Effects of Particle Abrasion Media and Pressure on Flexural Strength and Bond Strength of Zirconia.

OBJECTIVES: To compare the effects of particle abrasion medium and pressure on shear bond strength and biaxial flexural strength of three generations of zirconia (Lava Frame, Lava Plus, and Lava Esthetic) with the goal of optimizing the bond to zirconia. METHODS: 280 discs (14 mm diameter; 1 mm thickness) of each zirconia were milled and sintered. Specimens of each material were randomly distributed into 14 groups (n=20); half were tested for shear bond strength and half were tested for biaxial flexural strength. The specimens were particle abraded on one surface by 2 different media (50 µm alumina particles or 50 µm glass beads) for 10 seconds at three different pressures (15, 30, and 45 psi or 0.1, 0.2, 0.3 MPa). Untreated specimens served as positive control. A tube (1.50 mm diameter) filled with dual cured resin cement (Panavia SA) was placed onto the surface and light cured. Specimens were stored in water (37°C for 24 hours) and shear bond strength was measured in a universal testing machine (Instron). Biaxial flexural strength of each specimen was measured according to ISO 6872. Shear bond strength and biaxial flexural strength were compared individually with a 2-way analysis of variance (ANOVA) for factors surface treatment and zirconia composition. RESULTS: Significant differences were seen between surface treatments (p<0.01), zirconia composition (p<0.01) and their interaction (p<0.01) for both bond strength and flexural strength. With alumina particle abrasion, higher pressure produced higher bonds for Lava Frame and Lava Plus zirconia while the bond of Lava Esthetic declined with increased pressure. Higher pressure (>0.2 MPa or 30 psi) with alumina decreased biaxial flexural strength with Lava Esthetic zirconia. CONCLUSIONS: Particle abrasion with alumina produced a significantly better combination of bond strength while maintaining biaxial strength of three zirconia materials than particle abrasion with glass beads. The bond strength also depended upon the pressure of particle abrasion and the generation of zirconia used.

Questions for assessing higher-order cognitive skills: it's not just Bloom's.

We present an exploratory study of biologists' ideas about higher-order cognition questions. We documented the conversations of biologists who were writing and reviewing a set of higher-order cognition questions. Using a qualitative approach, we identified the themes of these conversations. Biologists in our study used Bloom's Taxonomy to logically analyze questions. However, biologists were also concerned with question difficulty, the length of time required for students to address questions, and students' experience with questions. Finally, some biologists demonstrated an assumption that questions should have one correct answer, not multiple reasonable solutions; this assumption undermined their comfort with some higher-order cognition questions. We generated a framework for further research that provides an interpretation of participants' ideas about higher-order questions and a model of the relationships among these ideas. Two hypotheses emerge from this framework. First, we propose that biologists look for ways to measure difficulty when writing higher-order questions. Second, we propose that biologists' assumptions about the role of questions in student learning strongly influence the types of higher-order questions they write.

Bone properties surrounding hydroxyapatite-coated custom osseous integrated dental implants.

Calcium phosphate (hydroxyapatite or HA) coatings have been applied to Custom Osseous Integrated Implants (COIIs) to improve the quality of the bone-implant integration, yet little is known concerning the biomechanical properties of bone surrounding the HA-coated implants in humans over the long term. The purpose of this study was to characterize the mechanical and histomorphometric properties of the bone along the implant interface. Specimens were prepared from three similar mandibular implants that were functional in three female patients for about 11 years. Histomorphometric analyses showed bone-implant contact averaging 75% for all specimens. Area coverage of residual HA-coating ranged from 52 to 70%. When compared with previous studies, these results show a relatively high percentage of residual HA after a decade in vivo. Nanoindentation showed similar average values of hardness and modulus (p = 0.53 and p = 0.56, respectively) comparing bone adjacent to residual HA-coating and regions where the coating was absent. The elastic modulus was significantly lower for bone near the bone-implant interface (<200 µm) as compared with bone distant (>1000 µm) from the interface (p = 0.05), thereby reflecting different properties of the bone near these interfaces. Backscattered electron imaging showed darker gray levels which indicated decreased mineral content in bone adjacent to the implant, consistent with the nanoindentation results.

