Pre-heating time and exposure duration: Effects on post-irradiation properties of a thermo-viscous resin-composite

ObjectiveTo evaluate the effects of pre-heating time and exposure duration on the degree of conversion (DC), maximum rate of polymerization (RP_max), polymerization shrinkage strain (PS) and surface micro-hardness (VHN) of Viscalor.MethodsViscalor syringes were pre-heated using a Caps Warmer (VOCO, Germany) in T3 mode (at 68 °C) for 30 s (T3-30s) and 3 min (T3-3min) and then the composite paste was extruded into appropriately sized molds. Light irradiation was applied at zero distance from the upper surface with a LED-LCU of mean irradiance 1200 mW/cm² for either 20 or 40 s. The real-time polymerization kinetics and DC at 5 min and 24 h post-irradiation (DC_5min and DC_24h) were measured using ATR-FTIR (n = 3). PS was obtained with the bonded-disk technique (n = 3). Top and bottom Vickers micro-hardness (VHN_top and VHN_bottom) were measured at 5 min post-irradiation and after 24 h dry storage (n = 5). Data were analysed using one-way ANOVA, two-way ANOVA, independent t-test and Tukey post hoc tests (p < 0.05).ResultsPolymerization kinetic curves of Viscalor from 0 to 15 min were similar for different pre-heating times and exposure durations. Pre-heated Viscalor (T3-30s and T3-3min) with 40 s exposure had greater VHN_top and VHN_bottom than for Viscalor (no heat) (p < 0.05). Exposure duration did not significantly affect DC, RP_max and PS (p > 0.05). After 24 h storage, DC and VHN increased. Pre-heating did not increase the DC_24h, relative to no pre-heating (p > 0.05). Two-way ANOVA showed that there was no significant interaction between pre-heating time and exposure duration (p > 0.05).SignificanceIncreasing irradiation time from 20 to 40 s did not affect DC, RP_max or PS, but increased VHN_top. Composite pre-heating had no adverse effect through any premature polymerization. For Viscalor, 3 min pre-heating and 20 s irradiation were sufficient to provide adequate hardness, without increasing PS or compromising polymerization kinetics.     

Pre-heating effects on extrusion force,stickiness and packability of resin-based composite

ObjectivesTo measure temperature effects on stickiness and packability of representative resin-based composites and the effect of pre-heating time on pre-cure properties of Viscalor, including extrusion force.MethodsFive resin-based composites (RBC) and an additional RBC, Viscalor, used with a Caps Warmer (VOCO, Germany) were studied. The extrusion force (N) and extruded mass (g) were measured from Viscalor compules heated in T3 mode for 30 s (T3-30 s) and 3 min (T3-3 min). For stickiness and packability measurements, RBCs were packed into a brass cylindrical cavity controlled at 22 and 37 °C. A flat-ended probe was lowered into the RBC pastes at constant speed. Stickiness: F_max (N) and W_s (N mm), and packability: F_p (N), were measured. Viscalor was LED photo-cured at 1200 mW/cm² for 40 s. The degrees of conversion at 5 min and 24 h post cure (DC_5min and DC_24h) of Viscalor (no heat, T3-30 s and T3-3 min) were measured by ATR-FTIR. Data were analysed by one-way ANOVA, independent t-test and Tukey post-hoc tests (p < 0.05).ResultsThe maximum temperature of the Caps Warmer, in T3 mode, reached 68 °C in 20 min. Viscalor temperatures of 34.5 °C and 60.6 °C were recorded after 30 s and 3 min pre-heating, respectively. Pre-heating significantly reduced extrusion force and increased extruded mass, especially after 3 min. RBCs varied in F_max, W_s and F_p (p < 0.05). Temperature also affected F_max (p = 0.000), W_s (p = 0.002) and F_p (p = 0.000). Pre-heating Viscalor for either 30 s or 3 min did not increase the post-cure DC at either 5 min or 24 h, relative to no pre-heating (p > 0.05).SignificanceThe composites varied to an extent in stickiness and packability but the overall magnitudes remained within a clinically acceptable range. Pre-heating was beneficial in placement of Viscalor and caused no adverse effects through premature polymerization.     

