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At least 1,621 records · Page 90Linked to original sources
PubMed1989

A stress-relieved resin-bonded fixed partial denture.

Reports of bonding failures with resin-bonded fixed partial dentures (commonly called the "Maryland Bridge") are common. Failures are due to individual tooth mobility as much as they are to bonding inadequacy. The incorporation of stress relievers in the design of resin-bonded fixed partial dentures has created a dramatic reversal in bonding failures.

Dental Abutments↗
PubMed1990

Total knee replacement: radiologic findings in failure of porous-coated metal-backed patellar component.

One technique for replacing the articular surface of the patella in total knee replacement is the use of a cementless porous-coated metal-backed polyethylene component. Anteroposterior, lateral, and Merchant or skyline radiographs in 10 cases of porous-coated metal-backed components that failed were evaluated for component alignment, component displacement, radiolucencies, loose beads, and integrity of the patellar component. Component failure was documented by surgery in all 10 cases. Seven cases of failure involved the patellar pegs or junction of the pegs with the metal backing and three cases involved the polyethylene portion. In the seven cases of peg-metal backing failure, three cases showed loose beads before failure and seven cases showed displacement of the metal backing at time of failure. All three cases of polyethylene failure showed narrowing or displacement of the polyethylene portion. Our experience shows that displacement of the metal backing, displacement of the polyethylene, and disruption of patellar pegs are seen in failed porous-coated metal-backed patellar components. Loose beads may be seen before peg-metal backing failure.

Humans↗
PubMed2006

Constipation as a reversible cause of ventriculoperitoneal shunt failure. Report of two cases.

Ventriculoperitoneal (VP) shunt failure is a common problem encountered by pediatric neurosurgeons. The majority of such failures are due to obstruction of the device. Conditions in which intraabdominal pressure is chronically elevated, such as pregnancy, have been associated with shunt failure. Chronic constipation may also result in abnormally elevated intraabdominal pressure and may be an underrecognized cause of distal VP shunt failure. The authors describe the cases of two children who presented with clinical and imaging evidence of VP shunt failure and who were also severely constipated. Treatment of their constipation resulted in both clinical and imaging-documented resolution of their shunt failure.

Child, Preschool↗
PubMedDate not supplied

Tensile stress in glass-ceramic crowns: effect of flaws and cement voids.

The objective of this study was to analyze the relative effect of loading site, occlusal thickness, ceramic flaws, elastic modulus of the cement, and voids in the cement layer on tensile stress that develops in molar glass-ceramic crowns under applied loads. Finite-element stress analyses were performed. Resin cement with a thickness of 0.05 mm was used. A central conical flaw (0.05 mm [diameter] x 0.05 mm) and a circular grooved flaw located under the cusp tips were included in all flaw cases. A void space confined within the occlusal region of the cement layer was also included in selected cases. For a ceramic thickness of 0.5 mm and a vertical distributed load applied at a distance of 1.3 mm from the vertical axis, the maximum tensile stresses were 100 MPa for a crown with flaws and a void, 87 MPa for a crown with no flaws and a void, and 75 MPa for a crown with flaws and no void. For a 1.5-mm-thick crown with flaws and a void, the tensile stress decreased to 22 MPa. When the load of 600 N was concentrated at the central point of the occlusal region, the peak tensile stress in a crown with flaws and no void was increased to 325 MPa. For the conditions analyzed in this study a large void in a flawed occlusal region of a thin molar crown (0.5 mm) is proposed as a mechanism of crown failure.

Crowns↗
PubMed1988

Shrinkage of centrifuged cement.

Two postulated mechanisms for the failure of prosthetic implants secured with bone cement are: failure of the cement itself, and loosening at the bone/cement interface. Failure rate with cement can be reduced by increasing the strength of the cement, and loosening can be reduced by minimizing cement shrinkage during polymerization. This paper shows that centrifuging cement to reduce porosity (and presumably increase strength) results in a substantial increase in cement shrinkage over uncentrifuged cement. A second set of experiments demonstrated that pressurization of cement to four atmospheres during polymerization resulted in tensile strengths comparable with those reported for centrifuged cement. Thus, the use of uncentrifuged bone cement, pressurized during polymerization, should minimize implant failure rates.

Atmospheric Pressure↗
PubMed1988

The correlation between the roentgenographic appearance and operative findings at the bone-cement junction of the socket in Charnley low friction arthroplasties.

In a series of 200 Charnley low friction arthroplasties revised for various reasons, the preoperative anteroposterior roentgenograms were categorized in terms of demarcation at the bone-cement interface of the socket and compared with the operative findings of movement at the bone-cement junction. All sockets showing no demarcation were found to be fixed soundly. Seven percent of the sockets showing demarcation of the outer one-third only were loose, and when two-thirds of the sockets were demarcated, 71% were loose. Ninety-four percent of the sockets with complete demarcation and all sockets that had migrated were found to be loose at revision. There is a definite correlation between roentgenographic demarcation and socket loosening. The more extensive the demarcation, the more likely it is that the socket is loose. Radiographic demarcation of the cemented socket is a prognostic sign for eventual failure.

Adult↗
PubMed1996

Stress corrosion cracking in Björk-Shiley convexo-concave prosthetic heart valves due to random in vivo electrochemical pulsing.

