Fracture Resistance Of Zirconia Crowns Research Articles

The effect of cyclic loading on the fracture resistance of 3D-printed and CAD/CAM milled zirconia crowns—an in vitro study

ObjectivesThe aim of this study was to evaluate the effect of cyclic mechanical loading on the fracture resistance of 3D-printed zirconia crowns in comparison to milled zirconia crowns.Materials and methodsMonolithic zirconia crowns (n = 30) were manufactured using subtractive milling (group M) and 3D additive printing (group P). Nine samples of each group were fractured under one-time loading while the other 6 samples were subjected to cyclic loading for 1.2 million cycles before being subjected to one-time loading until fracture. Scanning electron microscope (SEM) fractographic analysis was carried out on fractured fragments of representative samples.ResultsThe mean for fracture resistance of group M was 1890 N without cyclic loading and 1642 N after being subjected to cyclic loading, and they were significantly higher than that of group P (1658 N and 1224 N respectively).ConclusionsThe fabrication technique and cyclic loading affect the fracture resistance of zirconia crowns. Although the fracture resistance values for the 3D-printed crowns were lower than those of the milled, still they are higher than the masticatory forces and thus could be considered being clinically acceptable.Clinical relevanceConcerning fracture resistance, 3D-printed crowns can withstand the masticatory forces for the long term without any cracks or failure.

Fracture Resistance of Zirconia Restorations with Four Different Framework Designs.

Objectives: This study assessed the fracture resistance of zirconia crowns with four framework designs, fabricated by computer-aided design/computer-aided manufacturing (CAD/CAM) technology. Materials and Methods: In this experimental study, a maxillary central incisor was prepared and scanned with a CAD/CAM scanner, and 40 frameworks with 4 designs (N=10) were fabricated as follows: simple core, dentine core with a design similar to dentine, 3mm trestle design collar in the lingual aspect with proximal buttresses, and monolithic or full-contour. After porcelain applying and 20h immersion in distilled water (37°C), crowns were cemented on metal dies using zinc phosphate cement. Fracture resistance was measured by a universal testing machine. Data were analyzed with one-way ANOVA (alpha=0.05). Results: Fracture resistance was maximum in the monolithic group, followed by the dentine core, trestle design, and simple core groups, respectively. The mean fracture resistance of the monolithic group was significantly higher than that of the simple core group (P<0.005). Conclusion: Zirconia restorations with frameworks that provided higher and more support for porcelain, showed increased fracture resistance.

Survivability and fracture resistance of monolithic and multi-yttria-layered zirconia crowns as a function of yttria content: A mastication simulation study.

To compare four different types of monolithic zirconia crowns in terms of survival rate and fracture resistance after thermocycling and/or thermo-mechanical loading in a chewing simulator. Partially stabilized zirconia (PSZ) crowns with fiber-reinforced resin die assemblies (n=80) were fabricated using: multi-yttria-layered 5Y-PSZ/3Y-PSZ, multi-yttria-layered 5Y-PSZ/4Y-PSZ, monolithic 4Y-PSZ, and monolithic 3Y-PSZ as control (n=20). Half of the samples in each group were subjected to thermo-mechanical loading under 110N, 1.4Hz, 1.2 million cycles with simultaneous thermocycling (10,000cycles, 5-55°C). The other half were subjected to thermocycling alone. The samples were loaded to failure to measure their fracture resistance. The data were analyzed using by two-way ANOVA and Tukey's HSD post-hoc test (α=0.05). All specimens survived the aging protocols. The yttria content significantly affected the fracture resistance of the crowns (p<0.0001). The mean fracture resistance, from highest to lowest: 3Y-PSZ, 4Y-PSZ, followed by the two multi-yttria-layered systems. The mean difference between the two multi-yttria-layered systems were not statistically significant (p=0.98). The mechanical loading protocol did not affect the mean fracture resistance within each group (p=0.18). Within each group, there was no difference in fracture resistance after thermocycling alone and thermo-mechanical loading. However, increasing the yttria concentration at the occlusal third of the crown decreased its fracture resistance. The term "monolithic zirconia" alone without specifying the actual yttria content is misleading. This term represents different materials with different mechanical properties. The yttria content has an inverse relationship with the fracture resistance of zirconia crowns. The fracture resistance of multi-layer zirconia crowns is determined by the amount of the weaker zirconia phase at the occlusal part of the restoration rather than enforced by the stronger zirconia at the cervical part of the crown.

In vitro Simulation of Periodontal Ligament in Fatigue Testing of Dental Crowns.

