Fracture frequency of all-ceramic crowns during dynamic loading in a chewing simulator using different loading and luting protocols

OBJECTIVE: The purpose of this laboratory study was to compare the frequency of failures (complete fractures or partial cracks) of molar crowns made of two different all-ceramic materials during dynamic loading in a chewing simulator, as well as the fracture load when subjected to static loading, in relation to different dynamic loading and luting protocols. METHODS: One hundred and forty-four molar crowns fabricated with IPS Empress or an experimental e.max Press material with high translucency (e.max Press Exp) were luted on CAD/CAM milled PMMA abutments (first lower molar, circular chamfer) either with Variolink or glass-ionomer cement (GIC). All crowns were loaded according to three different loading protocols (n=12 per group) and two force profiles (sinusoidal, rectangular) in a pneumatically driven chewing simulator with a steel stylus (? 8mm) and they underwent simultaneous thermocycling (5 degrees C/55 degrees C). After each phase the crowns were evaluated with regard to fractures or cracks. After dynamic testing, the crowns that did not fail were subjected to compression loading until complete fracture in a universal testing machine (UTM). As control groups, unloaded crowns were also subjected to a UTM. Survival statistics with log-rank tests were applied for the results of the dynamic loading, while ANOVA with post hoc Tukey B was used for the fracture load results and two-way ANOVA was carried out for logarithmically transformed data. Weibull statistics were calculated for pooled fracture load data of the dynamically loaded and control groups. RESULTS: In the 144 IPS Empress crowns, complete fractures were observed in 9 crowns and partial cracks in another 3 crowns. When the data was pooled, a statistically significant increase in fractures occurred when the sinusoidal force profile was applied compared to a rectangular force profile (log-rank, p<0.05). No fractures occurred in the e.max Press Exp crowns. The two-way ANOVA showed that the type of luting protocol used had the most significant effect on the fracture load of both materials. In conjunction with Empress, however, the luting material influenced the variability twice as much as in e.max Press Exp. There was no statistically significant difference in the fracture load of GIC-luted e.max Press Exp crowns and that of the Variolink luted Empress crowns. The force profile had a significant effect on the fracture load only of the Empress crowns but not of the e.max Press Exp crowns. Weibull statistics revealed a higher scattering of the data of dynamically loaded crowns compared to that of the control groups. CONCLUSIONS: For testing all-ceramic materials, dynamic loading is indispensable to draw valid conclusions on clinical performance of all-ceramic molar crowns. A sinusoidal profile is advisable, while a gradual increase of the force amplitude does not significantly affect the results.     

Thyroplasty Type I with Ceramic Shim

Abstract: To prevent side effects from a silicone shim in Isshiki thyroplasty type I, we used a ceramic shim in 10 patients with unilateral recurrent laryngeal nerve paralysis. No published reports have described the use of ceramic in this type of surgery. According to the degree of glottic insufficiency, ceramic shims of various heights were inserted into the fenestration made in the thyroid ala. All patients experienced subjective improvement of voice postoperatively. Laryngoscopies in most cases showed that glottic insufficiency improved postoperatively. In the postoperative examination, the maximum phonation time improved an average of 3.7 s, and the mean flow rate improved an average of 331 ml/s. We have analyzed the relationship of these improvements to the degree of glottic insufficiency and have compared our results with those of other investigators.     

A scanning electron microscopy study of the interface between ceramics and bone

By use of scanning electron microscopy (SEM), together with energy dispersive chemical analysis, a study has been made of the comparison of an in vitro method of assessing interface reactions between bone and ceramic implants with the naturally occurring changes seen in the rat ear model. Interface reactions between bone and two ceramic materials were examined following 4 wk in culture and 4 wk implantation. In both cases a gradual chemical change occurred at the calcium silicate surface during the fibrous growth onto the ceramic material. Gradual mineralization of the connective fibres was found at the interface of the calcium silicate material, whereas, in the case of alumina ceramic a connective fibrous bond had formed with no associated chemical change at the ceramic surface.     

Membranes for endotoxin removal from dialysate: considerations on feasibility of commercial ceramic membranes

As the quality of water in dialysis fluid varies considerably, dialysate is often contaminated by large amounts of bacteria and endotoxins. Membrane properties and operating pressures are acknowledged to give high-flux dialysis with bicarbonate the bacteriological potential to favor passage of endotoxin fragments from the dialysate into the blood stream. Therefore, a sterile dialysate will have to become a standard. Ultrafiltration across hydrophobic synthetic membranes was shown to remove endotoxins (and their fragments) from dialysis water by the combined effect of filtration and adsorption. However, each module can be used for a limited time only. Ceramic membranes may represent an alternative to polymeric membranes for endotoxin removal. In this article, we tested the capacity of different commercial ceramic membranes with nominal molecular weight cut-off down to 1,000 to retain endotoxins from Ps. aeruginosa. The tested membranes did not generally produce dialysate meeting the Association for the Advancement of Medical Instrumentation standard. When using aluminum-containing membranes, we detected aluminum leaking into the dialysate that could possibly be transported into the blood stream.     

青年期先天性髋关节脱位的全髋置换治疗

目的:探讨青年期先天性髋关节脱位的治疗方法.方法:先天性髋关节脱位患者13例,年龄16～19岁,全部存在髋臼、股骨头、颈发育不良.采用陶瓷-陶瓷假体给予全髋置换治疗.应用Harris评分进行功能评价.结果:13例患者Harris评分81～94分,步态正常,患髋无痛感.结论:对青年期先天性髋关节脱位患者,采取陶瓷-陶瓷假体全髋置换手术治疗可以取得满意的疗效,但其昂贵的价格限制了使用范围.     

