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Results for “Polymethyl Methacrylate”

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PubMed1997

Lased and sandblasted denture base surface preparations affecting resilient liner bonding.

STATEMENT OF PROBLEM: Adhesive failure between the liner and the denture base creates an environment for potential bacterial growth and accelerated breakdown of the soft liner resulting in a deteriorating prosthesis. PURPOSE: This study evaluated the effects of a specific sandblasted or lased preparation on the interfacial bonding of polymethyl methacrylate and silicone and polyethyl methacrylate resilient liners. MATERIAL AND METHODS: Polymethyl methacrylate test specimens were fabricated and received one of three surface treatments: untreated (control), sandblasted (250 microns aluminum oxide particles), and lased (carbon dioxide). Polyethyl methacrylate and silicone resilient lining materials were applied to these surfaces and the peel strengths were determined with the American Society for Testing and Materials peelin-adhesion test. RESULTS: Altering the polymethyl methacrylate surface by sandblasting significantly reduced the peel strengths for the polymethyl methacrylate/polyethyl methacrylate and polymethyl methacrylate/silicone specimens. Altering the polymethyl methacrylate surface by delivering carbon dioxide laser energy to form a grid pattern produced lower peel strengths that were statistically significant from the controls for the polymethyl methacrylate/polyethyl methacrylate specimens, but not so for the polymethyl methacrylate/silicone specimens. Untreated polymethyl methacrylate/polyethyl methacrylate peel strengths were significantly higher than polymethyl methacrylate/silicone. CONCLUSIONS: Results of this study imply that mechanical surface preparation of denture bases before application of a resilient liner may not be warranted.

Adhesiveness↗

PubMed2006

Comparison of temperature increase in the pulp chamber during the polymerization of materials used for the direct fabrication of provisional restorations.

STATEMENT OF PROBLEM: Polymerization of resin materials used for the fabrication of provisional restorations is associated with an exothermic reaction. This temperature rise may present a serious biological problem, since it can cause iatrogenic thermal trauma to the pulp. PURPOSE: This in vitro study compared the temperature increase in the pulp chamber of a molar placed in contact with different resins used for the direct fabrication of provisional restorations. MATERIAL AND METHODS: Polymethyl methacrylate (Jet), polyethyl methacrylate (Snap), polyvinylethyl methacrylate (Trim), Bis-acrylic composite (Protemp II), and a VLP urethane dimethacrylate (Revotec LC) were compared with respect to their exothermic reaction properties during polymerization. A mandibular molar prepared for a complete coverage restoration was placed in an acrylic resin block. A thermal probe connected to a digital thermometer was placed into the pulp chamber. Specimens were submerged in a water bath to simulate intraoral conditions. The provisional resin materials tested were measured and mixed according to manufacturer's instructions. The resin mixture was placed into a vacuum-formed acetate template and was then positioned on the prepared molar tooth. The temperature was recorded during polymerization at 30-second intervals until it was evident that the peak temperature had been reached. Temperature increase was measured ( degrees C) for both the initial crown fabrication and the reline procedures. Data were analyzed with descriptive statistics, 1-way analysis of variance, and Tukey Honestly Significant Difference tests (alpha=.05). RESULTS: One-way ANOVA revealed significant differences (F=57.010, P<.0001) in temperature rise for different provisional resin materials. Mean temperature increase for the provisional crown fabrication ranged from 37.76 degrees C for the polyvinylethyl methacrylate to 39.40 degrees C for the polymethyl methacrylate. Mean temperature rise for the reline procedures ranged from 36.80 degrees C for the polyvinylethyl methacrylate to 37.69 degrees C for the polymethyl methacrylate. All of the tested materials produced an exothermic chemical reaction. CONCLUSIONS: Polymethyl methacrylate produced the higher exothermic reaction in both initial crown fabrication and reline procedures. Polyethyl methacrylate, polyvinylethyl methacrylate, and Bis-acrylic resins tested were not significantly different from each other.

