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At least 343 records · Page 19Linked to original sources

PubMed1982

Effect of a cement-bone composite layer and prosthesis geometry on stresses in a prosthetically resurfaced tibia.

A comparative study of stress distributions in the component materials of a number of models of a prosthetically resurfaced tibia is presented. Although the geometry is idealized to be axisymmetric, the loadings for which the finite element analyses are performed are considered to be nonaxisymmetric, simulating more realistically the loading conditions in vivo. The different models are chosen with the view of determining the influence of changes in the prosthesis design on the induced stress distribution in the component materials. The changes considered are in the thickness of the cement and the cement-bone composite layers, and in the shape of the prosthesis. Experimentally measured values of strains are compared with the analytically predicted values to check the validity of the assumptions used in the finite element modeling. The comparison of induced stresses in the different materials reveals the desirability, from a mechanical behavior point of view, of introducing a cement-bone composite layer and using a prosthesis with domed subsurface in the fixation system. It is shown that for a model incorporating these features, considerable reduction of stresses in the cement, in its bulk and at its interface with the prosthesis plate, is achieved. The reduced stresses can be expected to have beneficial effects on the long-term behavior of the cement and its interfaces in the fixation system.

Bone Cements↗

PubMed2000

Treatment outcomes of fixed or removable implant-supported prostheses in the edentulous maxilla. Part I: patients' assessments.

STATEMENT OF PROBLEM: Distinct clinical parameters determine whether fixed or removable implant-supported prostheses are indicated to restore the edentulous maxilla. However, there is a strong belief that fixed implant prostheses meet with greater patient acceptance and satisfaction, but this may differ from the patients' perceptions, their psychological responses to treatment, and their assessments of the treatment outcome. PURPOSE: This prospective clinical study compared the treatment outcomes of fixed and removable implant-supported restorations in the edentulous maxilla with the main emphasis on the patient's point of view. MATERIAL AND METHODS: Twenty patients who requested an implant-supported superstructure to restore the edentulous maxilla were asked to complete a questionnaire measuring their satisfaction with the present situation and the psychologic impact of their oral health status with their responses marked on a Visual Analog Scale (VAS). Ten patients were treated with a fixed, screw-retained implant prosthesis (group 1), and 10 were treated with a removable, implant-supported and bar-retained overdenture (group 2). Six months after prosthetic rehabilitation, patients were again given the questionnaire to assess their psychologic well-being and satisfaction with the implant-supported restoration. RESULTS: Both prosthesis designs were associated with significant improvements in comfort and retention, function, esthetics and appearance, taste, speech, and self-esteem. No difference was found between the 2 groups with respect to how the patients assessed the implant therapy. However, the results indicated that patients in group 2 experienced greater differences between pretreatment and posttreatment scores for the parameters esthetics, taste, and speech. Treatment costs per unit were significantly higher in group 1 than in group 2. CONCLUSION: Patients in groups 1 and 2 were similarly satisfied with their implant-supported prostheses in the edentulous maxilla with regard to their well-being and the cost-utility, irrespective of whether the restoration was fixed or removable.

Adult↗

PubMedDate not supplied

Mechanical testing of shoulder prostheses and recommendations for glenoid design.

Glenoid component loosening generates the greatest concern among surgeons performing total shoulder arthroplasty. Laboratory testing of glenoid prostheses may lead to improved design, subsequently leading to a reduction in the incidence of clinical loosening. The goals of this study were to develop a laboratory test method to address glenoid loosening and to apply this method to a variety of prosthesis designs. With use of a biaxial apparatus, glenoid components were cyclically subjected to superoinferior edge loading, mimicking the off-center rocking-horse phenomenon thought to contribute to glenoid loosening clinically. Before and after the rocking test was performed, compression and distraction of the superior and inferior edges were measured with the humeral head displaced to each edge. Rocking performance could not be predicted from initial measurements, indicating the necessity for dynamic loading to evaluate the likelihood of loosening. A roughened fixation surface for outperformed a smooth fixation surface, a curved backing showed almost half the distraction of a flat backing, and a nonconstrained prosthesis distracted less than a more constrained prosthesis.

