Influence of veneering composite composition on the efficacy of fiber-reinforced restorations (FRR)

This study investigated the influence of fiber reinforcement on the flexural properties of four commercial (Artglass, Belleglass HP, Herculite XRV and Solidex) veneering composites (Series A) and two experimental composites (Series B&C). This study investigated how the composition of the veneering composites influenced the enhancement of strength and modulus produced by fiber reinforcement. The formulation of the experimental composites were varied by changing the filler load (Series B) or the resin matrix chemistry (Series C) to assess the effect these changes would have on the degree of reinforcement. In Series A, the commercial veneering composites were reinforced by an Ultra-High-Molecular-Weight Polyethylene fiber (UHMW-PE/Connect) to evaluate flexural properties after 24 hours and six months. In Series B, experimental composites with the same organic matrix but with different filler loads (40% to 80% by weight) were also reinforced by Connect fiber to evaluate flexural properties. In Series C, experimental composites (Systems 1-4) with the same filler load (76.5% by weight) but with different organic matrix compositions were reinforced by Connect fiber to evaluate flexural properties. For Series B and C, flexural properties were evaluated after 24 hours water storage. All the samples were prepared in a mold 2 mm x 2 mm x 25 mm and stored in distilled water at 37 degrees C until they were ready for flexural testing in an Instron Universal Testing Machine using a crosshead speed of 1 mm/minute. The results showed no significant differences in the flexural strength (FS) between any of the commercial reinforced composites in Series A. The flexural modulus (FM) of the fiber-reinforced Belleglass HP group was significantly higher than for Artglass and Solidex. Water storage for six months had no significant (p>0.05) effect on the flexural strength of three of the four reinforced veneering composites. The flexural strength for Artglass was significantly reduced (p<0.05) by six-month water storage. In Series B, however, increasing the amount of filler loading improved the flexural modulus of the reinforced experimental composite but had no effect on its flexural strength. In Series C, changing the organic matrix formulation had no affect on flexural strength but affected the flexural modulus of the reinforced experimental composite.     

Intra‐oral adhesive systems for ceramic repairs: a comparison

The aim of this investigation was to compare the bond strength of restorative composite resin to dental ceramic conditioned with primers and adhesives of various commercial repair kits. Three intra‐oral ceramic repair systems—Silistor (Heraeus Kulzer), Cimara (Voco), Ceramic Repair (Vivadent)—were used on all‐ceramic (IPS Empress 2, Ivoclar‐Vivadent) substrate. Shear bond strength of restorative composite resin to substrate was tested after thermocycling and without thermocycling (n=10). Substrate surfaces of the specimen after loading were examined microscopically (SEM). The highest bond strengths in both water‐stored (7.0±5.7 MPa) and thermocycled conditions (2.5±1.8 MPa) were obtained with the Vivadent repair system, while the lowest values were observed with the Cimara system (0.6±1.4 MPa and 0.0±0.0 MPa, respectively). Shear bond strengths appeared to be significantly affected by thermocycling (ANOVA, P<0.05). It is concluded that there are significant differences in the bond strengths of resin composites and ceramic substrate. The roughened surface does not necessarily provide a better bond strength; the bond strength of composite decreases with storage in water and after thermocycling. Bond strength values were generally low for all of the tested materials.     

The effects of thermocycling on the flexural strength and flexural modulus of modern resin-based filling materials