Human postmortem device retrieval and analysis--orthopaedic, cardiovascular, and dental systems.

On the basis of decades of analyzing implant devices, tissues, and clinical records from revision surgical explants (called device failure), studies now include postmortem donors and in situ conditions (called success). A key issue has been information exchange from an interdisciplinary team where basic physical and biological studies complement details of the clinical conditions for each device. Overall, the summary information has shown that most revisions were based on factors associated with the patient health, disease, and compliance, with few outcomes directly correlated with technology and device-specific factors. However, because of the large numbers of devices implanted annually (millions), any sampling that reveals adverse circumstances could result in a high level of importance and the need for additional studies of this type. Experience from prior retrieval and analysis demonstrates significant value where peer reviewed results from investigations have altered the discipline and have improved the quality and longevity of health care associated with implanted devices. This report summarizes completed and ongoing studies of cardiovascular, dental, and orthopaedic systems. Endovascular stents from autopsies showed damage including fretting and corrosion from overlapping and intersecting conditions, plus some corrosion and element transfers to tissues from individual stents. Studies are proposed to increase numbers to evaluate clinical significance. Dental implants from postmortem donors that functioned more than 10 years provided evaluations of cobalt alloy devices and calcium phosphate bone graft substitutes originally investigated in the 1970s. Tissue integration and stability correlated with data from prior laboratory in vitro and in vivo investigations. Studies of articulation and fixation from orthopaedic total joint arthroplasties showed some limitations related to surface changes of YTZ zirconia, specific damage due to implantation procedures, which led to modified instrumentation and techniques, and several examples of conditions leading to longer-term device-to-bone fixation. These types of multidisciplinary studies are continuing.

Predictors of death or bronchopulmonary dysplasia in preterm infants with respiratory failure.

OBJECTIVES: To identify the variables that predict death/physiologic bronchopulmonary dysplasia (BPD) in preterm infants with severe respiratory failure. STUDY DESIGN: The study was a secondary analysis of data from the NICHD Neonatal Research Network trial of inhaled nitric oxide (iNO) in preterm infants. Stepwise logistic regression models and Classification and Regression Tree (CART) models were developed for the outcome of death or physiologic BPD (O(2) at 36 weeks post-menstrual age). RESULT: Death and/or BPD was associated with lower birth weight, higher oxygen requirement, male gender, additional surfactant doses, higher oxygenation index and outborn status, but not the magnitude of response in PaO(2) to iNO. The positive predictive value of the CART model was 82% at 95% sensitivity. CONCLUSIONS: The major factors associated with death/BPD were an increased severity of respiratory failure, lower birth weight, male gender and outborn status, but not the magnitude of initial response to iNO.

Inhaled nitric oxide in infants >1500 g and <34 weeks gestation with severe respiratory failure.

OBJECTIVE: Inhaled nitric oxide (iNO) use in infants >1500 g, but <34 weeks gestation with severe respiratory failure will reduce the incidence of death and/or bronchopulmonary dysplasia (BPD). STUDY DESIGN: Infants born at <34 weeks gestation with a birth weight >1500 g with respiratory failure were randomly assigned to receive placebo or iNO. RESULTS: Twenty-nine infants were randomized. There were no differences in baseline characteristics, but the status at randomization showed a statistically significant difference in the use of high-frequency ventilation (P=0.03). After adjustment for oxygenation index entry strata, there was no difference in death and/or BPD (adjusted relative risk (RR) 0.80, 95% confidence interval (CI) 0.43 to 1.48; P=0.50), death (adjusted RR 1.26, 95% CI 0.47 to 3.41; P=0.65) or BPD (adjusted RR 0.40, 95% CI 0.47 to 3.41; P=0.21). CONCLUSIONS: Although sample size limits our ability to make definitive conclusions, this small pilot trial of iNO use in premature infants >1500 g and <34 weeks with severe respiratory failure suggests that iNO does not affect the rate of BPD and/or death.

Effects of early erythropoietin therapy on the transfusion requirements of preterm infants below 1250 grams birth weight: a multicenter, randomized, controlled trial.

