Prevention of in vitro secondary caries with an experimental fluoride-exchanging restorative resin

Recurrent caries models to assess dental restorations: A scoping review

OBJECTIVES

To review the literature on recurrent caries models used to evaluate restorative materials, compare reported methodology and parameters, and devise specific recommendations to be considered in future investigations.

DATA

The following were extracted: study design, sample characteristics, source of teeth, name of restorations compared including controls, recurrent caries model type, type of demineralizing and remineralizing solutions, type of biofilm used, methods to detect recurrent caries.

SOURCES

Literature searches were performed in OVID Medline, EMBASE, SCOPUS, and Cochrane Library.

STUDY SELECTION

For a study to be included, it had to examine dental materials for tooth restoration purposes only with a valid control group and evaluate restorative dental materials regardless of the form of the teeth caries model used or nature of the tooth structure used. A total of 91 studies were included. Most of the studies presented were in vitro. Human teeth were the main source of specimens utilized. Around 88% of the studies used specimens without an artificial gap, and 44% used a chemical model. S. mutans was the main bacterial species used in microbial caries models.

CONCLUSION

The findings of this review provided an insight into the performance of available dental materials assessed using different recurrent caries models, yet this review cannot be used as a guideline for material selection. Selecting the appropriate restorative material relies on several patient-related factors such as microbiota, occlusion, and diet that are not comprehensively taken into consideration in recurrent caries models and thus hinder reliable comparison.

CLINICAL SIGNIFICANCE

Due to the heterogenicity of variables among studies on the performance of dental restorative materials, this scoping review aimed to provide insights for dental researchers concerning the available recurrent caries models, testing methods used, and aspects of comparison between these materials including their characteristics and limitations.

Clinical/Photographic/Scanning Electron Microscopy Analysis of Pit and Fissure Sealants After 22 Years: A Case Series

Pit and fissure sealant is a clinical technique adopted to prevent caries lesion development. Ionomeric and/or resin-based materials are commonly used for this purpose. This article presents a case series of sealed teeth with 22-year follow-up evaluated by clinical, photographic, and microscopic analysis. In 1992, sixteen patients (9-14 years of age) had at least three teeth sealed with one of the following materials: resin-modified glass ionomer cement (RMGIC, Vitrebond or Fuji II LC) or polyacid-modified resin composite (PMRC, VariGlass VLC), totaling 86 sealed permanent teeth. After 22 years, 10 patients were recalled, representing 41 teeth. The retention of sealants was assessed by three methods: clinical analysis by visual inspection; photography; and scanning electron microscope (SEM) images and classified as retained (pits and fissures filled by sealant material); partially retained (pits and fissures partially filled by sealant material); or totally lost (no material was found in pits and fissures). The SEM images provided a higher number of retained sealants when compared with the clinical and photographic evaluations. Also, no totally lost scores were found with SEM analysis, regardless of the sealing material. No caries lesions were found. A fully or partially retained sealant in pits and fissures was capable of preventing caries lesions after 22 years within the patient pool analyzed.

Evaluation of Fluoride-Releasing Dental Materials by Means of in Vitro and in Vivo Demineralization Models: Reaction Paper

It is essential that we understand the dose-response mechanisms of fluoride delivered intra-orally at sites in intimate contact with dental tissues. Many studies show that extremely low levels of fluoride can inhibit caries. However, few of these studies provide a direct comparison between fluoride release and the inhibition of secondary caries. For this, laboratory, animal, and in situ caries models are required which can predict clinical efficacy. This paper supplements Dr. Erickson's presentation (Erickson and Glasspoole, 1995) by illustrating the adaptation of currently used demineralization and caries models to the development and evaluation of fluoride-containing resin materials. As representative of this class of material, those which release by ion-exchange are reviewed. It is concluded that model systems designed for topical fluorides and non-fluoride dental materials can be adapted for use with fluoride-releasing materials. Further, the use of materials with a long history of clinical efficacy as inhibitors of marginal caries, such as the silicates, is a useful means of determining target values for developing new fluoride-releasing materials. The minimum concentration of F- that must be maintained in the immediate vicinity of a material to provide caries protection at localized sites is not yet known. Nor is it known what combination of release rate, pattern of release, and duration of release is needed to optimize either localized or full-mouth protection. These issues deserve closer examination to aid our understanding of F- action when delivered from dental materials, so that improved caries model systems can be designed for use with dental materials.