Arthroplasty↗

PubMed2003

Posterior implants for distal extension removable prostheses: a retrospective study.

Common complaints associated with the Kennedy Class I (bilateral free end) and Class II (unilateral free end) removable partial denture situations are lack of stability, minimal retention, and unesthetic retentive clasping. Some of the same complaints have been reported for implant overdentures with only anterior implants. Starting in 1995, 10 of these patients were treated at the University of Washington with posterior osseointegrated implants to provide stability and/or retention of the removable prostheses, eliminating the need for clasps when possible. This article describes implant alternatives and prosthesis designs and presents a follow-up clinical evaluation of at least 1 year consisting of patient satisfaction, radiographic examination, and soft tissue health. Two groups were evaluated. Group 1 included patients whose implants were used as vertical stops for mandibular distal extension prostheses. Care was taken to ensure that the implants were not loaded laterally by creating a single-point contact at the center of a modified healing abutment. In these cases, sufficient retention was available from the anterior teeth and/or implant abutments. Group 2 included patients whose implants required retention because of lack of adequate tooth abutments. In those cases, a resilient type of attachment was used, which allowed for a small divergence from the path of insertion. Results indicated consistent increased satisfaction in all patients, minimal component wear, no radiographic evidence of excessive bone loss, and stable peri-implant soft tissues.

Aged↗

PubMed1994

Use of the sandwich method with an ultra-high-molecular-weight polyethylene prosthesis and Marlex mesh in sternal reconstruction: report of a case.

A 52-year-old Japanese man with a slow-growing chondroma originating from the sternal bone was referred to our hospital. A subtotal resection of the sternum was performed, hereafter termed the "sandwich method," and an originally designed prosthesis made from ultra-high-molecular-weight polyethylene and Marlex mesh was used for reconstruction. The postoperative course was uneventful without any symptoms due to paradoxical movement of the chest or regional abscess, and no disturbance in the movement of the upper limbs, such as a surgical sequelae, was observed.

Bone Neoplasms↗

PubMed2003

Finite element thermal analysis of bone cement for joint replacements.

A finite element technique was developed to investigate the thermal behavior of bone cement in joint replacement procedures. Thermal tests were designed and performed to provide the parameters in a kinetic model of bone cement exothermic polymerization. The kinetic model was then coupled with an energy balance equation using a finite element formulation to predict the temperature history and polymerization development in the bone-cement-prosthesis system. Based on the temperature history, the possibility of the thermal bone necrosis was then evaluated. As a demonstration, the effect of cement mantle thickness on the thermal behavior of the system was investigated. The temperature profiles in the bone-cement-prosthesis system have shown that the thicker the cement, the higher the peak temperature in the bone. In the 7 mm thick cement case, a peak temperature of over 55 degrees C was predicted. These high temperatures occurred in a small region near the bone/cement interface. No damage was predicted in the 3 mm and 5 mm cement mantle thickness cases. Although thermal damage was predicted in the bone for the 7 mm mantle thickness case, the amount of thermal necrosis predicted was minimal. If more cement is used in the surgical procedure, more heat will be generated and the potential for thermal bone damage may rise. The systems should be carefully selected to reduce thermal tissue damage when more cement is used. The methodology developed in this paper provides a numerical tool for the quantitative simulation of the thermal behavior of bone-cement-prosthesis designs.

Animals↗

PubMed2002

Effect of a speech prosthesis on electromyographic activity levels of the levator veli palatini muscle activity during syllable repetition.