OBJECTIVES: Infants of

The precautionary principle in environmental science.

Environmental scientists play a key role in society's responses to environmental problems, and many of the studies they perform are intended ultimately to affect policy. The precautionary principle, proposed as a new guideline in environmental decision making, has four central components: taking preventive action in the face of uncertainty; shifting the burden of proof to the proponents of an activity; exploring a wide range of alternatives to possibly harmful actions; and increasing public participation in decision making. In this paper we examine the implications of the precautionary principle for environmental scientists, whose work often involves studying highly complex, poorly understood systems, while at the same time facing conflicting pressures from those who seek to balance economic growth and environmental protection. In this complicated and contested terrain, it is useful to examine the methodologies of science and to consider ways that, without compromising integrity and objectivity, research can be more or less helpful to those who would act with precaution. We argue that a shift to more precautionary policies creates opportunities and challenges for scientists to think differently about the ways they conduct studies and communicate results. There is a complicated feedback relation between the discoveries of science and the setting of policy. While maintaining their objectivity and focus on understanding the world, environmental scientists should be aware of the policy uses of their work and of their social responsibility to do science that protects human health and the environment. The precautionary principle highlights this tight, challenging linkage between science and policy.

Comparison of costs and referral rates of 3 universal newborn hearing screening protocols.

OBJECTIVE: To investigate the costs and referral rates of 3 universal newborn hearing screening programs: transient evoked otoacoustic emissions (TEOAE), automated auditory brainstem response (AABR), and a combination, two-step protocol in which TEOAE and AABR are used. STUDY DESIGN: Clinical outcomes (referral rates) from 12,081 newborns at 5 sites were obtained by retrospective analysis. Prospective activity-based costing techniques (n = 1056) in conjunction with cost assumptions were used to analyze the costs based on an assumed annual birth rate of 1500 births. RESULTS: Referral rates differed significantly among the 3 screening protocols (AABR, 3.21%; two-step, 4.67%; TEOAE, 6.49%; P <.01), with AABR achieving the best referral rate at discharge. Although AABR had the lowest referral rate at discharge and the highest pre-discharge costs, the total pre- and post-discharge costs per infant screened (AABR, $32.81; two-step, $33.05; TEOAE, $28.69) and costs per identified child (AABR, $16,405; two-step, $16,527; TEOAE, $14,347) were similar among programs. CONCLUSION: Although AABR incurs higher costs during pre-discharge screening, it has lower referral rates than either the TEOAE or two-step program. As a result, the total costs of newborn hearing screening and diagnosis are similar among the 3 methods studied.

Radioimaging of implants in rats using Tc-99m-MDP.

Radiopharmaceutical isotopes are widely used clinically to detect tumors of osteogenic origin. One example is Technetium-99m methylene diphosphonate (Tc-99m-MDP). When viewed with a gamma camera, the concentration of the isotope (increased gamma activity) indicates an area of increased bone activity. This technology provides an opportunity to measure bone growth around implants in vivo. The purpose of this study was to measure Tc-99m-MDP activity around titanium alloy implants placed in the tibiae of rats. Some implant sites were treated with a growth factor; other sites served as controls. The hypothesis tested was that implants placed with a growth factor would have greater associated Tc-99m-MDP activity. Twelve adult male Sprague-Dawley rats were anesthetized and surgical access to the medial proximal tibiae was obtained. Titanium alloy screw implants were placed in six animals along with 65 microgram of acidic fibroblast growth factor (FGF-1); the other six animals received implants only and served as controls. After five days, rats were injected with 1500 microCi of Tc-99m-MDP. After 3 hours, rats were imaged with a gamma camera. The Tc-99m-MDP intensity associated with each implant was quantified and the means for each group were compared using ANOVA. Implants treated with FGF-1 demonstrated significantly more Tc-99m-MDP activity than implants alone. This suggests that Tc-99m-MDP analysis may be a useful tool for determining bone growth around implants in laboratory animals in vivo.

Analysis of Ti-6Al-4V implants placed with fibroblast growth factor 1 in rat tibiae.

