Resin Cement Material Research Articles

The Effect of Different Dentin Desensitizers and Self- Adhesive Resin Cement on Shear Bond Strength: In Vitro Study

Objectives: The aim of this study is to evaluate and compare the bond strength of different dentin desensitizers and self-adhesive resin cements to dentin surfaces. Methods: The flat dentin surfaces of 72 wisdom molar teeth were randomly divided into six groups for bond strength analysis (n=12): Group CP: No desensitizer + Primer II A&B+ Panavia F 2.0, Group CM: No desensitizer+ Primer A&B+ Multilink N, Group TP: Tokuyama Shield Force+ Primer II A&B + Panavia F 2.0, Group TM: Tokuyama Shield Force + Primer A&B+ Multilink N, Group UP: Universal dentin sealant + Primer II A&B+ Panavia F 2.0 and Group UM: Universal dentin sealent + Primer A&B+ Multilink N. The shear bond strength test was performed using a universal testing machine (0.5 mm/min). ANOVA test was used to detect significant differences at a p < 0.05. Results: The results indicated that bond strength values varied according to the desensitizing and resin cement materials (p < 0.05). The Tokuyama Shield Force desensitizer did not affect the bond strength of the resin cements to dentin (p > 0.05). Conclusion: The different types of dentin desensitizer applications affected on the shear bond strength results of the self-adhesive resin cements.

Finite element stress analysis of dental cement application on endocrown and onlay restoration.

The aim of the study was to evaluate the influence of resin cement material types on tooth with endocrown and onlay restorations. The first molar was scanned using Micro-CT and underwent a modelling process to obtain the 3D model for computational simulation. Eight models were simulated in the current study with two loading conditions (720N vertical load and 200N oblique load), two types of restoration (onlay and endocrown restorations), and two resin cement variants (dual-cure resin cement and light-cure resin cement). The tooth with onlay restoration showed a significant stress reduction (up to 70%) when using light-cure resin cement compared to dual-cure resin cement. In contrast, types of cement did not affect stress distribution in the tooth with endocrown restoration. The current study found that dual-cure resin cement was preferable in Endocrown and Onlay restorations, due to dual-cure resin cement provided better bond strength compared to light-cure resin cement.

Study on the properties of C-S-H/epoxy nanocomposite structure doped with silica nanoparticles

Nano-SiO2 can promote cement hydration, and it is important to study the effect of nano-doping technology on the microstructure of C-S-H/epoxy resin to improve the performance of epoxy resin cement materials. In this paper, the coupling agent (kh550) molecules were grafted on the surface of nano-SiO2, and the nano-SiO2-modified epoxy resin with different grafting rates was modeled and compounded with C-S-H. The structural properties and interfacial interaction mechanism were discussed utilizing molecular dynamics (MD) simulations. The results show that: nano-SiO2 doping into epoxy resin can increase its atomic surface area, reduce the porosity and thus enhance the stiffness of the composite, and the mechanical properties are best at a surface grafting rate of 15%; with the increase of nano-SiO2 doping and cross-linking degree, the amorphous characteristics of the composite structure are reduced and the crystalline structure of C-S-H in molecular motion is optimized. At the same time, the spacing between the C-S-H layer and epoxy resin layer in the composite structure is reduced, and the interfacial binding energy is increased; due to the improved adsorption performance, the diffusion rate of Ca ions between the C-S-H and epoxy resin layers is enhanced, this phenomenon facilitates the production of hydration products.