Acrylic Resins↗

PubMed2004

Ultraviolet radiation absorption of intraocular lenses.

OBJECTIVES: To record and compare the spectral transmittance curves of intraocular lenses (IOLs) made out of polymethyl methacrylate (PMMA), acrylic, hydrogel, and silicone from different manufacturers; to evaluate their ultraviolet radiation absorption capacities; and to contrast the recorded transmittance curves with that of the natural lens. DESIGN: Experimental study. METHODS: We studied 17 different 21-diopter IOLs. A high-performance spectrophotometer with a diffuse transmittance accessory was employed to measure the transmittance of wavelengths from 200 nm to 800 nm through a 1.5-mm aperture. MAIN OUTCOME MEASURES: Transmittance percentage and 10% transmittance cutoff wavelength. RESULTS: All studied IOLs offered good ultraviolet radiation protection in the ultraviolet C (200-280 nm) and ultraviolet B (280-315 nm) ranges. A number of silicone, PMMA, and acrylic lenses showed different and, at times, only low degrees of absorption in the ultraviolet A (315-400 nm) range. CONCLUSIONS: Intraocular lenses of different compositions have ultraviolet radiation absorption characteristics different from that of the crystalline lens.

Absorption↗

PubMed2000

Bioactive polymethyl methacrylate-based bone cement: comparison of glass beads, apatite- and wollastonite-containing glass-ceramic, and hydroxyapatite fillers on mechanical and biological properties.

A new bioactive bone cement (designated GBC) consisting of polymethyl methacrylate (PMMA) as an organic matrix and bioactive glass beads as an inorganic filler has been developed. The bioactive beads, consisting of MgO-CaO-SiO(2)-P(2)O(5)-CaF(2) glass, have been newly designed, and a novel PMMA powder was selected. The purpose of the present study was to compare this new bone cement GBC's mechanical properties in vitro and its osteoconductivity in vivo with cements consisting of the same matrix as GBC and either apatite- and wollastonite-containing glass-ceramic (AW-GC) powder (designated AWC) or sintered hydroxyapatite (HA) powder (HAC). Each filler added to the cements amounted to 70 wt %. The bending strength of GBC was significantly higher than that of AWC and HAC (p < 0.0001). Cements were packed into intramedullar canals of rat tibiae in order to evaluate osteoconductivity as determined by an affinity index. Rats were sacrificed at 2, 4, and 8 weeks after operation. An affinity index, which equaled the length of bone in direct contact with the cement expressed as a percentage of the total length of the cement surface, was calculated for each cement. At each time interval studied, GBC showed a significantly higher affinity index than AWC or HAC up to 8 weeks after implantation (p < 0.03). The value for GBC increased significantly with time up to 8 weeks (p < 0.006). The handling property of GBC was comparable with that of PMMA bone cement. Our study revealed that the higher osteoconductivity of GBC was due to the higher bioactivity of the bioactive glass beads at the cement surface and the lower solubility of the new PMMA powder to MMA monomer. In addition, it was found that the smaller spherical shape and glassy phase of the glass beads gave GBC strong enough mechanical properties to be useful under weight-bearing conditions. GBC shows promise as an alternative with improved properties to the conventionally used PMMA bone cement.

Animals↗

PubMed2004

Augmentation of pedicle screw fixation strength using an injectable calcium phosphate cement as a function of injection timing and method.

