The implant density does not change the correction rate of the main and the accompanying curves: A comparison between consecutive and intermittent pedicle screw constructs

OBJECTIVE

The aim of this study was to evaluate the clinical outcomes and the coronal correction rate of the main and accompanying curves of adolescent idiopathic scoliosis (AIS) corrected with pedicle screws inserted consecutively or intermittently.

METHODS

The prospectively collected data of 60 patients (8 men and 52 women; mean age: 14.6±2.5 years) who underwent corrective surgery for AIS between January 2010 and December 2015 were reviewed retrospectively. Two groups were constituted according to the pedicle screw construct type: consecutive pedicle screw construct (CPSC) and intermittent pedicle screw construct (IPSC) groups. The preoperative, early postoperative, and 24-month follow-up radiographs and the Scoliosis Research Society-22 (SRS-22) scores were reevaluated. The Cobb angle of the main and accompanying curves, the correction rate, and the flexibility of the curves were calculated.

RESULTS

The mean preoperative Cobb angles were 57.03° and 57.46°, the mean postoperative Cobb angles were 14.93° and 14.4°, and the mean correction rates were 76.22% and 75.31% in IPSC and CPSC groups, respectively (p>0.05). The preoperative and postoperative accompanying curve magnitudes and correction rates were similar (p>0.05). These radiographic outcomes were also consistent with the SRS-22 scores.

CONCLUSION

Both the pedicle screw constructs had satisfactory outcomes following the surgery, which were confirmed by both the SRS-22 scores and radiographs taken perioperatively and at follow-ups. The IPSC and CPSC groups did not demonstrate a significant change in the correction rate of the main and minor or major accompanying structural and nonstructural curves, and also in the SRS-22 scores.

LEVEL OF EVIDENCE

Level III, Retrospective comparative study.

A bioceramic scaffold composed of strontium-doped three-dimensional hydroxyapatite whiskers for enhanced bone regeneration in osteoporotic defects

Reconstruction of osteoporotic bone defects is a clinical problem that continues to inspire the design of new materials. Methods: In this work, bioceramics composed of strontium (Sr)-doped hydroxyapatite (HA) whiskers or pure HA whiskers were successfully fabricated by hydrothermal treatment and respectively named SrWCP and WCP. Both bioceramics had similar three-dimensional (3D) porous structures and mechanical strengths, but the SrWCP bioceramic was capable of releasing Sr under physiological conditions. In an osteoporotic rat metaphyseal femoral bone defect model, both bioceramic scaffolds were implanted, and another group that received WCP plus strontium ranelate drug administration (Sr-Ran+WCP) was studied for comparison. Results: At week 1 post-implantation, osteogenesis coupled blood vessels were found to be more common in the SrWCP and Sr-Ran+WCP groups, with substantial vascular-like structures. After 12 weeks of implantation, comparable to the Sr-Ran+WCP group, the SrWCP group showed induction of more new bone formation within the defect as well as at the implant-bone gap region than that of the WCP group. Both the SrWCP and Sr-Ran+WCP groups yielded a beneficial effect on the surrounding trabecular bone microstructure to resist osteoporosis-induced progressive bone loss. While an abnormally high blood Sr ion concentration was found in the Sr-Ran+WCP group, SrWCP showed little adverse effect. Conclusion: Our results collectively suggest that the SrWCP bioceramic can be a safe bone substitute for the treatment of osteoporotic bone defects, as it promotes local bone regeneration and implant osseointegration to a level that strontium ranelate can achieve.

Does 6 Hours of Contact With Alginate Impression Material Affect Dental Cast Properties?

Alginate impression (irreversible hydrocolloid) material is commonly used in dental practice because it is easy to mix, low in cost, and well tolerated by patients. The material is not dimensionally stable, however; thus, it is necessary to pour the impression immediately after the molding is accomplished, or within 60 minutes if the impression is kept in 100% humidity. Excessive contact of the alginate impression with the cast model over time may affect the model's properties. In this study, the authors tested the effect of contact time between an alginate impression and type III dental stone on cast model properties. Sixty-seven cast models were obtained from a stainless steel cylinder by using irreversible hydrocolloid impression material and type III dental stone. Thirty-seven cast models were separated from the impression after 1 hour (control group) and 30 cast models were separated after 6 hours (study group). The samples were evaluated under light microscope for surface details and measured by digital caliper for dimensional stability. An indentation on the cast was made and the depth of the indentation was then measured with a digital caliper to measure hardness. The dimensional stability of the cast models was not affected when contact time was increased from 1 hour to 6 hours (P = .507). Surface details did not deteriorate when contact time was increased, as all of the samples could reproduce all details after the 1-hour and 6-hour interval periods. However, hardness was greater after 1 hour of contact time (P = .001) than after 6 hours of contact time. In conclusion, contact between alginate impression material and type III dental stone up to 6 hours did not affect the dimensional stability and richness of the surface; hardness, though, was significantly affected.

Microtensile bond strength test bias caused by variations in bonded areas

PURPOSE

While it has been shown that no method produces specimens with exactly the same cross-sectional bonded area (BA), BA variations within and between studies are a well-known covariate in microtensile test results. However, no method has yet been described to accurately account for its influence. A procedure is presented that allows controlling for variations of BA effects on results. Further, a proposal for reporting is presented which enables results of different studies to be compared.

MATERIALS AND METHODS

Partially using the results of the report in which the microtensile test was originally described, 144 both general (caused by differences in BA) and specific (due to a material's performance differences and intrinsic biological variability of specimens) variabilities were separated through linear regression of microtensile (MPa) to BA (mm2) pooled results. Comparing the specific variability of specimens - the residuals to the regression line - of groups allowed assessing differences between groups.

RESULTS

A means comparison of residuals showed that specific differences were significant (t-test, p = 0.0004). The null hypothesis could be rejected: materials' performances were different. This could not be determined in the original report, since BA variability was very high. A proposal for reporting of results to facilitate their clinical interpretation and comparison between studies is presented.

CONCLUSION

Controlling for general variability caused by differences in BA size allows precise comparison of microtensile tests results.

Fitting characteristics of N95 filtering-facepiece respirators used widely in China

BACKGROUND

Millions of people rely on N95 filtering facepiece respirators to reduce the risk of airborne particles and prevent them from respiratory infections. However, there are no respirator fit testing and training regulations in China. Meanwhile, no study has been conducted to investigate the fit of various respirators. The objective of this study was to investigate whether people obtained adequate fit when wearing N95 filtering facepiece respirators (FFRs) used widely in China.

METHODS

Fifty adult participants selected using the Chinese respirator fit test panel donned 10 common models of N95 FFRs. Fit factors (FF) and inward leakage were measured using the TSI PortaCount Plus. Each subject was tested with three replications for each model. A subject was considered to pass the fit test when at least two of the three FFs were greater than 100. Two models were conducted fit tests before and after training to assess the role of training.

RESULTS

The geometric mean FFs for each model and trained subjects ranged from <10 to 74.0. The fifth percentile FFs for only two individual respirator models were greater than 10 which is the expected level of performance for FFRs. The passing rates for these two models of FFRs were 44.7% and 20.0%. The passing rates were less than 10.0% for the other eight models. There were 27 (54%) participants who passed none of the 10 FFRs. The geometric mean FFs for both models when the subjects received training (49.7 and 74.0) were significantly larger than those when the same group of subjects did not receive any training (29.0 and 30.9) (P<0.05).

CONCLUSIONS

FFRs used widely in China should be improved according to Chinese facial dimensions. Respirator users could benefit from respirator training and fit testing before using respirators.

New re-entry device for revascularization of chronic coronary total occlusions: preliminary single Japanese center experience

BACKGROUND

Although retrograde approach for coronary chronic total occlusion (CTO) has been introduced, the procedure is still time and resource consuming. A simplified antegrade approach mightbe another resort. The aim of this study was to evaluate a new device designed to facilitate guidewire re-entry into the true lumen of a CTO from the adjacent subintimal space.

METHODS

Patients with CTO were entered into a prospective registry regardless of lesion characteristics. A new metal-tip catheter was used initially in primary use cases. If it created subintimal tracking, a new re-entry tool (a flat balloon with 2 exit ports offset by 180 degrees) was used as a platform to attempt guidewire penetration into the distal true lumen. In rescue use cases after unsuccessful conventional wiring, the re-entry procedure was subsequently attempted.

