Dual-cured Resin Research Articles

Effect of Different Nd:YAG Laser Power Outputs on Bond Strength of Resin Cement to Zirconia in Comparison to Sandblasting.

Introduction: This study investigated the effect of various laser powers on the shear bond strength (SBS) of resin cement to the zirconia surface. Methods: Seventy-five zirconia disks were prepared and assigned to five groups including no surface treatment (control group), sandblasting with 50 µ Al2 O3 particles (second group), and Nd:YAG laser treatments with 2 W, 2.5 W and 3 W powers respectively (third, fourth and fifth groups). Afterwards, composite resin cylinders were cemented on zirconia disks using dual-curing resin cement. Before thermocycling (2000 cycles, 5-55°C), all samples were placed in distilled water at 37°C for 24 hours. Using a universal testing machine at the crosshead speed of 0.5 mm/min, the SBS was examined. Also, using a stereomicroscope, the failure type was determined. Data analyses were performed using Welch and Games-Howell tests (P < 0.05). Results: The mean bond strength difference between the control group and the other groups was significant. The respective bond strength from the highest to the lowest was observed in the sandblast group, the laser group with 2.5 W power, the laser group with 3 W power, the laser group with 2 W power, and finally the control group. However, no significant difference was observed between different laser groups (P < 0.05). Also, there was no significant difference between the sandblast and laser groups with 2.5 W and 3 W power (P < 0.05). Most of the failures in the sandblasting and laser groups with powers of 2.5 W and 3 W were mixed, but in the control and 2 W laser groups, most of the failures were of adhesive nature. Conclusion: The highest bond strength was achieved by sandblasting with Al2 O3 particles and then using an Nd: YAG laser with a power of 2.5 W.

Compressive strength of lithium disilicate inlay cementation on three different composite resins

Background/purposeCeramic restorations have been increasingly applied over recent years. But the performance of cement is still unknown after cementation. This study was aimed to compare the compressive strength and the performances of three different types of composite resin after lithium disilicate inlay cementation. Materials and methodsTwenty-four human maxillary premolars were embedded in resin blocks, finished a MOD inlay preparation and scanned with an extraoral scanner. Lithium disilicate ceramic inlays (IPS e.max, Ivoclar Vivadent, Liechtenstein) were fabricated according to the scanner's model. All the specimens were then etched, bonded, and cemented with three different composite resins. Right after 5000 thermal cyclings, the specimens were accepted compressive tests to evaluate the compressive strength and failure types. Moreover, the fracture fragments of the specimens were examined using scanning electron microscopy (SEM) to verify the fracture type. ResultsDual-cured resin cement (Rely X Ultimate) showed the highest compressive strength (1002 ± 508 N), followed by the light-cured flowable resin (Z350 XT) (971 ± 209 N) and light-cured bulkfill (Filtek Bulkfill) resin (581 ± 191 N). Type IV (root fracture) failures in the dual-cured resin cement group was 25%, and light-cured flowable resin was 37.5%. But none of type IV fracture was found in the light-cured bulkfill flowable group. ConclusionDual-cured resin cement demonstrates the highest compressive strength after ceramic inlay cementation. Light-cured bulkfill resin shows the lowest compressive strength, but catastrophic failure is absent in this group.

Influence of feldspar ceramic thickness on the properties of resin cements and restorative set.

This in vitro study evaluated the influence of feldspathic ceramic thickness on the properties of light- and dual-cured resin cements. For each cement (RelyX Veneer, Allcem Veneer, RelyX Ultimate, and Allcem Dual), three ceramic specimens were prepared, with seven thicknesses for each (0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5mm). The degree of conversion, Vickers microhardness, irradiance power, color variation (ΔE00 ), and translucency parameters were assessed. Microhardness and irradiance power were analyzed using analysis of variance (ANOVA) with post hoc Tukey's test, while ΔE00 , translucency parameters, and degree of conversion were analyzed using ANOVA of ranks with post hoc Duncan's Multiple Range Test. The relationship between each of the dependent variables (degree of conversion, ΔE00 , and translucency parameter tests) and the specimen thickness was described using linear regression for each of the four resin cements. The significance level for all analyses was set at 5%. RelyX Ultimate yielded the lowest degree of conversion values among all resin cements. Allcem Veneer produced the lowest microhardness values, without statistical differences between thicknesses, of up to 1mm. Allcem Dual produced the highest ΔE00 and translucency parameter values. Feldspathic ceramic thickness influenced the mechanical properties of resin cements and optical aspects of the restorative set.