Analysis of the effect of thermocycling on bonding cements to zirconia

ObjectiveThe aim of this study was to evaluate the effect of thermocycling on shear bond strength (SBS) of several resin cement materials to different types of zirconia dental ceramics. Materials and Methods120 square shaped disc specimens were fabricated using two types of zirconia blocks (Sagemax and Sirona). Each zirconia group was divided into three sub-groups based on the resin cement bonded to the specimens. Three different self-adhesive resin cements were used (Calibra, Breeze and RelyX). The specimens were further grouped into experimental and control groups (n = 10). The experimental specimens were exposed to a thermo-cycling protocol of 1500 cycles in water bath at 5c and 55c. Specimens were then stored at 37c for 24 h then all specimens underwent SBS test with an Instron machine. Mode of failure was inspected visually and microscopically. Data were statistically analyzed using multivariate analysis of variance followed by one-way analysis of variance, Tukey’s multiple comparison test, student’s t-test for independent samples were used to compare the mean values of SBS in relation to the categorical study variables. ResultsThe mean SBS values of experimental groups were significantly lower than control groups for all the 6 combinations of Zirconia and cement types (p < 0.0001). The higher mean difference (14.29 MPa) was observed in the combination of Sagemax and Rely-X. Rely-X displayed the highest SBS among all the cements while no significant difference was found in mean SBS values of Calibra and Breez cements in all groups. The mean SBS values of Sagemax zirconia were significantly higher than the Sirona with all three types of cements (p < 0.0001) within control groups. Microscopic and visual analysis demonstrated a majority of adhesive mode of failure. ConclusionThermocycling significantly reduced the SBS between the zirconia materials and self-adhesive resin cements tested. The amount of reduction varies according to cement and zirconia types.

Microgap Formation between a Dental Resin-Matrix Computer-Aided Design/Computer-Aided Manufacturing Ceramic Restorative and Dentin after Various Surface Treatments and Artificial Aging

The potential formation and the size of microgaps at the material/dentin interface after various surface modifications of a resin-matrix computer-aided design/computer-aided manufacturing (CAD/CAM) ceramic following artificial aging was investigated. Fifty human third molars were used, and a resin-matrix CAD/CAM ceramic, Lava Ultimate, and a resin cement material, Rely X Ultimate, were tested. CAD/CAM blocks were sectioned, and each slab was luted on the tooth surface using the same resin cement. The surface material was modified using the following treatments: Group 1—no treatment (control); Group 2—hydrofluoric acid (HF) + silane; Group 3—air abrasion with Al2O3 particles (29 μm); Group 4—air abrasion with Al2O3 particles (53 μm); and Group 5—erbium, chromium:yttrium–scandium–gallium–garnet (Er,Cr:YSGG) (2780 nm) laser treatment. The specimens were submitted to thermocycling (5000 cycles: 5 °C–55 °C) and then transversely cut in the middle and examined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Larger microgaps were observed in the control and laser-treated groups, with no significant differences (p = 0.452). By contrast, the other three groups presented lower microgap formation, and in some cases, no microgaps were detected. Air-abrasion groups exhibited the lowest microgap formation (p &lt; 0.05). Different surface modifications of the material presented significant differences in the formation of microgaps at the adhesive interface after artificial aging, implying differences in bond strengths among the groups. Air-abrasion pretreatments with Al2O3 particles presented more beneficial results regarding microgap formation.

Assessment of push-out bond strength of post-surface pretreatment before salinization using hydrogen peroxide, aluminum trioxide, and natural photosensitizers to radicular dentin

ObjectiveThe study aimed to evaluate the effect of different post surface pretreatment methods i.e., 24% hydrogen peroxide (H2O2), riboflavin photosensitizer (RFP), curcumin photosensitizer (CP) and aluminum oxide (Al2O3), and silane only on the bond values of glass fiber post to resin cement Materials and MethodsFifty single-rooted human teeth were obtained and crowns were sectioned coronally to the cementoenamel junction (CEJ). Protaper universal file system was used for canal cleaning and shaping followed by obturation. Post space was prepared and all the posts were then randomly divided into five groups depending on the surface pretreatment used (n = 10). Group 1: 24% H2O2 + silane, Group 2: RFP + silane, Group 3: CP + silane, Group 4: Al2O3 + silane, Group 5: silane only. Post-surface treatment was followed by post-placement using a self-etch dual-cure cement Panavia F 2.0. Acrylic blocks were used to hold the specimens perpendicularly and all the samples were sectioned by slow-speed saw into coronal, middle, and apical third. The universal testing machine determines pushout bond strength and failure mode was analyzed by stereomicroscope. One-way analysis of variance (ANOVA) and Tukey multiple comparison tests were used to analyze data. ResultThe coronal section of group 4 (Al2O3 + silane) displayed the highest PBS (8.23±0.14 MPa). Whereas, an apical third of group 2 (RFP + silane) exhibited the lowest PBS (2.02±0.12 MPa). PBS values in samples in group 1 surface treated with 24% H2O2 + silane displayed comparable outcomes to samples in group 4 at all three levels (p>0.05). Samples in group 2 (RFP + silane) group 3 (CP + silane) and group 5 (Silane Only) demonstrated comparable PBS (p>0.05). ConclusionGlass fiber reinforced post-surface pretreatment method using hydrogen peroxide and aluminum trioxide along with silane improves push-out bond strength at all three levels (coronal, middle, and apical). The use of a silane coupling agent on glass fiber posts alone does not improve bond values. The practice of photosensitizer on post-surface needs to be investigated further.

