Streptococcal adhesion to novel low-shrink silorane-based restorative

ObjectivesThe aim of the present study was to compare the susceptibility of one novel silorane-based and four widely used conventional methacrylate-based resin composites to adhere oral streptococci and to relate any differences to surface roughness, hydrophobicity and type of matrix.MethodsSpecimens of restoratives Filtek Silorane, Filtek Z250, Tetric EvoCeram, Quixfil and Spectrum TPH were prepared (10.0-mm diameter, 2.0-mm height). Surface roughness was assessed by perthometer measurements and hydrophobicity according to water contact angles was determined by computerized image analysis. Bacterial suspensions of Streptococcus oralis, Streptococcus sanguinis, Streptococcus gordonii and Streptococcus mutans were incubated for 2.5 h at 37 °C with 15 test specimens for each material and adhesion was quantified with fluorescence dye Alamar Blue/Resazurin and an automated multi-detection reader. Glass served as reference. Statistical analysis was performed using the Mann–Whitney U-test (α = 0.05).ResultsMedian roughness values of all composites ranged between 0.04 and 0.11 μm, median contact angles between 59.7° and 92.1°. Significantly lowest fluorescence intensities of all test materials were found on Filtek Silorane for three of four streptococcal strains. The fluorescence intensities of the four conventional methacrylate resin composites were significantly higher and comparable among each other.SignificanceWhen compared against four conventional methacrylate composite resins, a general significance to a lower quantity of adhering streptococci was found on the novel silorane-based composite resin, which might result from its increased hydrophobicity. The low adhesion potential of the silorane-based composite may potentially improve the longevity of direct fillings and reduce recurrent caries.     

Effect of different composite modulation protocols on the conversion and polymerization stress profile of bulk-filled resin restorations

ObjectiveThe aim of this in vitro study was to test the effect of different composite modulation protocols (pre-heating, light-curing time and oligomer addition) for bulk filling techniques on resin polymerization stress, intra-pulpal temperature change and degree of conversion.MethodsClass I cavities (4 mm depth × 5 mm diameter) were prepared in 48 extracted third molars and divided in 6 groups. Restorations were completed with a single increment, according to the following groups: (1) Filtek Z250XT (room temperature – activated for 20 s); (2) Filtek Z250XT (at room temperature – activated for 40 s); (3) Filtek Z250XT (pre-heated at 68 °C – activated for 20 s); (4) Filtek Z250XT (pre-heated at 68 °C – activated for 40 s); (5) Filtek BulkFill (at room temperature – activated for 20 s); (6) Filtek Z250XT (modified by the addition of a thio-urethane oligomer at room temperature – activated for 40 s). Acoustic emission test was used as a real-time polymerization stress (PS) assessment. The intra-pulpal temperature change was recorded with a thermocouple and bottom/top degree of conversion (DC) measured by Raman spectroscopy. Data were analyzed with one-way ANOVA/Tukey's test (α = 5%).ResultsPre-heating the resin composite did not influence the intra-pulpal temperature (p = 0.077). The thio-urethane-containing composite exhibited significantly less PS, due to a lower number of acoustic events. Groups with pre-heated composites did not result in significantly different PS. Filtek BulkFill and the thio-urethane experimental composite presented significantly higher DC.SignificanceResin composite pre-heating was not able to reduce polymerization stress in direct restorations. However, thio-urethane addition to a resin composite could reduce the polymerization stress while improving the DC.     

Degree of conversion of Filtek Silorane Adhesive System and Clearfil SE Bond within the hybrid and adhesive layer: An in situ Raman analysis