Titanium-aluminum-vanadium (Ti-6Al-4V) implants were placed in the tibiae of 32 rats (male Sprague-Dawley, 350 g) to examine healing and bone response. Half of the implants were treated with fibroblast growth factor 1 (FGF-1) delivered in an activated fibrinogen matrix. Animals were injected with a radiopharmaceutical imaging agent, technetium-99m-methylene diphosphonate (Tc-99m-MDP), which concentrates in bone, especially in areas of higher osteoblastic activity. Binding of Tc-99m-MDP to the implant was detected in vivo by Anger gamma camera imaging. Fourteen days after implant surgery, specimens were recovered and prepared for histomorphometric analysis. Histologic examination revealed that samples treated with FGF-1 demonstrated significantly greater amounts of bone-to-implant contact (P < .05) compared to controls. Also, FGF-1-treated samples showed significantly greater amounts of bone (percent volume) adjacent to implants (P < .005). These findings were supported by analyses of the non-invasive Tc-99m-MDP images, which demonstrated significantly greater uptake of Tc-99m-MDP adjacent to FGF-1-treated implants (P < .05). Results of the experiments supported the hypothesis that FGF-1 could increase bone production around implants in a rat model.

Strength analysis of Le Fort I osteotomy fixation: titanium versus resorbable plates.

PURPOSE: The purpose of this study was to compare the biomechanical characteristics of metallic and polymeric fixation systems using a 3-dimensional skull model to simulate clinical conditions of maxillary advancement and loading. MATERIAL AND METHODS: Standard titanium, prebent titanium, and resorbable plates and mesh were applied to surgically altered polyurethane skulls. The constructs were loaded using an Instron machine (Instron Inc, Canton, MA) in anterior-posterior (AP) and inferior-superior (IS) directions. The load displacement, load to failure, and deformation magnitudes and modes of failure were recorded. Statistical studies included analysis of variance (ANOVA) at P <.05. RESULTS: Elastic stiffness was different among groups in the AP direction, but no significant difference was found in the IS direction. The IS loading direction load displacement (stiffness) was significantly greater than that on AP loading. The maximum load for permanent deformation was larger in the AP direction, while the maximum load for breaking was larger in the IS direction. CONCLUSION: The overall evaluation of the model and test analyses supported the relative value of this in vitro system and study procedure. All systems showed load capacity magnitudes above 285 N (64 lbs) and more elastic resistance in the IS direction. The resorbable systems showed lower elastic stiffness compared with the titanium systems, but they appear to be adequate for fixation and withstanding the forces of mastication.

Implants in regenerated bone in a primate model.

BACKGROUND: Earlier publications from our laboratory described the use of guided bone regeneration to fill large bone voids in the mandible created through en bloc resection in primates. The present report describes placement of implants into the regenerated bone with subsequent prostheses construction and loading. METHODS: Lesions were created in the mandibles of 9 monkeys in a standardized mandibular defect of 8 x 19 mm. Reinforced expanded polytetrafluoroethylene membranes were placed in the animals and held in place with mini screws and sutures for anywhere from 1 to 12 months. No material was added to the defect. In each animal a root-form implant was placed 12 mm distal to the abutment teeth into the regenerated bone and was loaded with a prosthesis for 12 months. These implants were compared to original implants placed in the same monkeys years earlier in the same location in non-regenerated bone. Digital radiology and histomorphometry are described. RESULTS: The results show that root-form implants placed in regenerated bone show the same radiological and histomorphometric characteristics as in normal bone when loaded. In addition, the percentage of bone contact with implants seen in regenerated bone versus non-regenerated bone is the same when both are loaded (65 +/- 13% SD in regenerated bone versus 59 +/- 15% SD in non-regenerated bone). CONCLUSIONS: In a primate model root-form implants placed in regenerated bone and prosthetically loaded show no difference when compared to root-form implants placed in non-regenerated bone and prosthetically loaded.

Very low birth weight outcomes of the National Institute of Child health and human development neonatal research network, January 1995 through December 1996. NICHD Neonatal Research Network.