The effect of different cleaning agents and resin cement materials on the bond strength of contaminated zirconia

The purpose of this study was to examine the effect of different cleaning methods and resin cements on the shear bond strength (SBS) of contaminated zirconia. A total of 92 disc-shaped zirconia specimens were contaminated with different procedures. Then, the specimens were grouped according to cleaning methods and resin cements: no cleaning + Variolink Esthetic DC (CNV ), no cleaning + Panavia V5 (CNP ), sandblasted + Variolink Esthetic DC (SBV ), sandblasted + Panavia V5 (SBP ), Ivoclean + Variolink Esthetic DC (ICV ), Ivoclean + Panavia V5 (ICP ), Katana Cleaner + Variolink Esthetic DC (KCV ), and Katana Cleaner + Panavia V5 (KCP ). Following an aging protocol in a 37°C for 1week, SBS analysis was performed with a universal test machine. For the surface topography and elemental analysis, scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDS) were used. Significance was evaluated as p< .05 and p< .01. The highest SBS results were found in the SBP group, showing a statistically significant difference from all other groups (p <.05). For the same cleaning method, Panavia V5 showed statistically significantly higher SBS values than Variolink Esthetic DC (p< .01), except the CNP -CNV (p= .880) and KCP -KCV (p= .082) groups. The most detected surface elements by EDS were Zr, O, C, and N, respectively. The contaminated zirconia surfaces must be cleaned for successful adhesion. The use of phosphate-containing adhesives in combination with sandblasting will increase the adhesion strength, and universal cleaning agents can be a good alternative to sandblasting.

Influence of Cement Thickness on the Polymerization Shrinkage Stress of Adhesively Cemented Composite Inlays: Photoelastic and Finite Element Analysis

The objective of this study was to analyze the effect of cement thickness on the strain and stresses resulting from the polymerization of resin cement using photoelasticity and Finite Element Analysis (FEA). For this study, twenty upper first premolars with inlay cavity preparation were constructed from photoelastic resin and restored with composite resin inlay. The samples were divided into two groups (n = 10) according to the film thickness of resin cement material. For Group 1, the film thickness was 100 μm; for Group 2, the film thickness was 400 μm. After polymerization of the cement, photoelastic analysis and finite element analysis (FEA) were performed. In the photoelastic analysis, Group 2 showed higher strain with the presence of second-order fringe even after 24 h. In Group 1, the formation of first order fringes was not observed, even after 24 h. In the FEA analysis, the greatest cusp deflection and tensile stress occurred in Group 2 (0.00026 mm and 0.305 MPa, respectively) due to the polymerization shrinkage in the lingual cusp compared to Group 1 (0.000107 mm and 0.210 MPa, respectively). It can be concluded that the thickness of the resin cement influences the cusp deflection, with the greater thickness of the cement layer, the greater stresses and deformations in the tooth structure occur.

Cytotoxic effects of different self-adhesive resin cements: Cell viability and induction of apoptosis.

