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(1) Background: Due to advantages such as avoidance of chipping, pulp-friendly tooth preparation and cost reduction, zirconia is increasingly being used monolithically without veneering. Nevertheless, to enable good aesthetics, various multilayer systems have been developed. The aim of this study was to investigate the impact of different zirconia multilayer strategies and yttria levels on fracture load, fracture pattern, stress distribution and surface roughness. (2) Methods: Monolithic three-unit anterior FDPs were made from three different color-gradient zirconia multilayer materials with different yttria levels corresponding to varying strength and degrees of translucency grades (Katana HTML, STML, UTML, Kuraray) and one strength-gradient zirconia multilayer material (Katana YML, Kuraray) and artificially aged in a chewing simulator (1.2 × 106 load cycles, 50 N, 2 × 3000 thermocycles, 5–55 °C). Analyses of fracture load, fracture pattern, fracture surfaces, stress distribution and roughness were performed after the fracture load test. Shapiro–Wilk, Kruskal–Wallis, Mann–Whitney U-tests and one-way ANOVA were used (p < 0.05). (3) Results: Fracture loads of the high strength color-gradient material HTML and the strength-gradient material YML were comparable after 5 years of aging (p = 0.645). Increasing yttria levels resulted in a decrease in fracture resistance of 42–57% (p < 0.05). Surface roughness of different zirconia generations is comparable after polishing and aging. (4) Conclusions: Color-gradient multilayer zirconia materials and new strength-gradient zirconia materials with similar yttria levels in the basal layers show comparable mechanical properties and are suitable for anterior FDPs.

Implant-supported cement–screw-retained crowns combine the advantages of screw-retained and cement-retained crowns. However, the occlusal screw access hole interrupts porcelain integrity, which may...

INTRODUCTION: On rare occasions, fractures of the tibial plateau may occur after uni-compartmental knee arthroplasty (UKA) and account for 2% of total UKA failures. The purpose of this narrative review is to identify and discuss potential risk factors that might lead to prevention of this invalidating complication. MATERIALS AND METHODS: Electronic database of Pubmed, Scopus, Cochrane and Google Scholar were searched. A total of 457 articles related to the topic were found. Of those, 86 references were included in this narrative review. RESULTS: UKA implantation acts as a stress riser in the medial compartment. To avoid fractures, surgeons need to balance load and bone stock. Post-operative lower limb alignment, implant positioning, level of resection and sizing of the tibial tray have a strong influence on load distribution of the tibial bone. Pain on weight-bearing signals bone-load imbalance and acts as an indicator of bone remodeling and should be a trigger for unloading. The first three months after surgery are critical because of transient post-operative osteoporosis and local biomechanical changes. Acquired osteoporosis is a growing concern in the arthroplasty population. Split fractures require internal fixation, while subsidence fractures differ in their management depending of the amount of bone impaction. Loose implants require revision knee arthroplasty. CONCLUSION: Peri-prosthetic fracture is a rare, but troublesome event, which can lead to implant failure and revision surgery. Better knowledge of the multifactorial risk factors in association with a thorough surgical technique is key for prevention.

