Re-assessing the notion(s) of craft standardization through diversity statistics: A pilot study on Late Chalcolithic pottery from Arslantepe in Eastern Anatolia

This paper proposes a new range of diversity indexes applicable to ceramic petrographic and geochemical data and potentially to any archaeological data of both metric and non-metric nature in order to assess the degree of craft standardization. The case study is the Late Chalcolithic pottery from Arslantepe in eastern Anatolia, ideal to test the standardization hypothesis, i.e. the assumed correspondence between craft standardization and increased rates of production, which in turn correlate with economic specialization. The results suggest that the procurement and processing of raw materials are more sensible indicators of standardization than vessel shape variability. Higher standardization is connected with the scale of production rather than with the use of the wheel or its rotational speed. The socio-economic centralization marks a process of labor division within the operational sequence and, more generally, a shift from communal to more segregated potting practices. As a result, the variability of both technical procedures and end products increases. In contrast univocal trends towards standardization can be found in coeval contexts from northern Mesopotamia, where the incipient urbanization served to create bonds between vessel makers, favoring the transmission of models and practices regardless of the centralized power.

Methodology and model-based DSS to managing the reallocation of inventory to orders in LHP situations. Application to the ceramics sector

Lack of homogeneity in the product (LHP) is a problem when customers require homogeneous units of a single product. In such cases, the optimal allocation of inventory to orders becomes much more complex. Furthermore, in an MTS environment, an optimal initial allocation may become less than ideal over time, due to different circumstances. This problem occurs in the ceramics sector, where the final product varies in tone and calibre. This paper proposes a methodology for the reallocation of inventory to orders in LHP situation (MERIO-LHP) and a model-based decision-support system (DSS) to support the methodology, which enables an optimal reallocation of inventory to order lines to be carried out in real businesses environments in which LHP is inherent. The proposed methodology and model-based DSS were validated by applying it to a real case at a ceramics company. The analysis of the results indicates that considerable improvements can be obtained with regard to the quantity of orders fulfilled and sales turnover.

Preparation and characterisation of ceramic-based thoron sources for thoron calibration chamber

The aim of this study is to explore the correlations between the properties of the source's material and the thoron flux produced. This means a complex procedure that involves morphological characterisation (the determination of specific surface area and pore size distribution) and thoron emanation and exhalation measurements as well. In this work, the preparation of 27 thoron sources has been carried out. Three types of ceramics with different morphological properties were used as a matrix material with three different thorium contents. Spheres were formed from the dollop, and they were fired at different temperatures (200, 600 and 900°C). The phase analysis of the samples was performed by powder X-ray diffraction. The pore size distribution was determined by mercury penetration. The thoron emanation was measured using an accumulation chamber; the measured thoron emanation coefficients were from 0.34 ± 0.03 to 7.69 ± 0.13 %. Based on the results, the preparation parameters of the thoron source optimised for the calibration procedure have been given.

A unified in vitro evaluation for apatite-forming ability of bioactive glasses and their variants

The aim of this study was to propose and validate a new unified method for testing dissolution rates of bioactive glasses and their variants, and the formation of calcium phosphate layer formation on their surface, which is an indicator of bioactivity. At present, comparison in the literature is difficult as many groups use different testing protocols. An ISO standard covers the use of simulated body fluid on standard shape materials but it does not take into account that bioactive glasses can have very different specific surface areas, as for glass powders. Validation of the proposed modified test was through round robin testing and comparison to the ISO standard where appropriate. The proposed test uses fixed mass per solution volume ratio and agitated solution. The round robin study showed differences in hydroxyapatite nucleation on glasses of different composition and between glasses of the same composition but different particle size. The results were reproducible between research facilities. Researchers should use this method when testing new glasses, or their variants, to enable comparison between the literature in the future.

Effect of production variables on microbiological removal in locally-produced ceramic filters for household water treatment

Diarrhoeal diseases cause an estimated 1.87 million child deaths per year. Point-of-use filtration using locally made ceramic filters improves microbiological quality of stored drinking water and prevents diarrhoeal disease. Scaling-up ceramic filtration is inhibited by lack of universal quality control standards. We investigated filter production variables to determine their affect on microbiological removal during 5-6 weeks of simulated normal use. Decreases in the clay:sawdust ratio and changes in the burnable decreased effectiveness of the filter. Method of silver application and shape of filter did not impact filter effectiveness. A maximum flow rate of 1.7 l(-hr) was established as a potential quality control measure for one particular filter to ensure 99% (2- log(10)) removal of total coliforms. Further research is indicated to determine additional production variables associated with filter effectiveness and develop standardized filter production procedures prior to scaling-up.

