Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Equipment Failure Analysis”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed2000

The effect of repeated bonding on the shear bond strength of a composite resin orthodontic adhesive.

One of the problems clinicians face during treatment is bracket failure. This is usually the result either of the patient's accidentally applying inappropriate forces to the bracket or of a poor bonding technique. As a result, a significant number of teeth have to be rebonded in a busy orthodontic practice. The purpose of this study was to evaluate the effect of repeated bonding on the shear bond strength of orthodontic brackets. Fifteen freshly extracted human molars were collected and stored in a solution of 0.1% (wt/vol) thymol. The teeth were cleaned, polished, and etched with a 37% phosphoric acid gel. The brackets were bonded with the adhesive and light cured for 20 seconds. The teeth were sequentially bonded and debonded 3 times with the same composite orthodontic adhesive. At each time, all 15 teeth were debonded within a half hour after bonding to simulate the clinical condition at which a newly bonded bracket is attached to the arch wire. The results of the analysis of variance comparing the shear bond strength at the 3 debonding attempts indicated the presence of no significant differences among the 3 groups (P = .104). However, when the overall change in shear bond strength within each tooth was evaluated between debonding sequences 1 and 3, 10 teeth had a significant (P = .001) decrease (mean +/- SD, -4.6+/-2.5 MPa) in bond strength, whereas 5 teeth had a significant (P = .02) increase (mean +/- SD, 2.8+/-1.6 MPa). The present findings indicated that in general, the highest values for shear bond strength were obtained after the initial bonding. Rebonded teeth have significantly lower and inconsistent shear bond strength; ie, bond strength may further decrease or increase after the second debonding, and the changes in bond strength may be related to the changes in the morphologic characteristics of the etched enamel surface as a result of the presence of adhesive remnants.

Analysis of Variance↗
PubMedDate not supplied

Measurement of DNA biomarkers for the safety of tissue-engineered medical products, using artificial skin as a model.

To test the hypothesis that the process of tissue engineering introduces genetic damage to tissue-engineered medical products, we employed the use of five state-of-the-art measurement technologies to measure a series of DNA biomarkers in commercially available tissue-engineered skin as a model. DNA was extracted from the skin and compared with DNA from cultured human neonatal control cells (dermal fibroblasts and epidermal keratinocytes) and adult human fibroblasts from a 55-year-old donor and a 96-year-old donor. To determine whether tissue engineering caused oxidative DNA damage, gas chromatography/isotope-dilution mass spectrometry and liquid chromatography/isotope-dilution mass spectrometry were used to measure six oxidatively modified DNA bases as biomarkers. Normal endogenous levels of the modified DNA biomarkers were not elevated in tissue-engineered skin when compared with control cells. Next, denaturing high-performance liquid chromatography and capillary electrophoresis-single strand conformation polymorphism were used to measure genetic mutations. Specifically, the TP53 tumor suppressor gene was screened for mutations, because it is the most commonly mutated gene in skin cancer. The tissue-engineered skin was found to be free of TP53 mutations at the level of sensitivity of these measurement technologies. Lastly, fluorescence in situ hybridization was employed to measure the loss of Y chromosome, which is associated with excessive cell passage and aging. Loss of Y chromosome was not detected in the tissue-engineered skin and cultured neonatal cells used as controls. In this study, we have demonstrated that tissue engineering (for TestSkin II) does not introduce genetic damage above the limits of detection of the state-of-the-art technologies used. This work explores the standard for measuring genetic damage that could be introduced during production of novel tissue-engineered products. More importantly, this exploratory work addresses technological considerations that need to be addressed in order to expedite accurate and useful international reference standards for the emerging tissue-engineering industry.

Biomarkers↗
PubMed2004

Torsional fatigue and endurance limit of a size 30.06 ProFile rotary instrument.

AIM: To evaluate the torsional cyclic fatigue characteristics and specifically the endurance limit (EL) of a nickel-titanium rotary instrument. METHODOLOGY: Size 30.06 taper ProFile instruments were evaluated. The equipment was assembled according to the ANSI/ADA Specification No. 28. The motor was programmed to repeatedly rotate to a selected deflection angle (DA) and then return to zero (cycle). Testing started at 200 degrees and was continued at decreasing angles until 10(6) cycles were reached without instrument fracture. Ten instruments were tested at each DA. The mean log number of cycles to fracture and standard deviation were determined for each DA at which fracture occurred. The DA at which 10(6) cycles were reached without instrument fracture corresponded by definition to the EL. Analysis of variance and pairwise comparisons using Duncan's multiple range test were performed to detect significant differences among the mean log number of cycles of the different DA. Significance was determined at the 95% confidence level. RESULTS: Instruments cycled at larger DA consistently demonstrated fewer cycles to fracture than those cycled at smaller DA. The differences among the mean log number of cycles of the different DA were statistically significant (P < 0.001). Cycles of 10(6) were completed without instrument fracture at 2.5 degrees. CONCLUSIONS: A torsional fatigue profile was generated for a specific NiTi rotary instrument. The EL was 2.5 degrees.