RESULTS

In 11 CTO lesions attempted, device success was achieved in 8 cases (72.7%). Re-entry procedure success rate was higher in primary use cases (80%) compared to rescue use cases (33.3%). Retrograde approach was conducted immediately after unsuccessful antegrade procedure using this device in the other 3 cases and successful recanalization was achieved in all cases. All lesions were stented, resulting in TIMI 3 flow without major complications.

CONCLUSION

A new coronary re-entry device may provide another strategic option in the antegrade approach to recanalize CTOs.

Effects of recycled glass substitution on the physical and mechanical properties of clay bricks

In this study, wasted glasses from structural glass walls up to 45 wt.% were added into clay mixtures in brick manufacturing process. Physical and mechanical properties of clay bricks were investigated as functions of the wasted glass content and the firing temperature. The results indicated that with proper amount of wasted glasses and firing temperature, clay bricks with suitable physical and mechanical properties could be obtained. The compressive strength as high as 26-41 MPa and water absorption as low as 2-3% were achieved for bricks containing 15-30 wt.% of glass content and fired at 1100 degrees C. When the glass waste content was 45 wt.%, apparent porosity and water absorption was rapidly increased.

Influence of content and particle size of waste pet bottles on concrete behavior at different w/c ratios

The goal of this work was to study the mechanical behavior of concrete with recycled Polyethylene Therephtalate (PET), varying the water/cement ratio (0.50 and 0.60), PET content (10 and 20 vol%) and the particle size. Also, the influence of the thermal degradation of PET in the concrete was studied, when the blends were exposed to different temperatures (200, 400, 600 degrees C). Results indicate that PET-filled concrete, when volume proportion and particle size of PET increased, showed a decrease in compressive strength, splitting tensile strength, modulus of elasticity and ultrasonic pulse velocity; however, the water absorption increased. On the other hand, the flexural strength of concrete-PET when exposed to a heat source was strongly dependent on the temperature, water/cement ratio, as well as on the PET content and particle size. Moreover, the activation energy was affected by the temperature, PET particles location on the slabs and water/cement ratio.

Accelerated test system strength models based on Birnbaum-Saunders distribution: a complete Bayesian analysis and comparison

Several models for studies related to tensile strength of materials are proposed in the literature where the size or length component has been taken to be an important factor for studying the specimens' failure behaviour. An important model, developed on the basis of cumulative damage approach, is the three-parameter extension of the Birnbaum-Saunders fatigue model that incorporates size of the specimen as an additional variable. This model is a strong competitor of the commonly used Weibull model and stands better than the traditional models, which do not incorporate the size effect. The paper considers two such cumulative damage models, checks their compatibility with a real dataset, compares them with some of the recent toolkits, and finally recommends a model, which appears an appropriate one. Throughout the study is Bayesian based on Markov chain Monte Carlo simulation.

Optimal aggregate testing using Vandermonde polynomials and spectral methods

Recycled aggregate (RA) has been used in various construction applications around the world mainly as sub-grade, roadwork and unbound materials, but not in higher-grade applications. The major barrier encountered is the variation of quality within RA, which causes lower strength, and poorer quality. This work studies the relationships among six parameters describing the characteristics of RA: (i) particle size distribution, (ii) particle density, (iii) porosity and absorption, (iv) particle shape, (v) strength and toughness, and (vi) chemical composition. Samples of RA from 10 demolition sites were obtained with service life ranging from 10 to 40 years. One additional set of samples was specifically collected from the Tuen Mun Area 38 Recycling Plant. The characteristics of these eleven sets of samples were then compared with normal aggregate samples. A Vandermonde matrix for interpolation polynomial coefficient estimation is used to give detailed mathematical relationships among pairs of samples, which can be used to work out redundant tests. Different orders of interpolation polynomials are used for comparison, hence the best-fit equations with the lowest fitting errors from different orders of polynomials can be found. Fitting error distributions are then studied by using spectral methods such as power spectra and bispectra. From that, the best equations for result estimations can be obtained. This study reveals that there is strong correlation among test parameters, and by measuring two of them: either "particle density" or "porosity and absorption" or "particle shape" or "strength and toughness", and "chemical content", it is sufficient to study RA.

Study on use of MSWI fly ash in ceramic tile

In this work, MSWI (municipal solid waste incineration) fly ash is used as a blending in production of ceramic tile by taking advantage of its high contents of SiO(2), Al(2)O(3) and CaO. Besides, macro-performance and microstructure of the product as well as its leaching toxicity in practical application were studied by means of XRD, IR and SEM analysis, and leaching toxicity and sequential chemical extraction analysis of the product. It is found that when 20% fly ash is added, the product registers a high compressive strength of 18.6MPa/cm(2) and a low water absorption of 7.4% after being sintered at 960 degrees C. It is found that the glazed tile shows excellent resistance against leaching, in accordance with HVEP stand, of heavy metals with Cd<0.0002ppm, Pb<0.0113ppm and Zn<0.0749ppm, and Hg below the low detection limit. These results show that heavy metals are cemented among the solid lattice in the product and can hardly be extracted. Leaching toxicity of heavy metals in the product, especially Hg, Pb, Zn and Cd, is substantially reduced to less than one-tenth of that in fly ash. In addition, specifications of Hg, Pb, Zn and Cd are largely changed and only a small portion of these heavy metals exists in soluble phases. These results as a whole suggest that the use of MSWI fly ash in ceramic tile constitutes a potential means of adding value.

The polymethyl methacrylate cervical cage for treatment of cervical disk disease Part III. Biomechanical properties

BACKGROUND

In a previous article, we used the PMMA cervical cage in the treatment of single-level cervical disk disease and the preliminary clinical results were satisfactory. However, the mechanical properties of the PMMA cage were not clear. Therefore, we designed a comparative in vitro biomechanical study to determine the mechanical properties of the PMMA cage.

METHODS

The PMMA cervical cage and the Solis PEEK cervical cage were compressed in a materials testing machine to determine the mechanical properties.

RESULTS

The compressive yield strength of the PMMA cage (7030 +/- 637 N) was less than that of the Solis polymer cervical cage (8100 +/- 572 N). The ultimate compressive strength of the PMMA cage (8160 +/- 724 N) was less than that of the Solis cage (9100 +/- 634 N). The stiffness of the PMMA cervical cage (8106 +/- 817 N/mm) was greater than that of the Solis cage (6486 +/- 530 N/mm). The elastic modulus of the PMMA cage (623 +/- 57 MPa) was greater than that of the Solis cage (510 +/- 42 MPa). The elongation of PMMA cage (43.5 +/- 5.7%) was larger than that of the Solis cage (36.1 +/- 4.3%).

CONCLUSIONS

Although the compressive yield strength and ultimate compressive strength of the PMMA cervical cage were less than those of the Solis polymer cage, the mechanical properties are better than those of the cervical vertebral body. The PMMA cage is strong and safe for use as a spacer for cervical interbody fusion. Compared with other cage materials, the PMMA cage has many advantages and no obvious failings at present. However, the PMMA cervical cage warrants further long-term clinical study.

CUSUM: a tool for early feedback about performance?

BACKGROUND

Modern day clinical practice demands evidence justifying our choice of treatment methods. Cumulative sum techniques (cusum) are amongst the simplest statistical methods known. They provide rapid analysis and identification of trends in a series of data. This study highlights use of these techniques as an early performance indicator of a clinical procedure before its implementation.

METHODS

Twenty consecutive patients who underwent total hip or knee arthroplasty received a simple dressing--blue gauze and Tegaderm. Cusum charting was used to assess the dressing with regards to skin blistering. At an acceptable level of performance the curve would oscillate about the horizontal axis and the overall trend therefore said to be flat. If performance is unacceptable, the cusum slopes upward.

RESULTS

The cusum plot for the twenty patients did not cross the specified control limits. This showed that our simple dressing met specified standards with regards to wound blistering postoperatively.

CONCLUSION

We recommend the use of this simple, yet versatile cusum technique in the early evaluation of a clinical procedure before its implementation.

Occupational exposure in Greek industrial radiography laboratories (1996-2003)

More than 40 industrial radiography laboratories are operating in Greece using X-ray or gamma-ray sources and more than 250 workers occupationally exposed to ionising radiation in these facilities are monitored on a regular basis. This study presents the evolution of individual doses received by radiographers during the past years. The mean annual dose (MAD) of all workers as well as of exposed workers is estimated, and correlated to the types of laboratories and practices applied. The MAD of the exposed workers in industrial radiography is compared with the doses of workers in other specialties and with the doses of radiographers in other countries. Furthermore, the study attempts to propose dose constraints for the practices in industrial radiography, according to the BSS European directive and the relevant Greek radiation protection legislation. The proposed value was defined as the dose below which the annual doses of 75% of the exposed radiographers are expected to be included.

