Difference in opalescence of restorative materials by the illuminant

ObjectivesTo determine the differences in the opalescence parameter (OP) of indirect and direct resin composites, veneer ceramics and bovine enamel relative to the CIE standard illuminants D65, A and F2.MethodsBelleGlass NG (indirect resin; 10 shades) and Estelite Sigma (direct resin; 12 shades), and 4 shades of veneer ceramics were investigated. Bovine enamel was used as a reference. Reflected and transmitted colors of specimens were measured relative to the illuminants D65, A and F2 with a reflection spectrophotometer. OP values relative to the three illuminants [OP(D65), OP(A) and OP(F2)], difference in OP (ΔOP) and OP difference ratio relative to OP(D65) [ΔOP/OP(D65)] by the change of illuminants were calculated. Within each restorative material, ΔOP and ΔOP/OP(D65) values were analyzed with two-way analysis of variance (ANOVA), with the fixed factors of the shade designation and the combination of illuminants (α = 0.05).ResultsΔOP and ΔOP/OP(D65) values were influenced by the two factors within each restorative material based on two-way ANOVA. High opalescent materials showed higher ΔOP values. OP(D65) was lower than OP(F2) and OP(A) values. Restorative materials showed lower ΔOP/OP(D65) values than bovine enamel. Correlation coefficients between OP values relative to different illuminants were higher than 0.961 (P < 0.01).SignificanceDirect resin composites instead of ceramics or indirect resin composites should be recommended in clinical dentistry since they showed similar opalescence properties as compared with natural tooth enamel.     

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.     

Translucency thresholds for dental materials

Objective

To determine the translucency acceptability and perceptibility thresholds for dental resin composites using CIEDE2000 and CIELAB color difference formulas.

Influence of microcapsule parameters and initiator concentration on the self-healing capacity of resin-based dental composites

ObjectiveFracture is one of the main causes for failure of resin-based composite restorations. To overcome this drawback, self-healing resin-based composites have been designed by incorporation of microcapsules. However, the relationship between their self-healing capacity and microcapsule and resin parameters is still poorly understood. Therefore, the objective of this study was to systematically investigate the effect of initiator concentration (in the resin) and microcapsule size and concentration on the self-healing performance of commercially available flowable resin-based composites.MethodsPoly(urea-formaldehyde) (PUF) microcapsules containing acrylic healing liquid were synthesized in small (33 ± 8 μm), medium (68 ± 21 μm) and large sizes (198 ± 43 μm) and characterized. Subsequently, these microcapsules were incorporated into a conventional flowable resin-based composite (Majesty Flow ES2, Kuraray) at different contents (5–15 wt%) and benzoyl peroxide (BPO) initiator concentrations (0.5–2.0 wt%). Fracture toughness (K_IC) of test specimens was tested using a single edge V-notched beam method. Immediately after complete fracture (K_IC-initial), the two fractured parts were held together for 72 h to allow for healing. Subsequently, fracture toughness of the healed resin-based composites (K_IC-healed) was tested as well.ResultsThe fracture toughness of healed dental composites significantly increased with increasing microcapsule size and concentration (2 wt% BPO, p < 0.05). The highest self-healing efficiencies (up to 76%) were obtained with microcapsules sized 198 ± 43 um.Significancecommercially available resin-based composites can be rendered self-healing most efficiently by incorporation of large microcapsules (198 ± 43 μm). However, long-term tests on fatigue and wear behavior are needed to confirm the clinical efficacy.     

The addition of nanostructured hydroxyapatite to an experimental adhesive resin

ObjectivesWas produced nanostructured hydroxyapatite (HA_nano) and evaluated the influence of its incorporation in an adhesive resin.MethodsHA_nano was produced by a flame-based process and was characterized by scanning electron microscopy. The surface area, particle size, micro-Raman and cytotoxicity were evaluated. The organic phase was formulated by mixing 50 wt.% Bis-GMA, 25 wt.% TEGDMA, and 25 wt.% HEMA. HA_nano was added at seven different concentrations: 0; 0.5; 1; 2; 5; 10 and 20 wt.%. Adhesive resins with hydroxyapatite incorporation were evaluated for their radiopacity, degree of conversion, flexural strength, softening in solvent and microshear bond strength. The data were analyzed by one-way ANOVA and Tukey's post hoc test (α = 0.05), except for softening in solvent (paired t-test) and cytotoxicity (two-way ANOVA and Bonferroni).ResultsHA_nano presented 15.096 m²/g of specific surface area and a mean size of 26.7 nm. The radiopacity values were not different from those of 1-mm aluminium. The degree of conversion ranged from 52.2 to 63.8%. The incorporation of HA_nano did not influence the flexural strength, which ranged from 123.3 to 143.4 MPa. The percentage of reduction of the microhardness after immersion in the solvent became lower as the HA_nano concentration increased. The addition of 2% nanostructured hydroxyapatite resulted in a higher value of microshear bond strength than the control group (p < 0.05).ConclusionsThe incorporation of 2% of nanostructured hydroxyapatite into an adhesive resin presented the best results.Clinical significanceThe incorporation of nanostructured hydroxyapatite increases the adhesive properties and may be a promising filler for adhesive resin.     