STUDY DESIGN: Axial pullout tests using fresh cadaveric thoracolumbar vertebral bodies. OBJECTIVES: To evaluate the effect of a new injectable calcium phosphate cement on the axial pullout strength of both revised and augmented pedicle screws in comparison with polymethyl methacrylate and in terms of injection method. SUMMARY OF BACKGROUND DATA: Failure of pedicle screws by loosening and back out remains a significant clinical problem and is of particular concern for patients with low bone quality. Polymethyl methacrylate was shown to significantly improve the screw pullout strength. However, polymethyl methacrylate is known to have a high polymerization temperature, which may damage surrounding tissues, and a short handling time, and it lacks long-term biocompatibility. Bone mineral cements such as calcium phosphate have a longer working time, very low thermal effect, and are biodegradable as well as having good mechanical strength. Recently, new calcium phosphate cement with improved infiltration properties for better injectability has been introduced, but its performance in augmenting the pedicle screw fixation has not been tested yet. METHODS: The bone mineral densities of 52 vertebral bodies (T11-L5) were measured using dual-energy x-ray absorptiometry. In each vertebral body, a 6.5-mm-diameter and 45 +/- 5-mm-long pedicle screw was inserted into either the right or left pedicle, representing an initial intact implantation. These intact screws were pulled axially until failure at 10 mm/min. Following failure of the intact pedicle, 3.0 cc of cement was injected into the failed screw hole, representing a revision case, and the prepared screw hole in the contralateral intact pedicle representing an augmentation case. The cement was injected either to the distal tip of the screw hole (calcium phosphate-1 group, n = 19) or along the entire length of the screw hole (calcium phosphate-2 group, n = 20), and the screws were inserted. The cement was then allowed to cure for 24 hours at room temperature before both screws were pulled to failure. In 13 specimens, polymethyl methacrylate was injected along the entire length of the screw hole (polymethyl methacrylate group). Kruskal-Wallis and Mann-Whitney tests were used to compare the screw pullout strengths for study groups, whereas linear relationships between variables were assessed with scatter plots and Spearman correlation coefficients with a significance level of 0.05. RESULTS: Mean bone mineral densities of all groups were similar. A significant positive correlation was seen between bone mineral density and intact pullout strength. In revision, the pullout strength of calcium phosphate-1 was similar to that of intact, whereas the pullout strength of calcium phosphate-2 and polymethyl methacrylate was significantly greater than that of intact. In augmentation, all 3 injection methods significantly improved the pullout strength over intact. Injection of the calcium phosphate cement along the entire screw length was found to produce significantly higher pullout strengths than injection only at the distal tip of the screw in revision case. Injection of polymethyl methacrylate produced significantly higher pullout strengths than the injection of calcium phosphate by either method in both revision and augmentation. CONCLUSION: Results of this study demonstrate that the new calcium phosphate cement can improve the axial pullout strength of revised and augmented pedicle screws when injected along the entire length of the screw. This suggests that the injection method may be crucial for revision of failed pedicle screws. Considering inherent properties more favorable for in vivo application, such as nonexothermal polymerization and longer working time, and significant improvement in pullout strength, the new calcium phosphate cement may be a good alternative to polymethyl methacrylate for the augmentation of pedicle screw fixation.

Aged↗

PubMed1999

Haemodialysis-membrane biocompatibility and mortality of patients with dialysis-dependent acute renal failure: a prospective randomised multicentre trial. International Multicentre Study Group.

BACKGROUND: There is controversy as to whether haemodialysis-membrane biocompatibility (ie, the potential to activate complement and neutrophils) influences mortality of patients with acute renal failure. We did a prospective randomised multicentre trial in patients with dialysis-dependent acute renal failure treated with two different types of low-flux membrane. METHODS: 180 patients with acute renal failure were randomly assigned bioincompatible Cuprophan (n=90) or polymethyl-methacrylate (n=90) membranes. The main outcome was survival 14 days after the end of therapy (treatment success). Odds ratios for survival were calculated and the two groups were compared by Fisher's exact test. Analyses were based on patients treated according to protocol (76 Cuprophan, 84 polymethyl methacrylate). FINDINGS: At the start of dialysis, the groups did not differ significantly in age, sex, severity of illness (as calculated by APACHE II scores), prevalence of oliguria, or biochemical measures of acute renal failure. 44 patients (58% [95% CI 46-69]) assigned Cuprophan membranes and 50 patients (60% [48-70]) assigned polymethyl-methacrylate membranes survived. The odds ratio for treatment failure on Cuprophan compared with polymethyl-methacrylate membranes was 1.07 (0.54-2.11; p=0.87). No difference between Cuprophan and polymethyl-methacrylate membranes was detected when the analysis was adjusted for age and APACHE II score. 18 patients in the Cuprophan group and 20 in the polymethyl-methacrylate group had clinical complications of therapy (mainly hypotension). INTERPRETATION: There were no differences in outcome for patients with dialysis-dependent acute renal failure between those treated with Cuprophan membranes and those treated with polymethyl-methacrylate membranes.