Confocal laser scanning microscopy using dialkylcarbocyanine dyes for cell tracing in hard and soft biomaterials

The aim of this work was to study, in vitro, cell colonization of two biomaterials currently used for bone and cartilage repair, this step being important to understand the function of engineered tissues. Current methods that use histological approaches are not always suited to tissue-engineering analysis. We, therefore, set up a protocol to assess cell distribution, utilizing noninvasive confocal microscopy and fluorescent labels with a far red emission wavelength to optimize scaffold transparency and minimize light scattering. Hard (ceramic substitute) and soft (collagen sponge) biomaterials were seeded respectively, on one side of the scaffold, with human fibroblasts and bovine chondrocytes labelled with carbocyanine dyes (DiD and DiR). The mean penetration depth for DiR labelled fibroblasts and chondrocytes in the two scaffolds, around 270 m, was greater than for DiD (136-218 microm) labelled cells. These depths were independent of cell origin but were influenced by the nature of the scaffolds. Collagen sponge is transparent in contrast to ceramic substitutes where measurements could only be made in opened macropores. Besides the limits of the equipment, the limits of the supports were diffusion for collagen sponges and transmission for ceramic substitutes. Confocal microscopy techniques could thus be used to address the question of cell colonization of porous biomaterials in a noninvasive manner.

Anterior cervical fusion with polyetheretherketone (PEEK) cages in the treatment of degenerative disc disease. Preliminary observations in 36 consecutive cases with a minimum 12-month follow-up

STUDY DESIGN

Retrospective analysis of 36 cases of degenerative disc disease treated by interbody fusion with polyetheretherketone (PEEK) cages.

OBJECTIVE

To determine the safety and efficiency of PEEK cages for anterior cervical fusion (ACF).

SUMMARY OF BACKGROUND DATA

ACF with autologous bone has been reported since over 50 years ago. The recent development of cages housing materials inducing osteogenesis simplifies the technique of interbody fusion. The main purposes of bone substitutes for ACF are immediate biomechanical support, osteo-integration of the graft, and elimination of local side effects at the donor site. This report shows our results using PEEK cages.

MATERIALS AND METHODS

During an 18-month period, 36 consecutive patients had cervical fusions at 43 levels between C3 and C7. All operations involved one or two disc spaces for degenerative disc disease. We implanted all disc spaces with PEEK cages (Stryker Corporation, Kalamazoo, MI) containing granulated coralline hydroxylapatite (Pro-Osteon 200, Interpore Cross International, Irvine, CA) or deantigenated pig bone in a gel solution (Gen-Os, Tecnoss, Torino, Italy).

RESULTS

About 97% of patients had a good to excellent outcome; the result in one myelopathic patient was fair. The cervical fusion rate was 16.7% at 3 months, 61.1% at 6 months, and 100% at one year.

CONCLUSIONS

PEEK cages appear to be safe and efficient for ACF. In order to confirm our preliminary impressions studies on larger series with long term follow-up are warranted.

[Clinical evaluation of a quality criteria system for ceramic inlay restorations]

The aim of this study was to test the utilization of a generally accepted quality criteria system (United States Public Health Services Modified Quality Criteria) in the authors' practice, in the cases of all ceramic inlays and onlays. 41 ceramic inlays/onlays--29 pressed and 12 laminated--were made for 28 patients. Restorations were controlled after 2 years of cementation. According to the USPHS criteria system the following characteristics were controlled: anatomic contour, marginal integrity, marginal discoloration, color match, secondary caries, and surface roughness. In addition, postoperative sensitivity, patient's satisfaction and tooth vitality were examined as well. The USPHS quality criteria system together with the complementary data proved to be an objective examination method that was easily applicable to our clinical practice. On the basis of these studies the utilization of this system together with patient's satisfaction, tooth vitality and sensitivity records appeared a good basis for a regular quality control system of ceramic inlays and onlays.

[Effect of prism length on the notchless triangular prism fracture toughness test]

PURPOSE

The purpose of this study was to clarify the effect of holding condition with different prism length on the Notchless Triangular Prism (NTP) fracture toughness test and to define the prism length as a measuring condition.

METHODS

Two kinds of NTP prism (ceramic and composite resin) were fabricated by CAD/CAM and each prism was adjusted to one of three lengths (8.0 mm, 12.0 mm, 16.0 mm). NTP was conducted for prism specimens made under six different conditions. The displacement of prism specimen holder gap (Delta d) and maximum fracture load (Pmax) were recorded and then a fractogram of each prism was inspected by SEM.