Effects of ZnO/TiO2 nanoparticle and TiO2 nanotube additions to dense polycrystalline hydroxyapatite bioceramic from bovine bones

ObjectivesA bovine dense hydroxyapatite ceramic (HA) was produced as new biomaterial, however, the production of a material with consistently high flexural strength remains challenging. The objective of this study was to evaluate the effects of ZnO nanoparticles, TiO₂ nanoparticles, and TiO₂ nanotubes (1%, 2%, and 5% by weight) on the microstructure and flexural strength of a bovine dense hydroxyapatite ceramic (HA).MethodsDiscs (Ø = 12.5 mm; thickness = 1.3 mm) were prepared and subjected to X-ray diffraction (XRD), and observation with a field emission scanning electron microscope (FE-SEM), biaxial flexural strength (BFS) testing, and Vickers hardness (VH) testing. The BFS and VH data were subjected to ANOVA and Tukey post-hoc tests (α = 0.05) and Weibull analysis.ResultsThe XRD showed that the addition of nanomaterials caused the formation of a secondary phase when 5% of the ZnO nanoparticles was used, or when all percentages of the TiO₂ nanoparticles/nanotubes were used, and the HA crystallographic planes were maintained. Differences were not observed between the higher BFS values obtained with pure HA and those obtained with the 5% addition of TiO₂ nanoparticles. However, the results were different compared with the other groups (α = 0.05). The results obtained by Weibull analysis revealed that the 1%, 2%, and 5% addition of TiO₂ nanotubes, and the 1% and 2% addition of TiO₂ nanoparticles decreased the HA characteristic strength (σ₀), while the Weibull modulus (m) increased when 5% of TiO₂ nanoparticles, 1% and 2% of ZnO nanoparticles, and 2% of TiO₂ nanoparticles were added, but with no statistical difference from the pure HA. The 5% addition of ZnO₂ nanoparticles decreased the σ₀ without changing m. Moreover, the 5% addition of TiO₂ nanoparticles resulted in an m closest to that of pure HA. Regarding the VH results, the blend of HA with 1% and 2% addition of TiO₂ nanoparticles exhibited the higher values, which were similar between the different addition ratios (p = 0.102). Moreover, the addition of 5% TiO₂ nanoparticles resulted in higher value compared with pure HA.SignificanceThis study demonstrated that the HA blend with 5% of TiO₂ nanoparticles has the greatest potential as a bovine HA dense bioceramic reinforcement.     

Development of 3D printed resin reinforced with modified ZrO2 nanoparticles for long-term provisional dental restorations

ObjectiveTo characterize and investigate efficacy of loading functionalized ZrO₂ nanoparticles in 3-dimensional (3D) printed acrylate ester-based resin subjected to accelerated aging in artificial saliva. As well as to evaluate the effect of ZrO₂ nanoparticle volume fraction addition on mechanical and physical properties of printed composite.MethodsFunctionalized ZrO₂ nanoparticles were characterized using TEM and Raman spectroscopy. 3D printed dental resin was reinforced, with ZrO₂ nanoparticles, in the concentration range (0–5 wt.%). The resulted nanocomposites, in term of structure and physical/mechanical properties were evaluated using different mechanical testing, microscopic and spectroscopic techniques.ResultsZrO₂ based nanocomposite was successful and formed composites were more ductile. Degree of conversion was significant at the highest level with blank resin and 1 wt.%. Sorption revealed reduction associated with volume fraction significant to neat resin, however solubility indicated neat and 4 wt.% had the lowest significant dissolution. Vickers represented critical positive correlation with filler content, while nanohardness and elasticity behaved symmetrically and had the maximum strength at 3 wt.% addition. In addition, 3 wt.% showed the highest fracture toughness and modulus. Improvement of flexural strength was significantly linked to filler concentration. Overall properties dramatically were enhanced after 3 months aging in artificial saliva, especially degree of conversion, microhardness, nanoindentation/elasticity, and flexural modulus. However, significant reduction was observed with flexural modulus and fracture toughness.SignificanceThe outcomes suggest that the newly developed 3D printed nanocomposites modified with ZrO₂ nanoparticle have the superior potential and efficacy as long-term provisional dental restoration materials.     

