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bulk filling sistem
  Bulk-fill Resin-basedComposites: An  In Vitro  Assessment of TheirMechanical Performance N Ilie    S Bucuta    M Draenert Clinical Relevance In an attempt to speed up the restoration process, a new class of resin-based composite(RBC) material, the bulk-fill RBC, was recently introduced on the market, enabling up to 4-or 5-mm thick increments to be cured in one step. Their mechanical properties varyrelative to those of flowable and nonflowable nanohybrid and microhybrid RBCs. SUMMARY The study aimed to assess the mechanicalperformance of seven bulk-fill RBCs (VenusBulk Fill, Heraeus Kulzer; SureFil SDR flow,Dentsply Caulk; x-tra base and x-tra fil, VOCO;Filtek Bulk Fill, 3M ESPE; SonicFill, Kerr;Tetric EvoCeram Bulk Fill, Ivoclar Vivadent)by determining their flexural strength ( r ),reliability (Weibull parameter, m), flexuralmodulus (E flexural ), indentation modulus(Y  HU ), Vickers hardness (HV), and creep (Cr).The significant highest flexural strengthswere measured for SonicFill, x-tra base, andx-tra fil, while x-tra base, SureFil SDR flow,and Venus Bulk Fill showed the best reliabil-ity. The differences among the materials be-camemoreevident intermsofE flexural andY  HU ,with x-tra fil achieving the highest values,while Filtek Bulk Fill and Venus Bulk Fillachieved the lowest. The enlarged depth of cure in bulk-fill RBCs seems to have beenrealized by enhancing the materials’ translu-cency through decreasing the filler amountand increasing the filler size. The manufactur-er’s recommendation to finish a bulk-fill RBCrestoration by adding a capping layer made of regular RBCs is an imperative necessity, sincethe modulus of elasticity and hardness of certain materials (SureFil SDR flow, VenusBulk Fill, and Filtek Bulk Fill) were consider-ably below the mean values measured in reg-ular nanohybrid and microhybrid RBCs. *Nicoleta Ilie, PhD, Department of Restorative Dentistry,Dental School of the Ludwig-Maximilians-University, Mu-nich, GermanyStefan Bucuta, Department of Restorative Dentistry, DentalSchool of the Ludwig-Maximilians-University, Munich, Ger-manyMiriam Draenert, Dr, Department of Restorative Dentistry,Dental School of the Ludwig-Maximilians-University, Mu-nich, Germany*Corresponding author: Goethe Str 70, Munich, 80336,Germany; e-mail: nilie@dent.med.uni-muenchen.deDOI: 10.2341/12-395-L   Operative Dentistry, 2013,  38-6,  618-625  The class of bulk-fill RBCs revealed similarflexural strength values as the class of nano-hybrid and microhybridRBCs, andsignificant-ly higher values when compared to flowableRBCs. The modulus of elasticity (E flexural ), theindentation modulus (Y  HU ), and the Vickershardness (HV) classify the bulk-fill RBCs asbetween the hybrid RBCs and the flowableRBCs; in terms of creep, bulk-fill and theflowable RBCs perform similarly, both show-ingasignificantlylower creepresistancewhencompared to the nanohybrid and microhybridRBCs. INTRODUCTION Time-saving restorative materials are an ongoingdemand for posterior applications. A new resin-based composite (RBC) material class, the bulk-fillRBCs, has been introduced in the past few years.They are an attempt to speed up the restorationprocess by enabling up to 4- or 5-mm thickincrements to be cured in one step, thus skippingthe time-consuming layering process. Bulk-fill RBCsare also marketed as restoratives that are particu-larly well suited for patients with limited compli-ance. Moreover, the rheology of these materials isthought to have changed, thus allowing a betteradaption to the cavity walls and resulting in a self-leveling effect. For the same purpose, a sonic-activated bulk-fill RBC was also launched on themarket (SonicFill, Kerr, Orange, CA, USA). In spiteof the stated improved adaption to the cavity walls,microleakage analysis attested to a similar perfor-mance for bulk-fill RBCs (SDR, Dentsply Detrey,Konstanz, Germany), and x-tra base, VOCO, Cux-haven, Germany) as for conventional RBC (Grandio-SO, VOCO) in standardized Class II cavities. 