The (in)dependency of blood and sweat sodium, chloride, potassium, ammonia, lactate and glucose concentrations during submaximal exercise.

PURPOSE: To reduce the need for invasive and expensive measures of human biomarkers, sweat is becoming increasingly popular in use as an alternative to blood. Therefore, the (in)dependency of blood and sweat composition has to be explored. METHODS: In an environmental chamber (33 °C, 65% relative humidity; RH), 12 participants completed three subsequent 20-min cycling stages to elicit three different local sweat rates (LSR) while aiming to limit changes in blood composition: at 60% of their maximum heart rate (HRmax), 70% HRmax and 80% HRmax, with 5 min of seated-rest in between. Sweat was collected from the arm and back during each stage and post-exercise. Blood was drawn from a superficial antecubital vein in the middle of each stage. Concentrations of sodium, chloride, potassium, ammonia, lactate and glucose were determined in blood plasma and sweat. RESULTS: With increasing exercise intensity, LSR, sweat sodium, chloride and glucose concentrations increased (P ≤ 0.026), while simultaneously limited changes in blood composition were elicited for these components (P ≥ 0.093). Sweat potassium, lactate and ammonia concentrations decreased (P ≤ 0.006), while blood potassium decreased (P = 0.003), and blood ammonia and lactate concentrations increased with higher exercise intensities (P = 0.005; P = 0.007, respectively). The vast majority of correlations between blood and sweat parameters were non-significant (P > 0.05), with few exceptions. CONCLUSION: The data suggest that sweat composition is at least partly independent of blood composition. This has important consequences when targeting sweat as non-invasive alternative for blood measurements.

Non-tuberculous Mycobacteria isolated from lymph nodes and faecal samples of healthy slaughtered cattle and the abattoir environment.

Infections caused by non-tuberculous mycobacteria (NTM) are reported as emerging disease in many countries worldwide. The occurrence of NTM in different hosts and their implication as obligate or opportunistic pathogen remain largely unclear. Lymph nodes and faecal samples of clinically healthy Swiss cattle at slaughter were analysed for the presence of NTM. Based on the examined lymph nodes, NTM were detected in 20% of 108 cattle originating from different premises. The 22 isolates belonged to five different species of Mycobacteria (M. avium subsp. hominissuis, M. kansasii, M. persicum, "M. lymphaticum" and M. europaeum). M. avium subsp. hominissuis (63%) and M. kansasii (18%) thereby predominated and were found in lymph nodes with and without macroscopic changes. Moreover, M. persicum found in two cattle has recently been described as a human pathogen and is closely related to M. kansasii. Amongst cattle with lymph nodes positive for mycobacteria, viable NTM were occasionally also detected in bovine faeces. However, the isolated NTM species from lymph nodes and respective faecal samples (M. hassiacum, M. phlei and M. vaccae) did not coincide. Moreover, NTM species identified amongst isolates from the slaughterhouse environment clearly differed from those from lymph nodes and faecal samples, excluding cross-contamination of the tissue specimens through the environment or laboratory processing. Assuming that some NTM interfere with the detection of bovine tuberculosis (bTB), the present findings in healthy animals emphasize the need of more specific diagnostic tools for bTB eradication programs.

ADM guidance-ceramics: Fatigue principles and testing.

BACKGROUND: Clinical failure of dental ceramics is usually reported as partial fracture of the restoration (chipping) or as catastrophic fracture of the whole structure. In contrast to metals, ceramics are linear-elastic, brittle materials exhibiting extremely low damage tolerance to failure. Well documented clinical and lab reports have shown this fracture event often occurs at loads far below their fracture strength due to intrinsic fatigue degradation via slow crack growth or cyclic fatigue mechanisms. The presence and development of surface flaws have a dominant role in damage accumulation and lifetime reduction of ceramic structures. AIMS: This ADM guidance document aims to summarize the aspects related to fatigue degradation of dental ceramics, reviewing the concepts of fatigue testing and furthermore aims to provide practical guidance to young scientists entering into fatigue related research. The description of fatigue strength is always accompanied by a clear understanding of the underlying fracture mechanisms.

