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PubMedDate not supplied

Effects of attachment clips on occlusal force transmission in removable implant-supported overdentures and cantilevered superstructures.

Attachment clips are commonly used to provide retention for removable implant-supported overdentures. In this study, the effects of attachment clips on occlusal force transmission in four implant-supported overdentures with cantilever extensions were investigated using beam theory. Distributions of moments and of forces in overdenture, clips, cantilevered superstructure, and implants were calculated as functions of position, number, and stiffness of attachment clips. Three-, four-, and five-attachment clip configurations were analyzed. Results showed that maximum bending moments and forces in all components are strong functions of position, number, and retention of attachment clips, while the effects of attachment clip stiffness are negligible. Increasing the number of attachment clips from three to five results in a significant decrease of maximum bending moments in the superstructure and implant. For a wide range of attachment clip positioning, the maximum tensile force on the implants is as high as half the applied load. At least one attachment clip for all configurations is also subjected to tensile force, which can cause it to slip out from the superstructure and increase maximum bending moment in the superstructure and implants.

Acrylic Resins↗

PubMed1995

The ability of laparoscopic clips to withstand high intraluminal pressure.

OBJECTIVE: To determine if commercially available clips for laparoscopic surgery become displaced with high intraluminal pressures. DESIGN: In vivo model in which the splenic, renal, and mesenteric vessels together with the gallbladder of anesthetized living pigs were individually occluded using titanium and absorbable clips and then subjected to pressures of 300 mm Hg; and in vitro model in which the procedure was repeated on freshly removed human gallbladders with the attached segment of cystic duct. INTERVENTION: The intraluminal pressure of the occluded segment was increased until (1) the clip was released, (2) the vessel burst, or (3) the predetermined pressure (300 mm Hg) was obtained. RESULTS: A total of 90 clips were examined. No clip could be displaced from any porcine vessel at intraluminal pressures of up to 300 mm Hg. One vessel burst before the predetermined pressure was obtained, the clips remaining intact. Clips placed on the porcine and human models also could not be displaced by a pressure of 300 mg Hg. CONCLUSION: Commercially available titanium and absorbable clips do not disrupt when subjected to high intraluminal pressures. Postoperative bile leaks are more likely to result from necrosis of the cystic duct than displacement of the clip by the pressure within the biliary system.

Animals↗

PubMed1996

Motion and image artifacts of various intracranial aneurysm clips in a magnetic field.

Deflection angles of 36 types of Sugita intracranial aneurysm clips (Elgiloy), 2 types of Yasargil clips (Phynox), a Kirschner chip (SUS316) and a silver clip were examined by suspending each in a 1.5-tesla MRI (TOSHIBA MRT-200/FXII). Image artifacts of 5 types of intracranial aneurysm clips were also studied quantitatively with respect to their ratio of artifact/actual clip size using a spin-echo sequence with T1-weighted (Time of repetition (TR) = 500 ms, Time of echo (TE) = 20 ms) and T2-weighted (TR = 2000 ms, TE = 80 ms) images. All the Sugita clips from mini type to long type showed a deflection angle of less than 1.0 degree, the Yasargil clips less than 2.0 degrees, the Kirschner chip less than 6.0 degrees, and the silver chip did not move at all. Both brands of clips are therefore suitable for intracranial applications. The artifact size was directly proportional to the clip size and weight, though the ratio of artifact/actual width tended to decrease proportionately as the actual size and weight increased. The ratio of the width seemed slightly bigger than that of the length, but the difference did not reach statistical significance. There was no significant difference in the ratio of image artifacts/clip size between T1- and T2-weighted images.

Artifacts↗

PubMed1997

Torque-velocity relationship during cycle ergometer sprints with and without toe clips.

The torque-velocity relationship in cycling has been studied during all-out sprints (n = 6 subjects) with and without toe clips on an electronic Lode ergometer with strain gauges, to estimate the importance of the expected decrease in torque, velocity and power output. As previously found with different cycling protocols, the torque-velocity relationship was linear for all-out sprints with toe clips. A similar relationship was observed when cycling without toe clips but the torque-velocity relationship was inflected downwards at low or high velocities in several subjects who were not regular cyclists. The pulling action during the rise of the pedal at low velocities cannot explain why the torque-velocity relationship is not hyperbolic for cycling exercises with toe clips because similar relationships were observed without toe clips. The maximal power output was significantly higher during cycling with toe clips (782 W vs 668 W, P < 0.05), probably because of the pulling action at low and medium velocities as indicated by the higher value of the extrapolated maximal torque T0 (138 N x m vs 122 N x m, P < 0.05). In contrast, the maximal extrapolated velocity, V0 and peak velocity were not significantly improved by the use of toe clips. The comparison of the angle-torque patterns at low and high velocities suggested that the kinetic energy of the legs can be transformed into power output when cycling without toe clips as well as it can when cycling with toe clips.

