Indirect Restorative Materials Research Articles

Correlation between clinical performance and degree of conversion of resin cements: a literature review.

Resin-based cements have been frequently employed in clinical practice to lute indirect restorations. However, there are numerous factors that may compromise the clinical performance of those cements. The aim of this literature review is to present and discuss some of the clinical factors that may affect the performance of current resin-based luting systems. Resin cements may have three different curing mechanisms: chemical curing, photo curing or a combination of both. Chemically cured systems are recommended to be used under opaque or thick restorations, due to the reduced access of the light. Photo-cured cements are mainly indicated for translucent veneers, due to the possibility of light transmission through the restoration. Dual-cured are more versatile systems and, theoretically, can be used in either situation, since the presence of both curing mechanisms might guarantee a high degree of conversion (DC) under every condition. However, it has been demonstrated that clinical procedures and characteristics of the materials may have many different implications in the DC of currently available resin cements, affecting their mechanical properties, bond strength to the substrate and the esthetic results of the restoration. Factors such as curing mechanism, choice of adhesive system, indirect restorative material and light-curing device may affect the degree of conversion of the cement and, therefore, have an effect on the clinical performance of resin-based cements. Specific measures are to be taken to ensure a higher DC of the luting system to be used.

Indirect Restoration Thickness and Time after Light-Activation Effects on Degree of Conversion of Resin Cement.

This study evaluated the effects of indirect restorative materials, curing conditions and time on the degree of conversion (DC) of a dual-cured resin cement using infrared spectroscopy. The resin cement (RelyX Unicem 2, 3M ESPE) was applied to the diamond surface of a horizontal attenuated-total-reflectance unit and activated using one of following conditions: self-cure, direct light exposure, light exposure through indirect restorative materials (resin nano-ceramic: Lava Ultimate, 3M ESPE or feldspathic ceramic: Vita Blocks Mark II, Vita Zahnfabrik). Four thicknesses (0.5, 1.0, 1.5 or 2.0 mm) of each indirect material were analyzed, and the light-activation was performed using a blue LED light. Data (n=5) were analyzed by three-way ANOVA, Tukey's post hoc and Dunnett's tests (α=5%). No significant differences in DC were observed between indirect materials of similar thickness. All groups exhibited higher DC after 10 min than after 5 min. At both times points, the self-cure group exhibited significantly lower DC than all the light exposure groups. Only when the overlying indirect restoration had a thickness of 2 mm did DC decrease significantly. The presence of a thick, indirect restoration can decrease the DC of resin cement. DC after 10 min was higher than after 5 min. The self-cure mode yielded lower DC than the light-activating one.

Influence of Curing Units and Indirect Restorative Materials on the Hardness of Two Dual-curing Resin Cements Evaluated by the Nanoindentation Test.

To evaluate the hardness of a dual-curing self-adhesive resin cement (RelyX U200) and a conventional dual-curing resin cement (RelyX ARC) cured with different light curing units of different wavelengths (Elipar Freelight 2 LED [430 to 480 nm, conventional], Bluephase LED [380 to 515 nm, polywave], AccuCure 3000 Laser [488 nm]) by means of the nanoindentation test. Bovine incisors were cleaned and then sectioned at the cementoenamel junction to remove the crown. After embedding in acrylic, dentin surfaces of the specimens were exposed and ground flat to standardize the surfaces. To simulate clinically placing indirect restorations, ceramic (IPS e.maxPress/Ivoclar Vivadent) or indirect composite resin (SR Adoro/Ivoclar Vivadent) slabs were cemented on dentin surfaces. The specimens were sectioned longitudinally at low speed under constant irrigation and then polished. In the positive control group, the cement was light cured without the interposition of indirect restorative material; in the negative control group, after the indirect restorative material was cemented, no light curing was performed, allowing only chemical polymerization of the cement. All specimens were stored in distilled water at 37°C for 7 days. Nanoindentadion hardness of the cement layer was measured under a 100-mN load. Data were statistically analyzed using ANOVA and Tukey's test (p < 0.05). Although the self-adhesive cement is technically simple, conventional cement showed the best polymerization performance. The polywave LED technology did not differ significantly from other light-curing units. The hardness of the resin cements evaluated was negatively influenced by the interposition of an indirect restorative material; only the LEDs were able to maintain the same degree of cement polymerization when an indirect restorative material was used. The photoactivation step is required during the cementation of indirect restorations to ensure adequate polymerization of dual-curing resin cements.