RESULTS

Inclined stable fracture propagation was observed on the fractogram of the 8.0-mm prism. Both Delta d and Pmax of the 8.0-mm prism were significantly higher than those of the other lengths.

CONCLUSIONS

A prism length of at least 12.0 mm is needed for the NTP because the 8.0-mm prism did not have a sufficient holding condition. The fracture toughness of the ceramic (3.68+/-0.09 MPa.m(1/2)) was significantly higher than that of the composite resin (2.38+/-0.20 MPa.m(1/2)).

Dissolution control and cellular responses of calcium phosphate coatings on zirconia porous scaffold

Different types of calcium phosphates [hydroxyapatite (HA), fluorapatite (FA), tricalcium phosphate (TCP), and their composites (HA + FA, HA + TCP)] were coated on a zirconia (ZrO(2)) porous scaffold using a powder slurry method. The ZrO(2) porous scaffold was intended for a load-bearing implant, and the apatite layers were coated to improve osteoconductivity. The insertion of an FA intermediate layer between the coating layer and ZrO(2) scaffold effectively suppressed the reaction between the calcium phosphate and ZrO(2) and maintained the coating layer at the initial powder composition. The obtained coating layer, of a thickness of approximately 30 microm, was relatively microporous and firmly adherent to the ZrO(2) scaffold. Dissolution tests in physiological solution showed typical differences depending on the coating layers, with the dissolution rate increasing in the order TCP > HA + TCP > HA > HA + FA > FA. This result suggests the functional coating of the calcium phosphates in view of tailoring the solubility. Osteoblast-like cells, MG63 and HOS, responded similarly in terms of cell growth, morphology, and proliferation rate regardless of the coating types, indicating favorable and comparable cell viability. However, the alkaline phosphatase (ALP) activity of the cells on the pure HA and HA composite coatings (HA + FA and HA + TCP) expressed at higher levels compared to those on pure FA and pure TCP coatings for both MG63 and HOS cells, suggesting a selective cell activity depending on the coating types. All the calcium phosphate-coated-ZrO(2) scaffolds showed higher ALP levels compared to pure ZrO(2) scaffold.

Effect of additives on the microstructure and thermal properties of a mica-based glass-ceramic

Previous work has shown that lithium mica glass-ceramics were excellent potential candidates as dental ceramics. The purpose of this study was to evaluate the effect of various additives on the microstructure and thermal properties of a mica glass-ceramic in the system Li(2)O-K(2)O-SiO(2)-MgO-F. Five glass compositions were prepared: a base composition and four compositions with various additives. The compositions were melted at 1400 C for 2 h and cast into 50 x 8 mm ingots. Differential thermal analyses were performed on the glasses up to 1400 C. Bars (4 x 8 x 25 mm) were cut from the ingots and heat treated at various temperatures. The crystalline phases were analyzed by x-ray diffraction. The microstructure was investigated by scanning electron microscopy. The percent crystallinity, crystal density, and average particle size were calculated from stereology measurements. X-ray diffraction revealed that the major crystalline phase was taeniolite for all glass-ceramics. Differential thermal analyses showed that the crystallization exotherm occurred in the temperature range 600--700 C. The addition of calcium fluoride was most efficient in promoting the growth of mica crystals. Larger mica plate diameter could be beneficial to the crack-propagation resistance of the glass-ceramic. The addition of aluminum phosphate promoted nucleation rather than crystal growth and led to a significantly lower glass transition temperature and crystallization exotherm temperature.

Characterization of damage modes in dental ceramic bilayer structures

Results of contact tests using spherical indenters on flat ceramic coating layers bonded to compliant substrates are reported for selected dental ceramics. Critical loads to produce various damage modes, cone cracking, and quasiplasticity at the top surfaces and radial cracking at the lower (inner) surfaces are measured as a function of ceramic-layer thickness. It is proposed that these damage modes, especially radial cracking, are directly relevant to the failure of all-ceramic dental crowns. The critical load data are analyzed with the use of explicit fracture-mechanics relations, expressible in terms of routinely measurable material parameters (elastic modulus, strength, toughness, hardness) and essential geometrical variables (layer thickness, contact radius). The utility of such analyses in the design of ceramic/substrate bilayer systems for optimal resistance to lifetime-threatening damage is discussed.

