Dynamic and static elastic moduli of packable and flowable composite resins and their development after initial photo curing.

OBJECTIVE: The purpose of this study was to evaluate the dynamic (storage) shear modulus and the static shear modulus of elasticity of packable and flowable composite resins and to investigate their development after initial photo-curing. METHODS: Three pairs of a packable versus a flowable composite and a microfill composite resin were tested (Alert/Flow It, Filtek P60/Filtek Flow, Admira/Admira Flow, A 110). Cylindrical specimens (0.85 mm x 18 mm) were made for each material. All specimens were conditioned and tested dry at 21 degrees C. The specimens were tested at 30 min, 24h and 1 week after the end of photo curing. Storage shear modulus and loss tangent were determined by conducting dynamic torsional loading in the frequency range from 1 to 150 Hz. Static shear modulus measurements were made by applying a constant load (below the proportional limit of the materials) for 10s and recording the angular deformation of the specimens. Data were analyzed by ANOVA and Duncan's Post hoc test (alpha=0.05). RESULTS: Storage shear moduli (at 1 week measurement) ranged from 3.39 to 9.67 GPa, and loss tangents from 0.0735 to 0.0235; static shear moduli ranged between 2.66 and 9.80 GPa. High values of elastic moduli and low tandelta values were obtained with packable composites, while low moduli values were obtained with flowable composites. Statistically significant (alpha=0.05) differences were recorded between materials of the same category. Storage time, 24h and 1 week after initial polymerization, resulted in significant increases in both moduli of elasticity. Dynamic shear storage moduli were highly correlated to the static ones (r(2)=0.92; P<0.05). SIGNIFICANCE: The results of the aging studies showed that the rigidity of these materials increases significantly even 1 week after the clinician turns off the curing unit.

Lack of effect of fluoride releasing resin modified glass ionomer restorations on the contacting surface of adjacent primary molars. a clinical prospective study.

AIM: This prospective, split mouth control study was planned to clinically evaluate shown short-term caries protection of glass ionomer cement on tooth enamel placed in contact to it, as a result of fluoride release. STUDY DESIGN: The sample consisted of 83 children, aged 4-7 years, visiting a private practice during the years 1999 and 2000. All subjects met the following criteria: a Class II restoration was needed to a maxillary or mandibular primary molar on both sides of the mouth, the adjacent molars being radiographically diagnosed as sound or with caries in the relative proximal enamel only. METHODS: A resin modified glass ionomer restoration (Vitremer, 3M) was placed at the test side chosen by chance, while an amalgam or composite restoration was placed at the control side. Lesion initiation or progression adjacent to each restoration was categorized in 5 stages radiographically. STATISTICS: The non-parametric Marginal Homogeneity test for paired observations was used. RESULTS: Differences between test and control were not statistically significant (p>0.1). Two years after restorations were placed bitewings were taken from 36 children (41 pairs of restorations). Uncontrolled brushing with fluoride dentifrice was reported. Mean fluoride treatments performed were 2.2, initial visit included. Lesion progression was: 14 pairs--no progression in either side; 9 pairs--equal progression by 1 stage in both sides; 9 pairs--progression by 1 stage at test side, no progression at control side; 6 pairs--progression by 1 stage at control side, no progression at test side; 3 pairs--various other combinations of scores. CONCLUSIONS: Under these clinical conditions, fluoride release from Class II Vitremer restorations did not affect the rate of caries progression at the adjacent enamel of proximal primary teeth.

In vivo evaluation of microleakage from composites with new dentine adhesives.

