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At least 865 records · Page 48Linked to original sources
PubMed1986

Loosening of the cemented hip prosthesis. The importance of heat injury.

The cemented hip arthroplasty is one of the most successful orthopedic operations. However, the results do deteriorate with time because of mechanical loosening. Some hips with obviously loose prosthetic components are not painful. This discrepancy between symptoms and radiographic evidence of loosening has caused uncertainty about the diagnostic criteria that should be applied. This uncertainty has in turn led to confusion about the basic cause of loosening. The aims of this presentation were to find a favorable definition of loosening and to investigate the etiology of mechanical loosening of the cemented hip prosthesis. The diagnostic criteria of contrast and radionuclide arthrography, bone scintigraphy, and roentgen stereophotogrammetric analysis (RSA) were evaluated in 14 symptomatic hip arthroplasties examined by these methods. Loosening was found to be best defined as migration; regardless of diagnostic criterion, all loose prosthetic components were migrating, but no nonmigrating component was loose. The development of the radiolucent zone was analyzed in a simple model consisting of 6 cases of giant-cell tumor of bone successfully treated by curettage and cementing. In locations where the cement filling adjacent to cancellous bone was concave, a considerably wider zone developed. There was a positive correlation between the width of the zone and the volume of cement. The radiolucent zone in this model could be explained by heat injury during the polymerization of bone cement. The pattern of migration of the components in 20 cemented hip prostheses was studied with RSA and with conventional radiography over a period of 2 years postoperatively. Eleven acetabular and three femoral components migrated. After an initial 4-month period of rapid migration, most components migrated slowly. The initial rapid migration could be accounted for by the resorption of a layer of necrotic bone following heat injury during the polymerization. The less frequent migration of the metallic femoral component as compared with the polyethylene acetabular component could be explained by the metal acting as a heat sink. Radiographic examination was found to be unsatisfactory as a means of detecting mechanical loosening during the first 2 postoperative years. RSA, on the other hand, was capable of revealing migration as early as 4 months postoperatively. Migration of the components in 16 hip prostheses was studied with RSA for 1 year postoperatively following randomized use of low- and high-viscosity cement. As regards prosthetic migration, no difference was detected between the two types of cement; low-viscosity cement did not improve prosthetic fixation.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetabulum↗
PubMed1984

Comparative fatigue behavior of different bone cements.

Tensile and fatigue studies were performed on four different preparations of acrylic bone cement: (1) surgical Simplex-P inserted into molds in the dough stage, (2) Zimmer Low Viscosity Cement (LVC) inserted in the liquid phase, (3) an experimental cement inserted in the dough phase, and (4) the same experimental cement inserted in the liquid phase. The void characteristics of the cements appeared to dictate their mechanical performance. While tests revealed no difference in the tensile strengths of the four cement preparations, small but statistically significant differences in mean fatigue life were observed. The experimental cement used in the dough stage exhibited superior fatigue characteristics when compared with Simplex and LVC. LVC had the poorest mechanical properties of the four cement groups. Since the specimen preparation procedures can markedly influence the cement void characteristics and, consequently, the mechanical properties, general statements about different cement types are offered with considerable reservations.

Bone Cements↗
PubMed1981

Improved cementing techniques.

To obtain good-quality cement, one should follow seven steps: 1. Mix with low frequency. 2. Clean bony cavity to avoid contamination of cement. 3. Pressurize cement before insertion. 4. Insert early, at low viscosity. 5. Pressurize cement after insertion. 6. Fully constrain cement. 7. Use no stress risers. To obtain maximum fixation strength, one should follow four steps: 1. Use gouges to expose trabecular bone. 2. Use brush and lavage to clean bone. 3. Insert cement early at low viscosity. 4. Pressurize cement to force it into open trabeculas. It is fortunate that the steps overlap; they are not mutually exclusive. Both require cleanliness. Both require the use of cement at low viscosity. Both require pressurization of the cement. If the steps are followed it is our belief that the best possible fixation with the best possible cement will be obtained.