In vitro analysis of the cement mantle of femoral hip implants: development and validation of a CT-scan based measurement tool

We developed, validated and assessed inter- and intraobserver reliability of a CT-scan based measurement tool to evaluate morphological characteristics of the bone-cement-stem complex of hip implants in cadaver femurs. Two different models were investigated: the stem-cavity model using a double tapered polished femoral-stem that is removed after cement curing and the plastic-replica model using a stereolithographic stem replica that is left in place during CT-scanning. Software was developed to segment and analyze connective CT-images and identify the contours of bone, cement, and stem based on their respective gray values. Volume parameters (whole specimen, cement, stem, air contents of bone and cement), concentricity parameters (distances between centroids of stem and cement, cement and bone, stem and bone), contact surfaces (bone/air and cement/bone) and bone cement mantle thickness parameters were calculated. A three-dimensional protocol was developed to evaluate the minimal mantle thickness out of the CT-plane. The average accuracy for surfaces within CT-images was 7.47 mm2 (1.80%), for bone and cement mantle thickness it was 0.51 mm (9.39%), for distances between centroids it was 0.38 mm (18.5%) and contours: 0.27 mm (2.57%). The intra- and interobserver reliability of air content in bone and cement was sub-optimal (intraclass-correlation coefficient (ICC) as low as 0.54 with an average ICC of 0.85). All other variables were reliable (ICC>0.81, average ICC: 0.96). This in vitro technique can assess characteristics of cement mantles produced by different cementing techniques, stem types or centralizers.

Effect of cell phone magnetic fields on adjustable cerebrospinal fluid shunt valves

The rapid increase in the number of cell phone users has led to the suggestion that electromagnetic waves might affect medical devices. Cerebrospinal fluid shunt valves contain a magnetic device to allow the intracranial pressure setting to be adjusted transcutaneously. Among the valves tested, the settings of the Strata valve, the Hakim valve, and the Sophy valve were affected by magnetic flux densities of 6.0, 17.5, and, 40.0 mT, respectively. Cell phones produce a magnetic flux density of 3.0 to 40.0 mT. Although cell phones could theoretically influence shunt valves, this seems unlikely because the flux density decreases with the square of the distance.

The validity of reported tensile bond strength utilizing non-standardized specimen surface areas. An analysis of in vitro studies

PURPOSE

To assess and discuss the true value and perceived relevance of present day dental adhesive tensile bond strength studies. There are flaws and inconsistencies present in the data due to the inherent variations in testing methods, conditions, and types of samples prepared. In particular, surface areas of specimens need to be standardized. This review considers the significant impact of different surface areas of tooth specimens utilized in testing.

RESULTS

On review of the data, relatively higher MPa values do not necessarily indicate improved dental adhesive products or procedures.

Statistical Correlation Between Transient Pressure Drop and Cavitation at Closure of a Mechanical Heart Valve

Cavitation on a mechanical heart valve (MHV) is attributable to transient regional pressure drop at the instant of valve closure. As a cavitation bubble collapses, it emits shock waves, which have the characteristics of high frequency oscillations (HFO) on a pressure time trace. The potential for such HFO bursts to cause material damage on an MHV can be measured by the cavitation impulse I, which is defined as the area under the trace of the HFO bursts. In the present study, experiments were conducted on a bileaflet MHV in a durability tester, operated at pulse rates from 300-1,000 bpm. In each case, the transient pressure near an occluder was monitored for 60,000 beats via a transducer. The peak pressure drop Pm and the corresponding cavitation impulse I obtained for the 60,000 beat sequence are found to resemble sample records of two stationary stochastic processes, each of which follows a log normal distribution. Their first order probability density functions are estimated from the records. The correlation is investigated between I and Pm associated with each beat, which is found to be of statistical significance.

A study of the characteristics of single-injection insulated block needles in a biologic model

BACKGROUND AND OBJECTIVES

Single-injection block needles are manufactured in many different lengths, diameters, and tip designs, but the literature contains no reports of methods to assess clinical characteristics of regional-block needles. A novel animal model for the assessment of the characteristics of single-injection regional anesthesia needles is described.

METHODS

Nine different needles designed for peripheral nerve blocks that were fitted with identical hubs were used. Pork bellies were used as the biologic model. The bellies were mounted such that the needles passed from inside to outside. The last layer to be penetrated was the skin. Ten experienced and blinded anesthesiologists scored the feel, resistance, and usability of the 9 needles during their passage through similarly prepared pork bellies. Two identical (index) needles were included in the study to assess the internal validity of the study.

RESULTS

The overall scoring was acceptably consistent and repeatable and showed statistically significant differences between the needles tested. The needles that were judged the most usable were those with a moderate resistance to passage through the tissue and a high degree of feel, which was defined as the ability to appreciate the passage of the needle through the tissue planes. Needles with very high or very low resistances and those with poor feel scored poorly on the usability scale. Differences in individuals' assessment of the index needles suggested some within-subject variability during the study.

CONCLUSIONS

This type of biologic model can be used for the quantifiable and repeatable assessment of different needle tip designs. Needles with moderate resistance and high feel were preferred.

Ultrasound visibility of needles used for regional nerve block: an in vitro study

BACKGROUND AND OBJECTIVES

Ultrasound visibility of regional block needles is a critical component for safety and success of regional anesthetic procedures. The aim of the study was to formally assess factors that influence ultrasound visibility of needles used in regional anesthesia.

METHODS

Regional block needles between 17- and 22-G diameter were inserted in a tissue equivalent phantom at angles from 0 degrees to 65 degrees relative to the phantom surface. For visibility enhancement, the needles were primed with air or water in combination with stylets and different size guide wires. Ultrasound measurements of needle tips and shafts were performed using transversal and longitudinal imaging with a linear 15-MHz transducer. Univariate and multivariate statistical analyses were performed on 719 visibility measurements.

RESULTS

Hustead tip needles exhibited best ultrasound visibility. Ultrasound visibility of the needle tip was increased by insertion of a medium size guide wire. Water or air priming of the needle, insulation, and the insertion of a stylet did not influence needle visibility. Long axis imaging of the needle for shallow insertion angles (<30 degrees in relation to the phantom surface) and short-axis imaging for steep angles (>60 degrees ) provided the best ultrasound visibility of the needle tips. Needle visibility decreased linearly with steeper insertion angles ( P <.001) and smaller needle diameters ( P <.001).

CONCLUSIONS

The results of our in-vitro study suggest a number of factors enhancing ultrasound visibility of regional block needles. The use of needles in the largest possible size inserted with a medium-size guide wire provides the best ultrasound visibility. Analysis of the approach angle favors needle insertion parallel to the transducer. The consideration of these factors may improve safety and success of ultrasound-guided regional blocks.

Statistical characteristics of mechanical heart valve cavitation in accelerated testing

BACKGROUND AND AIM OF THE STUDY

Cavitation damage has been observed on mechanical heart valves (MHVs) undergoing accelerated testing. Cavitation itself can be modeled as a stochastic process, as it varies from beat to beat of the testing machine. This in-vitro study was undertaken to investigate the statistical characteristics of MHV cavitation.

METHODS

A 25-mm St. Jude Medical bileaflet MHV (SJM 25) was tested in an accelerated tester at various pulse rates, ranging from 300 to 1,000 bpm, with stepwise increments of 100 bpm. A miniature pressure transducer was placed near a leaflet tip on the inflow side of the valve, to monitor regional transient pressure fluctuations at instants of valve closure. The pressure trace associated with each beat was passed through a 70 kHz high-pass digital filter to extract the high-frequency oscillation (HFO) components resulting from the collapse of cavitation bubbles. Three intensity-related measures were calculated for each HFO burst: its time span; its local root-mean-square (LRMS) value; and the area enveloped by the absolute value of the HFO pressure trace and the time axis, referred to as cavitation impulse. These were treated as stochastic processes, of which the first-order probability density functions (PDFs) were estimated for each test rate.

RESULTS

Both the LRMS value and cavitation impulse were log-normal distributed, and the time span was normal distributed. These distribution laws were consistent at different test rates.

