Impact of varying step-stress protocols on the fatigue behavior of 3Y-TZP, 4Y-TZP and 5Y-TZP ceramic

ObjectiveTo test the impact of three varying step-stress protocols on the fatigue behavior of two 3Y-TZP, one 4Y-TZP and one 5Y-TZP zirconia materials.MethodsEight specimens per zirconia material (N = 32) were selected for static testing to determine the start load for dynamic tests (30% of the mean value of static fracture load). 45 specimens per material (N = 180) were used for dynamic load tests using three step-stress protocols: 1. 50 N/5000 cycles; 2. 5% of static load/5000 cycles, and 3. 10 N/1000 cycles. Following materials were tested: 3Y-TZP_{(<0.25 Al2O3)} (O: opaque) 3Y-TZP_{(<0.05 Al2O3)} (T: translucent), 4Y-TZP_{(<0.01 Al2O3)} (ET: extra translucent) and 5Y-TZP_{(<0.01 Al2O3)} (HT: high translucent). The specimens (4 ± 0.02 × 3 ± 0.02 × 45 mm) were placed centrally on the support rolls and the load was applied perpendicularly over the 4 mm specimen side (～4-point flexural strength according to the DIN 6872:2019). Data was analyzed with Kolmogorov–Smirnov-test, t-test, one-way ANOVA with post-hoc Scheffé-test, Chi-square-test, Kaplan–Meier with Log-Rank-test and two-parametric Weibull analysis (p < 0.05).ResultsThe step-stress protocols showed no impact on the fracture load or Weibull modulus within one zirconia material. However, the zirconia materials T, ET and HT showed differences in cycle number to fracture between the step-stress protocols (T: 3 > 2 > 1; ET: 2 > 3 > 1; HT: 2, 3 > 1) with lowest cycle number to fracture for protocol 1. Within one step-stress protocol, the cycle number to fracture varied according to the zirconia material as follows: 1: T, O ≥ O, ET > HT; 2: ET > O, T, HT; 3: O, T, ET > HT. Cracking started at the tensile side of the specimens at all times. All specimens showed typical compression curls (single or double). Fragmentation patterns were similar for all materials with a lot of crack branching and fragmentation due to secondary cracks indicating high energy fractures.SignificanceDynamic fatigue tests seem to provide important information on the long-term stability of zirconia materials. Zirconia materials with higher opacity seem to be more robust towards varying step-stress protocols than translucent zirconia materials. Regarding expenditure of time, a step-stress protocol with a load increase of 50 N every 5000 cycles seems favorable to gain information on the long-term stability of zirconia materials.     

Fatigue and damage accumulation of veneer porcelain pressed on Y-TZP

Objectives

This study compared the reliability and fracture patterns of zirconia cores veneered with pressable porcelain submitted to either axial or off-axis sliding contact fatigue.

Methods

Forty-two Y-TZP plates (12 mm × 12 mm × 0.5 mm) veneered with pressable porcelain (12 mm × 12 mm × 1.2 mm) and adhesively luted to water aged composite resin blocks (12 mm × 12 mm × 4 mm) were stored in water at least 7 days prior to testing. Profiles for step-stress fatigue (ratio 3:2:1) were determined from single load to fracture tests (n = 3). Fatigue loading was delivered on specimen either on axial (n = 18) or off-axis 30° angulation (n = 18) to simulate posterior tooth cusp inclination creating a 0.7 mm slide. Single load and fatigue tests utilized a 6.25 mm diameter WC indenter. Specimens were inspected by means of polarized-light microscope and SEM. Use level probability Weibull curves were plotted with 2-sided 90% confidence bounds (CB) and reliability for missions of 50,000 cycles at 200 N (90% CB) were calculated.

Results

The calculated Weibull Beta was 3.34 and 2.47 for axial and off-axis groups, respectively, indicating that fatigue accelerated failure in both loading modes. The reliability data for a mission of 50,000 cycles at 200 N load with 90% CB indicates no difference between loading groups. Deep penetrating cone cracks reaching the core–veneer interface were observed in both groups. Partial cones due to the sliding component were observed along with the cone cracking for the off-axis group. No Y-TZP core fractures were observed.

Conclusions

Reliability was not significantly different between axial and off-axis mouth-motion fatigued pressed over Y-TZP cores, but incorporation of sliding resulted in more aggressive damage on the veneer.     