Effect of process parameters on the characteristics of porous calcium phosphate ceramics for bone tissue scaffolds

Porous hydroxyapatite (HA) has already been widely used as a bone substitute due to its similarity with the mineral part of the bone. In this work, cylindrical tablets with micro and macro porosity were produced from stoichiometric and deficient hydroxyapatites by using naphthalene as porosifier agent. The influence of the processing parameters such as Ca/P ratio of start material, calcination temperature, and naphthalene content on the characteristics of porous calcium phosphate tablets was evaluated. Three mineral phases-HA, alpha-TCP (alpha tri-calcium phosphate), and beta-TCP (beta tricalcium phos-phate)-with variable contents were identified by x-ray diffraction (XRD) and Fourier-transformed infrared spectroscopy (FT-IR). Image analysis and density measurements were used to characterize sample porosity. As expected, the total porosity of the calcinated material is not dependent on the stoichiometry of the precursor hydroxyapatite. For calcium-deficient hydroxyapatite, the increase in naphthalene content contributes to stabilize alpha-TCP phase, altering the relative phases content.

[Quality assurance of powders for bioceramic applications with image analysis]

Bone substitute materials are very demanding with respect to their quality, in particular, a high toughness and durability are required. In case of producing the composites by sintering of mechanically generated powder mixtures, a high efficiency of mixture is demanded, too. The characterisation of such particle systems is difficult. An effective method is the image analysis supported by statistical evaluation of both the size and the shape distributions of particles and agglomerates. As it is proved by first results, powder mixtures of hydroxyapatite can be described by the geometry of voids in the agglomerate structure using the shape factor weighted by area of the respective image object. As a measure of the efficiency of mixture, the degree of reproducibility was introduced.

Elimination of low-quality ceramic posts by proof testing

OBJECTIVES

Prosthetic posts made of zirconia ceramics are beneficial because of their esthetic advantages. The mechanical reliability of ceramic posts is limited because of the strength level and the large scatter in strength of ceramic materials. The hypothesis of this study is that the failure of ceramic posts in vivo, which occur on low-quality posts because of critical microscopic defects can be excluded using the so-called proof test technology.

METHODS

The theory of the proof test technology is explained in detail in this study. In the experimental part 22 ceramic posts were tested at different proof load levels using a stepwise rotating four-point bending proof test device.

RESULTS

The experimental failures deviated from the theoretical failure probabilities by 0.24-12.69%. The deviation would be further reduced in a serial proof test using batches with a greater quantity of posts. The test eliminated those posts, which contained microscopic defects above a critical size of clinical relevance.

SIGNIFICANCE

The technology can help to reduce clinical failures of non-vital abutment teeth with ceramic posts, which are caused by critical microscopic defects of the ceramic material as a result of the industrial manufacturing process.

Rapid reduction of Staphylococcus aureus populations on stainless steel surfaces by zeolite ceramic coatings containing silver and zinc ions

This study demonstrates the anti-Staphylococcus aureus properties of stainless steel surfaces coated with zeolite containing 2.5% silver and 14% zinc ions. Stainless steel panels with and without the heavy-metal-containing coatings were inoculated with S. aureus and incubated at room temperature. Survival of S. aureus was significantly reduced by the silver/zinc coatings within 1 h. Many hospital surfaces could be constructed of stainless steel with silver/zinc zeolite coatings. Such measures may reduce rates of hospital-acquired S. aureus infection.

Computer-assisted generation of all-ceramic crowns and fixed partial dentures

The successful application of the concept of computer-assisted manufacturing in restorative dentistry requires that computer-assisted design (CAD) and computer-assisted machining (CAM) not only meet but actually exceed currently accepted standards for the material and clinical quality of dental restorations. In addition, the continued development of systems for polyvalent processing of disparate materials and objects must be assured. With these critical requirements in mind, the Precident system is a clinically proven and competitive system. The resolving power of the CCD chip is much improved compared to conventional cameras or charge-coupled devices. The scanner is able to scan entire casts in a fully automated process. In principle, this facilitates the production of frameworks for fixed prosthetic devices (FPD) of any size. It is also possible to create at least partial frameworks for removable prosthetic devices (RPD). A factor of great clinical and economic importance is the polyvalence of the process in materials processing: the numeric control (NC) machine can be programmed for metal alloys and ceramic materials as well as fiber-reinforced resins. At Aeskulap Klinik, the Precident System is routinely used for producing all single crowns and FPDs with up to four units. CAD/CAM all-ceramic crowns and FPDs currently cost about the same as metallo-ceramic or conventional all-ceramic restorations.