PURPOSEThe effects of four different self-adhesive resin cement materials on cell viability and apoptosis after direct and indirect exposure were evaluated using different cell culture techniques.MATERIALS AND METHODSSelf-adhesive cements were applied to NIH/3T3 mouse fibroblasts by the extract test method, cell culture inserts, and dentin barrier test method. After exposure periods of 24 h and 72 h, the cytotoxicity of these self-adhesive materials was evaluated using the MTT assay (viability) and the Annexin-V-FITC/PI staining (apoptosis).RESULTSThe lowest cell viability was found in cells exposed to BeautiCem SA for 24 h in the extract test method. Cell viability was reduced to 70.6% compared to negative controls. After the 72 h exposure period, viability rate of cell cultures exposed to BeautiCem SA decreased more than 2- fold (29.5%) while cells exposed to RelyX U200 showed the highest viability rate of 71.4%. In the dentin barrier test method, BeautiCem SA induced the highest number of cells in apoptosis after a 24 h exposure (4.1%). Panavia SA Cement Plus was the material that caused the lowest number of cells in apoptosis (1.5%).CONCLUSIONThe used self-adhesive cements have showed different cytotoxic effects based on the evaluation method. As exposure time increased, the materials showed more cytotoxic and apoptotic effects. BeautiCem SA caused significantly more severe cytotoxic and apoptotic effects than other cements tested. Moreover, cements other than BeautiCem SA have caused necrotic cell death rather than apoptotic cell death.

Evaluation of the core thickness and resin cement on the fracture strength of zirconia-based multilayer computer-aided design/computer-aided manufacturing ceramic crowns

Aim: The purpose of this study was to evaluate the effect of thickness of zirconia core and different resin cements on the fracture strength of veneered zirconia crowns designed by multilayer technique. Materials and Methods: Forty metal dies were constructed to replica maxillary molar. Forty zirconia cores (Sirona inCoris ZI) were designed and constructed (inLab 4.4) with different thicknesses. The thickness of zirconia core was selected as 0.5 and 0.7 mm. Forty Feldspathic ceramic (VITABLOCS Mark II) veneers were fabricated (inLab 4.4) onto the zirconia cores. The zirconia cores were divided into two subgroups, and veneers were cemented with one of the following resin cement: self-cure, self-adhesive resin cement with light-cured option (Multilink N), and a dual-cure resin cement (Panavia F 2.0). Then, crowns were cemented to the metal dies. All the specimens were subjected to thermal cycling 5000 times (5°C–55°C ± 2°C, immersion time: 30 s). A universal testing machine was used for fracture strength test at a crosshead speed of 1 mm/min. The data were analyzed with one-way analysis of variance (α = 0.05). Stereomicroscopy was used to evaluate the failure modes and surface structure. Results: Zirconia core thickness and resin cement material affected the fracture strength (P < 0.05). Increase in core thickness increased the fracture strength of multilayer veneer crown (P < 0.05). Higher fracture strength values were obtained with light-cured, self-adhesive cement in both core thicknesses. Conclusion: Although 0.5-mm thickness zirconia cores showed lower flexural strength, it was higher than the maximum loads which may occur clinically (Fmax= 600 N on one tooth). Furthermore, light-cured, self-adhesive resin cement is advisable to increase the fracture strength with different core thickness.

DEGREE OF POLYMERIZATION OF DUAL CURE RESIN CEMENT MEASURED BY FTIR

Introduction: The degree of polymerization of dental resin cement materi- als is very important for the longevity and quality of the clinical success of the restorative procedure. Insufficiently effective polymerization reaction of dental resin cement materials may result in adverse effects on the mechanical and adhesive performance of the material. It is believed that the proportion of triethylene glycol dimethacrylate (TEGDMA) mono- mers in the chemical structure of the material significantly influences the polymerization reaction. With the increase in TEGDMA, the degree of conversion of monomers into the polymer increases. Aim: The aim of this study has been to determine the degree of polymerization of dual cure dental resin cement. Material and methods: For the analysis of the degree of polymerization, Fourier transform infrared (FTIR) spectroscopy was used. 10 samples of dual cure resin based cement Variolink II were prepared in accordance with the manufacturer's instructions. Analysis was performed 24 hours after polymerization procedure. Results: Degree of polymerization of Variolink II resin based cement ranged from 69.2% to 98.7% with a mean value of 85.81%. Conclusion: Variolink II dual cure resin cement contains a significant percentage of TEGDMA which can be the cause of high degree of polymerization. The minimum accep- table percentage of the degree of polymerization of dental resin cement has not yet been established.