Review of Fluoride Release and Secondary Caries Reduction by Fluoridating Composites

Secondary caries is one of the main reasons to replace restorations. Due to the pressure to eliminate or reduce the number of amalgam restorations in many countries, fluoride-releasing composites have gained in importance. This review limits itself to information relevant to secondary caries near fluoride-releasing anterior or posterior composites. Although many parameters are very important in composite functioning, a weak spot near a filling is always the interface and the locally present interfacial gap between the composite and the hard tissues, where secondary caries takes place due to plaque action. Relevant parameters such as the amount of fluoride released in vitro in μg.cm-2, the rate of fluoride release, and the period of fluoride release are compared for several composites. In vitro F release has been measured for some fluoridating composites for more than five years. Unfortunately, F release in vivo or in situ cannot be measured adequately.

The fluoride released by the composites considered is partly taken up by the surrounding tissues, partly released to the saliva, and partly efficacious in possible marginal gaps and defects. A major part of this paper pertains to in vitro, in situ, and in vivo secondary caries reduction experiments. In vitro caries reductions in the order of 40% from F-releasing composites vs. controls have been found. In in situ model investigations under plaque and saliva conditions, secondary caries reduction percentages of between 40 and 50% have been experimentally measured in gaps in enamel near F composites.

Interfacial properties of three different bioactive dentine substitutes

Three different bioactive materials suitable as dentine substitutes in tooth repair have been studied: glass-ionomer cement, particulate bioglass, and calcium-silicate cement. On 15 permanent human molars, Class V cavities were prepared and the bottom of each cavity was de-mineralized by an artificial caries gel. After the de-mineralization, the teeth were restored with: (1) Bioglass®45S5 and ChemFil® Superior; (2) Biodentine™ and ChemFil® Superior; and (3) ChemFil® Superior for a complete repair. The teeth were stored for 6 weeks in artificial saliva, then cut in half along the longitudinal axis: the first half was imaged in a scanning electron microscope (SEM) and the other half was embedded in resin and analyzed by SEM using energy-dispersive X-ray analysis. The glass-ionomer and the bioglass underwent ion exchange with the surrounding tooth tissue, confirming their bioactivity. However, the particle size of the bioglass meant that cavity adaptation was poor. It is concluded that smaller particle size bioglasses may give more acceptable results. In contrast, both the glass-ionomer and the calcium-silicate cements performed well as dentine substitutes. The glass-ionomer showed ion exchange properties, whereas the calcium silicate gave an excellent seal resulting from its micromechanical attachment.

Synthesis and Characterization of New Antibacterial Fluoride-Releasing Monomer and Dental Composite

A new dimethacrylate chelating monomer containing a BisGMA-like backbone structure and a bis(carboxymethyl)-L-lysine chelating group and its ternary zirconium-fluoride complex (antibacterial fluoride-releasing monomer) have been synthesized. The monomer structures were confirmed by (1)H-NMR, (13)C-NMR, and ES-MS analysis. Several experimental fluoride-releasing dental composites containing different quantities of the new antibacterial fluoride-releasing monomer were formulated and tested for fluoride release, fluoride recharge, compressive and flexural strengths, water sorption and solubility. These composites displayed high fluoride release and recharge capabilities, as well as good physical and mechanical properties.

Ion migration from fluoride-releasing dental restorative materials into dental hard tissues

This study was carried out in order to determine the extent to which ions released from fluoride-containing dental restoratives migrated through the enamel and dentine of extracted teeth. A total of 40 permanent human 3rd molars were used. They were extracted for orthodontic reasons, and employed within 1 month of extraction. A cervical (Class V) cavity was prepared in each tooth, then filled with one of: a conventional glass-ionomer, a resin-modified glass-ionomer, a polyacid-modified composite resin ("compomer") or a fluoride-releasing resin composite. Ten samples were prepared per material. After 1 month, five specimens per material were prepared and examined under SEM/EDX. Concentrations of sodium, aluminium, strontium, fluorine, magnesium, silicon, phosphorus and calcium were determined within the tooth. After 18 months, the remaining five specimens for each material were prepared and studied in the same way. The greatest extent of ion migration into the tooth was found with the conventional glass-ionomer and least migration was found for the fluoride-releasing composite, which showed no evidence of fluoride migration at all. Levels of migrating ions were generally higher in the 18 month specimens than in the 1 month specimens, and also higher in the dentine than in the enamel. Ions released by restorative dental materials have been shown conclusively for the first time to be capable of migrating into the enamel and dentine surrounding the restoration. The conventional glass-ionomer showed the highest level of ion migration whereas the fluoridated composite resin showed little if any ion migration. This suggests that the conventional glass-ionomer has the greatest caries inhibiting effects of all the materials tested, and the fluoridated composite the least.