CONCLUSION

The present investigation was directed at understanding MHV cavitation as a stochastic process. The results provide a basis for establishing further the statistical relationship between cavitation intensity and time-evolving cavitation damage on MHV surfaces. These data are required to assess and compare the performance of MHVs of different designs.

Accelerated Aging Effects on Color and Translucency of Bleaching-Shade Composites

PURPOSE

This study was performed to evaluate the influence of accelerated aging on the color and translucency parameter (TP) of bleaching-shade resin composites.

MATERIALS AND METHODS

Thirty-three bleaching shades and two control conventional shades of microhybrid (MH) and microfill (MF) resin composite specimens (n = 5) were aged in an accelerated aging chamber set to standard CAM 180 cycles. One side of each specimen was evaluated for surface color and TP changes compared with baseline in increments of 150 kJ/m2 for intervals up to 450 kJ/m2 using a spectrophotometer. A deltaE* > or = 3.7 was considered to be a poor match, and the total TP range was divided into three equal parts representing low, medium, and high translucency. Data were analyzed with analysis of variance.

RESULTS

Compared to the baseline, deltaL*, deltaa*, deltab*, and deltaE* ranges at 450 kJ/m2 were -0.8 to 5.0, -0.6 to 1.2, -8.3 to 0.0, and 0.7 to 8.6 for MH and 0.2 to 1.3, 0.1 to 1.3, -2.5 to 1.1, and 1.7 to 2.7 for MF composites. Scheffé's S intervals (p = .05) for comparisons of deltaL*, deltaa*, deltab*, and deltaE* values of MH composites between baseline and 450 kJ/m2 were 1.6, 0.6, 1.7, and 1.5, respectively. Corresponding Tukey-Kramer intervals for MF composites were 0.7, 0.3, 0.6, and 0.6, respectively. TP values at baseline ranged from 0.9 to 4.3 for MH and from 1.4 to 2.2 for MF composites, whereas deltaTP for baseline minus 450 kJ/m2 ranged from -1.1 to 1.7 for MH and from -0.1 to 0.3 for MF composites. Scheffé's S interval (p = .05) for comparisons of deltaTP values of MH composites for baseline minus 450 kJ/m2 was 1.0. Corresponding Tukey-Kramer interval for MF composites was 0.4.

CONCLUSIONS

Aging-dependent color changes at 450 kJ/m2 were above the limit that indicated a poor match for 18/26 MH, while corresponding values for microfills were within acceptable range. Accelerated aging generally caused decreases in L* (specimens became darker) and a* values (specimens became redder), while b* values increased (specimens became more chromatic) for both MH and MF composites. TP was relatively stable during aging for both MH and MF composites.

Multiaxial pedicle screw designs: static and dynamic mechanical testing

STUDY DESIGN

Randomized investigation of multiaxial pedicle screw mechanical properties.

OBJECTIVES

Measure static yield and ultimate strengths, yield stiffness, and fatigue resistance according to an established model. Compare these measured properties with expected loads in vivo.

SUMMARY OF BACKGROUND DATA

Multiaxial pedicle screws provide surgical versatility, but the complexity of their design may reduce their strength and fatigue resistance. There is no published data on the mechanical properties of such screws.

MATERIALS AND METHOD

Screws were assembled according to a vertebrectomy model for destructive mechanical testing. Groups of five assemblies were tested in static tension and compression and subject to three cyclical loads. Modes of failure, yield, and ultimate strength, yield stiffness, and cycles to failure were determined for six designs of screw.

RESULTS

Static compression yield loads ranged from 217.1 to 388.0 N and yield stiffness from 23.7 to 38.0 N/mm. Cycles to failure ranged from 42 x 10(3) to 4,719 x 10(3) at 75% of static ultimate load. There were significant differences between designs in all modes of testing. Failure occurred at the multiaxial link in static and cyclical compression.

CONCLUSIONS

Bending yield strengths just exceeded loads expected in vivo. Multiaxial designs had lower static bending yield strength than fixed screw designs. Five out of six multiaxial screw designs achieved one million cycles at 200 N in compression bending. "Ball-in-cup" multiaxial locking mechanisms were vulnerable to fatigue failure. Smooth surfaces and thicker material appeared to be protective against fatigue failure.

Accuracy and reliability of torque wrenches used for halo application in children

BACKGROUND

Halo ring and vest application in children requires torque wrenches capable of delivering a spectrum of torque values ranging from 0.11 to 0.68 N-m (1 to 6 in-lb). Published evaluations of torque wrenches commonly used in adults have shown that the measured torque values were within 10% of the target torque in only 64% of trials. The objective of the present study was to evaluate the accuracy, reliability, and interobserver variability of halo wrenches capable of applying the lower torque levels commonly used in children.

METHODS

Torque wrenches from four distributors (Bremer, Jerome Medical, Mountz, and PMT) were tested with use of a calibrated torque-meter. Five wrenches of each type were tested by a single observer, with fifty trials performed at six different torque settings (0.11, 0.23, 0.34, 0.45, 0.57, and 0.68 N-m). One wrench of each type was then tested by two additional observers at a torque setting of 0.34 N-m, with each observer performing fifty trials per wrench.

RESULTS

The measured torque value was within 10% of the target value in 69.2% of the 6400 trials, including 50.7% of the trials performed with the PMT wrench, 51.8% of those performed with the Bremer wrench, 84.5% of those performed with the Mountz wrench, and 90% of those performed with the Jerome wrench. Significant variability (p < 0.05) was found between at least two, and as many as five, wrenches of the same variety at each of three torque settings used for comparison (0.23, 0.45, and 0.68 N-m). Significant interobserver variability (p < 0.05) was found between at least two observers during testing of the Jerome and Mountz wrenches, but no significant differences were shown between observers during testing of the PMT and Bremer wrenches.

CONCLUSIONS

The Jerome and Mountz wrenches are more accurate and reliable at low torque settings than the PMT and Bremer wrenches are. Variability among different wrenches from the same manufacturer may be seen with any of the wrenches studied.

Internal Stress Distribution in Cervical Intervertebral Discs

There is concern that cervical interbody fusion can result in accelerated degenerative changes occurring at adjacent spinal levels. The cervical spine clearly evolved to be mobile. It would seem to be desirable for spinal surgeons to have an alternative to fusion, and spinal arthroplasty is an appealing concept. The Bristol Disc is a mechanical device comprising two articulating components that result in motion with 6 df. It has been shown to have favorable kinematics when compared with intact and fused cadaveric spines. The current study attempts to record changes in the distribution of stresses within cervical intervertebral discs adjacent to the artificial disc or a simulated fusion. The technique used to measure intradiscal stress distributions is based on earlier work by McNally and Adams on lumbar intervertebral discs. The study generated stress profiles through cervical intervertebral discs statically loaded in four different postures in addition to recording changes in intradiscal pressure within both the nucleus and the annulus during flexion. Similar stress profiles were recorded from intact specimens and those with the artificial joint inserted. The artificial joint resulted in reduced stresses in the annulus compared with spines with a simulated fusion. The study demonstrates how different testing conditions can result in researchers being confronted with paradoxical data, and the simulation of muscle forces is recommended.

Static and dynamic analysis of five anterior instrumentation systems for thoracolumbar scoliosis

STUDY DESIGN

A nondestructive biomechanical investigation among five anterior spinal instrumentation systems for scoliosis.

OBJECTIVES

The purpose of this study is to analyze the static and dynamic biomechanical stability of five different systems.

SUMMARY OF BACKGROUND DATA

Although a variety of anterior spinal instrumentation systems for scoliosis are available, very few attempts have been made at comparative biomechanical studies.

METHODS

Thirty calf spines were underwent static biomechanical tests, including flexion-extension, axial rotation, and lateral bending loading modes in the multisegmental spinal model. Five anterior instrumentation systems included: 1) Texas Scottish Rite Hospital system; 2) Bad Wildungen Metz; 3) anterior ISOLA; 4) Cotrel-Dubousset Hoph; and 5) Kaneda Anterior Scoliosis System. The initial and postfatigue stability after a cyclic loading test were analyzed by measuring the range of motion at instrumented segments compared to the intact within the same specimen (% to intact).