Preparation and Characterization of Antibacterial Dental Resin Cement Material

Preparation and Characterization of Antibacterial Dental Resin Cement Material

Evaluation of color changes of dental luting materials in food colorant solutions.

The purpose of this study was to compare the color stability and water absorption of 3 commercially available resin cements in vitro by storing them in 0.15% erythrosine, dark brown and sunset yellow for 30 days. 2 self-adhesive resin cements and 1 dual/light curing, resin-based dental luting material were evaluated (total 120 samples). The CIE L, a, b of 10 mm diameter-2.0 mm height disk shaped samples was measured using a spectrophotometer for color stability on a white background, 10 mm diameter-1.0 mm height disk shaped samples were measured for water absorption before and after storage in food colorant solutions. The self-adhesive resin cement-sunset yellow group caused the most severe discoloration (27.89 ± 3.64) that is clinically unacceptable. The lowest discoloration was seen in the self-adhesive resin cement control group (3.35 ± 1.13). The highest water absorption was observed in the self-adhesive resin cement-dark brown group (2.41 ± 0.60) and the lowest water absorption in the dental luting material-control group (0.65 ± 0.17). Storage food colorant solutions affected the color stability and water absorption of different resin cement materials.

Effect of brand and shade of resin cements on the final color of lithium disilicate ceramic

Statement of problemResin cements are available in various shades from different manufacturers. However, there is no standard for the optical properties of these cements, which may result in differences in the color of translucent ceramic restorations. PurposeThe purpose of this in vitro study was to evaluate the effects of different shades and brands of resin cements on the color of a lithium disilicate ceramic. Materials and methodsTen ceramic disks (11×1.5 mm, shade A2) were fabricated from lithium disilicate high-translucency blocks. Eighty cement disks (11×0.2 mm) were fabricated from 4 brands (Maxcem; Variolink; Clearfil; and RelyX) of resin cements in translucent and universal (shade A2) shades. Color measurements of ceramic specimens were made without (control) and with each brand/shade of resin cement material (test) with a spectrophotometer, and International Commission on Illumination Lab (CIELab) color coordinates were recorded. Color differences (ΔE00) between the control and test groups were calculated. ΔE00 results were analyzed by 2-way ANOVA and subsequent pairwise testing. Comparisons were performed using the Student t test, and then all P values were corrected with the step-down Bonferroni procedure (α=.05). ResultsThe effect on the ΔE00 values (P<.001) of the brand and shade of resin cement materials was significant. Both shades of RelyX cement groups had significantly lower and Variolink_translucent cement group had significantly higher ΔE00 results than other brands (P<.05). Only RelyX_translucent and RelyX_universal were significantly different from each other for comparisons within brands (P<.05). The effect of RelyX_universal cement on the ceramic was not visually perceptible (ΔE00≤1.30). Clinically unacceptable results (ΔE00>2.25) were observed only for Variolink_translucent cement (2.36). ConclusionsSame-shade resin cements from different manufacturers had different effects on the color of lithium disilicate ceramic. The effects of different shades of resin cements from the same manufacturer on the color of lithium disilicate ceramic were statistically different for only RelyX, which may also be considered clinically different based on clinical acceptability thresholds for color difference values (ΔE00). Accordingly, this effect may be considered clinically different for Variolink but not clinically different for Maxcem and Clearfil.

