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PubMed2004

Prosthetic design considerations for anterior single-implant restorations.

UNLABELLED: The anterior single-implant restoration provides a predictable solution for the partially edentulous patient. The two main approaches in prosthesis design for the single-implant restoration are the screw-retained and cement-retained restorations. Although both approaches have been proven to work from a standpoint of long-term implant stability, other considerations arise when esthetic outcome and ease of fabrication and delivery are discussed. To guarantee a predictable outcome, the dentist should choose a design that offers maximum prosthetic versatility. Combining prosthetic versatility with ease of delivery is often a clinical and laboratory challenge. Prostheses designs that provide the freedom to select a wide variety of restorative materials may be cumbersome to deliver and maintain and vice versa. This article reviews the advantages and shortcomings of each design and provides an alternative prosthesis design that combines the favorable aspects of these two restorations. CLINICAL SIGNIFICANCE: Screw-retained and cement-retained prostheses are the common designs for single-implant restorations and possess clinical advantages and shortcomings. An alternative and affordable design, that is mainly beneficial when standard stock implants components are used, is presented. It enables the clinician to achieve optimal esthetics in the esthetic zone combined with a simple and time-efficient delivery.

Dental Implantation, Endosseous↗
PubMedDate not supplied

Communication between the dental laboratory technician and dentist: work authorization for fixed partial dentures.

PURPOSE: A questionnaire was sent to laboratory technicians to determine the level of communication between dentists and dental laboratories in specific areas of the work authorization forms for the fabrication of fixed partial dentures. MATERIALS AND METHODS: A select number of dental laboratories were randomly chosen from the National Association of Dental Laboratories (NADL) for each of the 50 states. The questionnaire was mailed to the laboratory directors for a total of 199 dental laboratories. The survey asked questions pertaining to the following areas of work authorization: legibility and thoroughness of prescriptions, patient information, choice of materials for the prosthesis, design of the prosthesis, and shade description. For each question, the number of responses received was tabulated and converted to a percentage. RESULTS: Of the 199 laboratories surveyed, 114 (57%) responded to the questionnaire. Results from this survey suggest that there is lack of communication between dentists and dental laboratories through work authorization forms regarding choice of metal alloy, type of porcelain to be used, and choice of margin and pontic design for the prosthesis. CONCLUSIONS: Information obtained from the responding laboratories included effectiveness of work authorization forms. There were some similar trends indicated by the large percentage of dental laboratories agreeing on lack of communication by the dentists as reflected by the work authorization forms.

Communication↗
PubMed2000

Custom design in lower limb prosthetics for athletic activity.

In summary, the prosthetist is the best source of information with regard to the fast-changing lower extremity prosthetics technology for sports. The needs and desires of the amputee should be outlined and balanced with the cost of the desired components and design. In many cases, one carefully designed prosthesis can serve in dual roles for everyday ambulation and certain athletic activities. In other cases, the amputee is limited severely by a prosthesis that is not designed for a specific activity. Using a prosthesis for activities that it was not designed to accommodate can cause physical injury to the amputee as well as structural failure of the device. A properly designed and fitted prosthesis can open a whole new world of activity to the amputee and helps him or her to reach the desired a vocational goals.

Activities of Daily Living↗
PubMed2003

[The hinged knee prosthesis: outdated design or valuable implant for difficult cases?].

There are excellent results after unconstraint or semiconstraint bi- or tricompartimental total knee arthroplasty in case of uncomplicated degenerative joint disease of the knee. In the Swedish knee study, cumulative survival of unconstraint or semiconstraint knee prostheses was about 90 % at 10 years. In studies of single institutions, survival rates of more than 90 % at 15 years are reported. However, there is a need of more constraint designs because of the increasing number of complex total knee arthroplasties with disrupted collateral ligaments, deformities with flexion extension gap imbalance, comminuted distal femur fracture, distal femoral non-union in elderly patients and revision with massive bone loss. Initial hinged total knee designs were associated with a high failure rate. More recent designs have improved the femorotibial articulation and reduced the polyethylene wear. The bone resection necessary in actual hinged designs is similar to the resection in modern condylar prostheses. Due to these improvements, long-term survival of the best hinged designs are similar to the best condylar designs. In our study of a consecutive series of 422 hinged Blauth prostheses, the cumulative survival of the prostheses was 94.4 % at 20 years. Therefore, the hinged knee prosthesis is a valuable implant in case of complex total knee arthroplasty.