氧化锆全瓷冠修复体40例临床效果评价

目的:探讨锆面氧化锆全瓷冠修复体的临床应用效果及边缘适合度.方法:选取2014年1月-2015年8月到静安区牙病防治所口腔修复科接受全瓷修复的患者40例,采用计算机辅助设计和计算机辅助制作(CAD/CAM)技术制作氧化锆全瓷冠修复体46件,其中上颌22件,下颌24件;前牙单冠21个,后牙单冠25个.参照美国加利福尼亚牙科医师协会全瓷修复体的临床标准进行效果评价,并以牙龈出血指数、牙周袋深度以及附着丧失3项指标对修复体的牙周状况进行评价.采用SPSS 13.0软件包对结果进行统计学分析.结果:全瓷冠患者初戴3个月后,2例出现牙龈炎,其余均未出现边缘着色和继发龋.初戴后6个月,2例出现轻微牙龈炎症;初戴后12个月,未出现牙冠裂纹和断裂、边缘着色和继发龋,3个冠修复体出现颜色不匹配.所有患者在3、6、12个月时间点的龈沟出血指数、牙周袋深度以及附着丧失指标与治疗前的相比无显著差异(P＞0.05).结论:氧化锆全瓷冠具有优良的生物相容性、良好的美学效果和良好的稳定性,是理想的临床美学修复体.     

Survival of implant-supported resin-matrix ceramic crowns: In silico and fatigue analyses

ObjectiveTo evaluate the fatigue survival, failure mode, and maximum principal stress (MP Stress) and strain (MP Strain) of resin-matrix ceramic systems used for implant-supported crowns.MethodsIdentical molar crowns were milled using four resin-matrix ceramics (n = 21/material): (i) Shofu Hard, (ii) Cerasmart (iii) Enamic, and (iv) Shofu HC. Crowns were cemented on the abutments, and the assembly underwent step-stress accelerated-life testing. Use level probability Weibull curves at 300 N were plotted and the reliability at 300, 500 and 800 N was calculated for a mission of 50,000 cycles. Fractographic analysis was performed using stereomicroscope and scanning electron microscope. MP Stress and MP Strain were determined by finite element analysis.ResultsWhile fatigue dictated failures for Cerasmart (β > 1), material strength controlled Shofu Hard, Enamic, and Shofu HC failures (β < 1). Shofu HC presented lower reliability at 300 N (79%) and 500 N (59%) than other systems (>90%), statistically different at 500 N. Enamic (57%) exhibited a significant reduction in the probability of survival at 800 N, significantly lower than Shofu Hard and Cerasmart; however, higher than Shofu HC (12%). Shofu Hard and Cerasmart (>93%) demonstrated no significant difference for any calculated mission (300–800 N). Failure mode predominantly involved resin-matrix ceramic fracture originated from occlusal cracks, corroborating with the MP Stress and Strain location, propagating through the proximal and cervical margins.SignificanceAll resin-matrix ceramics crowns demonstrated high probability of survival in a physiological molar load, whereas Shofu Hard and Cerasmart outperformed Enamic and Shofu HC at higher loads. Material fracture comprised the main failure mode.     

高度抛光无釉瓷氧化锆全瓷冠的临床效果研究

目的评估高度抛光无釉瓷氧化锆全瓷冠的临床效果。方法牙体缺损磨牙80颗,分为2组,40例40颗患牙进行高度抛光无釉瓷的氧化锆全瓷冠修复（试验组）,40例40颗患牙常规制作钯金烤瓷牙单冠修复（对照组）。戴固后即刻、3个月、6个月、12个月、24个月、36个月临床观察和评价修复体破损和对袷牙磨耗情况,比较2组修复体的存留率和成功率。结果试验组中有1件修复体出现小面积瓷裂,修复后12个月2件全瓷冠对冶天然牙牙出现I级磨耗。对照组中有3件修复体出现小面积瓷裂,但对殆天然牙均无明显磨耗。试验组和对照组修复体3年存留率分别为100％和97．5％,成功率分别为97．5％和90％,差异均无统计学意义（P〉0．05）。结论高度抛光无釉瓷氧化锆全瓷冠修复磨牙牙体缺损不易破损,对猞天然牙磨耗轻微,成功率高.     