ObjectivesTo examine the degree of conversion (DC) of the adhesive interfaces created by Filtek Silorane Adhesive and Clearfil SE Bond using micro-Raman spectroscopy.MethodsThe adhesives were applied on human dentin in accordance with manufacturer's instructions. Specimens were cut to expose the bonded interfaces to the micro-Raman beam (Ranishaw InVia; laser wl 785 nm). Raman spectra were collected along the dentin/self-etching primer/adhesive interface at 1 μm intervals. The relative intensities of bands associated with mineral (P–O functional group at 960 cm^?1) and adhesive (C–C–O group at 605 cm^?1) components within the bonded interface were used to detect monomer penetration into the dentin matrix and to calculate the degree of conversion (CC at 1640 cm^?1 as reaction peak, C–C–O at 605 cm^?1 as reference peak). Data were statistically analyzed with two-way ANOVA.ResultsDC of Filtek Silorane Adhesive was 69 ± 7% in the adhesive layer, increasing (p < 0.05) to 93 ± 5% in the primer and 92 ± 9% in the hybrid layer. Clearfil SE Bond showed a DC of 83 ± 3% in the hybrid and 85 ± 3% in the adhesive layer. Thus, Filtek Silorane Adhesive showed a higher DC than Clearfil SE Bond in the hybrid layer (p < 0.05), but a lower DC in the adhesive (p < 0.05).SignificanceAs high DC is a fundamental pre-requisite for the stability of the bond over time, this study supports the hypothesis that optimal stability of Filtek Silorane Adhesive can be obtained. However, further research is needed to investigate the mechanical properties of the hybrid layer created by Filtek Silorane Adhesive and its long-term stability.     

Oxygen inhibition and incremental layer bond strengths of resin composites

ObjectivesWhen dentists light cure resin composite restorations in increments or after contouring the surface layer to shape with a hand instrument the surface layer is exposed to air during polymerization. The presence of an oxygen inhibited resin surface layer may impact on clinical performance. Conflicting data has been produced in vitro regarding this topic.MethodsTo shed further light on this subject the current investigation assessed the thickness of the oxygen inhibited layer (OIL) and subsequent interfacial bond strength at various times post-cure of an “initial increment” for a range of experimental and commercial resin composites. The latter included conventional methacrylate-based composites and a novel low shrink Silorane resin chemistry product.ResultsA decrease in composite viscosity brought about by an increase in diluent monomer content in the matrix for the experimental composite formulations led to increase in OIL thickness. The OIL surface layer thickness for the commercial methacrylate-based RBC specimens cured in air were 19.2 ± 6.3 and 13.8 ± 5.3 μm, respectively and 9.0 ± 6.6 μm for Silorane. No test material exhibited a measurable OIL thickness polymerized in the nitrogen atmosphere.SignificanceFrom the current findings it may be concluded that incremental bond strength is not wholly reliant on surface inhibition since no differences in bond strength following immediate placement were observed between air and nitrogen atmosphere for any experimental or commercial material. For large restorations requiring multiple increments which are placed on fresh material, the bond strength between successive layers of Silorane should be no different to conventional methacrylate materials. Repair and bonding to aged Silorane restorations may be more problematic as inferior incremental bond strengths ensued when addition was delayed.     

Mechanistic aspects of fatigue crack growth behavior in resin based dental restorative composites

ObjectiveTo test the hypothesis that a commercial microhybrid resin based composite (Filtek? Z250) has superior fatigue resistance to a nanofill composite (Filtek? Supreme Plus) and to determine the related micromechanisms involved in the fatigue process.MethodsAfter 60 days of water hydration, the fatigue crack growth resistance of two different resin composites, one microhybrid (Filtek? Z250) and one nanofill (Filtek? Supreme Plus), was measured in wet conditions using compact-tension, C(T), specimens at a load ratio of 0.1 and frequency of 2 Hz. Cyclic fatigue behavior was quantified in terms of the fatigue crack growth rate, da/dN, as a function of the stress intensity range, ΔK.ResultsA sigmoidal da/dN-ΔK curve with three different fatigue crack growth regimes was identified for both composites. In general, fatigue crack growth ranged from ～10^?9 to 10^?5 m/cycle over ΔK of 0.54–0.63 MPa√m for the Z250 composite and ΔK of 0.41–0.67 MPa√m for the Supreme Plus composite. The Supreme Plus composite showed a lower fatigue threshold, ΔK_th, by ～0.13 MPa√m compared to the Z250 composite, while also showing a plateau in the fatigue crack growth curve that is likely related to environmental attack. SEM observations of the fatigue crack paths and fracture surfaces revealed an interparticle crack path and extrinsic toughening mechanisms of crack deflection and crack bridging. No fatigue degradation of reinforcing particles or clusters was found, but cluster–matrix debonding was evident in the Supreme Plus composite, also indicative of environmental attack due to water.SignificanceThis study increases the understanding of both the fatigue behavior and the micromechanisms of fatigue in resin based dental composites.     