Viscosity and stickiness of dental resin composites at elevated temperatures

ObjectiveTo investigate the influence of pre-heating different classes of dental resin composites on viscosity and stickiness at five different temperatures.MethodsSix flowable, five conventional packable, and one thermo-viscous bulk-fill resin composites were heated up to 54 °C in a plate-plate rheometer to determine their complex viscosity. Normal force measurements were carried out for the six packable materials to determine the unplugging force and unplugging work (stickiness) over the same temperature range. Data were analyzed using Kolmogorov–Smirnoff test, one-way ANOVA and Tukey Post Hoc test with α = 0.05 as level of significance.ResultsAt 23 °C packable composites showed viscosity between 6.75 and 19.14 kPa s, while flowable composites presented significantly lower viscosities between 1.31 and 2.20 kPa s. Pre-heating led to a drop of 30–82% in the viscosity of packable materials. The thermo-viscous material dropped to the level of flowables at 45 and 54 °C thus behaving as a packable composite at room temperature with flowable-like viscosity at higher temperatures. No statistically significant differences for viscosity were observed among flowable composites at any temperature.The unplugging force decreased for packable composites, while their unplugging work generally increased at elevated temperature. At 23 °C unplugging force was measured between 7.50 and 19.18 N, while pre-heating up to 54 °C led to values between 2.9 and 6.2 N. Regarding unplugging work at 23 °C the calculated values were between 3.0 and 8.9 × 10^?3 J and at 54 °C between 8.8 and 13.0 × 10^?3 J.SignificancePre-heating significantly reduced viscosity of highly viscous resin composites, while no influence was shown for flowable composites. In general stickiness, measured as unplugging work, increased at elevated temperatures. The thermo-viscous material showed low viscosity comparable to flowable composites at 45 and 54 °C, yet its stickiness did not increase significantly compared to the values at 23 °C.     

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.     

Release of monomers from different core build-up materials

ObjectiveThe aim of the present study was to evaluate and compare the elution of monomers from three different core build-up composite materials and correlate it with the degree of conversion.MethodsThree different core build-up composite materials (a chemically cured, a photo-cured, and a dual-cured) were tested. Ten samples (diameter: 4.5 mm and thickness: 2 mm) of each material were fabricated to evaluate the release of monomers. The photo-cured samples were polymerized for 40 s and the dual-cured samples for 20 s. The samples remained undisturbed for 10 min and then were stored in 1 ml of 75% ethanol at room temperature, and the storage medium was renewed after 24 h, 7 and 28 days. From the storage medium that was removed, samples were prepared and analyzed by LC–MS/MS. Additionally, four samples of each material were tested for the degree of conversion by using a FT-IR spectrometer.ResultsThe three composite materials differed significantly concerning the elution of monomers (BisGMA: p < 0.0001; TEGDMA: p < 0.0001; and Bisphenol A: p < 0.0001). A significantly higher amount of BisGMA and TEGDMA was released from the chemically cured composite compared to the other two materials. Between the photo-cured and the dual-cured material the latter eluted significantly higher amounts of BisGMA and TEGDMA. During the storage of the samples, the amounts of the eluted substances decreased. The degree of conversion of the chemically cured composite was significantly lower compared to the other two materials.SignificanceUsing the present parameters, the photo-cured material released less monomer and therefore they might be less dangerous with respect to toxicological effects.     