APACHE↗

PubMed2004

Prevention of posterior capsule opacification using different intraocular lenses (results of one-year clinical study).

AIM: To evaluate and to compare the preventive effect of different intraocular lenses from different material with a round or sharp optic edge design on posterior capsule opacification. METHODS: Our clinical study included 165 patients. Mean follow-up was 12.4+/-0.9 months, mean patient age was 67.5+/-7.8 years. Patients in the group 1 (n=46) were implanted acrylic three-piece hydrophobic intraocular lenses, sharp optic edge (AcrySof, MA3OBA, Alcon), in the group 2 (n=38)--acrylic hydrophobic single piece intraocular lenses, sharp optic edge (AcrySof, SA3OAL, Alcon), in the group 3 (n=39)--silicone three-piece intraocular lenses, sharp optic edge (CeeOn 911A, Pharmacia), and in the group 4 (n=42)--polymethyl methacrylate single piece intraocular lenses, round optic edge (Crystal, 5T, Alcon). The posterior capsule opacification was evaluated for the entire optic and in the central 3-mm zone using EPCO 2000 Software. RESULTS: Posterior capsule opacification values of the entire optic were 0.002+/-0.001 in the AcrySof MA3OBA group, 0.007+/-0.002 in the AcrySof SA3OAL group, 0.002+/-0.001 in the CeeOn 911A group, 0.029+/-0.008 in the polymethyl methacrylate intraocular lens group 6 months after surgery. The values were 0.011+/-0.005, 0.025+/-0.006, 0.014+/-0.005 and 0.122+/-0.021, respectively, one year after surgery. The intraocular lenses types with sharp-edge design (acrylic and silicone) showed significantly lower posterior capsule opacification values than round-edge optic design polymethyl methacrylate lenses (p<0.05). Posterior capsule opacification values of the central 3-mm zone were 0.000+/-0.000 in the AcrySof MA3OBA group, 0.001+/-0.001 in the AcrySof SA3OAL group, 0.000+/-0.000 in the CeeOn 911A group, 0.002+/-0.001 in the polymethyl methacrylate intraocular lens group 6 months after surgery. The values were 0.0001+/-0.0001, 0.018+/-0.007, 0.004+/-0.002 and 0.028+/-0.009, respectively, one year after surgery. Posterior capsule opacification values differences between AcrySof MA3OBA and polymethyl methacrylate intraocular lenses' groups and between CeeOn 911A and polymethyl methacrylate intraocular lenses' groups one year after cataract surgery were established (p<0.05). CONCLUSIONS: The sharp-edge foldable intraocular lenses types (AcrySof MA3OBA, AcrySof SA3OAL, CeeOn 911A) showed statistically significant difference in posterior capsule opacification values in one-year follow-up time. The effect of these foldable lenses for prevention of posterior capsule opacification is mainly a result of rectangular, sharp-edged optic design, which creates a sharp capsular bend. A role of material of intraocular lenses (hydrophobic acrylate and silicone) in prevention of posterior capsule opacification during one-year follow-up was not established.

Acrylic Resins↗

PubMed1977

The role of implant porosity on the development of infection.