Influence of porcelain veneering on the marginal fit of Digident and Lava CAD/CAM zirconia ceramic crowns

PURPOSE

Marginal fit is a very important factor considering the restoration''s long-term success. However, adding porcelain to copings can cause distortion and lead to an inadequate fit which exposes more luting material to the oral environment and causes secondary caries. The purpose of this study was to compare the marginal fit of 2 different all-ceramic crown systems before and after porcelain veneering. This study was also intended to verify the marginal fit of crowns originated from green machining of partially sintered blocks of zirconia (Lava CAD/CAM system) and that of crowns obtained through machining of fully sintered blocks of zirconia (Digident CAD/CAM system).

MATERIALS AND METHODS

20 crowns were made per each system and the marginal fit was evaluated through a light microscope with image processing (Accura 2000) at 50 points that were randomly selected. Each crown was measured twice: the first measurement was done after obtaining a 0.5 mm coping and the second measurement was done after porcelain veneering. The means and standard deviations were calculated and statistical inferences among the 2 groups were made using independent t-test and within the same group through paired t-test.

RESULTS

The means and standard deviations of the marginal fit were 61.52 ± 2.88 µm for the Digident CAD/CAM zirconia ceramic crowns before porcelain veneering and 83.15 ± 3.51 µm after porcelain veneering. Lava CAD/CAM zirconia ceramic crowns showed means and standard deviations of 62.22 ± 1.78 µm before porcelain veneering and 82.03 ± 1.85 µm after porcelain veneering. Both groups showed significant differences when analyzing the marginal gaps before and after porcelain veneering within each group. However, no significant differences were found when comparing the marginal gaps of each group before porcelain veneering and after porcelain veneering as well.

CONCLUSION

The 2 all-ceramic crown systems showed marginal gaps that were within a reported clinically acceptable range of marginal discrepancy.     

A 3-year retrospective and clinical follow-up study of zirconia single crowns performed in a private practice

Objectives

All-ceramic crowns have become increasingly used also in the posterior regions, but there are only few studies documenting the clinical outcome of these restorations. The aim was therefore to present the 3-year outcome of zirconia (NobelProcera™) single crowns.

Methods

All patients treated with porcelain-veneered zirconia single crowns in a private practice during the period October 2004 to November 2005 were included. The patient records were scrutinized for data on the restorations and the supporting teeth. Information was available for 161 patients and 204 crowns. At the 3-year recall appointments, a sample of 18 patients with 25 crowns was clinically examined and interviewed regarding patient satisfaction.

Results

Most crowns (78%) were placed on premolars and molars. The clinical outcome of the crowns was favourable. No zirconia core fractured and no caries was observed on the abutment teeth. Some types of complication were recorded for 32 (16%) crowns or abutment teeth. The most severe complications, in total 12 restorations (6%), were recorded as failures: abutment tooth was extracted (5), remake of crown due to lost retention (4), veneer fracture (2) and persistent pain (1). The CDA criteria for 25 crowns were rated favourably, and patient satisfaction with the zirconia crowns was in general high.

Conclusions

The porcelain-veneered zirconia crowns (NobelProcera™) showed good clinical results, were well accepted by the patients, and only few complications were reported over the 3-year follow-up period.     

Acoustic emission and finite element study on the influence of cusp angles on zirconia dental crowns

ObjectiveThe effect of cusp angle on the load-carrying capacity and failure behaviour of BionZ Diamond zirconia crowns is carried out using experimental and numerical investigations.MethodsThe experimental program using monolithic crowns were divided into three groups (n = 14) for three cusp angles, 60, 80 and 120 degrees and were tested to failure under the static load. A 2-channel acoustic emission (AE) system was used to monitor the failure process while the piezo sensors were attached to the rigid stainless-steel jig for recoding the AE events. Load-displacement and AE response were simultaneously monitored until failure of specimens. Parametric AE analysis was conducted for the factors such as amplitude, energy released, signal duration and cumulative counts, for each AE signal. Fast Fourier transform (FFT) was conducted to assess the frequency at failure. Linear finite element analysis (FEA) was carried out using commercial software Ansys Workbench 19.1 to present the stress distribution and failure modes. Post-failure surface morphology study was carried out using scanning electron microscopy (SEM) and statistical analysis was performed using Weibull analysis.ResultsAll the samples in three different groups have failed at the mid-line, splitting the zirconia crowns into two equal pieces. The load to failure was directly proportional to the cusp angle in crowns; 120° group had the highest load-carrying capacity of 2.93 ± 0.26 kN while 60 and 80° groups had a failure load of 2.46 ± 0.53 and 2.52 ± 0.16 kN, respectively. Parametric AE analysis revealed that the failure was instantaneous and 60-degree samples had higher AE signature. FE analysis showed the crack initiation at the occlusal surface of the crown which is in agreement with the SEM images. A close agreement of results for the load and stress distribution from FEA complemented with the experimental study.SignificanceOptimisation of cusp-angle could help clinicians to accurately design the monolithic zirconia crown focussing on maximum load-carrying capacity, increasing the restoration life.     