Flowability of composites is no guarantee for contraction stress reduction

ObjectivesThe purpose of this study was to measure the contraction stress development of three flowable resin-composite materials (Grandio Flow, VOCO GmbH, Cuxhaven, Germany; Tetric Flow, Ivoclar Vivadent, Schaan, Liechtenstein; Filtek Supreme XT Flowable Restorative, 3 M ESPE, ST. Paul, MN, USA) and an universal micro-hybrid composite resin (Filtek Z250, 3 M ESPE, St. Paul, MN, USA) during photopolymerization with a halogen curing light, using a novel stress-measuring gauge.MethodsCuring shrinkage stress was measured using a stress-analyzer. Composites were polymerized with a halogen curing unit (VIP, Bisco Inc., Schaumburg, IL, USA) for 40 s. The contraction force (N) generated during polymerization was continuously recorded for 180 s after photo-initiation. Contraction stress (MPa) was calculated at 20 s, 40 s, 60 s, 120 s and 180 s. Data were statistically analyzed.ResultsFiltek Supreme XT Flowable Restorative exhibited the highest stress values compared to other materials (p < 0.05), while the lowest values were recorded with Tetric Flow (p < 0.05). Tetric Flow was also the only flowable composite showing stress values lower than the conventional composite Filtek Z250 (p < 0.05).SignificanceFlowable composites investigated with this experimental setup showed shrinkage stress comparable to conventional resin restorative materials, thus supporting the hypothesis that the use of flowable materials do not lead to marked stress reduction and the risk of debonding at the adhesive interface as a result of polymerization contraction is similar for both type of materials.     

R-curve behavior and toughening mechanisms of resin-based dental composites: Effects of hydration and post-cure heat treatment

ObjectivesTo test the hypothesis that the fracture resistance of two different particulate resin composites degrade after water hydration and improve after post-cure heat treatment, and to correlate those changes with salient failure micromechanisms.MethodsTwo composites with different filler morphology were selected, denoted microhybrid (Filtek? Z250) and nanofill (Filtek? Supreme plus). Following initial light curing, hydrated samples were aged in water for 60 days at room temperature while post-cured samples were heat treated at 120 °C for 90 min. Fracture resistance was assessed using fracture resistance curves (R-curves) utilizing pre-cracked compact tension, C(T), specimens. The flexural strength of the hydrated composites also was evaluated in four-point bending using unnotched beams. Scanning electron microscopy (SEM) of crack paths and fracture surfaces was performed to determine the micromechanisms of fracture and toughening. The results were compared by two-way ANOVA and Tukey's multiple comparison test (p ≤ 0.05).ResultsSEM observations revealed a predominantly interparticle matrix crack path for all cases except the hydrated nanofill composite, which showed evidence of particle matrix debonding. Hydration lowered the strength for both composites and the peak toughness for the nanofill composite. The strength decrease was attributed to resin matrix plasticization and hydrolytic degradation in both cases, with additional interfacial degradation causing a larger strength decline and concomitant peak toughness decrease in the nanofill composite. The post-cure heat treatment noticeably changed the R-curve shape causing the peak toughness to be reached after shorter amounts of crack extension. Such changes help explain the increases in strength reported in other studies and is attributed to improved resin matrix properties.SignificanceResults from this study provide new insight into the micromechanisms of fracture in resin-based dental composites which should aid the future development and improvement of these materials.     

Determination of the optimal photoinitiator concentration in dental composites based on essential material properties