Aged↗
PubMed1996

Outcome of total hip arthroplasties with cement. Results after implantation of the Harris Design 2 prosthesis, 1983-1985.

Most reports of excellent long-term results of cemented total hip arthroplasty originate from studies of Charnley prostheses. A radiographic and clinical study was performed on 126 patients who underwent a cemented total hip arthroplasty from 1983 to 1985 with the Harris Design 2 prosthesis (Howmedica, Rutherford, NJ). The femoral component was cobalt-chromium and it had a broad, rounded medial border and a collar. The head diameter was 26 mm. A cemented all-polyethylene socket was used in all cases. At the last follow-up examination, 71% of the patients were completely free of pain and no patient had severe pain or pain at rest. Kaplan-Meier survival analysis estimated the revision rate at 10 years after operation to be 5 +/- 2% (mean +/- SEM) (including planned revisions). The rate of complete acetabular demarcation was 20% at 10 years, and femoral demarcation involving more than 50% of the bone-implant surface or endosteal cavitation was noted in only three cases. These results are as good as the best reported after total hip arthroplasty with the Charnley prosthesis.

Adult↗
PubMed2005

The influence of design, materials and kinematics on the in vitro wear of total knee replacements.

Debris-induced osteolysis due to surface wear of ultra high molecular weight polyethylene (UHMWPE) bearings is a potential long-term failure mechanism of total knee replacements (TKR). This study investigated the effect of prosthesis design, kinematics and bearing material on the wear of UHMWPE bearings using a physiological knee simulator. The use of a curved fixed bearing design with stabilised polyethylene bearings reduced wear in comparison to more flat-on-flat components which were sterilised by gamma irradiation in air. Medium levels of crosslinking further improved the wear resistance of fixed bearing TKR due to resistance to strain softening when subjected to multidirectional motion at the femoral-insert articulating interface. Backside motion was shown to be a contributing factor to the overall rate of UHMWPE wear in fixed bearing components. Wear of fixed bearing prostheses was reduced significantly when anterior-posterior displacement and internal-external rotation kinematics were reduced due to decreased cross shear on the articulating surface and a reduction in AP displacement. Rotating platform mobile bearing prostheses exhibited reduced wear rates in comparison to fixed bearing components in these simulator studies due to redistribution of knee motion to two articulating interfaces with more linear motions at each interface. This was observed in two rotating platform designs with different UHMWPE bearing materials. In knee simulator studies, wear of TKR bearings was dependent on kinematics at the articulating surfaces and the prosthesis design, as well as the type of material.

Biocompatible Materials↗
PubMed2006

Treatment planning of the edentulous maxilla.

The predictability of successful osseointegrated implant rehabilitation of the edentulous jaw as described by Branemark et al., introduced a new era of management for the edentulous predicament. Implant rehabilitation of the edentulous maxilla remains one of the most complex restorative challenges because of the number of variables that affect both the aesthetic and functional aspect of the prosthesis. Among the prosthesis designs used to treat the edentulous maxilla are fixed or removable implant-supported restorations. Since the aesthetic requirements and preoperative situation of each patient varies, considerable time must be spent on accurate diagnosis to ensure patient desires are satisfied and predictable outcomes are achieved. The purpose of this article is to compare the treatment options and prosthesis designs for the edentulous maxilla. Emphasis will be placed on diagnosis and treatment planning. Criteria will be given to guide the practitioner in deciding whether a fixed or removable restoration should be placed. This objective will be accomplished through the review of cases with regard to varying design considerations and factors that influence the decision-making process.

Aged↗
PubMed1999

Total knee replacement: should it be cemented or hybrid?

OBJECTIVE: To compare the complication rates associated with total knee arthroplasty against the types of fixation (hybrid or cemented), using a single total knee design (the anatomic modular knee [AMK] prosthesis). DESIGN: A prospective, nonrandomized, controlled trial. SETTING: University Hospital in London, Ont., a tertiary care teaching centre. PATIENTS: Two groups made up of 484 knees in 395 patients (89 bilateral). INTERVENTIONS: In 260 knees a hybrid configuration (cemented tibia and noncemented femur) was used (group 1). In 224 knees the femoral and tibial components were cemented (group 2). All patellae were cemented in both groups. MAIN OUTCOME MEASURES: Clinical results were assessed by The Knee Society Clinical Rating Scores at 3 months, 6 months and yearly intervals. Radiographic results were determined by 3-foot standing radiographs and at each follow-up visit standing knee radiographs, lateral and skyline views. Radiographs were analysed for alignment, presence or absence of radiolucent lines or changes in the position of the implant. All reoperations and nonoperative complications were recorded. RESULTS: At an average follow-up of 4.8 years, 8 knees (1.6%) required reoperation. An analysis of the complications leading to reoperation demonstrated no difference between the 2 groups. CONCLUSIONS: There was no difference in outcome whether the femoral component was cemented or not. Medium-term results of the AMK are excellent with a very low reoperation rate.

