Fractographic analyses of all-ceramic crowns: A study of 27 clinically fractured crowns

ObjectivesThe use of all-ceramic restorations has been steadily increasing in the decades since the introduction of high-strength core ceramics as an alternative to metal cores. Even with high-strength ceramic cores, the crowns are susceptible to fractures during clinical function, probably the major concern associated with all-ceramic restorations. The aim of this study was to analyze fracture features of clinically fractured crowns in order to determine crack initiation sites and crack propagation paths.MethodsFractographic methods were used to analyze 27 all-ceramic full coverage crowns with alumina cores and feldspatic veneering ceramic. The fractured crowns were supplied by dentists in private and public practices with information of type of cement and time in function if available.ResultsThe fractured crowns comprised 13 incisors, 3 premolars and 11 molars. The results revealed that all fractures initiated in the cervical margin of the crowns and usually from the approximal area close to the most coronally placed curvature of the margin. There was no statistically significant association between the cement used and time in function.SignificanceFractography of clinically failed all-ceramic crowns can provide information on the fracture modes and design considerations. The findings are in contrast to fracture modes from in vitro tests. The results suggest that more clinically relevant in vitro test methods to study the durability of ceramic crowns should be developed.     

Gap comparison between single crown and three-unit bridge zirconia substructures

PURPOSE

To compare marginal and internal gaps of zirconia substructure of single crowns with those of three-unit fixed dental prostheses.

MATERIALS AND METHODS

Standardized Co-Cr alloy simulated second premolar and second molar abutments were fabricated and subsequently duplicated into type-III dental stone for working casts. After that, all zirconia substructures were made using Lava™ system. Marginal and internal gaps were measured in 2 planes (mesial-distal plane and buccal-palatal plane) at 5 locations: marginal opening (MO), chamfer area (CA), axial wall (AW), cusp tip (CT) and mid-occlusal (OA) using Replica technique.

RESULTS

There were significant differences between gaps at all locations. The mean ± SD of marginal gap in premolar was 43.6 ± 0.4 µm and 46.5 ± 0.5 µm for single crown and 3-unit bridge substructure respectively. For molar substructure the mean ± SD of marginal gap was 48.5 ± 0.4 µm and 52.6 ± 0.4 µm for single crown and 3-unit bridge respectively. The largest gaps were found at the occlusal area, which was 150.5 ± 0.5 µm and 154.5 ± 0.4 µm for single and 3-unit bridge premolar substructures respectively and 146.5 ± 0.4 µm and 211.5 ± 0.4 µm for single and 3-unit bridge molar substructure respectively.

CONCLUSION

Independent-samples t-test showed significant differences of gap in zirconia substructure between single crowns and three-unit bridge (P<.001). Therefore, the span length has the effect on the fit of zirconia substructure that is fabricated using CAD/CAM technique especially at the occlusal area.     

Effect of changes in sintering parameters on monolithic translucent zirconia

ObjectivesAim of this study was to evaluate the effect of different sintering parameters on color reproduction, translucency and biaxial flexural strength of monolithic zirconia.MethodsTranslucent zirconia discs having 15 mm diameter, 1 mm thickness, and shade A3 were milled and divided according to the sintering temperatures (1460 °C, 1530 °C, and 1600 °C) into three groups (n = 30). Each group was later divided into three subgroups (n = 10) according to the sintering holding time (1, 2, and 4 h). Easyshade spectrophotometer (Vita, Bad Säckingen, Germany) was used to obtain the ΔE between the specimens and the shade A3. Mean ΔE values below 3.0 were considered “clinically imperceptible”, ΔE values between 3.0 and 5.0 were considered “clinically acceptable” and ΔE values above 5.0 were considered “clinically unacceptable”. Contrast ratio (CR) was obtained after comparing the reflectance of light through the specimens over black and white background. Biaxial flexural strength was tested using the piston-on-three balls technique in a universal testing machine.ResultsMean ΔE results ranged from 4.4 to 2.2. Statistically significant decrease in the Delta E was observed as the sintering time and temperature increased. CR decreased from 0.75 to 0.68 as the sintering time and temperature increased. No significant change in the biaxial flexural strength was observed.SignificanceSintering zirconia using long cycles and high temperatures will result in reduction of ΔE and CR. Biaxial flexural strength is not affected by changes in the evaluated sintering parameters.     