Bone Cements↗
PubMed1994

Current attitudes to cementing techniques in British hip surgery.

Aseptic loosening is the major problem in hip joint replacement. Improved cementing techniques have been shown to improve the long-term survival of implants significantly. To assess the use of modern cementing techniques in British surgeons, a detailed questionnaire was sent to all Fellows of The British Orthopaedic Association (BOA) regarding cement preparation, bone preparation, cementing technique and prostheses used in total hip arthroplasty. Excluding retired fellows, surgeons who use no cement, and those who had filled in forms inadequately, 668 responded, who between them performed 43,680 hip arthroplasties per year. In this survey, 21 different types of hip prostheses were implanted by the surgeons; 48% of hips implanted were Charnley type. Of the surgeons, 46% used Palacos with gentamicin as their cement for both the femur and acetabulum. For the femur, 44% of surgeons remove all cancellous bone, 40% use pulse lavage, 59% use a brush to clear debris, 94% dry the femur, 97% plug the femur, 76% use a cement gun and 70% pressurise the cement. For the acetabulum, 88% of surgeons retain the subchondral bone, 40% use pulse lavage, 100% dry the acetabulum, 22% use hypotensive anaesthesia and 58% pressurise the cement. Overall only 25% of surgeons (26% of hips implanted) use 'modern' cementing techniques. This has implications for the number of arthroplasties that may require early revision.

Acetabulum↗
PubMed1992

Evaluation of the interactions between amalgam, cement and gold castings.

The purpose of this study was to determine the interactive effects between a dental amalgam, cements and a gold alloy and therefore evaluate cements as barriers to corrosion. There were 48 castings cemented to either simulated amalgam cores or teeth using zinc phosphate (ZnPO4) or glass polyalkenoate (ionomer) cement. An additional 12 castings were placed in direct contact with the amalgam restoration. Half of the specimens were thermocycled between 5 degrees and 50 degrees C for 12 weeks. The other half were stored at 37 degrees C for the same period of time. The specimens were then encased in epoxy resin and sectioned. The sectioned specimens were examined for cement loss, as well as evidence and extent of corrosion. Significantly more cement loss occurred with the ZnPO4 compared with the glass polyalkenoate (ionomer) cement when the castings were cemented to amalgam cores. Evidence of corrosion was apparent in all specimens; thermocycling produced significantly more corrosion than the 37 degrees C environment. The direct-contact group produced significantly more corrosion compared with the specimens where castings were cemented with ZnPO4.

Corrosion↗
PubMed1981

Enamel fluoride uptake from orthodontic cements and its effect on demineralization.

This study was undertaken to determine the in vitro enamel fluoride uptake and distribution from fluoride-containing orthodontic cements after 21 days' exposure and the effect on acid demineralization. Three successive acid-etch biopsy specimens were taken from tne facial middle third of thirty maxillary central incisors. Orthodontic bands were cemented to these teeth, ten each with (A) zinc phosphate, (B) zinc phosphate containing 5 percent SnF2, and (C) silicophosphate cement, respectively. The teeth were suspended individually in synthetic saliva at 37 degrees C. in a shaking incubator for 21 days. The bands were removed, the cement was cleaned off, and three successive biopsies were carried out electrometrically and for calcium by atomic absorption spectroscopy. Fluoride concentrations were adjusted to depths of 10.0, 20.0, and 30.0 micron for the three biopsies, respectively. The acquired fluoride was calculated and the data were analyzed statistically. In addition, six teeth each with bands cemented with cements A, B, and C, respectively, were incubated in synthetic saliva for 21 days, after which the bands were loosened and the teeth were suspended for a further 3 months in a caries-producing medium. After careful cleaning, the enamel surfaces were examined by microradiography and scanning electron microscopy for demineralization. Results showed that acquired fluoride at the first depth was highest with cement C, followed by cement B, with cement A producing a net loss of fluoride. Further, the greater the fluoride uptake, the more resistant the enamel was to demineralization.