Influence of the color of composite resin foundation and luting cement on the final color of lithium disilicate ceramic systems

Statement of problemLithium disilicate restorations are commonly used, particularly in the anterior region. The color of the underlying composite resin foundation (CRF) and luting cement may negatively affect the color of lithium disilicate ceramic restorations. PurposeThe purpose of this in vitro study was to investigate the effect of CRF and resin cement materials on the color of lithium disilicate ceramics in 2 different translucencies. Material and methodsTwenty disks (11×1.5 mm, shade A2) were fabricated from medium-opacity (mo) (n=10) and high-translucency (ht) (n=10) lithium disilicate (Lds) blocks (IPS e.max Press). Five CRF disks (11×3 mm) were fabricated in 5 different shades (A1, A2, A3, B2, C2) and 30 resin cement disks (11×0.2 mm) in the shades of translucent (Tr), universal (Un=A2), and white-opaque (Wo). Ceramic specimens were placed on each CRF, and the resin cement combination and color was measured with a spectrophotometer. CIELAB color coordinates were recorded, and the color coordinates of both ceramics on the shades of the A2 CRF and resin cement were saved as the control. Color differences (ΔE00) between the control and test groups were calculated. Data were analyzed with 3-way analysis ANOVA and compared with the Tukey HSD test (α=.05). ResultsThe ΔE00 values were influenced by the shades of the CRF, resin cement materials, and also their interactions (P<.05). The ΔE00 values were not affected by the ceramic type. The ΔE00 values of the Wo cement groups (1.73 to 2.96) were significantly higher than those of the other cement shades (0.88 to 1.29) for each ceramic type and CRF shade (P<.05). ConclusionsLithium disilicate ceramics in 2 different translucencies were similarly influenced by the color of the underlying cement and CRF. When translucent and universal cement shades were used, the core shade did not affect the final color of the ceramics. White opaque cement caused clinically unacceptable color changes in both ceramics on all shades of CRFs except the C2 CRF and when high translucency ceramic was used on the A2 CRF. These changes were clinically acceptable, but perceptible.

Comparison of immediate and delayed light-curing on nano-indentation creep and contraction stress of dual-cured resin cements

Statement of problemPolymerization protocol of dual-cured resin cements plays a great role in the success of restorations. Knowledge about the effect of light-curing protocol on the contraction stress value and the mechanical properties would assist in the development, selection and handling of the resin cement material. PurposeThis study was undertaken to assess the effects of two different light-curing protocols on the polymerization shrinkage stress and nano-creep of two current dual-cured resin cements. Materials and methodsTwenty-four soda-lime glass disks, measuring 1mm in thickness, with a perforation in their center that measured 3mm in diameter, received four Vickers indentations at a distance of 500µ from the margin. The indent cracks were measured before and at 15-, 30- and 60-min intervals after restoration of the cavity with either CLEARFIL™ SA or RelyX™ Ultimate cement. Twelve specimens were prepared from each resin cement and divided into two groups according to the curing protocol used: immediate and delayed light-curing. Stresses at the indent impression were calculated by considering glass fracture toughness and the increase in crack length. Stress at the bonded interface was calculated using the Lame equation for thick-walled cylinder under an internal pressure. Nano-indentation hardness, modulus of elasticity and creep of each cement were measured under a 10-mN load for 20s holding time. The specimens were stored in distilled water at 37°C for 24h before the nano-indentation tests. Data were analyzed with two-way and repeated-measures ANOVA (α≤0.05). ResultsCuring protocol had a significant effect on both resin cements; higher stress values were recorded with the immediate curing mode (P=0.033). Curing mode did not exert a significant effect on the modulus of elasticity (P=0.595) and hardness (P=0.454) of resin cements. However, in relation to creep, it exhibited significant effects (P<0.0001). ConclusionsImmediate light-curing resulted in higher polymerization stress and lower nano-creep values compared to the delayed protocol with the resin cements assessed.

Simulated Wear of Self-Adhesive Resin Cements.