OBJECTIVES: To examine whether repeated production of a syllable effects levator veli palatini muscle activity for speakers with velopharyngeal incompetence and whether the effect can be changed by a speech prosthesis. DESIGN: Repeated-measures analysis; each subject produced the speech sample /pu/ more than 200 times in each of 2 experimental conditions. SETTING: Graduate dental school in Japan. PARTICIPANTS: Four patients with operated cleft palate with a speech prosthesis. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Electromyographic traces were highband-pass filtered at 30 Hz, rectified, and smoothed with a time constant of 30 ms. Electromyographic traces were made of each production in 2 conditions: (1) without the prosthesis and (2) with the prosthesis. The regression slope of the linear regressor line, when smoothed levator activity was the criterion variable and the number of productions was the explanatory variable, was calculated in each condition. RESULTS: The mean value of levator activity was significantly smaller with the prosthesis in than without it (P<.10, t test). With the prosthesis, the regression slope was significant for all 4 subjects, whereas it was insignificant without the prosthesis for 3 of 4 subjects (P<.10, t test). Absolute values of the regression slope were significantly smaller with the prosthesis than without it for all subjects (P<.10, t test). Comparison of the regression slopes for the 2 conditions identified a significant difference in slopes between the 2 conditions (P<.10, t test). CONCLUSION: In operated cleft palate patients with velopharyngeal incompetence, a speech prosthesis can stabilize both temporal changes in levator muscle activity and connected speech, such as conversation.

Adolescent↗

PubMed1999

Pubic bone suburethral stabilization sling: laparoscopic assessment of a transvaginal operation for the treatment of stress urinary incontinence.

The objective was to examine laparoscopically the mechanism and precision of a new transvaginal method for fixation of a suburethral stabilization sling prosthesis designed for the treatment of recurrent stress urinary incontinence. Nine patients with recurrent stress urinary incontinence after previous anti-incontinence surgery underwent transvaginal placement of a pretrimmed 2.0 x 5.5 cm synthetic pubic bone suburethral stabilization sling prosthesis with pubic bone anchors. Before the sling fixation sutures were tied, the space of Retzius was opened laparoscopically with an operative laparoscope, and sling placement was assessed. Patients were followed up postoperatively at routine intervals. All nine procedures were accomplished uneventfully and as planned. Laparoscopic surveillance demonstrated that bone anchor placement by palpation was accurate and that low-tension sling fixation necessitated 2.0- to 2.5-cm suture bridges between the lateral sling edges and the pubic bone anchors in all cases. Continence was restored in all cases; two patients experienced mild, transient urinary retention; one patient experienced transient detrusor instability. No significant postoperative complications were noted. Low-tension pubic bone suburethral sling placement requires suture bridging of approximately 2.0 to 2.5 cm per side when a prosthesis 5.5 cm long is employed.

Adult↗

PubMed1982

The results of early clinical trials with a microporus coated metal hip prosthesis.

In an attempt to find a better method of attaching a prosthesis to bone, a microporous coating system, with a pore width of approximately 50 microns was chosen for evaluation. A microporous coated Austin-Moore type prosthesis was inserted into 34 patients, and the results were studied for a three-year period. Four cases required reoperations, and ten cases demonstrated radiolucent lines around the prosthesis suggesting that bone ingrowth had not occurred. This article analyzes the reasons for failure of ingrowth and suggests modifications in the prosthesis design and postoperative management that hopefully will be effective.

Adult↗

PubMed2006

Improved retention of anterior cantilever resin-bonded prostheses by design alteration: an experimental and finite element study.