ObjectivesThe aim of this study was to determine the concentrations of the photosensitizer (camphoroquinone, CQ) and coinitiator (ethyl-4-dimethylaminobenzoate, EDMAB) that resulted in maximum conversion but generated minimum contraction stress in experimental composites.MethodsExperimental composites were prepared with an identical resin formulation [TEGDMA:UDMA:bis-GMA of 30.25:33.65:33.65]. Five groups of resin were prepared at varied CQ concentrations (0.1, 0.2, 0.4, 0.8 and 1.6 wt% of the resin). Five subgroups of resin were prepared at each level of CQ concentration, by adding EDMAB at 0.05, 0.1, 0.2, 0.4 and 0.8 wt% of the resin, resulting in 25 experimental resins. Finally, strontium glass (～3 μm) and silica (0.04 μm) were added at 71.5 and 12.6 wt% of the composite, respectively. Samples (n = 3) were then evaluated for Knoop hardness (KHN), degree of conversion (DC), depth of cure (DoC) and contraction stress (CS).ResultsThere was an optimal CQ and EDMAB concentration that resulted in maximum DC and KHN, beyond which increased concentration resulted in a decline in those properties. KHN testing identified two regions of maxima with best overlaps occurring at CQ:EDMAB ratio of 1.44:0.42 and 1.05:1.65 mol%. DC evaluation showed one region of maximum, the best overlap occurring at CQ:EDMAB ratio of 2.40:0.83 mol%. DoC was 4 mm. Overall, maximum CS was attained before the system reached the maximum possible conversion and hardness.Significance(1) Selection of optimal photoinitiator/amine concentration is critical to materials’ formulation, for excessive amounts can compromise materials’ properties. (2) There was no sufficient evidence to suggest that contraction stress can be reduced by lowering CQ/EDMAB concentration without compromising DC and KHN.     

Influence of surface treatments on the bond strength of repaired resin composite restorative materials

ObjectivesThe purpose of this study was to investigate the effect of different surface treatments on the bond strength (σ) of repaired, aged resin composites (ARC).MethodsForty blocks of Filtek Z250? (Z2) and Filtek Supreme? (SU) were made, stored in deionized water for 9 days, and randomly assigned to different surface treatment groups: hydrofluoric acid etching (HA), abrasion using a coarse diamond bur (AB), sandblasting with alumina particles (AO), and silica coating (SC). The average roughness (Ra) of the treated surfaces was measured with a profilometer. An adhesive system (SB-Adper Single Bond Plus?), a silane (SI) or a combination of both (SI + SB) were applied after each surface treatment. The blocks were restored with the same composite (RC) and cut to produce bars that were turned into dumbbell-shaped specimens (0.5 mm²) using a precision grinding machine. The specimens (n = 30) were tested in tension to fracture and the microtensile bond strength (σ) values were calculated (MPa). Data were analyzed using three-way ANOVA/Tukey test (α = 0.05) and Weibull statistics.ResultsAO and SC produced similar Ra values, which were greater than the value produced by HA. The σ values were statistically influenced by the type of RC (p < 0.0001), by the surface treatment (p < 0.0001) and by the surface coating (p < 0.0001). Treating the surface of Z2 with SC + SB produced the greatest m value.SignificanceAO and SC produced the greatest σ values, irrespective of the primer (SI, SB or SI + SB) used. Yet, the RC microstructure influenced the mean σ values, which were greater for Z2 than for SU. The HA should not be used for repairing ARC.     

Micro-sized erosions in a nanofilled composite after repeated acidic beverage exposures: consequences of clusters dislodgments

Objective

To evaluate the hardness (KHN), color stability (DE), and superficial micromorphology of two categories of composites after immersion in either distilled water or grape juice for up to 45 days.

Material and Methods

Cylindrical specimens (6 mm diameter x 2 mm thick) were obtained according to the factors: composite [Opallis (FGM) and Filtek Z350XT (3M ESPE)]; immersion solution (distilled water and grape juice); and evaluation time: 24 h and 7, 14, 21, 28, and 45 days. After photoactivation, the specimens were stored at 37ºC for 24 h. KHN (50 g/15 s) and ΔE were then repeatedly assessed according to the immersion solutions. Data were analyzed (three-way ANOVA/Tukey''s test). Scanning electron microscopy (SEM) topographic analysis was also performed.

Results

In general, KHN of both composites reduced after 24 h, irrespective of the immersion solution and time. A significantly lower KHN was noted for Opallis compared with Filtek Z350XT in all parameters. An increase in ΔE over time was noted for both composites, irrespective of the immersion solution. Significantly higher ΔE was noted for Filtek Z350XT immersed in grape juice compared with Opallis, regardless of the evaluation time. The grape juice caused significantly higher DE compared with water in all periods. SEM analysis showed eroded areas for Filtek Z350XT but not for Opallis.

Conclusions

The compositions and immersion solutions influence the composite hardness and the color stability. In spite of the higher hardness, the nanofilled composite is more susceptible to color change than the microhybrid when immersed in an acidic dyed solution.     