Analysis of Variance↗
PubMedDate not supplied

Experimental and numerical predictions of the ultimate strength of a low-cost composite transtibial prosthesis.

Saito et al. (Modern Plastics 1997;74:175-7) have developed a low-cost transtibial prosthesis made of fiber-reinforced plastic (FRP). The prosthesis is comprised of an aluminum pylon, a cosmetic cover, and a constant cross-section composite foot into which aluminum supports are screwed to increase load-bearing capacity. Replacing these supports with a single integrated FRP stiffener significantly reduced manufacturing cost while providing high strength, great durability, and smooth walking. The optimal location and orientation of the proposed FRP stiffener were determined by finite element (FE) analysis. When a replica of this component was tested according to ISO standard 10328, the experimental prosthesis catastrophically failed under 6,600 N of force. Maximum percent error of strain between experimental and numerical results was 18.6%, showing good correlation between the two data sets. The optimized design provides sufficient strength and reduces the cost of manufacturing and thus can be used to replace the original design.

Artificial Limbs↗
PubMed1993

The Australian Incident Monitoring Study. Equipment failure: an analysis of 2000 incident reports.

Of the first 2000 incidents reported to the Australian Incident Monitoring Study, 177 (9%) were due to "pure" equipment failure according to pre-defined criteria. Of these 107 (60%) involved anaesthetic equipment, 42 (24%) involved monitors, 17 (10%) other theatre equipment and 11 (6%) the gas or electricity supply. Ninety-seven (55% of the 177) were potentially life-threatening; of these two-thirds would be detected by the array of monitors recommended by the Australian and New Zealand College of Anaesthetists and all but 9 of the remainder would be handled by application of the crisis management algorithm recommended elsewhere in this symposium. Of the 9 remaining, 2 were electrical shock, 3 overheating of a humidifier or blood warmer, 2 the unavailability of a spare laryngoscope and 1 the consequence of a power failure. Meticulous adherence to the equipment checking and monitoring guidelines of the Australian and New Zealand College of Anaesthetists and application of a suitable crisis management algorithm should protect the patient from potentially life-threatening equipment failure in virtually all cases except electric shock, power failure and overheating of warming devices.

Anesthesiology↗
PubMedDate not supplied

Cost analysis of equipment failure of a radiology department and possible choices about maintenance.

PURPOSE: Our aim was to evaluate the economic impact of equipment failures in a radiology department with a view to guiding maintenance policy decisions. MATERIAL AND METHODS: We assessed the negative economic impact caused by the interruption of activity of a radiodiagnostics section due to equipment failure, taking into account: the effects occurring during the first day of equipment down-time (assuming that the equipment failure occurs in the middle of the shift) and the effects during the following days until the repair of the failure; the effects occurring in the short- and long-term. To exemplify the negative impact of inactivity due to equipment failure, we chose three radiology sections with different levels of technological and operational complexity (chest radiology, gastrointestinal radiology and remote-controlled diagnostics). For each, we evaluated the loss of contribution margin and the idle capacity costs (short- and long-term impact). RESULTS: The negative economic effects were: for thoracic radiology, 496,77 Euro in the first day, and 30,99 Euro from the second day onwards; for gastrointestinal radiology, 526,40 Euro for the first day, and 730,39 Euro from the second day onwards; for remote-controlled diagnostics, 786,25 Euro for the first day, and 927,67 Euro from the second days onwards. DISCUSSION: Our results indicate that the level of idle capacity costs (mainly equipment and staff) increases with the complexity of the equipment, whereas the contribution margin appears to fluctuate, because the charges are state-imposed and do not vary with the complexity of equipment. Moreover, our analysis shows that if the workload of a broken machine can easily be assigned to an additional shift using another machine, losses are considerably reduced from the second day onwards. Once the negative economic impact of equipment failures has been evaluated, the second step is to choose the best kind of maintenance. CONCLUSIONS: A sound calculation of the economic impact of equipment failures is very useful for guiding the head of department and the hospital manager in deciding whether to purchase maintenance services (or a long-term guarantee) from the equipment manufacturer, to set up an auxiliary centre for maintenance and repair, or to purchase a third-party maintenance contract.

