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PubMed2006

Improved mechanical properties of acrylic bone cement with short titanium fiber reinforcement.

Acrylic bone cements are widely used in total joint arthroplasties to grout the prosthesis to bone. The changes in the tensile properties and fracture toughness of polymethylmethacrylate (PMMA) bone cements obtained by the addition of control and heat treated short titanium fibers are studied. Heat treatment of titanium fibers is conducted to precipitate titania particles on the fiber surface to improve the biocompatibility of the metal. Control and heat treated short titanium fibers (250 micro long and 20 micro diameter) were used as reinforcements at 3 volume %. X-ray diffraction indicated the presence of a rutile form of titania due to the heat treatments. The tensile and fracture properties were improved by the addition of fibers. Bone cements reinforced with titanium fibers heated at 550 degrees C for 1 h followed by 800 degrees C for 30 minutes show the largest increase in fracture toughness along with the smallest changes in elastic modulus and needs to be further investigated.

Benzoyl Peroxide↗

PubMed2006

Optimisation of the composition of an acrylic bone cement: application to relative amounts of the initiator and the activator/co-initiator in Surgical Simplex P.

In cemented arthroplasties, the two-part self-curing acrylic bone cement is currently the only material used for anchoring the total joint replacement to the contiguous bone. In virtually all commercially available formulations of this cement, the agents used for the initiation and activation/co-initiation of the radical polymerisation reaction are benzoyl peroxide (BPO) and N, N dimethyl-para-toluidine (DMPT), respectively. There are no reports in the open literature on the rationale for the amounts of these and other constituents in the formulations of the cement. Given the concerns that have been raised in the literature regarding the effect of residual DMPT on the body, it is important to keep the starting amounts of BPO and DMPT as high and as low, respectively, as possible. In the present work, the focus is on the relative amounts of these two agents in the case of one widely used commercial formulation, Surgical Simplex(R) P. Thirty variants of this cement were formulated, covering three concentrations of the co-polymer/BPO (75%, 80%, and 85% of the mass of the powder) and DMPT amounts (ranging from 0.8 %v/v to 2.4% v/v.) The setting time (t(set)), the peak temperature reached during the cement polymerisation process (T(max)), and the ultimate compressive strength (UCS) of each of the formulations were determined in accordance with procedures specified in ISO 5833. A critical examination of all the results indicated that the optimum ratio of the concentration of the initiator (BPO embedded in the PMMA-sytrene co-polymer) to that of the activator/co-initiator (DMPT) in Surgical Simplex(R) P is 57.14 (80%w/w co-polymer + BPO per 1.4%v/v DMPT). The mean values of t(set), T(max), and UCS of this optimum formulation were determined to be 12.30 min, 68 degrees C, and 101 MPa, respectively, all of which are within the limits specified in ISO 5833. The commercially available formulation of this cement contains 2.5%v/v DMPT, while the optimum formulation, as found in the present work, has 44% less DMPT, which may translate to a smaller amount of residual DMPT that is available for elution into the periprosthetic tissue in a cemented arthroplasty, over the in vivo life of the joint replacement.

Adhesiveness↗

PubMed1986

Effect on experimental palatal candidosis in the Wistar rat of removal and re-insertion of acrylic appliances.

Palatal candidosis was produced by inoculating Candida albicans 3091 (serotype A) under an acrylic appliance. Two weeks was allowed for infection to occur. Removal of the appliance for a further period of 2 weeks resulted in complete resolution of the lesion histologically but Candida organisms could still be recovered from the mucosal surface. Re-fitting these appliances at the end of this recovery period, without subsequent inoculation, produced a recrudescence of palatal candidosis after a further 2 weeks. One possible explanation is that C. albicans was encouraged to change from the commensal to the pathogenic form in the presence of the palatal appliance.

Animals↗

PubMed1987

Treatment of unstable trochanteric fractures with Dimon-Hughston osteotomy displacement fixation and acrylic cement.

For the management of unstable trochanteric fractures, a new method consisting of Dimon-Hughston medial displacement osteotomy, fixation with a sliding screw sleeve-plate device, with augmentation of the posterior and medial upper femoral cortical defect with acrylic cement, was performed in 84 patients. All patients were allowed full weight bearing on the affected extremity within 1 week of operation. Sixty-five patients were available for follow-up more than 12 months after operation. Complication rates were low and 77 per cent of the patients achieved excellent and good functional results.