OBJECTIVE: Evaluation of flexural strengths and flexural moduli of hybrids, packables, ormocers, compomers and flowables prior to, and after, thermocycling. MATERIALS AND METHODS: Twenty specimens, size (25 +/- 2) mm x (2 +/- 0.1) mm x (2+/-0.1) mm, of Herculite (HE), Point 4 (P4), TetricCeram (TC), Miris (MI), TetricCeram HB, (HB), Solitaire 2 (SO), Surefil A (SU), Definte (DE), Admira (AD), Dyract AP (DY), Compoglass (CO) and TetricFlow (TF) were made according to ISO 4049. A three-point-bending test was carried out for the first 10 specimens after 24 h water storage at 37 degrees C and for the second 10 specimens after 30-day water storage at 37 degrees C, followed by 5000 thermocycles between +5 and +55 degrees C. For each test series flexural strengths and flexural moduli were calculated. Statistical significance was p < 0.05. RESULTS: Flexural strengths of DY and CO missed the 80 MPa limit of ISO 4049 for occlusal fillings prior to and after thermocycling. AD missed it after thermocycling. HE, P4, TC, MI, HB, SO, SU, DE and TF did not significantly differ prior to and after thermocycling. Flexural strength of SO and AD significantly decreased after thermocycling. No change of the flexural moduli could be observed for any of the test materials. Only SU exceeded 10,000 MPa prior to and after thermocycling. SIGNIFICANCE: Only DY and CO missed the flexural strength limit of ISO 4049 for occlusal fillings. Only SU exceeded a flexural modulus of 10,000 MPa prior to and after thermocycling.     

The effect of core material, veneering porcelain, and fabrication technique on the biaxial flexural strength and weibull analysis of selected dental ceramics

Purpose: The objective of this study was to compare the effect of veneering porcelain (monolithic or bilayer specimens) and core fabrication technique (heat‐pressed or CAD/CAM) on the biaxial flexural strength and Weibull modulus of leucite‐reinforced and lithium‐disilicate glass ceramics. In addition, the effect of veneering technique (heat‐pressed or powder/liquid layering) for zirconia ceramics on the biaxial flexural strength and Weibull modulus was studied. Materials and Methods: Five ceramic core materials (IPS Empress Esthetic, IPS Empress CAD, IPS e.max Press, IPS e.max CAD, IPS e.max ZirCAD) and three corresponding veneering porcelains (IPS Empress Esthetic Veneer, IPS e.max Ceram, IPS e.max ZirPress) were selected for this study. Each core material group contained three subgroups based on the core material thickness and the presence of corresponding veneering porcelain as follows: 1.5 mm core material only (subgroup 1.5C), 0.8 mm core material only (subgroup 0.8C), and 1.5 mm core/veneer group: 0.8 mm core with 0.7 mm corresponding veneering porcelain with a powder/liquid layering technique (subgroup 0.8C‐0.7VL). The ZirCAD group had one additional 1.5 mm core/veneer subgroup with 0.7 mm heat‐pressed veneering porcelain (subgroup 0.8C‐0.7VP). The biaxial flexural strengths were compared for each subgroup (n = 10) according to ISO standard 6872:2008 with ANOVA and Tukey's post hoc multiple comparison test (p≤ 0.05). The reliability of strength was analyzed with the Weibull distribution. Results: For all core materials, the 1.5 mm core/veneer subgroups (0.8C‐0.7VL, 0.8C‐0.7VP) had significantly lower mean biaxial flexural strengths (p < 0.0001) than the other two subgroups (subgroups 1.5C and 0.8C). For the ZirCAD group, the 0.8C‐0.7VL subgroup had significantly lower flexural strength (p= 0.004) than subgroup 0.8C‐0.7VP. Nonetheless, both veneered ZirCAD groups showed greater flexural strength than the monolithic Empress and e.max groups, regardless of core thickness and fabrication techniques. Comparing fabrication techniques, Empress Esthetic/CAD, e.max Press/CAD had similar biaxial flexural strength (p= 0.28 for Empress pair; p= 0.87 for e.max pair); however, e.max CAD/Press groups had significantly higher flexural strength (p < 0.0001) than Empress Esthetic/CAD groups. Monolithic core specimens presented with higher Weibull modulus with all selected core materials. For the ZirCAD group, although the bilayer 0.8C‐0.7VL subgroup exhibited significantly lower flexural strength, it had highest Weibull modulus than the 0.8C‐0.7VP subgroup. Conclusions: The present study suggests that veneering porcelain onto a ceramic core material diminishes the flexural strength and the reliability of the bilayer specimens. Leucite‐reinforced glass‐ceramic cores have lower flexural strength than lithium‐disilicate ones, while fabrication techniques (heat‐pressed or CAD/CAM) and specimen thicknesses do not affect the flexural strength of all glass ceramics. Compared with the heat‐pressed veneering technique, the powder/liquid veneering technique exhibited lower flexural strength but increased reliability with a higher Weibull modulus for zirconia bilayer specimens. Zirconia‐veneered ceramics exhibited greater flexural strength than monolithic leucite‐reinforced and lithium‐disilicate ceramics regardless of zirconia veneering techniques (heat‐pressed or powder/liquid technique).     