Damage tolerance of indirect restorative materials (including PICN) after simulated bur adjustments

ObjectiveTo analyze the damage tolerance of indirect restorative materials after grinding with diamond burs to simulate adjustments by clinicians and technicians. MethodsSeven commercially available restorative materials (Mark II, ENAMIC, In-Ceram Alumina, VM 9, In-Ceram YZ, IPS e.max CAD) and an experimental one (PICN) were analyzed. Forty bending bars per material were fabricated according to manufacturer's instructions and lapped with 15μm diamond suspension. The initial flexural strength was determined in three-point-bending on 10 specimens. Additionally the elastic modulus and Poisson's ratio were determined by the resonant frequency method. The remaining bending bars were divided into six groups (n=5) and subjected to standardized grinding with three different diamond grit burs (coarse, 151μm; medium, 107μm and extra fine 25μm) and two grinding directions (transversal and longitudinal). The ground specimens were subsequently loaded to fracture and analyzed by SEM. ResultsExcept for the YTZP bending bars, the initial materials strength of all tested materials decreased significantly with all diamond burs upon adjustments in both transversal and longitudinal grinding directions. The resistance of the ground materials to strength reduction follow the order from highest to least damage tolerant material: PICN>ENAMIC>Mark II>VM 9>In-Ceram Alumina>IPS e.max CAD. The loss in strength of all examined materials after longitudinal grinding is generally less compared to transversal grinding. The lowest loss in strength occurred for VM 9 (7.79%) and ENAMIC (9.18%) upon longitudinal grinding direction with extra fine and medium diamond grit bur, respectively. SignificanceThe damage tolerance of restorative materials upon adjustments depends on specific mechanical properties and the adjustment procedure. The outcomes of the simulated grinding protocols of this study can be adopted clinically in terms of the selection of appropriate materials, burs and adjustment parameters.

Bonding performance of a self-adhering flowable composite to indirect restorative materials

Simplified restorative materials may be a logical next step for dental manufacturers. Objective: The aim of this study was to evaluate the shear bond strength of a self-adhering flowable composite to four substrates used in indirect technique. Material and methods: Twenty-four samples (5 mm wide, 15 mm length and 2 mm thick / six blocks each substrate) were prepared in the dental prosthetic laboratory. The following materials were used: ceromer (SR Adoro/AD, Ivoclar Vivadent), leucite ceramic (IPS Empress Esthetic/EE, Ivoclar Vivadent), zirconia ceramic (ZirCAD/ZI, Ivoclar Vivadent); metal ceramic alloy (Fit Cast SB/ME, Talladium do Brasil). Samples of each substrate were divided into two groups (n = 3). Two flowable composites (Control/FF – Filtek Z350 XT Flow/3M ESPE, and the self-adhering/DF – Dyad Flow/Kerr) were bonded to the four substrates. Four Tygon tubings were positioned over each sample, which were filled in with the composites FF and DF, and visible light-cured for 20 s. The tubings were removed to expose the specimens (12 per group) in format of cylinders and samples were stored in distilled water at 37±2°C for one week. After this period, each sample was attached to testing machine and the specimens were submitted to the shear bond strength test at speed of 1.0 mm/min, until failure. The results were analyzed by two-way ANOVA and Tukey test (p &lt; 0.05). Results: The means (SD) were (in MPa): AD + FF = 34.4 ± 4.9; AD + DF = 28.2 ± 4.2; EE + FF = 29.7 ± 5.8; EE + DF = 32.3 ± 6.9; ZI + FF = 23.2 ± 5.4; ZI + DF = 8.5 ± 1.5; ME + FF = 28.9 ± 4.2; ME + DF = 31.7 ± 4.5. Conclusion: The efficacy of flowable composites is material-dependent. The self-adhering composite provided lower bond strength only to zirconia ceramic. Comparing with the control group, Dyad Flow showed lower bond strength to the ceromer and zirconia ceramic.

Effects of barriers on chemical and biological properties of two dual resin cements.