Comparison between Different Shades of Monolithic Zirconia over Microhardness and Water Solubility and Sorption of Dual-cure Resin Cement

To compare the different shades of monolithic zirconia over microhardness and water solubility and water sorption of dual-cure resin cement. Eighty specimens were included in the study. They were categorized into four categories having 20 samples each. Category one: No ceramic disks were present in the control group; the cement was directly activated. Category two: Curing of the resin cement with one shade of monolithic zirconia topping. Category three: Curing of the resin cement with an overlaying layer A monolithic zirconia version with two shades. Category four: Curing of the resin cement with an overlaying layer A three-tone monolithic zirconia version. In each category, two subgroups were further created (n = 10). One subgroup consisted of conventional dual-cure resin-based cement, while the other subgroup consisted of self-adhesive dual-cure resin-based cement. Vickers microhardness, water solubility, and water sorption of resin cement sorption were precisely measured after 24 hours of storage in an incubator at 37°C. The statistical analysis was undertaken with the help of statistical tests like two-way analysis of variations (ANOVA), one-way ANOVA, independent t-tests, Tukey's test, and Tamhane's T2 test. The p ≤0.05 was considered statistically significant. Microhardness was more excellent in conventional dual-cure resin-based cement in comparison with self-adhesive dual-cure cement. At the same time, the water solubility and water sorption were lower in conventional dual-cure resin-based cement than self-adhesive dual-cure resin cement. The effect of shade of monolithic variant of zirconia was significant over the microhardness of both dual-cure resin-based cement; however, the impact was nonsignificant over the water solubility and water sorption of the resin-based resin cement. Further, it was also observed that the use of a monolithic variant of zirconia led to a decrease in microhardness of both dual resin-based cement in comparison to the condition when no ceramics were used. The effect of shade of monolithic variant of zirconia was statistically significant over the microhardness of both dual-cure resin-based cement; however, the result was not significant over the water solubility and water sorption of the resin-based cement. The use of a monolithic variant of zirconia led to a decrease in the microhardness of both dual resin-based cement compared to the condition when no ceramics were used. The quantity of polymerization in resin-based cement affects their clinical effectiveness for a more extended period. It is believed that the measurement of microhardness is a reliable and straightforward process for evaluating the amount of polymerization of resin-based cement. Very few studies have been conducted in the past to compare the shades of monolithic zirconia over the microhardness, water solubility, and water sorption of the dual-cure resin-based cement.

Evaluation of microhardness and water sorption/solubility of dual-cure resin cement through monolithic zirconia in different shades.

Aim:The objective is to evaluate the effect of shades of monolithic zirconia on the microhardness and sorption/solubility of the underlying two dual-cured resin types of cement.Materials and Methods:Eighty samples of two dual-cured resin cement discs were polymerized under 60 monolithic zirconia discs in three shades and directly activated resin discs of cement were used as the control group (n = 10). After 24 h storage at 37°C in an incubator, Vickers microhardness and the sorption and solubility were measured.Statistical Analysis Used:Two-way ANOVA , one-way ANOVA, Independent t-test, Tukey's honestly significant difference, and Tamhane's T2 tests.Results:The mean microhardness of the Variolink N resin cements were significantly higher than Panavia SA ones (P < 0.001). Furthermore, Variolink N cements exhibited lower sorption/solubility than Panavia SA resin cements (both P < 0.05). The ceramic shade had a significant influence on the microhardness of both cements (P < 0.001) but had no significant effect on the sorption/solubility of resin cements (P > 0.05).Conclusion:Interposition of monolithic zirconia decreases the microhardness of resin cement especially Panavia SA. In Variolink N, by increasing the chroma saturation of ceramics, the microhardness decreased, however in Panavia SA, it was altered by the shades, but not in a specific pattern. For both cements, there were no statistical differences between the sorption/solubility of samples photo-cured under different shades. There was a reverse correlation between microhardness and water sorption/solubility of both cements.

Microhardness of resin cements after light activation through various translucencies of monolithic zirconia.

