material investigated contained 23 wt% of filler, and the ratios of calcium fluoride to chlorhexidine diacetate were 8/2, 5/5, and 2/8. The release was conducted in pH 4, 5, and 6 acetate buffers. The results showed that release of either agent increased as the pH of the medium decreased. The presence of fluoride salt substantially reduced the chlorhexidine release, while the presence of a specific quantity of chlorhexidine significantly increased fluoride release. This interaction can be utilized to optimize the release of either agent for therapeutic purposes.