STATEMENT OF PROBLEM: Anterior cantilever resin-bonded prostheses fail as a result of a labio-lingual peeling action, which creates a stress concentration within the adhesive layer. PURPOSE: The purpose of this study was to identify the factors that determine the retention of an anterior resin-bonded prosthesis and to seek to eliminate the stress concentration within the adhesive layer by fundamentally altering the prosthesis design. MATERIAL AND METHODS: The first experiment involved 40 Ni/Cr (Wiron 99) beams with a width of 5 mm, thickness of 0.5 mm, and lengths ranging from to 13 to 22 mm. The beams were cemented onto a block of the same material using an adhesive resin luting agent (Panavia 21). The length of the beam that was bonded ranged from 1 to 10 mm, resulting in a bonded area ranging from 5 to 50 mm(2). A load was applied onto the cantilevered portion of the beam 2 mm from the end, causing a peeling action. The force (N) required to debond these beams was measured using a pull-to-fracture test. Subsequently, a second experiment was undertaken, and 7 beams with an altered point of attachment (new design) were tested. The new design had the point of attachment of the cantilevered portion located centrally on the bonded area of the beam. Implementing this new design clinically would result in a cantilevered resin-bonded fixed partial denture that would have the connector arm attached more centrally on the retainer wing. The data were analyzed using a 1-way analysis of variance (alpha = .05), and a Tukey pairwise comparison test was used when the results was statistically significant. Two finite element analysis (FEA) models, one simulating the first experimental design and the other simulating the new design, were created. A load was then applied on the cantilevered portion of the beams similar to the experimental models, and the stress patterns were examined. The numerical values of these resultant stresses were plotted graphically. RESULTS: The direction of load application, which may be transferred to a clinical setting as labio-lingual forces, was identified as the dominant force responsible for debonding. The new design, which addressed this problem, showed a significant increase (P < .001) in retention. The FEA models identified the stress concentrations within the adhesive layer of the traditional design, which were eliminated when the new design was tested. CONCLUSIONS: For the in vitro model, loads that may be interpreted clinically as labio-lingual forces resulted in the lowest forces required to cause debonding, and these forces were independent of the surface area of bonding. Altering the point of attachment of the cantilevered portion onto the retainer caused a significant increase in the forces needed to cause debonding.

Biomechanical Phenomena↗

PubMed1995

[Artificial urinary sphincter].

The artificial urinary sphincter is a totally implantable hydraulic prosthesis designed to restore continence without inducing dysuria. It is composed of 3 silicone elastomer elements: a periurethral or pericervical cuff, a pressure regulating reservoir balloon inserted in the retropubic space, and a pump situated in the scrotum or labia majora. The prosthesis is filled with a liquid containing a contrast agent. Pressure on the pump allows passage of liquid from the cuff towards the balloon and allows micturition. After 3 to 4 minutes, the liquid is automatically transferred from the balloon to the cuff to restore continence. The artificial sphincter is currently a very effective therapeutic solution in cases of severe urinary incontinence with 3 main indications: persistent incontinence after prostatic surgery, recurrent incontinence in women due to sphincter insufficiency, and certain forms of neurogenic incontinence. The Pitié-Salpêtrière Urology Department's experience currently consists of 200 implantations performed over the last 10 years. The overall success rate varies from 80 to 90% according to sex and the aetiology of incontinence, in patients in whom the sphincter remains in place. In fact, there is a risk of explantation due to erosion of the tissues by the cuff or infection, but this risk is less than 15%. The risk of prosthesis failure is about 20%, but after correction of the defective element, cure is achieved in almost every case. Analysis of the results in the first 120 patients with the two most frequent aetiologies and with at least three years' follow-up (range: 3 to 10 years) reveals: in a series of 75 men, treated for severe incontinence persisting more than one year after surgery for benign prostatic hyperplasia, the explantation rate was 15% and, in the patients in whom the sphincter remained in place, complete cure was obtained in 73% of cases without any incontinence, while 17% of patients suffered from minimal incontinence, not requiring protection, 7% had moderate incontinence requiring protection and 3% were considered to be failures. The revision rate for technical failure was 24%. In a series of 45 women with recurrent incontinence after surgery, due to sphincter insufficiency, the explanation rate was 13% and, in women in whom the sphincter remained in place, complete success was obtain in 78% of cases without any incontinence, while 17% suffered from minimal incontinence, usually not requiring protection, 5% require protection, with no failures and a revision rate for technical failure of 24%.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗

PubMed2004

[Anticoagulation in patients with cardiac valve prostheses].

Patients with heart valve prostheses carry a higher risk of thromboembolic events compared to the normal population. In many cases anticoagulation is required after heart valve replacement. Thromboembolic risk is related to valve prosthesis design, patient own characteristics and adequacy of anticoagulation. Recent advance in the understanding of the pathophysiology of thrombus formation and pharmacological characteristics of most used anticoagulants are discussed. Suggestions for anticoagulation regimen are given according to recent randomised clinical trials based on prosthesis type, site of implant and patients clinical characteristics. Emphasis is given for cumbersome situations such as pregnancy and major hemorrhage in which anticoagulation has to be interrupted.

