Fracture Strength Values Research Articles

Fracture resistance of structurally compromised and normal endodontically treated teeth restored with different post systems: An in vitro study

With the aim of developing methods that could increase the fracture resistance of structurally compromised endodontically treated teeth, this study was conducted to compare the effect of three esthetic post systems on the fracture resistance and failure modes of structurally compromised and normal roots. Forty five extracted and endodontically treated maxillary central teeth were assigned to 5 experimental groups (n=9). In two groups, the post spaces were prepared with the corresponding drills of the post systems to be restored with double taper light posts (DT.Light-Post) (group DT.N) and zirconia posts (Cosmopost) (group Zr.N). In other 3 groups thin wall canals were simulated to be restored with Double taper Light posts (DT.W), double taper Light posts and Ribbond fibers (DT+R.W) and Zirconia posts (Zr.W). After access cavity restoration and thermocycling, compressive load was applied and the fracture strength values and failure modes were evaluated. Data were analyzed using two-way ANOVA, Tukey and Fisher exact tests (P<0.05). The mean failure loads (N) were 678.56, 638.22, 732.44, 603.44 and 573.67 for groups DT.N, Zr.N, DT.W, DT+R.W and Zr.w respectively. Group DT+R.W exhibited significantly higher resistance to fracture compared to groups Zr.N, DT.W and Zr.w (P<0.05). A significant difference was detected between groups DT.N and Zr.W (P=0.027). Zirconia posts showed significantly higher root fracture compared to fiber posts (P=0.004). The structurally compromised teeth restored with double taper light posts and Ribbond fibers showed the most fracture resistance and their strengths were comparable to those of normal roots restored with double taper light posts. More desirable fracture patterns were observed in teeth restored with fiber posts.

Reattachment of Fractured Anterior Teeth—Determining Fracture Strength using Different Techniques: An in vitro Study

The aim of this in vitro study was to evaluate and compare the shear bond strength of teeth reattached with sixth generation dentin bonding agent: Xeno III and microhybrid resin composite: Esthet-X, using three different techniques: (1) Simple reattachment, (2) overcontour and (3) internal dentinal groove. A total of 70 human maxillary central incisors were selected and divided into four groups as follows. Group I: Control group comprised of 10 samples. Group II: Simple reattachment, group III: Overcontour and group IV: Internal dentinal groove. Groups II, III and IV comprised of 20 samples each. The teeth in three study groups were sectioned using a diamond disk and the fragment was reattached with Esthet-X and Xeno III using three different techniques. Specimens were stored in tap water for 24 hours and shear bond strength was determined using universal testing machine using a knife edge chisel (0.5 mm in cross-section) at a crosshead speed of 1 mm/minute. The results of this study showed following mean value of fracture strength in Kgf: Group I: Control-27.71; group II: Simple reattachment-9.78; group III: Overcontour-24.41; group IV: Internal dentinal groove-23.83. The overcontour technique had the highest strength recovery while the simple reattachment had the lowest. The overcontour technique provided strength recovery almost similar to intact teeth emphasizing that tooth preparation influenced fracture resistance.

Effect of Glass Fiber Length on Flexural Strength of Fiber-reinforced Composite Resin

ABSTRACT The aim of this study was to determine experimentally maximum fracture load of fiber-reinforced composite with different span lengths and to determine the effect of glass fiber on this parameter. Materials and methods Six fiber-reinforced groups (n = 10) were made with three different lengths (10, 15, 20 mm) with or without glass fiber in split mold. The specimens were early cured and then post-cured with a labolite unit, then specimens were subjected to three-point flexural test by a universal testing machine. Data were analyzed with ANOVA and LSD post-hoc test (p &lt; 0.05). Results Maximum fracture load of specimens increased with decreasing lengths (p &lt; 0.001) and fiber-containing group showed significantly higher fracture load than fiberless groups (p &lt; 0.001). Conclusion It was concluded that by increasing the span length, the maximum fracture load values (N) decreased incorporation of fiber results in higher fracture strength values. How to cite this article Omid T, Venus MM, Farahnaz S, Asghar AA. Effect of Glass Fiber Length on Flexural Strength of Fiber-reinforced Composite Resin. World J Dent 2012;3(2):131-135.

