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PubMed1989

Experimental method for the in vitro testing of the initial stability of cementless hip prostheses.

Micromotions at the interface between bone and prosthesis are believed to induce bone resorption and ultimately lead to loosening of the implant. Thus the initial stability achieved by a hip prosthesis is an important factor for the long-term function of the implant. Knowing the biological consequences of the mechanical conditions, it appears to be mandatory to measure the extent of these three-dimensional movements. An in vitro dynamic method for measurement of the micromotion of the femoral component of hip prostheses has been developed. Tests in cemented prostheses have confirmed that the use of cement reduces sinkage and rotation manyfold and have yielded reference values for stability. Comparison with two types of cementless prostheses has shown that certain cementless implants may achieve stability comparable to cemented ones in some load directions.

Bone Cements↗
PubMed1992

A computer-based biomechanical analysis of the three-dimensional motion of cementless hip prostheses.

A computer-based mathematical technique was developed to measure and completely describe the migration and micromotion of a femoral hip prosthesis relative to the femur. This technique utilized the mechanics of rigid-body motion analysis and apparatus of seven linear displacement transducers to measure and describe the complete three-dimensional motion of the prosthesis during cyclic loading. Computer acquisition of the data and custom analysis software allowed one to calculate the magnitude and direction of the motion of any point of interest on the prostheses from information about the motion of two points on the device. The data were also used to replay the tests using a computer animation technique, which allowed a magnified view of the three-dimensional motion of the prosthesis. This paper describes the mathematical development of the rigid-body motion analysis, the experimental method and apparatus for data collection, the technique used to animate the motion, the sources of error and the effect of the assumptions (rigid bodies) on the results. Selected results of individual test runs of uncemented and cemented prostheses are presented to demonstrate the efficacy of the method. The combined effect of the vibration and electrical noise resulted in a resolution of the system of about 3-5 microns motion for each transducer. Deformation effects appear to contribute about 3-15 microns to the measurement error. This measurement and analysis technique is a very sensitive and powerful means of assessing the effects of different design parameters on the migration and micromotion of total joint prostheses and can be applied to any other case (knee, dental implant) where three-dimensional relative motion between two bodies is important.

Biomechanical Phenomena↗
PubMed1980

Accetability of orbital prostheses.

This study was made to determine if those patients apparently dissatisfied with an orbital prosthesis might accept an eye patch more readily. The study included 27 patients who were seen during the past 8 years. A total of 60 orbital and eye patch proshteses were prepared for the patients. Eighteen patients responded to the questionnaire. Twelve of these patients are presently wearing their prostheses, and five of them are not. Reasons given by the patients for not using their prostheses were discomfort, lack of retention, skin irritation due to daily application and removal of the adhesive, change in defect, ill-fitting prostheses, and surgical reconstruction of the site. The study shows that given a choice, 67% of the patients would prefer the orbital prosthesis. Seventy-five percent of the patients who had an eye patch would prefer an orbital prosthesis.

Acrylic Resins↗
PubMed1984

Sectional prostheses connected by samarium-cobalt magnets.

Large acquired defects with undercuts can be restored with sectional prostheses. Sections of the prosthesis can be connected with small Sm-Co magnet pairs. The advantages of Sm-Co magnets are that (1) sections of prostheses can be connected by magnets less than 1 cm in size, (2) they can be embedded in thin sections of acrylic resin, (3) they are easy to place, (4) insertion is easy (magnetic attraction enhances), (5) hollow obturators can be used, and (6) tissue undercuts can be used for additional retention of prostheses.

Cobalt↗
PubMed1989

Microwave techniques for fabrication of provisional facial prostheses.

Timely rehabilitation of facial defects necessitates provisional prostheses during the period following surgery. The possibilities of using microwave radiation in the drying of gypsum casts, the preparation of stone molds, the curing of silicone elastomers, and the extrinsic coloring of silicone prostheses are presented. Microwave radiation has the potential for saving time, energy, and resources during the fabrication of provisional facial prostheses.