The clinical performance of ceramic inlays: a review

The availability of improved ceramic materials, bonding techniques, new technology and issues of amalgam safety have led to a revival of interest in ceramic inlays in dentistry over the past ten years. Clinical studies have been carried out during this time using various evaluation techniques to assess the clinical performance of these restorations. In this paper, recent clinical studies are examined and a review of the current state of knowledge regarding the clinical performance and survival statistics of ceramic inlays is presented. The major problems associated with ceramic inlay therapy appear to be fracture, hypersensitivity, degree of fit, maintenance of marginal integrity, microleakage, bond failures and cement wear. Other areas which also affect the clinical performance of ceramic inlays are ceramic wear, opposing tooth wear, plaque accumulation, gingivitis, secondary caries, colour stability, anatomic form and radiopacity. Recommendations based on the findings of clinical studies are also presented and whilst no specific material or technique has been shown to be clearly superior, certain principles which predispose to success can be identified. When compared with other forms of aesthetic intracoronal restorations, ceramic inlays perform well. However, their high cost and extreme technique sensitivity would appear to restrict their use to certain limited clinical situations.

[Study on relationship of different thickness and opaquing capacity of various opaques]

OBJECTIVE

To evaluate the relation between different opaque thickness and color difference.

METHODS

Model made of the thin plastic paper was used to control the ceramic thickness. The data of chromaticity was measured by TC-PIIG auto color difference meter and its results were processed by computer.

RESULTS

There are two thickness values which can be considered as ideal range of opaque thickness for color opaquing: one is the values of ceramic thickness which is based on the color difference values of the infinite chromaticity thickness (ICT) and the other is the values of ceramic thickness which is depended on the color difference values which is 1.5 compared with ICT. The ideal range for VITA is (0.207-0.152) mm, SHOFO is (0.190-0.160) mm, CARAT is (0.140-0.074) mm and EXCELCO is (0.169-0.144) mm.

CONCLUSION

There is a relationship of non linear direct ratio between opaque thickness and its shadow capacity. However, no more increase of color difference values in respect to the thickness was found when the ceramic thickness reach a certain value. Different ceramic porcelain needs different ideal range of thickness.

[Two years clinical observation of a kind of castable ceramic--IPS Empress]

We used this material in clinic since 1995.

OBJECTIVE

Discussion on the prosthetic effects of the above-mentioned material to spreat it clinically.

METHODS

Through half to two years clinical observations to evaluate the effect of IPS Empress crowns in anterior teeth and inlays in posteriors.

RESULTS

and

CONCLUSION

Prosthesis made of this kind of material IPS Empress is one kind of excellent all-ceramic prosthetic material. IPS Empress also could be used in post crowns and the clinical effect was satisfactory.

Impact resistance of ceramic brackets according to ophthalmic lenses standards

The overall resistance to accidental blows of the many ceramic brackets that are sold today has not been explored. Facing a similar diversity, the eyeglasses industry has chosen to standardize the testing of lenses by subjecting them to the drop of a steel ball. By slightly modifying this test, 10 brands of ceramic brackets were examined. In most cases, the findings coincided with those found by other authors when duplicating debonding. Thus, polycrystalline ceramics with bulkier structures and glazed surfaces were found to be more resistant to impact than the monocrystalline brackets, the loftier real "twins," and the less dense attachments. Protruding tie wings and bases were liabilities, and domed configurations seemed to deflect the blows. Bulkier "single" designs alone did not offer a guarantee of impact resistance when not accompanied by an appropriate microstructure and a smooth surface. The ceramic brackets most resistant to impact were found to be 20/20 by American Orthodontics and Fascination by Dentaurum. Medium resistance was displayed by Lumina by Ormco, Allure III and Allure by GAC, Transcend 2000 and Transcend by Unitek/3M; the last was not as good as the other four. The least resistant were Illusion by Ortho-Organizers, Intrigue by Lancer Orthodontics, and Starfire TMB by "A"-Co. Probably because of its real twin design, the last bracket lends itself to the highest probability for accidental breakage. Although resistance to impact and accidental debonding is desirable from the point of view of treatment, the advantage should be weighted against the chance of enamel fracture. Indeed a weak bracket attached with a soft adhesive may be preferable when the chance of an increased exposure to accidental blows is probable. In such cases, the ceramic may take the brunt of the force, instead of the tooth.