TiN x O y coatings facilitate the initial adhesion of osteoblasts to create a suitable environment for their proliferation and the recruitment of endothelial cells.

Titanium-nitride-oxide coatings (TiN x O y ) improve osseointegration of endosseous implants. The exact mechanisms by which these effects are mediated are poorly understood except for an increase of osteoblast proliferation while a high degree of differentiation is maintained. One hypothesis holds that TiN x O y facilitates the initial spreading and adhesion of the osteoblasts. The aim of this work was to investigate the molecular mechanisms of osteoblast adhesion on TiN x O y as compared to microrough titanium SLA. A global view of the osseointegrative process, that is, taking into account other cell groups, especially endothelial cells, is also presented. To this aim, gene expression and focal adhesion analysis, cocultures and wound assays were performed early after seeding, from 6 h to 3 days. We demonstrated that TiN x O y coatings enhance osteoblast adhesion and spreading when compared to the standard microrough titanium. The integrin ß1, either in association with α1 or with α2 plays a central role in these mechanisms. TiN x O y coatings optimize the process of osseointegration by acting at several levels, especially by upregulating osteoblast adhesion and proliferation, but also by supporting neovascularization and the development of a suitable inflammatory environment.

Coxiella burnetii Infections in Small Ruminants and Humans in Switzerland.

The recent Q fever epidemic in the Netherlands raised concerns about the potential risk of outbreaks in other European countries. In Switzerland, the prevalence of Q fever in animals and humans has not been studied in recent years. In this study, we describe the current situation with respect to Coxiella (C.) burnetii infections in small ruminants and humans in Switzerland, as a basis for future epidemiological investigations and public health risk assessments. Specific objectives of this cross-sectional study were to (i) estimate the seroprevalence of C. burnetii in sheep and goats, (ii) quantify the amount of bacteria shed during abortion and (iii) analyse temporal trends in human C. burnetii infections. The seroprevalence of C. burnetii in small ruminants was determined by commercial ELISA from a representative sample of 100 sheep flocks and 72 goat herds. Herd-level seroprevalence was 5.0% (95% CI: 1.6-11.3) for sheep and 11.1% (95% CI: 4.9-20.7) for goats. Animal-level seroprevalence was 1.8% (95% CI: 0.8-3.4) for sheep and 3.4% (95% CI: 1.7-6) for goats. The quantification of C. burnetii in 97 ovine and caprine abortion samples by real-time PCR indicated shedding of >104 bacteria/g in 13.4% of all samples tested. To our knowledge, this is the first study reporting C. burnetii quantities in a large number of small ruminant abortion samples. Annual human Q fever serology data were provided by five major Swiss laboratories. Overall, seroprevalence in humans ranged between 1.7% and 3.5% from 2007 to 2011, and no temporal trends were observed. Interestingly, the two laboratories with significantly higher seroprevalences are located in the regions with the largest goat populations as well as, for one laboratory, with the highest livestock density in Switzerland. However, a direct link between animal and human infection data could not be established in this study.

Fracture Rates and Lifetime Estimations of CAD/CAM All-ceramic Restorations.

The gathering of clinical data on fractures of dental restorations through prospective clinical trials is a labor- and time-consuming enterprise. Here, we propose an unconventional approach for collecting large datasets, from which clinical information on indirect restorations can be retrospectively analyzed. The authors accessed the database of an industry-scale machining center in Germany and obtained information on 34,911 computer-aided design (CAD)/computer-aided manufacturing (CAM) all-ceramic posterior restorations. The fractures of bridges, crowns, onlays, and inlays fabricated from different all-ceramic systems over a period of 3.5 y were reported by dentists and entered in the database. Survival analyses and estimations of future life revealed differences in performance among ZrO2-based restorations and lithium disilicate and leucite-reinforced glass-ceramics.

