In vitro performance of 2-step, total etch adhesives modified by thiourethane additives.

OBJECTIVES: Thio-urethane oligomeric additives have been shown to improve the mechanical properties of dental composites and resin cements. To try to harness those same properties in dental adhesives, in this study, these oligomers (TU) were added to the matrix and/or as filler functionalization of experimental adhesives, and the effects on conversion and mechanical properties were analyzed. METHODS: BisGMA and HEMA (60/40 wt%) were used as the monomer matrix, made polymerizable by the addition of 0.2 wt% 2,2-dimethoxy-2- phenylacetophenone. 2,6-di-tert-butyl-4-methylphenol was added at 0.5 wt% as the inhibitor. This material was used as the unfilled control (BH). TU oligomers were added at 20 wt % to the matrix (BH+20%TU, unfilled) and/or used as filler functionalization (TF, 10 wt%). Fillers functionalized with methacrylate (MF, 10 wt%) served as the control. The experimental adhesives groups containing fillers were: BH+10%MF; BH+10%TF; BH+20%TU+10%MF; BH+20%TU+10%TF. Flexural properties were tested in three-point bending (wet and dry). Polymerization kinetics was followed in real-time in near-IR. Water Sorption/Solubility (WS/SL, ISO 4049) and Viscosity (rotational rheometry) were also evaluated. For Microtensile bond strength 40 vol% ethanol was added to adhesives, which was applied onto sound dentin from third human molars. The data were analyzed with one-way ANOVA and Tukey post-hoc test, and test t for the comparison between storage time of the microtensile bond strength test (alpha = 0.05). RESULTS: There was no significant difference between groups when yield strength (YS) and flexural modulus (FM) were evaluated in dry conditions. After water storage, all the groups containing TU in the matrix showed statistically lower YS/FM values. This was true in spite of the statistically higher conversion for those same groups. The maximum rate of polymerization (Rpmax) was higher for BH+10%TF and no significant difference was found for the groups BH and BH+10% MF. The lowest Rpmax values were found for BH+20%TU+10%TF and BH+20%TU. BH+20%TU+10%TF showed the highest viscosity values followed by BH+20%TU+10%MF and BH+20%TU, with statistically significant difference between them. For the microtensile bond strength test at 24h (p = 0.13) and 6 months (p = 0.11) and WS/SL (p > 0.05), no significant difference was found among groups. The storage time (24 h and 6 months) did not affect the microtensile bond strength results. CONCLUSION: In spite of improving the conversion, the addition of TU in the matrix reduced the mechanical properties of the adhesives tested after water storage. This did not affect the bond strength at 24 h or 6 months.

Two methods to simulate intrapulpal pressure: effects upon bonding performance of self-etch adhesives.

AIM: To evaluate the effects of two methods to simulate physiological pulpal pressure on the dentine bonding performance of two all-in-one adhesives and a two-step self-etch silorane-based adhesive by means of microtensile bond strength (µTBS) and nanoleakage surveys. METHODOLOGY: The self-etch adhesives [G-Bond Plus (GB), Adper Easy Bond (EB) and silorane adhesive (SIL)] were applied to flat deep dentine surfaces from extracted human molars. The restorations were constructed using resin composites Filtek Silorane or Filtek Z350 (3M ESPE). After 24 h using the two methods of simulated pulpal pressure or no pulpal pressure (control groups), the bonded teeth were cut into specimens and submitted to µTBS and silver uptake examination. Results were analysed with two-way anova and Tukey's test (P < 0.05). RESULTS: Both methods of simulated pulpal pressure led statistically similar µTBS for all adhesives. No difference between control and pulpal pressure groups was found for SIL and GB. EB led significant drop (P = 0.002) in bond strength under pulpal pressure. Silver impregnation was increased after both methods of simulated pulpal pressure for all adhesives, and it was similar between the simulated pulpal pressure methods. CONCLUSIONS: The innovative method to simulate pulpal pressure behaved similarly to the classic one and could be used as an alternative. The HEMA-free one-step and the two-step self-etch adhesives had acceptable resistance against pulpal pressure, unlike the HEMA-rich adhesive.

Effect of Surface Treatment with Zirconium Dioxide Slurry on the Bond Strength of Resin Cement to Ultratranslucent Zirconia.