Welded downstream struts of Björk-Shiley Convexo-Concave heart valves show failure in vivo, but not in in vitro testing. A pyrolytic carbon pivoting disk occluder closes against a Haynes 25 alloy ring, which is electrochemically machined from solid with the upstream retaining struts. The weld area is de-alloyed, with residual porosity and carbide inclusions. The valve becomes a short-circuited electrochemical cell when fully open or closed. It is an aggressive chloride electrolyte, whose high pulsed flow (2 m/s) ensures that supply of oxygen-rich cathode reactant is not mass-transport-limited. During the flight of the occluder, the cell is randomly at open circuit. A random current pulse is applied to the metal parts on circuit closure. Failure is not from simple mechanical fatigue, but from stress-corrosion-cracking and erosion of the less noble weld area caused by these pulses. All welded valves of this type may be susceptible to ultimate in vivo failure.

Biocompatible Materials↗
PubMed2002

An association of silicone-gel breast implant rupture and fibromyalgia.

Silicone-gel breast implant rupture is common. Silicone-gel from ruptured implants may escape the scar capsule that forms around breast implants and become "extracapsular silicone." Our previously published study found that women with extracapsular silicone gel were at higher risk of reporting that they were diagnosed with fibromyalgia. There has been a limited number of studies addressing this association in the literature. Some studies addressing the issue of silicone breast implants and connective tissue disease specifically exclude patients with fibromyalgia from the sample or do not include the syndrome in the analysis. Case series describing fibromyalgia in patients with implants have been published, but many of these papers lack information on extracapsular silicone and are not representative because the patients are typically from referral populations. In addition, most studies do not have control groups of women without implants for comparison or do not distinguish between saline and silicone implants. Additional observational studies of women from nonreferral populations are necessary to validate an association. These studies should provide information on how the rupture is diagnosed, state whether the rupture extended beyond the capsule, and provide an appropriate control group for comparison. The findings from such studies may be important to physicians as they describe potential risks associated with implants to their patients. These findings should also be important for regulatory decision making on silicone-gel breast implants.

Breast Implants↗
PubMed2006

Improved mechanical reliability of the HeartMate XVE left ventricular assist system.

BACKGROUND: The HeartMate XVE left ventricular assist device is a valuable treatment option for patients with end-stage heart failure. During the past several years, the XVE has undergone a series of design enhancements to improve reliability. We compared the reliability of the two most recent design iterations of the XVE pump (stitch modification to the inflow valve assembly and new inflow valve housing redesign) to the earlier VE version. METHODS: A retrospective evaluation of device reliability was performed for 268 devices implanted in 245 patients (VE: n = 167 devices, 147 patients, implant dates October 16, 1998, to December 19, 2003; XVE: n = 101 devices, 98 patients, implant dates August 1, 2002, to April 14, 2004). RESULTS: Median duration of device support for the VE and XVE was 159 days (range, 0 to 1,206 days) and 229 days (range, 0 to 693 days), respectively (p = 0.495). Significantly fewer major device malfunctions occurred within the XVE group as compared with the VE group (6 versus 36, respectively; p = 0.0003). The number of major device malfunctions per patient-year of support for inflow valve dysfunction, bearing wear, and other failures for the VE and XVE were 0.2 versus 0.04 (p = 0.006), 0.16 versus 0.01 (p = 0.005), and 0.06 versus 0.04 (p = 1.000), respectively. The freedom from major device malfunction at 1 year was 76% +/- 6% for the VE and 97% +/- 2% for the XVE device (p < 0.001). The freedom from death as a result of major device malfunction at 1 year was 97% +/- 2% for the VE and 98% +/- 2% for the XVE (p = 0.698). CONCLUSIONS: Design enhancements to the HeartMate XVE have significantly reduced the incidence of major device malfunctions compared with the earlier VE model because of a reduction in failure modes from bearing wear and inlet valve dysfunction. Further follow-up is necessary to establish the long-term durability of the most recent XVE pump version.

Adolescent↗
PubMed2005

A comparative radiological assessment of polylactide pins over 3 years in vivo.

Biodegradable polylactide implants allow secure fixation of osteochondral fractures with minimal adverse effects. The goal of this prospective, randomized animal study was to show whether osteoconductive effects can be achieved through the development of poly-L/DL(70/30)lactide composite implants with 10% beta-tricalcium phosphate, and whether degradation can be positively influenced and adverse effects minimized using such implants. An additional goal was to clarify which radiological procedure is most suitable to observe the course of follow-up. Thirtysix medial femoral condyle osteotomies of sheep were fixed with either 3 poly-L/DL-lactide pins or 3 composite pins, and the pin canal widths were measured with conventional radiographs, with CT, MRI, and histologically after 3, 18, and 36 months. All fractures healed completely without displacement or clinically relevant complications. The pin canals dilated secondary to pin degradation at the 12th month, and then decreased in size later. At 36 months, the pins had microscopically disappeared, and the canals were filled with bone or scar tissue. There were no statistically significant differences between the pin-types. Poly-L/DL-lactide pins and composite C-pins are suitable for secure fixation of small osteochondral fractures. Osteoconductive effects of biocompatibility or osseous integration relating to composite development were not evident. Conventional radiography and computer tomography were suitable techniques for observation of pin canals. Due to frequently observed artifact, MRI was not suitable to observe the course of the implants.

Absorbable Implants↗