Anticoagulants↗

PubMed1996

An experimental study of damage accumulation in cemented hip prostheses.

OBJECTIVE: To develop a methodology to characterize the pattern of crack initiation and damage accumulation in intramedullary fixated cemented prostheses. DESIGN: An experimental physical model of intramedullary fixation was developed which both represents the implant structure and permits monitoring of fatigue crack growth. BACKGROUND: Many joint replacement prostheses are fixed into the medullary cavity of bones using a poly(methylmethacrylate) 'bone cement', which forms a mantle around the prosthesis and locks it to the bone. The endurance of the replacement is, to a great extent, determined by the mechanical durability of the cement and the implant interfaces under cyclic stresses generated by dynamic loading. The cement mantle is subjected to complex multiaxial stresses which vary in particular distribution depending on the prosthesis design. METHODS: Damage accumulation is reported in terms of the number of cracks, the location of cracks, and the rate of crack growth. RESULTS: The results clearly show the nature of damage accumulation in the cement mantle, and that many of the cracks which propagate within the cement mantle are related to cement porosity. CONCLUSION: This study gives experimental evidence to support the hypothesis of a damage accumulation failure scenario in cemented hip reconstructions. RELEVANCE: Cementing is the most popular technique for the fixation of joint replacement prosthesis. However, the sequence of events leading to the failure of cemented fixation is not fully understood. In this paper it is shown that damage accumulation can be directly monitored in an experimental model of cemented intramedullary fixation.

Journal Article↗

PubMed1993

Esthetic and functional considerations for implant restoration of the partially edentulous patient.

Many esthetic and functional considerations are reviewed for the partially edentulous implant candidate. With the availability of adjunctive grafting procedures, it is time for the implant team to change the traditional treatment planning approach that allows patient anatomy to dictate implant position and prosthesis design. Dimensions of the edentulous space and evaluation of occlusal relationships are discussed. Soft tissue ridge contour and creation of favorable cervical harmony are also reviewed. Functional demands unique to the partially edentulous patient are outlined in addition to the challenges of creating a prosthesis with natural cervical form and emergence profile.

Dental Implantation, Endosseous↗

PubMed1997

[The use of "self-locking" artificial vertebral prosthesis in surgical treatment for spinal tumor].

OBJECTIVE: To evaluate the use of "self-locking" artificial vertebral prosthesis in surgical treatment for spinal tumor. METHODS: From 1992 to 1996, 14 cases with spinal tumor and paraplegia were treated with "self locking" artificial vertebral prosthesis designed by one of the authors (Ye Qibin) in our department. There were malignant giant cell tumor 2 cases; myeloma 4 cases; metastatic tumor 4 cases and one each with chondrosarcoma, malignant fibrous histocytoma, fibrosarcoma, hemangioma. After radical resection of the tumor and thorough decompression, the vertebral prosthesis was applied to reconstruct the spinal stability. Adjunctive chemotherapy or/and radiotherapy was given postoperatively. RESULTS: At the average follow-up period of 20.6 months 10 cases are still alive, 5 of them had survived for more than 2 years. 4 cases died with the average survival period of 19.8 months after operation. Almost all the patients obtained the improvement of the quality of the life with relative pain-free and intact neurologic function after operation. CONCLUSION: With "self-locking" artificial vertebral prosthesis after thorough anterior resection of spinal tumor, it is possible to provide solid internal fixation to reconstruct the spinal stability.

Adult↗

PubMedDate not supplied

Conversion of non-tunneled to tunneled hemodialysis catheters.