The effect of a fiber reinforced cavity configuration on load bearing capacity and failure mode of endodontically treated molars restored with CAD/CAM resin composite overlay restorations.

OBJECTIVES: To evaluate the fracture strength and the mode of failure of endodontically treated molars restored with CAD/CAM overlays with fiber reinforced composite build-up of the pulp chamber. METHODS: 40 Devitalized molars were cut over the CEJ and divided into five groups (n=8). The pulp chamber area was filled with: group 0 (control), no resin build-up; group 1, hybrid composite build-up (G-aenial posterior, GC); group 2, as in group 1 but covered with 3 nets of bi-directional E-glass fibers (EverStickNET, Stick Tech Ltd.); group 3, a FRC resin (EverX posterior, GC); group 4, as in group 3 but covered by the bi-directional fibers. The crowns were restored with CAD-CAM composite restorations (Lava Ultimate, 3M ESPE). Maximum fracture loads were recorded in Newton and data were analyzed using Kruskal-Wallis test (p<0.05). Fragments were analyzed using SEM. RESULTS: The mean static loads in Newton were: group 0: 2448 (546); group 1: 2817 (873); group 2: 2128 (952); group 3: 2429 (1091); group 4: 2577 (833). No significant differences were found between the groups (p>0.05). All specimens fractured in a catastrophic way, under the CEJ. The main crack evolved in the corono-apical direction. In groups 2 and 4 secondary fracture paths with apico-coronal direction were detected close to the bi-directional fibers' layer. CONCLUSIONS: For the restoration of endodontically treated molars, the incorporation of FRCs did not influence the load-bearing capacity of the tooth-restoration complex. The SEM analysis showed a low ability of the bi-directional fibers net in deviating the fracture but this effect was not sufficient to lead more favorable fracture patterns, over the CEJ. CLINICAL SIGNIFICANCE: The use of FRCs to reinforce the "core" of devitalized molars against vertical fractures under static loads seems useless when the thickness of the CAD/CAM composite overlay restoration is high.

Effect of different surface treatments on the hydrothermal degradation of a 3Y-TZP ceramic for dental implants.

OBJECTIVES: Implant surface modifications are intended to enhance bone integration. The objective of this study was to assess the effect of different surface treatments on the resistance to hydrothermal degradation, hardness and elastic modulus of a 3Y-TZP ceramic used for dental implants. METHODS: Samples grouped according to their surface morphologies (AS, as-sintered; C, coated; P, dry-polished; R, roughened; PA, polished and annealed; RA, roughened and annealed) were subjected to accelerated hydrothermal degradation (LTD) by exposure to water steam (134°C, 2bars) for 100h. The t-m phase transformation was quantified by grazing incidence X-ray diffraction (GIXDR) and by combined focused ion beam and scanning electron microscopy (FIB-SEM). Elastic modulus and hardness before- and after prolonged aging (100h) were assessed by nanoindentation. RESULTS: AS and C specimens presented a better resistance to hydrothermal degradation than P and R samples. After prolonged aging, the depth of the monoclinic transformed layer ranged from 11µm to 14µm. Hydrothermal degradation led to a significant decrease of elastic modulus and hardness. SIGNIFICANCE: Surface treatments affected the resistance to hydrothermal degradation of the 3Y-TZP ceramic. Dry mechanical surface modifications should be avoided since a high t-m transformation rate associated to the initial monoclinic content was observed. Annealing was useful to reverse the initial t-m transformation, but did not improve the resistance to hydrothermal degradation.

MALDI-TOF MS for identification of porcine Brachyspira species.