Powder preparation for a shell mold using a new coating process

A new coating process in the powder preparation for a shell mold has been developed to increase the fracture strength of the shell mold. It is due to the homogeneous formation of a glass phase on the starting particles and the increase in the glassification efficiency by the reduction in the loss of inorganic precursors. The inorganic binder system used for the new coating process is composed of tetraethyl orthosilicate (TEOS) and sodium methoxide (NaOMe) as the silica (SiO2) and sodium oxide (Na2O) precursors, respectively. Three different coating processes are employed for the powder preparation with a high glassification efficiency. In process I, the starting particles are coated with NaOMe, and then TEOS are coated on the particles treated with NaOMe. Process II is the reverse sequence of process I. Process III involves coating of the particles with a mixture of TEOS and NaOMe. The particles coated with an individual or mixture precursor were fixed with an organic binder and then heated at 1000°C for 1h. Molds prepared through the new coating processes, especially process III, show a higher fracture strength value compared with that of the conventional convert mold process, which may be caused by the increase in the glassification efficiency of the precursors. Powder prepared by process III shows a more uniform coating of the glass phase than those by other processes, resulting from an enhancement in the phase mixing between SiO2 and NaOH molecules.

Simulating Distal Radius Fracture Strength Using Biomechanical Tests: A Modeling Study Examining the Influence of Boundary Conditions

Distal radius fracture strength has been quantified using in vitro biomechanical testing. These tests are frequently performed using one of two methods: (1) load is applied directly to the embedded isolated radius or (2) load is applied through the hand with the wrist joint intact. Fracture loads established using the isolated radius method are consistently 1.5 to 3 times greater than those for the intact wrist method. To address this discrepancy, a validated finite element modeling procedure was used to predict distal radius fracture strength for 22 female forearms under boundary conditions simulating the isolated radius and intact wrist method. Predicted fracture strength was highly correlated between methods (r = 0.94; p < 0.001); however, intact wrist simulations were characterized by significantly reduced cortical shell load carriage and increased stress and strain concentrations. These changes resulted in fracture strength values less than half those predicted for the isolated radius simulations (2274 ± 824 N for isolated radius, 1124 ± 375 N for intact wrist; p < 0.001). The isolated radius method underestimated the mechanical importance of the trabecular compartment compared to the more physiologically relevant intact wrist scenario. These differences should be borne in mind when interpreting the physiologic importance of mechanical testing and simulation results.

Effect of silica coating on fracture strength of glass-infiltrated alumina ceramic cemented to dentin.

To examine the availability of sol-gel processed silica coating for alumina-based ceramic bonding, and determine which silica sol concentration was appropriate for silica coating. Sixty disks of In-Ceram alumina ceramic were fabricated and randomly divided into 5 main groups. The disks received 5 different surface conditioning treatments: Group Al, sandblasted; Group AlC, sandblasted + silane coupling agent applied; Groups Al20C, Al30C, and Al40C, sandblasted, silica coating via sol-gel process prepared using 20 wt%, 30 wt%, and 40 wt% silica sols, and then silane coupling agent applied. Before bonding, one-step adhesives were applied on pre-prepared ceramic surfaces of all groups. Then, 60 dentin specimens were prepared and conditioned with phosphoric acid and one-step adhesive. Ceramic disks of all groups were cemented to dentin specimens with dual-curing resin cements. Fracture strength was determined at 24 h and after 20 days of storage in water. Groups Al20C, Al30C, and Al40C revealed significantly higher fracture strength than groups Al and AlC. No statistically significant difference in fracture strength was found between groups Al and AlC, or among groups Al20C, Al30C, and Al40C. Fracture strength values of all the groups did not change after 20 days of water storage. Sol-gel processed silica coating can enhance fracture strength of In-Ceram alumina ceramic after bonding to dentin, and different silica sol concentrations produced the same effects. Twenty days of water storage did not decrease the fracture strength.