Experimental composites containing quaternary ammonium methacrylates reduce demineralization at enamel-restoration margins after cariogenic challenge

ObjectiveThis study evaluated the influence of experimental composites containing quaternary ammonium monomers (QAM) at different concentrations and alkyl chains on demineralization at enamel-composite margins after cariogenic challenge.MethodsStandardized 4 × 4 mm cavities were cut into 35 bovine enamel blocks, which were randomly divided into seven groups (n = 5) and restored with the following experimental composites and commercial materials: (G12.5) – 5% dimethylaminododecyl methacrylate (DMADDM) with a 12-carbon alkyl chain (G12.10) – 10% DMADDM, (G16.5) – 5% dimethylaminohexadecyl methacrylate (DMAHDM) with a 16-carbon alkyl chain (G16.10) – 10% DMAHDM, (CG) – control group (without QAM), (GZ250) – commercial composite (Filtek Z250^®), and (GIC) – glass ionomer cement (Maxxion R^®). After restorative procedures, initial microhardness was measured and experimental composites were subjected to Streptococcus mutans biofilm formation for 48 h. After cariogenic challenge, the samples were washed and microhardness was reassessed. A 3D non-contact profilometer was used to determine surface roughness and enamel demineralization was assessed by micro-CT. Microhardness results were analyzed by the Kruskal–Wallis and Mann-Whitney tests and micro-CT results were analyzed by Tukey’s HSD test (95% confidence interval).ResultsNone of the materials could prevent mineral loss at the enamel-restoration margins. The addition of 10% DMAHDM yielded the lowest, albeit statistically significant, mineral loss (p < 0.05). 3D non-contact profilometry showed enamel surface roughness modification after biofilm exposure. The CG had the highest roughness values. Micro-CT analysis revealed mineral loss, except for GIC.SignificanceThe addition of 10% QAM with a 16-carbon chain in experimental composites reduced mineral loss at the enamel-restoration margins after cariogenic challenge.     

Volumetric polymerization shrinkage and its comparison to internal adaptation in bulk fill and conventional composites: A μCT and OCT in vitro analysis

ObjectiveTo quantify the volumetric polymerization shrinkage (VPS) of different conventional and bulk fill resin composites, through micro-computed tomography (μCT), and qualitative comparison of gap formation through optical coherence tomography (OCT).MethodsBox-shaped class I cavities were prepared in 30 third-molars and divided into 5 groups (n = 6): G1- Filtek Z100 (Z100); G2- Tetric Evoceram Bulk Fill (TEC); G3- Tetric EvoFlow Bulk fill (TEF); G4- Filtek Bulk fill (FBU); and G5- Filtek Bulk fill Flowable (FBF). All groups were treated with Adper Single Bond Plus adhesive and light cured (Bluephase 20i). Each tooth was scanned three times using a μCT apparatus: after cavity preparation (empty scan); after cavity filling (uncured scan) and after light curing of the restorations (cured scan). The μCT images were imported into a three-dimensional rendering software, and volumetric polymerization shrinkage percentage was calculated (%) for each sample. In the same images, interfacial gaps in the pulpal floor were qualitatively evaluated. After μCT evaluation, the pulpal floor from each tooth was polished until a thin tooth structure was obtained and OCT images were obtained by scanning the pulpal portion. Gap formation was observed and qualitatively compared to the μCT images.ResultsVPS means ranged from 2.31 to 3.96% for the studied resin composites. The bulk fill materials, either high viscosity or flowable, were not statistically different from each other (p > 0.05). The conventional resin composite Z100 presented statistically higher VPS than both high viscosity bulk fill materials studied (p < 0.05), although it was statistically similar to the flowable bulk fill materials studied (p > 0.05). Both μCT and OCT methodologies enabled gap formation visualization, and images from both technologies could be associated. Gap formation was mostly observed for G1-Z100, G4-FBU, and G5-FBF. VPS% and pulpal gap formation could not be completely associated with each other for all groups and samples. Voids were observed in most of the resin composite fillings, and most VPS were observed in the occlusal area of the samples.SignificanceVolumetric polymerization shrinkage was material-dependent, although bulk fill materials did not differ from each other. Both μCT and OCT enabled interfacial pulpal gap formation visualization. VPS and gap formation cannot be completely associated with one another.     

