Regular Poly Methyl Methacrylate Research Articles

Crazing Initiation and Growth in Polymethyl Methacrylate under Effects of Alcohol and Stress

Polymer crazing is typically a precursor to damage and considerably reduces the mechanical performance of polymer materials. The concentrated stress caused by machines and the solvent atmosphere created during machining exacerbates the formation of crazing. In this study, the tensile test method was employed to examine the initiation and progression of crazing. The research focused on polymethyl methacrylate (PMMA), both regular and oriented, and the impact of machining and alcohol solvents on the formation of crazing. The results showed that the alcohol solvent influenced PMMA through physical diffusion, whereas machining primarily affected crazing growth via residual stress. Treatment reduced the crazing stress threshold of PMMA from 20% to 35% and produced a threefold increase in its sensitivity to stress. The findings revealed that oriented PMMA exhibited 20 MPa higher resistance to crazing stress compared with regular PMMA. The results also indicated that the extension of the crazing tip and thickening were in conflict, with the crazing tip of regular PMMA severely bending under tensile stress. This study provides valuable insight into the initiation of crazing and the methods of its prevention.

Comparison of Flexural Strength of Kevlar, Glass, and Nylon Fibers Reinforced Denture Base Resins With Heat Polymerized Denture Base Resins.

ABSTRACTIntroduction:Polymethyl methacrylate (PMMA) has been widely accepted and used in dentistry owing to its working characteristics, aesthetics and stability in the oral environment, ease in manipulation, and inexpensive processing methods and equipment.Aim and Objectives:The aim of this study was to evaluate the flexural strength of a high-impact PMMA denture base resin material and flexural strength of a commonly available heat cure PMMA denture base material with Kevlar, glass, and nylon fibers.Materials and Methods:The test samples were studied under two groups. The Group I (control group) comprised pre-reinforced PMMA (Lucitone 199; Dentsply Sirona Prosthetics, York, Pennsylvania, USA) consisting of 12 samples and second group comprised regular PMMA (DPI, Mumbai, India) reinforced with different fibers. The second test group was further divided into three subgroups as Group 2, Group 3, and Group 4 comprising 12 samples each designated by the letters a–l. All the samples were marked on both ends. A total of 48 samples were tested. Results were analyzed and any P value ≤0.05 was considered as statistically significant (t test).Results:All the 48 specimens were subjected to a 3-point bending test on a universal testing machine (MultiTest 10-i, Sterling, VA, USA) at a cross-head rate of 2 mm/min. A load was applied on each specimen by a centrally located rod until fracture occurred; span length taken was 50 mm. Flexural strength was then calculated.Conclusion:Reinforcement of conventional denture base resin with nylon and glass fibers showed statistical significance in the flexural strength values when compared to unreinforced high impact of denture base resin.

Exfoliation syndrome and heparin surface modified intraocular lenses

Either heparin surface modified (HSM) or regular polymethyl methacrylate (PMMA) intraocular lenses (IOLs) were implanted after extracapsular cataract extraction in 40 human eyes with exfoliation syndrome in a double-masked, randomized study. The patients were investigated preoperatively, and then 1 day, 1 week, 3, 6 and 12 months postoperatively. In eyes implanted with the HSM IOL, 26% had a fibrinoid reaction anterior to the IOL, while this complication was found in 50% of eyes implanted with the regular IOL. Pigment and cell deposits were more frequent on the regular IOLs than on the HSM lenses postoperatively. Posterior synechia formation between the iris and the implant or lens capsule was more common in the eyes with regular IOL compared to HSM IOL. No difference in visual acuity between the two groups was found either before or after surgery. The results suggest that in eyes with exfoliation syndrome, a heparin surface modified IOL reduces clinical complications associated with cataract surgery.

Performance of vertebral cancellous bone augmented with compliant PMMA under dynamic loads

Increased fracture risk has been reported for the adjacent vertebral bodies after vertebroplasty. This increase has been partly attributed to the high Young’s modulus of commonly used polymethylmethacrylate (PMMA). Therefore, a compliant bone cement of PMMA with a bulk modulus closer to the apparent modulus of cancellous bone has been produced. This compliant bone cement was achieved by introducing pores in the cement. Due to the reduced failure strength of that porous PMMA cement, cancellous bone augmented with such cement could deteriorate under dynamic loading. The aim of the present study was to assess the potential of acute failure, particle generation and mechanical properties of cancellous bone augmented with this compliant cement in comparison to regular cement. For this purpose, vertebral biopsies were augmented with porous- and regular PMMA bone cement, submitted to dynamic tests and compression to failure. Changes in Young’s modulus and height due to dynamic loading were determined. Afterwards, yield strength and Young’s modulus were determined by compressive tests to failure and compared to the individual composite materials. No failure occurred and no particle generation could be observed during dynamical testing for both groups. Height loss was significantly higher for the porous cement composite (0.53 ± 0.21%) in comparison to the biopsies augmented with regular cement (0.16 ± 0.1%). Young’s modulus of biopsies augmented with porous PMMA was comparable to cancellous bone or porous cement alone (200–700 MPa). The yield strength of those biopsies (21.1 ± 4.1 MPa) was around two times higher than for porous cement alone (11.6 ± 3.3 MPa).