Shear bond strength vs interfacial fracture toughness — Adherence to CAD/CAM blocks

ObjectiveTo compare shear bond strength (SBS) and interfacial fracture toughness (IK_IC) results when assessing the effect of surface roughness and thermocycling on the adherence of a resin composite luting agent (RCLA) to a CAD/CAM resin composite block (RCB).MethodsTetric CAD HT along with the recommended bonding system, Adhese Universal and Variolink Esthetic LC, were used. Surface roughness was achieved with 600/320/60 grit SiC papers. Samples were stored 24 h in 37 °C water or thermocycled 10000× (5 °C–55 °C) prior to testing. Results were analyzed by univariate ANOVA and Scheffé modified t-tests (α = 0.05). Fractured specimens were viewed with a stereo microscope and selected specimens with a scanning electron microscope.ResultsSBS results showed a significant difference between the 60 grit group and the other groups, both after 24 h and thermocycling. A large number of SBS samples showed cohesive fracture or subsurface damage in RCB. Thermocycling led to a significant decrease in SBS in all groups. IK_IC results showed no significant differences due to surface preparation after 24 h storage in 37 °C. After thermocycling, there was a significant difference between the 60 and the 600 grit groups. All K_IC samples fractured adhesively at the RCB surface. K_IC of the RCLA was significantly higher than IK_IC of all groups.SignificanceThe results endorse the use of fracture mechanics methodology for the assessment and characterization of adherence, while identifying difficulties in its implementation. The results suggest also that adherence to CAD/CAM RCB may be limited by the strength of the resin composite block — adhesive interface.     

Post-curing in dental resin-based composites

Objective

To determine the post-curing in six commercial contemporary resin-based composites (RBCs) using axial shrinkage, the degree of conversion, and Vickers hardness.

Spatial and cure-time distribution of dynamic-mechanical properties of a dimethacrylate nano-composite

ObjectiveThe purpose of this study was to evaluate a nano-filled dental composite, with varying cure irradiation-time, in terms of the spatial distribution of dynamic-mechanical properties determined at nanometre scale and the resultant distinction between filler, matrix and inter-phase regions.Materials and methodsSpecimen groups (n = 5) of the composite Filtek Supreme XT were cured in 2 mm deep molds for 5, 10, 20 and 40 s, and stored for 24 h in distilled water at 37 °C. Properties were measured at 2 mm depth, on the lower specimen surfaces. Nano-dynamic-mechanical parameters (complex, storage and loss modulus, tan δ) were determined at an array of 65,000 locations in a 5 μm × 5 μm area. Micro-mechanical properties (hardness, modulus of elasticity, creep and elastic/plastic deformation) were also measured and additionally the real-time degree of cure, by ATR-FTIR, for 10 min after photo-initiation and after storage.ResultsThe spatial distribution of nano-dynamic-mechanical properties varied significantly enabling four distinguishable matrix, filler-cluster and inter-phase regions to be identified. Proceeding from matrix to filler-cluster locations, complex-moduli increased linearly and loss-factors decreased linearly, consistent with visco-elastic composite theory. Curing time strongly affected all measured properties at 2 mm depth. The organic matrix was shown to be inhomogeneous for all curing times. By increasing cure-time, the proportion of less well polymerized area decreased from 37.7 to 1.1%, resulting in a more homogeneous organic matrix.SignificanceThe experimentally observed graduated transition, in complex modulus and related dynamic-mechanical properties, across the matrix – inter-phases – filler-cluster regions is conducive to low internal stresses, in contrast to the abrupt modulus transitions anticipated or observed in many other particulate composite structures. The identification of these phase-regions provides a realistic basis for accurate nano- and micro-mechanical computational modelling.     