RESULTS

Two-rod systems showed a significant decrease in range of motion compared to one-rod systems in flexion-extension (P < 0.001) and axial rotation (P < 0.05). In lateral bending, all systems demonstrated a significant decrease in range of motion of less than 40% to the intact (P < 0.001). After cyclical loading test, all systems increased in range of motion. In flexion-extension, one-rod systems depicted a significant increase in range of motion, compared to two-rod systems (P < 0.05).

CONCLUSIONS

In the initial stability analysis, two-rod systems are superior to one-rod systems. For one-rod systems, repeated physiologic loading may result in reduced stability in flexion-extension.

Mechanical performance of the new posterior spinal implant: effect of materials, connecting plate, and pedicle screw design

STUDY DESIGN

A newly designed spinal implant was tested to evaluate multicycle stiffness and fatigue resistance.

OBJECTIVES

To investigate the effect of different materials, connecting plate, and pedicle screw design on the mechanical performance of the spinal implant.

SUMMARY OF THE BACKGROUND DATA

The addition of cross-linkages did not significantly increase implant compression/flexion stiffness, but accelerated fatigue failure at the rod junctions. Both Ti-6Al-4V spinal implants and the 316L stainless-steel counterparts have been used extensively for clinical cases; however, design factors establishing the proposed superiority of the Ti-6Al-4V implant for fatigue resistance have not, as yet, been extensively studied.

METHODS

Twenty implants with connecting plates (two materials by two screw designs by five implants) and five implants without connecting plates were assembled to UHMWPE blocks and cyclically loaded from 60 N to 600 N at a frequency of 5 Hz.

RESULTS

Failure sites for the tested prototypes were at the cephalic screw hubs or rod-plate junctions. All Ti-6Al-4V implants demonstrated reduced stiffness compared to the structurally identical 316L analogs. The use of connecting plates raised the stiffness of the 316L prototypes without cross-links. However, elimination of the connecting plate avoided stress concentration at the rod/plate junctions and increased fatigue life. The Ti-6Al-4V new system with the minimal notch effect at the screw hubs achieved greater fatigue resistance than its 316L counterpart. By contrast, enlargement of the inner-hub diameter resulted in greater gains for fatigue resistance than for stiffness, especially for Ti-6Al-4V variants.

CONCLUSIONS

Although Ti-6Al-4V was superior to 316L for endurance-limit properties, structural design of the Ti-6Al-4V implant dramatically affects fatigue resistance. This may explain the differences between existing studies and the current report, comparing fatigue life for implants made from these two materials. Our results reveal that Ti-6Al-4V must be carefully treated because of sensitivity to notch, with special consideration given to screw-hub design.

Prediction of multiaxial mechanical behavior for conventional and highly crosslinked UHMWPE using a hybrid constitutive model

The development of theoretical failure, fatigue, and wear models for ultra-high molecular weight polyethylene (UHMWPE) used in joint replacements has been hindered by the lack of a validated constitutive model that can accurately predict large deformation mechanical behavior under clinically relevant, multiaxial loading conditions. Recently, a new Hybrid constitutive model for unirradiated UHMWPE was developed Bergström et al., (Biomaterials 23 (2002) 2329) based on a physics-motivated framework which incorporates the governing micro-mechanisms of polymers into an effective and accurate continuum representation. The goal of the present study was to compare the predictive capability of the new Hybrid model with the J(2)-plasticity model for four conventional and highly crosslinked UHMWPE materials during multiaxial loading. After calibration under uniaxial loading, the predictive capabilities of the J(2)-plasticity and Hybrid model were tested by comparing the load-displacement curves from experimental multiaxial (small punch) tests with simulated load-displacement curves calculated using a finite element model of the experimental apparatus. The quality of the model predictions was quantified using the coefficient of determination (r(2)). The results of the study demonstrate that the Hybrid model outperforms the J(2)-plasticity model both for combined uniaxial tension and compression predictions and for simulating multiaxial large deformation mechanical behavior produced by the small punch test. The results further suggest that the parameters of the HM may be generalizable for a wide range of conventional, highly crosslinked, and thermally treated UHMWPE materials, based on the characterization of four material properties related to the elastic modulus, yield stress, rate of strain hardening, and locking stretch of the polymer chains. Most importantly, from a practical perspective, these four key material properties for the Hybrid constitutive model can be measured by relatively simple uniaxial tension or compression tests.

Image analysis measurements of roughness by texture and fractal analysis correlate with contact profilometry

Surface properties of a biomaterial are important factors that govern in part its biocompatibility. Among them, surface roughness is now recognized as a very important factor for cell interactions. Surface roughness (Ra) is routinely measured by contact profilometry but other methods are presently usable. We compared two methods (contact profilometry and image analysis of scanning electron microscopic images SEM) on a series of 12 titanium test pieces. The texture analysis of SEM pictures was done by the heterogeneity and run-length methods. Fractal geometry was also used with the "skyscraper" and "blanket" methods providing respectively the D(SKY) and D(BLANK) fractal dimensions. The fractal dimension of the profilometric curve was also computed (D(MINK)). Computer-simulated textures were used to evaluate the pertinence of the algorithms. A significant correlation was found between Ra and all the texture descriptors except heterogeneity. The correlation coefficient was dependent on the microscopic magnification. The fractal dimension of the curve was correlated with D(SKY) and D(BLANK). Run-length, D(SKY) and D(BLANK) were highly correlated, independent of the magnification used, a finding related to the self-similarity of the images. Image texture analysis can be a useful alternative to profilometry with brittle or soft materials or with objects having a complex shape.

Bone ingrowth fixation of artificial intervertebral disc consisting of bioceramic-coated three-dimensional fabric

STUDY DESIGN

The bone-bonding characteristic of the new artificial intervertebral disc consisting of bioceramic-coated three-dimensional fabric was evaluated mechanically and histologically in an in vivo sheep model.

OBJECTIVES

To investigate the mechanical properties and the histologic appearance of the interface between the three-dimensional fabric disc and the vertebral body, and to evaluate these alterations in vivo under a spinal segmentally mobile condition.

SUMMARY OF BACKGROUND DATA

Bone ingrowth to the bioceramic-coated three-dimensional fabric surface had been demonstrated already under a stable environment in preliminary animal studies.

METHODS

For this study, 20 sheep underwent two-level lumbar intervertebral disc replacement with three-dimensional fabric discs (Group I) or bioceramic spacers as a comparative material (Group II). All operative segments were stabilized temporarily with spinal instrumentation for the initial ingrown phase. Four animals each were killed at 4, 6, 15, and 24 months in Group I and at 6 months in Group II, and the operative segments were subjected to either a detachment test or histologic evaluation.

RESULTS

The interfacial tensile strength at 6 months was significantly higher in Group I than in Group II. No significant decrease in tensile strength was detected until 24 months after surgery in Group I. Histologically, bone ingrowth to the three-dimensional fabric surface was observed 4 months after surgery, and no aseptic loosening occurred until 24 months after surgery.

CONCLUSIONS

The findings show that the three-dimensional fabric disc was firmly fixed to the vertebral body by bone ingrowth, and that this biologic fixation was preserved even under the spinal segmentally mobile condition.

The pylon concept of pelvic anchorage for spinal instrumentation in the human cadaver

STUDY DESIGN

Human cadavera morphometric analysis of the iliac columns and biomechanical implant testing of traditional Galveston technique compared to intrailiac instrumentation of the entire iliac column.

OBJECTIVES

To describe the anatomy of the iliac columns and to evaluate the strength in forward flexion of a large implant spanning the entire column length compared to standard Galveston technique.

SUMMARY OF BACKGROUND DATA

We have observed substantial and straight columns of bone in the pelvis, connecting the acetabula to the sacrum, which may allow for improved spinopelvic instrumentation.

METHODS

Twenty adult cadaveric pelves were used. Each specimen was oriented in the computed tomography scanner to obtain a cross-section of the iliac columns, which begin from 2 cm caudal to the posterior iliac spines and end above the acetabula at the anterior inferior iliac spines. Two different instrumentation techniques were used. Standard Galveston pelvic fixation with paired 6.25-mm diameter rods extending 8 cm into the pelvis (Group 1) was compared to paired 8-mm diameter, 15-cm long custom implants, placed within the length of the entire iliac columns and connected to 6.25-mm spinal rods (Group 2). Both constructs had two rigid cross-links connecting the rods. Testing in forward flexion was performed for each construct with the MTS model 881 at 5 N/sec until failure occurred.