Biocompatible Materials↗
PubMed1989

A retrospective multicenter evaluation of the survival rate of osseointegrated fixtures supporting fixed partial prostheses in the treatment of partial edentulism.

Whether the excellent prognosis of the osseointegration technique also applies for the rehabilitation of partially edentulous jaws was investigated through a multicenter retrospective study. Six centers from three continents participated in the study, which included 133 fixtures in 38 patients. Forty fixtures were installed in the upper jaw and 93 in the lower jaw. The observation time varied between 6 and 36 months after prosthetic reconstruction. Clinical evaluation included mobility measurement of the restorations and control of infectious or neurologic complication. Radiologically the absence of radiolucency around the fixtures was checked by a single observer who also calculated the distance between the marginal bone and the top of the fixture. Fifty-eight percent of the prostheses were connected to natural teeth. The success rate for the individual fixtures in the upper and lower jaws was 87% and 92%, respectively. The most failures occurred before the prosthetic rehabilitation. The mean maximum distance between the margin of the bone and the fixture-abutment junction was 2.5 mm. Since only two of the 53 fixed prostheses were lost during the observation period, and since most fixture losses occurred before the prosthetic phase of the treatment, this study supports the concept that osseointegrated prostheses can also be applied to the rehabilitation of partial edentulism.

Adolescent↗
PubMed1992

A study of 589 consecutive implants supporting complete fixed prostheses. Part II: Prosthetic aspects.

In 91 consecutive edentulous patients, 103 jaws were treated with complete fixed prostheses supported by Brånemark Implants (n = 589). As a result of fixture loss in each of two patients (two jaws), an overdenture instead of a fixed prosthesis was installed. For one patient (two jaws), data were not available after abutment connection. At the end of the seventh year, the cumulative failure rates for the remaining 99 prostheses reached 4.9% for mandibles and 10.1% for maxillae. After loading, 12 fixtures showed signs of nonintegration, but only one patient had to revert to complete dentures. Neither the fixture location nor the cantilever length revealed a significant difference in marginal bone loss around the supporting fixtures. Patients with fixture-supported fixed prostheses in both jaws showed significantly more marginal bone loss than did those with only one fixed prosthesis opposed by either natural dentition (50%) or a complete denture (50%). Component complications were limited to fixture fracture (3/564), abutment screw fracture (5/564), and gold screw fracture (7/564). The predictability of Brånemark implants in the treatment of completely edentulous jaws is confirmed.

Alveolar Bone Loss↗
PubMed1994

Problems with prostheses on implants: a retrospective study.

Prosthetic parameters for implant success have not been well defined but should include patient satisfaction and prosthesis maintenance, including adjustments and repairs. In addition, differences between fixed and removable implant-supported prostheses (ISPs) should be quantified. This study retrospectively evaluated both patient satisfaction and maintenance for 156 patients. Removable ISPs averaged almost three times as many adjustments per prosthesis (2.1 versus 0.8 per fixed ISP) and more than twice as many repairs (1.9 per removable ISP versus 0.9 per fixed ISP). The most common adjustments were to the contour of both types of prosthesis, and the most frequent repairs involved the retentive clips with removable ISPs and the gold screws with fixed ISPs. The incidence of repeat repairs was more than twice as high with removable prostheses compared with fixed prostheses. However, the repairs to opposing dentures most often needed were for conventional dentures opposing fixed ISPs. The vast majority of repairs were needed within the first year of service. Despite the high maintenance needed, patients were satisfied with both types of ISP, with the exception of limited satisfaction with cleansability, particularly with fixed restorations. The high incidence of early repairs, and the greater potential for a removable ISP requiring adjustment and repair, should be considered both when discussing options with the patient and when estimating treatment and maintenance costs before the commencement of implant therapy.