Aged↗

PubMed1984

Improvement of mechanical properties of acrylic bone cement by fiber reinforcement.

Acrylic bone cement is significantly weaker and less stiff than compact bone. Bone cement is also weaker in tension than in compression. This limits its use in orthopaedics to areas where tensile stresses are minimum. We have attempted to improve the mechanical properties of PMMA by reinforcing it with metal wires, and graphite and aramid fibers. Normal, carbon fiber reinforced and aramid fiber reinforced bone cement specimens were tested in compression. Addition of a small percentage (1-2% by weight for carbon and up to 6% for aramid) of these fibers improved the mechanical properties significantly. Due to the improved mechanical properties of fiber reinforced bone cement, its clinical use may reduce the incidence of cement fracture and thus loosening of the prosthesis.

Biomechanical Phenomena↗

PubMed1994

In vitro fatigue fracture of an acrylic resin-based partial denture: an exploratory study.

In this study the fatigue life of heat-cured acrylic resin test specimens shaped as maxillary partial dentures was examined. Ten test specimens were prepared from polymethyl methacrylate and were tested by a constant force fatigue test at 150 N immersed in +37 degrees C water. The fatigue-fracture surfaces of the test specimens were compared with a one-bend fracture surface of the control specimen by scanning electron microscopy. The correlation coefficient between the number of loading cycles required to cause fatigue failure in the midline section was calculated as was the concentration of residual methyl methacrylate. Results revealed that the fatigue life of the test specimens varied greatly (483 x 10(3) +/- 371 x 10(3) cycles) and that the correlation between the number of loading cycles and the midline section was poor (r -0.455). The correlation coefficient between the number of loading cycles and the concentration of residual methyl methacrylate was r 0.476 and p > 0.5. The fatigue-fracture surface of the test specimens was smoother in texture on the tension side than on the one-bend fracture surface.

Denture Design↗

PubMed1994

Acrylic resin-fiber composite--Part I: The effect of fiber concentration on fracture resistance.

This study tested the effect on the fracture resistance of acrylic resin test specimens when different amounts of fibers were incorporated in the resin matrix. The fibers used included glass, carbon, and aramid fibers, with 30 test specimens of each concentration of fibers. Transverse sections of the specimens were studied by scanning electron microscope to establish how the fibers behave in the polymerization process. The results indicated that an increase in the amount of fibers enhanced the fracture resistance of the test specimens (p < 0.001). The SEM micrographs of transverse sections of test polymerized specimens revealed void spaces of different sizes inside the fiber roving.

Analysis of Variance↗

PubMed1994

Sea nettle (Chrysaora quinquecirrha) lethal factor: purification by recycling on m-aminophenyl boronic acid acrylic beads.

Experiments were performed to define the best isolation method for isolating Chrysaora fishing tentacle nematocyst organelles in order to minimize non-nematocyst contaminating proteins and proteases and stabilize crude nematocyst venom lethal activity. Techniques employed to disrupt the tentacles included autolysis, homogenization, or digestion using either trypsin or collagenase. Sephacryl-200 gel-filtration chromatography separated two lethal fractions. An immobilized serine protease inhibitor column, m-aminophenyl boronic acid acrylic beads, which reversibly bound one of the two lethal factors, was used in the second and third purification steps. By this means, a 105,000 mol wt. protein was purified, as judged by silver stained SDS-polyacrylamide gels. Lethal activity was inhibited by exposure to the serine protease inhibitor, L-1 chloro 3[4-tosylamido]-7-amino-2-heptanone-HCl, after purification. Although this lethal factor has some characteristics of a serine protease, it is not proteolytically active.

Amino Acids↗

PubMed1979

Fracture processes in acrylic bone cement containing barium sulphate dispersions.

This paper describes the effects of dispersions of barium sulphate (BaSO4) particles on crack nucleation and growth in a commercially available surgical acrylic bone cement. A simple model is presented which is based on the nucleation and growth of voids around each BaSO4 particle. The model assumes that the local stress at a particle depends on the strain applied to the material, whereas the overall stress on the system depends on the volume fraction of particles. The effects of saline solution and blood serum on crack propagation are described.

Barium Sulfate↗

PubMed1983

Selection of acrylic bone cements for use in joint replacement.