One of the primary areas of concern with luting agents is marginal gap erosion and attrition. The purpose of this laboratory study was to evaluate bulk and marginal slit (gap) generalized wear of self-adhesive resin cements. Three self-adhesive resin cements were used in this study: G-CEM LinkAce (LA), Maxcem Elite (ME), and RelyX Unicem2 Automix (RU). A custom stainless-steel fixture with a cavity 4.5 mm in diameter and 4 mm deep was used for simulated generalized (bulk) wear. For simulated marginal gap wear, a two-piece stainless-steel custom fixture was designed with a slit (gap) 300 μm wide and 3 mm in length. For both wear models, 20 specimens each for each of the three adhesive cements were made for both light-cure and chemical-cure techniques. The cured cements were polished with a series of carbide papers to a 4000-grit surface and subjected to 100,000 cycles using the slit (gap) wear model and 400,000 cycles for generalized (bulk) wear in a Leinfelder-Suzuki (Alabama machine) wear simulator (maximum load of 78.5 N). Flat-ended stainless-steel antagonists were used in a water slurry of poly(methylmethacrylate) beads for simulation of generalized contact-free area wear with both wear models. Before and after the wear challenges, the specimens were profiled with a Proscan 2100 noncontact profilometer, and wear (volume loss [VL] and mean facet depth [FD]) was determined using AnSur 3D software. Two-way analysis of variance (ANOVA) and Tukey post hoc tests were used for data analysis for the two wear models. Scanning electron microscopy (SEM) was used to examine polished surfaces of the resin cements and the worn surfaces after the wear challenges. The two-way ANOVA of VL using the generalized (bulk) wear model showed a significant effect among the three resin cement materials for the factor of resin cement (p<0.001) and the interaction of the cement and cure method (p<0.001), but not for the cure method (p=0.465). The two-way ANOVA for FD also found a significant difference for the factor of resin cement (p<0.001) and the interaction of the resin cement and cure method (p<0.001), but not for the cure method (p=0.277). The simulated generalized (bulk) wear for the light-cure groups was as follows: VL (mm(3)): RU 0.631 (0.094), LA 0.692 (0.112), and ME 1.046 (0.141) and FD (μm): RU 43.6 (6.5), LA 47.0 (7.7), and ME 72.5 (9.9). The simulated generalized (bulk) wear for the chemical-cure groups was as follows: VL (mm(3)): LA 0.741 (0.105), RU 1.231 (0.234), and ME 1.305 (0.143) and FD (μm): LA 50.7 (7.2), RU 84.5 (16.1), and ME 91.7 (10.2). Simulated wear using the slit (gap) model for the light-cure groups was as follows: VL (mm(3)): RU 0.030 (0.006), LA 0.031 (0.006), and ME 0.041 (0.009) and FD (μm): RU 49.6 (5.7), LA 57.2 (8.4), and ME 70.9 (10.7). The wear values for the chemical-cure slit (gap) groups were as follows: VL (mm(3)): LA 0.031 (0.004), ME 0.038 (0.007), and RU 0.045 (0.009) and FD (μm): LA 53.9 (6.7), ME 63.5 (9.1), and RU 74.2 (12.9). Pearson correlation tests revealed a strong relationship between the two wear models for the light-cure groups and a good relationship for the chemical-cure groups. The observations using SEM showed differences in filler particle shape and size among the cements and the resultant effect of the wear challenges. The worn surfaces of each cement were essentially the same for both light-cure and chemical-cure methods. The bulk wear model and new slit (gap) model for evaluation of simulated generalized wear of luting agents demonstrated significant differences (p<0.05) in relative wear among three self-adhesive resin cements and between visible light- and chemical-cure techniques.

Rheological properties of dental resin cements during polymerization

Purpose: The purpose of this study was to observe the change of viscoelastic properties of dental resin cements during polymerization. Materials and methods: Six commercially available resin cement materials (Clearfil SA luting, Panavia F 2.0, Zirconite, Variolink N, RelyX Unicem clicker, RelyX U200) were investigated in this study. A dynamic oscillation-time sweep test was performed with AR1500 stress controlled rheometer at 32℃. The changes in shear storage modulus (G'), shear loss modulus (G''), loss tangent (tan δ ) and displacement were measured for twenty minutes and repeated three times for each material. The data were analyzed using one-way ANOVA and Tukey's post hoc test (α =0.05). Results: After mixing, all materials demonstrated an increase in G' with time, reaching the plateau in the end. RelyX U200 demonstrated the highest G' value, while RelyX Unicem (clicker type) and Variolink N demonstrated the lowest G' value at the end of experimental time. Tan δ was maintained at some level and reached the zero at the starting point where G' began to increase. The tan δ and displacement of the tested materials showed similar pattern in the graph within change of time. The displacement of all 6 materials approached to zero within 6 minutes. Conclusion: Compared to other resin cements used in this study, RelyX U200 maintained plastic property for a longer period of time. When it completed the curing process, RelyX U200 had the highest stiffness. It is convenient for clinicians to cement multiple units of dental prostheses simultaneously. (J Korean Acad Prosthodont 2014;52:82-9)