PURPOSEThis study aimed to investigate the Vickers Hardness Number (VHN) of light- and dual cured resin cements cured through monolithic zirconia specimens (VITA YZ) of various translucencies: translucent (T); high translucent (HT); super translucent (ST); and extra translucent (XT) at 0, 24, and 48 h after curing.MATERIALS AND METHODSFour zirconia specimens from each translucency were prepared. Two light-cured resin cements (Variolink N LC; VL and RelyX Veneer; RL) and two dual-cured resin cements (Variolink N DC; VD and RelyX U200; RD) were used. The cement was mixed and loaded in a mold and cured for 20 s through the zirconia specimen. The upper surface of cements was tested for VHN using a microhardness tester at 0, 24, and 48 h after curing. The VHN were analyzed using two-way repeated, Brown-Forsythe ANOVA with Games Howell post-hoc analysis and independent t-tests (P < .05).RESULTSAll cements showed significantly higher VHN from 0 h to 24 h (P < .001). At 48 h, the VHN of light-cured cements were significantly lower when cured under the T groups than under XT groups (P = .001 in VL, P = .014 in RL). At each post curing time of each translucency, VD showed higher VHN than VL (P < .05), and RD also showed higher VHN than RL (P < .05).CONCLUSIONThe translucency of zirconia has an effect on the VHN for light-cured resin cements, but has no effect on dual-cured resin cements. Dual-cured resin cement exhibited higher VHN than the light-cured resin cement from the same manufacturer. All resin cements showed significantly higher VHN from 0 h to 24 h.

Diagnosis and treatment of dens invaginatus with open apex in a young adult patient by using cone-beam computed tomography and operative microscope.

Dens invaginatus is a developmental anomaly that can affect both deciduous and permanent dentition. The anomaly is caused by the invagination of the enamel organ into the dental papilla prior to the calcification of the dental tissues. The treatment option changes according to the classification, from the simple filling of the invaginated enamel area to root canal treatment with or without retrograde surgery, intentional re-implantation, or the extraction of the affected tooth. In this study we report a case of a maxillary lateral incisor invaginatus in a young adult patient. The periapical endoral X-ray showed the presence of a periapical radiolucency in tooth 22, that had a structure similar to a tooth inside it and an immature apex. Cold thermal testing showed that it was not a vital tooth. CBCT confirmed the diagnosis of Oehler Class II dens invaginatus. The treatment plan involved root canal treatment of both the "true" and the "invaginated" canal using calcium hydroxide-based intermediate medication. Then, after removing the hard internal structure with the aid of an operative microscope, MTA was used to close the immature apex. Finally, the large endodontic space was filled with self-etching, self-adhesive, dual curing resin cement. The patient was included in a follow-up programme to monitor and verify the complete healing of the periapical bone of the affected tooth. The use of technology and of special materials allowed an adequate management and resolution of the case reported.

A comparative evaluation of colour stability of different resin cements and its influence on the final shade of All-Ceramic Restorations: An in-vitro Study.

Colour changes of the luting material can become clinically visible affecting the aesthetic appearance of thin ceramic veneers. Therefore, unfortunately, the long-term success of veneers is tied to the colour stability of the luting agent used to cement them. To compare the colour stability of different resin cements and its influence on the final shade of overlying ceramic using two different thicknesses of ceramic. Sixty disc-shaped specimens of high translucency (HT) A2 shade of two thicknesses (0.5 mm & 1 mm) were prepared from lithium disilicate glass-ceramic. The discs of each thickness were further divided into three groups randomly depending upon the resin cements used. Group A - light cure resin cement - Variolink N LC by Ivoclar Vivadent in clear shade, Group B - base paste of dual-cure resin cement - Variolink N by Ivoclar Vivadent in transparent shade and Group C dual-cure resin cement - Clearfil esthetic cement EX by Kuraray in clear shade were used to compare their colour stability. A spectrophotometer was used for the colour measurements of the specimens before and after accelerated ageing. The colour stability was determined by colour differences (ΔE) using the coordinates L*, a* and b* in the pre and post accelerated ageing. Results: On comparing the three resin cements, Group A showed the lowest ΔE, whereas the highest ΔE was observed in Group B. This finding was constant for discs of both thicknesses. Even though statistically significant results were observed between the groups, they were not visibly differentiable.