Novel F-releasing composite with improved mechanical properties

In recent years, the authors have been developing novel fluoride-releasing dental composites containing ternary zirconium fluoride chelates. The aim of this study was to improve the physical and mechanical properties of these composites by improving the formulation of the monomers and photoinitiators. The hypothesis was that reduction of hydrophilic monomers and improvement of the photoinitiators could reduce water sorption and significantly increase the mechanical properties of the composite. The degree of conversion of the composites containing different compositions of photoinitiators was studied by Fourier transform near-infrared spectroscopy (FT-NIR). Ten experimental composites containing different compositions of ethoxylated bisphenol-A dimethacrylate (EBPADMA), 1,6-hexanediol dimethacrylate (HDDMA), triethylene glycol dimethacrylate (TEGDMA), and 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy) phenyl]-propane (BisGMA) were tested for flexural strength, viscosity, and water sorption. The experimental composite containing 20% synthesized fluoride-releasing monomer, 30% BisGMA, 30% EBPADMA, and 20% HDDMA showed significantly higher fluoride release and recharge, but physical and mechanical properties similar to those of the control composite containing 40% BisGMA, 40% EBPADMA, and 20% HDDMA.

Effect of acetic NaF solutions on fluoride-containing dental restorative materials

The aim of this study was to evaluate the effect of acetic NaF solutions on fluoride-containing restorative materials. As the pH value of solution decreased, the degree of microhardness change in restorative materials increased- regardless of product. Dyract AP (DA) and F2000 (F2) (polyacid-modified resin composites) showed the greatest decrease in microhardness after immersion for three days. Similarly, as the pH value decreased, volumetric weight change (loss) increased in all products. DA and F2 showed the greatest--but similar-weight change in pH 3.5 solution among the products. In terms of color change, most specimens showed a slight color change after immersion for one and three days-regardless of pH value. However, F2 in pH 3.5 solution showed a noticeable color change (deltaE*=2.1). In terms of surface morphology, specimens in distilled water showed only minor surface modification. However, in pH 3.5 solution, DA and F2 showed randomly propagating cracks, while Solitaire 2 and Tetric Ceram (resin composites) lost many fillers less than 2 microm in size.

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

OBJECTIVES

The purpose of this article was to review the fluoride release and recharge capabilities, and antibacterial properties, of fluoride-releasing dental restoratives, and discuss the current status concerning the prevention or inhibition of caries development and progression.

METHODS

Information from original scientific full papers or reviews listed in PubMed (search term: fluoride release AND (restorative OR glass-ionomer OR compomer OR polyacid-modified composite resin OR composite OR amalgam)), published from 1980 to 2004, was included in the review. Papers dealing with endodontic or orthodontic topics were not taken into consideration. Clinical studies concerning secondary caries development were only included when performed in split-mouth design with an observation period of at least three years.

RESULTS

Fluoride-containing dental materials show clear differences in the fluoride release and uptake characteristics. Short- and long-term fluoride releases from restoratives are related to their matrices, setting mechanisms and fluoride content and depend on several environmental conditions. Fluoride-releasing materials may act as a fluoride reservoir and may increase the fluoride level in saliva, plaque and dental hard tissues. However, clinical studies exhibited conflicting data as to whether or not these materials significantly prevent or inhibit secondary caries and affect the growth of caries-associated bacteria compared to non-fluoridated restoratives.

SIGNIFICANCE

Fluoride release and uptake characteristics depend on the matrices, fillers and fluoride content as well as on the setting mechanisms and environmental conditions of the restoratives. Fluoride-releasing materials, predominantly glass-ionomers and compomers, did show cariostatic properties and may affect bacterial metabolism under simulated cariogenic conditions in vitro. However, it is not proven by prospective clinical studies whether the incidence of secondary caries can be significantly reduced by the fluoride release of restorative materials.

Visual evaluation of in vitro cariostatic effect of restorative materials associated with dentifrices