PURPOSE To evaluate the effect of endodontic access hole preparation on fracture resistance of translucent zirconia (5Y) and conventional zirconia crowns (3Y) with varying occlusal thicknesses. MATERIALS AND METHODS Polymethylmethacrylate (PMMA) dies, representing a prepared tooth, were milled. Zirconia crowns with 1 mm thick axial walls and varying occlusal thicknesses were milled from 3Y (Cercon HT) or 5Y (Cercon XT) zirconia discs and sintered. 160 crowns were divided into 16 groups (n = 10 per group) based on the zirconia type (3Y, 5Y), occlusal thickness (0.5, 1.0, 1.5, 2.0 mm), and access hole preparation (with access hole, control). Crowns were cemented on the PMMA dies with resin-modified glass ionomer cement (Rely X Luting Plus) under constant weight (500 g) and thermocycled for 10,000 cycles. In half of the samples, following 5000 cycles of thermocycling, a uniform endodontic access hole was created using a diamond bur and restored immediately with resin composite (Filtek Supreme Ultra, 3M ESPE). The fracture resistance of the specimens was tested on an Instron 5566 universal testing machine with a stainless steel ball indenter (9.0 mm dia.) and the maximum load before failure was recorded as fracture load (N). Three-way ANOVA testing examined the effect of zirconia type, occlusal thickness, and access hole preparation on fracture loads of the crowns. Statistical tests were two-sided and significance level was set at 95% (α = 0.05). RESULTS Fracture load was significantly affected by the type of zirconia, occlusal thickness, and access hole preparation (p < 0.001). Pairwise comparisons revealed that access hole preparation significantly reduced the fracture load of 3Y crowns with 0.5 or 1.0 mm of occlusal thickness and 5Y zirconia crowns with 0.5, 1.0, or 1.5 mm of occlusal thickness (p < 0.05). Increasing occlusal thickness reduced the effect of access hole preparation on fracture load. CONCLUSION Type of zirconia, occlusal thickness, and access hole preparation had significant effects on the fracture load of zirconia crowns. The effect of endodontic access was significant on the 3Y and 5Y zirconia crowns with ≤1.0 and ≤1.5 mm occlusal thicknesses, respectively.

Purpose To evaluate the effect of three two-retainer designs of a resin-bonded fixed dental prosthesis (RBFDP) on fracture resistance. Materials and methods A total of 21 three-unit, all-ceramic RBFPDs were fabricated to replace a missing maxillary lateral incisor. The prostheses were divided into three groups of 7 each: Group L (labial RBFPD); Group ML (modified labial RBFPD, fabricated the same as in Group L with additional preparation that included a shallow proximal groove at the pontic side); and Group P, an all-ceramic palatal RBFPD that acted as control. Preparations were done on the maxillary left central incisor and canine of a typodont model, and 21 epoxy resin models were duplicated for the three groups. The RBFPDs were designed using CAD software and constructed using the heat-pressed technique, after which the prostheses were bonded to their corresponding epoxy resin model according to the manufacturer's instructions. A fracture resistance test was performed on all specimens following aging. Data were analyzed using one-way ANOVA. Results The highest fracture load values were recorded in Group P (547.5 N), followed by Group ML (462.6 N) and then Group L (418.3 N). The difference among the three designs was not statistically significant (F = 2.5, P = 0.1). Conclusion Both labial and modified labial RBFDPs could be a viable alternative treatment option for replacement of missing maxillary lateral incisors.

The optimization of welding parameters of the welded joints of TC4 titanium alloys/304 stainless steel (TC4/304 SS) by friction stir lap welding (FSLW) based on orthogonal test was researched. The results show that under low heat input (low rotating speed and high traversing speed), there was a damaging defect in stir zone (SZ) and cracks started from the defect under the tension. Under high heat input (high rotating speed and low traversing speed), the intermetallic compounds were barely formed, and the cracks formed from 304 SS blocks existed in thermal mechanically affected zone of TC4 titanium alloys (TMAZTC4), eventually obtaining the highest fracturing load. However, under middle heat input (middle rotating speed and low traversing speed), the intermetallic compounds and the maximum hardness were found at the interface, and cracks started from these compounds under the tension, getting a middle fracture load. In conclusion, the joints with good properties can be obtained with high rotating speed and low traversing speed.

