Higher Fracture Resistance Research Articles

Ceramic resurfacing: the future and challenges

Ceramics have a history of use in total hip replacement (THR) including early use in hip resurfacing. Improvements in ceramics over the past two decades have resulted in the BIOLOX ® delta material which has a higher fracture resistance, low wear and excellent biocompatibility compared to other orthopaedic biomaterials. Cobalt Chromium Molybdenum (CoCrMo) metal alloy continues to be used in hip resurfacing but is generally limited to use of larger sizes in active males due to a legacy of concerns with metal ion release from discontinued devices and large diameter modular head trunnions. A novel hip resurfacing device (ReCerf ® , MatOrtho Ltd., UK) utilises BIOLOX ® delta, removing CoCrMo metal from the prosthesis. ReCerf ® is based on a clinically successful design from the same manufacturer (ADEPT ® , MatOrtho Ltd., UK) and although BIOLOX ® delta is a clinically proven material in THR, it requires significant testing to prove safety in the clinical environment. Increasing regulations particularly in Europe, has increased the time to market for new devices such as this and whilst the changes are being implemented to ensure the lowest risk for patients, they are also leaving patients unable to access new treatment routes. Ultimately, it is long term clinical outcomes that are required to determine whether the future of resurfacing is in using alternative materials such as ceramic and whether these compare favourably with the established, successful metal designs which have been in clinical use for over 20 years.

Fracture Resistance and Retention of CAD/CAM Endo-Crowns Using Different Preparation Designs

Purpose: to study the influence of different preparation designs on fracture resistance and retention of CAD/CAM endocrowns. Materials and methods: Forty human mandibular molars were selected to conduct the present study. All teeth were randomly divided into 2 groups (n=20 each) according to the preparation design of endocrown, Group (1): Endodontically treated teeth without ferrule (butt joint). Group (2): Endodontically treated teeth with 1mm ferrule. All prepared teeth were restored using IPS e-max CAD endocrowns. After cementation of endocrowns all specimens were subjected to thermal cycling in automated thermocycling machine in order to mimic the intra-oral condition. Then retention was measured using material testing machine, also fracture resistance was measured using material testing machine. The recorded data were collected, tabulated and statistically analyzed. Results: Endodontically treated molar with 1mm ferrule showed high fracture resistance and retention than endodontically treated molar without ferrule. Conclusions: All obtained fracture resistance and retention values lie within the clinically accepted ranges, endocrowns with 1mm ferrule have fracture resistance and retention higher than endocrowns without ferrule (butt joint).

The effects of design parameters on mechanical failure of Ti-6Al-4V implants using finite element analysis

The failure of dental implant is frequently occurred as the result of mechanical complications under daily biting forces. The long-term stability and the success of a dental implant are highly depended upon developing an implant system having high fracture resistance under cyclic biting forces. The design of implant has a crucial role in improving the fracture resistance of implant by decreasing stress concentration around the implant system. In the present study, three-dimensional (3D) models of the internally connected Ti-6Al-4V implant systems were developed in different dimensions and the failure analysis of these implants was performed under real biting forces according to ISO 14801 using Finite Element Analysis (FEA). In these models, the design parameters (implant diameter, abutment diameter, taper angle of abutment, implant wall thickness, etc.) were optimized in order to prevent the failure of implants in long-term use. The implant model exhibiting the best biomechanical behavior was determined and the stress value was decreased to 170.34 MPa (von-Mises stress) in this implant under cyclic biting loads. Besides the high fracture resistance of this model, longer service life was predicted and relatively smoother stress transmission was achieved from the implant to the bone tissues under biting forces. The implant stability was also increased by optimizing implant tightening torques. Additionally, the mechanical behavior of this implant model was investigated under different biting conditions.