The aim of this study was to investigate the degree of conversion, monomer release, and cytotoxicity of two dual-cure resin cements (Cement-One and SmartCem2), light-cured across two indirect restorative materials in an attempt to simulate in vitro the clinical conditions. The results obtained show that the degree of conversion was influenced by both barriers, but the effect of the composite material was greater than that of the ceramic one. The amount of monomers released from the polymerized materials in the absence of barriers was significantly lower than that released in the presence of either the ceramic or the composite barrier. However, a higher amount of monomers was released in the presence of the ceramic barrier. All materials, in all the experimental conditions employed, induced slight cytotoxicity (5-10%) on human pulp cells. Our examinations showed that the two resin cements had similar chemical and biological properties. The decreased degree of conversion of the dual-curing self-adhesive composite showed that the light-curing component of these materials has an important role in the polymerization process. In clinical practice, it is therefore important to pay attention to the thickness of the material used for the reconstruction.

Wear behavior of human enamel against lithium disilicate glass ceramic and type III gold

The wear behavior of human enamel that opposes different prosthetic materials is still not clear. The purpose of this in vitro study was to investigate and compare the friction and wear behavior of human tooth enamel that opposes 2 indirect restorative materials: lithium disilicate glass ceramic and Type III gold. Friction-wear tests on human enamel (n=5) that opposes lithium disilicate glass ceramic (n=5) and Type III gold (n=5) were conducted in a ball-on-flat configuration with a reciprocating wear testing apparatus. The wear pairs were subjected to a normal load of 9.8 N, a reciprocating amplitude of approximately 200 μm, and a reciprocating frequency of approximately 1.6 Hz for up to 1100 cycles per test under distilled water lubrication. The frictional force of each cycle was recorded, and the corresponding friction coefficient for different wear pairs was calculated. After wear testing, the wear scars on the enamel specimens were examined under a scanning electron microscope. Type III gold had a significantly lower steady-state friction coefficient (P=.009) and caused less wear damage on enamel than lithium disilicate glass ceramic. Enamel that opposed lithium disilicate glass ceramic exhibited cracks, plow furrows, and surface loss, which indicated abrasive wear as the prominent wear mechanism. In comparison, the enamel wear scar that opposed Type III gold had small patches of gold smear adhered to the surface, which indicated a predominantly adhesive wear mechanism. A lower friction coefficient and better wear resistance were observed when human enamel was opposed by Type III gold than by lithium disilicate glass ceramic in vitro.

Effect of ferrule location on fracture resistance of crowned premolars

s of the Academy of Dental Materials Annual Meeting, 8–11 October 2014, Bologna, Italy Session 1 – Indirect Restorative Materials (Thursday 9th, October, 11 am).

Evaluation of the effect of a home-bleaching agent on the surface characteristics of indirect esthetic restorative materials: part I--roughness.

Pressing esthetic demands of good looking make people undergo bleaching procedures. However, the effect of bleaching agents on esthetic restorative materials with different surface preparations has been poorly studied. The aim of this study was to examine the effect of a homebleaching agent (carbamide peroxide: CP 38%) on the surface roughness of the polished fiber reinforced composite (FRC), overglazed, autoglazed, or polished ceramic samples. Twenty standardized cylindrical specimens were made of each of the following groups: over-glazed, autoglazed, polished porcelain and also FRC. The test specimens exposed to the CP 38%, 15 minutes, twice a day for 2 weeks according to the manufacturer's recommendation. Six samples from each group were selected randomly to form negative controls. Surface roughness measurements (Ra, micrometer) for baseline, test and control specimens were performed by use of a profilometer. Paired t-test, Mann-Whitney test, and Kruskal-Wallis test were used for statistical analyses. The data showed that bleaching with CP 38% significantly increased the surface roughness of all the test samples (p < 0.05). The type of surface preparation caused significant differences between the susceptibility of porcelain subgroups to bleaching (p < 0.05). The polished porcelain specimens showed the highest changes after bleaching. CP 38% significantly increases the surface roughness of the porcelains and FRC. The type of surface condition affects the amenability of the porcelain surface to the bleaching agent. Glazed porcelains were more resistant to roughness than the polished porcelains and also the composite. Roughening of porcelain and FRC occur following bleaching procedure. No special surface preparation of indirect esthetic restorative materials can completely preserve these materials from adverse effects of bleaching agents.