The purpose of this study was to investigate microleakage in V class composite restorations with total etch versus self-etching adhesives. Experiments were conducted in vivo and were also evaluated interfacial micromorphology. Forty class V cavities were prepared on the buccal surfaces of teeth in three healthy dogs. The cavities were randomly assigned into five groups of eight teeth and restored with one of the following adhesive systems: Etch and Prime 3.0/Definite flow/Definite, Prompt L-pop/Filtek flow/P-60, Admira bond/Admira Flow /Admira, Bond 1/Flow it/Alert, Stae/Wave/Glacier. After 60 days the animals were killed and the teeth were extracted. The teeth were then immersed in a solution of 0.5% basic fuchsin dye for 24 h, sectioned and scored for microleakage. Features of the tooth/restoration interfaces were also examined using Scanning electron microscopy. Student-Newman-Keuls and one-way anova revealed significance differences among the groups for overall wall scores (P < 0.05). The total-etch adhesives revealed significantly less microleakage scores than the self-etching adhesive systems tested. Wilcoxon Signed Ranks Test revealed significant differences between the occlusal and gingival microleakage scores for each adhesive restorative system, with the exception of Admira (P < 0.05).

Inhibition of demineralization in vitro around fluoride releasing materials.

Replacement of restorations because of secondary caries is a continuing problem in restorative dentistry. This investigation assessed the capacity of fluoride-releasing restorative materials to resist caries in vitro when used in roots. Class 5 cavities were prepared in buccal and lingual surfaces of 30 extracted premolars and restored with one of three polyacid modified resin composites (F-2000, Hytac and Compoglass F), a resin modified glass-ionomer cement (Fuji II LC) a conventional glass ionomer (Ketac-Fil), and a resin composite (Z-100). After 5 weeks in an acid gel for caries-like lesion formation, the teeth were sectioned longitudinally and examined with polarized light. The results showed that restoration of caries with polyacid modified resin composites and resin modified glass ionomer cements may be of great importance in the prevention of secondary caries around the restorations in roots. Clinical Relevance Light cured fluoride-releasing restorations may inhibit caries-like lesions. Inhibition of demineralization in vitro around fluoride releasing materials.

Fluoride release and uptake by four new fluoride releasing restorative materials.

The present study compared the initial fluoride release and release following refluoridation of a conventional glass-ionomer Ketac-Molar (ESPE), a resin-modified glass-ionomer, Vitremer (3M), and two compomers F-2000 (3M) and Hytac (ESPE). Fifteen test specimens were prepared for each brand and immersed in deionized water. The fluoride released was measured every 2 days for 22 days. Refluoridation of the test specimens was done with solutions of 0.02, 0.04 and 0.2% NaF for 5 min on days 22, 30, 38 and 46. The fluoride released from recharged specimens was measured every 2 days until day 54. The fluoride release was highest during the first days after preparation, after which it decreased sharply and then more slowly. The four materials became 'recharged' with fluoride following repeated fluoride exposure in solution, the 0.2% solution being the most effective. From a clinical point of view, the results from this study imply that all the restorative materials tested may act as intra-oral devices for the controlled slow release of fluoride at sites at risk of recurrent caries. Fluoride release and uptake by four new fluoride releasing restorative materials.

The effect of home-use fluoride gels on glass-ionomer, compomer and composite resin restorations.

The purpose of this study was to investigate the resistance to dissolution by two home-use fluoride gels on the surface integrity of glass-ionomer, resin modified glass-ionomer, compomer and composite resin restorations. Class V cavities prepared in extracted teeth were restored with a glass-ionomer (Fuji II), a resin modified glass-ionomer (Vitremenr), two compomers (Dyract and F-2000) and a composite resin (Z-100). Groups of five specimens of each material were treated for 24 h with one of the following: (i). distilled water, (ii). neutral fluoride gel and (iii). acidulated phosphate fluoride (APF) gel. Surface degradation of the restorations was studied using standard electron microscopy (SEM), rated according to specific criteria and statistically analysed by the Wilcoxon test (rank sums). Acidulated phosphate fluoride was found to have a significant effect on all examined materials, while minimal effects resulted from the neutral fluoride gel compared with the control group. The effect of home-use fluoride gels on glass-ionomer, compomer and composite resin restorations.

In vitro cytotoxicity of six dentin bonding agents.