Diego Rivera and His Extraordinary Art of Medicine and Surgery

Diego Rivera (1886–1957), the superb Mexican muralist, made significant contributions to the art of medicine and surgery unmatched by any other painter of his stature in the world. Rivera intensively embraced medical and surgical knowledge through his legendary artistic career in a manner never seen before.

Rivera's first surgical theme can be traced to 1920, when he attended and drew the wonders of the surgical operation of Dr. Fauré in Paris. The artist was particularly moved by surgical and medical events, and this surgical clinic enhanced his appetite for these important professional activities. In 1932, Rivera introduced several medico-surgical panels in Detroit automobile industry frescos. Among them, vaccination, the human embryo, the pharmaceutical industry, the germ cell, and surgery are the most representative themes included.

Two years later, in Man, Controller of the Universe, the artist emphasized the effect disease and technology had on the rest of humanity. In 1944, Rivera produced The History of Cardiology, two movable extraordinary frescos that represent the history of this field of medicine. In 1953, the creative vein of this prodigious genius created The History of Medicine in Mexico, in which medicine and surgery are exceptionally well-conceived and analyzed. In brief, Rivera incorporated the best of his art and knowledge into the better understanding of medicine and surgery as he saw it during his outstanding artistic life.     

涂覆烧结金膏处理对三种钛瓷粉与纯钛结合强度的影响

目的 探讨纯钛表面金膏涂覆烧结处理对3种钛瓷粉与纯钛结合强度的影响.方法 根据IS0 9693要求制备预成纯钛试件60个,以3种钛瓷粉(I:Initial Ti;S:Super porcelain Ti-22;T:TitanKeramik)进行分组,并根据烧结金膏涂层(G:Deckgold)与否进行亚组细分(GI、GS、GT、I、S、T组),每亚组10个钛-瓷标准试件.场发射扫描电镜观察钛-瓷结合界面的微观形貌.三点弯曲法测定钛-瓷结合强度,并进行统计学分析.体视显微镜观察各组钛-瓷断裂模式.结果 场发射扫描电镜显示金膏涂层与钛、瓷结合紧密,内部偶见裂隙,以混合断裂为主;而未烧结金膏涂层组以界面断裂为主.GS和GI组结合强度分别为(37.08±4.32)和(36.20±2.40) MPa,相应高于S和I组[分别为(31.56±3.74)和(30.88±2.60) MPa] (P＜0.05),而GT与T组差异无统计学意义(P＞0.05).结论 在本项研究条件下,涂覆烧结金膏涂层可显著提高两种钛瓷粉与预成纯钛的结合强度.     

纳米陶瓷人工骨修复骨缺损的实验研究

目的通过动物实验探讨纳米陶瓷人工骨的骨缺损修复作用及相关问题,为其应用于骨缺损的修复提供依据。方法青紫兰兔45只在单侧桡骨制备骨缺损动物模型,随机分成3组(每组15只),然后用纳米陶瓷人工骨材料植入骨缺损处进行修复作为实验组,以植入陶瓷人工骨为对照组,空白组不植入任何材料;术后4、8、12周分别行大体标本观察、组织学、X线检查、扫描电镜(SEM)测试,比较三组间骨缺损区的成骨情况。结果纳米陶瓷人工骨成骨作用明显优于陶瓷人工骨组和空白对照组,差异有显著性意义(P<0．05)。结论纳米陶瓷人工骨具有良好的成骨能力、生物相容性和一定的降解率,是一种替代自体骨修复骨缺损较理想的材料。     