Study of the structural degradation of steel 15Kh5M upon continuous duty

Structural degradation of the material upon long-term thermal and force impacts is a complex process which includes migration of the grain boundaries, diffusion of the active elements of the external and technological environment, hydrogen embrittlement, aging, grain boundary corrosion and other mechanisms. Application of the fractal and multifractal formalism to the description of microstructures opens up wide opportunities for quantitative assessment of the structural arrangement of the material, clarifies and reveals new aspects of the known mechanisms of structural transformations. Multifractal parameterization allows us to study the processes of structural degradation from the images of microstructures and identify structural changes that are hardly distinguishable visually. Any quantitative structural indicator can be used to calculate the multifractal spectra of the microstructure, but the most preferable is that provides the maximum range of variation in the numerical values of the multifractal components. The results of studying structural degradation of steel 15Kh5M upon continuous duty are presented. It is shown that structural degradation of steel during operation under high temperatures and stresses is accompanied by enlargement of the microstructural objects, broadening of the grain boundaries and allocation of the dispersed particles which are represented as point objects in the images. The processes of structural degradation lead to an increase in the range of changes in the components of the multifractal spectra. High values of complex indicators of structural arrangement indicate to an increase in heterogeneity and randomness at the micro-scale level, but at the same time, to manifestation of the ordered combinations of individual submicrostructures. Those structural transformations adapt the material to external impacts and provide the highest reliability and fracture resistance of the material.

Auxetic graphene oxide-porous foam for acoustic wave and shock energy dissipation

Auxetic cellular structures have garnered huge research interest as a candidate for energy absorption due to their appealing features, including extremely high indentation resistance and fracture resistance. However, auxetic foams reported so far typically can only sustain a very limited loading force and impact with a counter-intuitive behavior. Here, we report a highly efficient sound and shock absorber based on three-dimensional (3D) auxetic foam with two-dimensional (2D) wrinkled graphene oxide. Compared with pure polyurethane foam, the auxetic heterostructured polyurethane foam interconnected with 2D corrugated graphene oxide shows a sound absorbing capacity of 99.7% at a frequency of 2,236 Hz and a shock energy absorbing time of 189% during the impact loading. The synergistic effects between 3D auxetic foam and 2D wrinkled graphene oxide result in stable compressive cycling performance, more indentation resistance, and more energy dissipation during local impact loads. This 3D engineered auxetic porous structure with 2D crumpled graphene oxide provides a new and cost-effective strategy to effectively absorb acoustic and shock energy.

Fracture strength of endodontically treated teeth restored with different fiber post and core systems.

The aim of this study was to investigate the effects of different post and core systems, CAD/CAM crown placement on fracture strength of endodontically treated mandibular premolar teeth. One hundred forty single-rooted premolar teeth were randomly divided into a control group and six experimental groups as follows: control group (Group 1); FiberSite post luting with Clearfil DC Core Plus (Group 2); RelyX Fiber post luting and core build up with Clearfil DC Core Plus (Group 3); RelyX Fiber post luting with Clearfil DC Core Plus and core build up with Filtek Bulk Fill Posterior (Group 4); specimens that received CAD/CAM crowns after the same procedures performed in Groups 2, 3, and 4, respectively (Groups 5, 6, and 7). Fracture strength tests were performed, and the failure modes were recorded. Data were statistically analyzed using one-way ANOVA and post hoc Tukey tests. The highest fracture resistance was observed in the control group and among the experimental groups in Group 4. Groups 3 and 5 showed similar fracture resistance followed by Group 2. The lowest fracture resistances were seen in the samples of Groups 6 and 7. While the fracture strength of Group 2 increased after the crown placement (Group 5), the fracture strength of Group 3 and Group 4 decreased (P < 0.05). While the specimens in Groups 1, 2, 3, and 4 predominantly showed favorable failure, unfavorable failure was more frequent in Groups 5, 6, and 7.

Influence of luting cement on the clinical outcomes of Zirconia pediatric crowns: A 3-year split-mouth randomized controlled trial.