The effect of TiO2 and SiO2 nanoparticles on flexural strength of poly (methyl methacrylate) acrylic resins

PurposeTiO₂ and SiO₂ nanoparticles are products of nanotechnology which have been incorporated to acrylic resins (AR) in order to induce antimicrobial properties. However, as additives they can affect the mechanical properties of the final product. The aim of this study was to survey the effects of TiO₂ and SiO₂ nanoparticles on flexural strength (Fs) of poly (methyl methacrylate) acrylic resins.MethodsAcrylic specimens (Selecta Plus) in size of 5 × 10 (±0.2) × 3.3 (±0.2) mm were prepared and divided into 7 groups: AR containing nanoTiO₂, SiO₂ and TiO₂ with SiO₂ in two concentration of 1% and 0.5%, in addition to a control group. To prepare nano AR, nanoparticles were added to the monomer. All specimens were stored in 37 °C distilled water and underwent Fs test by universal testing machine (Zwick).ResultsThe maximum mean flexural strength (43.5 MPa) belongs to the control group and AR containing 0.5% of both TiO₂ and SiO₂ demonstrated the minimum mean Fs (30.1 MPa). Resins contained TiO₂, demonstrated lower values of Fs than those contained SiO₂ with the same concentration, but the differences were not significant (P > 0.05).ConclusionIncorporation of TiO₂ and SiO₂ nanoparticles into acrylic resins can adversely affect the flexural strength of the final products, and this effect is directly correlated with the concentration of nanoparticles.     

Surface dissolution and transesterification of thermoset dimethacrylate polymer by dimethacrylate adhesive resin and organic catalyst-alcohol solution

ObjectivesTo evaluate transesterification based dissolution of dimethacrylate and epoxy polymers, the former containing ester groups. Polymer substrates were treated with an adhesive resin (Stick™ Resin) and an organic catalyst-alcohol solution (ethylene glycol and triazabicyclodecene). The surface was chemically and nanomechanically analyzed with Fourier Transform-Infrared (FTIR) spectroscopy, surface profile peak (R_p) and nanohardness and modulus of elasticity.MethodsA total of 100 specimens each of light-cured dimethacrylate polymer and heat-cured diepoxy polymer were prepared. 20 specimens were randomly selected and used as control group (0 s). The remaining specimens were randomly divided into 40 each for treatment with an Stick™ resin and ethylene glycol + triazabicyclodecene. Within each group the 40 specimens were randomly subdivided into 20 each for treatment at 5 min and 24 h, with 10 specimens for FTIR and nanohardness and modulus of elasticity, and the other 10 for SEM and surface R_p analyses.ResultsDimethacrylate polymer showed a reduction in the nanohardness and modulus of elasticity, R_p values and SEM also showed significant topographical changes after being treated with either Stick™ resin or ethylene glycol + triazabicyclodecene, whereas epoxy resin substrate did not. FTIR analyses affirmed changes in the intensity of ester groups.SignificanceEster group containing dimethacrylate polymer showed a reduction in NMP within 5 min of exposure to the treatment agents with softening by solution ethylene glycol + triazabicyclodecene associated to the reduction of ester groups in the polymer structure by transesterification. Epoxy polymer without ester groups was not affected by surface softening with treatment agents. Adhesive resin caused surface swelling.     