Strength and elastic modulus of fiber-reinforced composites used for fabricating FPDs

PURPOSE: The purpose of this study was to examine the flexural strength and elastic modulus of a new fiber-reinforced composite used for the fabrication of inlay-retained fixed partial dentures (FPD). MATERIALS AND METHODS: A total of six materials were used: Vectris, FibreKor, and an experimental material, BR-100, were the types of glass fiber preimpregnated with resin used for making the frameworks; Targis, Sculpture, and Estenia were used as the veneering composites. Five specimens of each material were prepared. Flexural strength and elastic modulus were determined using the three-point bending test. In addition, laminate specimens were fabricated by combination of the veneering composite and framework materials (Targis/Vectris, Sculpture/FibreKor, and Estenia/BR-100), and fracture loads of these specimens were determined. Laminate specimens were fabricated with three different framework thicknesses for Estenia/BR-100. RESULTS: Estenia had the greatest strength and highest modulus of elasticity of the veneering composites. All three framework materials had flexural strength values (567 to 686 MPa) more than three times as great as those of the veneering composites (132 to 193 MPa). Of the laminate specimens, the Estenia/BR-100 with a framework thickness of 1.0 mm had a fracture load more than 50% greater than Targis/Vectris and Sculpture/FibreKor. CONCLUSION: The combination of the experimental framework material BR-100 and the composite Estenia showed higher fracture loads than the other combinations tested.     

Bis-(acrylamide)s as new cross-linkers for resin-based composite restoratives

OBJECTIVES: The objective of this study was to investigate the use of three new bis-(acrylamide)s as cross-linker in resin-based composite restoratives. Selected mechanical properties such as flexural strength and flexural modulus of model composites containing bis-(acrylamide)s were investigated and compared to the properties of composites that are based on only conventional dimethacrylates. In addition, the hydrolytic stability of composites containing an acidic monomer was examined. METHODS: The flexural strength and flexural modulus of elasticity were determined according to ISO 4049:2000. For this purpose, test specimens (2 mm x 2 mm x 25 mm) of the composites investigated were prepared in stainless steel moulds and light-cured (150 mW/cm2, 2 x 180 s). The flexural strength and flexural modulus were measured after the samples had been stored in dry conditions or in water for 24 h at 37 degrees C as well as after they had been stored in water for 7 days at 37 degrees C, and in certain cases, after they had been boiled for 24 h in water. RESULTS: Visible light cured mixtures of dimethacrylates with bis-(acrylamide)s and composites based on these mixtures show a similar reactivity, flexural strength and flexural modulus of elasticity compared to materials that contain only dimethacrylate. The composites did not show any deterioration of the mechanical properties after water storage. Only when strongly acidic monomers were added to the composites containing dimethacrylates or bis-(acrylamide)s did the flexural strength and flexural modulus of the samples decrease after they were stored in water. SIGNIFICANCE: Bis-(acrylamide)s were similarly reactive than dimethacrylates and therefore can be used as diluents to substitute dimethacrylate diluents in composites. Although the bis-(acrylamide)s are entirely soluble in water, non-ionic materials based on bis-(acrylamide)s did not strongly change their mechanical properties during storage in water.     

Influence of artificial aging on the fracture strength and stiffness of Targis/Vectris fixed partial dentures.