Influence of the supporting die structures on the fracture strength of all-ceramic materials

This study investigated the influence of the elastic modulus of supporting dies on the fracture strengths of all-ceramic materials used in dental crowns. Four different types of supporting die materials (dentin, epoxy resin, brass, and stainless steel) (24 per group) were prepared using a milling machine to simulate a mandibular molar all-ceramic core preparation. A total number of 96 zirconia cores were fabricated using a CAD/CAM system. The specimens were divided into two groups. In the first group, cores were cemented to substructures using a dual-cure resin cement. In the second group, cores were not cemented to the supporting dies. The specimens were loaded using a universal testing machine at a crosshead speed of 0.5 mm/min until fracture occurred. Data were statistically analyzed using two-way analysis of variance and Tukey HSD tests (α = 0.05). The geometric models of cores and supporting die materials were developed using finite element method to obtain the stress distribution of the forces. Cemented groups showed statistically higher fracture strength values than non-cemented groups. While ceramic cores on stainless steel dies showed the highest fracture strength values, ceramic cores on dentin dies showed the lowest fracture strength values among the groups. The elastic modulus of the supporting die structure is a significant factor in determining the fracture resistance of all-ceramic crowns. Using supporting die structures that have a low elastic modulus may be suitable for fracture strength tests, in order to accurately reflect clinical conditions.

Influence of remaining coronal structure and finish line on the fracture strength of roots restored with metallic posts

The purpose of this study was to evaluate the fracture strength of roots that were prosthetically restored with metallic posts with or without any remaining coronal structure and with different finish lines. Sixty bovine incisors were sectioned below the cementoenamel junction, endodontically treated, and randomly divided into six experimental groups (n = 10) containing teeth with or without any remaining coronal structure, and with a beveled shoulder, a bevel, or a shoulder finish line design. The metallic posts were luted with dual-cured resin cement. The cores were made with composite resin, and metal crowns were cemented with zinc phosphate cement. The specimens were subjected to a tangential compressive load (135º angle) at a crosshead speed of 0.5 mm/min until failure, using a universal testing machine. The fracture strength data were analyzed using the ANOVA and LSMeans (least square means) tests (α= 0.05). The data indicated that the teeth with 2 mm of remaining coronal structure showed the highest fracture strength values when compared with the teeth without any remaining structure (p < 0.05). As to the different finish line designs, the highest fracture strength values were obtained for the beveled shoulder, followed by the bevel and then by the shoulder designs (p < 0.05). It may be concluded that, to increase fracture strength, a beveled shoulder and 2 mm of remaining coronal structure are the ideal conditions.

Optimization of hot extrusion process for AZ61 magnesium alloy carriers

This study applies fuzzy-base Taguchi method to investigate the optimal process parameters of the multiple performance characteristics index (MPCI) for the hot extrusion process of AZ61 magnesium alloy products. Flattening strength, fracture strength and extrusion load are taken as the input data of MPCI. Since the optimal combination of process parameters for Taguchi method varies with individual quality characteristic, the optimal combination of parameters for different quality characteristics may be contradictory to each other. In order to consider the larger-the-better quality characteristic of flattening strength and T-slot fracture strength values as well as the smaller-the-better quality characteristic of extrusion load, the fuzzy-base Taguchi method is used to analyze and to obtain the optimal combination of process parameters for the MPCI. First of all, orthogonal array is applied to arrange the experimental combination of extrusion process. The signal-to-noise (S/N) ratios of the three quality characteristics of flattening strength, T-slot fracture strength and extrusion load for the products acquired from experiments are calculated. The S/N ratio serves as the input variable of fuzzy control unit, whereas MPCI serves as a single output variable. The acquired MPCI is employed to analyze the optimal process parameters. In this study, an optimal combination of process parameters of AZ61 carrier for MPCI is obtained, and the verification experiments are conducted to prove the accuracy. Moreover, mechanical properties of AZ31 and AZ61 magnesium alloy carriers are tested for further comparison.

The effects of cyclic loading and preparation on the fracture strength of zirconium-dioxide implants: an in vitro investigation

Zirconia is a potential material for the fabrication of oral implants. The aim of this study was to evaluate the effects of cyclic loading and preparation on the fracture strength of a zirconia implant system. Forty-eight one-piece implants were divided into two groups of 24 implants: group A (without modification) and group B (1 mm chamfer preparation). Groups A and B were divided into three subgroups of eight implants each (1 = no artificial load, 2 = artificial load [98 N; 1.2 million loading cycles], and 3 = artificial load [98 N; 5 million loading cycles]). After completion of the loading, the fracture strength of each implant was determined in a universal testing machine. A two-way analysis of variance was used, the continuous response variable (fracture strength in Newtons) is modeled as a function of preparation, cycles, and the corresponding interaction as explanatory variables. The mean fracture strength values obtained for the groups were: A1 (no preparation, no load) = 1928.73 N, A2 (no preparation, 1.2 million cycles) = 2044.84 N, A3 (no preparation, 5 million cycles) = 1364.50 N, B1 (preparation, no load) = 1221.66 N, B2 (preparation, 1.2 million cycles) = 967.11 N, and B3 (preparation, 5 million cycles) = 884.89 N. Fracture values were significantly different between subgroups A1 vs. A3 and B1 vs. B3. There was no significant difference between subgroups A1 vs. A2 and B1 vs. B2. Preparation as well as cyclic loading can decrease the fracture strength resistance of zirconia implants. Nevertheless, even the lowest values of mean fracture strength of the implants used in our study seem to withstand average occlusal forces even after an extended interval of artificial loading.