UNLABELLED: The aim of this study consisted in evaluating MALDI-TOF MS as a tool for the identification of the genus Brachyspira (B.) and its relevant species for the pig industry. First, a database was created with 30 control strains, and superspectra for five different porcine Brachyspira species were calculated. In a second step, 67 field isolates were investigated using MALDI-TOF MS, and results were compared to those obtained using nox gene-based RFLP (reference method) and biochemical tests. Among the 67 field isolates, five different Brachyspira species were detected using nox gene-based RFLP analysis. MALDI-TOF MS analysis correctly assigned all isolates to the genus Brachyspira and identified all isolates from B. hyodysenteriae (29/29), B. pilosicoli (11/11), B. intermedia (4/4) and B. innocens (11/11). In terms of B. murdochii, MALDI-TOF MS assigned one of 12 isolates ambiguously as B. innocens/B. murdochii. The results of this study indicate that MALDI-TOF MS facilitates the diagnosis of swine dysentery and porcine intestinal spirochaetosis. SIGNIFICANCE AND IMPACT OF THE STUDY: Current methods for the discrimination of pathogenic Brachyspira hyodysenteriae and Brachyspira pilosicoli from Brachyspira species with low pathogenic potential have proven to be laborious and time-consuming and are therefore not suitable for routine diagnostics. This study describes the evaluation of MALDI-TOF MS for the identification of different porcine Brachyspira species in routine diagnostic laboratories. The results suggest that MALDI-TOF MS is an effective method for the identification of porcine Brachyspira spp. and accelerates diagnosis of swine dysentery and porcine intestinal spirochaetosis.

Post-hot isostatic pressing: a healing treatment for process related defects and laboratory grinding damage of dental zirconia?

OBJECTIVE: Processing parameters (powder granulation, compaction, debinding, greenbody shaping, sintering) and post-sinter rough, even fine grinding are influencing the final mechanical properties of 3Y-TZP. The hypothesis of this study was that post-sinter hot isostatic pressing (post-HIP) would be beneficial for improving reliability and strength of both sintered and coarse ground sintered zirconia by closing or reducing surface and/or small volume defects. METHODS: 75 sintered bars of an experimental 3Y-TZP (3mm×4mm×45mm) with chamfered edges and 15µm diamond surface finish were provided by the manufacturer (Ivoclar Vivadent) and randomly distributed in five groups of N=15 each. G1 served as control (as received); G2 was post-HIPed at 1400°C and G3 at 1350°C, both using a pressure of 195MPa in Ar for 1h; G4 was coarse ground with 120µm diamond disk grain size; G5 was ground 120µm and post-HIPed at 1350°C at 195MPa, 1h in Ar. The specimens were fractured in air in 4 point-bending. Weibull characteristic strength (σ0) in MPa, m parameter (reliability) and confidence intervals (CI) at 90% confidence level are reported. Identification of the critical flaw was performed by SEM on the fractured surface of all specimens and XRD performed in all groups. RESULTS: G1: σ0=973 (932-1016), m=10.6 (7.45-15.1); G2: σ0=930 (871-995), m=6.9 (4.87-9.9); G3: σ0=898 (848-952), m=7.94 (5.6-11.4); G4: σ0=921 (857-991), m=6.35 (4.48-9.11); G5: σ0=881 (847-918), m=11.4 (8.03-16.3). G5 had a significantly lower σ0 than G1. No significant differences were seen in the reliability (m) among the groups. Fractography revealed critical intrinsic subsurface flaws of 10-60µm present in all groups resulting from the processing parameters. No "healing" (i.e. closing of defects by densification) resulted after post-HIP. Grinding sintered zirconia with 120µm diamond disks induced radial cracks of 10-20µm and an important pseudo-cubic phase transformation (56wt%) that was not completely removed after post-HIP. Post-HIP increased slightly the relative density by 0.1% but without improving the strength and reliability. SIGNIFICANCE: Post-HIP was not efficient in closing large (10-60µm) subsurface (volume) processing defects.

Climate and host plant characteristics effects on lepidopteran caterpillar abundance on Miconia ferruginata DC and Miconia pohliana Cogn (Melastomataceae).