Colour perception of laboratory-fired samples of body-coloured ceramic

The objective of this investigation is to test by common perception, the colour fidelity of laboratory-fired samples of ceramic. Thirty-two ceramic discs were constructed in a thickness similar to that used for ceramic veneers using eight shades from each of four different manufacturers. A group of 20 'adept' observers colour matched the samples in strictly controlled viewing conditions using a Vita Lumin (Vita Zahnfabrik) shade guide. Samples were categorised as 'positive matches'(matching the expected shade), 'agreed shades' (matching an unexpected shade), or as 'unidentified shades' (no match). The Vita Lumin (Vita Zahnfabrik) colour 'value' index was used as a reference to categorise colour 'value' differences between observed and expected shade. Colour 'value' selection was divided into three groups: (1) matching colour 'value', (2) shades of higher colour 'value' than expected or (3) shades of lower colour 'value' than expected. Only six of the 32 samples examined were perceived to be 'positive matches' with the recommended shade guide. Fourteen 'agreed shades' were found while the remaining 12 shades were regarded as 'unidentified shades'. The vast majority of observations disagreed with the manufacturers' designated shade. A significant trend was found favouring higher 'value' (lighter) shades than those specified by the manufactures. Significant differences in the pattern of shade matches and disagreements between brands were also found. Alternative shade determination systems and/or ceramic colour modifications are required if colour fidelity between the shade guide and the materials tested is to be improved.

[Standardization of zirconia ceramics for hip endoprostheses]

Bioceramics are used in a wide range of different clinical applications, the most important being femoral heads in total hip replacement. Because of their very attractive mechanical properties, zirconia ceramics (ZrO2) have recently been used as implant material. At the present time, two medical-grade types of zirconia are available: Mg-PSZ and Y-TZP. For the Y-TZP, an international standard (ISO) was issued. The standard is discussed, and the properties that are of importance in the field of orthopaedics are identified.

Injection moulded hydroxyapatite ceramics

The injection moulding of hydroxyapatite (HA) and properties (relative density, shrinkage, microstructure, thermal strength and phase composition) of HA ceramics sintered at temperatures of 1373-1773 K were studied. Particles of oval shape and size of 0.5 microns were most suitable for injection moulding. Polymer/HA mixture contained 63 vol% of the HA powder. Maximum relative density (98.7%) and shrinkage (16%) of HA ceramics were obtained at a sintering temperature of 1523 K. Maximum flexural strength (60 MPa) of HA ceramics occurred at a sintering temperature of 1473 K. The strength of these ceramics decreased at sintering temperatures higher than 1473 K. Loss in strength was owing to the grain growth and decomposition of HA ceramics. The relationship between grain size and strength is described by the equation: sigma = 53.3d1/2. The calculated activation energy of grain growth obtained was 215kJ mol-1 K-1. The decomposition of HA to alpha-tricalcium phosphate was important at temperatures greater than 1573 K.

Fatigue and fracture of pyrolytic carbon: a damage- tolerant approach to structural integrity and life prediction in "ceramic" heart valve prostheses

BACKGROUND AND AIMS OF THE STUDY

The fracture and fatigue properties of Si-alloyed LTI pyrolytic carbon and pyrolytic carbon-coated graphite are described as a framework for establishing damage-tolerant analyses for maintaining structural integrity and for predicting the lifetimes of mechanical heart valve prostheses fabricated from these materials.

METHODS

The analyses are based on fracture-mechanics concepts and provide conservative (worst-case) estimates of the time, or number of loading cycles, before the valve will fail, or more precisely for pre-existing defects in valve components to grow subcritically to critical size under elevated physiologic loading and environmental conditions.

RESULTS

For structural life in excess of patient life-times, a minimum required detectable defect size is computed which must be detected by quality-control procedures prior to the device entering service; this defect size is typically of the order of tens of microns for such "ceramic" valves, compared to sizes in the hundreds of microns for corresponding metal valves.

CONCLUSIONS

It is concluded that in light of the brittle nature of pyrolytic carbon and the unacceptable cost of mechanical valve failures, the use of such analyses should be regarded as essential in order to provide maximum assurance of patient safety.

Staying calm under pressure: the secrets of bioceramics

For very good reasons, ceramics as a class of material have limited uses in medical devices. They do, however, have some interesting, relevant, and unique properties. This article explains this paradox in terms of the structural characteristics of those materials.

Tissue engineering scaffolds using superstructures

Here, scaffolds as cell and tissue carriers are approached from an engineering point of view, emphasizing material superstructuring in the design of supports. Superstructure engineering provides optimal spatial and nutritional conditions for cell maintenance by the arrangement of structural elements (e.g. pores or fibres) so as to vary the order of cell to cell contact. This approach is illustrated in the design of several scaffolds: knitted fabrics as three-dimensional superstructures for optimized osteosynthesis implants, a new injectable open porous implant system, an angiopolar non-degradable ceramic cell carrier, and an injectable or microsurgically implantable entangled carrier system. The implications for tissue engineering are discussed.