Adult↗

PubMed1984

Avoidance of artifacts on computerized tomograms by selection of appropriate surgical clips.

Surgical clips (metallic or plastic) are frequently used for hemostasis and tumor marking. This study evaluated the radiographic and computerized tomographic appearance of different clips and their relative interference with computerized tomographic scans. Metallic clips (stainless steel, tantalum, and titanium) can all be seen on plain radiographs. Tantalum clips caused extensive distortion on computerized tomographic scans which would interfere with scan interpretation. Both stainless steel and titanium clips resulted in much less artifact and interference on computerized tomographic scans. Recent studies have suggested that there may be some risk of torsion of stainless steel clips in nuclear magnetic resonance scanners resulting in tissue damage. Absorbable plastic clips cannot be seen on plain film but are visualized on computerized tomographic scans and do not appear to cause scan artifact. Overall, we recommend the use of either titanium hemostatic clips when tumor marking on plain film is required or plastic clips when tumor marking is less important.

Evaluation Studies as Topic↗

PubMed1995

Binding of major histocompatibility complex class II to the invariant chain-derived peptide, CLIP, is regulated by allelic polymorphism in class II.

Major histocompatibility complex class II-associated invariant chain (Ii) provides several important functions that regulate class II expression and function. One of these is the ability to inhibit class II peptide loading early in biosynthesis. This allows for efficient class II folding and egress from the endoplasmic reticulum, and protects the class II peptide binding site from loading with peptides before entry into endosomal compartments. The ability of Ii to interact with class II and interfere with peptide loading has been mapped to Ii exon 3, which encodes amino acids 82-107. This same region of Ii has been described as a nested set of class II-associated Ii peptides (CLIPs) that are transiently associated with class II in normal cells and accumulate in human histocompatibility leukocyte antigen-DM-negative cell lines. Currently it is not clear how CLIP and the CLIP region of Ii blocks peptide binding. CLIP may bind directly to the class II peptide binding site, or may bind elsewhere on class II and modulate class II peptide binding allosterically. In this report, we show that CLIP can interact with many different murine and human class II molecules, but that the affinity of this interaction is controlled by polymorphic residues in the class II chains. Likewise, structural changes in CLIP also modulate class II binding in an allele-dependent manner. Finally, the specificity and kinetics of CLIP binding to class II molecule is similar to antigenic peptide binding to class II. These data indicate that CLIP binds to class II in an analogous fashion as conventional antigenic peptides, suggesting that the CLIP segment of Ii may actually occupy the class II peptide binding site.

Alleles↗

PubMed1997

A continuous central motif of invariant chain peptides, CLIP, is essential for binding to various I-A MHC class II molecules.

Invariant chain (li) associates with MHC class II molecules and performs a number of crucial functions in antigen presentation. A nested set of class II-associated li peptides (CLIP) has been isolated, comprising the li sequence between residues 82 and 107. Recently, X-ray crystallographic analysis has revealed that residues 87-101 occupy the HLA-DR3 peptide-binding groove. Based on our previous results, Lee and McConnell have also proposed a model for the binding of CLIP to various mouse I-A molecules in the binding groove. CLIP sequences are able to bind many MHC class II molecules but the molecular basis of this promiscuity has not yet been resolved. We have shown recently that CLIP binding to I-A class II molecules is generally tolerant to side chain substitutions, suggesting that the backbone structure of CLIP may provide the features critical for its interaction with class II. In pursuit of this, backbone stereochemical disruptions by serial D-alanine substitutions in CLIP86-104 have been used in competitive binding assays to I-A class II molecules. These studies have revealed that the phylogenetically conserved central continuous region, CLIP91-99, is intolerant to such configurational substitutions. Experiments with truncated and frame-shift analogues of CLIP showed that for effective binding to class II, the sequence element CLIP90-100 must be incorporated into a peptide of 13 or more residues including at least three residues N-terminal to this motif. Additionally, it appears that different I-A molecules accommodate CLIP in different binding frames. These investigations of the relationship between the structure and binding of CLIP analogues lead us to propose that there is a general backbone motif of a periodic nature within the CLIP sequence that minimizes deleterious contacts and allows promiscuous binding to class II molecules.

Amino Acid Sequence↗

PubMed1986

Autoregulation of renal blood flow in two-kidney, one-clip hypertensive rats.