This laboratory study aimed to evaluate the effects of zirconium dioxide (ZrO2) slurry surface treatment on the bond strength of ultratranslucent zirconia to resin cement using different ceramic primers. The surface morphology was evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the interface was evaluated by SEM. Additionally, the phase composition was analyzed by X-ray diffraction (XRD). Specimens of zirconia (n=120) were obtained and divided into two groups according to the surface treatment: (1) airborne particle abrasion with 50-µm aluminum oxide (n=60) and (2) ZrO2 slurry (n=60). The 60 specimens were then further divided into three groups (n=20) according to the ceramic primer application: no primer (NP), Monobond N (MB), and Clearfil ceramic primer (CP). Four resin cement cylinders were built on each ceramic specimen. Half of the specimens (n=10) were subjected to a microshear bond strength (µSBS) test after 24 hours of storage in distilled water, and the other half (n=10) were subjected to a µSBS test after thermocycling. Additional specimens were prepared for SEM, AFM, and XRD analyses. According to the Kruskal-Wallis and Student-Newman-Keuls post hoc tests, the µSBS values were significantly higher for MB and CP than for NP (p<0.05), and there were no significant differences in µSBS for both surface treatments associated with MB and CP after 24 hours of storage (p>0.05). Thermocycling significantly decreased the µSBS values for all specimens, especially for the NP groups and ZrO2 slurry treatment groups, and gaps at the interface were observed by SEM. SEM and AFM analyses showed agglomerate-type irregularities on the ceramic surface for ZrO2 slurry treatment. XRD spectra showed that ZrO2 slurry did not cause phase transformation. It was concluded that ZrO2 slurry promoted irregularities on the ultratranslucent zirconia surface, not causing phase transformation; moreover, the values of µSBS were comparable to those of airborne particle abrasion with aluminum oxide. However, neither surface treatment nor ceramic primer prevented the degradation of the interface.

Effects of surface treatments, thermocycling, and cyclic loading on the bond strength of a resin cement bonded to a lithium disilicate glass ceramic.

SUMMARY Objectives : The aim of this present study was to investigate the effect of two surface treatments, fatigue and thermocycling, on the microtensile bond strength of a newly introduced lithium disilicate glass ceramic (IPS e.max Press, Ivoclar Vivadent) and a dual-cured resin cement. Methods : A total of 18 ceramic blocks (10 mm long × 7 mm wide × 3.0 mm thick) were fabricated and divided into six groups (n=3): groups 1, 2, and 3-air particle abraded for five seconds with 50-µm aluminum oxide particles; groups 4, 5, and 6-acid etched with 10% hydrofluoric acid for 20 seconds. A silane coupling agent was applied onto all specimens and allowed to dry for five seconds, and the ceramic blocks were bonded to a block of composite Tetric N-Ceram (Ivoclar Vivadent) with RelyX ARC (3M ESPE) resin cement and placed under a 500-g static load for two minutes. The cement excess was removed with a disposable microbrush, and four periods of light activation for 40 seconds each were performed at right angles using an LED curing unit (UltraLume LED 5, Ultradent) with a final 40 second light exposure from the top surface. All of the specimens were stored in distilled water at 37°C for 24 hours. Groups 2 and 5 were submitted to 3,000 thermal cycles between 5°C and 55°C, and groups 3 and 6 were submitted to a fatigue test of 100,000 cycles at 2 Hz. Specimens were sectioned perpendicular to the bonding area to obtain beams with a cross-sectional area of 1 mm(2) (30 beams per group) and submitted to a microtensile bond strength test in a testing machine (EZ Test) at a crosshead speed of 0.5 mm/min. Data were submitted to analysis of variance and Tukey post hoc test (p≤0.05). Results : The microtensile bond strength values (MPa) were 26.9 ± 6.9, 22.2 ± 7.8, and 21.2 ± 9.1 for groups 1-3 and 35.0 ± 9.6, 24.3 ± 8.9, and 23.9 ± 6.3 for groups 4-6. For the control group, fatigue testing and thermocycling produced a predominance of adhesive failures. Fatigue and thermocycling significantly decreased the microtensile bond strength for both ceramic surface treatments when compared with the control groups. Etching with 10% hydrofluoric acid significantly increased the microtensile bond strength for the control group.

Influence of glazed zirconia on dual-cure luting agent bond strength.