Clinical evaluation of direct composite restorations and inlays: Results at 12 months

Background: The purpose of this study was to compare the clinical performance of Class II direct and indirect composite restorations according to the United States Public Health Service criteria (USPHS). Materials and Methods: Seventy patients were included and four different composite resins, P60 (FP), SureFil Posterior (SP), Gradia Posterior (GP), and Bisco Aelite LS Packable (BAP) were used as direct restorative material. All of the composite resins except BAP were used as indirect restorative material. Instead of BAP, Tescera Laboratory composites were polymerized in Tescera inlay oven. All restorations were evaluated according to USPHS criteria during a one-year period. Results: There were no statistically significant differences between direct and indirect composite restorations according to the retention, marginal discoloration, surface staining, proximal contact continuity, and secondary caries. Indirect restorations have less surface roughness, postoperative sensitivity (P < 0.05), and soft tissue irritation (P < 0.1) than direct ones. Conclusion: The clinical performances of the indirect restorations were more satisfactory than the direct restorations.

Surface Roughness Analysis of Dental Ceramics Treated with Hydrofluoric Acid and Aluminum Oxide Jet

ABSTRACT The aim of this study was to evaluate the surface roughness of 5 indirect restorative materials treated with hydrofluoric acid to 10%, with aluminum oxide jet and a combination of both. The specimens was prepared with 10 mm in diameter and 2 mm thickness, divided into five groups: (1) Ceromer (CeseadII-Kuraray), (2) Leucite crystals ceramics (IPS EmpressIIIvoclarforcasket), (3) glass ceramic with fluorapatite (IPS D. Sign-Ivoclar), (4) lithium disilicate ceramic (IPS Empress II-Ivoclar restorations), (5) ceramics (Cergogold-Degussa). For all groups were performed the controls, and the surfaces with the 3 types of treatment. For testing roughness used the rugosimeter Taylor/Hobson-Precision, model form tracerSV-C525 high sensitivity. After confirmation of variance analysis with a significance level of 1% (p &lt; 0.01), there was equality between the average roughness of materials from groups 1, 3 and 5, and the group 2 was different from the others. It was also found that the ceramics of the group 5 behaved similar to group 4. However the lowest average roughness was observed in group 2 ceramic. In the evaluation between the types of treatment, the aluminum oxide jet and associations and blasting with hydrofluoric acid were similar, and different isolated hydrofluoric acid, and 3 types of treatment significantly higher than the control group. All treatments promoted superficial alterations in all tested materials. How to cite this article Porto TS, Tonetto MR, Lorenzetti CC, Bandéca MC, Borges AH, Neto STP, de Campos EA, Dinelli W. Surface Roughness Analysis of Dental Ceramics Treated with Hydrofluoric Acid and Aluminum Oxide Jet. World J Dent 2014;5(1):1-5.

The effect of prophylactic polishing pastes on surface roughness of indirect restorative materials.

The purpose of this study was to evaluate the influence of prophylactic polishing pastes (PPP; Detartrine (DT), Topex (TP)) on surface roughness (R a) of indirect composites (IRC; Tescera (TES), Gradia (GRD), and Estenia C&B (EST)), a glass ceramic (Empress 2 layering (E2)), and a leucite reinforced glass ceramic (Empress Esthetic (EE)) with two different (glazed (G); polished (P)) surface preparations. A total of 90 IRC and 120 ceramic discs, 8 mm in diameter and 2 mm thick, were prepared. E2 and EE specimens were randomly divided into two groups (n = 30). One group was glazed (GE2; GEE), while the other group was polished (PE2; PEE) the same as the IRCs. The specimens in each group were subsequently divided into three subgroups: control (C), DT, and TP. R a (μm) was evaluated with a profilometer. Data were analyzed by Kruskal Wallis, followed by the Dunn's multiple comparison tests (P < 0.05). DT and TP resulted in significant surface roughening for TES, GRD, and EST, while no significant differences were detected between DT and TP (P > 0.05). PE2 and PEE were not affected by DT or TP (P > 0.05), while GE2 and GEE exhibited significant roughening after TP (P < 0.05). Surface roughness of IRCs and glazed ceramics can be affected by PPP applications.