Renal blood flow (RBF) autoregulation was examined in the clipped and nonclipped kidneys in two groups of two-kidney, one-clip (2K-1C) hypertensive rats 10 wk after clipping. The arterial pressure distal to the clip and the renin secretion rate (RSR) were also examined. The blood pressure (BP) was 149 +/- 4 and 162 +/- 6 mmHg in the two hypertensive groups vs. 114 +/- 3 mmHg in the controls (P less than 0.02). The RBF (in ml X min-1 X kidney-1) was 4.27 +/- 0.41 in the nonclipped and 2.18 +/- 0.23 in the clipped kidneys (P less than 0.001). The pressure distal to the clip was 104 +/- 7 mmHg. The renal vascular resistance (RVR) (in mmHg X ml-1 X min-1 X g-1) was 25.0 +/- 1.4 in the control kidneys vs. 58.4 +/- 4.5 in the nonclipped (P less than 0.001) and 39.9 +/- 6.6 in the clipped kidneys (P less than 0.01). The RBF autoregulation was well preserved in the nonclipped kidneys but reset to a higher lower pressure limit of autoregulation of 106 +/- 4 mmHg, which was significantly higher than in the normotensive controls (84 +/- 6 mmHg) (P less than 0.01). In the clipped kidneys there was complete loss of RBF autoregulation. RSR decreased with reduction of the perfusion pressure in the clipped kidneys. The increased RVR might have been due to a combination of structural and functional changes in both kidneys.

Animals↗

PubMed1986

Effect of ketanserin on pressor response to vasoactive substances in early phase of one-kidney, one clip renal artery stenosis in rats and rabbits.

The effect of ketanserin (KET), a specific 5-hydroxytryptamine2 (5-HT2) receptor blockade, on pressor response to vasoactive substances was examined in rats with one-kidney, one clip renal artery stenosis of 2 days' duration (2-day clipped rat) and in rabbits with renal artery stenosis of 3 days' duration (3-day clipped rabbits). The 2-day clipped rats showed hyperresponsiveness to norepinephrine (NE), arginine vasopressin (AVP) and 5-HT. All hyperresponsiveness were attenuated by a subdepressor dose of KET. The infusion of KET, 10 micrograms/kg/min for 30 minutes, decreased mean arterial pressure of the 3-day clipped rabbits; the dose did not alter blood pressure of the normal controls. Exaggerated pressor response to NE was observed in the 3-day clipped rabbits and was abolished by a subdepressor dose of KET, 2.5 micrograms/kg/min. These results suggest that 5-HT may be involved in the enhanced pressor response to vasoconstrictor substances in the 2-day clipped rats and 3-day clipped rabbits, and that it may also play an important role in maintaining blood pressure in the 3-day clipped rabbits.

Animals↗

PubMed1985

Clip with enclosed spring for aneurysm surgery. Technical note.

A clip for aneurysm surgery has been designed with several unique features. The coil spring is fully hidden and protected within two hub sections so that it cannot be handled or become entrapped in tissue. The clip is milled from a piece of solid stock of nonmagnetic stainless steel to the desired size and shape by a computer milling process, thus avoiding the stresses and structural weaknesses caused by the bending, curling, and milling needed to prepare clips made from wire or sheet metal. The only means of opening the clip is by applying pressure to the solid milled surfaces, thus the spring cannot be weakened or bent by squeezing it or by trauma applied to the clip. The clip may be grasped in either a clip applier that holds the clip in one fixed position or in an applier that allows the clip to be rotated through an arc of 180 degrees.

Aneurysm↗

PubMed1991

Laparoscopic clips. Evaluation of absorbable and titanium with regard to hemostasis and tissue reactivity.

Advanced laparoscopic techniques require laparoscopic means of providing hemostasis. We tested the hemostatic ability of laparoscopic surgical clips and their tissue reactivity as assessed by adhesion formation in an animal model. Twenty-six New Zealand white rabbits were randomized at laparotomy to one of three treatment groups: titanium surgical clips, absorbable surgical clips (both applied with a laparoscopic clip applicator) and chromic sutures of equal mass. Either the right fallopian tube was transected, with clips or sutures applied proximally and distally to control bleeding, or the clips or sutures were applied 5 mm apart and the tube transected. A clip or suture of the same material was placed on the midportion of the left fallopian tube. Necropsy was performed at 42 days, and each clip/suture site was scored for adhesions. All the materials were easily applied and effective in achieving hemostasis. The adhesion scores tended to be lower with the absorbable clips; however, there were no statistically significant differences between the groups. Laparoscopic clips are effective in providing hemostasis, are easily applied and cause no more adhesion formation than do conventional suture materials.