Objective Fatigue testing of restorative material has been appreciated as an appropriate method to evaluate dental restorations. This study aims to investigate the influence of periodontal ligament (PDL) simulation on fatigue and fracture tests results of zirconia crowns. Materials and Methods A standard tooth preparation for all ceramic zirconia crown was made on a typodont mandibular molar. The prepared master die was duplicated using epoxy resin to produce 40 replicas. PDL simulation was made by surrounding the root of 20 dies with a 0.3-mm thick silicon layer. The other 20 specimens had no PDL simulation. Zirconia crowns were fabricated using computer-aided design/computer-aided manufacturing technology and cemented to the epoxy resin dies. Ten crowns from each group were subject to chewing simulation with simultaneous thermocycling (5–55°C). All specimens were then loaded until failure in universal testing machine. Statistical Analysis Statistical analysis was conducted using SPSS software. Shapiro–Wilk test confirmed the normal distribution of data. Descriptive statistic was performed and differences between the groups were analyzed using paired samples t -test. Results All fatigued crowns survived chewing simulation; no failure was observed after finishing simulation. The highest mean fracture load recorded was 3,987 ± 400 N for the no fatigue/no periodontal simulation group. Comparing the mean fracture load of the two groups with periodontal simulation and the two groups with no periodontal simulation showed no statistically significant difference ( p > 0.5). Conclusion Considering the testing set-up applied in this study, simulating PDL using resilient materials does not affect the in vitro survival and fracture resistance of zirconia crowns.

Influence of Antagonist Material on Fatigue and Fracture Resistance of Zirconia Crowns.

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.

The Effect of Finish Line Design on the Fracture Strength of Zirconia Copings

Statement of the Problem: One of the major concerns about all ceramic crowns is their fracture resistance. Purpose:The purpose of this in vitro study was to evaluate the effect of two marginal designs (shoulder 90°, shoulder 135°) on the fracture resistance of zirconia copings. Materials and Method: In this in vitro study, 20 brass dies were prepared using milling machine: 10 with 1mm width shoulder 90° marginal design and the other 10 with 1mm width shoulder 135° finish line design. Zirconia cores with 0.5mm thickness and 30μm cement space were fabricated on brass dies. The copings were cemented on the dies and fracture test was done using a universal testing machine. Data were analyzed using Mann-Whitney test. Results:The mean value of fracture resistance for shoulder 90° finish line design were 368.3±109.4 N and for shoulder 135° finish line design were 518.4±115.5 N. Data analysis revealed a statistically significant difference between groups (p< 0.05). Conclusion: The results of this study showed that the finish line design of zirconia copings influences their fracture resistance. A 135° shoulder finish line design can improve the fracture resistance of zirconia crowns.

The Effect of Finish Line Design on the Fracture Strength of Zirconia Copings.

Statement of the problem One of the major concerns about all ceramic crowns is their fracture resistance. Purpose The purpose of this in vitro study was to evaluate the effect of two marginal designs (shoulder 90°, shoulder 135°) on the fracture resistance of zirconia copings. Materials and method In this in vitro study, 20 brass dies were prepared using milling machine: 10 with 1mm width shoulder 90° marginal design and the other 10 with 1mm width shoulder 135° finish line design. Zirconia cores with 0.5mm thickness and 30μm cement space were fabricated on brass dies. The copings were cemented on the dies and fracture test was done using a universal testing machine. Data were analyzed using Mann-Whitney test. Results The mean value of fracture resistance for shoulder 90° finish line design were 368.3±109.4 N and for shoulder 135° finish line design were 518.4±115.5 N. Data analysis revealed a statistically significant difference between groups (p Conclusion The results of this study showed that the finish line design of zirconia copings influences their fracture resistance. A 135° shoulder finish line design can improve the fracture resistance of zirconia crowns.

Effect of different core design made of computer-aided design/computer-aided manufacturing system and veneering technique on the fracture resistance of zirconia crowns: A laboratory study.

Background:It is unclear how the different core designs made of computer-aided design/computer-aided manufacturing (CAD/CAM) system and veneering techniques affect the fracture resistance of endodontically treated teeth.Aim:The aim of this in vitro study is to investigate the effect of different core designs made of CAD/CAM system and veneering techniques on the fracture resistance of zirconia ceramic crowns.Materials and Methods:Two types of zirconia copings were designed; the first one with circumferential 0.5-mm chamfer and the second one with circumferential 1-mm deep chamfer. The core specimens (in subgroups) were veneered anatomically with either a layering technique (hand-layer) or with press-on technique resulting in four test groups (n = 12). All crowns were then cemented using self-adhesive resin cement. After that, all specimens were loaded in a universal testing machine until fractured.Statistical Analysis:Data were then analyzed with two-way analysis of variance (ANOVA) (α =0.05).Results:Mean (standard deviation) failure loads for groups ranged from 2412.7 N (±624.6) to 3020.1 N (±1099.8). Two-way ANOVA revealed no statistically significant differences among groups (P > 0.05). Almost all groups showed cohesive failure in the veneering ceramic.Conclusions:Within the limitations of this laboratory study, neither the core design nor the veneering technique affected the fracture resistance of all-ceramic crowns significantly.