To investigate the impact of different cleaning methods on the fracture load and two-body wear of additively manufactured three-unit fixed dental prostheses (FDP) for long-term temporary use, compared to the respective outcomes of milled provisional PMMA FDPs. Shape congruent three-unit FDPs were 3D printed using three different resin-based materials [FPT, GCT, NMF] or milled [TEL] (N = 48, n = 16 per group). After printing, the FDPs were cleaned using: Isopropanol (ISO), Yellow Magic 7 (YEL), or centrifugal force (CEN). Chewing simulation was carried out with a vertical load of 50 N (480,000 × 5 °C/55 °C). Two-body wear and fracture load were measured. Data were analyzed using global univariate ANOVA with partial eta squared, Kruskal-Wallis H, Mann-Whitney U, and Spearman’s rho test (p < 0.05). TEL showed less wear resistance than FPT (p = 0.001) for all cleaning methods tested. Concerning vertical material loss, NMF and GCT were in the same range of value (p = 0.419–0.997), except within FDPs cleaned in ISO (p = 0.021). FPT showed no impact of cleaning method on wear resistance (p = 0.219–0.692). TEL (p < 0.001) showed the highest and FPT (p < 0.001) the lowest fracture load. Regarding the cleaning methods, specimens treated with ISO showed lower fracture load than specimens cleaned with CEN (p = 0.044) or YEL (p = 0.036). The material selection and the cleaning method can have an impact on two-body wear and fracture load results. Printed restorations showed superior two-body wear resistance compared to milled FDPs but lower fracture load values. Regarding cleaning methods, ISO showed a negative effect on fracture load compared to the other methods tested.

Background: Ceramic veneers is one of the conservative esthetic treatment modality in dentistry. Success of veneer is very much dependent on the design preparation. Materials and Methods: Thirty selected teeth were categorized within three groups of 10 each with varying design preparations. After mounting the specimens, the incisal reduction was done, and porcelain laminate veneers were fabricated. Then cementation of the veneers was done with resin-cement, and fracture load was applied and recorded. Results: Multiple comparisons were done using post-hoc Tukey's test and modality of failure of veneers among the different designs were done using Chi-square test with the level of significance fixed at 0.05. Conclusion: Ceramic veneers preparation design including1 mm incisal reduction along with 1 mm of palatal-chamfer height revealed greater fracture toughness in contrast to incisal-reduction 1 mm along with butt-joint preparation design.

Aim The aim of this study was to evaluate the effect of cement on the fracture load of monolithic zirconia crowns with different yttria content (3 and 5 mol%). Methods A total of 62 monolithic zirconia crowns, 40 3Y-zirconia crowns (Prettau® Zirconia, Zirkonzahn) and 22 5Y-zirconia crowns (Prettau® 4 Anterior®, Zirkonzahn) were produced to a shallow chamfer molar preparation. The 3Y-crowns were divided into four groups and attached to composite abutment duplicates (SDR® flow+, Dentsply DeTrey GmbH) using the following four cementation techniques; (1) Self-adhesive resin-based cement, (2) Pre-treatment with air-abrasion and self-adhesive resin-based cement, (3) Zinc phosphate cement, (4) Glass-ionomer cement. The 5Y-crowns were divided into two groups and attached to the duplicates with; (1) Self-adhesive resin-based cement, or (2) Air-abrasion pre-treatment and self-adhesive resin-based cement. All crowns were loaded axially (0.5 mm/min) on the occlusal surface until fracture occurred. Results Among the 3Y-zirconia groups, the zinc phosphate cement group fractured at lower loads compared to the resin-based cement groups, with and without air-abrasion, (p

Utar, Merve/0000-0002-5876-3743 WOS:000562984900001 PubMed: 32845029 This study intended to analyze microcracks and fractographic markings on the surface of all ceramic crowns after milling and compare the fracture loads. 90 crowns were manufactured from two feldspathic (Priticrown-Pr and Vita Mark II-Vi) and a lithium disilicate (EmaxCAD-Em) blocks (n= 30). Two groups (n= 15) were prepared for each ceramic. In the first group, crowns were analyzed twice via the fluorescent penetrant method for microcrack detection, after the manufacturing process and thermal cycles. The load to fracture test was applied at a crosshead speed of 0.5 mm/min until catastrophic failure. Second group crowns were directly cemented onto the Co-Cr dies following the manufacturing process and loaded to fracture. Fractographic markings were analyzed through scanning electron microscope. Spearman correlation analysis, Kruskal-WallisHtest, Mann-WhitneyUtest, and Wilcoxon Signed Rank test were applied (alpha= .05). Fracture loads of Em crowns were higher than other groups (p .05). Thermal cycling did not affect microcrack numbers and fracture loads (p > .05). Tooth-shaped multilayered Pr blocks did not provide an advantage in terms of microcrack and fracture loads. Kirikkale University Scientific Projects Coordination UnitKirikkale University [2015-86] Kirikkale University Scientific Projects Coordination Unit, Grant/Award Number: 2015-86