Vertical and horizontal polymerization shrinkage in composite restorations

ObjectivePolymerization shrinkage developed in vertical and horizontal directions after light activation of light-curing composite restorative materials. The purpose of this study was to examine the effects of vertical and horizontal polymerization shrinkage on: (a) dimensional changes of resin composites in tooth cavities; (b) shear bond strengths to enamel and dentin; and (c) marginal gap width in a non-reacting Teflon mold.MethodsVertical and horizontal polymerization shrinkage in tooth cavities were measured immediately (3 min) after light activation. With the same time lapse, shear bond strengths to enamel and dentin and marginal gap widths in Teflon mold were also measured.ResultsThere was a significant correlation between vertical and horizontal polymerization shrinkage (r = 0.647, p = 0.043) in the tooth cavity. Composite materials which produced small vertical shrinkage also produced smaller horizontal shrinkage. Composite materials which produced small vertical shrinkage in the tooth cavity exhibited greater shear bond strengths to both enamel (r = −0.697, p = 0.025) and dentin (r = −0.752, p = 0.012). Composite materials which produced smaller horizontal shrinkage produced smaller marginal gap widths in the Teflon mold (r = 0.829, p = 0.003). No relationships were observed between horizontal shrinkage in the tooth cavity and shear bond strengths to both enamel and dentin (p > 0.05).SignificanceDuring the early stage of setting (<3 min) in tooth cavities, the vertical shrinkage of light-activated composite restorative materials was correlated with horizontal shrinkage.     

Mechanical stability of adhesives under water storage

ObjectivesTo evaluate the effects of storage condition (wet or dry) and storage time (24 h and 3 months) on the ultimate tensile strength (UTS) of Single Bond (SB), 3M-ESPE; Opti Bond Solo Plus (OB), Kerr; One Step (OS), Bisco, and Prime & Bond NT (PB), Dentsply adhesive resins.MethodsHourglass-shaped specimens were obtained from a metallic matrix. Each adhesive was dispensed to fill the molds completely and left undisturbed in a dark chamber for 4 min at 37 °C for solvent evaporation. They were individually light-cured for 80 s at 500 mW/cm² and randomly divided into three groups: 24 h of water storage; 3 months of water storage; 3 months of dry storage. The specimens were tested in tension at 0.5 mm/min using the microtensile method and data were analyzed by two-way ANOVA and SNK tests for each material.ResultsWater storage for 3 months did not cause significant changes in the UTS of any of the adhesives (p-value). Values for water storage ranged from 25.9 MPa for Single Bond at 24 h to 32.7 MPa for Prime & Bond NT after 3 months. Dry storage for 3 months yielded significantly higher UTS for most adhesives, which ranged from approximately 20% for Opti Bond to 160% higher values for Single Bond compared to their 3 months wet storage values.ConclusionThe effects of storage condition and time on the UTS of adhesives were material-dependent.     

Response of composite resins to preheating and the resulting strengthening of luted feldspar ceramic

ObjectiveThis study evaluated the influence of preheating different composite resins on their viscosity and strengthening yielded to ceramic.MethodsModulus of elasticity, Poisson’s ratio, and degree of CC conversion were measured for three restorative composite resins (Z100–microhybrid; Empress Direct–nanohybrid; Estelite Omega–supranano) and one photoactivated resin cement (RelyX Veneer). Viscosity was measured during a heating-cooling curve (25 °C–69 °C–25 °C) and also using isothermal analyses at 25 °C and 69 °C. Feldspar ceramic disks simulating veneers were bonded with the luting materials. Biaxial flexural strength, characteristic strength, and Weibull modulus were calculated at axial positions (z = 0 and z = −t₂) of the bilayers. Film thickness was measured and morphology at the bonded interfaces was observed. Data were statistically analyzed (α = 0.05).ResultsA gradual decrease in viscosity was noticed as the rheometer temperature gradually increased. Viscosity differences between the composite resins were large at the beginning of the analysis, but minor at 69 °C. At 25 °C, the composites were up to 38 times more viscous than the resin cement; at 69 °C the difference was 5-fold. CC conversion was similar between all resin-based agents. The resin cement yielded lower film thickness than the composites. All resin-based agents were able to infiltrate the ceramic porosities at the interface and strengthen the ceramic. However, the magnitude of the strengthening effect was higher for the preheated composite resins, particularly at z = −t₂.SignificanceSelection of composite resin impacts its response to preheating and the resulting viscosity, film thickness, and magnitude of ceramic strengthening.     