The Effect of the Shade of Indirect Restorations on the Microtensile Bond Strength of Dual-curing Resin Cements Using a Touch-cure System to Dentin

The Effect of the Shade of Indirect Restorations on the Microtensile Bond Strength of Dual-curing Resin Cements Using a Touch-cure System to Dentin

Lack of Neutralization of 10-MDP Primers by Zirconia May Affect the Degree of Conversion of Dual-cure Resin Cement.

Use of zirconia primers with a low pH and a high acidic monomer concentration should be employed in combination with dual-cure resin cements that are less sensitive to an acidic environment. Primers with lower 10-MDP concentrations attain better outcomes.

Comparative evaluation of effect of One Coat 7 Universal and Tetric N-Bond Universal adhesives on shear bond strength at resin-zirconia interface: An in vitro study.

Background:Success of all-ceramic restorations depends on their cementation process. Bonding crystalline materials like zirconia to an underlying substrate is challenging. Recently, universal adhesives have been developed. They claim to chemically bond to zirconia due to the presence of compounds like 10-methacryloyloxydecyl dihydrogen phosphate. But for majority of these adhesives, few studies demonstrating their effectiveness are available.Aims:This study aimed to assess the effect of two universal adhesives, One Coat 7 Universal and Tetric N-Bond Universal on shear bond strength at zirconia–resin junction.Materials and Methods:Thirty CAD-CAM milled zirconia cylinders (5 mm × 8 mm) were sandblasted and divided into three groups: Group A (control) received no treatment, while Groups B and C were primed by One Coat 7 Universal and Tetric N-Bond Universal, respectively. They were luted to composite surfaces by a dual-curing resin cement. After 24 h, a shear bond strength test was conducted and failure mode was analyzed.Statistical Analysis:One-way analysis of variance and post hoc Tukey's test were used for statistical analysis.Results:Both One Coat 7 Universal (24.43 ± 2.66 MPa) and Tetric N-Bond Universal (28.61 ± 3.11 MPa) had significantly higher strength than the control group (9.86 ± 2.00 MPa). Control group underwent 100% adhesive failures. Experimental groups had predominantly mixed/cohesive failures.Conclusion:Both universal adhesives increased the bond strength at resin–zirconia junction. Tetric N-Bond Universal exhibited the highest strength.

Effect of Different Surface Treatments on Retention of Cement-Retained, Implant-Supported Crowns

To evaluate the effect of different treatments applied to titanium implant abutment surfaces on the retention of implant-supported cement-retained crowns using resin cement. A total of 72 titanium implant abutments were divided into six groups (n = 12 each) based on the selected surface treatments: (1) untreated; (2) airborne particle abrasion; (3) hydrogen peroxide etching; (4) atmospheric plasma; (5) chemical mechanical polishing; and (6) titanium dioxide (TiO2) nano coating. After the surface treatments, scanning electron microscopy analyses and surface roughness measurements of the abutment surfaces were performed. Seventy-two metal copings were fabricated and cemented on the abutments with dual-curing resin cement. After a thermal cycling process, crown retention was measured using a universal testing machine. The experimental results were statistically evaluated with one-way analysis of variance, Tukey honest significant difference, and Tamhane's T2 tests. The highest surface roughness values were obtained with the airborne-particle abrasion group (1.44 μm), which also resulted in the highest retention values (828.5 N), followed by the hydrogen peroxide-etching group (490.7 N), the atmospheric plasma group (466.5 N), the chemical mechanical polishing group (410.8 N), and the control group (382.6 N). It was determined that airborne particle abrasion, hydrogen peroxide etching, and atmospheric plasma treatments significantly increased the crown retention and that all alternative treatments, except for TiO2 nano coating, worked better than the untreated control.

Immediate and long-term microshear bond strength of resin-based cements to core build-up materials.