PURPOSE To analyze the impact of different veneering techniques on the fracture load of telescopic secondary crowns made of a high-performance polymer (Ultaire aryl ketone polymer [UAKP]). MATERIALS AND METHODS Zirconia primary crown models (taper of 0 degrees) were prepared (N = 48), polished, scanned, and divided into four veneering groups (n = 12 each): premanufactured, digital, full anatomical, and vestibular. For all groups except vestibular, a standardized telescopic secondary crown (thickness: 0.6 mm, circular margin: 1 mm) was constructed, adapted to the corresponding primary crown, milled from UAKP, and veneered. The veneered master crown was developed based on the premanufactured group. After surface polishing, all specimens were artificially aged in a chewing simulator (1.2 million cycles, 50 N, 1.1 Hz, between 5°C and 55°C). Fracture load was tested in a universal testing machine with a piston (O = 6 mm, 1 mm/minute). Fracture patterns were analyzed. For statistical analysis, Kolmogorov-Smirnov test and descriptive statistics followed by one-way ANOVA with post hoc Scheffe test were conducted (P < .05). RESULTS Significant differences in fracture load were found between different veneering techniques (P < .001), with the highest values for the vestibular and digital groups, followed by the premanufactured group. Full anatomical veneering showed the significantly lowest fracture load (1,885 ± 397 N). For all specimens, cohesive brittle fractures with similar fracture patterns occurred, irrespective of the veneering technique. CONCLUSION The veneering technique of telescopic secondary crowns made of high-performance polymer affects overall stability. All veneering techniques provided sufficient fracture load values for telescopic secondary crowns made of UAKP. Digital veneers seem the most recommendable.

Objective This study investigates the influence of the most commonly used indenter materials on fatigue survival and fracture resistance of zirconia crowns. Materials and Methods A total of 40 zirconia crowns were prepared using computer-aided design (CAD)/computer-aided manufacturing (CAM) technology: 30 crowns were divided into three experimental groups of 10 specimens and the last 10 specimens acted as the control group. The experimental groups were subjected to chewing simulation with simultaneous thermocycling. Three indenter materials (steatite ceramic, stainless steel, and tungsten carbide) with identical diameter were used to load the specimens. All crowns were then subjected to single load to fracture test in universal testing machine. Load was applied vertically with a crosshead speed of 1 mm/min until failure, and fracture load was recorded. Statistical Analysis Normal distribution of data was confirmed using the Shapiro–Wilk test. Descriptive statistics including means and standard deviations were determined for all groups. Differences between groups were tested using Dunnett’s test and paired sample t-test. Results Chewing simulation for 1.2 million cycles resulted in 100% survival. The highest mean fracture load was recorded for the control group and the lowest one was for the group fatigued with stainless steel indenter. Chewing simulation statistically significantly (p < 0.05) reduced the mean fracture load of the crowns fatigued with stainless steel and steatite ceramic indenter. However, the mean fracture load for the crowns fatigued with tungsten carbide was not significantly different from that of the control group. Conclusion Steatite ceramic and stainless steel indenters produced close results and significantly reduced fracture load of zirconia crowns. However, tungsten carbide indenter caused nonsignificant reduction in the fracture load of zirconia crowns.