Adult↗
PubMed1994

Cobalt exposure evaluation in dental prostheses production.

Dental laboratory technicians may be exposed to a number of toxic materials including metal alloys that have been identified as potential health hazards. Particularly, alloys, such as vitallium, wisil, duralium and vironite which in dentistry are used in the production of crowns, bridges and dental prostheses. The most common constituents of these prostheses are cobalt (45-70%), chromium (25-30%), molybdenum, silica, nickle, tantalum and other metals in different amounts. The objectives of this paper are to describe the technology related to the production of dental prostheses, evaluating the most hazardous working jobs and reporting results concerning the monitoring of cobalt and chromium in the urine of 31 people employed in five laboratories of Bergamo, Italy, where workplace air monitoring has also been undertaken.

Adult↗
PubMed1993

Biodeterioration of medical-grade silicone rubber used for voice prostheses: a SEM study.

Silicone voice prostheses used for rehabilitation of speech after total laryngectomy are inserted in an non-sterile habitat. Deposits on explanted Groningen Button voice prostheses revealed a biofilm, due to heavy colonization of the silicone surface by bacteria and yeasts. Furthermore, it was demonstrated by scanning electron microscopy on sectioned explants that the silicone material was deteriorated by filamentous and vegetative yeast cells. The different explants showed a variety of sharp-edged, discrete yeast colonies. The yeasts grew just under the silicone surface and up to 700 microns into the silicone material. Finally, nine different types of defects in the silicone material created by the yeasts are described. This deterioration of the silicone by yeasts seems to be the main reason for the failure and the frequent replacement of the prostheses. The mechanisms of silicone deterioration are still hypothetical.

Bacterial Adhesion↗
PubMed1994

Supporting, microporous, elastomeric, degradable prostheses to improve the arterialization of autologous vein grafts.

Arterial reconstructions with vein grafts fail more frequently than with arterial grafts. One of the causes of graft failure is damage due to overstretching of the graft wall. Overstretching is caused because the vein graft, which has a poorly developed medium, cannot withstand the arterial blood pressures. The aim of this study is to evaluate whether damage due to overstretching can be prevented and a gradual adaptation of the vein graft to the arterial blood pressures can be induced by applying a microporous, elastomeric, degradable prosthesis around the vein graft. Therefore, autologous vein grafts (length 1.0 cm) with and without supporting prostheses (composite vein grafts and control vein grafts, respectively) were interposed into both carotid arteries of rabbits. Microporous, elastomeric, biofragmentable polyurethane-based prostheses and microporous, elastomeric, biodegradable prostheses made of poly-epsilon-caprolactone or a copolymer of epsilon-caprolactone and 3.6-dimethyl-1,4-morpholine-2,5-dione with a monomer ratio of 95.5:4.5 were prepared. The grafts were evaluated up to 6 wk after implantation. The control vein grafts showed severe destructive changes such as de-endothelialization, disruption of the media with oedema, degradation of the elastic laminae and infiltration of polymorphonuclear leucocytes into the vein graft wall, leading eventually to a fibrotic wall. In contrast, the composite vein grafts showed a preservation of the smooth muscle cell layers and the elastic laminae with only few polymorphonuclear leucocytes infiltrated into the vein graft wall.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

A study of some mechanical properties of an RTV polydimethylsiloxane for extraoral maxillofacial prostheses.

The construction of facial prostheses simulating the missing tissues as closely as possible is an imperative and demanding task. Such prostheses will be comprised of parts presenting different mechanical properties attempting to simulate facial tissues. In this study the mechanical properties of a room temperature vulcanized (RTV) silicone facial elastomer were modified, altering the molecular architecture by controlling the amount of cross-linking. A wide range of compliance was achieved which enables more lifelike facial prostheses to be made in clinical practice.

Cross-Linking Reagents↗
PubMed1988

Hip prostheses during pelvic irradiation: effects and corrections.