Mechanical and physical properties of silorane and methacrylate-based composites

ObjectivesThis study measured the degree of conversion (DC), sorption, solubility and microhardness of methacrylate (Filtek Z250 and Filtek Z350XT) and silorane-based composites (Filtek P90).MethodsDC was measured using near infrared spectroscopy immediately and 24 h after the photoactivation. Sorption and solubility measurements were performed after 24 h, 4 weeks and 12 weeks of storage in water. Knoop microhardness was measured after 24 h and after thermal cycling. The data were statistically analyzed using ANOVA followed by Tukey's, Tamhane or paired t-tests (α = 0.05).ResultsThe DC for P90 (37.22 ± 1.46) was significantly lower than the Z250 (71.44 ± 1.66) and Z350 (71.76 ± 2.84). Water sorption was highest in the Z250 and lowest in the P90. All the tested composites exhibited similar values after 24 h of immersion, and no significant differences were observed. No significant differences were observed between the solubilities of the P90 composite (12 weeks) and the Z250 or Z350 composites (4 weeks). KHN values were less elevated for the P90 composite and similar for the Z250 and Z350 composites. An effect of thermal cycling on KHN values was observed for all the composites (p < 0.001).ConclusionsSilorane produced the lowest DC and KHN values and exhibited lower water sorption and solubility compared to methacrylate-based composites. These differences suggest that silorane composites exhibit better hydrolytic stability after 3 months of water immersion compared to conventional methacrylate-based composites.Clinical significanceSilorane had higher hydrolytic stability after 3 months of water immersion than the methacrylate-based resins, despite the lower values of DC and KHN recorded.     

The effect of temperature and ionic solutes on the fluoride release and recharge of glass-ionomer cements

ObjectiveTo determine the effect of storage temperature and the presence of sodium chloride in solution on the fluoride uptake and release of glass-ionomer cements.MethodsSeveral commercial brands were used, and stored at either room temperature (21–23 °C) or 37 °C, in KF solution at a concentration of 1000 ppm F⁻ with and without 0.9% NaCl present. Fluoride levels in the storage solutions after 24 h were measured using a fluoride-ion selective electrode. Specimens were then stored in water, and fluoride release after 24 h was determined. Studies were also carried out to determine chloride levels when specimens were stored in 0.9% NaCl, with or without 1000 ppm fluoride, again using an ion selective electrode.ResultsAll glass-ionomer specimens took up fluoride, and most of the fluoride was retained over the next 24 h when the specimens were stored in water. There was a slight variation in the amount of fluoride taken up with storage temperature and with the presence of sodium chloride. All specimens also took up chloride, with greater uptake at higher temperatures, but little or no effect when KF was also present in solution.SignificanceThe substantial retention of fluoride after 24 h in deionised water confirms previous findings and suggests that an insoluble species, possibly SrF₂, forms in situ. Chloride uptake has not been reported previously, and its significance requires further investigation. Fluoride and chloride uptake were apparently independent of each other, which suggests that the ions are taken up at different sites in the cement. This may relate to differences in the respective sizes and hydration states of F⁻ and Cl⁻ ions.     