Folivore cerrado caterpillars are found on their host species in low frequencies, which vary between plants and throughout the year. We analysed the effects of climatic variation and of the characteristics of two host species (Miconia, Melastomataceae) on caterpillar abundance. The work was carried out in a cerrado sensu stricto area in Brasília, Federal District, Brazil, from May 1998 to September 1999. One hundred plants of each species were inspected monthly. All caterpillars found were collected and raised in the laboratory with Miconia leaves as food sources. Climatic data for the study area and plant characteristics such as local density, spatial distribution, foliar phenology, leaf pilosity and nutritional content were used to test the effects on caterpillar abundance. Less than 10% of the plants had larvae. Caterpillars were more frequent and abundant in M. pohliana, which was also present at higher densities than M. ferruginata. Low caterpillar frequency in host plants and an abundance peak during the dry season are consistent patterns for different cerrado Lepidoptera larvae. This abundance peak, however, is not coincident with higher leaf production in host species. We suggest that M. pohliana's higher local density and better leaf digestibility can account for the higher abundance of caterpillars in this species.

Climate and host plant characteristics effects on lepidopteran caterpillar abundance on Miconia ferruginata DC. and Miconia pohliana Cogn (Melastomataceae) / Efeitos do clima e das características das plantas hospedeiras na abundância de lagartas de Lepidoptera em Miconia ferruginata e Miconia pohliana

Folivore cerrado caterpillars are found on their host species in low frequencies, which vary between plants and throughout the year. We analysed the effects of climatic variation and of the characteristics of two host species (Miconia, Melastomataceae) on caterpillar abundance. The work was carried out in a cerrado sensu stricto area in Brasília, Federal District, Brazil, from May 1998 to September 1999. One hundred plants of each species were inspected monthly. All caterpillars found were collected and raised in the laboratory with Miconia leaves as food sources. Climatic data for the study area and plant characteristics such as local density, spatial distribution, foliar phenology, leaf pilosity and nutritional content were used to test the effects on caterpillar abundance. Less than 10 percent of the plants had larvae. Caterpillars were more frequent and abundant in M. pohliana, which was also present at higher densities than M. ferruginata. Low caterpillar frequency in host plants and an abundance peak during the dry season are consistent patterns for different cerrado Lepidoptera larvae. This abundance peak, however, is not coincident with higher leaf production in host species. We suggest that M. pohliana's higher local density and better leaf digestibility can account for the higher abundance of caterpillars in this species.

No cerrado, as lagartas de Lepidoptera, folívoras externas, são encontradas em baixas frequências e variam entre plantas e ao longo do ano. Este trabalho teve como objetivo analisar os efeitos das variações climáticas e das características das plantas (Miconia, Melastomataceae) na abundância das lagartas. O estudo foi feito no cerrado sensu stricto, Brasília, DF, de maio de 1998 a setembro de 1999. Mensalmente, 100 plantas de cada espécie foram vistoriadas. Todas as lagartas foram coletadas e criadas. Foram correlacionados com os resultados obtidos da abundância de lagartas, os dados climáticos e as seguintes características das plantas: densidade local, distribuição espacial, fenologia, pilosidade e conteúdo nutricional foliar. Menos de 10 por cento das plantas tinham lagartas. As lagartas foram mais frequentes e abundantes em M. pohliana que também foi a espécie de planta com maior densidade na área. A frequência baixa de lagartas em plantas do cerrado é um padrão bastante consistente, assim como o pico de abundância desses imaturos na estação seca. Entretanto, esse pico de abundância não coincide com a produção de folhas em nenhuma das espécies de plantas. A maior densidade local e digestibilidade das folhas de M. pohliana são os fatores que mais explicam a abundância de lagartas nessa espécie.

Psychoneuroendocrine effects of cognitive-behavioral stress management in a naturalistic setting--a randomized controlled trial.