BackgroundTo evaluate the microshear bond strength (μ-SBS) between resin-based cements and core build-up materials after water storage. Material and MethodsCylinders (1x1 mm) of conventional dual-cure resin cement (RelyX ARC, 3M ESPE), universal dual-cure resin cement (RelyX Ultimate, 3M ESPE) or self-adhesive resin cement (RelyX U200, 3M ESPE) were adhered to disks (6x2 mm) made with commercial core build-up materials (Bis-Core, Bisco or LuxaCore Z, DMG) or conventional nanocomposite resin (Filtek Z350 XT, 3M ESPE). The specimens (n=10) were submitted to μ-SBS test using a universal testing machine and fracture pattern analysis at 48 hours or after 9 months of water storage. The data were evaluated by three-way ANOVA for repeated measures and Tukey’s test (α=0.05). ResultsAfter 48 hours, regardless of the resin-based cement used, the μ-SBS to the conventional resin composite (Filtek Z350 XT) was greater compared to other materials. However, after 9 months, there was a statistically significant decrease in μ-SBS values between the conventional resin composite and evaluated luting agents. The μ-SBS values of core build-up commercial materials (Bis-Core and LuxaCore Z) did not change over time. Regardless of the composite used and storage time, there was no statistically significant difference between the resin-based cements. After 48 h, the most prevalent failure was mixed for all groups. However, after 9 months, the core build-up materials showed a predominantly mixed fracture pattern whereas the resin composite presented an adhesive pattern. ConclusionsCommercial core build-up materials achieved stable bonding performance with resin-based cements over time. Key words:Composite resins, resin cement, dental restoration failure.

Microshear bond strength of dual-cure resin cement in zirconia after different cleaning techniques: an in vitro study.

PURPOSEThis study aimed to compare the microshear bond strength (µSBS) of dual-cure resin cement in CAD-CAM zirconia after different cleaning techniques.MATERIALS AND METHODSFifty discs of zirconia-based ceramic from Ivoclar Vivadent were embedded in acrylic resin. The discs were divided into five groups according to the cleaning methods used: Group 1: drying with spraying + sandblasting with Al2O3; Group 2: washed with water and dried with spraying + sandblasting with Al2O3; Group 3: washed with distilled water and dried with spraying + sandblasting with Al2O3 + zirconium oxide (Ivoclean); Group 4: washed with distilled water and dried with spraying + sandblasting with Al2O3 + potassium hydroxide (Zirclean); and Group 5: washed with distilled water and dried with spraying + sandblasting with Al2O3 + 1% NaClO. All of the groups were contaminated with artificial saliva for 1 minute and then cleaned. Statistical analyses were performed using ANOVA and Tukey's tests. RESULTSThere were statistically significant differences among all groups for µSBS (P < .05). The group treated with zirconium oxide (Group 3) showed the highest µSBS (18.75 ± 0.23 MPa).CONCLUSIONWhen applied to zirconia, the cleaning methods affected the bonding with resin cement differently.

Effect of aging on color stability of amine-free resin cement through the ceramic laminate veneer.

Background:This study aimed to assess the color change of two amine-free dual-cure resin cements following aging in comparison with a light-cure resin cement.Materials and Methods:This in vitro, experimental study evaluated 6 groups (n = 10), including three groups of cements bonded to feldspathic porcelain and three groups of resin cements alone. Panavia V5 (Kuraray) and G-CEM LinkForce (GC) dual-cure resin cements and Choice 2 (Bisco) light-cure resin cements were bonded to porcelain according to the manufacturers’ instructions. The color parameters of the groups were measured before and after 5000 thermal cycles by spectrophotometry. Data were analyzed using two-way ANOVA and Tukey's post hoc test (α =0.05).Results:The color change (ΔE) of the cement groups alone was significantly greater than that of porcelain-bonded cements. The ΔE of G-CEM LinkForce cement group was significantly higher than that of Panavia V5 group (P = 0.020), and the ΔE of the latter group was significantly higher than that of Choice 2 cement group (P = 0.021).Conclusion:Considering the color change of cements evaluated in this study, Choice 2 and Panavia V5 cements bonded to porcelain showed acceptable color change, which indicates that they are suitable for cementation of esthetic dental restorations. Ceramic laminates have become an ideal esthetic treatment for anterior restorations. The resin cement discoloration can affect final appearance of these restorations. Besides that, exposed resin cement line can lead to the esthetic problem over time.