Fluoride-containing adhesive: Durability on dentin bonding

ObjectivesTo evaluate (1) the influence of fluoride-containing adhesive on microtensile bond strength (μTBS) and (2) in vitro secondary caries inhibition at the resin–dentin interface after 24 h and 3 months water-storage and (3) the degree of conversion of different adhesives after 24 h 1 month.MethodsFlat surfaces of human teeth were ground and randomly assigned to six groups: (SBMP-24) Scotchbond Multi-Purpose control [SBMP], 24 h; (SE-24) SBMP etch and primer + Clearfil SE Bond adhesive [SE], 24 h; (PB-24) SBMP etch and primer + Clearfil Protect Bond adhesive [PB], 24 h; (SBMP-3) SBMP, 3 months; (SE-3) SBMP + SE, 3 months; and (PB-3) SBMP + PB, 3 months. To evaluate the effect of the adhesive resin alone, all teeth were etched with 35% phosphoric acid and primed with SBMP primer prior to applying the adhesive resin. Bonded assemblies were prepared for μTBS and stored in distilled water at 37 °C for 24 h and 3 months. Sections of restored teeth of each group were exposed to an acid challenge. The specimens were sectioned, polished, and then observed with polarized light microscopy (PLM). Also, the degree of conversion (DC) of the adhesives was measured using Fourier Transform-Infrared spectroscopy (FTIR) at 24 h and 1 month, after polymerization.ResultsμTBS values obtained in MPa (24 h/3 m) were: (MP) 61.5 ± 10.5/52.9 ± 8.9, (SE) 55.5 ± 11.8/55.6 ± 13, and (PB) 50.3 ± 9.9/61.0 ± 13.6. For interface analysis by PLM, an inhibition zone (IZ) adjacent to the hybrid layer was created only when the fluoride-containing adhesive (PB) was used. The DC in percentage (24 h, 1 month) were: (MP) 60.5 ± 2.8/61.3 ± 0.6, (SE) 69.6 ± 1.3/70.7 ± 0.05, and (PB) 53.1 ± 0.4/58.3 ± 1.6.SignificanceThe fluoride-containing adhesive demonstrated significant increase of bond strength values after water-storage. This material was also able to create an acid inhibition zone in dentin. There was a significant increase of degree of conversion after 1 month only for PB.     

Polymerization shrinkage kinetics and degree of conversion of commercial and experimental resin modified glass ionomer luting cements (RMGICs)

ObjectivesTetrahydrofurfuryl-methacrylate (THFM) and hydroxypropyl-methacrylate (HPM) were used to partially or fully replace HEMA in experimental RMGICs. The experimental materials were compared with home and commercial products in terms of degree of conversion, polymerization shrinkage and exotherm.MethodsTwo commercial RMGICs used were Fuji-Plus (FP, GC, Japan) and RelyX-Luting (RX, 3M-ESPE, USA). Two additional in-house liquids were prepared based on the commercial materials liquids. Eight experimental liquid compositions (F1, F2, F3 and F4 based on Fuji-Plus; R1, R2, R3 and R4 based on RelyX-Luting) were prepared replacing 100% HEMA with HPM in F1 and R1 or 70%/30% HPM/THFM in F2 and R2. 50% HEMA was replaced with THFM in F3 and R3 compared to 30% in F4 and R4. All liquids were mixed with the corresponding commercial powder. Degree of conversion was determined using Fourier-transform infrared spectroscopy (FT-IR). Polymerization shrinkage and exotherm were measured using the bonded-disk method.ResultsCompositions containing HPM (F1 and R1) showed lower degree of conversion compared to experimental compositions containing THFM, home and commercial materials (p < 0.0001). FP-commercial showed significantly higher polymerization shrinkage and exotherm compared to all other materials in both groups (p < 0.0001). FP-commercial showed higher degree of polymerization shrinkage and exotherm at 5 min compared to all materials due to the incorporation of an additional cross-linker (glycerol-dimethacrylate). In general, compositions containing THFM, presented polymerization shrinkage and degree of conversion values similar to their corresponding commercial products.SignificanceTHFM monomer showed promising results and could be potentially useful in the development of new RMGICs with improved properties.     