1 Themarginal integrity of posterior RBC (CeramX Mono,Dentsply; Tetric EvoCeram, Ivoclar Vivadent,Schaan, Liechtenstein; Filtek Supreme XT, 3MESPE, Seefeld, Germany; and Venus Diamond,Heraeus Kulzer, Hanau, Germany) fillings to enameland dentin, made with and without a 4-mm flowablebase (SDR, Dentsply), was also similar, both, beforeand after thermomechanical loading. 2 However, themanufacturer’s statements with regard to the incre-mental thickness were confirmed in  in vitro  studies,as the degree of cure and the micromechanicalproperties were shown to remain constant within a4-mm layer at a irradiation time of up to 20 seconds(SDR, Dentsply; Venus Bulk Fill, Heraeus Kulzer). 3  A main concern of curing large increments is apotentially increased polymerization shrinkagestress at the tooth-material interface. A bulk-fillmaterial in its experimental version (SDR, Dentsply)revealed, however, that it had the lowest shrinkagestress and shrinkage-rate values in comparison toregular flowable and nonflowable nanohybrid andmicrohybrid methacrylate-based RBCs and a silor-ane-based microhybrid RBC. 4,5 Moreover, it wasshown that bulk-fill flowable RBCs (SDR, Dentsply;x-tra base, VOCO) significantly reduced cuspaldeflection in standardized Class II cavities comparedwith a conventional RBC (GrandioSO, VOCO)restored in an oblique incremental filling technique. 1 Regarding mechanical performance, bulk-fill mate-rials (SDR, Dentsply) proved to be more rigid (highermodulus of elasticity) and more plastic (higherplastic deformation and creep values) when com-pared to regular flowable RBCs, and generally withlower mechanical properties than regular nanohy-brid or microhybrid RBCs. 4 Other studies found,however, that bulk-fill RBCs exhibited a creepdeformation within the range of regular RBCs. 6 They also found that the flexure strength, wateruptake, and biocompatibility of bulk-fill RBCs (x-trafil, VOCO) were comparable to conventional RBCs. 7 The first bulk-fill material on the market, SureFilSDR flow (or SDR on the European market), as wellas Venus Bulk Fill, x-tra base, and Filtek Bulk Fill,require an additional final capping layer made of regular RBCs, while other materials in the samecategory (SonicFill, Tetric EvoCeram Bulk Fill, andx-tra fil) can be placed without it. This differentapplication of materials belonging to the samematerial class confuses many practitioners sincethey assume the materials’ behavior would besimilar.The aim of this study was, therefore, to assess themechanical performance of a new material class—the bulk-fill RBCs—at the macro and micro scale,and to compare its performance with an alreadypublished material database 8 determined underidentical conditions, comprised of modern flowableand nonflowable nanohybrid and microhybrid RBCs.The null hypotheses were: 1) there would be nosignificant difference in macromechanical (flexuralstrength [ r ] and flexural modulus [E flexural ]) andmicromechanical (Vickers hardness [HV], indenta-tion modulus [Y  HU ], and creep [Cr]) propertiesamong the bulk-fill RBCs; and 2) there would be nosignificant difference in the above mentioned prop-erties among the material class of bulk-fill RBCs andthe class of flowable and nonflowable nanohybridand microhybrid RBCs. Ilie, Bucuta & Draenert: Bulk-fill RBCs   619  MATERIALS AND METHODS The seven bulk-fill RBCs on the market up to thepresent (Table 1) were analyzed. Only SonicFill wassonic activated; this was done with an oscillatinghandpiece (step 3), as recommended by the manu-facturer.The flexural strength ( r ) and flexural modulus(E flexural ) were determined in a three-point bendingtest (n = 20). Therefore, 140 samples were made bycompressing the composite material between twoglass plates with intermediate polyacetate sheets,separated by a steel mold having an internaldimension of 2  3  2  3  16 mm. Irradiation occurredon the top and bottom of the specimens, as specifiedin ISO 4049:2009 standards 9 ; the time of the lightexposures was 20 seconds, with