Effect of pre-heating composites on film thickness

Resin composite has been suggested as a luting material for aesthetic indirect restorations and temperature affects material viscosity. Reports of film thickness from new composites are important. The aim of this study was to analyze the influence of pre-heating two resin composites on its film thickness in order to use it as a luting agent for indirect restorations (inlays and onlays). Three materials were divided into 5 groups. Two resin composites, nanofilled (Z350 XT/3MESPE) and microhybrid (Opallis/FGM), pre–heated and room temperature, and a resin cement (AllCem/FGM) were tested. Following the guidelines from ISO 4049, each material (0,05mL) was pressed under 15kg between two glass plates covered with polyester film for 180 seconds. After pressed, the material was light polymerized with a LED for 40s and the film thickness measured using a digital micrometer. When testing the groups of pre-heated resin composites the material was heated (64°C) on a specific device (CalSet/AdDent) before all procedures. Data were analyzed using t-Student, ANOVA and Tukey post hoc test (α=.05). Resin cement group showed the lower film thickness mean (28,2 µm), followed by the pre-heated microhybrid (45,3 µm). The higher values were obtained with nanofilled composite. Nanofilled room temperature group presented the highest thickness (96,1 µm). Statistical difference was found between all groups. Pre-heating influenced the film thickness of both composites. In this study a microhybrid composite showed better results among resin composite groups. Although not presenting the lower film thickness, as resin cement, some composites could be used for luting indirect restorations when heated.

Effect of light curing modes on mechanical properties of direct and indirect composites

Objective. To evaluate the degree of conversion (DC), flexural strength (FS) and Knoop microhardness (KHN) of direct and indirect composite resins polymerized with different curing systems. Materials and methods. Specimens of direct (Z250, 3M/Espe) and indirect (Sinfony, 3M/Espe) restorative materials were made and polymerized using two light curing units: XL2500 (3M/Espe) and Visio system (3M/Espe). Absorption spectra of both composites were obtained on a FTIR spectrometer in order to calculate the DC. FS was evaluated in a universal testing machine and surface microhardness was performed in a microhardness tester (50gf/15s). DC, FS and KHN data were submitted to two-way ANOVA and Tukey's test (α = 0.05). Results. Z250 showed higher DC, FS and KHN compared with Sinfony when the polymerization was carried out with XL2500 (p < 0.05). However, there is no statistical difference in DC between the materials when Visio was used (p > 0.05). Visio showed higher DC and KHN for Z250 and Sinfony than the values obtained using XL2500 light curing (p < 0.05). For FS, no significant difference between curing units was found (p > 0.05). Conclusion. Even though the Visio system could increase DC and KHN for some direct and indirect composites, compared with the conventional halogen curing unit, a high number of monomers did not undergo conversion during the polymerization.

Clinical success and survival of indirect resin composite crowns: Results of a 3-year prospective study

ObjectivesThe aim of this study was to test the new resin composite “NECO” as a material for indirect restorations clinically. MethodsForty-five patients were selected, of which 12 men and 33 women, with a mean age of 53. A total of 91 post-canine indirect resin composite NECO (Heraeus Kulzer, GmbH) restorations were placed, of which 86 full crowns and 5 onlays. Restorations were cemented with either resin cement (2bond2) or resin modified glass ionomer cement (Fuji Plus). The restorations were evaluated 1–2 weeks (baseline), 6 months, 1, 2, and 3 years after placement. At these recalls, success and survival data of the abutment teeth were documented. Survival was defined as the restoration being in situ, and success as the restoration in situ without complications. ResultsAfter 3 years in service, the restorations showed success and survival rates of 84.8 and 91.6%, respectively. Cementation with Fuji Plus showed a trend (p=0.054) toward higher success (93.1%) and survival (100%) rates compared to cementation with 2bond2 cement which showed success and survival rates of 81.4 and 87.9% respectively. Restorations on vital teeth resulted in success and survival rates of 86.8 and 95.3% respectively, while restorations on endodontically treated teeth showed success and survival rates of 82.6 and 87.5%. This difference was not statistically significant (p=0.296). SignificanceThree-year success and survival rates of NECO restorations were 84.8 and 91.6%, respectively. The design of the preparation and restoration should take the material properties into account in order to enhance the clinical performance.