There is no scientific evidence supporting the choice of luting cement for cementation of zirconia crowns. The purpose of this split-mouth study was to compare the efficacy of using bioactive cement versus packable glass ionomer for cementation of posterior pediatric zirconia crowns. Fifty first mandibular primary molars were restored by zirconia crowns and were randomly divided to be luted with either (a) bioactive cement or (b) packable glass ionomer. Crowns' retention, fracture, and gingival condition were evaluated at 1week, and 1-, 3-, 6-, 9-, 12-, 18-, 24-, and 36-month intervals. Statistical analysis was carried out using Fisher's exact test, Kaplan-Meier survival analysis, and Wilcoxon signed rank test. At 3- to 36-month follow-ups, there were statistically significant (P=.009-≤.001) less debonded crowns in packable glass ionomer group. There were no fractured crowns for either cements. There was no statistically significant difference between gingival index scores. Packable glass ionomer is more retentive than bioactive cement when used for cementing zirconia pediatric crowns. Posterior zirconia pediatric crowns have high fracture resistance after 36months of clinical performance, irrespective of luting cement. Luting cement for zirconia pediatric crowns has no apparent effect on gingival condition around crowns.

Comparative Evaluation of Short Fiber-reinforced Composite Resin Thickness on Fracture Resistance of Class II Composite Restoration: An In Vitro Study

This study aims to evaluate the difference in fracture resistance of the short fiber-reinforced composite (SFRC) thickness as intermediate layer of class II composite restoration. Thirty human maxillary premolars were selected and divided into three groups. In groups I, II, and III, class II cavities were prepared. Groups I and II were restored with 2 mm and 4 mm thickness of SRFC as intermediate layer. Group III as control group was restored with nanohybrid composite. Thermocycling procedure was performed manually 250 times. Fracture resistance was measured by using Universal Testing Machine. Data were analyzed statistically using One-way Analysis of Variance (ANOVA) and post hoc least significant difference (LSD) test. The result showed that group II had the highest fracture resistance and group III had the lowest fracture resistance. The difference between groups was statistically significant (p value < 0.05). The conclusion showed that adding 4 mm of SFRC as an intermediate layer increased the fracture resistance. The use of SFRC as intermediate layer enhanced the fracture resistance of class II composite restoration.

Comparative Study on Fracture Resistance of Endodontically Treated Tooth in Relation to Variable Ferrule Heights Using Custom-made and Prefabricated Post and Core: An In Vitro Study.

ABSTRACTIntroduction:Endodontically treated teeth have significantly differentphysical properties compared to vital teeth. To ensure functional longevity,endodontically treated teeth must have at least 5 mm of tooth structure coronalto the crestal bone, 2 mm of coronal tooth structure incisal to the preparationfinish line are necessary to ensure functional integrity.Aim and Objectives:To evaluate fracture resistance of endodontically treated teeth restored withcustom cast post, custom cast post with variable ferrule height and teethwithout ferrule, prefabricated post with variable ferrule height and teethwithout ferrule. To compare fracture resistance of teeth restored with customcast post and prefabricated post with variable ferrule heights.Materials and Methods:Methodology includes selection of teeth, root canal preparation,post space preparation, grouping of samples, Group A–custom cast post andcore with sub groups of variable ferrule height, pattern fabrication, Group A- pattern fabrication for customized cast post. Group B–pattern fabricationfor prefabricated post and core, investing and casting, cementation, custommade acrylic jig preparation, testing of specimens.Results:The differencein the fracture load between the samples of Group A was highly significantat the 0.001 level. Subgroup A4 had highest fracture resistance while GroupA, possessed the least fracture resistance. Subgroups A2, A3 had fractureresistance value intermediate between A1, A4.Conclusion:Increasing theferrule height significantly increases (P < 0.001) the fracture resistance ofendodontically treated teeth restored with both custom made cast post andcore and prefabricated post with metal core. Comparatively the custom madecast post and core with variable ferrule height, especially 2 mm ferrule showedsignificant fracture resistance than prefabricated post with metal core. Thepresence of 2 mm ferrule height significantly increases (P < 0.001).