Dental Caries↗
PubMed1980

An in vitro model for studying adsorption of oral streptococci to crown and bridge cements.

A sensitive, in vitro method has been developed for the study of bacterial adsorption to dental crown and bridge cements. The method employs heavily radiolabelled cells which adhere to the wall in wells made from the cements. Loss of radioactivity from the bacterial suspension during incubation is used to measure the degree of bacterial adherence to the materials. Strains of Streptococcus sanguis and Streptococcus mutans adhered in greater numbers than a strain of Streptococcus salivarius to both a zinc phosphate cement and a zinc carboxylate cement. The zinc phosphate cement supported adherence to a greater degree than did the zinc carboxylate cement. Pretreatment of the cement surfaces with human saliva tended to reduce bacterial adherence. Pretreatment of the bacteria with saliva slightly enhanced sorption of S. sanguis and S. salivarius, but tended to impair sorption of S. mutans to both types of cements. When both bacteria and cements had been pretreated with saliva, a strong inhibition of the adherence of S. mutans was observed.

Adhesiveness↗
PubMed1989

Effects of the porcelain firing sequence on the bond strengths of cements.

Bond strengths for the retention of ceramic bonded to metal alloys to the tooth structure involve cavity preparation variables, cement variables and ceramic bonded to metal alloy variables. The aim of this work was to evaluate the retentive strength differences between alloy surfaces, unfired and fired, for porcelain alloys retained with different dental cement compositions. The clinical situation was stimulated by using standardized tooth preparations, extracted teeth and castings cemented with zinc phosphate and polycarboxylate cements, which were debonded on an Instron. Jelenko O, Cameo, Jelstar and Genesis II alloys were compared unfired and fired to simulate porcelain application. Fired Jelenko O casting alloy cemented with polycarboxylate cement produced the greatest bond strengths (6.0 +/- 1.0 MPa). Polycarboxylate cemented castings had greater bond strengths for all alloys whether fired or not. The only effect of firing was an improvement with Jelenko O alloys produced with both cements. All of these differences were statistically significant at the P less than 0.01 level using Tukey's post hoc evaluation. The improvements observed were related to the oxide formation on the internal surfaces of the casting and the ability of polycarboxylate cement to adhere chemically to those layers.

Chromium Alloys↗
PubMed1983

Physical properties of some zinc phosphate and polycarboxylate cements.

Several physical properties were measured for two zinc phosphate and three polycarboxylate cements. The specimens were tested in compression 24 h after they had been made. Two series of specimens were examined. In one series the cement powders were given a correct treatment, protected from atmospheric humidity. In the other series the powders were exposed for 1 week to ambient conditions with the temperature varying between 20 degrees and 24 degrees C and the relative humidity between 40% and 59%. The zinc phosphate cements were characterized by high values of modulus of elasticity and by plastic deformations less than 0.2%. The polycarboxylate cements were more flexible and also exhibited large plastic deformations. Compared with the zinc phosphate cements, therefore, the polycarboxylate cements had high values of resilience and toughness. The storing of cement powders exposed to atmospheric humidity for 1 week did not change the measured properties of the polycarboxylate cements. However, both strength and resilience were significantly reduced for one phosphate cement.

Chemical Phenomena↗
PubMed1999

Contemporary evaluation of dental cements.

Today, the clinician has numerous dental cements available for luting of restorations to prepared teeth. Compared to traditional cements, many of the newer cements have improved physical properties. In this article, we analyze available cements in terms of these physical properties based on scientific data and attempts to determine their effect on long-term clinical performance. We conclude that these improved physical properties do not necessarily result in improved clinical performance. We also conclude that although these newer cements have specific clinical applications, they should not be routinely used for the cementation of metal castings because they are clearly more technique-sensitive than traditional luting agents. Zinc-phosphate cement remains the cement of choice for cementing cast gold and metal-ceramic restorations.