The cytotoxicity of six dentin bonding agents (Syntac, Solobond, Bond 1, Scotchbond 1, Heliobond and F-2000) was tested against an established cell line, L929. Under aseptic conditions 3, 5 and 10 microL dentin bonding agents were placed in the centre of Petri dishes. Each dish was covered with a 5-mL suspension of fibroblasts at a concentration of 40 000 cells mL(-1). The cultures were incubated at 37 degrees C and cytotoxicity was assessed by a quantitative technique at 24 and 72 h. All the dentin bonding agents were found to be cytotoxic. Scotchbond 1 and F-2000 showed the highest cytotoxicity followed by Solobond and Bond 1. Heliobond and Syntac were the least toxic materials.

Antibacterial properties of dentin bonding systems, polyacid-modified composite resins and composite resins.

This study examined the antibacterial activities of the bonding systems Syntac, EBS and Scotchbond 1, the polyacid-modified composite resins Hytac and Compoglass, and the composite resins Tetric, Z100 and Scalp-it. They were evaluated using the cariogenic bacteria Streptococcus mutans, Lactobacillus salivarius, Streptococcus sorbinus and Actinomyces viscosus in vitro with a modified cylinder drop plate agar diffusion assay. All adhesives of the dentin bonding systems and the polyacid-modified composite resins exhibited various degrees of antibacterial activity against all of the test bacteria. On the contrary, composite resins did not affect bacterial growth. The data suggest that the use of these adhesives and polyacid-modified composite resins may reduce the consequences of microleakage owing to their antibacterial properties.

Artificial caries formation around fluoride-releasing restorations in roots.

Secondary caries is one of the most important factors leading to replacement of dental restorations. This investigation assessed the capacity of fluoride-releasing restorative materials to resist caries in vitro when used in roots. Class 5 cavities were prepared in the buccal and lingual surfaces of 30 extracted premolars. The six materials used were: glass-ionomer cement (Fuji), glass-ionomer cement with silver particles added (Ketac-silver), fluoride-containing composite resin (Tetric), composite resin (Silux plus), fluoride-containing amalgam (Fluor-Alloy) and high-copper amalgam (Dispersalloy). After 5 weeks in an acid gel for caries-like lesion formation, the teeth were sectioned longitudinally and examined with polarized light. The results showed that repair with glass-ionomer materials of a carious lesion may be of great importance in the prevention of secondary caries around the restorations in roots.

Artificial secondary caries around two new F-containing restoratives.

Replacement of restorations due to secondary caries is a continuing problem in restorative dentistry. This investigation evaluated the ability of two new light-cured fluoride-containing restorative materials to inhibit caries in vitro. Class 5 cavities were prepared in buccal and lingual surfaces of 20 extracted premolars. The occlusal cavosurface margin of each preparation was on enamel and the gingival cavosurface margin was on root surface. The four materials used were: glass-ionomer cement (Fuji II), composite resin (Silux Plus), light-cured glass ionomer (Vitremer), and compomer (Dyract). After 5 weeks in an acid gel for caries-like lesion formation, the teeth were sectioned longitudinally and examined with polarized light. The results showed that use of a light-cured glass ionomer and/or compomer may prevent both secondary caries around restorations and primary caries in surface enamel adjacent to the restorations.

Secondary caries formation in vitro around glass ionomer-lined amalgam and composite restorations.

The aim of this in vitro secondary caries study was to examine the glass-ionomer liner's effect on wall-lesion inhibition when a conventional and a light-cured glass ionomer liner was placed under amalgam and composite resin restorations. Class V preparations in extracted upper premolars were used and ten restorations were used for each of the following groups: (i) two layers of copal varnish and amalgam; (ii) conventional glass-ionomer and amalgam; (iii) light-cured glass-ionomer and amalgam; (iv) bonding agent and light-cured composite resin; (v) conventional glass-ionomer, bonding agent and light-cured composite resin; (vi) light-cured glass-ionomer, extended 0.3 mm short of the enamel margin bonding agent and light-cured composite resin; and (vii) light-cured glass-ionomer, extended 1 mm short of the enamel margin, bonding agent and light-cured composite resin. The teeth were thermocycled and artificial caries were created using an acid-gel. The results of this study showed that artificial recurrent caries can be reduced significantly (P < 0.05) with a glass-ionomer liner under amalgam restorations. The results also showed that when the light-cured glass-ionomer liner was placed 0.3 mm from the cavosurface margin under composite resin restoration, the artificial recurrent caries reduced significantly (P < 0.05).