Fracture resistance and marginal fit of the zirconia crowns with varied occlusal thickness.

PURPOSEThe present study aimed to evaluate the clinical applicability of monolithic zirconia (MZ) crowns of different thickness via determination of fracture resistance and marginal fit.MATERIALS AND METHODSMZ crowns with 0.5, 0.8, 1.0, and 1.5 mm thickness and porcelain fused to metal (PFM) crowns were prepared, ten crowns in each group. Marginal gaps of the crowns were measured. All crowns were aged with thermal cycling (5 – 55℃/10000 cycle) and chewing simulator (50 N/1 Hz/lateral movement: 2 mm, mouth opening: 2 mm/240000 cycles). After aging, fracture resistance of crowns was determined. Statistical analysis was performed with one-way ANOVA and Tukey's HDS post hoc test.RESULTSFracture loads were higher in the PFM and 1 mm MZ crowns compared to 0.5 mm and 0.8 mm crowns. 1.5 mm MZ crowns were not broken even with the highest force applied (10 kN). All marginal gap values were below 86 µm even in the PFM crowns, and PFM crowns had a higher marginal gap than the MZ crowns.CONCLUSIONThe monolithic zirconia exhibited high fracture resistance and good marginal fit even with the 0.5 mm thickness, which might be used with reduced occlusal thickness and be beneficial in challengingly narrow interocclusal space.

Effect of material thickness on the fracture resistance and failure pattern of 3D-printed composite crowns.

AIM To evaluate the fracture resistance and failure pattern of 3D-printed and milled composite resin crowns as a function of different material thicknesses. MATERIALS AND METHODS Three typodont tooth models were prepared to receive a full coverage composite resin crown with different thicknesses (0.5, 1.0, and 1.5 mm). The prepared master casts were digitally scanned using an intraoral scanner, and the STL files were used to fabricate 60 nanocomposite crowns divided into two groups according to the material thickness (n = 10) and fabrication method: a 3D-printed group (3D) using an SLA printer with nanocomposite, and a milled group (M) using a milling machine and composite blocks. All crowns were adhesively seated on stereolithography (SLA)-fabricated dies. All samples were subjected to thermomechanical loading and fracture testing. The load to fracture [N] was recorded and the failure pattern evaluated. Data were statistically analyzed using a two-way ANOVA followed by a Bonferroni post hoc test. The level of significance was set at α = 0.05. RESULTS The 3D group showed the highest values for fracture resistance compared with the milled group within the three tested thicknesses (P < 0.001). The 3D and M groups presented significantly higher load to fracture for the 1.5-mm thickness (2383.5 ± 188.58 N and 1284.7 ± 77.62 N, respectively) compared with the 1.0-mm thickness (1945.9 ± 65.32 N and 932.1 ± 41.29 N, respectively) and the 0.5-mm thickness, which showed the lowest values in both groups (1345.0 ± 101.15 N and 519.3 ± 32.96 N, respectively). A higher incidence of irreparable fractures was observed for the 1.5-mm thickness. CONCLUSION 3D-printed composite resin crowns showed high fracture resistance at different material thicknesses and can be suggested as a viable solution in conservative dentistry.

High Toughness Inorganic Solid Electrolytes &lt;i&gt;via&lt;/i&gt; the Use of Reduced Graphene-Oxide

Ceramic solid electrolytes are important emerging materials that have the potential to enable the safe use of Li metal anodes. However, they suffer from inherently low fracture toughness which significantly limits battery performance and reliability. While small electrolyte dimensions are generally needed for faster ion transport, these length scales also restrict the approaches that can be used to engineer higher fracture resistance. Inspired by the toughening that reduced graphene oxide provides to polymer and engineering ceramics, this approach is explored as a means to enhance the toughness of an oxide-based lithium ion conductor. An average KIc enhancement of 120% is demonstrated without altering the ionic and electronic behavior of the material. To our knowledge this is the toughest ceramic solid electrolyte reported to date. Based on these results, an analytical framework is developed to provide guidelines for designing ultra-tough solid electrolytes using 2D materials.