OBJECTIVE: To evaluate the effect of artificial aging on the fracture strength and stiffness of fiber-reinforced composite fixed partial dentures (FPDs). METHOD AND MATERIALS: Twelve FPDs were replicated using Targis/Vectris resin composite (Ivoclar Vivadent) and randomly divided in 2 groups. Group A was artificially aged for 900 hours in a weathering machine using dry/wet cycles and 534 W/m2 irradiations with wavelengths ranging from 300 to 800 nm. Group B (control) was stored in 100% relative humidity at 37 degrees C +/- 1 degree C for 900 hours. The FPDs were luted on metal abutments with Variolink II resin cement (Ivoclar Vivadent). The flexure stress was applied on the pontic at a descending speed of 1.0 mm/min until complete failure. Fracture strength, stiffness, and number of cracks produced on the FPDs were statistically analyzed. RESULTS: Targis veneering material in the control group fractured at a mean of 913 +/- 130 N, whereas in the aged group it failed at a mean of 722 +/- 154 N (P = .042). The mean fracture load of aged FPD frameworks was slightly lower than that of the controls: 1,532 +/- 237 N and 1,578 +/- 257 N, respectively (P = .758). The stiffness at 400 N was not significantly different between the 2 groups. The number of cracks at Targis failure was higher in aged groups. CONCLUSION: Accelerated aging significantly reduced the strength of the Targis veneering composite, increasing its brittleness; however, it had no effect on the inner Vectris framework.     

Effect of fiber position and orientation on fracture load of fiber-reinforced composite

OBJECTIVES: The aim of this study was to determine the effect of fiber position and orientation on the initial and final fracture loads of fiber-reinforced composite (FRC). METHODS: Test specimens made of two indirect particulate composites (BelleGlass HP, Kerr, Orange, CA) or (Targis, Ivoclar Vivadent, Amherst, NY) were reinforced with ultra high molecular weight polyethylene (UHMWPE) fiber ribbon (Connect, Kerr, Orange, CA), woven E-glass fibers (Vectris Frame, Ivoclar Vivadent, Amherst, NY) or unidirectional R-glass fibers (Vectris Pontic, Ivoclar Vivadent, Amherst, NY). Fibers were placed with different positions, orientations or geometry into the rhombic test specimens (2 x 2 x 25 mm3). Control specimens did not contain fiber reinforcement. The test specimens (n=6) were stored in distilled water for 1 week at 37 degrees C before testing in a three-point loading test to determine the initial and final fracture load values. RESULTS: Initial failure loads varied from 22.6 to 172.1 N. The lowest value resulted from one UHMWPE reinforcement fiber located in diagonal orientation and the highest from two unidirectional glass fiber reinforcements, one located on the tension side and the second on the compression side. SIGNIFICANCE: Position and fiber orientation influenced the load to initial and final failure, and specimen deflection. Tension side reinforcement was most effective in increasing the load to initial and final fracture.     

Effect of silanization on bond strengths of fiber posts to various resin cements.

OBJECTIVES: To investigate the effects of pretreatment (silanization) on bond strengths between 3 different types of fiber posts and 4 resin cements, respectively. METHOD AND MATERIALS: Prefabricated quartz-fiber (Unicore Post, Ultradent) and prefabricated glass-fiber (FRC Postec, Ivoclar Vivadent) posts with a cross-linked polymer matrix and individually formed glass-fiber posts with an interpenetrating polymer network (IPN Post, Stick Tech) (n = 160 each) were inserted into resin composite disks (2 mm thick) using the following resin cements and silane solutions: Panavia F/Porcelain Bond Activator (Kuraray), PermaFlo DC/Silane (Ultradent), Variolink II/Monobond S (Ivoclar Vivadent) and RelyX Unicem/Espe Sil (3M Espe). Nonsilanated posts served as controls. The push-out bond strengths were determined before (n = 10) and after (n = 10) thermocycling (2,000 cycles, 5 degrees C to 55 degrees C, dwelling time 30 seconds). RESULTS: Bond strengths (mean [SD]) were significantly affected by the resin cement (P < .001), the pretreatment (P < .001), and the type of post (P < .001), but not by thermocycling (P = .955, 4-way ANOVA). The IPN post demonstrated significantly higher bond strengths compared to the other posts (P < .05; Tukey B). Silanization significantly increased bond strengths (15.2 [5.2] MPa) compared to those of the control groups (13.9 [4.9] MPa). CONCLUSION: The type of fiber post revealed a significant influence on bond strengths, whereas the effects of silanization appeared to be clinically negligible.     