PURPOSE: To determine the safety and efficacy of conversion of non-tunneled (temporary) catheters to tunneled catheters in hemodialysis patients. METHODS: A retrospective review of 112 consecutive conversions in 111 patients was performed over a period of 4 years. Fourteen patients were lost to follow-up. The remaining 97 patients had clinical follow-up. Temporary catheters were converted to tunneled catheters utilizing the same internal jugular venotomy sites and a modified over-the-wire technique with use of a peel-away sheath . Follow-up clinical data were reviewed. RESULTS: Technical success was achieved in all 112 procedures. None of the 97 patients with follow-up suffered early infection within 30 days. The total number of follow-up catheter days was 13,659 (range 2-790). Cases of confirmed and suspected bacteremia requiring catheter removal occurred at a frequency of 0.10 per 100 catheter days. Suspected catheter infection treated with antibiotics but not requiring catheter intervention occurred at a frequency of 0.04 per 100 catheter days. Frequency of all suspected or confirmed infections was 0.14 per 100 catheter days. Catheter interventions as a result of poor blood flow, inadvertent removal, catheter fracture, or kinking occurred at a rate of 0.18 per 100 catheter days. Life table analysis revealed primary patency rates of 86%, 64%, and 39% at 30 days, 90 days, and 180 days, respectively. CONCLUSION: Conversion of temporary catheters to tunneled catheters using the pre-existing venotomy sites is safe and has low rates of infection and malfunction. These rates are comparable to previously published rates for tunneled catheters placed de novo and tunneled catheter exchanges.

Adult↗

PubMed2000

Dental implantation for restoration of posttraumatic deformities: avulsion injuries.

Soft and hard tissue defects of the cranio- and maxillofacial area, especially after an avulsion injury, are challenging to reconstruct. Sophisticated soft and hard tissue transfer techniques have allowed satisfactory reconstruction of the gross anatomic structure. However, these methods do not allow optimal restoration of fine anatomic detail or function. The advent of dental implants and modified dental implants for craniofacial applications has allowed maximization of cosmetic and functional restoration. Prosthodontists are capable of fabricating subunits of the cranio- and maxillofacial area with fine detail, reproducing the coloring, texture, and idiosyncrasies of a patient's native skin. Dental implant technology has allowed these prostheses to be bone anchored, yielding a reproducible and stable attachment. This method of attachment in turn allows flexibility in the design of the prosthesis, to maximize restoration, and imparts an increased sense of confidence to the patient. Illustrated are six examples demonstrating the versatility of dental implants in the reconstruction of avulsion injuries of the cranio- and maxillofacial complex.

Alveolar Process↗

PubMed2006

Hearing improvement after stapedotomy using teflon loop prosthesis.

OBJECTIVE: To assess hearing improvement after stapedotomy for otosclerosis using teflon loop prosthesis. DESIGN: Quasy experimental study. PLACE AND DURATION OF STUDY: January 2001 to May 2003 in the Otorhinolaryngology Department, CMH, Rawalpindi. PATIENTS AND METHODS: Thirty diagnosed cases of otosclerosis were included in the study. Ear with greater air-bone gap was selected and stapedotomy was done using teflon loop prosthesis (size 4 - 4.5 mm). Mild vertigo occurred during immediate postoperative period, which subsided with Inj. Prochlorperazine. Patients were followed-up postsurgically at one month, two months, four months, six months and one year and postoperative air-bone gap was calculated. RESULTS: Out of 30 cases, there were 24 males and 06 females. The age ranged from 18 to 50 years. Twenty-one (70%) patients had bilateral hearing loss and 09 (30%) had tinnitis also. Pre-operative audiograms showed conductive deafness. Carhart's notch was present in 10 (33.3%) cases. Tympanogram revealed loss of stapedial reflex. Postoperatively good hearing improvement was seen in 56.7% (postoperative air-bone gap closure upto 10 dB), fair improvement in 30% (postoperative air bone gap closure from 11 to 20 dB) and poor results in 10% (postoperative air-bone gap more than 21 dB) cases. One patient developed dead ear. CONCLUSION: Stapedotomy using teflon loop prosthesis for otosclerosis is an effective method to restore hearing. Complications are uncommon.

Adolescent↗