This study evaluated in vitro the cariostatic effect of 6 restorative materials with and without fluoride release (Fuji II LC, F-2000, Degufil Mineral, Sure Fil and Z-250) associated with a fluoridated and a non-fluoridated dentifrice (Sensodyne Original Formula and Sensodyne Sodium Bicarbonate), on human enamel. Class V-like cavities were prepared on 240 enamel slabs, assigned to 12 groups (6 materials and 2 dentifrices). After cavity restoration, the slabs were submitted to a thermocycling regimen of 1000 thermal cycles and demineralization/remineralization cycles. During pH cycles, slurries of fluoridated and non-fluoridated dentifrices were applied for 5 min. Formation of artificial caries-like lesions was scored independently and blindly by 5 calibrated examiners according to an ordinal scale ranked 0 to 3 by visual examination. The results were analyzed statistically by the Kruskal-Wallis test and pair-wise comparisons (alpha=0.05). There were no significant differences (p>0.05) among the restorative materials associated with the fluoridated dentifrice. When used in association with the non-fluoridated dentifrice, Ketac-Fil showed the highest cariostatic effect followed by Fuji II LC and the other materials. Ketac-Fil was the only material that did not differ statistically when combined with either the fluoridated or the non-fluoridated dentifrice. In conclusion, under the tested experimental conditions, the association of restorative materials and fluoridated dentifrice yielded higher cariostatic effect, except for the conventional glass ionomer cement, whose cariostatic effect was not influenced by the type of dentifrice.

Formulation and characterization of a novel fluoride-releasing dental composite

OBJECTIVES

The aims of this study were to formulate a novel fluoride-releasing dental composite and to evaluate its mechanical properties, fluoride release and recharge capabilities, water sorption and solubility.

METHODS

A fluoride-releasing dimethacrylate monomer containing a ternary zirconium fluoride chelate was synthesized. Three experimental fluoride-releasing composites were fabricated with different monomer formulas (wt.%)-(1) Control A: 40 BisGMA/40 TEDMA/20 UEDMA; (2) EXPERIMENTAL: 20 F-releasing monomer/20 BisGMA/40 TEDMA/20 UEDMA; (3) Control B: the same formula as Control A except that it contained 10 wt.% (of total monomer) tetrabutylammonium fluoride (TBAF), which had a fluoride content equivalent to EXPERIMENTAL. All three materials had the same filler content: 55 wt.% silanized fluoroaluminosilicate particles (0.8 microm) and 10 wt.% silanized fumed silica (14 nm). All materials contained 0.17 wt.% camphorquinone (CQ) as a photoinitiator and 0.69 wt.% ethyl-4-dimethylaminobenzoate (4EDMAB) as an accelerator. The materials were tested for fluoride release (for 184 days), fluoride recharge, compressive and flexure strength, water sorption and solubility. The data were analyzed using ANOVA and Tukey-HSD tests, and Kruskal-Wallis test.

RESULTS

The experimental composite had significantly higher fluoride release and fluoride recharge capabilities than both Control composites. It had significantly better physical and mechanical properties than Control B.

SIGNIFICANCE

The combined use of the fluoride-releasing dimethacrylate monomer and fluoride-releasing filler can provide sustained high fluoride release and recharge as well as acceptable mechanical and physical properties. Simply adding organic fluoride salt in the monomer yields composites with poor mechanical and physical properties.

In vitro inhibition of caries-like lesions with fluoride-releasing materials

The aim of this study was to compare the in vitro caries inhibition of various resin-based materials. Class V cavities were prepared in twenty-five freshly extracted human premolar teeth which were then restored with glass-ionomer cement (Chemfill II), compomer (Compoglass F, Dyract AP) and composite resin (Tetric Ceram and Z 100). The teeth were submerged in an acid gel for 6 weeks. Each specimen was sectioned. These sections were left in water for 24 hours, and then examined using polarized light microscopy. The lesion consisted of two parts, the outer surface lesion and the cavity wall lesion. There was no significant difference in the body depth of the outer lesion and in the depth of the wall lesion among teeth restored with Compoglass F, Dyract AP and Chemfill II (P > 0.05). There was a significant difference between those restored with Z 100 and Tetric Ceram (P < 0.05). The length of the wall lesion for the teeth restored with Chemfill II was significantly smaller than that in the remaining groups (P < 0.05). The length of the wall lesion for teeth restored with Tetric Ceram and Z 100 was significantly higher than in the remaining groups (P < 0.05). These results suggest that composite materials and compomer provide less caries inhibition than glass-ionomer cements.

Compressive strength, fluoride release and recharge of fluoride-releasing materials

The compressive strength, fluoride releases and recharge profiles of 15 commercial fluoride-releasing restorative materials have been studied. The materials include glass ionomers (Fuji IX, Ketac Molar, Ketac Silver, and Miracle Mix), resin-modified glass ionomers (Fuji II LC Improved, Photac-Fil, and Vitremer), compomers (Compoglass, Dyract AP, F2000, and Hytac) and composite resins (Ariston pHc, Solitaire, Surefil and Tetric Ceram). A negative linear correlation was found between the compressive strength and fluoride release (r(2)=0.7741), i.e., restorative materials with high fluoride release have lower mechanical properties. The fluoride-releasing ability can be partially regenerated or recharged by using a topical fluoride agent. In general, materials with higher initial fluoride release have higher recharge capability (r(2)=0.7088). Five equations have been used in curve fitting to describe the cumulative fluoride release from different materials. The equation [F](c)=[F](I)(1-e(-bt))+betat best describes the cumulative fluoride release for most glass ionomers, resin-modified glass ionomers, and some high fluoride-releasing compomers and composites, whereas [F](c)=[F](I)/(t(1/2)+t)+alphat best describes the cumulative fluoride release for most compomers and composite resins. The clinic applications of different fluoride-releasing materials have also been discussed.