The current study evaluated the influence of a novel surface treatment that uses a low-fusing porcelain glaze for promoting a bond between zirconia-based ceramic and a dual-cure resin luting agent. Bond strengths were compared with those from airborne particle abrasion, hydrofluoric acid etching, and silanization-treated surfaces. Twenty-four yttrium-stabilized tetragonal zirconia (Cercon Smart Ceramics, Degudent, Hanau, Germany) discs were fabricated and received eight surface treatments: group 1: 110 µm aluminum oxide air-borne particle abrasion; group 2: 110 µm aluminum oxide airborne particle abrasion and silane; group 3: 50 µm aluminum oxide airborne particle abrasion; group 4: 50 pm aluminum oxide airborne particle abrasion and silane; group 5: glaze and hydrofluoric acid;group 6: glaze, hydrofluoric acid, and silane;group 7: glaze and 50 pm aluminum oxide airborne particle abrasion; and group 8: glaze,50 pm aluminum oxide airborne particle abrasion and silane. After treatment, Enforce resin cement (Dentsply, Caulk, Milford, DE, USA) was used to fill an iris cut from microbore Tygontubing that was put on the ceramic surface to create 30 cylinders of resin cement in each treatment group (n=30). Micro shear bond test-ing was performed at a cross head speed of 0.5mm/min. One-way analysis of variance, and multiple comparisons were made using Tukey's test (p<0.5). The bond strength was affected only by surface treatments other than silanization. The groups that utilized the low-fusing porcelain glaze with airborne particle abrasion or hydrofluoric acid showed bond strength values statistically superior to groups that utilized conventional airborne particle abrasion treatments with 50 or 110 pm aluminum oxide (p<0.001). The treatment that utilized low-fusing porcelain glaze and hydrofluoric acid showed bond strength values statistically superior to remaining groups (p<0.001). Treatment of zirconia ceramic surfaces with a glaze of low-fusing porcelain significantly increased the bond strength of a dual-cure resin luting agent to the ceramic surface.

Influence of the volume of composite and photoactivation method on push-out bond strength and Knoop hardness of a resin composite.

AIM: The aim of this paper was to evaluate the influence of modulated photoactivation methods and volume of composite on Knoop hardness (KHN) and push-out bond strength (PBS) of Filtek Z350 to root dentin. METHODS: Three volumes (small, medium and large) of composite were bulk inserted in cavities prepared in 90 premolars. The specimens were photoactivated with continuous light, pulse-delay, or soft-start methods and submitted to PBS and KHN tests. The failure pattern was evaluated in stereomicroscope after the bond strength test. The data were submitted to two-way ANOVA and Tukey's test (P<0.05). RESULTS: Modulated photoactivation methods showed a higher PBS than continuous method (P<0.05). Medium volume of composite showed higher PBS than small and large volumes when photoactivated with continuous method (P<0.05). Pulse-delay significantly increased KHN for medium and large volumes in comparison to continuous method (P<0.05). Medium volume of composite showed KHN significantly higher than small and large volumes (P<0.05). CONCLUSION: The volume of composite influenced the PBS and KHN of resin composites. Pulse-delay showed the highest bond strength to dentin, as well KHN similar to the conventional method. The analysis of the failure pattern showed predominance of adhesive failure.

Evaluation of Cleaning Methods on Lithium Disilicate Glass Ceramic Surfaces After Organic Contamination.

The purposes of this study were to 1) evaluate the effectiveness of different cleaning methods from a previously etched and silanized lithium disilicate glass ceramic (EMX) surface after contact with organic fluids (saliva or human blood) and 2) assess the effect of applying a new silane layer after the cleaning methods on the microshear bond strength (mSBS) of resin cement to EMX. EMX discs were etched with 5% hydrofluoric acid (HF) and properly silanized. Three control groups were created (n=10): control (without contamination), saliva positive, and human blood positive. Later, after new contaminations, the samples were distributed into four groups according to the cleaning method (n=20): air-water spray (AWS), 35% phosphoric acid, 70% alcohol, or Ivoclean cleaning paste. After the cleaning methods, subgroups were submitted to a new silane layer application, or not (n=10). All samples received a thin layer of a bonding agent and, subsequently, three light-cured resin cement cylinders were prepared on each EMX surface for the mSBS test. This test was performed on a universal testing machine at a vertical speed of 1 mm/minute until rupture. Contaminated and cleaned silanized EMX surfaces were assessed by scanning electron microscopy (SEM) (n=1). The noncontaminated control group showed an average mSBS of 18.7 MPa, and the positive saliva and human blood control groups yielded a 34% and 42% reduction in bond strength, respectively, compared to the uncontaminated control (p<0.05). For saliva-contaminated surfaces, all cleaning methods were effective and not different from one another or the control group (p>0.05). However, for human blood contamination, only Ivoclean cleaning paste was effective in restoring µSBS to uncontaminated control group levels (p>0.05). SEM images showed a clean surface (ie, with no contaminant residues) after the cleaning methods, regardless of the organic contaminant type. All the assessed cleaning methods were effective in removing saliva from the silanized EMX surface; however, only Ivoclean was able to restore the adhesion quality when the silanized EMX surface was contaminated with human blood.