Aged↗
PubMed2001

An anthropometric study of the radial head: implications in the design of a prosthesis.

The dimensions of the native radial head were measured in 28 cadaveric upper extremities and radiographs of the contralateral elbows of 40 patients who had received a radial head replacement. The mean difference between the maximum and minimum radial head diameters was 1.7 +/- 0.7 mm (range, 0.12-3.27 mm). This variability suggests that although the native radial head is not circular, it does not have a consistently elliptic shape. The native radial head also is variably offset from the axis of the neck (4.2 +/- 2.5 mm), suggesting that a radial head hemiarthroplasty that precisely replicates normal anatomy would be difficult to achieve. There was a poor correlation between the radial head diameter and the medullary canal of the radial neck, suggesting that a modular implant system should be considered.

Aged↗
PubMed1988

The cross-linking and structure modification of the collagen matrix in the design of cardiovascular prosthesis.

Glutaraldehyde cross-linking of native or reconstituted collagen fibrils and tissues rich in collagen significantly reduces biodegradation. Other aldehydes are less efficient than glutaraldehyde in generating chemically, biologically, and thermally stable cross-links. Implants of collagenous materials cross-linked with glutaraldehyde are subject long-term to calcification, biodegradation, and low-grade immune reactions. We have attempted to overcome these problems by enhancing cross-linking through (a) bridging of activated carboxyl groups with diamines and (b) using glutaraldehyde to cross-link the epsilon-NH2 groups in collagen and the unreacted amines introduced by aliphatic dismines. This cross-linking reduces tissue degradation and nearly eliminates humoral antibody induction. Covalent binding of diphosphonates, specifically 3-amino-1-hydroxypopane-1, 1-diphosphonic acid (3-APD), and to a lesser extent chondroitin sulfate to collagen or to the cross-ling-enhanced collagen network reduces its potential for calcification. Platelet aggregation also is reduced by glutaraldehyde cross-linking and nearly eliminated by the covalent binding of chondroitin sulfate to collagen. The cytotoxicity of residual glutaraldehyde can be minimized by chemical neutralization and thorough rough rinsing.

Adenosine Diphosphate↗
PubMed1987

An alternative design of extension prosthesis.

Some patients with a congenitally shortened lower limb can be fitted with a total contact socket of one piece construction, dispensing with the need for removable panels or split socket construction. This gives advantages in weight, strength and cosmesis. The technique is described and compared with those conventionally used.

Artificial Limbs↗
PubMed2006

Factors influencing calcification of cardiac bioprostheses in adolescent sheep.

OBJECTIVE: We determined the possible effects of age, antimineralization treatments, circulatory implant conditions, prosthesis design, and valve-related structural aspects on valve calcification in adolescent sheep. METHODS: Calcium content was measured by means of atomic absorption spectrometry in bioprostheses implanted in 120 sheep (age <1 year) for a period of 3 or 6 months. RESULTS: Bioprostheses calcified significantly in adolescent sheep, but the extent of calcification was multifactorial. Multivariate analysis of the calcium content reveals that age, mitral or pulmonary implant position, prosthesis design (stented or stentless), structure (porcine or pericardial, wall portion or cusp), and antimineralization treatment are independent factors influencing calcification; implant duration beyond 3 months was not. In juvenile sheep (age 5 months) the wall portion, as well as the cusps of the prosthesis, calcified significantly more than in adolescent sheep (age 11 months). Irrespective of age, the cusps of valves implanted in the mitral position calcified more than those in the pulmonary position. The wall portion of stentless valves calcified more than that of stented valves, and pericardial valves calcified less than porcine valves. The surfactant (Tween 80, No-React, and alpha-amino-oleic acid) and alcohol (ethanol and octanediol) treatment significantly reduced cusp calcification; sodium dodecylsulfate did not. None of the anticalcification treatments was able to prevent wall calcification in stentless porcine valves. CONCLUSION: These findings suggest that tissue valve calcification is determined by many independent factors, which can be identified by using adolescent sheep as a preclinical in vivo model.

Age Factors↗