Water sorption and solubility of core build-up materials

ObjectivesTo investigate the variation in water sorption and solubility across a range of different core build-up materials.MethodsFive materials were tested, four of which are resin-based materials (Grandio Core, Core.X Flow, Bright Flow Core, Speedee) and one resin-modified glass ionomer (Fuji II LC). All specimens (n = 10) were immersed in 10 ml distilled water in individual glass containers and weighed at one week, 14 and 28 days. After a total immersion time of 28 days, 7 specimens were dried to a constant mass, in a desiccator for 28 days. Three samples of each material were not dried, but were left in distilled water for 1 year, to determine the long-term water sorption properties. Specimens were weighed at monthly intervals until 6 months and then at the 9th and 12th months. Each specimen was measured using a digital electronic caliper (Mitutoyo Corporation, Japan).ResultsAfter 28 days immersion, the change in water sorption and solubility of the materials ranged from 12.9 to 67.1 μg/mm³ (P < 0.001) and 0.9–6.4 μg/mm³ respectively (P < 0.001). Except for Fuji II LC, an independent T-test showed significantly higher water sorption and solubility for the other materials after 1-year total immersion in water compared to 1 month (P < 0.05). Using repeated measures ANOVA, all materials showed mass changes over time (1 month) (P < 0.001).SignificanceGrandio Core had the lowest water sorption and solubility among the tested materials. According to the ISO 4049 standards, all the tested materials showed acceptable water sorption and solubility, apart from the water sorption behavior of Fuji II LC.     

Effects of residual ethanol on the rate and degree of conversion of five experimental resins

ObjectivesThis study examined the extent of ethanol retention in five comonomer blends of experimental methacrylate-based dental adhesives, containing (10, 20, or 30 wt.%) ethanol, after solvent evaporation, as well as observing the effect of residual ethanol and exposure duration on degree of conversion (DC). The null hypothesis that was tested was that residual, unevaporated ethanol has no effect on the rate or extent of DC of polymerized adhesive resins.MethodsA known mass of each mixture was placed in glass wells and evaporated for 60 s. The mass of the mixtures before and after evaporation was measured, allowing calculation of the gravimetric ethanol loss/retention.ResultsThe concentration of retained ethanol increased significantly with ethanol concentration (p < 0.01): 1.1–1.9 mole/L for 10% ethanol/90% comonomers, 2.2–3.5  mole/L for 20% ethanol, and 2.6–3.7 mole/L for 30% ethanol/70% comonomers. As ethanol is evaporated from solvated comonomer mixtures, the molar concentration of comonomers increases, reducing the vapor pressure of the remaining ethanol. Thus, the fractional loss of ethanol solvent decreases as the comonomer concentration increases. The DC of 10, 20, and 30 wt.% ethanol blends increased with ethanol concentration in four of the five experimental resins (p < 0.05), increasing by 30–45% when 10 or 20 wt.% ethanol was added to neat resins, regardless of exposure duration. Depending on the resin system, inclusion of 30% ethanol lowered DC at 20 s but increased DC after 40–60 s of light exposure.SignificanceSince 10 and 20 wt.% ethanol–resin blends increased the DC of solvated resins by 30–45% over neat resins, the test null hypothesis is rejected. Even with prolonged evaporation, 4–9% residual ethanol concentration can remain in 90/10 (wt./wt.) comonomer–ethanol mixtures. This is thought to be because comonomers lower the vapor pressure of ethanol. This amount of residual ethanol facilitates DC but lowers the rate of polymerization.     

Fabrication and characterization of remineralizing dental composites containing calcium type pre-reacted glass-ionomer (PRG-Ca) fillers