A direct relationship has been reported between yttria concentration and translucency in zirconia restorations. However, increased yttria concentration also increases the cubic phase of the zirconia, which reduces its strength. The effect of increased yttria content on the fracture resistance of zirconia as a function of material thickness after fatigue testing requires evaluation.The purpose of this in vitro study was to use the biaxial flexural test to evaluate the effect of yttria concentration on the mean fracture load (N) before and after fatiguing and thermocycling as a function of zirconia thickness.Disk-shaped specimens of 5 mol% yttria partially stabilized zirconia (5Y-PSZ, BruxZir Anterior Solid Zirconia) and 3 mol% yttria partially stabilized zirconia (3Y-PSZ, BruxZir Shaded Zirconia) were prepared to thicknesses of 1.2 and 0.7 mm. For each thickness, the biaxial flexural test was used to measure the fracture load (N) before and after fatigue testing, with 1.2 million cycles at a 110-N load and simultaneous thermocycling at 5 °C to 55 °C (n=20). The data were analyzed by repeated-measures ANOVA (α=.05).Yttria concentration, thickness, and exposure to fatiguing had a statistically significant effect on the mean biaxial flexural load (yttria concentration: P.001; thickness: P.001; fatiguing: P=.004 for the 3Y-PSZ). One of the major findings in this study was that 30% of the 1.2-mm-thick 5Y-PSZ specimens and 80% of the 0.7-mm-thick 5Y-PSZ specimens fractured during fatiguing. All specimens of the 3Y-PSZ groups survived the fatiguing protocol. The 3Y-PSZ groups had statistically significant higher flexural loads than the 5Y-PSZ groups. The 1.2-mm thickness groups had statistically significant higher flexural loads than the 0.7-mm thickness groups.Yttria concentration had a significant effect on the strength of zirconia. 5Y-PSZ was considerably less resistant to fracture before and after fatigue testing than 3Y-PSZ. Decreasing the thickness of zirconia reduces its fracture resistance, regardless of the zirconia type.

ObjectiveThe objective of this in vitro study was to investigate fracture load, fracture types, and impact of chewing simulation of human molars restored with 3D printed indirect polyetheretherketone (PEEK) inlays and compare these with milled indirect PEEK inlays, direct resin composite fillings, and sound teeth.Materials and methodsA total of 112 molars with form congruent class I cavities were restored with (n = 16/group) 3D printed indirect PEEK inlays via fused layer manufacturing (FLM): (1) Essentium PEEK (ESS), (2) KetaSpire PEEK MS-NT1 (KET), (3) VESTAKEEP i4 G (VES), (4) VICTREX PEEK 450G (VIC), (5) milled indirect PEEK inlays JUVORA Dental Disc 2 (JUV), and (6) direct resin composite fillings out of Tetric EvoCeram (TET). Sound teeth (7) acted as positive control group. Half of the specimens of each group (n = 8) were treated in a chewing simulator combined with thermal cycling (1.2 million × 50 N; 12,000 × 5 °C/55 °C). Fracture load and fracture types of all molars were determined. Statistical analyses using Kolmogorov-Smirnov test and two-way ANOVA with partial eta squared (ηp2) followed by Scheffé post hoc test, chi square test and Weibull modulusmwith 95% confidence interval were computed (p ResultsESS and TET demonstrated the lowest fracture load with a minimum of 956 N, whereas sound molars showed the highest values of up to 2981 N. Chewing simulation indicated no impact (p = 0.132). With regard to Weibull modulus, KET presented a lower value after chewing simulation than JUV, whereas TET had the highest value without chewing simulation. All indirect restorations revealed a tooth fracture (75–100%), direct resin composite fillings showed a restoration fracture (87.5%), and 50% of the sound teeth fractured completely or had cusp fractures.ConclusionsAll 3D printed and milled indirect PEEK inlays as well as the direct resin composite fillings presented a higher fracture load than the expected physiological and maximum chewing forces.Clinical relevance3D printing of inlays out of PEEK via FLM provided promising results in mechanics, but improvements in terms of precision and esthetics will be required to be practicable in vivo to represent an alternative dental material.