Biocompatible Materials↗
PubMedDate not supplied

A split-mouth randomized clinical trial of single crowns retained with resin-modified glass-ionomer and zinc phosphate luting cements.

PURPOSE: This study compared the influence of two luting cements on the clinical performance of single crowns. MATERIALS AND METHODS: Twenty patients received 39 pairs of metal-ceramic and Procera crowns cemented with zinc phosphate and resin-modified glass-ionomer luting cement (Vitremer) in a split-mouth randomized pattern blinded to the recipient. The crowns were examined immediately after cementation, after 2 weeks, after 6 months, and then yearly. Clinical performance was scored according to CDA criteria, Silness and Loe criteria, patient satisfaction, and operator-appraised general clinical criteria. Three clinicians in private general practice carried out all procedures. RESULTS: During the observation period, which varied between 80 and 104 months, seven clinical events were recorded. Two abutments fractured vertically, two underwent retrograde endodontic surgery, and one developed pulp necrosis. Two crowns were recemented. Estimated survival, defined as no negative events observed, was 89% at 102 months (85% for crowns cemented with zinc phosphate and 93% for crowns cemented with resin-modified glass-ionomer). Estimated survival, defined as no recementation or loss of pulp vitality, was 96% at 102 months (95% with zinc phosphate and 97% with resin-modified glass-ionomer). The differences between cements were not statistically significant. CONCLUSION: A resin-modified glass-ionomer luting cement was at least as good as zinc phosphate cement to retain single crowns over a 102-month observation period.

Cariostatic Agents↗
PubMedDate not supplied

Experimental facial augmentation with hydroxyapatite cement.

OBJECTIVE: To study the results of implantation of preformed hydroxyapatite (HA) disks and HA cement in onlay augmentation. METHODS: In this prospective study involving 16 adult New Zealand rabbits, HA disk and HA cement samples were implanted separately and together along the bony and cartilaginous nasal dorsum as well as over the supraorbital bone. Gross and histologic examinations of the implants were performed at intervals ranging from 3 to 24 months. RESULTS: There was no evidence of infection, adverse reaction, or implant extrusion in the 15 rabbits surviving the planned period. Grossly, all rabbits had prominent noses and supraorbital regions that were immobile on digital palpation. No measurable change in HA disk height and width was noted but there was a 15% decrease in height and width in the HA cement implant. Microscopically, preformed HA disks were found to be enclosed in a vascularized fibrous capsule. When disks were combined with HA cement, a vascular fibrous capsule was still noted around the implant but there was osteoconversion in the underlying cement layer. Used alone, HA cement underwent both osteoconversion and osteointegration. Neither the preformed HA disk with and without HA cement nor the HA cement alone elicited giant cell reaction or inflammatory changes. The HA cement alone was found to have microscopic fissures at the edges. CONCLUSION: This animal study suggests that preformed HA implants and HA cement, alone or in combination, can be used to augment the non-stress-bearing craniofacial skeleton.

Animals↗
PubMed2003

Influence of polymeric additives on the biological properties of brushite cements: an experimental study in rabbit.

The resorbability and ability of calcium phosphate hydraulic cements to promote new bone formation was investigated in vivo. The effects of two hydrosoluble polymeric additives (hyaluronic acid, and xanthan gum,) on the biological response of two brushite cement formulations (BHC-A vs BHC-B) was investigated. The brushite cements differed in P/Ca (0.71 vs 0.98) and S/Ca (0.10 vs 0.005) atomic ratios and by the presence of calcium sulfate hemihydrate in BHC-A. Polymer-free cements were used as controls. Cement specimens were injected in cylindrical bone defects manually drilled in the distal condyle of rabbit femora. The implants were harvested at 12 and 24 weeks after implantation and subjected to quantitative histomorphometry. The study showed a significantly lower resorption rate for cement BHC-A, which induces the formation of well-mineralized bone in close apposition to the residual material. In contrast, cement BHC-B showed a significant increase of bone formation period and the formation of a thick layer of unmineralized osteoid tissue at the bone/residual cement interface. The presence of xanthan gum made the biological response even worse, particularly in the case of cement BHC-B. The presence of hyaluronic acid has little effect, except for a slight decrease in initial resorption rate, in the case of cement BHC-A.