It is assumed that chronic or extensive release of cortisol due to stress has deleterious effects on somatic and psychological health, making interventions aiming to reduce and/or normalize cortisol secretion to stress of interest. Cognitive-behavioral stress management (CBSM) has repeatedly been shown to effectively reduce cortisol responses to acute psychosocial stress. However, the effects of CBSM on psychoneuroendocrine responses during "real-life" stress have yet not been examined in healthy subjects. Eight weeks before all subjects took an important academic exam, 28 healthy economics students were randomly assigned to four weekly sessions of cognitive behavioral stress management (CBSM) training or a waiting control condition. Psychological and somatic symptoms were repeatedly assessed throughout the preparation period. Salivary cortisol (cortisol awakening response and short circadian cortisol profile) was repeatedly measured at baseline and on the day of the exam. In addition, cognitive appraisal was assessed on the day of the exam. Subjects in the CBSM group showed significantly lower anxiety and somatic symptom levels throughout the period prior to the exam. On the day of the exam, groups differed in their cortisol awakening stress responses, with significantly attenuated cortisol levels in controls. Short circadian cortisol levels did not differ between groups. Interestingly, groups differed in their associations between cortisol responses before the exam and cognitive stress appraisal, with dissociation in controls but not in the CBSM group. The results show that CBSM reduces psychological and somatic symptoms and influences the ability to show a cortisol response corresponding to subjectively perceived stress. In line with current psychoneuroendocrine models, the inability to mount a cortisol response corresponding to the cognitive appraisal in controls could be a result of a dysregulated HPA axis, probably as a consequence of longlasting stress.

Stimulating effect of implant loading on surrounding bone. Comparison of three numerical models and validation by in vivo data.

A number of algorithms have been proposed to model the adaptive behavior of bone under load. However, the predictions of several models have neither been compared nor have they been systematically related to in vivo data. To this end, the stress states of loaded implant-bone interfaces were analyzed before and after osseointegration using finite element (FE) techniques. In a preliminary step, an FE mesh of a cylindrical implant encased in a cancellous core surrounded by a cortical layer was constructed, and the stresses and strains that developed at the interface were determined. The implant was loaded with 100 N vertical and 30 N lateral loads. Using this structure, the peak compressive and tensile stresses were determined. Then bone remodeling predictions were assessed using three different models: von Mises equivalent strain, strain energy density and effective stress. Finally, a systematic search of the literature was conducted to relate the numerical predictions to existing in vivo data. The FE simulations led to the following conclusions: (1) calculated compressive stresses were lower than the ultimate compressive stresses of cortical and cancellous bone. (2) Calculated tensile stresses were generally superior to experimental data on the tensile strength of the bone-implant interface. (3) With one exception, the predictions of all models were homogeneously grouped on the stimulus scales. (4) The predictions of the models as to bone gain or loss were not consistent and at times contradictory. It is hypothesized that this effect is linked to a lazy zone that is too narrow. With respect to the application of the numerical models to in vivo data, peak strains and strain energy densities were consistent with in vivo data. No in vivo data were found that supported effective stress as a stimulus.

Mechanical characterization of bovine periodontal ligament.

This study is part of a research program that aims to develop a constitutive three-dimensional model of the periodontal ligament (PDL) through the identification of pertinent material parameters. As part of this program, bovine PDL was utilized to establish stress-strain responses under tensile and compressive loading conditions. Fresh bovine molars were secured, frozen and prepared to appropriate dimensional specifications. Bar-shaped specimens that comprised portions of dentine, PDL and bone were produced. Push-pull tests were conducted using a specifically constructed loading machine. Full range monotonic stress-strain diagrams were generated. The effect of a rate increase on cyclic S-E diagrams was also determined. The influence of specimen thickness was expressed in terms of modulus of elasticity, strength, uniaxial maximizer strain, and strain energy density. The overall load-response was heavily hysteretic in compression. On the tensile side, after a steep rise, the curve tended to flatten out asymptotically. Variations in rate that spanned four orders of magnitude had no effect on reciprocal load responses. The E-modulus was in the 4-8 MPa range, the strength of the PDL was 1-2 MPa, the maximizer strain was at 45-60% and the strain energy density ranged between 0.3 and 0.4 MPa.