Survival of resin-bonded porcelain veneer crowns placed with and without metal reinforcement

OBJECTIVES: The purpose of this retrospective case study of dental records was to compare the long-term failure rates and modes for resin-bonded sintered feldspathic porcelain veneer crowns (RBPVCs) either containing or without metal substructure reinforcement. METHODS: Two prosthodontists placed 62 RBPVCs fabricated with, and 167 without, metal reinforcement in 143 older adolescent and adult patients treated in a private practice. Clinical judgement determined the type of crown design placed. Preparation margins were generally finished on enamel, and all crowns occluded with opposing teeth. Observations included the patients, operators, crown designs and failure modes. Chi-square or Fisher's exact tests and life table survival statistics were used to evaluate the findings (alpha = 0.05). RESULTS: Over five years, failures occurred in 14.5% of RBPVCs fabricated with, and in 18.6% without, metal reinforcement. Cumulative survival estimates were 74.3 +/- 8.5(Standard Error)% and 72.9 +/- 4.8(SE)%, respectively (P = 0.96). Mandibular posterior crowns comprised 27.1% of the placements, but 47.5% of the failures. Bulk fracture of porcelain occurred in 7.0% of the crowns, all without metal reinforcement. Minor porcelain fractures and debonding were less frequent in both types of crowns. Persistent pulpitis occurred in 3.5% of all teeth. CONCLUSIONS: There was a significant risk of failure for sintered porcelain RBPVCs placed as posterior restorations. Although metal reinforcement was able to reduce the risk of bulk fracture of porcelain, other causes of failure were less affected.     

Monolithic CAD/CAM laminate veneers: Reliability and failure modes

Objectivesto evaluate the probability of survival and failure modes of lithium-disilicate, feldspathic-ceramic, and resin-nanoceramic anterior veneers cemented on dentin analog substrates after sliding-contact step-stress accelerated life testing (SSALT).MethodsA virtual incisor tooth preparation was produced with a reduction of 1.5 mm at the incisal edge and of 0.7 mm buccally. A .STL file of the preparation was generated and CAD/CAM based G10 dentin-analog material was used for testing. Laminate veneers were milled in three different materials: lithium-disilicate (LDS, E.max CAD), resin-nanoceramic (RN, Lava Ultimate), and feldspathic-ceramic (FELDS, Vita Blocks). SSALT was employed where a spherical indenter contacted the veneer, slided along its interface with G10 to lift off and start a new cycle at 2 Hz in water. Qualitative fractography was performed. The probability of survival (90% confidence-bounds) was calculated for several load/cycle missions.ResultsThe probability of survival for a mission of 50,000 cycles decreased from 50 up to 150 N equally for all groups and were not different between them. At 200 N, the probability of survival was significantly lower for FELDS (10%) compared to RN veneers (41%), whereas LDS presented intermediate values (22%). The characteristic strength of RN (247 N) was significantly higher than LDS (149 N), and FELDS (151 N). In FELDS and LDS, hackles, wake hackles and twist hackles indicated the direction of crack propagation. In RN, hackles were observed.ConclusionsDifferences in probability of survival were observed only at 180 and 200 N between groups. Failure modes were similar with veneer fracture down to the tooth-analog substrate.     

Influence of veneering porcelain thickness and cooling rate on residual stresses in zirconia molar crowns

Objective

The aim of this study was to investigate the influence of increasing veneering porcelain thickness in clinically representative zirconia molar crowns on the residual stresses under fast and slow cooling protocols.