The Radiology of Antibiotic-Impregnated Cement

The purpose of this article is to illustrate the radiologic appearances of the various forms of antibiotic-impregnated cement. Although the radiologic appearances of antibiotic-impregnated polymethyl methacrylate (PMMA) and regular PMMA are identical, peculiarities in the position and morphology of antibiotic-impregnated cement, as illustrated in this review, usually enable the radiologist to differentiate between the two. Its presence indicates one of two things: Either infection was present at the time the PMMA cement was inserted, or there was a high potential for the development of local sepsis, such as in cases of an open fracture. On the basis of this finding, the radiologist should carefully search for evidence of osteomyelitis.

Heparin and heparin-surface-modification reduce Staphylococcus epidermidis adhesion to intraocular lenses.

Bacterial adherence to intraocular lenses (IOLs) could be the cause of endophthalmitis following cataract surgery and lens implantation. The majority of cases of postoperative endophthalmitis are caused by microflora that reside on or near the eye of the patient. Staphylococcus epidermidis commonly colonizes the eyelid margin and conjunctiva and is the most common organism causing postoperative endophthalmitis. In this study, the in vitro adherence of S. epidermidis to regular poly-methyl methacrylate (PMMA) IOLs and to heparin-surface-modified (HSM) PMMA IOLs was investigated. The effects of heparin and antibiotics in solution on the adherence of bacteria to regular PMMA IOLs were evaluated. Adhesion of bacterial cells to IOLs was determined by counting the viable cells attached to the lenses. Significantly, fewer S. epidermidis attached to HSM-PMMA IOLs and to regular PMMA IOLs treated with heparin than to PMMA IOLs (p < 0.001). Furthermore, bacteria attached in significantly lower numbers to regular PMMA IOLs treated with heparin than to HSM-PMMA IOLs (p = 0.0031). Antibiotics in solution had no significant effect on bacterial adherence to PMMA IOLs. These data indicate that the use of HSM-PMMA IOLs and treatment of PMMA IOLs with heparin could diminish the incidence of postoperative endophthalmitis and intraocular inflammation associated with IOL implantation.

A comparison of heparin-coated and uncoated intraocular lenses in glaucoma patients undergoing combined cataract extraction and trabeculectomy and in diabetic patients undergoing cataract extraction

The postoperative course of cataract extraction and IOL implantation combined with trabeculectomy in glaucoma patients and of cataract extraction with intraocular lens (IOL) in diabetic patients is more complicated than that of cataract extraction with IOL implantation in otherwise healthy eyes. The main complications are fibrin in the anterior chamber, pigment dispersion, and posterior synechiae. In an attempt to determine whether heparin-coated lenses reduce the rate of these complications, a prospective study was conducted on 19 glaucomatous eyes of 19 patients who underwent a combined procedure of trabeculectomy and extracapsular cataract extraction with IOL and 20 eyes of 20 diabetic patients subjected to extracapsular cataract extraction with IOL. In each category of patients, the early postoperative course in those who received heparin-coated lenses and those who received regular polymethyl methacrylate (PMMA) lenses was compared with respect to the inflammatory reaction, assessed by the amounts of cells and flare, and complications in terms of fibrin, posterior synechiae and pigment dispersion. The results of this preliminary study indicate a slightly higher rate of early postoperative complications with the heparin-coated lenses as compared to PMMA lenses.

Cellular Reactions on Heparin Surface-modified versus Regular PMMA Lenses during the First Postoperative Month: A Double-masked and Randomized Study Using Specular Microphotography

Specular microscopy was used for investigation of cellular reactions on the intraocular lens (10L) anterior surface of Heparin surface-modified (HSM) versus regular polymethyl methacrylate (PMMA) lenses (Pharmacia types 7000 versus 700B, respectively). The double-masked randomized study included 53 patients investigated at 1 and 4 weeks postoperatively. Giant cells were only found on control lenses and more frequently at 4 weeks. Small cells were found on both lens types, but in a higher frequency on the control lenses. The number of small cells decreased during the first 4 weeks on both the control and HSM lenses. However, those control lenses that had giant cells on their surface showed an increase in the number of small cells during the same time. The results of the current study show that HSM lenses give rise to less postoperative inflammatory cellular reactions than regular PMMA lenses.