RESULTS

The rectangular shaped iliac columns averaged 15.2 (SD 0.8) cm in length, 2.5 (SD 0.3) cm in width and were consistently straight. The iliac column orientation as viewed in the transverse plane was 22 degrees laterally directed from the midsagittal plane. For the Galveston technique, failure with a flexion force occurred at a mean of 682 (SD 217) N. The iliac column implants failed at a mean of 2153 (SD 1370) N (P < 0.004).

CONCLUSION

The human adult pelvis has substantial and straight columns of bone extending from 2 cm below the posterior iliac spine, traversing above the sciatic notch, and ending at the anterior iliac spine. The shape resembles a weight-bearing long bone such as the tibia. Analogous to the architectural pylon, in this cadaver model, large implant instrumentation of the entire length of these pelvic columns provides at least three times stronger anchorage for spinal instrumentation compared to standard Galveston technique.

The effects of an interspinous implant on intervertebral disc pressures

STUDY DESIGN

Measurement of intradiscal pressure was performed after placement of an interspinous implant in a cadaver model.

OBJECTIVE

To understand the likelihood of accelerated adjacent-level disc degeneration as a result of the implant.

SUMMARY OF BACKGROUND DATA

An interspinous implant has been developed to treat lumbar neurogenic claudication secondary to spinal stenosis that places the stenotic segment in slight flexion and prevents extension. Previous biomechanical studies demonstrated that fusing one level may significantly increase the intradiscal pressures at adjacent levels. Moreover, clinical studies have reported an increased incidence of adjacent-level degeneration after lumbar spinal fusion.

METHODS

Eight cadaver lumbar specimens (L2-L5) were loaded in flexion, neutral, and extension. A pressure transducer measured intradiscal pressure and annular stresses during each of the three positions at each of the three disc levels. An appropriately sized implant was placed at L3-L4, and the pressure measurements were repeated.

RESULTS

The pressures at the adjacent discs were not significantly affected by the interspinous implant insertion. There was a significant decrease in intradiscal pressure at the L3-L4 disc in the posterior annulus and nucleus in the neutral and extended positions.

CONCLUSIONS

The implant does not significantly change the intradiscal pressures at the adjacent levels, yet it significantly unloads the intervertebral disc at the instrumented level in the neutral and extended positions. On the basis of the current findings, it does not appear that the implant causes accelerated disc degeneration at the adjacent levels.

The biologic response to particles from a lumbar disc prosthesis

STUDY DESIGN

Particles of a proprietary polyolefin rubber compound used in a lumbar disc prosthesis were generated in vitro and tested for biocompatibility in two animal models. OBJECTIVE To characterize any tissue response to polyolefin rubber particles.

SUMMARY OF BACKGROUND DATA

Intervertebral disc prostheses are emerging as alternatives to fusion techniques for the treatment of symptomatic disc degeneration. The biocompatibility of all novel components used in the construction of these devices must be verified before they can be considered for general use.

METHODS

Laboratory-generated polyolefin rubber particles were either injected into dorsal subcutaneous air pouches of 30 rats or placed directly onto the lumbosacral dura and nerve roots of 9 sheep. Histologic sections of tissues from, and remote from, the site of implantation were examined for evidence of inflammation and wound-healing responses.

RESULTS

Polyolefin rubber particle debris induced a tissue response that was consistent with a normal foreign body reaction to large particles. The response was not significantly greater than that seen with similar size particles of ultrahigh molecular weight polyethylene. There was no evidence of particle migration from the site of implantation, and there was no evidence of local or systemic toxic effects.

CONCLUSION

Polyolefin rubber particles induce only localized tissue response that is consistent with a normal foreign body reaction to large nontoxic particles.

Reusable sensors in intrapartum foetal reflection pulse oximetry

OBJECTIVES

To evaluate the accuracy of intrapartum foetal pulse oximetry (SO(2POX)) using reusable sensors and the effect of a sensor performance test on data quality. Furthermore, to assess the sensor-related costs by using reusable sensors and sensor performance test.

METHODS

36 reusable sensors were used for SO(2POX) during labour of 289 term foetuses. A sensor performance test device assessing the emitter and receiver capability and the firmness of attachment of the sensors had been developed and used in the last 134 measurements before each resterilisation. Oxygen saturation (SaO(2)) at birth was measured spectrophotometrically after cord blood sampling. The accuracy of SO(2POX) was evaluated by analysing its relationship to SaO(2). The valid SO(2POX) data, as confirmed by subsequent sensor test in the second group, was considered comparable with those with single sensor use. Sensor-related average cost (sensors, test device and sterilisation) of such measurements was compared with that of single sensor use.

RESULTS

Eight sensors failed performance test despite valid pulse oximetry signal output during their last measurements. There were significant overall linear correlations between SO(2POX) and SaO(2) (r=0.45, P<0.0001). Separate analyses of regression in the group without sensor performance testing showed an r(2) of 0.41, whereas in the group with subsequent sensor performance testing, the r(2) was 0.52 (P<0.05). By reusing the sensors, the sensor-related cost per valid measurement was $18.9 and 71% lower compared to single use of sensors ($65).

CONCLUSIONS

Pulse oximetry may reflect fetal oxygen saturation. Data quality may be compromised by insufficient sensor performance, even though the reflection signal quality is acceptable. If sensor performance is tested before each measurement, reusable sensors may reduce the costs of fetal pulse oximetry.

Measurement of polyethylene wear - a new three-dimensional methodology

Studies in the field of polyethylene wear of the acetabular cup have been generally discussed using a two-dimensional assumption on the coronal plane; significant errors thus appear. The present study proposes a new, advanced methodology in order to accurately estimate the polyethylene wear. Through the usage of the distance between X-ray focus and film and only one follow-up, anteroposterior (AP) radiograph, a three-dimensional (3D) algorithm is introduced here. Here, 91 primary total hip joint replacements in 67 patients have been examined and three findings are obtained. Results show that the mean rate of 3D linear wear of the polyethylene estimated by the current method is 0.230+/-0.036 mm per year, that of the 2D linear wear is 0.148+/-0.028 mm per year. Moreover, the wear depth of the femoral head on the sagittal plane is 0.173+/-0.043 mm per year by the current method. This study also shows that the adoption of only one AP radiograph in the evaluation of the 3D penetration of femoral head is possible. Furthermore, the methodology proposed here is more convenient than others.

Central and juxta-endplate vertebral body screw placement: a biomechanical analysis in a human cadaveric model

STUDY DESIGN

In vitro biomechanical testing of transvertebral body screws in different positions in both axial pull-out and toggle.

OBJECTIVES

To determine the relative strength of unicortical versus bicortical screw fixation within the vertebral body and to determine comparative strength of juxta-endplate and central screw positions with and without staples in both axial pull-out and toggle modes.

SUMMARY OF BACKGROUND DATA

Loss of fixation is common in centrally placed screws at the rostral end of a construct. To preserve segmental vessels, juxta-endplate screw positions are often used. The biomechanical strength of such screw placement methods has not been measured.

METHODS

Eighty-three human cadaveric vertebral bodies were tested for axial pull-out and toggle with and without staples. Screw positions included central, juxta superior, and inferior endplate. Juxta-endplate screws were toggled in both the rostral and caudal directions perpendicular to the screw axes.

RESULTS

Unicortical fixation resulted in a 93% decrease in axial pull-out strength compared with bicortical fixation. Centrally placed screws and juxta-endplate screws were equivalent in axial pull-out if no staples were used. The juxta-endplate screw with a staple that was toggled away from the endplate had the highest yield strength, followed by the central screw with a staple, and then the juxta-endplate screw without a staple toggled away from the endplate.

CONCLUSIONS

Bicortical fixation is much stronger than unicortical fixation. Centrally placed screws are significantly stronger when used with a staple. When preservation of segmental vessels is desirable, juxta-endplate screws should be placed in such a manner that compressive forces are directed away from the endplate.

The effect of surface roughness and contaminant on the dynamic friction of porcelain tile

Surface roughness affects friction, but it is not clear what surface roughness characteristics are better correlated with friction. The average of the maximum height above the mean line in each cut-off length (Rpm) and the arithmetical average of surface slope (deltaa) had the highest correlation with dynamic friction coefficient in a previous study. The previous study was expanded to two different footwear materials and four different contaminants on a porcelain tile in the current investigation. The results showed that dynamic friction decreased as the interface speed and glycerol content in the contaminant were increased due to the hydrodynamic lubrication effect. Deltaa had the highest correlation with friction for most of the test conditions with neolite. For Four S rubber, friction coefficient appeared to have the highest correlation with the parameters related to the surface void volume at 30% glycerol content, related to the surface slope at 70 and 85% glycerol contents, and related to the peak to valley distance at 99% glycerol content. A good indicator of surface slip resistance probably should consist of the surface parameters representing the surface slope, the surface void volume and the surface peak-to-valley distance with the coefficients determined by the system parameters.