Fracture behavior of root-amputated teeth at different amount of periodontal support \u2013 a preliminary in vitro study

BackgroundThe purpose of this study was to evaluate the effect of the amount of periodontal support on the fracture resistance of root-amputated maxillary molar teeth restored with either direct class. I. restorations or class II. mesio-occluso-distal (MOD) indirect overlay restorations with cuspal coverage.MethodsSixty sound maxillary first molars were collected and randomly divided into four groups. In Groups 1 and 2, MOD cavities were prepared and all cusps were reduced by 2 mm, whereas in Group 3 and 4, only a conservative Class I. cavity was prepared. Subsequently, root canal treatment was performed and the mesio-buccal roots were amputated. Groups 1 and 2 were restored with indirect composite overlay, while Groups 3 and 4 received direct composite fillings. After restoration, teeth were embedded as follows: Groups 1 and 3: normal bone level, Groups 2 and 4: furcation involvement. The specimens were submitted to static fracture resistance testing. Fracture thresholds and fracture patterns were measured and evaluated.ResultsGroup 1 had the highest fracture resistance (2311,6 N) among the restored groups and showed statistically significant difference compared to Group 2 (p = 0.038) and Group 4 (p = 0.011). There was no statistically significant difference in terms of fracture resistance between the rest of the groups. In terms of the fracture patterns, Group 3 was characterized by the highest percentage (60%) of mostly favorable fractures, while the rest of the groups showed predominantly unfavorable ones.ConclusionsThe amount of periodontal support seems to influence the fracture resistance of root-amputated and restored maxillary molars.

Fracture resistance of teeth restored with endocrowns: An in vitro study.

The objective of this study is to evaluate the fracture resistance and failure mode of endodontically treated teeth restored with lithium disilicate endocrowns of different crown thicknesses. A total of 30 endodontically treated permanent mandibular first molars were sectioned horizontally 2 mm above the highest point of the cemento-enamel junction. The specimens were divided into three groups, and each group was restored with lithium disilicate (IPS e-max press) endocrowns of different crown thicknesses (3, 4.5, and 6 mm, respectively). After cementation, specimens were stored in room temperature for 72 hours, followed by subjecting them to compressive strength testing until failure. The fracture loads and the failure mode were recorded. Statistically analysis was performed using one-way analysis of variance. A statistically significant difference was found in the fracture resistance between the three groups with the highest fracture resistance in the 3 mm group, followed by the 4.5 mm group, and the least in the 6 mm group (P < .05). Most of the failures were accompanied with tooth fracture (90% in 3 mm group, 100% in 4.5 mm group, and 80% in 6 mm group). Increasing the crown thickness of the endocrowns reduced the fracture resistance of restored teeth. Minimum fracture loads for all teeth restored with endocrowns were significantly higher than the maximum occlusal forces reported in the literature. Fracture resistance and mode of failure of lithium disilicate (IPS e-max press) endocrowns varies widely between crown thicknesses. Clinicians should be cautious with crown thickness for endocrown restorations.

Are Metal-Free Monolithic Crowns the Present of Prosthesis? Study of Mechanical Behaviour.