Animals↗

PubMed1998

Surgical clips: a cause of late recurrent gallstones.

The formation of gallstones around surgical clips after cholecystectomy is a rare complication, with only seven reported cases in the English literature since its initial description in 1979. Three other cases report clip migration into the common bile duct and obstruction. We report a recent experience with "clip cholelithiasis." A 78-year-old female, 16 years following cholecystectomy, presented with a several-month history of colicky abdominal pain worsened by meals, and a 1 week history of jaundice, anorexia, nausea, and vomiting. An abdominal ultrasound demonstrated dilatation of the biliary tree without visible choledocholithiasis. Endoscopic retrograde cholangiopancreatography demonstrated a 1.5-cm radiolucent stone in the common bile duct containing a central surgical clip. She was successfully treated with endoscopic sphincterotomy and stone retrieval. The first report of clip cholelithiasis occurred in 1979. Six additional cases have been reported as well as three cases of clip migration without stone formation into the common bile duct. The incidence of clip cholelithiasis may increase in frequency with the increased use of metallic clips during laparoscopic cholecystectomy. The occurrence of cholelithiasis around inert metals is rare and may be prevented using absorbable clips; however, stone formation is also reported around absorbable materials.

Absorption↗

PubMed1983

[Is tubal sterilization with the Tupla-clip a reversible method?].

Between 1976 and 1981 402 tubal sterilizations were performed with Tupla-clip most of them by laparoscopic application. 11 tubes were removed between 15 and 47 months following the sterilization with the Tupla-clip. The local changes both macroscopically and microscopically to the tupla-clip were evaluated. The possibility of tubal patency following removal of the clips was tested by carbon dioxide pertubation. The tubal-occlusion with the tupla-clip is definitive since all tubes had a fibrous tissue strand where the clip had been applied which still carried blood vessels. No tube was patent with the carbon dioxide pertubation. The intra-operative testing of correct application of the clip and the documentation of this correct application is again mentioned. This is especially important in view of the recent judgements of the federal supreme court regarding liability in failed tubal sterilizations. The excellent chance of reversal by tubal anastomosis and the 100% success rate of this method of sterilization within the 6 years under observation will increase the acceptance of the tupla-clip as a method for tubal sterilizations.

Female↗

PubMedDate not supplied

The MHC class II-associated invariant chain-derived peptide clip binds to the peptide-binding groove of class II molecules.

Major Histocompatibility Complex (MHC) class II proteins bind to peptides derived from processed foreign antigens, and display them on the cell surface of antigen presenting cells for recognition by CD4+ regulatory T lymphocytes. Prior to their binding to antigenic peptides in endosomal compartments, class II molecules are associated with a nested set of peptides CLIP derived from amino acids 80 to 107 of the invariant chain (Ii). Currently the interaction between the CLIP peptide and class II molecules is not clear. Using an FITC-labeled CLIP peptide and soluble empty class II molecules synthesized in insect cells, we have investigated the direct binding of the CLIP peptide to class II molecules, and the influence of localized polymorphic residues in the peptide-binding groove on the binding. We found that the human class II HLA-DR1 molecule contains a single-binding site for the CLIP peptide as well as the antigenic peptide MP19-31, as analysed by Scatchard analysis. Further studies also showed that occupancy of the peptide-binding groove by antigenic peptides inhibited the binding of CLIP to DR1 molecules and vice versa. Most importantly, the polymorphic residues beta 85 and 86, which define the major peptide-binding pocket, strikingly influence the CLIP-DR1 interaction, as assayed by the SDS-stability of class II-peptide complexes and the affinity of class II-peptide interactions. These data indicate that the peptide-binding pocket and thus the peptide-binding groove of the class II molecule are directly involved in the association with the CLIP peptide.

Antigens, Differentiation, B-Lymphocyte↗

PubMed1996

Surgical clips in planning the electron boost in breast cancer: a qualitative and quantitative evaluation.