Benzoyl germanium derivatives as novel visible light photoinitiators for dental materials.

OBJECTIVES: The objective of this study was to investigate the use of benzoyl germanium derivatives as a novel visible light photoinitiator of resin-based dental composites. Selected mechanical properties, such as flexural strength and flexural modulus, setting time, storage stability, and UV light stability, of the composites based on the novel photoinitiators benzoyltrimethylgermane (BTMGe) or dibenzoyldiethylgermane (DBDEGe) were investigated and compared to the properties of materials that are cured with a mixture of camphorquinone (CQ) and ethyl 4-(N,N-dimethylamino)benzoate (EMBO). METHODS: The flexural strength and flexural modulus of elasticity were determined according to ISO 4049. For this purpose, test specimens (2 mm x 2 mm x 25 mm) of the composites investigated were prepared in stainless steel moulds and light-cured (150 mW/cm2, 2 s x 180 s). The flexural strength and flexural modulus of elasticity were measured after immersing the cured specimens in water for 24h at 37 degrees C and in certain cases, after they had been boiled for 24h in water. In addition, the setting time, curing depth, storage and UV stability of selected composites were determined. RESULTS: The novel photoinitiators BTMGe or DBDEGe can be used to substitute the binary photoinitiator CQ/EMBO in visible light-cured restorative composites. Especially, DBDEGe showed a significantly higher photocuring activity in composites with a filler load of about 60 wt. % in comparison to that of CQ/EMBO. In addition, composites based on BTMGe or DBDEGe showed an improved UV stability and a storage stability comparable to that of CQ/EMBO-based composites.     

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

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

氧化锆和金属基底饰面瓷机械性能与微观结构的比较研究

目的比较分析氧化锆和金属基底饰面瓷的机械性能及微观结构。方法选择5种氧化锆基底饰面瓷Vintage ZR(ZR),Cerabien ZR(CZR),VitaVM9(VM9),Cercon ceram KISS(KISS),IPS e.max ceram(e.max)及烤瓷熔附金属用饰面瓷Vintage MP(MP)。每种饰面瓷各制作10个试件,测定表面粗糙度﹑三点弯曲强度(ISO 6872)和维氏硬度。计算断裂韧性。微观结构通过X射线衍射和扫描电镜分析。结果与其它饰面瓷相比,氧化锆基底用KISS的弯曲强度最高(P﹤0.05),CZR的弯曲强度最低(P﹤0.05);金属基底用MP的断裂韧性明显高于所有氧化锆用饰面瓷(P﹤0.001)。结论与氧化锆基底用饰面瓷相比较,金属基底用饰面瓷不易断裂,更具有临床可靠性。     

Shear bond strength of techniques for bonding esthetic veneers to metal

STATEMENT OF PROBLEM: New composites with improved qualities have been introduced to the dental profession as alternatives to porcelain. There is concern about the strength and reliability of new metal-resin bonding systems when these composites are used as esthetic veneers over metal frameworks. PURPOSE: This in vitro study compared the shear bond strength of 2 metal-resin bonding techniques with the bond strength of conventional porcelain fused-to-metal (PFM). Effects of water storage and thermocycling were also evaluated. MATERIAL AND METHODS: Ninety disks, cast in a medium gold, high noble PFM alloy, were divided equally into 6 groups, and received 3 treatments for veneering: conventional feldspathic porcelain on 1 group, and a composite (Artglass) bonded to the metal, using 2 metal-resin bonding techniques. Specimens were tested in shear, half of them after a 24-hour dry storage at room temperature and the rest after 10-day storage in normal saline solution at 37 degrees C and thermocycling. Fractured specimens were evaluated under x10 magnification to determine the nature of failure. Statistical analysis was performed with 2-factor analysis of variance (ANOVA). RESULTS: Mean shear bond strength values before and after wet storage and thermocycling were 29.66 and 22.91 MPa for the PFM group; 21.43 and 17.92 MPa for the Siloc group; and 19.34 and 15.64 for the etched group, respectively. The PFM group exhibited significantly higher bond strength values compared with the other 2 groups (P<.001). All groups showed a significant decrease in bond strength values after wet storage and thermocycling (P<.001). CONCLUSION: Wet storage and thermocycling caused a significant decrease in shear bond strength of all specimens. Shear bond strength of conventional feldspathic PFM was significantly higher than that of the 2 metal-resin bonding techniques tested. The 2 latter techniques did not reveal any statistically significant differences.     