Effect of reduced exposure times on the cytotoxicity of resin luting cements cured by high-power led

ObjectiveApplications of resin luting agents and high-power light-emitting diodes (LED) light-curing units (LCUs) have increased considerably over the last few years. However, it is not clear whether the effect of reduced exposure time on cytotoxicity of such products have adequate biocompatibility to meet clinical success. This study aimed at assessing the effect of reduced curing time of five resin luting cements (RLCs) polymerized by high-power LED curing unit on the viability of a cell of L-929 fibroblast cells.Material and MethodsDisc-shaped samples were prepared in polytetrafluoroethylene moulds with cylindrical cavities. The samples were irradiated from the top through the ceramic discs and acetate strips using LED LCU for 20 s (50% of the manufacturer's recommended exposure time) and 40 s (100% exposure time). After curing, the samples were transferred into a culture medium for 24 h. The eluates were obtained and pipetted onto L-929 fibroblast cultures (3x104 per well) and incubated for evaluating after 24 h. Measurements were performed by dimethylthiazol diphenyltetrazolium assay. Statistical significance was determined by two-way ANOVA and two independent samples were compared by t-test.ResultsResults showed that eluates of most of the materials polymerized for 20 s (except Rely X Unicem and Illusion) reduced to a higher extent cell viability compared to samples of the same materials polymerized for 40 s. Illusion exhibited the least cytotoxicity for 20 s exposure time compared to the control (culture without samples) followed by Rely X Unicem and Rely X ARC (90.81%, 88.90%, and 83.11%, respectively). For Rely X ARC, Duolink and Lute-It 40 s exposure time was better (t=-1.262 p=0,276; t=-9.399 p=0.001; and t=-20.418 p<0.001, respectively).ConclusionThe results of this study suggest that reduction of curing time significantly enhances the cytotoxicity of the studied resin cement materials, therefore compromising their clinical performance.

Curing efficiency of various resin-based materials polymerized through different ceramic thicknesses and curing time

PURPOSEThe aim of this in vitro study was to examine the curing efficiency of various resin-based materials polymerized through ceramic restorations with 3 different thicknesses. Curing efficiency was evaluated by determining the surface microhardness (VHN) of the resin specimens.MATERIALS AND METHODSFour kinds of resin materials were used. Z350 (3M ESPE Filtek™ Z350: A2 Shade), Z250 (3M ESPE Filtek™ Z250: A2 Shade) and Variolink® II (VL: Ivoclar vivadent, base: transparent) either with or without a self-curing catalyst (VLC: Ivoclar vivadent, catalyst: low viscosity/transparent) were filled into the silicone mold (10 mm diameter, 1 mm thick). They were cured through ceramic discs (IPS e.max Press MO-0 ingot ivoclar vivadent, 10 mm diameter, 0.5, 1 and 2 mm thicknesses) by LED light-curing units for 20 and 40 seconds. Vicker's microhardness numbers (VHNs) were measured on the bottom surfaces by a microhardness tester. Data were analyzed using a 3- way analysis of variance (ANOVA) at a significance level of 0.05.RESULTSThe thickness of ceramic disc increased, the VHNs of all four resin types were decreased (P<.05). The mean VHN values of the resins light cured for 40 seconds were significantly higher than that of LED for 20 seconds in all four resin materials (P<.05). VLC showed significantly higher VHN values than VL regardless of other conditions (P<.05). Z350 and Z250 showed higher values than VL or VLC (P<.01).CONCLUSIONThinner ceramic disc with increased curing time resulted higher VHN values of all resin materials. The use of a catalyst produced a greater hardness with all polymerization methods. Restorative resin materials (Z350, Z250) showed higher VHN values than resin cement materials (VL, VLC).