Methods

Six veneered zirconia copings (Procera, Nobel Biocare AB, Gothenburg, Sweden) based on a mandibular molar form, were divided into 3 groups with flattened cusp heights that were 1 mm, 2 mm, or 3 mm. Half the samples were fast cooled during final glazing; the other half were slow cooled. Vickers indentation technique was used to determine surface residual stresses. Normality distribution within each sample was done using Kolmogorov–Smirnov & Shapiro–Wilk tests, and one-way ANOVA tests used to test for significance between various cusp heights within each group. Independent t-tests used to evaluate significance between each cusp height group with regards to cooling.

Results

Compressive stresses were recorded with fast cooling, while tensile stresses with slow cooling. The highest residual compressive stresses were recorded on the fast cooled 1 mm cusps which was significantly higher than the 2 and 3 mm fast cooled crowns (P < 0.05). There was a significant linear trend for residual stress to decrease as veneering porcelain thickness increased in the fast cooled group (P < 0.05). No significant differences were found between the various cusp heights during slow cooling (P ≥ 0.05).

Significance

Cooling rate and geometric influences in a crown anatomy have substantially different effects on residual stress profiles with increasing veneering porcelain thickness compared to the basic flat plate model.     

计算机辅助设计与制作氧化锆全瓷冠桥的临床应用

目的 评价运用牙科计算机辅助设计与制作(CAD-CAM)氧化锆全瓷固定冠桥修复体的临床应用效果.方法 选择2010年1月至5月接受氧化锆全瓷冠桥修复的患者113例,共计167件修复体,通过计算机印模采集系统获取工作模型及对(牙合)牙咬合记录的三维数据,将两者虚拟拼合后,采用inLab V3.85软件的Reduced程序...     

Effect of the shades of background substructures on the overall color of zirconia-based all-ceramic crowns

PURPOSE

The objective of this study was to determine the effect of the color of a background substructure on the overall color of a zirconia-based all-ceramic crown.

MATERIALS AND METHODS

Twenty one posterior zirconia crowns were made for twenty subjects. Seven premolar crowns and six molar crowns were cemented onto abutments with metal post and core in the first and second group. In the third group, eight molar crowns were cemented onto abutments with a prefabricated post and composite core build-up. The color measurements of all-ceramic crowns were made before try-in, before and after cementation. A repeated measure ANOVA was used for a statistical analysis of a color change of all-ceramic crowns at α=.05. Twenty four zirconia specimens, with different core thicknesses (0.4-1 mm) were also prepared to obtain the contrast ratio of zirconia materials after veneering.

RESULTS

L^*, a^*, and b^* values of all-ceramic crowns cemented either on a metal cast post and core or on a prefabricated post did not show significant changes (P>.05). However, the slight color changes of zirconia crowns were detected and represented by ΔE^*_ab values, ranging from 1.2 to 3.1. The contrast ratios of zirconia specimens were 0.92-0.95 after veneering.

CONCLUSION

No significant differences were observed between the L^*, a^*, and b^* values of zirconia crowns cemented either on a metal cast post and core or a prefabricated post and composite core. However, the color of a background substructure could affect the overall color of posterior zirconia restorations with clinically recommended core thickness according to ΔE^*_ab values.     

The influence of simulated masticatory loading regimes on the bi-axial flexure strength and reliability of a Y-TZP dental ceramic

OBJECTIVES: The purpose of the current study was to examine the influence of simulated masticatory loading regimes, to which all-ceramic crown or bridge restorations will routinely be subjected during their service-life, on the performance of a yttria-stabilised tetragonal zirconia polycrystalline (Y-TZP) dental ceramic. METHODS: Ten sets of 30 Y-TZP ceramic discs (13 mm diameter, 1.48-1.54 mm thickness) supplied by the manufacturer were randomly selected. Six groups were loaded for 2000 cycles at 500 N (383-420 MPa), 700N (536-588 MPa) and 800 N (613-672 MPa) with three groups maintained dry and the remaining three groups loaded while immersed in water at 37+/-1 degrees C. A further two groups underwent extended simulated masticatory loading regimes at 80 N (61-67 MPa) for 10(4) and 10(5)cycles under dry conditions. The mean bi-axial flexure strengths, standard deviations and associated Weibull moduli (m) were determined. The surface hardness was also determined using the Vickers hardness indentation technique. RESULTS: No significant difference (P>0.05) was identified in the bi-axial flexure strength of the simulated masticatory loading regimes and the control specimens loaded dry or wet. A significant increase in m was identified for the Y-TZP specimens following loading while immersed in water (8.6+/-1.6, 8.5+/-1.6 and 10.3+/-1.9) compared with the control (7.1+/-1.3). However, the extended loading regime to 10(5)cycles resulted in a significant reduction in the m of the Y-TZP specimens (5.3+/-1.0) compared with the control. Localised areas of increased surface hardness were identified to occur directly beneath the spherical indenter. CONCLUSIONS: The occurrence of localised areas of increased surface hardness could be the result of either a transformation toughening mechanism or crushing and densification of the material beneath the indentor manifested as the formation of a surface layer of compressive stresses that counteracted the tensile field generated at the tip of a propagating crack which increased the Weibull modulus of the Y-TZP specimens. The reduced reliability of the Y-TZP specimens loaded to 80 N for 10(5)cycles was associated with the accumulation of subcritical damage as a result of the extended nature of loading.     