Costs and Cost Analysis↗
PubMed2004

Effect of fiber position and orientation on fracture load of fiber-reinforced composite.

OBJECTIVES: The aim of this study was to determine the effect of fiber position and orientation on the initial and final fracture loads of fiber-reinforced composite (FRC). METHODS: Test specimens made of two indirect particulate composites (BelleGlass HP, Kerr, Orange, CA) or (Targis, Ivoclar Vivadent, Amherst, NY) were reinforced with ultra high molecular weight polyethylene (UHMWPE) fiber ribbon (Connect, Kerr, Orange, CA), woven E-glass fibers (Vectris Frame, Ivoclar Vivadent, Amherst, NY) or unidirectional R-glass fibers (Vectris Pontic, Ivoclar Vivadent, Amherst, NY). Fibers were placed with different positions, orientations or geometry into the rhombic test specimens (2 x 2 x 25 mm3). Control specimens did not contain fiber reinforcement. The test specimens (n=6) were stored in distilled water for 1 week at 37 degrees C before testing in a three-point loading test to determine the initial and final fracture load values. RESULTS: Initial failure loads varied from 22.6 to 172.1 N. The lowest value resulted from one UHMWPE reinforcement fiber located in diagonal orientation and the highest from two unidirectional glass fiber reinforcements, one located on the tension side and the second on the compression side. SIGNIFICANCE: Position and fiber orientation influenced the load to initial and final failure, and specimen deflection. Tension side reinforcement was most effective in increasing the load to initial and final fracture.

Analysis of Variance↗
PubMed2006

Fracture resistance of single-tooth implant-supported all-ceramic restorations: an in vitro study.

STATEMENT OF PROBLEM: High-strength ceramic materials can be used to fabricate esthetic and stable implant-supported single-tooth restorations. No study was identified that compared the fracture resistance of individual components of single-tooth implant-supported all-ceramic restorative systems after artificial aging. PURPOSE: The purpose of this in vitro study was to evaluate the fracture resistance of single-tooth implant-supported all-ceramic restorations consisting of alumina all-ceramic restorations on different implant abutments and to identify the weakest component of the restorative system. MATERIAL AND METHODS: Forty-eight standardized maxillary central incisor alumina crowns (Procera) were fabricated for each of the 3 test groups (n = 16) (Control group Ti, titanium abutments; Group Al, alumina abutments; Group Zr, zirconia abutments) for the Replace implant system. The crowns were adhesively luted using a resin luting agent (Panavia 21) and artificially aged through dynamic loading and thermal cycling. Afterwards, all specimens were tested for fracture resistance using compressive load on the palatal surfaces of the crowns. Kruskal-Wallis analysis of variance and post hoc Wilcoxon rank sum tests were performed to test for differences in fracture resistance values (alpha = .05). RESULTS: All test specimens survived the artificial aging process using simulated oral conditions. No screw loosening was recorded. The median fracture resistance was 1454 N, 422.5 N, and 443.6 N for groups Ti, Al, and Zr, respectively. Significant differences were found for the fracture resistance comparisons of group Ti with groups Al and Zr (Kruskal-Wallis test, P < .001). The test results for the comparison of groups Al and Zr were not significant. CONCLUSION: All 3 implant-supported restorations have the potential to withstand physiologic occlusal forces applied in the anterior region.

Aluminum Oxide↗
PubMed1997

Relationship between static chemical and cyclic mechanical fatigue in a feldspathic porcelain.

OBJECTIVES: The goal of this study was to determine if static chemical and cyclic mechanical fatigue are independent, or if they interact to produce greater than additive strength loss in a feldspathic porcelain. METHODS: A blunt indentation technique was used to investigate the response of a feldspathic dental porcelain to cyclic mechanical fatigue and static chemical fatigue. All specimens were fabricated in a dry inert environment and then mechanically fatigued by cyclic loading and strength-tested in dry inert nitrogenous, ambient or wet environments. A series of experiments were performed to evaluate the effects of chemical and mechanical fatigue, and their interaction on strength loss; to determine the effects of, and interaction between, the factors of cyclic fatigue environment and strength test environment on strength; to ascertain if the type of environment during strength testing influenced specimen strength; and to distinguish between chemical damage caused by exposure to moisture alone and stress corrosion damage resulting from the strength testing environment, using a pair of two-way analysis of variance, a single one-way analysis of variance and a t-test (p < 0.05). RESULTS: These experiments indicated that both static chemical fatigue and cyclic mechanical fatigue significantly reduced specimen strength, but they did not interact to produce greater than summative effects. It was also learned that chemical fatigue was not detected on initial exposure to moisture and that it occurred to a small extent during mechanical fatigue cycling, and primarily occurred during strength testing through a stress-corrosion phenomenon. Micrographs visually evaluated the effects of mechanical and chemical fatigue on surface contact damage. SIGNIFICANCE: As both static chemical and cyclic mechanical fatigue influenced porcelain strength, they should both be considered in future evaluations. However, because they largely acted independently, they can be studied separately.