Commercial acrylic bone cements have been compared in terms of their mechanical, thermal and rheological properties. Significant differences have been found between the tensile strengths, shear strengths and peak polymerization temperatures of the cements tested. Large differences have been found between the viscosities of different formulations and the duration of their working periods during polymerization. Optimum cement selection is found to depend critically upon ambient conditions within the operating theatre considered in combination with the characteristics of the cements themselves. It is proposed that, at present, the only differences between commercial bone cements of relevance to successful joint replacement lie in the area of rheological properties during polymerization.

Bone Cements↗

PubMed1983

Fracture toughness of acrylic denture base.

This paper describes the application of two fracture toughness tests, the compact tension (CT) and the double torsion (DT) to homogenous poly(methyl methacrylate) and two-phase acrylics. Materials were tested in air as processed and after saturation for one month in water. Most materials gave stable crack propagation with these tests, allowing accurate measurement of crack velocity. Modulus and un-notched fracture strength (sigma f) were determined at an identical strain rate in bending to that used in the fracture toughness tests, allowing accurate calculation of the flaw size (a) for a material and an assessment of how applicable Linear Elastic Fracture Mechanics are to these materials.

Denture Bases↗

PubMed1996

New aspects of the effect of size and size distribution on the setting parameters and mechanical properties of acrylic bone cements.

The effect of the size and the size distribution of poly(methyl methacrylate) (PMMA) beads on the classical kinetic parameters, peak temperature and setting time, for acrylic bone cement formulations prepared with PMMA particles in the range 10-60 microns of average diameter and a relatively wide size distribution is analysed. In addition, the combined effects of the concentration of the free radical initiator benzoyl peroxide and the activator N, N-dimethyl-4-toluidine for the different particle sizes are studied and compared with those commercially available formulations like CMW or Rostal. The results obtained indicated that the use of PMMA particles with average diameter of 50-60 microns, and a relatively wide size distribution (10-140 microns diameter), significantly changes the curing parameters (peak temperature and setting time) of the cement formulations in comparison with the classical behaviour of the commercial systems of CMW and Rostal, without any noticeable loss in the mechanical properties, such as tensile strength, elastic moduli, and compressive strength and plastic strain.

Benzoyl Peroxide↗

PubMed1992

Determination of doughing and manipulation times of acrylic resin denture base material and a proposal for a specification for a packing plasticity test.

The doughing and manipulation times of a range of acrylic resin denture base polymers are presented in this study. The methods evaluated were: (i) probing following American Society for testing materials specification, F451-76; (ii) hole penetration following British Standard, 2487: 1989 and International Standard Organisation, 1567: 1988; (iii) probing using a penetrometer employing a 20 g load and 1 mm diameter needle; (iv) oscillating rheometer apparatus used at a fixed frequency of 1 Hz by sweeping through a programmed linear increase in strain. The results indicate that each of the methods is capable of evaluating the doughing and manipulation times of the unprocessed polymers. It is concluded that the Bohlin VOR Oscillating Rheometer is excellent for investigating the flow properties of denture base polymers but it cannot be recommended for a standards specification test because of the high cost. The penetrometer method has been shown to be superior to the current standards specification test and would be ideal for a packing plasticity standards test.

Denture Bases↗

PubMed1982

Site binding as a local equilibrium. Mn2+ binding to poly(acrylic acid) as a function of the degree of ionization.

Mn2+ binding to poly(acrylic acid) at different degrees of ionization, alpha, has been studied from the frequency dependence of the water protons' relaxation rates T1(-1) and T2(-1). Site binding is treated as an equilibrium with the concentration of free ions at the immediate vicinity (CIV) of the polyion. The CIV is calculated as the solution of the Poisson-Boltzmann equation at the surface of the cylindrical polyion. A single value of K is shown to fit the results at all values of alpha. The amount of site binding is higher than the total amount of condensed divalent counterions predicted for a finite polyion concentration in the presence of monovalent counterions by Manning's theory.

Journal Article↗

PubMed1988

Fabrication of the acrylic splint Herbst appliance.

This article describes the fabrication of one type of Herbst appliance, a removable or fixed functional appliance that causes the posturing of the mandible in a forward position. The type of Herbst appliance described in this article consists of a wire framework to which are attached the various parts of the Herbst bite-jumping mechanism. The acrylic part of the appliance is fabricated from splint Biocryl or from methylmethacrylate. The steps of the fabrication of the appliance are described in detail.