ObjectiveTo fabricate and characterize dental composites with calcium type pre-reacted glass-ionomer (PRG-Ca) fillers.MethodsPRG-Ca fillers were prepared by the reaction of calcium fluoroaluminosilicate glass with polyacrylic acid. Seven dental composites were produced from the same organic matrix (70/30 wt% Bis-GMA/TEGDMA), with partial replacement of barium borosilicate (BaBSi) fillers (60 wt%) by PRG-Ca fillers (wt%): E0 (0) – control, E1 (10), E2 (20), E3 (30), E4 (40), E5 (50) and E6 (60). Enamel remineralization was evaluated in caries-like enamel lesions induced by S. mutans biofilm using micro-CT. The following properties were characterized: degree of conversion (DC%), roughness (Ra), Knoop hardness (KHN), flexural strength (FS), flexural modulus (FM), water sorption (W_sp), water solubility (W_sl), and translucency (TP). Data were analyzed to one-way ANOVA and Tukey’s HSD test (α = 0.05).ResultsAll composites with PRG-Ca induced enamel remineralization. E0 and E1 presented similar and highest DC% than E2 = E3 = E4 = E5 = E6. Ra and KHN were not influenced by PRG-Ca fillers (p < 0.05). The higher the content of PRG-Ca, the lower FS, FM and TP (p < 0.05). W_sp increased linearly with the content of PRG-Ca fillers (p < 0.05). E6 presented the highest W_sl (p < 0.05), while the W_sl of the other composites were not different from each other (p > 0.05).SignificanceIncorporation of 10–40 wt.% of PRG-Ca fillers endowed remineralizing potential to dental composites without jeopardizing the overall behavior of their physicochemical properties. Dental composites with PRG-Ca fillers seems to be a good alternative for reinforcing the enamel against caries development.     

Preparation and characterization of Bis-GMA-free dental composites with dimethacrylate monomer derived from 9,9-Bis[4-(2-hydroxyethoxy)phenyl]fluorene

Objective

Synthesize a new BPA-free monomer for use in methacrylate-based materials and evaluate critical properties of resin and composite materials based on the monomer.

The mechanical properties of nanofilled resin-based composites: The impact of dry and wet cyclic pre-loading on bi-axial flexure strength

ObjectivesTo determine the influence of nano-sized filler particles and agglomerates of nanoparticles (‘nanoclusters’) in resin-based composite (RBC) materials on the bi-axial flexure strength (BFS) following cyclic pre-loading and storage in a ‘dry’ or ‘wet’ environment.MethodSeven commercially available RBC restoratives, Heliomolar (Ivoclar Vivadent, Schaan, Liechtenstein), Z100 MP Restorative, Filtek? Z250, Filtek? Supreme (3M ESPE, St. Paul, MN, USA) in Body (FSB) and Translucent (FST) shades, Grandio and Grandio Flow (VOCO, Cuxhaven, Germany), containing differing filler particle types and morphologies were investigated. Specimens were pre-loaded at 20, 50 or 100 N for 2000 cycles and stored in a ‘dry’ or ‘wet’ environment prior to BFS testing.ResultsA general linear model analysis of variance highlighted a reduction in the BFS following pre-loading, however, individual RBC materials responded differently. The RBCs containing agglomerated nano-sized particles or ‘nanoclusters’ (Filtek? Supreme) demonstrated distinctive and unique patterns of response to pre-loading. Cyclic pre-loading at 20 and 50 N significantly increased the Weibull modulus of both FSB (8.53 ± 1.91 and 10.23 ± 2.29) and FST (16.89 ± 3.78 and 10.91 ± 2.45) compared with FSB and FST control (no pre-cyclic load) specimens (5.98 ± 1.34 and 7.99 ± 1.78, respectively). BFS of FSB and FST was maintained or significantly increased compared with the other materials following 20 and 50 N cyclic pre-load (P < 0.05).SignificanceThe ‘nanoclusters’ provided a distinct reinforcing mechanism compared with the microhybrid, microfill or nanohybrid RBC systems resulting in significant improvements to the strength and reliability, irrespective of the environmental storage and testing conditions. Silane infiltration within interstices of the nanoclusters may modify the response to pre-loading induced stress, thereby enhancing damage tolerance and providing the potential for improved clinical performance.     