Microtensile bond strength of resin-based composites to Ti–6Al–4V

ObjectiveThe purpose of this study was to determine the microtensile bond strength of various resin composite/adhesive systems to alumina particle abraded Ti–6Al–4V substrate after aging for 24 h, 10 days, and 30 days in distilled water at 37 °C.MethodsFour laboratory resin composite veneering systems (Gradia, GR; Solidex, SOL; Ceramage, CER; and Sinfony, SF) were bonded to 25 mm diameter machined disks of Ti–6Al–4V with their respective adhesive and methodology, according to the manufacturer's instructions. Microtensile bars of approximate dimensions 1 mm × 1 mm × 6 mm were prepared for each resin composite/adhesive system. After cutting, groups (n = 12) from each adhesive system were separated and either stored in water at 37 °C for 24 h (baseline) or aged for 10 or 30 days prior to loading to failure under tension at a cross head speed of 1.0 mm/min. Failure modes were determined by means of scanning electron microscopy (SEM). Statistical analysis was performed through one-way ANOVA and Tukey's test at 95% level of significance.ResultsSignificant variation in microtensile bond strength was observed for the different systems and aging times. SOL and GR showed the highest mean bond strength values followed by SF and CER at baseline. Aging specimens in water had an adverse effect on bond strength for SOL and CER but not for the SF and GR groups.SignificanceIn vitro bond strength of laboratory resin composites to Ti–6Al–4V suggests that strong bonds can be achieved and are stable for certain systems, making them useful as an alternative for esthetic fixed prosthetic restorations.     

Curing potential and color stability of different resin-based luting materials

PurposeTo determine the curing potential and color stability of resin-based luting materials for aesthetic restorations.Material and MethodsFour resin-based luting agents were tested: traditional dual-activated resin cement (RelyX ARC, ARC), amine-free dual-activated resin cement (RelyX Ultimate, ULT), light-activated resin cement (RelyX Veneer, VEN), and pre-heated restorative resin composite (Filtek Supreme, PHC). Degree of C = C conversion was determined by infrared spectroscopy (n = 3) with direct light exposure or with interposition of 1.5-mm-thick ceramic (e.max Press HT) between the luting material and light. The curing potential considered the ratio between these two scenarios. Color difference (n = 6) was determined by CIELAB (ΔE_ab) and CIEDE2000 (ΔE₀₀) methods, by spectrophotometer measurements made 24 h after photoactivation and 90 days after storage in water. Data was submitted to ANOVA and Tukey’s test (α = 0.05).ResultsThe luting agents affected both conversion and color stability. With ceramic, ARC produced the highest conversion among the tested groups (75 ± 1%) and the pre-heated composite (PHC) the lowest one (51 ± 3%), but the curing potential was similar for all materials. ULT produced lower ΔE_ab than ARC. PHC presented the lowest color difference when considered both CIELAB and CIE2000 methods (ΔE_ab 2.1 ± 0.4; ΔE₀₀ 1.6 ± 0.2).SignificanceAll luting strategies presented high curing potential. Amine-free dual-activated material was able to reduce color difference than that formulated with the amine component. Pre-heated composite produced the least color variation after storage.     

Fracture toughness of cross-linked and non-cross-linked temporary crown and fixed partial denture materials

ObjectivesTemporary crowns and fixed partial dentures are exposed to considerable functional loading, which places severe demands on the biomaterials used for their fabrication (= temporary crown & bridge materials, t-c&b). As the longevity of biopolymers is influenced by the ability to withstand a crack propagation, the aim of this study was to investigate the fracture toughness of cross-linked and non-cross-linked t-c&bs.MethodsFour different t-c&bs (Luxatemp AM Plus, Protemp 3 Garant, Structur Premium, Trim) were used to fabricate bar shaped specimens (2 mm × 5 mm × 25 mm, ISO 13586). A notch (depth 2.47 mm) was placed in the center of the specimen using a diamond cutting disc and a sharp pre-crack was added using a razor blade. 60 specimens per material were subjected to different storage conditions (dry and water 37 °C: 30 min, 60 min, 4 h, 24 h, 168 h; thermocycling 5–55 °C: 168 h) prior to fracture (3-point bending setup). The fracture sites were inspected using SEM analysis. Data was subjected to parametric statistics (p = 0.05).ResultsThe K_IC values varied between 0.4 and 1.3 MPa m^0.5 depending on the material and storage time. Highest K_IC were observed for Protemp 3 Garant. Fracture toughness was significantly affected by thermocycling for all dimethacrylates (p < 0.05) except for Structur Premium. All dimethacrylates showed a linear-elastic fracture mechanism, whereas the monomethacrylate showed an elasto-plastic fracture mechanism.SignificanceDimethacrylates exhibit a low resistance against crack propagation immediately after curing. In contrast, monomethacrylates may compensate for crack propagation due to plastic deformation. However, K_IC is compromised with increasing storage time.     