A nonlinear elastic model of the periodontal ligament and its numerical calibration for the study of tooth mobility.

A large strain nonlinear elastic isotropic "split" law is proposed for modeling the behaviour of the periodontal ligament. This law allows for a better description of the stiffening response of this tissue and, concomitantly, for a more accurate calibration of its elastic properties. Indeed, fine finite element simulations of an upper human incisor attached to its surrounding alveolar bone by an intermediate layer of ligament were run using that "split" law for the ligament. A good correlation was established with available experimental data on such a tooth under axial loading. Values of 0.010-0.031 MPa for the initial Young's modulus and of 0.45-0.495 for Poisson's ratio were determined. A sensitivity analysis of the results with respect to material and numerical parameters of the model was also carried out. Finally, a comparison of the simulation results using this "split" law with standard ones obtained with the linear elastic law, shows a significant improvement.

Incidence of fractures and lifetime predictions of all-ceramic crown systems using censored data.

PURPOSE: To determine Kaplan-Meier survival estimates and Weibull lifetime predictions for four all-ceramic crown systems from long-term data (> 5 yrs). MATERIALS AND METHODS: Single unit crowns of Cerestore (n = 30), Dicor (n = 30), Hi-Ceram (n = 22) and In-Ceram (n = 68) were placed in 95 patients treated in a university clinic. They were cemented using glass-ionomer (GI) for Cerestore, zinc phosphate (ZP) for Dicor, and 75% ZP (n = 51), 20% GI (n = 13) and 5% resin-based cement (n = 4) for In-Ceram crowns. The follow-up times were 8 yrs for Cerestore, 7 yrs for Dicor, 6 yrs for Hi-Ceram and 5 yrs for In-Ceram. The statistical analyses were based on censored data sets. A progressively censored Weibull distribution allowing for lifetime predictions beyond the actual observation time was used as well as the Kaplan-Meier Survival Product Limit Estimate (PLE), which provides survival estimates up to the maximum time of follow-up. RESULTS: Cerestore, Dicor and Hi-Ceram demonstrated molar fractures in the first 2 yrs, whereas for In-Ceram these occurred during the third and fourth year of the study. The Kaplan-Meier Survival PLE was 69% for Cerestore at 8 yrs, 86% for Dicor at 7 yrs, 81% for Hi-Ceram at 6 yrs, 92% for In-Ceram at 5 yrs. The predicted Weibull characteristic time T0 (time at which 63% of the restorations would have failed) was 23 yrs for Cerestore, 34 yrs for Dicor, 31 yrs for Hi-Ceram, and 16 yrs for In-Ceram. However, when using data sets arbitrarily limited to the three first years of follow-up, T0 decreased significantly for Cerestore, Dicor and Hi-Ceram due to the number of early fractures. Such Weibull lifetime data illustrate the risk of predicting long-term (> 5 yrs) survival using short-term (< or = 3 yrs) data on ceramic restorations, which exhibit fracturing in the initial years.

Effect of water exposure on the fracture toughness and flexure strength of a dental glass.