OBJECTIVES: To determine the mortality and morbidity for infants weighing 401 to 1500 g (very low birth weight [VLBW]) at birth by gestational age, birth weight, and gender. STUDY DESIGN: Perinatal data were collected prospectively on an inborn cohort from January 1995 through December 1996 by 14 participating centers of the National Institute of Child Health and Human Development Neonatal Research Network and were compared with the corresponding data from previous reports. Sociodemographic factors, perinatal events, and the neonatal course to 120 days of life, discharge, or death were evaluated. RESULTS: Eighty four percent of 4438 infants weighing 501 to 1500 g at birth survived until discharge to home or to a long-term care facility (compared with 80% in 1991 and 74% in 1988). Survival to discharge was 54% for infants 501 to 750 g at birth, 86% for those 751 to 1000 g, 94% for those 1001 to 1250 g, and 97% for those 1251 to 1500g. The incidence of chronic lung disease (CLD; defined as receiving supplemental oxygen at 36 weeks' postmenstrual age; 23%), proven necrotizing enterocolitis (NEC; 7%), and severe intracranial hemorrhage (ICH; grade III or IV; 11%) remained unchanged between 1991 and 1996. Furthermore, 97% of all VLBW infants and 99% of infants weighing <1000 g at birth had weights less than the 10th percentile at 36 weeks' postmenstrual age. Mortality for 195 infants weighing 401 to 500 g was 89%, with nearly all survivors developing CLD. Mortality in infants weighing 501 to 600 g was 71%; among survivors, 62% had CLD, 35% had severe ICH, and 15% had proven NEC. CONCLUSIONS: Survival for infants between 501 and 1500 g at birth continued to improve, particularly for infants weighing <1000 g at birth. This improvement in survival was not associated with an increase in major morbidities, because the incidence of CLD, proven NEC, and severe ICH did not change. However, poor postnatal growth remains a major concern, occurring in 99% of infants weighing <1000 g at birth. Mortality and major morbidity (CLD, severe ICH, and NEC) remain high for the smallest infants, particularly those weighing <600 g at birth.

Medical devices, health care, and consensus standards.

ASTM Committee F04 on Medical and Surgical Materials and Devices has been creating standards for this field since 1962. Dr. Jack Lemons provides a quick overview of the past, present, and future of this committee.

Guided bone regeneration of large mandibular defects in a primate model.

BACKGROUND: An earlier publication from our laboratory described the use of guided bone regeneration to fill large bone voids in the mandible created through en bloc resection in primates. The present report is an embellishment of this paper and describes bone regeneration experiments in 18 adult male Macaca mulatta monkeys to determine how long membranes must be in position to promote guided bone regeneration. METHODS: Thirty-six lesions were created in the mandibles of 18 monkeys in a standardized mandibular defect of 8 x 19 mm. Reinforced ePTFE membranes were placed in the animals and held in place with mini screws and sutures for anywhere from 1 to 12 months. No material was added to the defect. In addition to clinical studies, digital subtraction radiology and fluorescent labeling with tetracycline and histomorphometry are described. RESULTS: The results indicate that no bone gain was observed in membranes exposed for 1 month or less, but bone gain (approximately well over 90% of defects) was observed at 12 months when membranes were left in situ for 2 to 12 months (P <0.0001). No significant difference in the amount of bone gained at 12 months was observed for membranes left in place for intervals ranging from 2 to 12 months. A significant correlation between the amount of bone gain observed at 3 and 12 months was observed (P <0.0001). CONCLUSIONS: Data therefore suggest that membranes left in situ for 1 month or less result in minimal bone gain compared with membranes left in place from 2 to 12 months. In addition, labeling and stained sections clearly showed that the bone produced after 2 months of membrane placement is mature.

Sex differences in outcomes of very low birthweight infants: the newborn male disadvantage.