Determining low levels of fluoride released from resin based dental materials

Fluoride release determinations were made on two resin matrix dentine bonding systems using an ion-selective electrode and ion chromatography. Calibrations were made on serially diluted samples of standard fluoride solutions. The electrode method consistently gave higher values than the chromatographic method for one of the materials, and this was considered to be due to the use of total ionic strength adjustment buffer in electrode determinations. The lower limit of fluoride determination using the electrode was 0.5-0.1 p.p.m. Below this concentration the output from the electrode became meaningless. The chromatographic method gave meaningful results down to 0.001 p.p.m. The fluoride release results for the meter were meaningful only for the first 2 d for one test material and for up to 10 d for the other material. Using chromatography, fluoride release could be monitored for the full 44 d of the trial for both materials. Over the range of concentrations where fluoride determinations were possible by both methods, the values were correlated (R = 0.98). Ion chromatography appears to have an advantage over the ion-selective electrode for measuring low levels of fluoride release from dental materials.

In vitro dentin demineralization inhibition effects of an experimental fluoridated HEMA and water wetting agent

The ability of fluoride-releasing resins to inhibit dentin demineralization remains controversial. The purpose of this study was to evaluate the caries inhibition of resin composite restorations with an experimental fluoridated hydroxyethyl methyl methacrylate (HEMA) and water wetting agent. Standardized Class V preparations were placed in 40 molars, the gingival margin placed below the cementoenamel junction. Two dentin primers (sodium fluoride, HEMA and water; HEMA and water) were placed in equal numbers of 20 preparations, then One-Step Dental Adhesive (Bisco) was applied as recommended by the manufacturer, followed by the placement of a resin composite restoration. Amalgam restorations with no primer/adhesive were placed in 10 preparations and 10 preparations were restored by placing One-Step Dental Adhesive, then resin composite. All teeth were subjected to an artificial caries challenge (pH 4.4) for 5 days. Results demonstrated the mean areas (microm2 +/- s.d.) of demineralization 100 microm from the restoration/dentin margin to be: amalgam 5,570 +/- 873; One-Step 7,038 +/- 2,099; HEMA and water 6,126 +/- 634; fluoridated HEMA and water 3,411 +/-593. ANOVA and Duncan's test (P < 0.05) demonstrated the fluoridated HEMA and water wetting agent to have significantly less adjacent dentin demineralization than the other three groups. Eighty percent of HEMA and water wetting agent, 80% of One-Step Dental Adhesive and 100% of amalgam restorations demonstrated wall lesions. One hundred percent of restorations with fluoridated HEMA and water wetting agent demonstrated inhibition zones in adjacent dentin.

Properties of fluoride-releasing light-activated resin cement

OBJECTIVES

Fluoroaluminosilicate glass and poly(acrylic acid) in small water phase was incorporated into resin composite cements to reduce or prevent secondary caries around luted restorations. The purpose of this study was to investigate the physical properties and the amounts of fluoride released from four types of visible light-activated resin cements.

METHODS

A powder was composed of silanized SiO2 filler and 4.5 wt.% (G-4.5), 9.5 wt.% (G-9.5) or 19.5 wt.% (G-19.5) fluoroaluminosilicate glass and 0.5 wt.% reducing agent. The 45.25 wt.% triethylene glycol dimethacrylate (TEGDMA), 45.25 wt.% 2-hydroxyethyl methacrylate (HEMA), 9 wt.% poly(acrylic acid) solution in water and 0.5 wt.% camphorquinone were contained in a liquid. The powder and liquid were mixed at a 3:1 ratio by weight and the three types of specimen disks were cured using a photo-curing lamp. The TEGDMA-based composite cement was used as control (G-0). The specimens were immersed in water at 37 degrees C for 24 h or 6 months and compressive strength (CS) and diametral tensile strength (DTS) were evaluated for the four experimental materials. Disks prepared from the four resin cements were also immersed in deionized distilled water at 37 degrees C, and the fluoride released was measured over a period of 24 weeks.