OBJECTIVES: The low fusing dental glass (Duceram LFC) has been advertised as presenting a superior chemical resistance and augmented strength after 16h exposure to water or 4% acetic acid. The purpose of this study was to evaluate the effect of prolonged exposure to water on two mechanical properties (fracture toughness and flexure strength) of LFC. METHODS: Disks and bars were mirror polished and annealed prior to aging in: (1) air (control), (2) water for 24h at 80 degrees C and (3) water for 8 weeks at 80 degrees C. Fracture toughness (K(Ic)) was determined by indentation fracture (IF) and indentation strength (IS) using a 19.6N Vickers indentation load. Flexure strength values were obtained from three-point bending at 0.1mm/min. Statistical analysis was performed using the Weibull distribution, Tukey and Bartlett tests (P<0.05). RESULTS: Both techniques (IS and IF) showed a significant improvement in the K of Duceram LFC after 8 weeks in water (0.88 and 1.14MPa m(0.5)) as opposed to the 24-h values both in water and air (0.77-0.78MPa m(0.5)). However, for flexure strength the Weibull characteristic (S(0)) and the m parameter did not change significantly with water storage (S(0)=90-100MPa, Weibull m =7-8). SIGNIFICANCE: The increase in toughness of Duceram LFC after aging in water is an interesting and favorable observation for a restorative material exposed to the oral environment. Nevertheless, in comparison with other contemporary ceramics, the toughness of this LFC remains in the range of soda-lime-glass or classic feldspar porcelains.

Mechanical and structural characteristics of commercially pure grade 2 Ti welds and solder joints.

This study aimed at determining whether data previously gathered for a laser welds and IR brazings using a Au-Pd alloy were applicable to titanium joints. As to its resistance under fatigue loading, Au-Pd alloy had shown a poor response to pre-ceramic laser welding and post-ceramic brazing. The present study was designed to assess the mechanical resistance, the microstructure and the elemental diffusion of laser welded, electric arch welded and brazed joints using commercially pure titanium as substrate metal. Mechanical resistance was determined by determining the joints' ultimate tensile strength and their resistance to fatigue loading. Elemental diffusion to and from the joints was assessed using microprobe tracings. Optical micrographs of the joints were also obtained and evaluated. Under monotonic tensile stress, three groups emerged: (1) the GTAW and the native (i.e. as received) substrate, (2) the annealed substrate and the laser welds and (3) the brazed joints. Under fatigue stress, the order was: first the native and annealed substrate, second the brazings and laser welds, third the GTAW joints. No Au-filler brazing withstood the applied fatigue loading. The micrographs showed various patterns, an absence of HAZ cracking and several occurrences of Widmanstätten structures. Elemental diffusion to and from the Ti substrate was substantial in the Ti filler brazings and virtually nil in the Au-based brazings. Under fatigue stress application, the titanium-based brazings as well as the laser- and electric arc welds performed equally well if not better than a previously tested AuPd alloy. There was a definite increase in grain size with increased heat application. However, no feature of the microstructures observed or the elemental analysis could be correlated with the specimen's resistance to fatigue stress application.

Microstructures of brazings and welds using grade 2 commercially pure titanium.

PURPOSE: Microstructural analyses of commercially pure titanium (CpTi) are scarce. The present report presents the micrographs, fractographs, elemental characteristics, and hardness profiles of brazed joints and weldments using machined rods of CpTi. MATERIALS AND METHODS: CpTi rods were joined using four techniques: laser welding, electric-arc welding, electron-beam welding, and gold- and Ti-filler brazing. The specimens were then subjected to tensile and fatigue loading. After sectioning and patterning, optical micrographs of intact joints were obtained. Fractured surfaces were investigated using scanning electron microscopy (SEM). The joint's composition was determined by SEM-energy dispersive x-ray analysis. Hardness was determined at specific locations using a microindenter. RESULTS: While laser welding left the parent metal's equiaxed structure fairly intact, electric-arc welding, electron-beam welding, and brazing created a heat-affected zone in the vicinity of the joint. The extent and characteristics of the heat-affected zone depended on the amount of heat transferred to the specimens. In this respect, brazing essentially increased grain size and altered their shape. Electron-beam welding augmented this phenomenon, yielding grains that encompassed the full diameter of the joint. Electric-arc welding disrupted the granular pattern and generated highly lamellar/acicular structures. CONCLUSION: Hardness was not a good indicator of mechanical resistance, nor was the joint's structural continuity with the parent substrate. Still, acicular microstructures were characterized by a peculiar behavior in that such joints were highly resistant to tensile stresses while their fatigue strength ranged among the lowest of the joints tested.