The role of implant porosity as a determinant of infection was studied. Standardized porous and nonporous polymethyl methacrylate implants were fabricated for this investigation. In rabbits, the premolded polymethyl methacrylate implants were placed under the paravertebral fascia, just superficial to the paravertebral muscle fascia, before inoculation with a measured number of staphylococci. The polymethyl methacrylate implants did not enhance the infection rate of the contaminated wounds. The presence of pores within the implants did not damage tissue defenses. Polymethyl methacrylate implants did not alter the success of antibiotic treatment. Antibiotics prevented the development of infection in wounds containing 10(6) organisms, even in the presence of an implant. When higher levels of organisms were delivered to the wound, antibiotic treatment had a negligible benefit in the implant and control wounds.

Animals↗

PubMed2004

Biomechanics of prophylactic vertebral reinforcement.

STUDY DESIGN: The effects of bone cement placement, volume, and bone density on the degree of biomechanical reinforcement on cadaveric vertebral bodies were studied using experimentally calibrated detailed finite element models. OBJECTIVES: To investigate the efficacy of prophylactic vertebroplasty on intact vertebral bodies with respect to biomechanical recovery and fracture risk reduction. SUMMARY OF BACKGROUND DATA: Vertebroplasty is a potentially effective fracture prevention treatment, but the risk of complications due to cement leakage must be minimized. Therefore, the least amount of bone cement required to improve vertebral strengths to low fracture risk levels need to be determined. METHODS: Six different polymethyl methacrylate volumes--1, 2.5, 3.5, 5, 7.5 and 9 cm--were virtually implanted into previously validated vertebral body finite element models, following bipedicular and posterolateral vertebroplasty approaches. Stiffness and fracture load of the treated and untreated vertebral body models under uniaxial compression were determined. RESULTS: Greater augmentation effects were observed for vertebral bodies with average quantitative computed tomography densities below 0.1 g/cm injected with polymethyl methacrylate volumes higher than 20% compared to lower injection volumes and higher bone densities, as well as for the bipedicular approach versus posterolateral. Vertebral bodies at high risk of fracture required at least 20% fill of polymethyl methacrylate to improve the mechanical integrity of vertebral bodies to low fracture risk levels, whereas 5% to 15% polymethyl methacrylate volumes were needed for the medium-risk vertebral bodies. CONCLUSION: Prophylactic vertebroplasty can be effective in reducing fracture risk. However, for the polymethyl methacrylate volume (20%) required for the successful reinforcement of high-risk vertebral bodies, the risk of complications will be as high as that for current vertebroplasty procedure for fracture repair. Therefore, alternative materials have to be investigated for prophylactic vertebroplasty. Furthermore, bipedicular vertebroplasty is the recommended approach due to its higher strengthening effect and easier surgical access than the posterolateral case.

Adult↗

PubMed1993

Influence of haptic materials on the adherence of staphylococci to intraocular lenses.

A recent case-control study indicated that the insertion of an intraocular lens with polypropylene (Prolene) haptic materials was a significant risk factor for postoperative endophthalmitis (odds ratio = 4.5, P < .01). In the present study, we used quantitative techniques to evaluate adherence of Staphylococcus epidermidis to two intraocular lens types--lenses with polypropylene haptic materials and all-polymethyl methacrylate optic and three-piece all-polymethyl methacrylate lenses--using a quantitative culture method, a radioisotope technique, and scanning electron microscopy. All three methods demonstrated approximately twice as many bacteria adherent to lenses with polypropylene haptic materials as to all-polymethyl methacrylate lenses. Scanning electron microscopy showed preferential bacterial adherence to the polypropylene haptic materials. These data provide a pathogenic mechanism to explain our epidemiologic findings of an increased risk of postoperative endophthalmitis associated with implantation of intraocular lenses with polypropylene haptic materials.

Adsorption↗

PubMed1994

Effect of the dialysis membrane in the treatment of patients with acute renal failure.