Activator Appliances↗

PubMed1993

The acrylic-splint Herbst appliance: a cephalometric evaluation.

The purpose of this study was to investigate the skeletal and dental effects of the removable acrylic-splint Herbst appliance cephalometrically. Radiographs of 46 patients were collected, traced, digitized, and analyzed. Cephalometric measurements indicated that the treatment group was Class II before treatment and Class I after treatment, with no change in the vertical skeletal pattern. There was significantly more mandibular growth (Co-Gn) than in an untreated Class II control sample (P < or = 0.001), and less forward maxillary growth (nasion perpendicular to A) (P < 0.05). Molar correction was obtained by 21% more skeletal change and overjet correction by 25% more skeletal change than reported for the banded Herbst. Patients with higher mandibular plane angles had greater correction of Class II indicators than did patients with low angles. There was no significant change in the sagittal position of the condyle.

Adolescent↗

PubMed2006

A long-term evaluation of the mandibular Schwarz appliance and the acrylic splint expander in early mixed dentition patients.

INTRODUCTION: The aim of this prospective longitudinal clinical study was to evaluate the short-term and long-term changes in dental-arch dimensions in patients treated with either an acrylic splint rapid maxillary expander alone (RME-only) or a rapid maxillary expander combined with a mandibular removable Schwarz plate (RME-Sz) in the early mixed dentition, followed later by fixed appliances in the permanent dentition. METHODS: The dental casts of 27 RME-only patients were compared with those of 23 RME-Sz patients and 16 untreated controls (CTRL) with constricted maxillary arches at 4 times: pretreatment (T1), after expansion but before fixed appliance therapy (T2), after fixed appliance therapy (T3), and at long-term observation (T4). The mean ages for the treated groups were approximately 9 years at T1, 12 years at T2, 14 years at T3, and 20 years at T4. Arch width, arch depth, arch perimeter, and molar angulation were assessed in all subjects at all observation times. T1-T2, T2-T3, T3-T4, and T1-T4 changes were compared statistically in the treated groups with respect to the CTRL. RESULTS: Treatment with an RME-only or an RME-Sz followed by fixed appliances produced significant short-term and long-term increases in maxillary arch widths compared with the CTRL. The RME-Sz led to significantly more favorable results than the RME-only protocol: (1) significantly greater increases in the transverse width of the mandibular arch and mandibular arch perimeter in the long term, and (2) uprighting of the mandibular posterior teeth buccally, thus allowing for an amount of maxillary expansion that was clinically effective for the correction of moderate tooth size-arch size discrepancies. In the overall observation interval, the significant increases in maxillary and mandibular arch perimeters in the RME-Sz group were 3.8 and 3.7 mm, respectively, when compared with the CTRL. The RME-only protocol produced modest long-term increases in maxillary arch perimeter (2.6 mm); the average long-term increase in mandibular arch perimeter (2.0 mm) in the RME-only group was not statistically significant. CONCLUSIONS: The RME-Sz led to significantly more favorable results than the RME-only protocol.

Analysis of Variance↗

PubMed2005

Fluoride-containing acrylic bone cement in total hip arthroplasty. Randomized evaluation of 97 stems using radiostereometry and dual-energy x-ray absorptiometry.

Ninety patients (97 hips) scheduled for total hip arthroplasty were stratified to fixation of the femoral component using fluoride-containing cement or Palacos with gentamicin. Whole polyethylene Reflection and press-fit Trilogy cups were used. All patients received Spectron EF stem. The micromotions of the stem were measured with radiostereometric analysis and the periprosthetic bone mineral density with automatic and manual dual-energy x-ray absorptiometry (DEXA) analysis. At 2 years, the choice of cement did not influence the subsidence or rotations of the stem. The DEXA analysis revealed more loss of periprosthetic bone mineral density in fluoride cement group. We speculate that forming of fluorapatite crystals, toxic effects of the fluoride, or lower radiopacity of the fluoride cement might explain this finding. According to our study with 2-year of follow-up, there is no obvious advantage of addition of fluoride to acrylic bone cement when used to fixate the femoral component in total hip arthroplasty.

Absorptiometry, Photon↗