Influence of several fibre‐reinforced composite restoration techniques on cusp movement and fracture strength of molar teeth

To compare mean cusp movement in molar teeth with endodontic access and mesial-occlusal-distal (MOD) cavities before and after restoration with several fibre-reinforced composite restoration techniques under loading and to evaluate the effect of restoration technique on fracture strength. Reference points were marked at the mesial cusp ridges of extracted human mandibular molar teeth. Digital images were taken under loading (300 N) using a stereomicroscope (Leica MZ16A; Wetzlar, Germany). Three-dimensional (3D) distances between the reference points were recorded (Leica, Stereo-Explorer, 2.1) as controls. Standard MOD cavities were prepared and restored as follows (n = 10), group 1: composite restoration (Clearfil AP-X; Kuraray, Tokyo, Japan); group 2: cavity lined with polyethylene fibre (Ribbond, Ribbond Inc., Seattle, WA, USA) in combination with flowable resin (Protect-Liner F; Kuraray, Tokyo, Japan) before composite restoration; group 3: polyethylene fibre inserted on occlusal surface of the tooth from buccal to lingual after finishing the composite restoration; group 4: missing walls were restored with composite resin and inner surfaces of the axial walls were then reinforced with polyethylene fibre placed circumferentially before the composite restoration. The restored teeth were re-loaded, digital images were re-taken and the 3D distance between the reference points was recorded in μm. Comparisons of the restoration techniques, the effectiveness of restoration for each group were analysed statistically (Kruskall-Wallis, paired-samples t-test). The teeth were then loaded until failure (5 mm min(-1) ), the data were recorded (N) and analysed statistically (Kruskall-Wallis test). A significant difference occurred amongst the groups in terms of cusp movement (P = 0.018). All the groups revealed a decrease in inter-cuspal width when compared to their initial records. The mean values of these decreases were as follows: group 1 17.6 (P = 0.003), group 2 6.7 (not sig), group 3 6.6 (not sig) and group 4 0.85 (not sig) μm. No significant difference was found amongst the fracture strength values (P = 0.22). In group 1, 90% of the fractures were non-restorable, whereas in group 3 100% of the fractures were restorable. Regardless of restoration technique, fibre reinforcement of composite restorations decreased cusp movement in molar teeth with MOD and endodontic access cavities but did not affect fracture strength.

Fracture Characteristics of Dental Ceramic Crown according to Zirconia Coping Design

Fracture characteristics of the ceramic crown according to the zirconia coping design have been researched using various experimental methods. The 3D contour dimension of a mandibular first molar acrylic model tooth was scanned with Optical scanner (S600, Zirkonzahn, Italy), and then a classic crown preparation was created in CAD software (Zirkonzahn.Modellier, Zirkonzahn, Italy). The CAD file of the prepared tooth was imported into a milling machine, and acrylic resin (PMMA) dies were generated. Four different coping designs based on the thickness of zirconia marginal collar were used: 0.0mm zirconia collar (Group1), 0.5mm (Group2), 1.0mm (Group3), and 2.0mm (Group4). Copings were fabricated with CAD/CAM System (CAD CAM M5, Zirkonzahn, Italy) and veneering porcelain (IPS e.max Ceram) was build-up with layering technique. All the samples were cemented (RelyX Unicem, 3M/ESPE) onto corresponding dies. All specimens were tested in 4 groups (n=10 for each group) based on the thickness of zirconia collar. Fracture load test was performed on eight crowns from each group, and the remaining crowns (n=2) were subjected to fatigue test. Fracture strength was tested with a universal testing machine at a crosshead speed of 1.0mm/min to the vertical axis of the tooth 0.5mm lingually down the mesio-distal cusp. For the testing of fatigue failure, specimens were subjected to 50,000 cycles of cyclic loading 200N, at a rate of 15Hz and then loaded dynamically at a crosshead speed of 1.0mm/min, until failure. Fracture location and fracture surface of failed crowns were observed with a field emission scanning electron microscope (FE-SEM S-4800, Hitachi, Japan). Mean of fracture strength values of veneering porcelain were: 1411N for Group1, 1428N for Group2, 1596N for Group3 and 1621N for Group4. And according to increasing of thickness on zirconia collar, zirconia coping showed more fracture strength value with increasing of fracture strength of porcelain veneered it up. And examined using FE-SEM, two interesting features were shown from the fracture surface, sudden fracture and gradual fracture. And failure of specimens was mainly occurred by crack growth initiated from porosities within the veneering porcelain. In conclusion, according to the fracture test, the more thickness of zirconia collar, the higher fracture strength of veneering porcelain. Thus, zirconia coping design with 2.0mm marginal collar width is recommended for both functional longevity and esthetics of zirconia-ceramic restoration.