BACKGROUND: The mortality rate among patients with acute renal failure remains high, and the role of the biocompatibility of the dialysis membrane in the resolution of this disorder is not known. METHODS: We prospectively studied 72 patients with acute renal failure who required hemodialysis and assigned them to two treatment groups. One group underwent dialysis with the widely used cuprophane dialysis membrane, which activates the complement system and leukocytes, and the other group underwent dialysis with a synthetic polymethyl methacrylate membrane, which has a more limited effect on complement and leukocytes. Scores on the Acute Physiology, Age, and Chronic Health Evaluation (APACHE II) were calculated at the initiation of dialysis. Survival and the recovery of renal function were determined with the use of proportional-hazards and exact logistic-regression analyses. RESULTS: When dialysis was initiated, the patients in the two groups were similar in terms of age, APACHE II scores, the prevalence of oliguria, and biochemical indexes of renal failure. Twenty-three of the 37 patients (62 percent) in the group undergoing dialysis with the polymethyl methacrylate membrane recovered renal function, as compared with 13 of the 35 patients (37 percent) in the group undergoing dialysis with the cuprophane membrane (P = 0.04 after adjustment for the APACHE II score). The median number of dialysis treatments required before the recovery of renal function was 5 in the former group and 17 in the latter group (P = 0.02). Twenty-one patients (57 percent) undergoing dialysis with the polymethyl methacrylate membrane survived, as compared with 13 patients (37 percent) undergoing dialysis with the cuprophane membrane (P = 0.11). Of the 20 patients in each group who initially had nonoliguric acute renal failure, the survival rates were 80 percent with the polymethyl methacrylate membrane and 40 percent with the cuprophane membrane (P = 0.01). CONCLUSIONS: Among patients with acute renal failure requiring hemodialysis, the use of the polymethyl methacrylate membrane, as compared with the cuprophane membrane, resulted in improved recovery of renal function.

APACHE↗

PubMed2004

Serious pyogenic spondylitis following vertebroplasty--a case report.

STUDY DESIGN: The aim of this case report is to examine the problem of serious pyogenic spondylitis that may follow vertebroplasty. OBJECTIVES: To report 1 case of serious pyogenic spondylitis caused by percutaneous vertebroplasty with polymethyl methacrylate. SUMMARY OF BACKGROUND DATA: Serious pyogenic spondylitis caused by percutaneous vertebroplasty with polymethyl methacrylate is a rare complication. We herein report a case of pyogenic spondylitis that occurred after the patient had undergone vertebroplasty. METHODS: A 78-year-old woman with a T12 osteoporotic compression fracture, and without a magnetic resonance imaging sign of infection, underwent percutaneous vertebroplasty using polymethyl methacrylate without complication. RESULTS.: About 1 month after the operation, the patient was readmitted because of severe backache, and the diagnosis of pyogenic spondylitis was made using radiograph and magnetic resonance imaging. Anterior inter-body fusion with a strut bone graft after debridement and posterior instrumentation were then performed. CONCLUSIONS: Vertebroplasty should proceed under sterile conditions. Excluding the possibility of spinal infection before surgery and a detailed evaluation assuring that the patient is without systemic infectious disease before the vertebroplasty procedure is crucial.

Abscess↗

PubMed2003

Percutaneous vertebroplasty: treatment of painful vertebral compression fractures with intraosseous vacuum phenomena.