Effect of water-bath post-polymerization on the mechanical properties,degree of conversion,and leaching of residual compounds of hard chairside reline resins

ObjectivesThis study evaluated the effect of water-bath post-polymerization at 55 °C for 10 min (WB) on the content and leaching of residual compounds, degree of conversion, flexural strength, and hardness of hard chairside reline resins (Kooliner: K, New Truliner: N, Ufi Gel hard: U, and Tokuso Rebase Fast: T).MethodsLeaching experiments were made by storing specimens (n = 48) in artificial saliva at 37 ± 1 °C and analyzing residual monomers and plasticizer by HPLC. Analysis of residual monomer and plasticizer content (n = 48) was also made by HPLC. Degree of conversion (n = 40) was analyzed by using FT-Raman spectroscopy. A 3-point loading test was used to evaluate the flexural strength of the specimens (n = 80). One fragment of each flexural test specimen was then submitted to Vickers microhardness test.ResultsWB produced a significant decrease (p < 0.050) in the amount of residual compounds eluted from the materials within the first hour of immersion. With the exception of material U, WB decreased the duration of release of the residual compounds evaluated. All materials evaluated exhibited significantly (p < 0.050) lower values of residual monomer and plasticizer (material N) after WB compared with the control groups. WB increased the degree of conversion of K and T resins and the hardness of N, K, and T resins (p < 0.050). Only material K showed an increase in flexural strength after WB (p < 0.050).SignificanceImmersion of relined dentures in water at 55 °C for 10 min can be used to reduce the amounts and duration of release of residual compounds and improve mechanical properties of some of the materials evaluated.     

Microhardness of resin cements in the intraradicular environment: Effects of water storage and softening treament

ObjectivesTo analyze the microhardness of four dual-cure resin cements used for cementing fiber-reinforced posts under the following conditions: after 7 days of storage in water, after additional 24 h of immersion in 75% ethanol, and after 3 months of storage in water. Hardness measurements were taken at the cervical, middle and apical thirds along the cement line.MethodsRoot canals of 40 bovine incisors were prepared for post space. Fibrekor^® glass fiber-reinforced posts (Jeneric/Pentron) of 1 mm in diameter were cemented using Panavia F 2.0 (Kuraray), Variolink (Ivoclar-Vivadent), Rely X Unicem (3M ESPE) or Duolink (Bisco) (N = 10). After 7 days of water storage at 37 °C, half the sample (N = 5) was longitudinally sectioned and the initial microhardness measured along the cement line from cervical to apex. These same samples were further immersed in 75% ethanol for 24 h and reassessed. The remaining half (N = 5) was kept unsectioned in deionized water at 37 °C for 3 months, followed by sectioning and measuring. Data were analyzed by a series of two-way ANOVA and Tukey tests at α = 5%.ResultsStatistically significant differences were identified among the cements, thirds and conditions. Significant interactions were also observed between cements and thirds and between cements and conditions. Panavia F exhibited significantly higher initial microhardness than the other three cements, which showed no statistical difference among themselves. Variolink and Duolink showed significantly higher microhardness values in the cervical third, without significant difference among the thirds for the other cements. Immersion in ethanol significantly reduced the hardness values for all cements, regardless of the thirds. Storage in water for 3 months had no influence on the hardness of most of the cements, with the exception of Unicem that showed a significant increase in the hardness values after this period.SignificanceResults showed heterogeneity in the microhardness of the cements inside the canal. All cements presented some degree of softening after ethanol treatment, which suggests instability of the polymer. The quality of curing of resin cements in the root canal environment seems unpredictable and highly material dependent.