Detection of Bisphenol A in dental wastewater after grinding of dental resin composites

ObjectivesThis study evaluated the release of bisphenol A (BPA) in wastewater after grinding of resin composites and tested three filtration materials.MethodsThree resin composites (Ceram X, Filtek Supreme XTE and Core-X flow) were used. Samples (5 mm × 2 mm, n = 10) were prepared using a metal mold and were polymerized for 20 s according to manufacturers’ instructions. A dental unit was disconnected from wastewater circulation and composite samples were ground under standardized procedures (200,000 rpm; 90 s). Wastewater was collected in glass bottles. Water samples were collected as control by performing the same procedure without grinding resin composite. All samples were stored at 7 °C for 6 months to simulate storage. Then they were analyzed by HPLC–FLD. Three filtration materials (Zeosorb, Katalox Light and Catalytic Carbon) were used for water treatment to remove BPA. BPA-water solutions were prepared; corresponding to the highest amount released by the resin composites. These solutions were analyzed before and after filtration by HPLC–FLD and their efficacy (%) was calculated.ResultsBPA was detected in all composite solutions: Ceram X and Filtek Supreme XTE showed similar findings (p > 0.05) which were significantly higher than the control (p < 0.001) and Core-X flow (p = 0.001). The efficacy of the filtration materials was: Katalox Light (5.09%) < Zeosorb (7.91%) < Catalytic Carbon (99.38%). Only Catalytic Carbon caused a clinically significant reduction of BPA (p < 0.05).SignificanceBPA can be released in wastewater during dental procedures. This release seems to be material dependent. Among the filtration methods tested, Catalytic carbon seems to be effective for BPA reduction in water.     

Effects of ethanol addition on the water sorption/solubility and percent conversion of comonomers in model dental adhesives

ObjectivesThis study evaluated the kinetics of water uptake and percent conversion in neat versus ethanol-solvated resins that were formulated to be used as dental bonding agents.MethodsFive methacrylate-based resins of known and increasing hydrophilicities (R1, R2, R3, R4 and R5) were used as reference materials. Resins were evaluated as neat bonding agents (100% resin) or they were solvated with absolute ethanol (95% resin/5% ethanol or 85% resin/15% ethanol). Specimens were prepared by dispensing the uncured resin into a circular mold (5.8 mm × 0.8 mm). Photo-activation was performed for 80 s. The water sorption/diffusion/solubility was gravimetrically evaluated, while the degree of conversion (DC) was calculated by Fourier-transform infrared spectroscopy.ResultsWater sorption increased with the hydrophilicity of the resin blends. In general, the solvated resins exhibited significantly higher water sorption, solubility and water diffusion coefficients when compared to their corresponding neat versions (p < 0.05). The only exception was resin R1, the least hydrophilic resin, in which neat and solvated versions exhibited similar water sorption (p > 0.05). Addition of ethanol increased the DC of all resins tested, especially of the least hydrophilic, R1 and R2 (p < 0.05). Despite the increased DC of ethanol–solvated methacrylate-based resins, it occurs at the expense of an increase in their water sorption/diffusion and solubility values.SignificanceNegative effects of residual ethanol on water sorption/solubility appeared to be greater as the hydrophilicity of the resin blends increased. That is, the use of less hydrophilic resins in dental adhesives may create more reliable and durable bonds to dentin.     

Color stability of siloranes versus methacrylate-based composites after immersion in staining solutions

Objectives

The purpose of this study was to determine, by using a spectrophotometer device, the color stability of silorane in comparison with four methacrylate-based composites after being immersed in different staining solutions such as coffee, black tea, red wine, orange juice, and coke, and distilled water as control group.

Methods

Four restorative methacrylate-based composites (Filtek Z250, TetricEvoCeram, Venus Diamond, and Grandio) and one silorane (FiltekSilorane) of shade A2 were selected to measure their color stability (180 disk samples) after 4 weeks of immersion in six staining solutions: black tea, coffee, red wine, orange juice, coke, and distilled water. The specimen's color was measured each week by means of a spectrophotometer (CIE L*a*b* system). Statistical analysis was carried out performing an ANOVA and LSD Test in order to statistically analyze differences in L*a*b*and ?E values.

Results

All materials showed significant discoloration (p?<?0.05) when compared to the control group (immersed in distilled water). The Highest ?E observed was with red wine, whereas coke led to the lowest one. Silorane showed the highest color stability compared with methacrylate-based composites.

Conclusions

Methacrylate-based materials immersed in staining solutions showed lower color stability when compared with silorane. Great differences in ?E were found among the methacrylate-based materials tested.

Clinical relevance

Although color stability of methacrylate-based composites immersed in staining solutions has been widely investigated, this has not been done for long immersion periods with silorane-based composites.