Characterization of the resistance of pyrolytic carbon to abrasive wear

Si-alloyed pyrolitic carbon (PyC) is currently employed in many biomedical devices, due to its fairly good biological compatibility and non biodegradeability. For prosthetic heart valve applications, required to operate safely for many years, the resistance to abrasive wear is one of the limiting factors which must be accurately evaluated. The present study reports on abrasive wear testing of Ti/PyC and PyC/PyC sliding couples. For both couples it was found that the wear behaviour can be shifted from a low wear regime, characterised by very small wear rates and reduced scatter, to a high wear regime, characterised by high wear rates and high scatter, due to the presence of particle contamination coming from the environment and/or from the specimen polishing process. Actual biomedical devices, particularly heart valves, should not experience the high wear regime, due to the absence of any hard particle contamination source. The wear observed in these items is in fact minimal and may depend on mechanisms other than abrasive wear. In these conditions the experimental evaluation of the wear behaviour should definetely be performed by tests on actual devices.

Blood-contacting biomaterials: bioengineering viewpoints

The investigation of blood-contacting biomaterials is an important challenge and is relevant for an improvement in the clinical application of biomaterials. With the purpose of improved clinical treatment, bioengineering viewpoints of blood-contacting biomaterials cover the material options and selection, the utilization of materials, the development of materials with better properties, and processing characteristics, and the design of relevant evaluation procedures. The bioengineering objective remains that of achieving an enhanced understanding of the relationship between a biomaterial and the biological response.

Development of a ceramic conduit valve prosthesis for corrective cardiovascular surgery

This paper reports some of the ways in which biomaterial considerations have influenced the design, development and construction methods for a prototype conduit valve prosthesis in which the valve body is made from alumina. This material is used principally for its ability to grow and support a thin (< 0.1 mm) tissue covering on the surfaces in contact with the blood. This non-vascular covering does not interfere with the operation of the valve, but is thick enough to camouflage the underlying surface from any further interaction with the blood. This is important for any conduit valve because of the large internal surface area, but would be especially beneficial for children if it could obviate the need for chronic anticoagulation.

Fracture toughness and flexural strength of dental ceramics for titanium

Three brands of dental ceramics for veneering to titanium: TitanBond (O'Hara), Ti-Ceram (Ducera) and Titankeramik (Vita) were tested to compare their fracture properties in wet and in dry conditions. Eight polished and precracked specimens of each material were stored in water at 37 degrees C for 28 d and then preloaded in a four-point bending jig with a constant load of 50 N for 24 h under water. Five of the specimens were fractured by a four-point bending test also under water at 37 degrees C. Crack depths were measured in three different positions in each of the remaining three specimens. Fracture load and crack depths were used to calculate the fracture toughness. Another ten polished specimens were used to measure the flexural strength with a four-point bending test after storage in water at 37 degrees C for 28 d. Equal procedures and numbers of specimens were used to measure fracture toughness and flexural strength without preloading and storage in water.

Elastic and fracture properties of dental direct filling materials

Five dental direct filling materials were tested in tension and compression in order to define their stress-strain behaviour for both types of applied stress. In addition, fracture toughness was determined from three-point bending tests. Linear and non-linear stress-strain behaviour was observed, and the response was specific for each material and also to the type of applied stress. Fracture resistance was also found to be material specific, which was related to differences in composition.

Cemented ceramic acetabular component: a 7-year review

A 7-year review of 30 cases of cemented ceramic acetabular components has shown that all components rapidly become surrounded by a lucent zone between the cement and bone that appears to be nonprogressive. Although these prostheses have functioned well, some separation inferiorly between the ceramic cup and the cement suggests that "creep" of the cup within the cement occurs and that the cup should be modified to provide greater "pull out" resistance from the cement. This study has failed to substantiate some of the theoretical advantages of ceramic cups.

An investigation of Bioglass powders: quality assurance test procedure and test criteria

Bioglass, in bulk form, has been used to bond to the body's hard and soft tissues in many surgical and dental applications over the past 18 years. There is also a large potential use of Bioglass, in powder or paste from, to fill irregular-shaped bony defects caused by local or systemic disease, congenital malformations, or trauma in the fields of otolaryngology and dental sciences. A quality assurance test procedure to analyze powdered Bioglass to guarantee that the bioactivity of the glass has been maintained during manufacturing was developed. Herein states the quality assurance test procedure, test variables, and test criteria to assure the bioactivity of Bioglass powders made from known bioactive bulk Bioglass samples. Also described herein is the path taken to develop the test procedure and test criteria and experiments performed to study the test variables.