Aluminum Silicates↗
PubMed2001

Micromotion and dynamic fatigue properties of the dental implant-abutment interface.

STATEMENT OF PROBLEM: Clinical loading may result in micromotion and metal fatigue in apparently stable implant screw joints. This micromotion may contribute to tissue inflammation and prosthesis failure. PURPOSE: This study investigated dental implant screw joint micromotion and dynamic fatigue as a function of varied preload torque applied to abutment screws when tested under simulated clinical loading. MATERIAL AND METHODS: Fifteen noble alloy single-tooth implant restorations, each containing a hexed UCLA-style gold cylinder, were randomly assigned to 3 preload groups (16, 32, and 48 N.cm). Each group consisted of 5 implants (each 3.75 x 15 mm) and 5 square gold alloy abutment screws. A mechanical testing machine applied a compressive cyclic sine wave load between 20 and 130 N at 6 Hz to a contact point on each implant crown. A liquid metal strain gauge recorded the micromotion of the screw joint interface after 100, 500, 1,000, 5,000, 10,000, 50,000, and 100,000 cycles. Baseline data at 0 N.cm were collected before the application of the specified preload torque. RESULTS: The 16 N.cm group exhibited greater micromotion (P<.001) than both the 32 and 48 N.cm groups at all cycle intervals (2-way ANOVA, Tukey HSD). Micromotion of the implant-abutment interface remained constant (P=.99) for each of the preload groups through 105 cycles. CONCLUSION: Under the loading parameters of this study, no measurable fatigue of the implant-abutment interface occurred. However, dental implant screw joints tightened to lower preload values exhibited significantly greater micromotion at the implant-abutment interface.

Analysis of Variance↗
PubMed2006

Fracture resistance of single-tooth implant-supported all-ceramic restorations after exposure to the artificial mouth.

The purpose of this in vitro study was to evaluate the fracture resistance of single-tooth implant-supported all-ceramic restorations, composed of zirconium dioxide all ceramic restorations on different implant abutments, and to identify the weakest component of the restorative system. Forty-eight standardized maxillary central incisor zirconia crowns (Procera) were fabricated for two test groups and one control group (group Al: alumina abutments; group Zr: zirconia abutments; control group Ti: titanium abutments). All abutments were placed on the implants (Replace) using titanium screws. The crowns were adhesively luted using a resin luting agent (Panavia 21) and artificially aged through dynamic loading and thermal cycling. Afterwards, all specimens were tested for fracture resistance using compressive load on the palatal surfaces of the crowns. Pair-wise Wilcoxon rank tests were performed to test for differences in fracture resistance values with a global significance level of 0.05. All test specimens survived aging in the artificial mouth. No screw loosening was recorded. The median fracture resistance was 1251, 241 and 457 N for groups Ti, Al and Zr respectively. Statistically significant differences were found for the comparisons of group Ti with groups Al and Zr (P < 0.00001), and for the comparison of group Al with Zr (P < 0.00001). Results of this study showed that all tested implant-supported restorations have the potential to withstand physiological occlusal forces applied in the anterior region. Because of the low fracture resistance values of group Al, the combination of zirconia crowns and alumina abutments should carefully be considered before clinical application.

Aluminum Oxide↗
PubMed2004

Efficiency considerations for the purely tapered interference fit (TIF) abutments used in dental implants.

A tapered interference fit provides a mechanically reliable retention mechanism for the implant-abutment interface in a dental implant. Understanding the mechanical properties of the tapered interface with or without a screw at the bottom has been the subject of a considerable amount of studies involving experiments and finite element (FE) analysis. In this paper, approximate closed-form formulas are developed to analyze the mechanics of a tapered interference fit. In particular, the insertion force, the efficiency, defined as the ratio of the pull-out force to insertion force, and the critical insertion depth, which causes the onset of plastic deformation, are analyzed. It is shown that the insertion force is a function of the taper angle, the contact length, the inner and outer radii of the implant, the static and the kinetic coefficients of friction, and the elastic modulii of the implant/abutment materials. The efficiency of the tapered interference fit, which is defined as the ratio of the pull-out force to insertion force, is found to be greater than one, for taper angles that are less than 6 deg when the friction coefficient is 0.3. A safe range of insertion forces has been shown to exist. The lower end of this range depends on the maximum pull-out force that may occur due to occlusion in the multiple tooth restorations and the efficiency of the system; and the upper end of this range depends on the plastic deformation of the abutment and the implant due to interference fit. It has been shown that using a small taper angle and a long contact length widens the safe range of insertion forces.