OBJECTIVE: This study was undertaken to determine the efficacy of percutaneous vertebroplasty in treating patients with painful compression fractures of the thoracic and lumbar vertebrae that contain intraosseous vacuum phenomena. MATERIALS AND METHODS: Nineteen cases of painful vertebral compression fractures with intraosseous phenomena occurring in 18 patients (six men, 12 women; age range, 59-88 years; mean age, 75.5 years) were identified from 393 percutaneous vertebroplasties performed in 199 patients during 32 and a half months. All patients had osteoporosis, with severe vertebral compression to less than one third of the vertebral body height in 13 of 19 cases. Affected levels were T6 (n = 1), T8 (n = 2), T9 (n = 1), T11 (n = 1), T12 (n = 4), L1 (n = 5), L2 (n = 2), L3 (n = 1), L4 (n = 1), and L5 (n = 1). All cases had the typical intravertebral body vacuum cleft appearance on radiographs. Imaging and clinical features were analyzed. RESULTS: The mean volume of polymethyl methacrylate injected was 7.43 mL (range, 4.0-15.0 mL). Typically, the polymethyl methacrylate filled the intravertebral vacuum cleft. Complications during radiography consisted of minimal polymethyl methacrylate leakage into the adjacent disk (15/19 cases) and the paravertebral soft tissues (8/19 cases). No complications required surgical intervention. At clinical follow-up, pain relief was complete in eight patients (44.4%), partial in six patients (33.3%), and unchanged in four patients (22.2%). CONCLUSION: Percutaneous vertebroplasty is effective in the treatment of patients with painful vertebral compression fractures with intraosseous vacuum phenomena.

Aged↗

PubMed2004

Spectra analysis of Nd(DBM)3(TPPO)2 in MMA solution and PMMA matrix.

The absorption spectra of Nd(DBM)3(TPPO)2 (DBM = dibenzoylmethane; TPPO = triphenylphosphine oxide) in methyl methacrylate (MMA) and polymethyl methacrylate (PMMA) were measured. Slater-Condon parameters (F2, F4, F6), Lander parameter (zeta4f), nephelauxetic effect parameters (beta, delta) and Judd-Ofelt parameters (Omega2, Omega4, Omega6) were calculated on the basis of the absorption spectra. Analysis of the relationship between the structure of rare-earth complexes and the nephelauxetic effect, Judd-Ofelt parameter Omega2 was carried out. The radiative properties of Nd(DBM)3(TPPO)2 in PMMA were also predicted according to the Judd-Ofelt theory. The values of the radiative lifetime and the emission cross-section of 4F3/2 --> 4I11/2 fluorescence transition are comparable with those shown by glasses used in the solid-state laser applications.

Chalcones↗

PubMed2006

Long-term effects of storage and thermal cycling on the marginal adaptation of provisional resin crowns: a pilot study.

STATEMENT OF PROBLEM: Provisional resin crowns may be used for an extended period while complex treatments are completed. The crowns function intraorally; therefore, moisture absorption and thermal cycling may affect the physical properties of acrylic resin, causing a change in marginal gap size. PURPOSE: The purpose of this pilot study was to examine the effect of long-term water absorption and thermal cycling on marginal gap size of polymethyl methacrylate copolymer and bis-acrylic composite resin crowns. MATERIAL AND METHODS: Specimens (n = 10) were fabricated from 2 acrylic resins: a polymethyl methacrylate (Alike) and a bis-acrylic composite resin (Provitec). Specimens were first fabricated on a metal master die. Custom die stems were fabricated for each specimen from a low-fusing alloy (Cerroblend) to eliminate the factor of polymerization shrinkage. Specimens were then fitted to assure a standardized, pre-experimental marginal gap range of < or = 25 microm. Specimens were stored in a humidor at 37 degrees C and 97% relative humidity for 1 year and subsequently thermal cycled (5 degrees C to 60 degrees C, 6-second dwell time, for 8000 cycles). Measurements in micrometers of the marginal gap were recorded using a microscope equipped with a digital video camera and image analysis software before and after treatment. A 2-way analysis of variance with a split design was performed for factors of materials and treatment (alpha = .05). RESULTS: For the factor of material, there was no significant difference; however, there was a significant difference between treatments, with a significantly greater increase in marginal gap size after thermal cycling (P < .002). CONCLUSION: Provisional crowns made from either a bis-acrylic resin composite or a polymethyl methacrylate copolymer demonstrated loss of marginal adaptation during a simulated long-term period of service.