RESULTS

G-9.5 specimens showed almost the same CS and DTS as G-4.5 and G-0 specimens and significantly higher values for both parameters than G-19.5 specimens after 6 months of water storage. The amount of fluoride released from the three fluoride-containing resin cements continued to increase over the entire experimental period. The fluoride release rates of G-9.5 and G-19.5 resin cements were almost the same and were significantly greater than that of the G-4.5 resin cement.

SIGNIFICANCE

G-9.5 containing 9.5 wt.% fluoroaluminosilicate glass may be a clinically useful resin cement due to its favorable physical properties and fluoride release.

Evaluating the effects of fluoride-releasing dental materials on adjacent interproximal caries

BACKGROUND

The authors examined several restorative materials to evaluate their ability to inhibit demineralization and enhance remineralization of incipient carious lesions on the interproximal enamel of teeth adjacent to those restored with the materials.

METHODS

Twenty-one subjects in need of a crown on a mandibular molar and a Class II inlay on an adjacent tooth took part in this six-phase study. Artificial enamel lesions were created and positioned within the interproximal portion of a crown. Lesions were photographed with polarized light microscopy and characterized before and after 30-day intraoral exposures. Each phase included the placement of a new section in the crown model and a new Class II inlay restorative material in the adjacent tooth.

RESULTS

Results demonstrated that nonfluoridated resin composite, fluoridated resin composite and resin-modified glass ionomer restorative materials, when placed in subjects who brushed with a fluoridated dentifrice, demonstrated significantly (P < .05) less enamel demineralization than the nonfluoridated resin composite control placed in subjects who brushed with a nonfluoridated dentifrice. The resin-modified glass ionomer cement, however, even when brushed with a nonfluoridated dentifrice, exhibited significantly (P < .05) less demineralization than the nonfluoridated resin composite control brushed with a nonfluoridated dentifrice.

CONCLUSIONS

Resin-modified glass ionomer cement appears to significantly inhibit demineralization of interproximal enamel of teeth adjacent to those restored with the material.

CLINICAL IMPLICATIONS

Resin-modified glass ionomer cement restorations can enhance prevention of enamel demineralization on adjacent teeth.

In vivo biocompatibility of an acrylic, fluoride-releasing, anion-exchange resin

This study evaluated the biocompatibility of an unfilled, fluoride-releasing acrylic resin by subcutaneous implantation in guinea pigs. The experimental fluoride resin was compared to a nonfluoride, dental pit and fissure sealant (DELTON) of similar composition. Thirty-four male albino guinea pigs received four Teflon tubes each, implanted in the dorsal area. The tubes were open at both ends, three contained the experimental fluoride resin and one held the nonfluoride resin. The tubes and surrounding tissue were excised in 1-2 cm blocks, by necropsy, at 14 and 84 days. Histological evaluation showed that inflammatory response was none-to-slight at 14 days for 95% of the fluoride and 100% of the nonfluoride specimens. Five percent of the fluoride specimens produced a moderate tissue response. At 84 days, inflammatory response was none-to-slight for 82.5% of the fluoride and 61.5% of the commercial nonfluoride specimens, while 17.5% of the fluoride and 38.5% of the nonfluoride specimens produced moderate tissue responses. Chi-squared analysis and Fisher's Exact test revealed no statistically significant difference (p less than or equal to 0.05) in tissue response between the two resins at either 14 or 84 days. Hence it is concluded that the experimental, fluoride-releasing resin produces a very mild subcutaneous tissue response and that its biocompatibility is comparable to that of a widely used nonfluoride dental resin. It can, therefore, be considered as having a high potential for biological safety as a dental restorative resin or adhesive, or for other biomedical applications.

In vitro dentine fluoride uptake from three fluoride-containing composites and their acid resistance

OBJECTIVES

The purpose of this study was to determine the dentine fluoride uptake from three fluoride-containing composites (FluorEver, FluoroCore and Pertac-Hybrid) and to investigate their ability to affect the resistance of dentine to an artificial caries challenge.

METHODS

Three dentine slabs were prepared from each tooth. The baseline, total and bound fluoride concentrations of each tooth were determined by three successive abrasion biopsies performed on each slab followed by adjusting to standardized depths of 10 microns. Next, dentine slabs ligated with the composites were suspended in synthetic saliva for 1 week. After removal of the composites, these specimens and controls were immersed in an artificial caries medium (pH 4.5) for 5 days. Each slab was sectioned and analysed by quantitative microradiography.