Alumina‐reinforced zirconia implants: survival rate and fracture strength in a masticatory simulation trial

Alumina-toughened zirconia (ATZ) is a possible alternative material to titanium for oral implants. No data are available on the fracture strength of ATZ oral implants. The purpose of this study was to examine one-piece implants made of ATZ ceramic under artificial loading conditions and to compare the fracture strength of these implants with implants fabricated from tetragonal zirconium dioxide poylcrystal (TZP)-A. A total of 72 implants, 48 ATZ implants (groups A and B) and 24 TZP-A implants (group C), were investigated. A chamfer preparation at the implant heads was performed on all implants of groups B and C. Eight implants of each group underwent 1.2 or five million thermomechanical loading cycles in the chewing simulator (load value: 98 N). Further eight implants of each group were not cyclic loaded. Finally, the fracture strength of all implants was determined using a universal testing machine. No implant fractured during loading in the chewing simulator. All implants were placed in the universal testing machine to evaluate fracture strength. The mean fracture strength values±standard deviations for the implants without artificial loading were 1734±165 N (ATZ, no preparation), 1220±85 N (ATZ, with preparation), and 578±49 N (TZP-A, with preparation); 1489±190 N (ATZ, no preparation), 1064±121 N (ATZ, with preparation), and 607±57 N (TZP-A, with preparation) with 1.2 million loading cycles; and 1358±187 N (ATZ, no preparation), 1098±97 N (ATZ, with preparation), and 516±45 N (TZP-A, with preparation) with five million cycles. The ATZ implants showed significantly higher mean fracture strengths compared with the TZP-A implants. Modification of the implant head using diamond burs and increased loading time also led to a significant decrease in fracture strength. The ATZ implants showed an increased mechanical stability compared with the TZP-A. Modification of the implant head resulted in a decrease in fracture strength. However, within the limits of this in vitro investigation it can be concluded that ATZ implants will withstand functional loading over an estimated period of 20 years.

An evaluation of various materials and tooth preparation designs used for reattachment of fractured incisors

The present study was undertaken to evaluate and compare the fracture strength of various restorative materials and designs used in the reattachment of anterior fractured teeth. Sound human maxillary central incisors were selected for the study. These teeth were fractured using universal testing machine so as to obtain Ellis class II fracture with intact fragment. The fractured fragment was reattached to the tooth using three restorative materials namely, bonding agent, resin luting cement and nano-composite, and designs incorporated were simply bonding the fragment to the tooth and other one included a chamfer along the fractured line. The reattached teeth were again fractured and the mean fracture strength values recorded. A combination of nano-composite (best material) and chamfer preparation (best design) gave the highest mean fracture strength values.

Influence of Silicon on Interface Reaction during Aluminium-Silicon Carbide Bonding

The effects of Si on the interfacial characteristics of Al-6.25 Si alloy/SiC and Al-11.12 Si alloy / SiC were investigated. The different compositions of aluminium and silicon carbide samples were prepared at various processing temperatures with constant holding time. The characteristics of interface between Al alloy and SiC were evaluated using tensile test and microhardness test. The interface morphologies were evaluated using scanning electron microscope and energy dispersive spectroscopy. The results shown that the interface fracture strength and microhardness values increased at the interface when Si concentration levels were increased.