Influence of photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites

ObjectiveTo establish the relationship between photoinitiator system and nanofiller size on the optical properties and cure efficiency of model composites.MethodsModel composites based on BisGMA/TEGDMA (60:40 mol%) were loaded with 40 wt% of 7 nm or 16 nm-sized filler particles. One of the following photoinitiator systems was added: camphorquinone (CQ) associated with an amine (EDMAB), monoacylphosphine oxide (TPO), or bysacylphosphine oxide (BAPO). The optical properties of disk-shaped specimens were measured 24 h after curing and repeated after storage in water for 90 days and coffee for 15 days. A large spectrum LED unit (Bluephase G2, Ivoclar Vivadent) was used for photoactivation. CIE L*a*b* parameters, color difference (ΔE), and translucency parameter (TP) were calculated. Knoop hardness readings were taken at top and bottom composite surfaces. Cure efficiency was determined by bottom/top hardness ratio. Data were statistically analyzed at α = 0.05 significance level.ResultsComposites formulated with 16 nm particles had higher CIE L* than those with 7 nm particles in all storage conditions. BAPO-based composites generally had lower CIE a* than the other composites. The group TPO + 16 nm before storage and all groups with 16 nm-sized particles after storage had lower CIE b* (i.e. lower degree of yellowing) than the other groups. TPO-based materials had higher color stability. The cure efficiency was not significantly affected by photoinitiator system or particle size. CQ + 7 nm had the lowest and BAPO + 16 nm the highest hardness values.SignificanceCombination of photoinitiator system and filler particle size might affect the optical properties of composites, with low influence on cure efficiency.     

Improved mechanical performance of self-adhesive resin cement filled with hybrid nanofibers-embedded with niobium pentoxide

ObjectivesIn this study hybrid nanofibers embedded with niobium pentoxide (Nb₂O₅) were synthesized, incorporated in self-adhesive resin cement, and their influence on physical-properties was evaluated.MethodsPoly(D,L-lactide), PDLLA cotton-wool-like nanofibers with and without silica-based sol–gel precursors were formulated and spun into submicron fibers via solution blow spinning, a rapid fiber forming technology. The morphology, chemical composition and thermal properties of the spun fibers were characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC), respectively. Produced fibers were combined with a self-adhesive resin cement (RelyX U200, 3 M ESPE) in four formulations: (1) U200 resin cement (control); (2) U200 + 1 wt.% PDLLA fibers; (3) U200 + 1 wt.% Nb₂O₅-filled PDLLA composite fibers and (4) U200 + 1 wt.% Nb₂O₅/SiO₂-filled PDLLA inorganic–organic hybrid fibers. Physical properties were assessed in flexure by 3-point bending (n = 10), Knoop microhardness (n = 5) and degree of conversion (n = 3). Data were analyzed with One-way ANOVA and Tukey’s HSD (α = 5%).ResultsComposite fibers formed of PDLLA-Nb₂O₅ exhibited an average diameter of ∼250 nm, and hybrid PDLLA + Nb₂O₅/SiO₂ fibers were slightly larger, ∼300 nm in diameter. There were significant differences among formulations for hardness and flexural strength (p < 0.05). Degree of conversion of resin cement was not affected for all groups, except for Group 4 (p < 0.05).SignificanceHybrid reinforcement nanofibers are promising as fillers for dental materials. The self-adhesive resin cement with PDLLA + Nb₂O₅ and PDLLA + Nb₂O₅/SiO₂ presented superior mechanical performance than the control group.     