RESULTS

The results indicate that dentine acquired significantly different amounts of fluoride from the three composites. The acid resistance of dentine in contact with the composites was also significantly different among the composites and followed the same order as for fluoride uptake.

CONCLUSIONS

Dentine fluoride uptake and artificial caries inhibition were significantly greater with FluorEver followed by FluoroCore and Pertac-Hybrid.

Resin composites in dentistry: the monomer systems

The present review outlines the history of monomers used in resin composites, motivates further development, and highlights recent and ongoing research reported in the field of dental monomer systems. The monomer systems of most present-day resin composites are based on BisGMA, developed some 40 years ago, or derivatives of BisGMA. In the remaining resin composites, urethane monomers or oligomers are used as the basis of the monomer system. The main deficiencies of current resin composites are polymerization shrinkage and insufficient wear resistance under high masticatory forces. Both factors are highly influenced by the monomer system, and considerable efforts are being made around the world to reduce or eliminate these undesirable properties. The use of fluoride-releasing monomer systems, some of which are under investigation, has been suggested to mitigate the negative effects of marginal gaps formed in consequence of polymerization shrinkage. The very crux of the problem has also been approached with the synthesis of potentially low-shrinking/non-shrinking resin composites involving ring opening or cyclopolymerizable monomers. By the use of additives with a supposed chain transfer agent function, monomer systems have been formulated that improve the degree of conversion of methacrylate double bonds and mechanical properties. Many promising monomer systems have been devised, the implementation of which may be expected to improve the longevity of resin composite fillings and expand the indications for resin composites.

In vitro evaluation of matrix-bound fluoride-releasing orthodontic bonding adhesives

Sustained fluoride-releasing composite resins have the potential to prevent decalcification of enamel that may occur during the course of orthodontic treatment. The purpose of this study was to evaluate the potential of matrix-bound fluoride-releasing adhesives (MBF) for orthodontic use by comparing the shear bond strengths (in MPa) and remnant adhesive on debonding (ARI scores) of these resins with commercially available orthodontic adhesives. Two types of resins were evaluated in separate groups: The light-cured resins (group I) consisted of two light-cured MBF, designated resins LA and LB, and five nonfluoride releasing resins, designated LC, LD, LE, LF, and LG. The self-cured resins (group II) consisted of one MBF, designated resin SA, and six nonfluoride releasing resins, designated resins SB, SC, SD, SE, SF, and SG. These resins were used to attach upper right central incisor metal (foil mesh based) orthodontic brackets to 210 freshly extracted bovine incisors in groups of 15 each. Student-Newman-Keuls multiple comparison tests were performed at p < 0.05 to determine significant differences among the resin types. Resin LA was significantly higher in bond strength (mean = 27.4 MPa) compared with LD and LG (mean = 18.9, 10.7 MPa, respectively). Further, LA demonstrated a higher mean bond strength compared with LB, LC, LE, and LF (mean = 21.9, 24.1, 24.3, and 20.8 MPa, respectively). Resin LB had significantly lower ARI scores (mean = 0.33) compared with LF and LG (mean = 1.20 and 1.80). LA, LB, LC, LD, and LE (mean = 0.47, 0.33, 0.60, 0.73, and 0.73, respectively) were not significantly different in their ARI scores. Resin SB demonstrated significantly lower bond strength (mean = 17.2 MPa) compared with SC, SD, SE, SF, and SG (mean = 23.9, 23.7, 23.4, 23.8, and 22.9 MPa, respectively). Resin SA (mean = 19.0 MPa) was not significantly different in bond strength from SB, SC, SD, SE, SF, and SG. Resin SA demonstrated significantly lower ARI scores (mean = 0.73) compared with SD and SE (mean = 2.13 and 1.87). Resin SA had lower mean ARI scores compared with SB, SC, SF, and SG (mean = 1.00, 1.27, 1.13 and 0.87, respectively). Sustained fluoride-releasing (matrix-bound) orthodontic adhesive systems demonstrated bond strength and ARI scores that compared favorably with commercially available orthodontic adhesives.