Acrylic Resins↗

PubMed2004

Test of hyperelasticity in highly nonlinear solids: sedimentary rocks.

We report measurements of three-wave mixing amplitudes on systems whose third order elastic constants have also been measured by means of the elastoacoustic effect. Because attenuation and diffraction are an important aspect of our measurement technique we analyze our results using a modified Khoklhov-Zabolotskaya-Kuznetsov equation in the frequency domain. We find that the value of beta so deduced for polymethyl methacrylate agrees quite well with that predicted from the stress dependent sound speed measurements, establishing that polymethyl methacrylate may be considered as a hyperelastic solid. The beta values of sedimentary rocks, though they are typically 2 orders of magnitude larger than, e.g., polymethyl methacrylates, are still a factor 3-10 less than those predicted from the elastoacoustic effect.

Journal Article↗

PubMed2006

Transoral vertebroplasty for renal cell metastasis involving the axis: case report.

STUDY DESIGN: Case report. OBJECTIVE: This is one of the first reported cases of transoral vertebroplasty for a solid metastatic tumor at C2 body. SUMMARY OF BACKGROUND DATA: Percutaneous vertebroplasty has gained popularity as a treatment option for painful neoplastic lesions of the spine. The technique has been useful in reducing pain and stabilizing the spinal segment that is vulnerable to fracture. However, there is very little experience with vertebroplasty in the cervical spine and, more specifically, at C2. METHODS: We present a case of metastatic renal cell carcinoma of the C2 body. The patient, a 61-year-old woman, presented with an excruciating neck pain. Diagnostic workup revealed the presence of tumor in the right kidney. Multiple spinal levels were involved in addition to C2, and the C2 lesion was treated for palliative purpose. Under biplanar fluoroscopy, a vertebroplasty trocar was placed transorally into the central portion of the C2 body, and polymethyl methacrylate was injected. RESULTS: The transoral vertebroplasty achieved complete pain relief and enhanced stability of an extensive osteolytic lesion involving the C2 body. CONCLUSIONS: This minimal access procedure was effective in completely relieving pain from a metastatic deposit at C2, while adequately stabilizing the vulnerable segment by the injection of polymethyl methacrylate. The transoral route requires meticulous fluoroscopic control to prevent the leakage of polymethyl methacrylate but provides the most direct access to the C2 body.

Axis, Cervical Vertebra↗

PubMed1999

Surface cytologic features on intraocular lenses: can increased biocompatibility have disadvantages?

OBJECTIVE: To compare the anterior surface cytologic features and effect on blood-aqueous barrier of polymethyl methacrylate, silicone, and hydrogel intraocular lens (IOL) implants to give an indication of their biocompatibility. METHODS: This prospective study was performed at an English-teaching hospital. Ninety eyes were randomized to receive a polymethyl methacrylate, silicone, or hydrogel implant. A standardized surgical protocol was performed by a single surgeon using phacoemulsification. Patients were seen at intervals for 1 year. Measurements of visual acuity, contrast sensitivity, and anterior chamber laser flare and cells were obtained; and an assessment of lens cytologic features using specular microscopy of the anterior IOL surface was performed. RESULTS: Visual acuity and contrast sensitivity were not significantly different among the 3 groups. Hydrogel IOLs were associated with fewer inflammatory cells on their surface than polymethyl methacrylate and silicone IOLs (P<.001), but with significantly more lens epithelial cells (LECs) (P<.001). Patients with hydrogel implants without LECs had greater blood-aqueous barrier breakdown than those with LECs. CONCLUSIONS: The hydrogel IOLs were associated with a reduced inflammatory cell reaction but had many more LECs on their anterior surface. Those IOLs associated with increased blood-aqueous barrier damage did not develop LECs. If an IOL is too biocompatible, then it may incite the growth of LECs over its surface, which could have disadvantages.

Aged↗