Alternative monomer for BisGMA-free resin composites formulations

ObjectiveWater sorption, high volumetric shrinkage, polymerization stress, and potential estrogenic effects triggered by leached compounds are some of the major concerns related to BisGMA-TEGDMA co-monomer systems used in dental composites. These deficiencies call for the development of alternative organic matrices in order to maximize the clinical lifespan of resin composite dental restorations. This study proposes BisGMA-free systems based on the combination of UDMA and a newly synthesized diurethane dimethacrylate, and evaluates key mechanical and physical properties of the resulting materials.Methods2EMATE-BDI (2-hydroxy-1-ethyl methacrylate) was synthesized by the reaction between 2-hydroxy-1-ethyl methacrylate with a difunctional isocyanate (1.3-bis (1- isocyanato-1-methylethylbenzene) – BDI). The compound was copolymerized with UDMA (urethane dimethacrylate) at 40 and 60 wt%. UDMA copolymerizations with 40 and 60 wt% TEGDMA (triethylene glycol dimethacrylate) were tested as controls, as well as a formulation based in BisGMA (bisphenol A-glycidyl methacrylate)-TEGDMA 60:40% (BT). The organic matrices were made polymerizable by the addition of DMPA (2.2-dimethoxyphenoxy acetophenone) and DPI-PF6 (diphenyliodonium hexafluorophosphate) at 0.2 and 0.4 wt%, respectively. Formulations were tested as composite with the addition of 70 wt% inorganic content consisting of barium borosilicate glass (0.7 μm) and fumed silica mixed in 95 and 5 wt%, respectively. All photocuring procedures were carried out by a mercury arc lamp filtered to 320–500 nm at 800 mW/cm². The experimental resin composites were tested for kinetics of polymerization and polymerization stress in real time. Flexural strength, elastic modulus, water sorption, and solubility were assessed according to ISO 4049. Biofilm formation was analyzed after 24 h by luciferase assay. Data were statistically analyzed by one-way ANOVA and Tukey's test (α ≤ 0.05).ResultsIn general, the addition of 2EMATE-BDI into the formulations decreased the maximum rate of polymerization (RP_MAX), the degree of conversion at RP_MAX (DC at RP_MAX), and the final degree of conversion (final DC). However, these reductions did not compromise mechanical properties, which were comparable to the BT controls, especially after 7-day water incubation. The incorporation of 60 wt% 2EMATE-BDI reduced water sorption of the composite. 2EMATE-BDI containing formulations showed reduction in polymerization stress of 30% and 50% in comparison to BT control and TEGDMA copolymerizations, respectively. Biofilm formation was similar among the tested groups.SignificanceThe use of the newly synthesized diurethane dimethacrylate as co-monomer in dental resin composite formulations seems to be a promising option to develop polymers with low-shrinkage and potentially decreased water degradation.     

Effect of the amount of 3-methacyloxypropyltrimethoxysilane coupling agent on physical properties of dental resin nanocomposites

ObjectivesThe purpose of this study was to evaluate the effect of the amount of 3-methacryloxypropyl-trimethoxysilane (γ-MPS) coupling agent on some physical–mechanical properties of an experimental resin composite for understanding the optimum amount of silanization.MethodsSilica nanoparticles (Aerosil OX 50) used as filler were silanized with 5 different amounts of γ-MPS 1.0, 2.5, 5.0, 7.5 and 10 wt% relative to silica. The silanizated silica nanoparticles were identified by FT-IR spectroscopy and thermogravimetric analysis (TGA). Then the silanized nanoparticles (60 wt%) were mixed with a Bis-GMA/TEGDMA (50/50 wt/wt) matrix. Degree of conversion of light cured composites was determined by FT-IR analysis. The static flexural strength and flexural modulus were measured using a three-point bending set up. The dynamic thermomechanical properties were determined by DMA analyzer. Sorption, solubility and volumetric change were determined after storage of composites in water or ethanol/water solution. Thermogravimetric analysis was performed in air and in nitrogen atmosphere from 50 to 800 °C.ResultsAt lower silane amounts used (1.0, 2.5 wt%) the silane molecules must have a parallel orientation relative to the silica surface. At higher silane amounts (>2.5 wt%) silane molecules form a layer around the filler particles which now have to occupy a random, parallel and perpendicularly orientation relative to the silica surface. No significant statistic difference was found to exist between the flexural strength and flexural modulus values of composites with different silane contents. Dynamic elastic modulus E′ showed a maximum value for the composite contained 5 wt% silane. The composites with the higher amounts of silane showed the lower values for the tan δ at the T_g revealing that these composites have better interfacial adhesion between filler and matrix.SignificanceThe amount of silane used for the silanization of silica particles affect the orientation of the silane molecules relative to the silica surface. This seems to affect the dynamic mechanical properties of composites.     

Composite resin reinforced with fluorescent europium-doped hydroxyapatite nanowires for in-situ characterization