Three-point bending testing of fibre posts: critical analysis by finite element analysis.

AIM: To evaluate the effect of taper, specimen supports and the isotropic and orthotropic properties of the posts on flexure and stress response during three-point bending using finite element analysis. METHODOLOGY: A three-dimensional finite element model of a fibre post was created. The occlusal portion was cylindrical whilst the apical portion was tapered. Five different support positions were evaluated during a simulated three-point bending test: M1 - support distance of 10 mm centralized and no tilt; M2 - 10 mm centralized with tilt; M3 - 10 mm not centralized and no tilt; M4 - 10 mm not centralized with tilt; M5 - 6 mm not centralized with no tilt. A sixth post model (M6) was a centralized post without tapered section. The applied properties were elastic and orthotropic. RESULTS: Tilting the tapered posts to level them in the test setup had little effect on the outcome. Flexure increased when 50% of the bent portion involved taper (M1, M2). If only 20% of the bent post involved taper (M3, M4), the flexure values were close to M6 (no taper). The orthotropic properties also caused increased flexure compared to an isotropic post. Maximum stresses were only a little higher when 50% of the bend structure involved taper, whilst the orthotropic properties had little effect. CONCLUSIONS: Regardless of levelling, the flexural stress determination with tapered fibre posts in the three-point bending test was valid as long as the tapered portion was limited in length.

Comparison between two methods to evaluate temperature changes produced by composite light curing units and polymerization techniques.

AIM: This study evaluated the temperature change into the pulp chamber during the light curing of composite resin by direct (bovine tooth) and indirect (matrix) methods. METHODS: Direct method: fifty standardized cavities (2x2x2 mm) were prepared in bovine incisors, which were randomly assigned to evaluation of the temperature changes in the pulp chamber. Indirect method: temperature changes were evaluated through a dentine slice of 1.0 mm thickness in a elastomer cubic mold (2x2x2 mm). Filtek Z250 composite resin (3M/ESPE) was photo-activated using three light curing units: quartz-tungsten-halogen (QTH) by continuous, soft-start or intermittent light modulations; light emitting diode (LED); and plasma arc-curing (PAC). Ten groups (N.=10) were established according to technique evaluation and photo-activation methods. All experiments were carried out in a controlled environment (37 °C and 50 ± 10% relative humidity). The temperature changes were recorded using a digital thermometer attached to a type-K thermocouple in contact with the dentin slice (indirect method) or in contact with the axial wall (dentin) of pulp chamber (direct method). The results were submitted to ANOVA and Tukey's test (α=0.05). RESULTS: Temperature changes were statistically higher for the matrix indirect method (2.56 ºC) than bovine teeth direct method (1.17ºC). The change temperature was statistically higher for the PAC (1.77 ºC) when compared to other photo-activation modes in bovine teeth direct method. CONCLUSION: The two methods of temperature evaluation were different, however indirect method detected the higher temperature increase. Higher energy density arising from the light curing units and polymerization techniques promoted higher temperature increase.

Effect of curing-light attenuation on color stability and physical and chemical properties of resin cements containing different photoinitiators.