three light expo-sures, overlapping one irradiated section no morethan 1 mm of the diameter of the light guide (1241mW/cm 2 , Elipar Freelight 2, 3M ESPE, Seefeld,Germany) to prevent multiple polymerizations. Afterremoval from the mold, the specimens were groundwith silicon carbide paper (grit size P 1200/4000[Leco]) to remove protruding edges or bulges, andthen stored for 24 hours in distilled water at 37 8 C.The samples were loaded until failure in a universaltesting machine (Z 2.5, Zwick/Roell, Ulm, Germany)in a three-point bending test device, which wasconstructed according to the guidelines of NIST 4877with a 12-mm distance between the supports. 10 During testing, the specimens were immersed indistilled water at room temperature. The crossheadspeed was 0.5 mm/min. The universal testingmachine measured the force during bending as afunction of deflection of the beam. The bendingmodulus was calculated from the slope of the linearpart of the force-deflection diagram. Micromechanical Properties Fragments larger than 8 mm (n = 10) from the three-point bending test specimens of each group wereused to determine the micromechanical properties(HV, Y  HU , Cr) according to DIN 50359-1:1997-10 11 by means of a universal hardness device (Fischer-scope H100C, Fischer, Sindelfingen, Germany).Prior to testing, the samples were polished with agrinding system (EXAKT 400 CS, EXAKT, Norder-stedt, Germany) using silicon carbide paper P 2500followed by P 4000. Measurements were done on thetop (n = 10) of the slabs, about 4 mm away from thebreaking edge, with six measurements per sample.The test procedure was carried out with controlledforce, and the test load increased and decreased witha constant speed between 0.4 mN and 500 mN. Theload and the penetration depth of the indenter werecontinuously measured during the load-unload-hys-teresis. The universal hardness is defined as the testforce divided by the apparent area of the indentationunder the applied test force. From a multiplicity of measurements stored in a database supplied by themanufacturer, a conversion factor (0.0945) betweenuniversal hardness and HV was calculated by themanufacturer and entered into the software such Table 1:  Materials, Manufacturer, and Chemical Composition of Matrix and Filler as Well as Filler Content by Weight (Wt) and Volume (Vol)  Bulk Fill RBCs Manufacturer,Color, BatchResin Matrix Filler Filler Wt%/Vol% Tetric EvoCeram Bulk Fillnanohybrid RBCIvoclar Vivadent, IVA,P48872Bis-GMA, UDMA Ba-Al-Si glass, prepolymer filler (monomer, glass filler,and ytterbium fluoride),spherical mixed oxide79-81 (including 17%prepolymers)/ 60-61Venus Bulk Fill nanohybridRBCHeraeus Kulzer,Universal 010026UDMA, EBPDMA Ba-Al-F-Si glass, SiO 2  65/38SureFil SDR flow flowablebase RBCDentsply Caulk,Universal, 100407Modified UDMA,TEGDMA, EBPDMABa-Al-F-B-Si glass andSt-Al-F-Si glass as fillers68/44x-tra base hybrid RBC VOCO, universal,V 45226Bis-GMA, UDMA 75/ x-tra fil hybrid RBC VOCO, universal1202359Bis-GMA, UDMA,TEGDMA86/70.1SonicFill nanohybrid RBC Kerr, A3, 4252497 Bis-GMA, TEGDMA,EBPDMASiO 2 , glass, oxide 83.5/ Filtek Bulk Fill nano RBC 3M ESPE, universalN387662Bis-GMA, UDMA, Bis-EMA, Procrylat resinsZirconia/silica, ytterbiumtrifluoride64.5/42.5 Abbreviations: Bis-EMA, Bisphenol-A polyethylene glycol diether dimethacrylate; Bis-GMA, Bisphenol-A diglycidyl ether dimethacrylate; EBPDMA, ethoxylated Bisphenol-A-dimethacrylate; TEGDMA, triethylene glycol dimethacrylate; UDMA, urethane dimethacrylate  . 