Purpose: To analyze in vitro the mechanical behavior of five types of complete coverage crowns fabricated from different materials. Materials and methods: Seventy-five full coverage crowns were divided into five groups according to material: Group I, metal core with feldspathic ceramic covering (MC- control group); Group II, zirconia core with feldspathic ceramic covering (CZ); Group III, tetragonal monolithic zirconia (TMZ); Group IV, cubic monolithic zirconia (CMZ); Group V, high molecular weight polymethyl methacrylate (PMMAG) doped with graphene nanoparticles. All crowns underwent in vitro fatiguing by dynamic loading in wet conditions to simulate the masticatory forces to which prosthodontic materials are subject in the oral medium. Lastly, fracture resistance was evaluated by static compression testing. Results: The fracture resistance values obtained were as follows: Group MC, 2443.6 ± 238.6 N; Group CZ, 2095.4 ± 329.2 N; Group TMZ, 2494.6 ± 236.6 N; Group CMZ, 1523.6 ± 325.2 N; and Group PMMAG, 1708.9 ± 386.6 N. Group MC presented higher strength with statistically significant differences in comparison with Groups CZ (P = 0.002), CMZ (P < 0.001), and PMMAG (P < 0.001). Weibull distribution showed less probability of cumulative biomechanical failure in Groups MC and TMZ. Conclusions: Metal-ceramic and tetragonal zirconia showed high fracture resistance, while cubic zirconia and PMMA doped with graphene nanoparticles obtained lower values.

Arapaima Fish Scale: One of the Toughest Flexible Biological Materials

Summary For fish scales to provide protection from predators without severely compromising mobility, they must be lightweight, flexible, and tough. The arapaima fish scale is a superb example of this, enabling its survival in piranha-infested lakes of the Amazon. These elasmoid scales comprise two layers: a laminate composite of parallel collagen fibrils arranged in a Bouligand-like pattern and a highly mineralized surface layer that prevents initial penetration damage. Here, we measure its J-integral fracture toughness and find that the crack-growth toughness is ∼100–200 kJ⋅m−2, representing a very high fracture resistance for a natural material. This toughness results from multiple deformation mechanisms acting in concert in the twisted plywood structure of the scale, involving the collagenous lamellae at varying orientations retarding crack advance through stretching, reorientation, delamination and shear, and fracture. The toughness values obtained for the arapaima scales indicate that they are among the toughest of nature's flexible biological materials.

Is a Zirconia Dental Implant Safe When It Is Available on the Market?

The market share of zirconia (ZrO2) dental implants is steadily increasing. This material comprises a polymorphous character with three temperature-dependent crystalline structures, namely monoclinic (m), tetragonal (t) and cubic (c) phases. Special attention is given to the tetragonal phase when maintained in a metastable state at room temperature. Metastable tetragonal grains allow for the beneficial phenomenon of Phase Transformation Toughening (PTT), resulting in a high fracture resistance, but may lead to an undesired surface transformation to the monoclinic phase in a humid environment (low-temperature degradation, LTD, often referred to as ‘ageing’). Today, the clinical safety of zirconia dental implants by means of long-term stability is being addressed by two international ISO standards. These standards impose different experimental setups concerning the dynamic fatigue resistance of the final product (ISO 14801) or the ageing behavior of a standardized sample (ISO 13356) separately. However, when evaluating zirconia dental implants pre-clinically, oral environmental conditions should be simulated to the extent possible by combining a hydrothermal treatment and dynamic fatigue. For failure analysis, phase transformation might be quantified by non-destructive techniques, such as X-Ray Diffraction (XRD) or Raman spectroscopy, whereas Scanning Electron Microscopy (SEM) of cross-sections or Focused Ion Beam (FIB) sections might be used for visualization of the monoclinic layer growth in depth. Finally, a minimum load should be defined for static loading to fracture. The purpose of this communication is to contribute to the current discussion on how to optimize the aforementioned standards in order to guarantee clinical safety for the patients.