Various protocols are available to preclinically assess the fracture resistance of zirconia oral im plants. The objective of the present review was to determine the impact of different treatments (dynamic load ing, hydrothermal aging) and implant features (e.g., material, design or manufacturing) on the fracture re sistance of zirconia implants. An electronic screening of two databases (MEDLINE/Pubmed, Embase) was per formed. Investigations including > 5 screw‐shaped implants providing information to calculate the bending moment at the time point of static loading to fracture were considered. Data was extracted and meta‐analyses were conducted using multilevel mixed‐effects generalized linear models (GLMs). The Šidák method was used to correct for multiple testing. The initial search resulted in 1864 articles, and finally 19 investigations loading 731 zirconia implants to fracture were analyzed. In general, fracture resistance was affected by the implant de sign (1‐piece > 2‐piece, p = 0.004), material (alumina‐toughened zirconia/ATZ > yttria‐stabilized tetragonal zir conia polycrystal/Y‐TZP, p = 0.002) and abutment preparation (untouched > modified/grinded, p < 0.001). In case of 2‐piece implants, the amount of dynamic loading cycles prior to static loading (p < 0.001) or anatomical crown supply (p < 0.001) negatively affected the outcome. No impact was found for hydrothermal aging. Het erogeneous findings of the present review highlight the importance of thoroughly and individually evaluating the fracture resistance of every zirconia implant system prior to market release., Ziel dieser Übersichtsarbeit und Meta-Analyse ist es, auf Basis existierender Untersuchun-gen, die Bruchresistenz von dentalen Zirkonoxidimplantaten zu beurteilen. Zudem soll ermit-telt werden, welche Faktoren die Bruchresistenz beeinflussen. Betrachtete Einflussfaktoren sind unterschiedliche Merkmale der Versuchsprotokolle einbezogener Studien (Variation von Einbettwinkel und Hebelarm, verschiedene künstliche Belastungsverfahren, anatomische und nicht-anatomische Suprakonstruktionen der Implantate oder ein Beschleifen des Abutments) und individuelle Eigenschaften des Implantatkörpers (Durchmesser, Ausgangsmaterial, Design, Herstellungsverfahren, Verbindungsart von 2-teiligen Implantaten). Um passende Studien zu identifizieren, wurde eine Suchstrategie für die Datenbanken Pub-Med (Medline) und Embase entwickelt. Die Suche ergab 1864 Treffer, von denen diejenigen in die Meta-Analyse integriert wurden, die mindestens 5 schraubenförmige Zirkonoxidimplantate untersuchten und ausreichend Informationen zur Berechnung des Biegemoments zum Zeitpunkt des Bruchs beinhalten. Es wurden 17 Untersuchungen in die Meta-Analyse aufgenommen. Zudem konnten zwei weitere zum Zeitpunkt der Recherche noch unveröf-fentlichte Arbeiten durch Koautoren in der Übersichtsarbeit berücksichtigt werden. Insgesamt 731 Zirkonoxidimplantaten wurden durch ein multilevel generalisiertes gemischt-lineares Modell (GLMs) analysiert. Die Šidák-Methode wurde zur Korrektur von Mehrfachprüfungen verwendet. Die Meta-Analyse ergab, dass das Biegemoment zum Zeitpunkt des Bruchs durch das Im-plantatdesign (1-teilig > 2-teilig; p = 0,004), Ausgangsmaterial (engl.: alumina‐toughened zirconia / ATZ > yttria‐stabilized tetragonal zirconia polycrystal / Y-TZP; p = 0,002) und Modi-fikation des Abutments (unberührt > beschliffen; p < 0,001) signifikant beeinflusst wird. Auf die Bruchresistenz von 2-teiligen Implantaten wirkte sich außerdem eine hohe Anzahl von dynamischen Belastungszyklen (p < 0,001) und eine anatomische Kronenversorgung (p < 0,001) negativ aus. Der Erarbeitungsprozess und die Ergebnisse dieser systematischen Übersichtsarbeit und Me-ta-Analyse verdeutlichen, dass existierende präklinische Testprotokolle einer Überarbeitung und bei Anwendung einer exakten Einhaltung bedürfen. Dentale Zirkonoxidimplantate erfül-len die Anforderungen einer physiologischen Kaubelastung, eine Ausnahme bilden Implanta-te mit einem Durchmesser von ≤ 3,3mm. Die Heterogenität der Ergebnisse unterstreicht zu-dem die Wichtigkeit der Prüfung eines jeden einzelnen Zirkonoxidimplantatsystems vor sei-ner Markteinführung.