Animals↗
PubMedDate not supplied

Investigation of the fracture resistance of three types of zirconia posts in all-ceramic post-and-core restorations.

PURPOSE: All-ceramic post-and-core restorations offer a number of advantages compared with systems that use metal cores. In certain clinical cases, however, fractures at the junction between the post and the core have been reported. The objective is therefore to improve the strength between the post and the core. MATERIALS AND METHODS: Three different methods were used to fabricate all-ceramic post-and-core restorations: pressing IPS Empress cores directly to CosmoPost zirconia posts, adhesively luting IPS Empress cores to CosmoPost zirconia posts, and Celay milling In-Ceram zirconia blanks to one-piece post-and-core restorations. Ten restorations were prepared with each of the three methods. The post-and-core complexes were tested to failure with the load applied perpendicular to the post axis. The load and deflection at fracture were recorded. RESULTS: The highest breaking load and highest deflection were recorded for the luting technique, with values of 25.3 N and 394 microns, respectively. The corresponding values for the pressed cores and the milled zirconia cores were 22 N and 301 microns, and 13 N and 160 microns. All differences were statistically significant at P < .05. Regarding the load dependence of the deflection, the luted cores again demonstrated the highest mean value, with 15.5 microns/N, while this value was 13.6 microns/N and 13 microns/N for the pressed-on and milled cores, respectively. These differences were not statistically significant. CONCLUSION: Adhesively luted all-ceramic cores on zirconia posts offer a viable alternative to the conventional pressed technique.

Aluminum Oxide↗
PubMedDate not supplied

An assessment of the clinical effectiveness of surgical drapes.

Questioning whether a 'sterile' material is actually sterile is something that many clinicians may not have considered. The equipment that comprises a sterile field for a major surgical or invasive procedure may also be taken for granted as the sterile pack would normally include sterile drapes. Under discussion is whether using sterile drapes is more effective than not using them. In furthering the debate, examination of the literature is centred on the degree of effectiveness of sterile drapes.

Bedding and Linens↗
PubMed2006

Evaluation of welded titanium joints used with cantilevered implant-supported prostheses.

STATEMENT OF PROBLEM: Early failure of laser-welded titanium implant frameworks in clinical practice has prompted an investigation of the strength and durability of welded cantilevered titanium sections. PURPOSE: The purpose of this study was to determine the effect that the use of filler wire in laser welding of titanium cantilever frameworks had on the flexural strength and fatigue resistance of the welded joints. MATERIAL AND METHODS: Sixty titanium implant-supported frameworks with 12-mm cantilevers were fabricated in 4 groups (n=15), using 3 different laser welding protocols with 0, 1, and 2 weld passes with filler wire, and 1 conventional tungsten inert gas welding method. The volume of filler wire used (mean volumes 0, 1.7, 3.4, and 8.3 mm(3)) was determined by measurement of the length of wire before and after welding each joint. Ten frameworks from each group were tested for ultimate flexural strength by loading the cantilevers 10 mm from the abutment. The remaining 5 frameworks from each group were similarly tested under a simulated masticatory load of 200 N until failure, or to 1 million cycles. A 2-way analysis of variance was used to examine the flexural strengths, and log-rank statistics were applied to cyclic test data (alpha=.05). RESULTS: There were significant differences between the 4 groups for ultimate flexural strength (P<.001) and resistance to cyclic loading (P=.002). The volume of filler wire added was a significant predictor of ultimate flexural strength (P=.03), and was a borderline determinant of the number of cycles to failure at 200 N (P=.05). Each laser weld pass with filler wire roughly doubled the ultimate flexural strength and fatigue resistance of the joint relative to the previous weld. Tungsten inert gas welding with efficient argon shielding deposited the most filler wire and produced the strongest and most fatigue-resistant joints. CONCLUSION: The ultimate flexural strength and fatigue resistance of cantilevered joints in laser-welded titanium prostheses are improved by the use of filler wire. Tungsten inert gas welding with efficient argon shielding can be used in situations when a high-strength joint is required.

Analysis of Variance↗