Fluoride release in vitro from a resin-modified glass ionomer after exposure to NaF solutions and toothpastes

The aims of the present investigation were: (i) to study the release of fluoride from a resin-modified glass ionomer cement (Vitremer) after exposing ("recharging") the material with NaF toothpastes and NaF solutions with different fluoride concentrations, and (ii) to study the effect of covering the material with a sealant layer (glaze) in this respect. Totally 160 specimens were made, which were placed in water for 13 weeks to receive a low fluoride release value. The specimens were then randomly divided into 10 groups with 16 discs each. Five of the groups were exposed once a day for 7 days to one of the following fluoride agents: 0.05, 0.2 or 2% NaF solutions and slurries of two NaF toothpastes (Acta and Pepsodent). The other five groups received the same treatment twice a day. All treatments had a recharging effect. However, the 2% NaF solution resulted in significantly more fluoride release than the other solutions and toothpastes. Treatment twice a day gave higher total release than once a day, but the difference were only significant for the 0.2 and 2% NaF solutions. With glaze material covering the specimens, almost no fluoride release was observed. However, when the glaze was removed, a burst of fluoride occurred.

Mechanical characterization of brushite cements: a Mohr circles' approach

Dry and wet brushite cements with various solid/liquid ratios were tested in compression and tension. Two different testing techniques were used to determine tensile strength: Direct Tensile test (DT) and Diametral Compression test (DC) (Brazilian test), which is an indirect way of measuring tensile strength on brittle materials. Statistical analysis of the results obtained on dry cements points out a constant ratio between the values measured by DT and Brazilian tests (DC/DT = 85%). The Mohr's circles representation allows us to understand that, for a material like our cement, ultimate stress measured with the Brazilian test can only underestimate tensile strength, because the compressive/tensile strength ratio is lower than 8. The second consequence of this low ratio is that, in the Brazilian test, the plane along which fracture initiates undergoes not only a normal tensile stress, but also a tangential stress component. Thus, the state of stress on the fracture plane differs from the one taking place in the direct tensile test. Consequently, with such a material (sigma(c)/sigma(t) < 8), the Brazilian test does not estimate the true tensile strength.

Toward standardization of methods of determination of fracture properties of acrylic bone cement and statistical analysis of test results

A succinct critical review of the literature on the fatigue, fatigue crack propagation, and fracture toughness (herein collectively termed "fracture properties") of acrylic bone cement is presented, whereby it is pointed out that a plethora of test conditions have been used. This situation precludes meaningful interstudy comparisons and mitigates against a definitive delineation of the effect of a named variable on a specified fracture property. A case for standardization of test conditions is thus made, culminating in the presentation of a recommended set of such conditions. In addition, it is shown that many literature parametric studies employed inappropriate statistical methods for performing pairwise comparisons, and all these studies have not addressed the issue of possible interactions between the parameters being investigated. A methodology for addressing these deficiencies is presented in the present report, and its use is illustrated with a set of notional fatigue test results.

Development and application of a new abrasion testing device

STATEMENT OF PROBLEM

Wear of gypsum materials is a significant problem in the fabrication of accurately fitting cast prosthetic devices. Unfortunately, there is little agreement on how to measure it.

PURPOSE

This study was designed to evaluate the efficacy of a newly designed abrasion device and to develop a test methodology that provides a clinically relevant measure of material loss from gypsum material.

MATERIAL AND METHODS

In this study, a unique benchtop microabrasion/microimpact device was created. The device consists of a vertical arm with a variably loaded stylus and a reciprocating table that moves the specimen under the stylus. Type IV gypsum samples (Silky Rock, Whip Mix Corp, Louisville, Ky.) were made with 1 mm vertical, 45-degree angled ridges used to represent crown margins. Samples (n = 30) were separated 1 hour after pouring and allowed to bench set for 24 hours or 7 days. Three loads (15, 50, and 75 g) were used, and the resulting defect was evaluated after 5, 10, 15, or 20 cycles of loading. Changes in mass and volume were recorded.

RESULTS

At both 24 hours and 7 days, there was an increase in both mass and material volume loss with increasing load on the stylus (P<0.0001). There was no significant change in mass after 5 cycles of loading (P<0.05), but an increase in the volume loss occurred because of compaction of the walls of the defect (P<0.0001).

CONCLUSION

Under these conditions, the increasing load had a greater effect than the number of load cycles on gypsum brittle fracture.

Effect of variable light intensity on composite shrinkage

STATEMENT OF PROBLEM

Polymerization shrinkage is a critical limitation of dental composites and may contribute to postoperative pain, tooth fracture, microleakage, and secondary caries. Polymerization with high-intensity light sources has been related to increased depth of cure and improved mechanical properties. However, high-intensity light initiation has also been associated with greater polymerization shrinkage.

PURPOSE

The purpose of this study was to investigate the effect of sequentially increasing light intensity on the polymerization shrinkage of 2 composites, a hybrid and a microfil. A Knoop hardness test was used to evaluate effectiveness of the cure with each intensity increase.

MATERIAL AND METHODS

Four groups of 12 samples were measured for polymerization shrinkage by using a linometer. Light intensity curing sequences were as follows: full-intensity control (100% intensity for 40 seconds), low-intensity control (25% intensity for 40 seconds), test group 1 (25% intensity for 20 seconds, 50% for 10 seconds, 100% for 10 seconds), and test group 2 (25% intensity for 10 seconds, 50% for 10 seconds, 100% for 20 seconds). Statistical comparisons were made using a 1-factor ANOVA and a Tukey multiple comparisons test within each material.

RESULTS

Results showed a significant difference (P<. 05) in mean linear shrinkage between the full-intensity control group and the other 3 sequences for both composites. No difference existed within the other 3 groups for either composite. Knoop hardness was similar for the full-intensity control and test group 2. The low-intensity control group and test group 1 were also similar but significantly lower.

CONCLUSION

Curing composites for 10 seconds at 25% intensity, 10 seconds at 50%, and 20 seconds at 100% significantly reduced polymerization shrinkage while not compromising depth of cure.

Effect of pressure of helium, argon, krypton, and xenon on the porosity, microstructure, and mechanical properties of commercially pure titanium castings

STATEMENT OF PROBLEM

Porosity is a frequently observed casting defect in dental titanium alloys.

PURPOSE

This study evaluated the effect of pressure of helium, argon, krypton, and xenon on the porosity, microstructure, and mechanical properties of commercially pure titanium (cp Ti) castings.

MATERIAL AND METHODS

Eight groups (A-H) of 16 rectangular wax patterns each (30 mm in length, 3 mm in width, and 1 mm in depth) were prepared. The wax patterns were invested with a magnesia-based material and cast with cp Ti (grade II). Groups A, C, E, and G were cast under a pressure of 1 atm, and groups B, D, F, and H were cast under a pressure of 0.5 atm of He, Ar, Kr, and Xe, respectively. The extent of the porosity of the cast specimens was determined radiographically and quantified by image analysis. Three specimens of each group and 3 cylinders of the as-received cp Ti used as a reference were embedded in resin and studied metallographically after grinding, polishing, and chemical etching. These surfaces were used for determination of the Vickers hardness (VHN) as well. Eight specimens from each group were fractured in the tensile mode, and the 0.2% yield strength, fracture stress, and percentage elongation were calculated. Porosity was analyzed with 2-way ANOVA and the Newman-Keuls multiple range test. VHN measurements and tensile properties for specimen groups were compared with 1-way ANOVA and the Newman-Keuls multiple range test (95% significance level).

RESULTS

The porosity levels per group were (%): A = 5.50 +/- 4.34, B = 0.77 +/- 1.27, C = 2.44 +/- 3.68, D = 0.06 +/- 0.12, E-H = 0. Two-way ANOVA showed that there was no detectable interaction (P<.05) between gas type and applied pressure. Metallographic examination revealed no differences in microstructure among the groups studied. A finer grain size was observed in all cast groups compared with the original cp Ti. The VHN of the as-received cp Ti was significantly greater than all the cast groups tested. Groups cast under He showed the highest VHN, yield strength, and fracture stress. No significant differences were found in percentage elongation values among the groups.