This study aimed to evaluate the effect of light attenuation by ceramic veneers on the degree of conversion (DC), flexural strength (FS) and color change (CC) of resin cements containing different photoinitiators. Thus, samples included resin cements containing different photoinitiators: (a) camphorquinone (CQ)/ethyl 4-(dimethylamino)benzoate (EDMAB); (b) CQ/4-(N,N-dimethylamino) phenethyl alcohol (DMPOH); (c) CQ/2(dimethylamino) ethyl methacrylate (DMAEMA); (d) CQ/ethyl 4-(dimethylamino)benzoate (EDMAB) + diphenyl(2,4,6-trimethylbenzoyl)-phosphine oxide (TPO); (e) TPO; and (f) phenylbis(2.4.6-trimethylbenzoyl)phosphine oxide (BAPO). Ceramic veneers (10 × 10 mm) were 0.4 mm, 0.7 mm, 1.0 mm or 1.5 mm thick. The light irradiance of a multiple-peak LED through ceramic veneers was measured (n = 5) using a spectrometer. DC (micro-Raman spectrometer) and FS (Bar-shaped specimens) were tested in cements with and without the veneers. Color change was evaluated before and after UV artificial aging. Data were submitted to ANOVA and Tukey's test (α = 0.05). The violet spectrum showed the lowest irradiance values through the veneer, considering all thicknesses. BAPO had the highest DC values for all veneers. CQ/EDMAB + TPO, CQ + EDMAB, and CQ + DMPOH showed similar DC values concerning all thicknesses. TPO (1.0 mm) showed the lowest DC and FS values. CQ + TPO and CQ/amines showed similar FS values. CQ + EDMAB and CQ + DMAEMA showed the highest color change values while TPO showed the lowest. It was concluded that the physical and chemical properties of the resin cement were improved with BAPO. CQ/EDMAB + TPO showed the greatest color stability, considering all veneer groups and control, without affecting the other properties assessed.

Effect of monomer content in the monomer-polymer proportion on the adaptation of complete denture bases.

AIM: This study verified the effect of the monomer/polymer proportion on the base adaptation of the complete upper dentures. METHODS: Thirty stone cast-wax baseplate sets were packed in metallic flasks and the acrylic resin polymerized in water at 74 °C for nine hours. Three transverse cuts were made through each stone cast-resin base set, corresponding to regions: A) canines (anterior); B) first molars (median), and C) posterior palate (posterior). Measurements were made using an optical micrometer at five points for each cut to determine base adaptation: left and right marginal limits of the flanges, left and right ridge crests, and midline. Data were analyzed using to ANOVA and Tukey's test (5%). RESULTS: In region A there was significant difference among the monomer-polymer proportions, with a greater value of misfit for the content -25% monomer group and lower for the manufacturer's proportion group. In region B there was significant difference between the manufacturer's content (lowest value) and the monomer contents of +25% and -25% (both statistically similar). In region C there was significant difference among the monomer-polymer proportions, with greater value for the -25% monomer group than for the manufacturer's proportion. There was significant difference when the regions were compared in relation to the same monomer content. The best adaptation was in the region A and the worst in the region C. CONCLUSION: The amount of monomer exerted different effects on the adaptation of the denture base. In all regions, the smallest misfit was observed when the manufacturer's recommended proportion was used and the greatest misfit was observed in the -25% monomer.

Assessment of the polymerization contraction stress of composites photoactivated by halogen light and light-emitting diode.

AIM: The aim of this study was to compare the polymerization contraction stress of composites photoactivated by two light sources: quartz tungsten halogen light (QTH) and light emitting diode (LED). METHODS: Glass rods were fabricated (5.0 mm X 5.0 cm) and one of the surfaces was air abraded with aluminum oxide. An adhesive was applied to this surface and photoactivated by LED. The glass rods were assembled to a Universal Testing machine (Instron - 5565) and the composite were applied to the lower rod using a manual instrument. The upper rod was placed closer, at 2 mm, and an extensometer was attached to the rods. The twenty composites were polymerized by either by QTH (N.=10) or LED (N.=10). Polymerization was carried out using two apparatuses positioned in opposite sides, which were simultaneously activated for 30 seconds. Contraction stress was analyzed twice: shortly after polymerization (t30s) and 30 minutes later (t30min). RESULTS: The contraction stress for all composites was higher at t30min than at t30s, regardless of the activation source. Z100 showed lower contraction stress values (P<0.05) compared to the other composites. Regarding to Charisma and TPH, the photoactivation source had no influence on contraction stress, except for Z100 at t30min. CONCLUSIONS: It was concluded that composite composition is the factor that most influence the polymerization contraction stress.

Light-emitting Diode Beam Profile and Spectral Output Influence on the Degree of Conversion of Bulk Fill Composites.