A study of the microstructure of some dental retention pins and prefabricated root canal posts.

Pins and root canal posts are generally considered indispensible aids in clinical restorative dentistry. To secure the long-term efficiency of pins and posts, such devices should be of sufficient strength to carry the relevant loads. It is, however, essential that their properties do not decline as a consequence of corrosion, or that corrosion of metallic pins and posts does not cause unfavourable effect in contacting biological tissues. The microstructure of certain commercially available dental retention pins and prefabricated root canal posts has been investigated using optical microscopy and standard metallographic techniques. The specimens were then examined by scanning electron microscope and energy dispersive X-ray analysis (EDAX). The results indicate differences in microstructure and condition between the types examined. The results also showed the presence of included particles in some pins and posts. These differences and the presence of inclusions may have an important bearing on service life and corrosion resistance.

Secondary caries formation in vitro around fluoride-releasing restorations.

Secondary caries is one of the most important factors leading to replacement of dental restorations. This investigation assessed the capacity of fluoride-releasing restorative materials to resist caries in vitro. Class 5 cavities were prepared in buccal and lingual surfaces of 18 extracted premolars. The six materials used were: high-copper amalgam (Dispersalloy), fluoride-containing amalgam (Fluor-Alloy), composite resin (Valux), fluoride-containing composite resin (Heliomolar), glass-ionomer cement (Fuji), and glass-ionomer cement with silver particles added (Ketac-Silver). After 15 weeks in an acid gel for caries-like lesion formation, the teeth were sectioned longitudinally and examined with polarized light. The results showed that restoration of caries with glass-ionomer materials and fluoride-containing amalgam may be of great importance in the prevention of both secondary caries around the restorations and primary caries in surface enamel adjacent to the restoration.

Lesions in vitro associated with a Fl-containing amalgam and a stannous fluoride solution.

Secondary caries is one of the most important factors leading to replacement of amalgam restorations. This investigation compared the anticariogenic effect of a fluoride-containing amalgam, a stannous fluoride application in the cavity prior to restoration with conventional amalgam, and the combination of the fluoride treatment with the well-recognized technique of cavity varnishing. Class 5 cavities were prepared in the middle third of both buccal and lingual surfaces of 20 extracted premolars. Conventional amalgam was inserted in 10 cavities (control group). Fluoride-containing amalgam was inserted in 10 cavities (second group). The third group received a treatment of 8% SnF2 and the fourth group received the SnF2 and a cavity varnish application before insertion of the conventional amalgam. After 15 weeks in an acid-gel for caries-like lesion formation, the teeth were sectioned longitudinally and examined with polarized light. The results showed that both fluoride-containing amalgam and conventional amalgam with prior treatment of the cavity with the stannous fluoride solution and varnish had an inhibitory effect on the development of artificial cavity wall caries in vitro.

Sensitivity to ambient light of visible light-cured composites.

Fourteen representative visible light-cured composite materials, including a total of 29 shades, have been examined for sensitivity to ambient light. The assessment was based upon a procedure recommended in an International Standard (ISO/DIS 4049). All but four of the 29 formulations exceeded the critical working time of 60 s when exposed to ambient illumination of 20 klx. These four composite resins exhibited working times greater than 60 s under 10 klx illumination, and the maximum working time observed at 10 klx was 227 s. These data confirm the finite working time of light-cured resins under clinical lighting conditions.

Dynamic mechanical properties of an inlay composite.

A visible light-cured composite resin (Brilliant DI) has been studied over a wide range of temperature and frequency by a dynamic mechanical flexural method. The derived data of logarithmic modulus and loss tangent (tan delta) show considerable changes following a secondary-cure process applied to the material. This involved the application of heat and intense light with temperatures rising to 120 degrees C in 7 min. Following this oven-cure the resin phase exhibited enhanced stiffness with the activation-energy barrier for molecular motion at the glass-transition rising from 220 to 291 kJ/mol. This study clarifies the nature and extent of the internal molecular changes which may be produced in the fabrication of a composite inlay.