Evaluation of different custom angulated elastic glass fibre post on fracture resistance of maxillary central incisor: an in vitrostudy

Background: Restoring Endodontically treated teeth (ETT) can be challenging for most dentists, particularly when a significant tooth structure is lost. Depending on the coronal tooth structure remaining and the technique used (direct or indirect), endodontic anchorage can involve either a cast post and core or a prefabricated post. Aim: This study aimed to investigate the effect of different custom angulated, i.e.,0°,5°,10°,15° elastic glass fibre post (Everstick post) on fracture resistance of maxillary central incisors. Materials and methods: A total of forty-eight single-rooted maxillary central incisors were selected. All the samples were decoronated 2mm above the CEJ and endodontically treated. Post-space preparation was done for all the samples using peesoreamers ranging in size from 1-3. The samples were then randomly divided into four groups (n=12) based on the different angulations, i.e., the angle between the core and the long axis of the root, with 0°, 5°, 10°, and 15° angulations, respectively. The fit of each post in the root canal was verified. Before cementation, the coronal part of each post was bent according to their respective groups. Dual-cure resin cement was used for luting the posts and cured subsequently. The fracture resistance of all the samples was evaluated using the universal testing machine after they were mounted in self-cure acrylic resin blocks. The data were analysed using One- way ANOVA and Tukey’s post-hoc test. Results: Group I exhibited the highest mean fracture resistance compared to other groups. However, One-way ANOVA showed no significant differences (p=0.161) between the four groups. Conclusion: Everstick fibre posts are a preferable alternative for maxillary central incisors with core angulations up to 15° between coronal and radicular segments as they provide better fracture resistance with a more favourable stress distribution.

Fracture Resistance of Lithıum Disilicate, Indirect Resin Composite and Zirconıa by Using Dual Cure Resin Cements

Objective: The aim of the study was to examine the fracture resistance of lithium disilicate, indirect resin composite and zirconia by using dual cure resin cements.Methods: Three groups of 180 samples (n= 60) of E-max, zirconia and indirect resin composite materials (10mm diameter and 1 mm thickness). Discs were fabricated and cemented with three dual curing resin cements. Aging treatment was then applied to the discs by using thermal cycle machine (at 5°C to 55°C/dwell time: 20s), 10000 cycles for 168 hours’ 7 days. Fracture tests were performed to the sample discs using piston on three balls test to determine the biaxial flexure strength of the 180 discs of the three materials. The results were analysed by using one-way analysis of variance (ANOVA) and t-test.Results: Statistically significant difference was found between control groups (before cementation and thermal cycle) and both group B (after cementation before thermal cycle) and group C (after cementation and thermal cycle) in all materials (P&amp;lt;0.05). Comparing Zirconia, Gradia and E-max all control groups showed statistically significant difference and Zirconia was showed greater flexural resistance against other materials. In addition, all materials also showed statistically significant difference in Variolink/Multilink cemented Group B and C. In Nexus cemented Group B and C statistically significant difference was found only Zirconia material. Similar to control group results, Zirconia material was showed greater flexural resistance values with both cements in Group B and C.Conclusion: There is a difference between flexural strength of the three materials, Zirconia has a better flexural strength when compared to lithium disilicate and indirect resin composite.

Effect of Adhesive Gap Setting on Fracture Resistance of All-ceramic Crowns

Background:Several factors might affect the fracture resistance of all-ceramic crowns, including cement thickness.Aim:To evaluate the influence of cement thickness on the fracture resistance.Objective:To determine the effect of varying the adhesive gap thickness on the fracture loads of all-ceramic CEREC 3D molar crowns.Methods:Standardized prepared epoxy resin molar dies (Viade Inc.) were fabricated. A standard molar crown was designed using a CEREC 3D machine (Sirona Dental Systems). Twenty-four crowns were milled from Vita Mark II blocks (Vita Zahnfabrik), using adhesive gap settings of 30, 60 and 90 µm (n=8). A dual-cure resin cement (PanaviaF 2.0, Kuraray) was used to cement the crowns to their respective dies, following manufacturer's recommendation. After 1 week of storage in distilled water at 37°C, each crown was loaded in compression until complete failure in a universal testing machine (Instron 8501) and fracture loads (N) were recorded. Fractured specimens were sectioned to determine cement thickness. Sections were examined using a traveling light microscope to measure cement thickness. Data were statistically analyzed using one-way ANOVA test and Pearson's correlation at (α=0.05).Results:The mean fracture loads and standard deviation values in N were 1,267.57 (122.82), 1,225.20 (179.46) and 1,180.76 (161.77) for the crowns with 30, 60 and 90µm, respectively. ANOVA indicated no significant differences among mean fracture strength values (p= 0.55). All crowns failed in a catastrophic mode and were not repairable.Conclusions:Adhesive cement gap as achieved with three CEREC 3D settings from 30 to 90µm had no significant effect on fracture strength of crowns made from Vita Mark II blocks.