CONCLUSION

Porosity and mechanical properties of cp Ti castings are dependent on the gas type and pressure, whereas the microstructure remains unaffected.

Bond strength of three porcelains to two forms of titanium using two firing atmospheres

STATEMENT OF PROBLEM

Problems with casting and porcelain bonding are encountered when titanium is used in metal-porcelain restorations. The oxidation characteristics of titanium are the main problem. The bonding mechanisms in titanium-porcelain systems are complex and poorly understood.

PURPOSE

An in vitro investigation was performed to evaluate the bonding characteristics of 3 titanium-porcelain systems in various firing conditions.

MATERIAL AND METHODS

This study evaluated the bonding strength of 3 commercial titanium porcelains fired in a vacuum and in an argon atmosphere to cast and noncast commercially pure titanium, using a 3-point bending test according to DIN 13927 and SEM with energy-dispersive spectrometry analysis. The results were compared with an Ni-Cr alloy and a conventional porcelain that was chosen as a control.

RESULTS

The Ni-Cr-conventional porcelain system fired in an argon atmosphere had significantly higher bond strength than the other systems (P<.001). In addition, the bond strength of the titanium-spark erosion-Noritake Ti22 combination, fired in an argon atmosphere, was significantly higher than the other titanium-porcelain groups, which had results similar to those obtained with the vacuum-fired, Ni-Cr-conventional porcelain and argon-fired titanium-cast-Noritake Ti22 groups. On the other hand, the bond strength of the titanium-TiBond and titanium-Vita Titankeramik groups was below the lower limit value in the DIN 13927 standard for the 3-point bending test (25 MPa). Although the results of the Duncan multiple range test showed that firing in an argon atmosphere did not affect the bond strength of the titanium-Vita Titankeramik groups, the titanium-spark erosion-TiBond group, or the titanium-cast-Noritake Ti22 group, argon firing improved the bond strengths of the Ni-Cr-conventional porcelain group, the titanium-cast-TiBond group, and the titanium-spark erosion-Noritake Ti22 porcelain group. It was also found that there were no significant differences between the bond strengths of cast and non-cast titanium groups; an exception was the titanium TiBond groups in which the porcelain was fired in a vacuum.

CONCLUSION

The oxide layer produced on titanium was considered to have a potentially adverse effect on titanium-porcelain bonding. It was also concluded that matching the titanium-porcelain combination is the main determinant for optimal bonding. Firing in an argon atmosphere that limited the oxidation of titanium improved the titanium-porcelain bond in some of the groups.

Effect of a new metal primer on the bond strength between a resin cement and two high-noble alloys

STATEMENT OF PROBLEM

With the development of new adhesive resin cements, the question of surface treatment of noble metal castings with primers has become an important issue.

PURPOSE

This study compared the tensile bond strength and its durability of a new metal primer (Alloy Primer, Kuraray) to 2 noble metal alloys (Au-Ag-Cu-Pt and Au-Pt-Pd-Ag-In).

MATERIAL AND METHODS

Sixty cast disk specimens of each alloy were polished, grit blasted with 50 microm Al(2)O(3), and ultrasonically cleaned in 96% isopropanol. Then, they were either nonprimed or primed only with the Alloy Primer or Alloy Primer combined with ED Primer (Kuraray). Plexiglas tubes filled with self-curing composite resin (Clearfil FII, Kuraray) were bonded to the metal samples with the use of an alignment apparatus and a self-curing luting cement (Panavia 21 Ex). The samples were stored in water, either for 3 days with no thermal cycling or for 150 days with 37,500 thermal cycles. After the different storage conditions, the tensile bond strengths of the specimens were determined.

RESULTS

The mean bond strengths increased over storage time for all groups, except for the grit-blasted Au-Pt-Pd-Ag-In group. However, only in the grit-blasted and the primed groups for the Au-Ag-Cu-Pt alloy was this increase significantly different (P<.01). After 150 days of storage, the mean bond strength to Au-Ag-Cu-Pt alloy was 38.8 MPa without priming, whereas it was 40.6 to 40.8 MPa with the use of the primers. After the same time, the mean bond strength to the Au-Pt-Pd-Ag-In alloy was 20.6 MPa without priming, whereas it was 31. 9 to 37.8 MPa with the use of the primers. When comparing the different bonding methods and different storage times for the alloys, the superiority of the usage of both primers in combination was determined. Conclusion. The tested Alloy Primer significantly improved the bond strength of the dental adhesive resin cement (Panavia 21 Ex) to noble alloys. However, this effect depended on the alloy composition and was much greater for the Au-Pt-Pd-Ag-In alloy than for the Au-Ag-Cu-Pt alloy.

Ultra-low wear rates for rigid-on-rigid bearings in total hip replacements

With the increased clinical interest in metal-on-metal and ceramic-on-ceramic total-hip replacements (THRs), the objective of this hip simulator study was to identify the relative wear ranking of three bearing systems, namely CoCr-polyethylene (M-PE), CoCr-CoCr (M-M) and ceramic-on-ceramic (C-C). Volumetric wear rates were used as the method of comparison. The seven THR groupings included one M-PE study, two M-M studies and four C-C studies. Special emphasis was given to defining the 'run-in' phase of accelerated wear that rigid-on-rigid bearings generally exhibit. The hypothesis was that characterization of the run-in and steady state wear phases would clarify not only the tribological performance in vitro but also help correlate these in vitro wear rates with the 'average' wear rates measured on retrieved implants. The implant systems were studied on multichannel hip simulators using the Paul gait cycle and bovine serum as the lubricant. With 28 mm CoCr heads, the PE (2.5 Mrad/N2) wear rates averaged 13 mm3/10(6) cycles duration. This was considered a low value compared with the clinical model of 74 mm3/year (for 28 mm heads). Our later studies established that this low laboratory value was a consequence of the serum parameters then in use. The mating CoCr heads (with PE cups) wore at the steady state rate of 0.028 mm3/10(6) cycles. The concurrently run Metasul M-M THRs wore at the steady state rate of 0.119 mm3/10(6) cycles with high-protein serum. In the second Metasul M-M study with low-protein serum, the THR run-in rate was 2.681 mm3/10(6) cycles and steady state was 0.977 mm3/10(6) cycles. At 10 years, these data would predict a 70-fold reduction in M-M wear debris compared with the clinical PE wear model. All M-M implants exhibited biphasic wear trends, with the transition point at 0.5 x 10(6) cycles between run-in and steady state phases, the latter averaging a 3-fold decrease in wear rate. White surface coatings on implants (coming from the serum solution) were a confounding factor but did not obscure the two orders of magnitude wear performance improvement for CoCr over PE cups. The liners in the alumina head-alumina cup combination wore at the steady state rate of 0.004 mm3/10(6) cycles over 14 x 10(6) cycles duration (high-protein serum). The zirconia head-alumina cup THR combination wore at 0.174 and 0.014 mm3/10(6) cycles for run-in and steady state rates respectively (low-protein serum). The zirconia head and cup THR combination wore slightly higher initially with 0.342 and 0.013 mm3/10(6) cycles for run-in and steady state rates respectively. Other wear studies have generally predicted catastrophic wear for such zirconia-ceramic combinations. It was noted that the zirconia wear trends were frequently masked by the effects of tenacious white surface coatings. It was possible that these coatings protected the zirconia surfaces somewhat in this simulator study. The experimental ceramic Crystaloy THR had the highest ceramic run-in wear at 0.681 mm3/10(6) cycles and typical 0.016 mm3/10(6) cycles for steady state. Since these implants represented the first Crystaloy THR sets made, it was likely that the surface conditions of this high-strength ceramic could be improved in the future. Overall, the ceramic THRs demonstrated three orders of magnitude wear performance improvement over PE cups. With zirconia implants, while the cup wear was sometimes measurable, head wear was seldom discernible. Therefore, we have to be cautious in interpreting such zirconia wear data. Identifying the run-in and steady state wear rates was a valuable step in processing the ceramic wear data and assessing its reliability. Thus, the M-M and C-C THRs have demonstrated two to three orders of reduction in volumetric wear in the laboratory compared with the PE wear standard, which helps to explain the excellent wear performance and minimal osteolysis seen with such implants at retrieval operations.