ObjectiveThe object is to find an easy but efficient way to illustrate the in-situ dispersion of nano-scaled one-dimensional fillers in composite resins, and to correlate their dispersion status with the properties of composite resins.MethodsFluorescent europium-doped hydroxyapatite nanowires (HANW:Eu) were synthesized via the hydrothermal method. The HANW:Eu was mixed into Bis-GMA/TEGDMA (60/40, w/w) at different contents (1–5 wt.%), and different processing methods (kneading, grinding, stirring) were tested to achieve good dispersion of HANW:Eu with the aid of fluorescent imaging system. Then, the mixtures of HANW:Eu and barium glass powder (BaGP) were kneaded into resin at a fixed content (70 wt.%) while at different mixing ratios. In addition to the 3D fluorescent imaging, characterizations were carried out on mechanical properties, fractured surface, wear resistance and polymerization shrinkage, to correlate the composite properties of with the dispersion status of the incorporated HANW:Eu.ResultsBy doping calcium with 5 mol.% of europium, the obtained HANW:Eu displayed strong fluorescence, which made the illustration of its in-situ dispersion status within composites being possible. And this helped to judge that kneading was more efficient to homogeneously disperse HANW:Eu than grinding and stirring. However, it was illustrated vividly that HANW:Eu aggregated severely when it was co-incorporated with BaGP into composites at the total content of 70 wt.%, which had not been previously revealed by other microscope observations. In comparison with composites containing 70 wt.% of BaGP, improvements in the mechanical properties of resulting composites were identified for the cases containing 3 wt.% of HANW and 67 wt.% of BaGP, however, their wear volume loss and the polymerization shrinkage did not decrease as expected due to the HANW aggregations.SignificanceThe fluorescent filler prepared in this study provides a feasible strategy to illustrate the in-situ dispersion status of inorganic fillers, which provides guidance for the processing of composite resins.     

Effects of glazing methods on the optical and surface properties of silicate ceramics

PurposeThis study aims to evaluate the effect of different glazing methods on translucency parameter (TP), contrast ratio (CR), opalescence parameter (OP), surface roughness (Ra) and topography of the silicate ceramics.MethodsSeventy specimens (10 × 10 × 1 mm) were fabricated from lithium disilicate (IPS e.max CAD, abbreviated as E) and zirconia-reinforced lithium silicate (Vita Suprinity, abbreviated as VS) ceramics and divided into 7 subgroups (n = 10) according to the polishing and glazing procedures: (1) mechanical polishing before-crystallization (m-BC), (2) mechanical polishing after-crystallization (m-AC), (3) glaze powder/liquid after-crystallization (pl-AC), (4) glaze-paste before-crystallization (gp-BC), (5) glaze-paste after-crystallization (gp-AC), (6) glaze-spray before-crystallization (gs-BC), (7) glaze-spray after-crystallization (gs-AC). Color and Ra measurements were performed. CIEL*a*b* and CIEXYZ parameters were recorded and TP, CR, and OP values were calculated. Data were analyzed using two-way ANOVA and Tukey HSD tests (α = 0.05).ResultsIn E groups, the highest Ra value was found in gs-AC (1.66 ± 0.14 μm) while the lowest value was found in pl-AC (0.68 ± 0.08 μm). In VS groups, the highest Ra value was found in gp-BC (1.64 ± 0.25 μm) while the lowest value was found in m-AC (0.77 ± 0.06 μm) (p < 0.05). The mean TP value of E (17.62 ± 0.73) was found to be higher than VS (15.37 ± 1.16). The CR (0.72±0.030) and OP (12.06 ± 0.74) values of VS were found higher than CR (0.57 ± 0.02) and OP (6.72 ± 0.40) values of E.ConclusionsZirconia-reinforced silicate ceramics have higher opalescence and lower translucency values than lithium disilicate ceramics. Increase in surface roughness reduces translucency. Glaze powder/liquid after-crystallization is the most effective way to reduce surface roughness of lithium disilicate ceramics while that is mechanical polishing after-crystallization for zirconia-reinforced silicate ceramics.     

Adhesion procedures for CAD/CAM indirect resin composite block: A new resin primer versus a conventional silanizing agent

PurposeThe purpose of this study was to evaluate the effectiveness of both a resin primer containing methyl methacrylate (MMA) and a silanizing agent on bonding to indirect resin composite blocks, using two types of build-up hybrid resin composites.MethodsSHOFU BLOCK HC (Shofu) specimens were blasted with alumina, after which one of two surface treatments was applied: CERA RESIN BOND (Shofu, the Silane group) or HC primer (Shofu, the MMA group). Resin composites made using either Solidex Hardura (SDH, Shofu) or Ceramage Duo (CMD, Shofu) were built up and micro-tensile bond strength (μTBS) values were measured after storage in water for either 24 h or 6 months (n = 24 per group). The fracture surfaces after μTBS measurements and the resin block/build-up resin interfaces were observed by scanning electron microscopy (SEM).ResultsThe bond strength of the Silane/SDH group significantly decreased after 6 months (p < 0.001), whereas in the MMA group there was no significant loss after 24 h or 6 months (p = 0.99). In the CMD group, the bond strength after 6 months was significantly lowered in both the Silane group (p < 0.001) and the MMA group (p < 0.001), but the latter still showed greater adhesion. SEM images demonstrated that the matrix resin was partially destroyed at the fracture surfaces of the MMA group and fracture surface unevenness was observed.ConclusionsA primer containing MMA produced stronger bonding to CAD/CAM resin even after long-term aging compared to a silane treatment.     