A partially aromatic urethane dimethacrylate as a new substitute for Bis-GMA in restorative composites.

OBJECTIVES: The objective of this study was to investigate the use of a new, partially aromatic urethane dimethacrylate in visible-light cured resin-based composite restoratives. Selected mechanical properties, such as flexural strength and flexural modulus of elasticity, of model monomer mixtures and composites containing the new urethane dimethacrylate were investigated and compared to the properties of materials that are based on Bis-GMA, at present the most frequently used cross-linker in restorative composites. In addition, the polymerization shrinkage and the water sorption of selected composites were determined. METHODS: The flexural strength, flexural modulus of elasticity, and the water sorption were determined according to ISO 4049:2000. Test specimens (rods: 2 mmx2 mmx25 mm; discs: d=15 mm and h=1 mm) of the investigated composites were prepared in stainless steel molds and light-cured (150 mW/cm2, 2x180 s). The flexural strength and flexural modulus of rods were measured after the samples had been stored under dry conditions or in water for 24 h at 37 degrees C as well as after they had been stored in water for 7 days at 37 degrees C. The water sorption was determined with discs. The polymerization shrinkage was calculated from the densities of the uncured composite pastes and cured composites. RESULTS: Visible light cured mixtures of dimethacrylate diluents with the new urethane dimethacrylate and composites based on these mixtures show a reactivity, flexural strength, flexural modulus of elasticity, polymerization shrinkage and water sorption similar to those of materials that are based on Bis-GMA. The composites did not show any strong deterioration of the mechanical properties after water storage.     

Influence of surface characteristics of four silica-based machinable ceramics on flexural strength and bond strength of a dual-curing resin luting agent

PURPOSE: The aim of the present study was to evaluate the crystalline phase and microstructure of 4 commercial machinable ceramic blocks--Cerec Vitablocs Mark II (Vita), ProCAD (Ivoclar/Vivadent), GN-I (GC), and GNCeram (GC)--and compare flexural strength and shear bond strength between a dual-curing resin luting agent and the ceramics treated with a silane coupling agent. MATERIALS AND METHODS: Specimens were examined using scanning electron microscopy/energy-dispersive x-ray spectroscopy, and x-ray diffractometry. Three-point bending tests were performed with polished specimens 20 mm long, 4 mm wide, and 1.2 mm thick. Two differently shaped specimens for each of the 4 machinable ceramics were treated with a silane coupling agent. The specimens were then cemented together with a dual-curing resin luting agent. Half of the specimens were stored in water at 37 degrees C for 24 h and the other half were thermocycled 20,000 times. RESULTS: Chemical composition, crystalline phase, and crystallinity were significantly different between brands. The Vitablocs Mark II material had the significantly lowest flexural strength (101.7 +/- 15.3 MPa), while the GNCeram material had the highest (174.8 +/- 10.3 MPa). The use of a silane coupling agent yielded high shear bond strength after 20,000 thermocycles (Vitablocs Mark II: 37.7 +/- 3.7 MPa, ProCAD: 41.2 +/- 3.1 MPa, GNCeram: 50.2 +/- 2.1 MPa), except with the GN-I material (23.9 +/- 4.4 MPa). CONCLUSION: It appeared that crystal distribution and particle size of leucite crystal, not crystallinity, in the feldspar glass matrix of silica-based machinable ceramics might influence the flexural strength and efficacy of a silane coupling agent in bonding between a dual-curing resin luting agent and machinable ceramics.     