Animals↗
PubMed2005

Biocompatibility and degradation of poly(DL-lactic-co-glycolic acid)/calcium phosphate cement composites.

Injectable calcium phosphate (Ca-P) cement materials exhibit favorable osteocompatible behavior but are resorbed slowly because of a lack of a bone ingrowth-enabling macroporosity. In this study, poly(DL-lactic-co-glycolic acid) (PLGA) microparticles (average size 66 +/- 25 microm) were incorporated into Ca-P cement to obtain a macroporous Ca-P cement scaffold after PLGA hydrolysis in vivo. Preset PLGA/Ca-P cement composite discs of various weight ratios (0/100, 15/85, 30/70, and 50/50) were implanted subcutaneously and in cranial defects in rats for 12 weeks. Histological analysis revealed that all macropores in the PLGA-containing composites (average pore size 73 +/- 27 microm) were filled with fibrous tissue and blood vessels (subcutaneous implants) and/or bone (cranial implants). Histologically, bone formation appeared most abundant and most consistent in the 30/70 PLGA/Ca-P cement composites. Histomorphometrical evaluation revealed a significant increase in defect fill in the 15/85 and 30/70 PLGA/Ca-P cement composites. Finally, subcutaneous and cranial 50/50 PLGA/Ca-P cement composites had degraded to a large extent, without adequate replacement by bone in the cranial implants. Therefore, we conclude that PLGA/Ca-P cement composites enable tissue ingrowth and show excellent osteocompatibility in weight ratios of 15/85 and 30/70 PLGA/Ca-P cement. In this model, 30/70 PLGA/Ca-P cement composites showed the most favorable biological response.

Absorbable Implants↗
PubMed2004

Influence of oscillatory mixing on the injectability of three acrylic and two calcium-phosphate bone cements for vertebroplasty.

Injecting acrylic and, increasingly, calcium-phosphate cements into the porous bone structure is an emerging procedure, referred to as vertebroplasty, for the augmentation of osteoporotic vertebrae. Despite the benefits of vertebroplasty, it has limitations. The limitations of interest in this study are the injectability of bone cements and their mixing variability (i.e., low reproducibility of resulting viscosity). The objective of this study is to investigate the effect of oscillatory versus manual mixing on cement viscosity and mixing variability. Five cements are tested: (a) Vertebroplastic, (b) DP-Pour, (c) Antibiotic Simplex, (d) chronOS Inject, and (e) Biopex. Compared to manual mixing, oscillatory mixing significantly decreased the mean viscosity and the mixing variability, which was inferred from the coefficient of variation. For example, under oscillatory mixing, the viscosity and the variability for Vertebroplastic decreased to one-third of the corresponding values for manual mixing. Similar results were obtained for the other cements. The decrease in viscosity is attributed to the pseudo-plastic behavior of bone cements. The decrease in the variability of cement viscosity was attributed to greater dispersive mixing of the cement components under oscillatory mixing. The decrease in viscosity eases the injection by reducing the pressure required. The decrease in the variability of cement viscosity increases reproducibility of the cement injection. Oscillatory mixing appears to have the potential to contribute to improving vertebroplasty.

Bone Substitutes↗
PubMed2005

Radon exhalation of hardening concrete: monitoring cement hydration and prediction of radon concentration in construction site.