OBJECTIVES: To evaluate the beam profile and the spectral output of monowave and polywave light-emitting diodes (LEDs) and their influence on the degree of conversion (DC) of bulk fill composites. METHODS: A monowave LED (Smartlite Focus, Dentsply) and a polywave LED (Valo Cordless, Ultradent) were characterized using a resin calibrator and a laser beam profile analyzer. Two bulk fill composites, Sonic Fill 2 (SF) containing camphorquinone (CQ) and Tetric EvoCeram Bulk Fill (TEB) containing CQ associated with alternative photoinitiators, were placed in custom-designed molds (n=3) and photoactivated by the monowave or polywave LED with 20 J/cm2. To map the DC, longitudinal cross sections (0.5 mm thick) from the center of the restoration were evaluated using FT-NIR microscopy. SF and TEB light transmittances (n=3) through 4-mm-thick specimens were evaluated during curing. Data were analyzed using a split-plot analysis of variance and Tukey test (α=0.05; ß=0.2). RESULTS: The monowave LED had a radiant emittance of 20 ± 0.5 J/cm2 over 420-495 nm, and the polywave LED had an emittance of 15.5 ± 0.4 J/cm2 over 420-495 nm and of 4.5 ± 0.2 J/cm2 over 380-420 nm. The total radiant exposure at the bottom of TEB was 2.2 ± 0.2 J/cm2 with the monowave LED and 1.6 ± 0.3 J/cm2 with the polywave LED, and for SF it was 0.4 ± 0.1 J/cm2 for both LEDs. There were no differences in the curing profiles produced either by the monowave or the polywave LED (p=0.9), according to the regions under influence of blue and/or violet emission at the same depth. There was no statistical difference in the DC for SF using the monowave or polywave LED at any depth (p=0.29). TEB had a higher DC at up to 2 mm in depth when the polywave LED was used (p<0.004), but no differences were found when starting at 2.5 mm. CONCLUSIONS: Monowave and polywave LEDs emitted nonhomogeneous light beams, but this did not affect the DC homogeneity of bulk fill composites. For composites containing CQ associated with alternative photoinitiators, polywave LEDs had a higher DC, but only at the top part of the restoration; lower wavelength absorption photoinitiators were ineffective in deeper areas.

Effect of Hydrofluoric Acid Concentration and Etching Time on Bond Strength to Lithium Disilicate Glass Ceramic.

The aim of this study was to evaluate the influence of different concentrations of hydrofluoric acid (HF) associated with varied etching times on the microshear bond strength (µSBS) of a resin cement to a lithium disilicate glass ceramic. Two hundred seventy-five ceramic blocks (IPS e.max Press [EMX], Ivoclar Vivadent), measuring 8 mm × 3 mm thickness, were randomly distributed into five groups according to the HF concentrations (n=50): 1%, 2.5%, 5%, 7.5%, and 10%. Further random distribution into subgroups was performed according to the following etching times (n=10): 20, 40, 60, 120, and 20 + 20 seconds. After etching, all blocks were treated with a silane coupling agent followed by a thin layer of an unfilled resin. Three resin cement cylinders (∅=1 mm) were made on each EMX surface, which was then stored in deionized water at 37°C for 24 hours before testing. The µSBS was in a universal testing machine at a crosshead speed of 1 mm/min until failure. Data were submitted to two-way analysis of variance, and multiple comparisons were performed using the Tukey post hoc test (α=0.05). One representative EMX sample was etched according to the description of each subgroup and evaluated using scanning electron microscopy for surface characterization. The HF concentrations of 5%, 7.5%, and 10% provided significantly higher µSBS values than 1% and 2.5% (p<0.05), regardless of the etching times. For 1% and 2.5% HF, the etching times from 40 to 120 seconds increased the µSBS values compared with 20 seconds (p<0.05), but etching periods did not differ within the 5%, 7.5%, and 10% HF groups (p>0.05). The effect of re-etching was more evident for 1% and 2.5% HF (p<0.05). Different HF concentrations/etching times directly influenced the bond strength and surface morphology of EMX.

Strengthening of Porcelain Provided by Resin Cements and Flowable Composites.