Nada Heidari,1 Rasha Amawi,1 Przemek Seweryniak,2 Fahad Bakitian,3 Per Vult von Steyern1 1Department of Materials Science and Technology, Malmö University, Malmö, Sweden; 2Commercial Dental Laboratory, Malmö, Sweden; 3Department of Restorative Dentistry, Umm Al-Qura University, Makkah, Saudi ArabiaCorrespondence: Fahad Bakitian, Department of Restorative Dentistry, Faculty of Dentistry, Umm Al-Qura University, Makkah, 21511, Saudi Arabia, Tel +966500507661, Email fabakitian@uqu.edu.saPurpose: To evaluate the effect of different placing strategies performed in the connector area on fracture resistance and fracture behaviour of monolithic multi-layered translucent zirconia fixed dental prostheses (FDPs).Materials and Methods: Thirty 3-unit monolithic FDPs were produced and divided into three groups (n = 10) based on the different strategies for placing the connector area of FDPs in multi-layered zirconia blank with varying contents of yttria ranging from 4 to 5 mol%. The groups were as follows: FDPs with connectors placed in dentin layer with 4 mol% yttria content, FDPs with connectors placed in gradient layer, and FDPs with connectors placed in translucent layer with 5 mol% yttria content. A final group (n = 10) of conventional monolithic zirconia with a monolayer of yttria content (4 mol%) has been used as a control group. The specimens were artificially aged using thermocycling and pre-loading procedures and subsequently loaded to fracture using a universal testing machine. Fracture loads and fracture behaviour were analyzed using one-way ANOVA and Fisher’s exact tests and statistically evaluated (p ≤ 0.05).Results: There were no significant differences in fracture loads among the groups based on the placing strategies of the connector area of the FDPs in the multi-layered translucent zirconia blank (p > 0.05). There was no significant difference in fracture loads between monolithic multi-layered translucent zirconia and conventional monolithic translucent zirconia materials (p > 0.05). Fracture behaviour of FDPs with connector area placed in translucent layer differed significantly compared to FDPs with connector area placed in dentin layer and FDPs in control group (p = 0.004).Conclusion: The placing strategies of the connector used in the computer aided design and manufacturing procedures do not considerably affect fracture resistance of monolithic FDPs made of multi-layered translucent zirconia. Monolithic FDPs made of multi-layered translucent zirconia show comparable strength to FDPs made of conventional translucent zirconia, but with different fracture behaviour.Keywords: all-ceramic restorations, computer-aided designmanufacturing, fracture load, multi-layered zirconia, Y-TZP

This investigation focuses on modelling the fracture zone of four materials at different test speeds. The influence of these test speeds on the fracture zone formula was investigated as well. The fracture behaviour of materials is an important parameter which greatly affects the performance of these materials. In this paper, an empirical formula was generated to predict the fracture zone. This formula was produced from experimental characterisation of the fracture process at different loading rates for some engineering materials. Statistical analysis was done for the results being obtained from the experimental work to verify the accuracy of this formula, and it was found that it can introduce an accurate base for fracture zone prediction and determination. It was noted that at fracture process initiation, there are no significant effects of varying loading rate; this effect is increased with increasing the fracture process propagation.

The article describes the results of the investigation focused on the properties of the Zr,Hf-(Zr,Hf)N-(Zr,Hf,Me,Al)N coatings, where Me means chromium (Cr), titanium (Ti), or molybdenum (Mo). These coatings have three-layer architecture, including adhesion, transition, and wear-resistant layers, while the latter, in turn, has a nanolayer structure. Despite the fact that the coatings under study have close values of hardness and critical fracture load LC2, there are noticeable differences in wear resistance during the turning of steel. The tools with the coatings under study demonstrated better wear resistance compared to an uncoated tool and the tool with the commercial ZrN coating. The best wear resistance was detected for a tool with the Zr,Hf-(Zr,Hf)N-(Zr,Hf,Ti,Al)N coating. The study of the pattern of cracking in the structure of the coatings has found that, during the cutting process, active cracking occurs in the coating with Cr, which leads to the fracture of the coating, while the process of cracking is noticeably less active in the coatings with Ti or Mo.