Ribosomal gene activity in lymphocytes of female workers exposed to aromatic hydrocarbons in the ceramics industry

The ribosomal gene activity of peripheral blood lymphocytes was studied in a group of 27 females working in seven small pottery industries exposed to a mixture of aromatic hydrocarbons (AH) (xylene, toluene, trimethylbenzene isomers; tricloroethylene). All were relatively young and healthy women who have worked in this sector for an average of 9 years. The control group consisted of a sample of 27 women not employed in the ceramics industry matched for age ( +/- 2 years) residence and parity ( +/- 1). Lymphocyte cultures and chromosome preparations were set up by standard methods. Slides were silver stained and ribosome gene activity was evaluated in terms of the number of silver positive NORs (nucleolus organizing regions) per cell in 100 cells per subject by an observer who operated blind in the microscope. The difference in the mean number of NORs of the exposed group ( x = 8.00) compared to the control group ( x = 7.98) was not statistically significant. A multivariate analysis of the data was undertaken to study other possible characteristics of the subjects such as age, cigarette smoking, duration of exposure to AH, and work site. None of these variables contributed significantly to the variance in the values of ribosomal gene activity.     

Cyclic fatigue vs static loading for shear bond strength test of lithium disilicate and dentin substrates: A comparison of resin cement viscosities

ObjectiveTo explore the effect of resin cement viscosities on the shear bond strength under static and fatigue load of lithium disilicate and dentin substrates.MethodsBonded tri-layer samples (lithium disilicate ceramic cylinder, resin cement, and substrate – ceramic or dentin) was performed considering 2 factors (n = 15): “resin cement viscosity” (high, HV; or low, LV) and “loading mode” (static, s-SBS; or fatigue shear bond strength, f-SBS). The specimens were subjected to s-SBS (1 mm/min, 1 kN load cell) and f-SBS (cyclic fatigue, initial load: 10 N; step-size: 5 N; 10,000 cycles/step; underwater). Failure mode, topography, and finite element analysis (FEA) were performed.ResultsThe resin cement viscosity did not influence the s-SBS and f-SBS of lithium disilicate substrate; however, it affected the bond strength to dentin, with HV presenting the worst fatigue behavior (f-SBS = 6.89 MPa). Cyclic loading in shear testing induced a notorious detrimental effect with a relevant decrease (16–56 %) in bond strength and survival rates, except for dentin substrate and LV. Most failures were adhesive. A distinct pattern comparing the disilicate and dentin was identified and FEA demonstrated that there was a stress concentration on the top of the cement layer.SignificanceCyclic fatigue loading in shear testing has detrimental effects on the adhesive behavior and survival probabilities of bonded lithium disilicate sets, regardless of resin cement viscosity. In contrast, resin cement viscosity affects the bond strength and the survival rates of dentin substrate submitted to cyclic loading mode, in which a low viscosity results in better performance.     

K2O-Na2O-Al2O3-SiO2系统牙科微晶玻璃匹配氧化铝陶瓷的初步研究

目的:研究 K₂O-Na₂O-Al₂O₃-SiO₂系统牙科微晶玻璃匹配氧化铝陶瓷的热处理温度制度。方法:根据氧化铝陶瓷的热膨胀系数调整K₂O-Na₂O-Al₂O₃-SiO₂系统牙科微晶玻璃的原材料配比,利用K₂O-Na₂O-Al₂O₃-SiO₂系统牙科微晶玻璃的热处理温度制度形成微晶玻璃-氧化铝陶瓷复合材料;利用偏振光显微镜和X射线衍射分析仪观察样品的形态及显微结构特性,利用材料试验机测试材料的抗压强度。结果:经过原材料组份的调整,白榴石晶粒约1.0 μm、在玻璃基质中分布均匀;微晶玻璃-氧化铝陶瓷复合材料的抗压强度为500 MPa。结论:K₂O-Na₂O-Al₂O₃-SiO₂系统牙科微晶玻璃的热处理温度制度适合匹配氧化铝陶瓷。