The influence of surface finish and in-vitro pellicle on contact-angle measurement and surface morphology of three commercially available composite restoratives

Three commercially available composites (Concise, Occlusin and Heliomolar) had surface finishes of varying roughness. Concise and Occlusin were cured against glass and Mylar, or were polished with a white stone or Soflex discs, producing four different surface finishes. Heliomolar was cured against glass or finished with a Vivadent polisher. Each specimen was immersed in water (without pellicle) or artificial saliva (with pellicle) and photographed with a captive air bubble. The influence of pellicle on contact-angle measurements and hence adhesiveness was determined. Scanning electron microscopy of pellicle-free and pellicle-conditioned surfaces was also performed. The effect of the pellicle on all Concise specimens was profound, tending to increase adhesiveness of the smooth (glass and Mylar) surfaces and decrease adhesiveness of the roughened (white stone and Soflex disc) polished surfaces. The pellicle-conditioned smooth Occlusin surfaces behaved similarly, but not the polished specimens, having similar contact-angle measurements after pellicle deposition. Heliomolar had significantly reduced contact-angle measurements after pellicle formation, and thus increased adhesiveness. The influence of the pellicle on surface finish characteristics may be significant, and may vary according to the composite used.

Dental materials related to prevention--fluoride incorporation into dental materials: reaction paper

Rather than a specific commentary to Dr. Rawls' presentation, this reaction paper discusses the general concept of fluoride addition to dental materials. The genesis of the concept is reviewed, but more important is a critique of the rationale for the deliberate addition of fluoride to dental materials. Researchers and practicing dentists should realize that if the principal reason for the addition of fluoride is to prevent dental caries, the ultimate test of that rationale is a controlled clinical trial. Thus, although a number of questions need to be answered when fluoride is introduced into dental materials, the most important is: Does it inhibit dental caries?

Preventive resins in the management of radiation-induced xerostomia complications

The article focuses on caries problems that can arise in oncology patients following radiation of the salivary glands. Preventive restoration techniques are described that utilize fluoride-releasing resins. The particular difficulties associated with the management of areas of exposed incisal and gingival dentine in older patients are given special attention. Positive results are described for a 14-month period that appear to indicate that the technique leads to prevention of recurrent decay and retention of restorations in dehydrated areas of the mouth.

Biocompatibility testing of an experimental fluoride releasing resin using human gingival epithelial cells in vitro

Cell culture is a valuable method of evaluating the biocompatibility of new dental materials. The purpose of this study was to compare the in vitro biocompatibility of an experimental fluoride composite resin with fluoride and non-fluoride-releasing materials currently available. The dental materials tested were: MQ Silicate (silicate cement), KETAC-CEM and FUJI (type II glass ionomer cements), VISIO DISPERS (a light-cured, nonfluoridated, microfilled composite resin), and FR-17 (an experimental fluoride-releasing composite resin). The Smulow-Glickman (S-G) human gingival epithelial cell line, which exhibits semidifferentiated characteristics, was used in the study as a test system. Biocompatibility was quantified by counting the viable cells per unit area remaining after 24 and 48 h at two radial distances from cured specimens immersed in the cell culture medium. The test materials were observed to be most toxic to cells nearest the materials. A Time-Distance Cytotoxicity Index (TDCI) was calculated to relate the percentage of dead cells to viable cells at each diffusion distance for each exposure time compared to a nontoxic control. The relative toxicity ranking of the materials tested based on the TDCI was VISIO DISPERS (91%), FUJI (82%), FR-17 (30%), MQ Silicate (23%), and KETAC-CEM (10%), which exhibited the least toxicity. The cytotoxicity of the experimental resin FR-17 was within the range of cytotoxicity of currently accepted restorative materials.

Fluoride-releasing acrylics

There are numerous examples in dentistry where demineralization, or even frank caries, develops near or in association with restorative or prosthetic materials. Leaking cavity margins and demineralization under bite splints are two examples. A slow-release source of fluoride could help to prevent these problems and provide added protection throughout the mouth. For this purpose a family of fluoride-releasing resins has been developed for use in various adhesive applications, and also for preparing temporary crowns and removable acrylic devices. These materials contain fluoride ions held to covalently bound positive charge sites within the polymer network. Release is by a diffusion/exchange mechanism in which anions from oral fluids diffuse to the charge sites and exchange with fluoride. Fluoride then diffuses to the surface and is released into solution. This method of release allows for the retention of adequate physical properties and is capable of a linear release rate for terms ranging from days to years.

Effective delivery systems for prolonged fluoride release: review of literature

Controlled-release delivery systems have been investigated for use in fluoride therapy as a result of their ability to control the rate and site of fluoride release. Both sustained-release fluoride delivery systems and controlled-release fluoride preparations have been developed, including sustained-release fluoride tablets, fluoride-releasing polymers, microencapsulated fluoride in aerosols, and membrane-controlled fluoride reservoirs. Laboratory and clinical studies have confirmed the ability of these preparations to produce high levels of fluoride in saliva and plaque without toxic or adverse side effects. From these studies, it appears that controlled-release fluoride delivery systems have great potential as effective anticaries agents in cariesprone populations.