This study evaluated the effect of mechanical properties of resin-based luting agents on the strength of resin-coated porcelain. The luting agents tested were two flowable resin composites (Filtek Z350 Flow and Tetric-N Flow), a light-cured resin cement (Variolink Veneer [VV]), and a dual-cured resin cement (Variolink II) in either light-cured (base paste) or dual-cured (base + catalyst pastes [VD]) mode. Flexural strength (σf) and modulus of elasticity (Ef) of the luting agents were measured in three-point bending mode (n=5). Porcelain discs (Vita VM7) were tested either untreated (control) or acid etched, silanized, and coated with the luting agents. Biaxial flexural strength (σbf) of the porcelain discs was tested using a ball-on-ring setup (n=30). The σbf of the resin-coated specimens was calculated at z-axial positions for multilayer specimens in the ball-on-ring test: position z = 0 (ceramic surface at the bonded interface) and position z = -t2 (luting agent surface above ring). The σf and Ef data were subjected to analysis of variance and the Student-Newman-Keuls test (α=0.05). A Weibull analysis was performed for σbf data. Weibull modulus (m) and characteristic strength (σ0) were calculated. Linear regression analyses investigated the relationship between mechanical properties of the luting agents and the strengthening of porcelain. VD had higher and VV had lower mechanical strength than the other materials. At z = 0, all resin-coated groups had higher σbf than the control group. No significant differences between the luting agents were observed for σbf and σ0. At z = -t2, VD had the highest σbf and σ0, whereas VV had the poorest results. No significant differences in m were observed across groups. A linear increase in flexural strength of the porcelain was associated with increased σf and Ef of the luting agents at position z = -t2. In conclusion, resin coating and use of luting agents with better physical properties generally improved the mechanical performance of porcelain.

Reestablishing Biology, Function, and Esthetics for Fractured, Immature Incisors.

A seven-year-old boy with enamel-dentin fractures on both maxillary central incisors presented to the Piracicaba Dental School-UNICAMP seven days after the trauma. At the clinical evaluation, there were no clinical signs of pulp exposure, neither tooth was mobile, and both affected teeth presented a positive response to sensitivity tests and a negative response for percussion and palpation. The radiographic examination showed an undeveloped root and opened apex for both teeth. Indirect pulp capping was performed on the left maxillary central incisor, followed by a direct restoration. After one month, the patient complained of pain in the left central incisor, which responded negatively to sensitivity testing. Pulp revascularization was performed only on this tooth and was followed for 18 months. During this period, the left maxillary central incisor did not recover sensitivity, although radiographic examination showed apical closure, a slight increase in root length, and the formation of a mineralized barrier between the root canal and sealing material. The technique achieved its goal of restoring biological aspects, function, and esthetics of traumatized teeth when using this multidisciplinary approach.

The Effect of Hydrofluoric Acid Concentration on the Bond Strength and Morphology of the Surface and Interface of Glass Ceramics to a Resin Cement.

The purpose of this study was to evaluate the influence of various concentrations of hydrofluoric acid (HF) on the surface/interface morphology and µ-shear bond strength (µSBS) between IPS Empress Esthetic (EST) (Ivoclar Vivadent) and IPS e.max Press (EMX) (Ivoclar Vivadent) ceramics and resin cement. Ceramic blocks were divided into 12 groups for each kind of ceramic. Six different HF concentrations were evaluated: 1%, 2.5%, 5%, 7.5%, 10%, and 15%. All groups were silanated after etching, and half of the specimens within each group received a thin layer of unfilled resin (UR). Three resin cement cylinders were prepared on each ceramic block for µSBS testing. The specimens were stored in distilled water at 37°C for 24 hours. The µSBS test was carried out in a universal testing machine at a crosshead speed of 0.5 mm/min until fracture. The data were submitted to three-way analysis of variance and multiple comparisons were performed using the Tukey post hoc test (p<0.05). The etched surfaces and bonded interfaces were evaluated using scanning electron microscopy. µSBS means (MPa) for 1%, 2.5%, 5%, 7.5%, 10%, and 15% HF concentrations were, respectively, 25.2, 27.2, 30.1, 31.4, 33.3, and 31.8. µSBS means with or without UR application measured 32.24 and 27.4, respectively; EST and EMX measured 29.8 and 29.9, respectively. For the HF concentrations, 10% and 15% showed higher µSBS means than did 1% and 2.5% (p<0.05); 7.5% was higher than 1% (p<0.05); and no statistical differences were found among the other concentrations (p>0.05). When evaluating UR, µSBS mean was significantly higher and better infiltration was observed on the etched surfaces. No statistical difference was found between the ceramics. The HF concentration and UR influenced the bond strength and surface/interface morphology.