Ceramics: their place in dentistry

A transfer molded ceramic coping material, Cerestore, and a castable ceramic, Dicor, are commercially available for fabrication of all-ceramic crowns. The manufacturers indicate their use should be in single unit anterior or posterior crowns. Tooth preparations are similar and should have rounded lines angles to avoid sharp points which may cause stress concentration. The amounts of tooth reduction are also similar and range from 1.0 to 2.0 mm depending on the location of surfaces. There are variations in fabricating procedures but both involve heat treatment and special equipment. Cerestore requires eventual veneer build-up and shading. Dicor requires surface shading. Both are evaluated and classified by the Council on Dental Materials, Instruments and Equipment of the American Dental Association. At least three other ceramic systems are being developed but are not yet commercially available.

Scintigraphic studies to evaluate stability of ceramics (hydroxyapatite) in bone replacement

In this study, the suitability of a radionuclide bone imaging technique was examined in cases of hydroxyapatite implants for segmental replacements of long bones. The radionuclide bone imaging technique, using [99mTc]MDP was applied to estimate osseous changes at the sites of the hydroxyapatite implants up to 2 yr after their implantation in an animal experimental model. The results were correlated with histological and radiographical findings at the same time. The radionuclide bone imaging with technetium proved to be a useful method to estimate the intensity of osseous changes after bone replacement by a hydroxyapatite implant. It proved to be more sensitive than radiography. The differences in elasticity of the implanted material and adjacent bone may cause an increase of radionuclide uptake at the site of the implant 2 yr after implantation. These osseous changes cannot be detected by standard histological and radiographical methods but could be detected by radionuclide bone imaging. It is submitted that the radionuclide bone imaging is a noninvasive, sensitive, and useful method for the estimation of osseous changes in sites of long term bone implants.

Further cases of lead poisoning from wine

Lead intoxication has been reported to occur as a consequence of nonoccupational exposure, the source being mostly the leaching of lead from fluid containers in domestic use. Three such cases are described, for which the cause has been identified to be in the lining of the vat used to contain home-made wine. All cases are members of the same family.

[Review of implantation materials]

The use of nonmetalic, ceramic materials has led to encouraging developments. Some metal implants have proved to be more reliable in general practice in respect to the mechanics and statics; part of the developmental goal however should include compound materials. Metal implants, tolerated by the organism under favorable conditions, were not accepted as well as the ceramic material. Recently, the long-term prognosis therefore has been viewed with reservation. Even though the tensile values were favorable, the mechanical properties were good, and the corrosion rate in terms of adequate tissue tolerance was generally satisfactorily low for metal, the organism still responded to metal as a foreign body.

Effect of pulverized implantation materials (plastic and glass ceramic) on growth and metabolism of mammalian cell cultures

The effect of pulverized plastic and glass-ceramic materials (methylmetacrylate, MNA), which are used as implantation materials in surgical medicine, on cell growth, DNA synthesis rate (adjudged by incorporation of 3H-thymidine into DNA), glucose consumption and lactate production (glycolytic rate) was studied in asynchronous monolayer cultures of rather fast proliferating Ehrlich ascites tumor cells and rather slowly proliferating diploid human fibroblasts. Exposure of Ehrlich ascites cells to high concentrations (2 mg/ml; 10 ml medium per culture) of ceramic or plastic material resulted in a gradual inhibition of cell growth and DNA synthesis rate. Protein synthesis, as measured by the incorporation of 3H-leucine, was somewhat less affected than DNA synthesis. Also, the glycolytic rate of Ehrlich ascites cells was slightly but significantly decreased in the presence of 2 mg/ml ceramics or MMA. Exposure of Ehrlich ascites cells to 0.2 or 0.02 mg/ml over a period of 46 h revealed none or only slight inhibitory effects on growth, DNA synthesis or glycolytic rate. On the other side, growth, DNA synthesis and glycolytic rates of human fibroblasts were nearly not affected by the presence of the same concentrations (up to 2 mg/ml, incubation period: 92 h) of pulverized ceramic or plastic material (MMA). It is suggested that this differential cellular sensitivity might be related to differences in the binding (to the cell surface) or uptake of these substances and possibly to differential intracellular lysosomal activation.

[The properties required of bioceramics for artificial joints (author's transl)]

Tests of hip joint simulator proove the outstanding friction--and wear-behaviour of high density high purity allumina ceramics, being well known for many years from the field of engineering. According to a comparison of the characteristical physical properties of these special oxide ceramics with the requirements of materials for artificial joints, it is to be expected that wear components being made of high density alumina ceramics will show a very good behaviour in long time runs. This paper will also discuss the problems of body compatability breifly, which have been solved so far already.