Sorption and solubility characteristics of self-adhesive resin cements

ObjectiveThe aim of this in vitro study was to evaluate some sorption characteristics [sorption (S), solubility (SL) and the percentages of mass change (Mg%), solubility (SL%) as well as sorbed liquid (S%)] of self-adhesive resin cements when immersed in distilled water and lactic acid. MethodsA disc-shaped specimen of each self-adhesive resin cements [G-Cem (GC), SmartCem™ 2 (SC2), RelyX™ U100 (R1), RelyX™ Unicem 2 (RU2)] were prepared in a split-Teflon mold and irradiated by an Optilux 501 light cure at 580mW/cm2 for 40s in eight overlapping sections each side. The volume of each specimen was calculated and placed inside a desiccator containing anhydrous calcium chloride, then weighed on an analytical electronic balance. Two independent groups were established according to the immersion media or liquids (distilled water and 0.01M lactic acid) maintained at 37°C for the time intervals: 1, 6, 12, 24, 48 and 168h, where the sorption (S) property (μg/mm3) was calculated. However, the SL, Mg%, SL% and S% were measured after 168h of immersion. The data were statistically analyzed by repeated measures ANOVA, one-way ANOVA and post hoc Tukey's test (p<0.05). ResultsAnalysis of variance revealed highly significant differences between the materials for the sorption and solubility values examined with some exceptions (p<0.05). However, independent samples T-test expressed significant differences of all the sorption values between both water and lactic acid media for the resin cements with some border significances (p>0.05). The highest liquid's sorption was exhibited by GC material after immersion in lactic acid for 168h period followed by SC2 (37.83 and 34.15μg/mm3, respectively), while the lowest sorption was presented by RU2 cement after 1h immersion period in water (3.89μg/mm3). Stereomicroscope showed homogenous surface topography in RU2 and R1 samples, while some striated cracks and microvoids were observed in GC and SC2 materials, respectively. The SL values followed this order: RU2<R1<SC2<GC. SignificanceKnowing the best self-adhesive cement that can provide less sorption and solubility values will help the dentist to choose the most suitable luting material for indirect restorations.

Testing adhesion of direct restoratives to dental hard tissue - a review.

This articles concerns itself with the testing of adhesion between direct restoratives and dental hard tissue, ie, enamel and dentin. The aim is to survey available methods for adhesion testing and influential parameters affecting experimental outcome. The testing of adhesion to indirect restorative materials, eg, ceramics and metals, is beyond the scope of this article and shall be discussed elsewhere. The longevity and success of modern dental restorations very often relies on potent dental adhesives to provide durable bonds between the dental hard substance and the restorative composite. To predict the clinical outcome of such restorative treatment, a large variety of in vitro laboratory tests and clinical in vivo experiments have been devised, analyzed, and published. The purpose of this review is to provide a current overview of bond strength testing methods and their applicability to the characterization of dental adhesives. Regardless of the method employed, subtle variations in sample preparation may already severely impact test results, usually necessitating at least co-testing of a well-known internal reference to allow conclusive interpretation. This article attempts to list and discuss the most influential parameters, such as substrate nature, age, health status, storage, clinically relevant pre-treatment, and sample preparation. Special attention is devoted to the last aspect, as numerous publications have stressed the tremendous influence of preparatory parameters on the validity and scope of obtained data. Added to the large variety of such factors, an equally large diversity of load-applying procedures exists to actually quantify adhesion between composites and dental hard substance. This article summarizes the basics of macro and micro approaches to shear and tensile bond strength testing, as well as push- and pull-out tests. The strengths and weaknesses inherent to each method and influential test parameters are reviewed and methods for accelerated sample aging and simulation of clinical conditions presented. Alternatively to shear or tensile bond strength tests, fracture toughness is introduced together with its application to dental adhesives and an overview of its physical background.

Influence of Curing Light Attenuation Caused by Aesthetic Indirect Restorative Materials on Resin Cement Polymerization