Intra-oral adhesive systems for ceramic repairs: a comparison

The aim of this investigation was to compare the bond strength of restorative composite resin to dental ceramic conditioned with primers and adhesives of various commercial repair kits. Three intra-oral ceramic repair systems--Silistor (Heraeus Kulzer), Cimara (Voco), Ceramic Repair (Vivadent)--were used on all-ceramic (IPS Empress 2, Ivoclar-Vivadent) substrate. Shear bond strength of restorative composite resin to substrate was tested after thermocycling and without thermocycling (n = 10). Substrate surfaces of the specimen after loading were examined microscopically (SEM). The highest bond strengths in both water-stored (7.0 +/- 5.7 MPa) and thermocycled conditions (2.5 +/- 1.8 MPa) were obtained with the Vivadent repair system, while the lowest values were observed with the Cimara system (0.6 +/- 1.4 MPa and 0.0 +/- 0.0 MPa, respectively). Shear bond strengths appeared to be significantly affected by thermocycling (ANOVA, P < 0.05). It is concluded that there are significant differences in the bond strengths of resin composites and ceramic substrate. The roughened surface does not necessarily provide a better bond strength; the bond strength of composite decreases with storage in water and after thermocycling. Bond strength values were generally low for all of the tested materials.     

Investigations of subcritical crack propagation of the Empress 2 all-ceramic system.

INTRODUCTION: The mechanical properties and slow crack propapagation of the all-porcelain system Empress 2 (Ivoclar Vivadent, Schaan, Liechtenstein) with its framework compound Empress 2 and the veneering compounds "Empress 2 and Eris were examined. METHODS: For all materials, the fracture strength, Weibull parameter and elastic moduli were experimentally determined in a four-point-bending test. For the components of the Empress 2 system, the fracture toughness K(IC) was determined, and the crack propagation parameters n and A were determined in a dynamic fatigue method. Using these data, life data analysis was performed and lifetime diagrams were produced. The development of strength under static fatigue conditions was calculated for a period of 5 years. RESULTS: The newly developed veneering ceramic Eris showed a higher fracture strength (sigma(0)=66.1 MPa) at a failure probability of P(F)=63.2%, and crack growth parameters (n=12.9) compared to the veneering ceramic Empress 2 (sigma(0)=60.3 MPa). For Empress 2 veneer the crack propagation parameter n could only be estimated (n=9.5). This is reflected in the prognosis of long-term resistance presented in the SPT diagrams. For all materials investigated, the Weibull parameter m values (Empress 2 framework m=4.6; Empress 2 veneer m=7.9; Eris m=6.9) were much lower than the minimum demanded by the literature (m=15). SIGNIFICANCE: The initial fracture strength value alone is not sufficient to characterize the mechanical resistance of ceramic materials, since their stressability is time-dependent. Knowledge about the crack propagation parameters n and A are of great importance when preclinically predicting the clinical suitability of dental ceramic materials. The use of SPT diagrams for lifetime calculation of ceramic materials is a valuable method for comparing different ceramics.     

The influence of the veneering porcelain and different surface treatments on the biaxial flexural strength of a heat-pressed ceramic

STATEMENT OF PROBLEM: The strength of all-ceramic restorations can be adversely affected by surface defects, leading to restoration failures. Additionally, when a 2-layer all-ceramic restoration is required for esthetic purposes, part of the stronger ceramic core material is replaced by veneering porcelain. PURPOSE: This study evaluated the effect of different surface treatments on the strength of a ceramic core material and veneering porcelain, as well as the influence of veneering porcelain on the strength of a 2-layer ceramic structure. MATERIAL AND METHODS: Fifty heat-pressed ceramic cores and 30 veneering porcelain discs (17 mm diameter x 2 mm) were made. From the ceramic core group, 20 discs were selected and reduced to a thickness of 1 mm and veneered with 1 mm of porcelain. These specimens were divided into 2 groups of 10 each. The remaining 30 ceramic core and the 30 veneering porcelain discs were divided into 2 sets of 3 equal sized groups (n=10). Ceramic core groups were prepared for testing having the following surfaces: airborne-particle abrasion, ground, and overglazed. Veneering porcelain groups were tested: as fired (no additional treatment), ground, and overglazed. Biaxial flexural strength was measured using the ball-on-ring test method. All specimens were loaded to fracture. One and 2-way analysis of variance were used to analyze the data (alpha=.05). RESULTS: The ceramic core discs were significantly (P=.001) stronger than the veneering porcelain discs for the airborne-particle abrasion, as-fired, and ground surface treatments (82 +/- 11 MPa vs 51 +/- 8 MPa and 93 +/- 14 MPa vs 60 +/- 6 MPa, respectively). For the overglazed treatment, there was not a significant difference between the core (115 +/- 1 4 MPa) and the veneer materials (107 +/- 14 MPa). The ground 1-layer core was significantly (P=.015) stronger (93 +/- 14 MPa) than the 2-layer with the core tested in tension (72 +/- 19 MPa). There was no significant difference between 1-layer veneer overglazed (107 +/- 14 MPa) and 2-layer discs when tested with the veneer in tension (105 +/- 16 MPa). CONCLUSION: The overglazed surface treatment significantly improved the strength of the materials tested, as well as the strength of 2-layer discs with the veneer in tension. The veneering porcelain influenced the strength of 2-layer specimens only when tested with the ground ceramic core surface in tension.     