Fatigue resistance of ultrathin CAD/CAM ceramic and nanoceramic composite occlusal veneers

ObjectiveThe fracture resistance of different ultrathin occlusal computer-aided design/computer-aided manufacturing (CAD/CAM) veneers was investigated under cyclic mechanical loading to restore combined enamel-dentin defects.MethodsEighty-four molars were reduced occlusally until extensive dentin exposure occurred with a remaining enamel ring. Twenty-four molars were ground flat for examination of highly standardized specimens, of which 8 were treated with uniformly flat 0.3 mm IPS Empress CAD and 0.3 and 0.5 mm IPS e.max CAD restorations. Sixty-four molars were anatomically prepared until dentin exposure and were restored using occlusal veneers with fissure/cusp thicknesses of 0.3/0.5 mm from 3 different dental CAD/CAM materials: IPS Empress CAD, IPS e.max CAD and Lava Ultimate CAD/CAM. Teeth were etched with 37% phosphoric acid, and occlusal veneers were bonded using an adhesive luting system (Syntac Primer, Adhesive, Heliobond and Variolink II). Specimens were placed under cyclic mechanical loading in a chewing simulator (1 million cycles at 50 N) and were examined for cracks after each cyclic loading sequence. The anatomical 0.3/0.5 mm IPS e.max CAD specimens experienced an additional 1 million cycles at 100 N. Kaplan–Meier survival curves and log-rank tests were used for data analysis.ResultsAll highly standardized and 0.3/0.5 mm IPS e.max CAD specimens tolerated cyclic loading. One anatomical Lava Ultimate CAD/CAM and 10 IPS Empress CAD specimens showed cracks.SignificanceUltrathin occlusal veneers of lithium disilicate ceramic and nanoceramic composite showed remarkably high fracture strength under cyclic mechanical loading. These veneers might be a tooth substance preserving option for restoring combined dentin–enamel defects.     

Effect of hydrothermal and mechanical aging on the fatigue performance of high-translucency zirconias

ObjectivesThis study aimed to evaluate the impact of mechanical fatigue cycling using the step-stress approach along with hydrothermaldegradation (134 ºC with a constant pressure of 2 bars for 20 h), and a novel intercalated hydrothermal/fatigue aging protocol on different aspects of the aging resistance of three generations of dental zirconias.Methods“Y”Z T (VITA), INCORIS “T”ZI (Dentsply Sirona) and “K”ATANA UTML (Noritake Kuraray) ? 1st, 2nd and 3rd generation, respectively-, zirconia disks (N = 153), were divided into 6 groups (n = 3) for monotonic testing and 9 groups (n = 15) for mechanical fatigue testing, according to 3 proposed treatments for each zirconia: CF (control – only mechanical fatigue cycling); AF (aging in hydrothermal reactor at 134 °C for 20 h + mechanical fatigue cycling); AFA (Alternating protocol: 4 steps of 5 h of hydrothermal aging intercalated with mechanical fatigue cycling). Mechanical fatigue aging was performed according to the step-stress approach through biaxial flexural setup (piston-on-3-balls, initial strength: 100 MPa, step: 50 MPa/10,000, frequency: 20 Hz) until failure. Data were analyzed using Kaplan-Meier and Mantel-Cox test (α = 0.05), in addition to Weibull analysis. Fractured disks were analyzed in stereomicroscope, Scanning Electron Microscopy and X-Ray Diffraction.ResultsContinuous hydrothermal and mechanical fatigue cycling decreased the fatigue strength of YAF group (516 ± 38 MPa), while the alternating protocol increased it (730 ± 58 MPa). KATANA UTML showed no differences for both treatments and did not undergo t-m phase transformation. The TAF group showed the highest fatigue strength (810 ± 76 MPa) and cycles for failure (147,000.00 cycles). The fracture origin for all specimens was on the tensile side in pre-existing defects.SignificanceINCORIS TZI zirconia had higher fatigue strength and survival rates after hydrothermal and mechanical fatigue aging. Although less resistant, KATANA UTML did not suffer chemical degradation.     