The influence of incisal veneering porcelain thickness of two metal ceramic crown systems on failure resistance after cyclic loading

In some clinical situations, the length of either a prepared tooth or an implant abutment is shorter than ideal, and the occlusal clearance to be restored by a porcelain crown is large. Incisal thickness of the coping and the veneering porcelain should be considered to prevent mechanical failure of the crown. The purpose of this study was to investigate the influence of incisal veneering porcelain thickness of metal ceramic systems on failure resistance after cyclic loading. With a standardized technique, 60 metal ceramic anterior crowns with 2 different incisal thicknesses of porcelain veneer (2.0 and 4.0 mm) and 2 different metal alloys (Pisces Plus (B), base metal, and Leo (N), high noble metal) were fabricated to fit a custom abutment and divided into 4 groups (B20, B40, N20, N40) (n=15). The crowns were then cemented using resin cement (PANAVIA 21) and thermal cycled and mechanically cycle loaded (49-N load) for 2,000,000 cycles. The specimens were evaluated for cracks and/or bulk fracture with an optical stereomicroscope (x10) and assigned a score of success, survival, or failure. The specimens without bulk fracture after cyclic loading were loaded along the long axis of the tooth, on the incisal edge, in a universal testing machine at a crosshead speed of 1.5 mm/min until fracture. The fracture strength value (N) was recorded. The exact logistic regression and Fisher's exact test were used to study the effect of different alloys and porcelain incisal thicknesses on the success and survival rates after cycle loading. The forces at failure (fracture) of different groups were compared using the rank transform-based nonparametric 2-way ANOVA (alpha=.05). According to exact logistic regression, crowns of the high noble alloy group showed significantly higher success rates (P=.002) than those of the base metal group after cyclic loading. The success rate of the crowns with 2 mm of incisal veneering porcelain was significantly higher (P<.001) than that of the crowns with 4 mm of incisal veneering porcelain. For crowns with a 4-mm incisal thickness, N40 showed a significantly higher success rate than B40 (P=.04, Fisher's exact test). As for survival rate, the exact logistic regression indicated that neither metal type (P=.11) nor thickness (P=.60) had a significant effect. The 2-way ANOVA showed a significant effect of thickness (P=.001) and no significant effect of metal type (P=.08) on the failure load. The high noble metal ceramic crowns demonstrated a significantly higher success rate after cyclic loading than the base metal ceramic crowns. Crowns with a porcelain incisal thickness of 2 mm showed, for both metal ceramic systems, a greater success rate than those with a 4-mm incisal thickness.

Fracture strength of indirect resin composite laminates to teeth with existing restorations: an evaluation of conditioning protocols.

This study evaluated the fracture strength and failure types of indirect resin-based composite laminates bonded to teeth with aged Class III composite restorations that were conditioned according to various protocols. Maxillary central incisors (N = 60) with window-type preparations received laminates made of a highly-filled resin composite material (Estenia) (10 per group).On the mesial and distal side, Class III cavities (3 x 3 mm) were prepared using ultrasonic burs and filled with resin composite (Quadrant Anterior Shine). The unrestored teeth served as a control group (group 6). All restored teeth (n=50) were thermocycled (5 degrees C to 55 degrees C, 6000X) and subjected to one of the conditioning protocols: (1) air-particle abrasion with alumina particles coated with silica (30-microm SiO2, CoJet)+silanization, (2) air-particle abrasion with alumina particles (50 microm, Al2O3)+silanization, (3) 9.5% hydrofluoric acid (HF) for 90 s (Ultradent)+silanization and (4) protocol of Clearfil Repair Kit, (5) adhesive resin (Quadrant Unibond Sealer). A three-step bonding procedure and dual-polymerizing resin cement (Panavia F 2.0) were employed. The inner surfaces of the laminates were conditioned (CoJet-Sand, 30 mum SiO2) and silanized (ESPE-Sil). All specimens were stored in water at 37 degrees C for one month prior to the fracture test. A significant difference was observed in fracture strength values between the groups (ANOVA, p = 0.0261). The only significant difference was between group 2 (299 +/- 103 N) and group 3 (471 +/- 126 N) (p = 0.0239) (Tukey's test, alpha = 0.05). The majority of failures were type C (35/60) (chipping of the laminate with enamel exposure), followed by type B (21/60) (cohesive failure within the composite laminate). The fracture strengths of the laminates tested did not show significant differences, whether they were bonded to existing, aged Class III composite restorations or to intact teeth. The failure types, however, varied between the groups. The lowest strengths were obtained from the air-particle abraded (50 microm, Al2O3) and silanized group.