Masking of High-Translucency Zirconia for Various Cores.

Various core materials with different shades affect the final color of high-translucency monolithic zirconia restorations. The blue core shows the greatest color difference in final zirconia restorations followed by metal, A3 dentin-shade resin core, and white core. The purpose of this study was to evaluate the masking ability of high-translucency monolithic zirconia for various core materials. A computer-aided design-computer-aided manufacturing system was used to design a zirconia disc with a diameter of 10 mm and a thickness of 1.0 mm. Four groups of cores (n=15 each) were fabricated with blue-colored dual-cure resin, white-colored dual-cure resin, A3 dentin-shade composite resin, and titanium block with 10-mm diameter and 5-mm thickness.Dual-cure, self-adhesive resin cement discs with a thickness of 25.0 ± 0.02 μm were fabricated. The color was measured using a handheld spectrophotometer. Color measurements of all specimens were performed on a white background. To assess the masking ability of zirconia, the difference between the values measured with zirconia on a white background and the values measured with zirconia on each of the four types of core material as a background with the cement specimens interposed (zirconia + cement + core) was determined. To enhance the optical connection between the specimens, distilled water was applied between each layer during each measurement.The results showed that the value of ΔE was highest for the blue core followed by metal, A3 dentin-shade resin core, and white-resin core. No significant differences were observed between the metal core and the A3 dentin-shade resin core or between the A3 dentin-shade resin core and the white core. The blue core had the significantly highest ΔE value based on Tukey's honest significant difference test.Different core materials affect the final color of high-translucency monolithic zirconia restorations. Thus, our study showed that the final color of high-translucency monolithic zirconia restorations could be affected by the type of core material used.

Mechanical Properties of Nanohybrid Resin Composites Containing Various Mass Fractions of Modified Zirconia Particles.

PurposeThe aim of this study was to investigate the effect of various mass fractions of 10-methacry-loyloxydecyl dihydrogen phosphate (MDP)-conditioned or unconditioned zirconia nano- or micro-particles with different initiator systems on the mechanical properties of nanohybrid resin composites.MethodsBoth light-cured (L) and dual-cured (D) resin composites were prepared. When the mass fraction of the nano- or micro-zirconia fillers reached 55 wt%, resin composites were equipped with dual-cured initiator systems. We measured the three-point bending-strength, elastic modulus, Weibull modulus and translucency parameter of the nanohybrid resin composites containing various mass fractions of MDP-conditioned or unconditioned zirconia nano- or micro-particles (0%, 5 wt%, 10 wt%, 20 wt%, 30 wt% and 55 wt%). A Cell Counting Kit (CCK)-8 was used to test the cell cytotoxicity of the experimental resin composites. The zirconia nano- or micro-particles with MDP-conditioning or not were characterized by transmission electron microscopy (TEM), Fourier infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS).ResultsResin composites containing 5–20 wt% MDP-conditioned or unconditioned nano-zirconia fillers exhibited better three-point bending-strength than the control group without zirconia fillers. Nano- or micro-zirconia fillers decreased the translucence of the nanohybrid resin composites. According to the cytotoxicity classification, all of the nano- or micro-zirconia fillers containing experimental resin composites were considered to have no significant cell cytotoxicity. The FTIR spectra of the conditioned nano- or micro-fillers showed new absorption bands at 1719 cm−1 and 1637 cm−1, indicating the successful combination of MDP and zirconia particles. The XPS analysis measured Zr–O–P peak area on MDP-conditioned nano- and micro-zirconia fillers at 39.91% and 34.89%, respectively.ConclusionNano-zirconia filler improved the mechanical properties of nanohybrid resin composites, but cannot be the main filler to replace silica filler. The experimental dual-cured composites can be resin cements with better opacity effects and a low viscosity.