The unique properties of radon as a noble gas are used for monitoring cement hydration and microstructural transformations in cementitious system. It is found that the radon concentration curve for hydrating cement paste enclosed in the chamber increases from zero (more accurately - background) concentrations, similar to unhydrated cement. However, radon concentrations developed within 3 days in the test chamber containing cement paste were approximately 20 times higher than those of unhydrated cement. This fact proves the importance of microstructural transformations taking place in the process of cement hydration, in comparison with cement grain, which is a time-stable material. It is concluded that monitoring cement hydration by means of radon exhalation method makes it possible to distinguish between three main stages, which are readily seen in the time dependence of radon concentration: stage I (dormant period), stage II (setting and intensive microstructural transformations) and stage III (densification of the structure and drying). The information presented improves our understanding of the main physical mechanisms resulting in the characteristic behavior of radon exhalation in the course of cement hydration. The maximum value of radon exhalation rate observed, when cement sets, can reach 0.6 mBq kg(-1) s(-1) and sometimes exceeds 1.0 mBq kg(-1) s(-1). These values exceed significantly to those known before for cementitious materials. At the same time, the minimum ventilation rate accepted in the design practice (0.5 h(-1)), guarantees that the concentrations in most of the cases will not exceed the action level and that they are not of any radiological concern for construction workers employed in concreting in closed spaces.

Construction Materials↗
PubMed1998

Bond strength between cements and metals used for endodontic posts.

OBJECTIVES: Adhesive cements used with metal endodontic posts may decrease fracture in non-vital teeth. Results from studies that evaluate cements for post retention by pulling posts out of extracted teeth are difficult to interpret owing to the number of interfaces where fracture might occur. The objective of this study was to isolate the metal/cement interface for tensile bond strength testing and microscopic observation. METHODS: Three metals and seven cement treatments were examined for bond strength by using a truncated cone tensile test. The bond strength data were analyzed by a two-way ANOVA and Scheffé's multiple comparison test at p = 0.05. Specimens were examined at 50x magnification to determine the failure mode and with scanning electron microscopy (500x) to observe the surfaces after debonding. RESULTS: Significant differences in tensile bond strengths were found among cements compared within two of the metal groups. One of the metal groups had no significant differences among cement bonds. When comparing within cement treatment groups, two groups had significant differences in bond strength among the metals. Microscopic observations revealed adhesive, cohesive and mixed failure modes that varied with cement treatment and metal combination. The interaction between metal and cement was a critical determinant of the strength and characteristic fracture mode of the bond achieved. SIGNIFICANCE: Some of the cement treatments performed better (i.e., higher bond strength) with some metals than with others. Other cements had similar bond strengths with all three metals. Because of this interaction, careful consideration of the materials combination should help to maximize the bond at the metal/cement interface.

Adhesiveness↗
PubMed2002

Creep behavior comparison of CMW1 and palacos R-40 clinical bone cements.

The restrained dynamic creep behaviors of two clinical bone cements, Palacos R-40 and CMW1 have been investigated at room temperature and body temperature. It was found that the two cements demonstrated significantly different creep deformations, with Palacos R-40 bone cement demonstrating higher creep strain than CMW1 bone cement at each loading cycle. For both cements, two stages of creep were identified with a higher creep rate during early cycling followed by a steady-state creep rate. The test temperature had a strong effect on the creep performance of the bone cements with higher creep rate observed at body temperature. The relationship between creep deformation and loading cycles can be expressed by single logarithmic model. The SEM examinations revealed that CMW1 bone cement is more sensitive to defects within the specimen especially to the defects at the edges of the specimen than Palacos R-40 bone cement. However, in the absence of micro-cracks or defects within the inner surface layer, the dynamic loading (at less than 10.6 MPa) is unlikely to produce micro-cracks in the CMW1 bone cement. The different behaviors between the two bone cements may be attributed to differences in chemical compositions and molecular weight distributions.

Journal Article↗