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.     

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.     

Conversion kinetics of rapid photo-polymerized resin composites

ObjectiveTo measure the degrees of conversion (DC), conversion kinetics, and the effect of post-irradiation time on rapid photo-polymerized bulk-fill resin composites under conditions equivalent to clinical depths of 1 and 4 mm.Methods36 specimens (n = 3), based on two resin composites incorporating PowerCure rapid-polymerization technology in two consistencies (PFill; PFlow) and two comparators with matching consistencies (Eceram; EFlow), were investigated from the same manufacturer (Ivoclar AG, Liechtenstein). Specimens were prepared within 4 mm diameter cylindrical molds, of either 1 mm or 4 mm depths respectively, to simulate near-surface and deep locations in a bulk-fill restoration. The independent variables in this study were: materials, thickness and time. Two high irradiance polymerization protocols were utilized for PowerCure materials: 2000 and 3050 mW/cm² for 5 and 3 s, respectively. A standard (1200 mW/cm²) polymerization protocol was used with control materials. FTIR was utilized to measure DC in real-time for 24 h post-irradiation. The data were analyzed using Welch’s-ANOVA, Games-Howell post-hoc test, kinetic dual-exponential sum function and independent sample t-tests (p = 0.05).ResultsThe DC of the materials ranged between 44.7–59.0 % after 5 min, which increased after 24 h reaching 55.7–71.0 % (p < 0.05). Specimen thickness did not influence the overall DC. At 5 min, the highest DC was shown in EFlow. But PFlow, irradiated for 3 s and 5 s exhibited comparable results (p > 0.05). PFill composite irradiated with the 3 s and 5 s protocols did not differ from ECeram (p > 0.05). Specimen thickness and material viscosity affected polymerization kinetics and rate of polymerization (RP_max). Faster polymerization occurred in 1 mm specimens (except PFill-5 s and ECeram). PFill and PFlow exhibited faster conversion than the controls. RP_max varied across the specimen groups between 4.3–8.8 %/s with corresponding DC _RPmax between 22.2–45.3 %.SignificancePolymerization kinetics and RP_max were influenced by specimen thickness and material viscosity. PFill and PFlow materials produced an overall comparable conversion at 5 min and 24 h post-irradiation, despite the ultra-short irradiation times, throughout the 4 mm specimen thickness.     

Chlorhexidine preserves the hybrid layer in vitro after 10-years aging

ObjectiveThe present study investigated the ability of a chlorhexidine (CHX)-containing primer (0.2% aqueous solution) to inhibit dentinal enzymes, preserve the hybrid layer (HL) and remain within the HL, after 10 years of aging in artificial saliva at 37 °C.MethodsNon-carious extracted molars were assigned to two groups, cut into slabs exposing middle/deep dentin, etched and bonded with Adper Scotchbond 1XT (SB1XT) with or without 0.2% CHX aqueous solution pretreatment. Composite build-ups were made, and the specimens were cut in 1-mm thick bonded sticks. In situ zymography was performed on freshly prepared specimens (T₀) and specimens aged for 10 years (T_10-yr) at 37 °C in artificial saliva, to investigate endogenous gelatinolytic activity within the HL. At T_10-yr, specimens were also decalcified and embedded in epoxy resin for TEM analysis. Micro-Raman spectroscopy was performed at T₀ and T_10-yr to evaluate the chemical profiles in intertubular dentin and the HL.ResultsIn situ zymography showed less pronounced enzymatic activity in the CHX-pretreated group (p < 0.05) regardless of aging, maintaining a similar level of fluorescence at T₀ and T_10-yr (p > 0.05). TEM results showed that 98% of the HL had been degraded in the control group, while 95% of the HL was intact in the experimental group. Moreover, all the Raman spectra peaks assigned to CHX could be identified only in the CHX-pretreated group (T₀ and T_10-yr).SignificanceIn vitro, CHX remains in the HL after 10 years with its inhibitory effect preserved. This may be the underlying factor for HL preservation after this long aging period.