Treatment of pelvic malignancies frequently includes the use of lateral, arc, or rotational fields. The presence of hip prostheses in these treatment fields will perturb the dose distribution. Correction factors for metal-based alloys used in artificial hips have not previously been reported. Prostheses constructed from frequently used alloys were obtained and measurements were made of the transmission of 4MV and 10MV photons. These measured data were compared with computed correction factors. The computer uses the "ratio of tissue-maximum ratios (TMR's)" method of heterogeneity correction. The computer was provided with both the physical density and the relative electron density of each prosthesis for comparison purposes, since electron densities for hip prostheses are not widely known. Correction factors determined from electron densities demonstrated better agreement with measured data. The "ratio of TMR's" correction algorithm does not consider the contribution of scattered radiation in the dose computations. Consequently, a small adjustment to the relative electron density of the prosthetic hip was required at lower X ray beam energies. Agreement was satisfactory for higher energy X rays, and thus no adjustment was necessary. Relative electron densities and adjusted electron densities for alloys used in artificial hips are provided for computer-aided treatment planning. Recommendations for incorporating the hip prosthesis into the treatment planning process are also provided.

Electrons↗
PubMed1996

Failure of adjusted doses of subcutaneous heparin to prevent thromboembolic phenomena in pregnant patients with mechanical cardiac valve prostheses.

OBJECTIVES: This report describes our experience with the use of an anticoagulant regimen of adjusted doses of subcutaneous heparin during pregnancy in women with cardiac valve prostheses. BACKGROUND: Gravid patients with prosthetic heart valves require long-term anticoagulant therapy. To avoid the increased incidence of fetal morbidity and mortality associated with the use of coumarin agents in such patients during pregnancy, anticoagulation with subcutaneous heparin has been suggested. Controversy exists concerning the appropriate treatment of these patients. METHODS: Forty pregnancies in 37 women with prosthetic heart valves were prospectively followed up. Subcutaneous heparin was administered from the 6th until the end of the 12th week and in the last 2 weeks of gestation. Heparin was given every 8 h in the first 36 cases and every 6 h in the last 4 cases, and the dose adjusted to maintain the activated partial thromboplastin time at 1.5 to 2.5 times the control level. Acenocoumarol was used at other times. RESULTS: The incidence rate of spontaneous abortions was 37.5%; there was one neonatal death (2.5%) due to cerebral hemorrhage. No signs of coumarin-induced embryopathy were found in any of the 16 live-born infants studied by the geneticist. One mother died of gastrointestinal bleeding while receiving oral anticoagulant agents. There were two cases of fatal massive thrombosis of a mitral tilting-disk prosthesis during heparin therapy. The study was interrupted after the last of these two cases. CONCLUSIONS: The regimen of adjusted doses of subcutaneous heparin used in this study is not effective to prevent thrombosis of mechanical valve prostheses during pregnancy. The use of heparin from the 6th to the 12th week of gestation does not decrease the high incidence of fetal wastage associated with anticoagulant therapy. Coumarin agents provide adequate protection against thromboembolism during pregnancy in patients with mechanical valve prostheses.

Abnormalities, Drug-Induced↗
PubMed2006

Antibiotic cements in articular prostheses: current orthopaedic concepts.