Adhesive strength between fiber-reinforced composites and veneering composites and fracture load of combinations of these materials

PURPOSE: This study examined the influence of the adhesive strength between fiber-reinforced composites (FRC) and veneering composites on the fracture load of combinations of these materials. MATERIALS AND METHODS: Six materials were used. An experimental material called BR-100, Vectris, and FibreKor were the types of FRC. Estenia, Targis, and Sculpture were used as veneering composites. With the Estenia/BR-100 combination, the surface of the FRC was subjected to three different conditions before veneering. Ten specimens of each combination were fabricated and divided into two groups: One group was stored in 37 degrees C distilled water for 24 hours, and the other was thermocycled (4 degrees C/60 degrees C, 10,000 cycles). Adhesive strength between FRCs and veneering composites was determined using the compressive shear strength test. In addition, fracture loads of laminate specimens were determined. RESULTS: Good adhesive strength was obtained by leaving an unpolymerized layer on the surface of the FRC or by performing silane and bonding treatment. In the Estenia/BR-100 combination, when the adhesive strength was low, the fracture load of the laminate specimens was also low. However, the difference in fracture load was not as large as that seen in adhesive strength. The fracture load of each laminate specimen was significantly lower after thermocycling. CONCLUSION: The adhesive strength between the FRCs and veneering composite had an effect on the fracture load of the combination.     

Flexural strength of veneering ceramics for zirconia

OBJECTIVES: The flexural strengths of veneering ceramics for zirconia were compared. METHODS: With 10 different veneering ceramics for zirconia (test group) and three different veneering ceramics for the metal-ceramic technique (control group) three-point flexural strength and biaxial flexural strength according to ISO 6872: 1995 as well as four-point flexural strength according to EN 843-1: 2005 were measured (n=10). Statistical analysis was performed with one-way ANOVA and post hoc Scheffé test (SPSS, p<0.05). RESULTS: For the test group, three-point flexural strength ranged between 77.8+/-8.7 and 106.6+/-12.5MPa without any statistically significant differences, biaxial flexural strength between 69.1+/-4.8 and 101.4+/-10.5MPa with three homogeneous groups and four-point flexural strength between 59.5+/-6.2 and 89.2+/-9.5MPa with five homogeneous groups. The control group showed three-point flexural strength values ranging from 93.3+/-13.5 to 149.4+/-20.5MPa, biaxial flexural strength values from 93.4+/-10.0 to 141.2+/-11.6MPa, and four-point flexural strength values from 82.7+/-8.5 to 116.9+/-9.8MPa. In every case, the results of the four-point flexure test were significantly lower than those obtained in the three-point flexure test. The three-point flexural strengths of the test group are similar to those of two ceramics of the control group. The flexural strength of one ceramic of the control group significantly exceeded the strengths of all other ceramics investigated. CONCLUSION: Three-point flexural strength values of veneering ceramics for zirconia are similar to those of veneering ceramics for the metal-ceramic technique. The four-point flexure test among all three tests showed highest discrimination between the different ceramic materials.