The Effect of Two Bulk-Fill Resin Composites on Fracture Resistance of Endodontically Treated Teeth

Objectives: The aim of this study was to compare the effect of two commercially available bulk-fill restorative materials on the fracture resistance of endodontically treated human molar teeth. Materials and methods: A total of 44 mandibular third molar were divided into four groups: Group 1; 4 mm thick bulk-fill fluid composite (SDR ™, Dentsply, Konstanz, Germany) was applied to the cavities. The restoration of the proximal walls and the occlusal region was completed with posterior composite (Valux Plus, 3M ESPE, St. Paul, MN, USA). Group 2; 4 mm thick fiber-resin reinforced bulk-fill composite (EverX Posterior; GC Corp., Japan) was placed in the cavities and the procedure in Group 1 was repeated. Group 3 (negative control group); no restoration was applied to the cavities. Group 4 (positive control group); comprised intact molar teeth without any treatment. The root canals were shaped using rotary instruments, irrigated with NaOCl, and obturated. All samples were incubated in distilled water at 37˚C for 1 week and then fracture strength test was performed. The values were recorded in Newton and the data were evaluated using Kruskal Wallis and Mann-Whitney U test. Results: No statistically significant difference (p &amp;gt;0.05 ) was observed between group 1, 2, and the positive control group. However, the bulk-fill fluid composite material showed higher fracture resistance than the fiber-resin reinforced composite material (p&amp;lt;0.05). The highest fracture resistance was observed in the positive control group. The fracture resistance of the negative control group was statistically lower than the other groups (p&amp;lt;0.05). Conclusions: Both of the bulk-fill restorative materials in endodontically treated teeth showed similar fracture resistance to intact teeth. In addition, the clinical use of the bulk-fill fluid composites may be recommended because of their high fracture resistance and ease of application.

Structure, mechanics and material properties of claw cuticle from mole cricket Gryllotalpaorientalis.

Powerful shovel-like forelimbs with special shape, structure and biological materials enable mole cricket to digging efficiently. During digging, the tip of the claw needs to wedge into the soil, and the base needs to withstand considerable anti-shear force. In this study, we analysed the structural characteristics, material composition and mechanical properties of the claw teeth using scanning electron microscopy, plasma atomic emission spectroscopy, nanoindentation and finite element analysis. The results show that the tips of claw teeth have a dense and homogeneous structure and a higher hardness and contents of Mn and Zn compared with the base. The structure of the base of claw teeth has an obvious laminar structure and higher fracture resistance. Moreover, it is speculated from the simulation results that basal position of the claw teeth is tough enough to withstand high stress, and the presence of the ribs effectively improves the mechanical stability and load-bearing capacity of the teeth during excavation. The results of this study can provide inspiration for the design of efficient mechanical components and agricultural implements.

Comparison between Biaxial Flexural Strength and Microstructure of Polished and Glaze-Fired Specimens of Zirconia Lithium Silicate Glass Ceramic

Introduction: There has been a growing interest in glass ceramic systems with good esthetics, high fracture resistance, bonding durability, and simplified fabrication techniques using CAD/CAM. The aim of this study was to compare flexural strength in and and fired specimens of zirconium lithium silicate (ZLS) CAD/CAM blocks Celtra Duo. Methods: A total of 14 specimens of Celtra Duo (Dentsply Sirona, Germany) were designated and equally divided into two groups, including group I (n=7; as polished) and group II (n=7; as glazed and fired) according to the manufacturers’ instructions. Then biaxial flexural strength was tested according to ISO 6872 using a universal testing machine and piston-on-three-ball method after polishing, glazing, and firing. The fractured surfaces and microstructure were observed by scanning electron microscope (Jeol/GSM5300). Data were then statistically analyzed using SPSS software (version 20.0). Results: There were statistically significant differences in biaxial flexural strength between a polished and glaze-fired specimen of ZLS glass ceramic discs as biaxial flexural strength was lower in polished specimens (mean±standard deviation: 158.7±21.67 MPa), while the glazed specimens showed higher biaxial flexural strength (mean±standard deviation: 261.5±31.89 MPa). Conclusion: Glazing and firing of Celtra Duo specimens increased biaxial flexural strength significantly in comparison to polishing with no significant change in the microstructure.