To verify the effect of interposing different indirect restorative materials on degree of conversion (DC), hardness, and flexural strength of a dual-cure resin cement. Discs (2 mm-thick, n=5) of four indirect restorative materials were manufactured: a layered glass-ceramic (GC); a heat-pressed lithium disilicate-based glass-ceramic veneered with the layered glass-ceramic (LD); a micro-hybrid (MH); and a micro-filled (MF) indirect composite resin. The light transmittance of these materials was determined using a double-beam spectrophotometer with an integrating sphere. Bar-shaped specimens of a dual-cure resin cement (Nexus 2/SDS Kerr), with (dual-cure mode) and without the catalyst paste (light-cure mode), were photoactivated through the discs using either a quartz-tungsten-halogen (QTH) or a light-emitting diode (LED) unit. As a control, specimens were photoactivated without the interposed discs. Specimens were stored at 37 masculineC for 24h before being submitted to FT-Raman spectrometry (n=3), Knoop microhardness (n=6) and three-point bending (n=6) tests. Data were analyzed by ANOVA/Tukey's test (alpha=0.05). MH presented the highest transmittance. The DC was lower in light-cure mode than in dual-cure mode. All restorative materials reduced the cement microhardness in light-cure mode. GC and LD with QTH and GC with LED decreased the strength of the cement for both activation modes compared to the controls. Curing units did not affect DC or microhardness, except when the dual-cure cement was photoactivated through LD (LED>QTH). Flexural strength was higher with QTH compared to LED. Differences in transmittance among the restorative materials significantly influenced cement DC and flexural strength, regardless of the activation mode, as well as the microhardness of the resin cement tested in light-cure mode. Microhardness was not impaired by the interposed materials when the resin cement was used in dual-cure mode.

Colour Stability of Veneering Composites after Accelerated Aging

To investigate the colour stability of four indirect composite restorative materials after accelerated aging. Four indirect composites (Gradia, Signum+, HFO and Adoro) were used. For each material, six specimens were prepared and subjected to accelerated aging (Suntest CPS+, Atlas, Chicago, IL, USA) according to ISO 7491. A Dr. Lange Microcolor Data Station colorimeter (Braive Instruments, Liege, Belgium) was used to measure specimen colour before and after aging. Measurements were performed according to the CIE L*a*b* system, and the mean L*, a* and b* values for each material were calculated. The equation DeltaE = [(DeltaL*)2 + (Deltaa*)2 + (Deltab*)2](1/2) was used to measure the total colour change (DeltaE), where DeltaL*, Deltaa* and Deltab* are the differences in the respective values before and after aging. One-way ANOVA were used to determine statistically significant differences in DeltaL*, Deltaa*, Deltab* and DeltaE. No statistically significant differences were found in DeltaL*, Deltaa*, Deltab* and DeltaE among the materials tested (PDeltaL*=.063; PDeltaa*=.521; PDeltab*=.984 and PDeltaE=.408). After aging, Gradia specimens showed an increase in lightness (DeltaL*=0.36) and a green-yellow shift (Deltaa*=-1.18, Deltab*=0.6), while Signum+ specimens exhibited an increase in lightness (DeltaL*=0.5) and a green-blue shift (Deltaa*=-0.9, Deltab*=-0.45). HFO specimens exhibited an increase in lightness (DeltaL*=0.75) and a green-yellow shift (Deltaa*=-1.3, Deltab*=0.06), and Adoro specimens exhibited an increase in lightness (DeltaL*=2.07) and a green-yellow shift (Deltaa*=-1.3, Deltab*=0.68). Colour changes were found to be within accepted values of perceptibility and clinical acceptance after accelerated aging, and no statistically significant differences were found in DeltaL*, Deltaa*, Deltab* and DeltaE among the materials tested.

Influence of light-curing units and restorative materials on the micro hardness of resin cements

The aim of this study was to evaluate the effect of indirect restorative materials (IRMs) and light-curing units (LCUs) on the micro hardness of dual-cured resin cement. A total of 36 cylindrical samples (2 mm thick) were prepared with dual-cured resin cement (Relyx ARC) photo-activated with either a QTH (Optilight Plus) for 40s or a LED (Radii) light-curing unit for 65s. Photo-activation was performed through the 2-mm- thick IRMs and the samples were divided into six groups (n=6) according to the combination of veneering materials (without, ceramic and indirect resin) and LCUs (QTH and LED). In the control group, the samples were light-cured with a QTH unit without the interposition of any restorative material. Vickers micro hardness test was performed on the top and bottom surfaces of each sample (load of 50 g for 15 secs). The data were statistically analyzed using a three-way ANOVA followed by Tukey x s post-hoc test ( P < 0.05). There were no statistically significant differences on the top surface between the light curing-units ( P > 0.05); however, the LED provided greater hardness on the bottom surface when a ceramic material was used ( P < 0.05). The mean hardness in photo-activated samples, in which there was no interposition of indirect materials, was significantly greater ( P < 0.01). It may be concluded that the interposition of the restorative material decreased the micro hardness in the deeper cement layer. Such decrease, however, was lower when the ceramic was interposed and the cement light-cured with LED.