Wear performance of substructure ceramics and veneering porcelains

Aim

The aim of this in vitro study was to compare the two-body wear resistance of substructure zirconia and veneering porcelain versus steatite and human enamel antagonists, respectively.

Materials and methods

Two-body wear tests were performed in a chewing simulator with steatite and enamel antagonists (enamel cusps). A pin-on-block design with a vertical load of 50 N for 1.2 × 10⁵ cycles; (f = 1.6 Hz; lateral movement: 1 mm, mouth opening: 2 mm) was used for the wear test. For quantification of the wear resistance, wear tests were performed with standardized steatite spheres. Human enamel was used as a reference. Five zirconia ceramics and four veneering porcelains were investigated. One zirconia ceramic was tested with superficial glaze, which was applied after polishing or sandblasting, respectively. Surface roughness R_a (SP6, Perthen-Feinprüf, G) and wear depth were determined using a 3D-Profilometer (Laserscan 3D, Willytec, G). SEM (Quanta FEG 400, FEI, USA) pictures were used for evaluating wear performance of both, ceramics and antagonists.

Results

No wear was found for zirconia substructures. Veneering porcelain provided wear traces between 186.1 ± 33.2 μm and 232.9 ± 66.9 μm (steatite antagonist) and 90.6 ± 3.5 μm and 123.9 ± 50.7 μm (enamel). Wear of the steatite antagonists varied between 0.812 ± 0.256 mm² and 1.360 ± 0.321 mm² for zirconia and 1.708 ± 0.275 mm² and 2.568 ± 0.827 mm² for porcelain. Enamel generally showed wear, cracks or even fractures at the ridge, regardless whether opposed by zirconia or porcelain/glaze. Enamel was polished, when opposed to zirconia, or plowed, provoked and grinded, when opposed to porcelain/glaze.

Conclusion

The results of the wear test with steatite or enamel antagonists indicated no measurable wear on zirconia surfaces. Porcelain showed higher wear than zirconia, but comparable or lower wear than an enamel reference. Antagonistic wear against zirconia was found to be lower than wear against porcelain.     

Lifetime prediction of veneered versus monolithic lithium disilicate crowns loaded on marginal ridges

Objective

To evaluate the probability of survival of monolithic and porcelain veneered lithium disilicate crowns comprised by a conventional or modified core when loaded on marginal ridges.

Chipping behaviour of all-ceramic crowns with zirconia framework and CAD/CAM manufactured veneer

Objectives

The aim of this in vitro study was to assess the ultimate load to failure of zirconia based crowns veneered with CAD/CAM manufactured ceramic.

Methods

32 identical, anatoform zirconia (Sirona inCoris ZI, mono L F1) frameworks (thickness 0.6 mm) were constructed (Sirona inLab 3.80). Afterwards, 16 crowns were completed using a CAD/CAM manufactured lithium disilicate ceramic veneer (IPS e.max CAD, Ivoclar Vivadent). The remaining 16 frames were veneered using conventional manual layering technique. For the CAD/CAM manufactured veneers, the connection between framework and veneer was accomplished via a glass fusion ceramics. Before fracture tests, half of the specimens underwent thermocycling and chewing simulation (1.2 million chewing cycles, force magnitude F_max = 108 N). To further investigate the new technique, finite element computations were carried out on the basis of the original geometry.

Results

Nearly all (87.5%) conventionally veneered crowns failed already during chewing simulation, whereas crowns with CAD/CAM manufactured veneers were non-sensitive to artificial ageing. Crowns veneered with lithium disilicate ceramic displayed ultimate loads to failure of about 1600 N.

Conclusion

The CAD/CAM production of veneers for restorations with zirconia framework is a promising way to reduce failures originating from material fatigue.