Synthesis and characteristics of 80 vol.% tungsten (W) fibre/Zr based metallic glass composite

Based on full understanding of wettability between Zr based bulk metallic glass (BMG) matrix and tungsten (W) fibre, and liquid/solid interfacial atomic interaction, the high density and high strength 80 vol.% W fibre/Zr based BMG composite, with optimum interfacial layer, was successfully developed by strictly controlling the infiltration and solidification process. Its density was 17 g/cm 3. The average value of tensile fracture strength was 1685 MPa. Fracture mode represented instant rupture which was vertical to the axial direction. The average value of compressive fracture strength and strain were 2550 MPa and 23% respectively. Its fracture mode was complex splitting along loading direction. The initiation of shear bands occurred when the compressive specimen reached plastic strength. Shear bands' continuous expanding, branching, propagation and build up responded the improvement of plasticity under the continuous loading. Shear bands distributed on the fracture surface in two ways. One was consistent with the maximum shear force direction and at 45° angle with the loading direction. The other was nearly horizontal and vertical to the loading direction. The characteristics of plastic deformation and fracture were also investigated and discussed in detail.

Fracture Strength of Zirconia Implants after Artificial Aging

Zirconia (ZrO(2)) might be an alternative material to titanium (Ti) for dental implant fabrication. However, no data are available on the fracture strength of one-piece ZrO(2) oral implants. The objective of this study was to evaluate the fracture strength of ZrO(2) implants after exposure to the artificial mouth. One hundred twenty ZrO(2) and Ti implants were used. The Ti implants were divided into two control groups (A and B). ZrO(2) implants manufactured from yttria-stabilized tetragonal ZrO(2) polycrystal (Y-TZP) in group C, from Y-TZP dotted with alumina (Y-TZP-A) in group D, and from Y-TZP-A with a modified surface in groups E and F were used. In group F, the implant heads were prepared, and in group G, the implants were restored with ZrO(2) crowns. Each group included 16 samples with the exception of group D, which included 24 samples. A subgroup of each implant type (eight implants) was subjected to thermomechanical cycling in a chewing simulator prior to fracture testing. Test specimens were then loaded until a fracture occurred. Seven of the 120 samples failed in the chewing simulator. ZrO(2) implant fracture occurred at 725 to 850 N when the implants were not prepared, and at 539 to 607 N when prepared. The samples in group A fractured at the level of the abutment screw. All ZrO(2) implants fractured at the level of the Technovit resin (Heraeus Kulzer GmbH & Co., Wehrheim, Germany). No fracture of the ZrO(2) crowns in group G was observed. Mean fracture strength values obtained were all within the limits of clinical acceptance. However, implant preparation had a statistically significant negative influence on the implant fracture strength. Long-term clinical data are necessary before one-piece ZrO(2) implants can be recommended for daily practice.

Using ZrO2 or Al2O3 particles to enhance the mechanical properties of a LZSA glass-ceramic matrix

Investigations of a range of glass ceramic compositions have been developed in the last decades. These materials show a good potential to be used at room temperature as a substitute to other ceramic materials, due to their lower sintering temperature and costs. The mainly reason that limits the use of these materials is their low mechanical strength. In this work a Li2O-ZrO2-SiO2-Al2O3 (LZSA) glass powder was mixed with 30 wt. % of ZrO2 or Al2O3 (submicron size), uniaxially pressed under 40 MPa and sintered at 650 oC/30 min. In some samples a second sintering step at 1000 oC during 30 minutes was also performed, in order to improve the mechanical properties by increasing the crystallized fraction. The sintered samples were characterized by bending strength measurements, X-ray diffraction and scanning electron microscopy analyses. Apparent densities values were determined by the Archimedes's method. The results obtained in this work indicate that the addition of ZrO2 and Al2O3 (reinforcing particles) decreases the density of the glass-ceramic materials. X-ray diffraction analysis indicated an increase of the crystallized fraction in samples sintered at 1000 oC. Fracture strength values has showed to be dependent on the sintering temperature and also on the reinforcing crystalline particles.