Fabrication of a metal-ceramic crown to fit an existing partial removable dental prosthesis using ceramic pressed to metal technique: a clinical report

Fabricating a crown to retrofit an existing abutment tooth for a partial removable dental prosthesis (PRDP) is one of the most time-consuming and labor-intensive clinical procedures. In particular, when the patient is concerned with esthetic aspects of restoration, the task of fabricating becomes more daunting. Many techniques for the fabrication of all-metallic or metal-ceramic crowns have been discussed in the literature. This article was aimed to describe a simple fabrication method in which a retrofitting crown was fabricated for a precise fit using a ceramic-pressed-to-metal system.     

Bone and Ceramic Interaction in the Bone Union Process

This study applied an experimental rat model and ceramic as an artificial matrix to explore the ultrastructural development of new bone production in tibia defects. By X-ray diffraction control or energy-dispersive X-ray analysis the nature of ceramic was verified and routine histology and TEM investigation were used to demonstrate bone - ceramic interaction. The results show that biphasic ceramic can promote bone growth in an osseous defect and is therefore an alternative to autogenous bone matrix. The porousity and bioactivity of the biphasic ceramic enhanced bone formation and provided a scaffold for new lamellar bone invasion.     

OCT evaluation of the internal adaptation of ceramic veneers depending on preparation design and ceramic thickness

ObjectivesIn-vitro evaluation of the influence of preparation design and thickness of ceramic veneers on the interfacial bond using optical coherence tomography (OCT).MethodsSixty-four central incisors were randomly assigned to four preparation designs differing from no to complete dentine exposure (n = 16 each): non-prep (NP), minimal-invasive (MI, no dentine exposure), semi-invasive (SI, 50% dentine) and invasive (I, 100% dentine). Ceramic veneers (IPS InLine Veneer) of two thicknesses (0.2?0.5 mm (T1) and > 0.5–1.2 mm (T2)) were etched, silanized, and adhesively luted (Optibond FL, Variolink Veneer). After water storage (37 °C, 21d), thermocycling (2000 cycles, 5°-55 °C), and mechanical loading (2 + 1 million cycles, 50 + 100 N) specimens were imaged by spectral-domain OCT (Telesto II, Thorlabs). Adhesive defects at the ceramic-composite and tooth-composite interfaces were quantified on 35 equidistantly distributed OCT B-scans (length, %). Statistical differences were verified with Wilcoxon-/Mann-Whitney-U-test (α = 0.05).ResultsAdhesive defects appeared in all groups at both interfaces, albeit to differing extents (0.1 – 31.7%). NP and MI veneers showed no significant differences at the interfaces (p_i > 0.05). In groups, SI and I, significantly more adhesive defects appeared at the tooth-composite compared to the veneer-composite interface (p_i ≤ 0.039). The following preparation designs and veneer thicknesses showed differences (p_i ≤ 0.021): Veneer-composite: NP-T1 < I-T1, MI-T1 < I-T1, I-T1 > I-T2; Tooth-composite: NP-T1 < SI-T1, NP-T1 < I-T1, NP-T2 > MI-T2, MI-T1 < SI-T1, MI-T1 < I-T1, SI-T1 < I-T1, MI-T2 < SI-T2, MI-T2 < I-T2.SignificanceThe interface adhesion of ceramic veneers was influenced by the preparation design and the veneer thickness. A ceramic thickness of at least 0.5 mm and a preparation without exposing dentine is advantageous for the interfacial bond.     

Improvement on properties of experimental resin cements containing an iodonium salt cured under challenging polymerization conditions

ObjectiveThe use of resin cements in clinical practice entails photopolymerization through prosthetic devices, which precludes light penetration. The objective of this study was to modify experimental resin cements (ERCs) with diphenyliodonium hexafluorophosphate (DPI) in an attempt to improve chemical and mechanical properties of materials cured with reduced irradiance and final radiant exposure.MethodsA co-monomer base containing a 1:1 mass ratio of 2.2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (bis-GMA) and triethyleneglycol dimethacrylate (TEGDMA) was prepared, with 1 mol% of camphorquinone and 2 mol% of ethyl 4-(dimethylamino)benzoate as initiator system. The resin was divided into 4 fractions according to the DPI concentrations (0, 0.5, 1 and 2 mol%). The challenging polymerization condition was simulated performing the light activation (12, 23 and 46 s) through a ceramic block (3 mm thick). The irradiance was assessed with a calibrated spectrometer (1320 mW/cm²), resulting in three levels of radiant exposure (0.58, 1.1 and 2.2 J/cm²). The polymerization kinetics was evaluated in real-time using a spectrometer (Near-IR). Water sorption and solubility was analyzed and the cohesive strength of resins obtained through the microtensile test. Polymerization stress was assessed by Bioman method.ResultsResins containing DPI had higher degree of conversion and rate of polymerization than the control (without DPI). The use of DPI reduced water sorption and solubility, and led to higher cohesive strength compared to resins without the iodonium salt. However, the stress of polymerization was higher for experimental resins with DPI.SignificanceEven under remarkably reduced irradiance, cements containing a ternary initiating system with an iodonium salt can present an optimal degree of conversion and chemical/mechanical properties.