The impact of luting agents and stiffness of implant-abutments on marginal adaptation, chipping, and fracture resistance of zirconia crowns

ObjectivesThis in vitro study evaluated the impact of cements and implant analogs with different e-moduli on marginal adaptation, chipping, and the fracture resistance of zirconia crowns. Methods80 crowns (Cercon, DeguDent) were manufactured for 40 polyoxymethylene (POM) and 40 titanium (Ti) one-piece implant analogs and divided into 10 groups: A, zinc oxide phosphate (Hoffmann׳s Cement, Richter&Hoffmann, Berlin, D); B, zinc oxide eugenol (Temp Bond, KerrHawe, Bioggio, CH); C, resin (Variolink II, Ivoclar-Vivadent, Schaan, FL); D, zinc oxide without eugenol (Temp Bond NE, KerrHawe, Bioggio, CH); E, glass ionomer (Ketac Cem, 3M ESPE, Seefeld, D). All samples were thermally mechanically loaded (1.2×10(6)×50N; 3000×5°C/55°C). Marginal adaptation was semiquantitatively evaluated before and after ageing with a scanning electron microscope. After ageing, intact samples underwent a fracture resistance test. ResultsThe best sealed margins before ageing were achieved with resin and zinc oxide cement and with resin after ageing. Zinc oxide samples showed the most discontinuously sealed margins after ageing and the difference between POM and Ti samples was significant only for zinc oxide. The numbers of samples failing during TCML were as follows: A(Ti − POM)=0−1; B(Ti − POM)=0−5; C(Ti − POM)=1/1; D(Ti − POM)=2−2; E (Ti − POM)=0−2. Fracture resistance test [N]: A(Ti − POM)=1181−801; B(Ti − POM)=1469−1517; C(Ti − POM)=1704−1408; D(Ti − POM)=1992−883; E (Ti − POM)=2750−1015. ConclusionsTCML reduced the number of perfectly sealed samples and increased the number of chipped samples cemented onto POM implants with zinc oxide. This study could not show any significant impact on the fracture resistance of zirconia when different cements and implant analogs were used.

Fatigue and Fracture Resistance of Zirconia Crowns Prepared with Different Finish Line Designs

The aim of this study was to evaluate the effect of finish line design on the fatigue, fracture resistance, and failure type of veneered zirconia restorations. A CAD/CAM system (Cercon) was used to prepare zirconia frameworks (0.5 mm thick) for a maxillary central incisor. Three finish line designs were evaluated: a complete narrow chamfer, a narrow chamfer with a lingual ledge, and a complete ledge. The prepared frameworks were veneered using a press-on ceramic (Ceram Press) and were cemented on the corresponding prepared teeth using a resin cement (Panavia F2.0). The cemented specimens were thermocycled, subjected to dynamic fatigue, and finally loaded till fracture. Fractured specimens were examined under a scanning electron microscope to assess fracture type. One-way ANOVA and Bonferroni post hoc tests were used to analyze the data (α= 0.05). The finish line design did not have any significant statistical influence on the fracture resistance (F = 1.9, p= 0.346) or on the failure type of the tested specimens. Adjusted R squared value (R = 0.049) indicated a weak correlation between finish line design and fracture load of the tested specimens. All specimens failed due to cracking and fracture of the veneer ceramic. Meanwhile, the framework remained entirely intact. Three narrow chamfer finish line specimens demonstrated adhesive fracture of the veneer ceramic during dynamic fatigue testing, related to overextension of the veneer ceramic during the layering procedure. Within the limitations of this study, the finish line design did not influence the fatigue or the fracture resistance of veneered zirconia crowns. Selection of any of the finish line designs should be based on the clinical condition of the restored tooth.

Fracture strength of two oxide ceramic crown systems after cyclic pre‐loading and thermocycling

The aim of the present study was to investigate the fracture resistance of zirconia crowns and to compare the results with crowns made of a material with known clinical performance (alumina) in away that reflects clinical aspects. Sixty crowns were made, 30 identical crowns of alumina and 30 of zirconia. Each group of 30 was randomly divided into three groups of 10 crowns that were to undergo different treatments: (i) water storage only, (ii) pre-loading (10 000 cycles, 30-300 N, 1 Hz), (iii) thermocycling (5-55 degrees , 5000 cycles) + pre-loading (10 000 cycles, 30-300 N, 1 Hz). Subsequently, all 60 crowns were subjected to load until fracture occurred. There were two types of fracture: total fracture and partial fracture. Fracture strengths (N) were: group 1, alumina 905/zirconia 975 (P = 0.38); group 2, alumina 904/zirconia 1108 (P < 0.007) and group 3, alumina 917/zirconia 910 (P > 0.05). Total fractures were more frequent in the alumina group (P < 0.01). Within the limitations of this in vitro study, it can be concluded that there is no difference in fracture strength between crowns made with zirconia cores compared with those made of alumina if they are subjected to load without any cyclic pre-load or thermocycling. There is, however, a significant difference (P = 0.01) in the fracture mode, suggesting that the zirconia core is stronger than the alumina core. Crowns made with zirconia cores have significantly higher fracture strengths after pre-loading.