OBJECTIVE: To determine the differences in short term outcome of very low birthweight infants attributable to sex. METHODS: Boys and girls weighing 501-1500 g admitted to the 12 centres of the National Institute of Child Health and Human Development Neonatal Research Network were compared. Maternal information and perinatal data were collected from hospital records. Infant outcome was recorded at discharge, at 120 days of age if the infant was still in hospital, or at death. Best obstetric estimate based on the last menstrual period, standard obstetric factors, and ultrasound were used to assign gestational age in completed weeks. Data were collected on a cohort that included 3356 boys and 3382 girls, representing all inborn births from 1 May 1991 to 31 December 1993. RESULTS: Mortality for boys was 22% and that for girls 15%. The prenatal and perinatal data indicate few differences between the sex groups, except that boys were less likely to have been exposed to antenatal steroids (odds ratio (OR) = 0.80) and were less stable after birth, as reflected in a higher percentage with lower Apgar scores at one and five minutes and the need for physical and pharmacological assistance. In particular, boys were more likely to have been intubated (OR = 1.16) and to have received resuscitation medication (OR = 1.40). Boys had a higher risk (OR > 1.00) for most adverse neonatal outcomes. Although pulmonary morbidity predominated, intracranial haemorrhage and urinary tract infection were also more common. CONCLUSIONS: Relative differences in short term morbidity and mortality persist between the sexes.

Enhanced growth of preterm infants fed a new powdered human milk fortifier: A randomized, controlled trial.

OBJECTIVE: A prospective, double-blind, randomized, controlled trial was conducted to evaluate the growth and nutritional status of preterm infants receiving preterm human milk supplemented with a newly formulated powdered human milk fortifier (HMF), study fortifier (SF), or a powdered commercial HMF (CF). METHODS: Infants (n = 144) with a birth weight

Modulation of mechanical properties in multiple-component tissue adhesives.

In vitro, ex vivo, and in vivo studies were performed to investigate the effect of mixing upon the mechanical properties of a two-component tissue adhesive. The hypothesis investigated was that a more complete mixing of the two components would yield an increase in the mechanical performance of the adhesive. This in turn would be demonstrated by improved outcomes in models of clinical sealant application. In vitro stereological analysis of tissue adhesive mixed and delivered by several different applicators demonstrated variation in the amount of mixing provided by each type of delivery system. Ex vivo tensile adhesive strength showed that there was a correlation between the amount of mixing and bonding strength; that is, more thorough mixing demonstrated higher adhesive strength. No significant difference was seen, however, between the different applicator types and impact on in vivo dermal incisional closure strength. There was a correlation, though, in amount of mixing and in vivo hemostasis. In a rabbit spleen incision model, a more thoroughly mixed sealant corresponded with a decrease in time to obtain complete hemostasis, as well as less sealant used. The effects of mixing on tissue-adhesive mechanical performance were influenced somewhat by the amount of mixing provided by the applicator. This effect, however, was dependent upon the sealant formulation and the type of in vivo application.

Bone response to titanium alloy implants placed in diabetic rats.

Although dental implants continue to provide consistent and predictable treatment options for most patients, some people with uncontrolled systemic disease may be denied implant treatment. Diabetes is one such disease. According to the U.S. Centers for Disease Control and Prevention, diabetes is a leading cause of blindness, kidney failure, and amputations of the lower extremities. These complications result from microvascular disturbances associated with diabetes. The effect of diabetes on the healing of titanium implants has not been well established. In this study of 32 rats, diabetes was induced in 16 animals by injection of streptozotocin (65 mg/kg); the remaining 16 animals served as controls. Titanium alloy implants were placed in the tibiae of all 32 rats using standard surgical techniques. Implants healed for 14 days. Blood samples were obtained for serum glucose, osteocalcin, and alkaline phosphatase analyses. Implants were retrieved and processed for histomorphometric analyses. Three quantities were measured using light microscopy, video capture, and computer analysis: percent osseointegration (i.e., linear bone interface), associated bone volume percent, and contact frequency. Diabetic animals demonstrated significantly less osseointegration than controls. However, bone volume percent in diabetic animals was about 4 times greater than controls. Biochemical analyses were mixed; diabetic animals demonstrated increased serum osteocalcin levels compared to controls but decreased alkaline phosphatase. Based on the results of this study, it was concluded that the bone response associated with titanium alloy implants in the tibiae of diabetic rats is uniquely different from controls.