The possibilities and limits of antibiotic cements (ACs) have been assessed by many researchers. ACs are now approved by many drug agencies, including the US Food and Drug Administration (approval in 2003), with widespread use in prophylaxis and curative treatments. Laboratory experiments have achieved satisfactory antibiotic delivery without impairing the mechanical properties of ACs. Implantation in large animals (e.g. sheep) showed an antibiotic concentration in the bone cortex four times the minimal inhibitory concentration (MIC) 6 months after implantation. Human pharmacokinetics during total hip replacement (THR) show antibiotic concentrations 20 times the MIC in drainage fluids. No toxic concentrations have been detected in blood or urine, and no allergies, toxic effects, mechanical failures or selection of resistant microorganisms have been observed. Antibioprophylaxis has been assessed in prospective studies in over 1600 cases. In data from the Scandinavian arthroplasty registers, with an exhaustive follow-up of more than 240000 THRs, infection rate was reduced by ca. 50% (0.9% compared with 1.9%). In prostheses with severe infection, use of AC increases the infection control rate from 86% to 93% when using two-stage prosthetic exchanges. In moderate infection, a similar infection control rate (86%) was achieved either by two-stage exchange without local antibiotic or by one-stage exchange with AC; however, one-stage exchange achieved better functional results at lower cost and with reduced pain and hospital stay. Therefore, AC prophylaxis is widely used in countries with prostheses registers (Northern Europe), and use of ACs as treatment for infected prostheses is often considered as the gold standard in the EU and North America. However, AC is only an adjuvant treatment, and excision of infected and devascularized tissues as well as systemic antibiotic treatment managed by a multidisciplinary team remain the main factors of infection control.

Animals↗
PubMed2005

Grading of radiographic osteolytic changes after silastic metacarpophalangeal arthroplasty and a prospective trial of osteolysis following use of Swanson and Sutter prostheses.

The purpose of this study was to compare the incidence of radiographic osteolysis following insertion of 89 Swanson and 126 Sutter metacarpophalangeal implants in rheumatoid arthritis patients. The mean follow-up time in the two groups of patients was 57 (40-80) and 55 (36-79) months, respectively. This paper proposes a new method of classifying radiographic osteolysis. The remarkable number of osteolytic changes seen in the bones adjacent to MCP prostheses in this study would suggest that silastic prostheses should only be used when other surgical alternatives cannot be used and that long-term control by radiography be maintained after implantation of silicone prostheses into the MCP joint. In all grades of our classification, osteolysis was more frequent in the Sutter than in the Swanson group in this study, suggesting that use of the Sutter rather than the Swanson implant is questionable.

Aged↗
PubMed2006

The use of prostheses in skeletally immature patients.

Prosthetic reconstruction in the skeletally immature patient is challenging because of the necessity to cope with expected disruption of limb growth after resection of one or more major growth plates and the high demands placed on implants by young patients. Although prosthetic reconstruction in children is fraught with many problems, it is usually possible to obtain a good functional limb at skeletal maturity. Extendable prostheses are readily acceptable to patients and their parents. The availability of noninvasive extendable prostheses is expected to lead to fewer complications, fewer surgical interventions, and even improved function. This article reviews the indication, evolution, and clinical and functional results of extendable endoprostheses, drawing from experience in the last 30 years of using such prostheses in children.

Adolescent↗
PubMed2004

Minimizing complications in the use of titanium condylar head reconstruction prostheses.

OBJECTIVE: The study goals were to evaluate the use of titanium condylar prostheses in the setting of tumor resection and to discuss the techniques used to minimize complications. STUDY DESIGN AND SETTING: We conducted a retrospective review of a case series in a tertiary care hospital. Six patients underwent mandibulectomy, including the condyle, with primary reconstruction using titanium condylar prostheses. Charts were reviewed for operative technique, pathology, and complications. RESULTS: Pathology included squamous cell carcinoma, Ewing's sarcoma, embryonic rhabdomyosarcoma, giant cell granuloma, and adenocarcinoma. Three patients are alive without disease. Follow-up spanned 6.4 years with premorbid occlusion established in all cases, and there were no prosthesis extrusions or erosions. The condylar head was wrapped in preserved joint capsule or adjacent temporalis muscle/fascia and secured with permanent purse-string sutures; careful duplication of the length, and angulation of the native mandible from the angle to the superior extent of the condylar head. CONCLUSION: Titanium condylar prostheses are a viable choice in the setting of tumor resection and reconstruction, with appropriate technical precautions.

Adult↗