PURPOSE: To evaluate, qualitatively and quantitatively, the role of surgical clips in planning the tumor bed electron boost in patients undergoing breast conserving surgery and radiotherapy. METHODS AND MATERIALS: In 50 patients, the excision cavity boundaries were marked by clips at surgery. The electron boost field was first planned using clinical information, aiming to achieve a margin of 2 cm, and its accuracy evaluated by screening the surgical clips and, if necessary, adjusting the field to encompass all clips with 2 cm margins. Orthogonal radiographs were take with solder wire delineating the clinical and screened fields and the scar. Hypothetical clinical and radiological fields, with 1 and 3 cm margins, were reconstructed on the radiographs. RESULTS: The clinical field was inadequate in 34 patients (68%). The precision of each clinical setup was quantified by two indices. The Normal Tissue Index defined the percentage of the clinical field comprised of tissue, beyond the tumor bed, not at high risk of local recurrence, and gave an estimate of potential spring of normal tissue: median 14.6% (range 0-83.0), 17 out of 50 > 25%; median 13% (range 0-70.7), 12 out of 50 > 25%; median 9.7% (range 0-59.8), 10 out of 50 > 25%, for 1, 2, and 3 cm margins, respectively. The Geographical Miss Index defined the percentage of the radiologically defined field, at high risk of local recurrence, not predicted by the clinical field, and gave an estimate of the extent of geographical miss: median 32.9% (range 0-83.5), 28 out of 50 > 25%; median 26.1% (range 0-69.8%), 26 out of 50 > 25%; median 18.6% (range 0-60.3), 20 out of 50 > 25%, for 1, 2, and 3 cm margins, respectively. The median distance from the scar midpoint to the furthest clip was 3.8 (range 1.2-8.1) cm. The median maximal clip depth was 3.1 (range 1.4-5.2) cm. CONCLUSION: (a) Electron boost field planning by clinical landmarks alone was inaccurate in 68% of cases. (b) Quantitative measures, based on margins of 1, 2, and 3 cm, revealed that in 20-34% of patients more than one-quarter of the clinical field covered tissue at low risk of local recurrence, and in 40-56% of patients less than three-quarters of the final radiological field was predicted clinically. (c) The relative positions of the scar and clips may be widely disparate. (d) Clip depth measurements reveal a significant risk of underdosing at depth.

Breast Neoplasms↗

PubMed1995

In vitro changes in clips and bars used to retain implant overdentures.

Although implant-retained overdentures are a less expensive alternative to fixed implant-supported prostheses in certain situations, problems with retentive clips fracturing and needing frequent replacement have been reported. This study compared baseline and posttest retention of metal and plastic clip-retained overdenture analogs and monitored surface changes in bars and clips throughout the testing process. A laboratory model was made with two implant analogs processed into an acrylic resin platform to which three bars were fitted. Two overdenture analogs were made and retained on the model with metal or plastic clips. Each bar-clip assembly was subjected to 5500 insertion and removal cycles to simulate 3 years of in vivo insertion and removal. Although the differences in retention between metal and plastic clips and between clips before and after testing were statistically significant, it is questionable whether they are clinically significant. Neither clip fracture nor loss occurred during this study, which suggests that it may be functional or parafunctional loading and not repeated insertion and removal of an implant overdenture that may cause the stated problems.

Acrylic Resins↗

PubMed1996

The effect of simulated function on the retention of bar-clip retained removable prostheses.

Patients wearing bar-clip retained removable prostheses may have loss of retention because of changes within the bar-clip assembly. This in vitro study recorded and compared the retention of one- and two-clip retained simulated mandibular complete denture prostheses before and after simulated function. Cast metal Hader bars and clip holders were used to make 10 one-clip and 10 two-clip specimen pairs. Tensile removal values before and after simulated function were recorded and compared by repeated-measures analysis of variance and Student tau tests (significance level 0.05). The results revealed that the use of two clips instead of one significantly increased retention of the simulated prosthesis. It was also found that there was a significant loss of retention after the specimens were placed on the bars and then removed once for both the one- and two-clip groups. Simulated function did not cause a significant change in retention for either group.

Analysis of Variance↗

PubMed1997

Magnetic characteristics of Yaşargil aneurysm clips.

BACKGROUND: Metallic bioimplants are subject to great scrutiny in order to ensure that they are totally harmless to patients. Aneurysm clips are no exception to this rule. Considering the number of aneurysm clips used and their potential for injury, they should be evaluated very meticulously. Determining the magnetic characteristics of these clips is an important part of the evaluation process. In this study, a new method for evaluating magnetism is described and the importance of that information is briefly discussed. METHODS: Twenty Yaşargil aneurysm clips were analyzed using a vibrating sample magnetometer under 1.5 Tesla. This device is highly sensitive, and is capable of measuring the magnetism of small objects. RESULTS: Our measurements showed magnetism of the aneurysm clips ranged from 0.0334-0.1369 electromagnetic units (emu). CONCLUSIONS: Magnetometer measurements and real life tests under magnetic resonance imaging (MRI) have shown that these clips have a very low magnetism and are safe to use in 1.5 Tesla MRI scanners. This study also proves that the vibrating sample magnetometer is a useful device for analyzing the magnetism of aneurysm clips, and their emu values can be used as another industry standard in the production line to increase the safety of these clips.

Aneurysm↗