620  Operative Dentistry   that the measurement results were indicated in themore familiar HV units. Y  HU  was calculated from theslope of the tangent of the indentation depth-curveat maximum force. By measuring the change inindentation depth with a constant test force, arelative change in the indentation depth can becalculated. This is a value for the Cr of the materials. Field Emission Scanning Electron Microscope The structural appearance of the filler was estab-lished by a field emission scanning electron micro-scope (Zeiss Supra 55 VP, Zeiss NTS GmbH,Oberkochen, Germany) on unsputtered samples(Figure 1). Therefore, one fragment of the three-point bending test specimens of each group wasground and polished (P 4000) prior to examination.The backscattering method allows a distinction tobecome apparent between filler with different den-sities as well as to assess the fillers’ sizes andmorphologies. Statistical Analysis The Kolmogorov-Smirnov test was applied to verifythat the data were normally distributed. The resultswere compared using one-way and multiple-wayanalysis of variance (ANOVA) and Tukey post hoctest ( a = 0.05). A multivariate analysis (general linearmodel with partial eta-squared statistics) assessedthe effect of material, filler volume (%), and fillerweight (%) on the mechanical properties (version20.0, SPSS Inc, Chicago, IL, USA). A Pearsoncorrelation analysis among the tested parameterswas conducted, while the flexural strength data wereadditionally examined by means of a Weibullanalysis. A common empirical expression for the cumulativeprobability of failure  P  at applied stress is theWeibull model:  P  f  ( r c )  =  1    exp[  ( r c  /  r 0 ) m ] where  r c is the measured strength, m is the Weibull modulus,and  r 0  is the characteristic strength, which isdefined as the uniform stress at which the probabil-ity of failure is 0.63. The double logarithm of thisexpression is: ln ln[1/(1    P )]  =  m ln  r c    m ln  r 0  Byplotting ln ln[1/(1   P )] vs ln  r , a straight line resultswith the upward gradient m. RESULTS Post hoc multiple pairwise comparisons with Tukeytest (  p , 0.05) showed the significantly highestflexural strength values for SonicFill, x-tra base,and x-tra fil (Table 2). In terms of the material’sreliability, expressed by the Weibull modulus (m),two groups can be distinguished, one comprising x-tra base, SureFil SDR flow, and Venus Bulk Fill,which are characterized by a very high Weibullmodulus varying between 21.1 and 26.1, and the restof the materials, showing a moderate reliability,with Weibull modulus values varying between 10.4and 14.2 (Figure 1; Table 2). The differences amongthe materials became more evident in terms of E flexural  and indentation modulus Y  HU . x-tra filachieved the significantly highest values, whereasFiltek Bulk Fill and Venus Bulk Fill achieved thelowest. Moreover, an excellent correlation wasmeasured between E flexural  and Y  HU  (Pearson corre-lation coefficient = 0.91). There was also a very goodcorrelation within the micromechanical properties(Y  HU   HV  = 0.94; Y  HU   Cr =  0.76; and HV    Cr =  0.64, whereas the correlation within the macro-mechanical properties was only moderate (FS   E flexural  =  0.47).The influence of the parameters bulk-fill RBC(material), filler volume, and filler weight wereanalyzed in an ANOVA multivariate test (Table 3).The filler volume and filler weight data were takenas indicated by manufacturers. The macromechan-ical properties (flexural strength and modulus of elasticity in flexural test) and the micromechanicalproperties (indentation modulus, Vickers hardness,and creep) were selected as dependant variables. Thesignificance values of these three main effects wereless than 0.05, indicating that they all contribute tothe model. The results show that the strongestinfluence of the above mentioned parameters onthe mechanical properties (higher eta square values)was reflected in the E flexural  and Y  HU , followed by HV and Cr, while the influence on  r  was moderate.Generally, the strongest influence on the measuredproperties was performed by the filler volume,followed by the filler weight, followed by material.The material class of bulk-fill RBCs revealedsimilar flexural strength values when compared tothe class of nanohybrid and microhybrid RBCs, andsignificantly higher values when compared to theclass of flowable RBCs. E flexural , Y  HU , and HV place Figure 1.  Weibull analysis  . Ilie, Bucuta & Draenert: Bulk-fill RBCs   621
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