Effect of refrigeration on tensile bond strength of three adhesive systems.

The purpose of this study was to investigate the tensile bond strengths of three adhesive systems applied to dentin at refrigerated and room temperatures. Ninety bovine incisor teeth were obtained, embedded in self-cured acrylic resin, abraded on a lathe under water spray and polished to 400 and 600 grit to form standardized dentin surfaces before randomly assigning to six groups (n = 15). The adhesive systems Scotchbond Multi-Purpose, Single Bond and Prime & Bond NT were applied to dentin according to the manufacturers' instructions at refrigerated temperature (4 degrees C) and at room temperature (23 degrees C), before bonding resin-based composite (Z 100). The specimens were stored in distilled water at 37 degrees C for 24 hours and submitted to tensile bond strength tests on a universal testing machine (EMIC DL-2000) at a crosshead speed of 0.5 mm/min. The resulting data were statistically analyzed using analysis of variance and Tukey's test. No statistical differences were found when the adhesive systems were applied at refrigerated and room temperatures. Scotchbond Multi-Purpose and Single Bond had significantly stronger tensile bond strengths than Prime & Bond NT at room and refrigerated temperatures (p < 0.01). Scotchbond Multi-Purpose and Single Bond were statistically similar. No adverse effects upon tensile bond strength were observed when adhesive systems were taken directly from refrigerated storage.

[Effect of acrylic resin post-pressing time on dimensional change of total denture base]. / Efeito do tempo pós-prensagem da resina acrílica na alteração dimensional da base de prótese total.

The dimensional alterations of denture bases were verified in function of the acrylic resin post-pressing time. Twenty stone cast/wax base sets were confected for routine flasking procedure. Thermosetting acrylic resin (Clássico) was prepared according to the instructions of the manufacturer. After final pressing, the acrylic resin was submitted to polymerization in water at 74 degrees C during 9 hours, following the immediate, 6-, 12-, and 24-hour post-pressing times. The resin bases were fixed on the casts with instantaneous adhesive and the sets were laterally sectioned in the regions corresponding to the distal aspect of canines (A), mesial aspect of first molars (B), and posterior palatal zone (C). The gap between the stone cast and the resin base was measured with a comparative microscope at five referential positions for each kind of sectioning. Data submitted to ANOVA and Tukey's test showed that there was no statistically significant difference between the immediate and the 6-hour post-pressing times as well as between the 12- and the 24-hour post-pressing times. However, there was statistically significant difference between the immediate/6-hour groups and the 12-/24-hour groups.

Prolonged curing time reduces the effects of simulated pulpal pressure on the bond strength of one-step self-etch adhesives.

The aim of this study was to evaluate the effects of extended light-curing procedures on the microtensile bond strength (µTBS) of one-step self-etch adhesives (1-SEAs) submitted to simulated pulpal pressure. Coronal deep-dentin specimens were bonded using Clearfil S3 Bond (S3), Adper Easy Bond (EB), or G-Bond Plus (GB) following the manufacturers' recommendations and light-cured for 10 seconds or 40 seconds. The dentin-bonded specimens were stored in distilled water for 24 hours without pulpal pressure (control) or submitted to 20 cm H2O simulated pulpal pressure for 24 hours. The specimens were cut into matchsticks and subjected to µTBS testing. The data were statistically analyzed using the three-way analysis of variance and Tukey's tests (p<0.05). Debonded sticks were investigated through scanning electron microscopy. EB obtained higher bond strengths than GB and S3. However, prolonged light activation (40 seconds) provided higher µTBS for all adhesives when submitted to pulpal pressure. Conversely, pulpal pressure caused a drop in µTBS in EB and S3 when light-cured for 10 seconds. A mixed failure mode was mainly attained for the control groups, whereas the specimens submitted to pulpal pressure failed in the adhesive mode. The µTBS of GB was not affected by pulpal pressure when light-cured for 10 seconds. Adhesive was the most prevalent failure mode, except when light-cured for 40 seconds, which showed predominantly cohesive failure. Extended curing times improved the resistance of 1-SEAs to simulated pulpal pressure.