Background The aim of this study was to develop a mathematically valid method of assessing fracture resistance of roots. The model developed used mesial roots of lower molars instrumented using stainless steel hand files (SS) and two rotary nickel-titanium (NiTi) systems. Methods Eighty human lower molars were selected and randomly divided into four groups (n = 20). After instrumentation, the root canals were obturated using thermoplasticized gutta percha. The roots were covered with a simulated periodontal ligament and mounted vertically in autopolymerizing acrylic in PVC tubes. Using a universal testing machine, the force to fracture (N) was applied and the maximum load (FL) was recorded. Remaining dentine volume was calculated and the fracture resistance (FR) was recorded. The data were analyzed using SPSS version 22 with P Results There were no significant differences among the instrumentation methods for FL but in FR the roots instrumented using rotary NiTi showed significantly lower values than control groups and SS files (P Conclusions Considering the effect of root length, volume of the root, and volume of the instrumented canal as well as the maximum failure load may be a more objective method of reporting fracture resistance of roots.

Recently, translucent zirconia has become the most prevalent material used as a restorative material. This study aimed to compare the crown fracture load of the four most common different translucent zirconia brands available in the market at 1.5 mm thickness. Standardized tooth preparations for a full ceramic crown were designed digitally with software (AutoCAD) by placing a 1.0 mm chamfer margin and 1.5 mm occluso-cervical curvature for the crown sample manufacturing. Stylized crowns were chosen to control the thickness of the crown. The axial and occlusal thickness were standardized to 1.5 mm thickness except at the central pit, which was 1.3 mm thick. The STL file for the tooth dies was prepared using software (3Shape TRIOS® Patient Monitoring, Copenhagen, Denmark). The tooth dies were printed with a resin material (NextDent Model 2.0, Vertex-Dental B.V., Soesterberg, The Netherlands) using a 3D printing software (3D Sprint® Client Version 3.0.0.2494) from a 3D printer (NextDent™ 5100, Vertex-Dental B.V., Soesterberg, The Netherlands). The printing layer thickness was 50 µm. Then, a total of twenty-eight (N = 28) stylized crowns were milled out of AmannGirrbach (Amann Girrbach GmbH, Pforzheim, Germany) (n = 7), Cercon HT (Dentsply Sirona, Bensheim, Germany) (n = 7), Cercon XT (Dentsply Sirona, Bensheim, Germany) (n = 7), and Vita YZ XT (Zahnfabrik, Bäd Sackingen, Germany) (n = 7). Following sintering the crowns, sandblasting was performed and they were bonded to the tooth dies with the resin cement (RelyX U-200, 3M ESPE, Seefeld, Germany) and permitted to self-cure under finger pressure for 6 min. The crowns were loaded on the occlusal surface in a universal testing machine (MTS Centurion) with a stainless-steel ball indenter (7 mm radius) with a loading rate of 1 mm/min to contact the stylized crowns on each of the four cusps until failure. A rubber sheet (1.5 mm thickness) was positioned between the crown and indenter, which helped with the load distribution. Statistical analysis was done using SPSS version 20 (IBM Company, Chicago, USA). The fracture loads were analyzed using Dunnett’s T3 test, and the number of cracks was analyzed using the Mann–Whitney U test among the groups. The significant level was set at p value = 0.05. The mean fracture loads were 3086.54 ± 441.74 N, 4804.94 ± 70.12 N, 3317.76 ± 199.80 N, and 2921.87 ± 349.67 N for AmannGirrbac, Cercon HT, Cercon XT, and Vita YZ XT, respectively. The mean fracture loads for the surfaces with the greatest number of cracks (excluding the occlusal surfaces) were on the lingual surface for AmannGirrbach and Cercon HT, on the distal and mesial for Cercon XT, and on the buccal for Vita YZ XT. We found that the AmannGirrbach had the most overall cracks. Cercon XT had the greatest number of occlusal cracks and appeared to be the most shattered. Cercon HT had the least number of cracks. In conclusion, Cercon HT presented the best strength properties, the highest fracture load, and no visible cracks. AmannGirrbach presented the lowest strength properties.