Crystallization of cystineGirija, E.; Kalkura, S.; Ramasamy, P.
doi: 10.1007/BF00123439pmid: N/A
Cystine is an amino acid, which is a constituent of the urinary stones. It also is deposited in eyes, thyroid glands, bone marrow and white blood corpuscles. Crystals of cystine have been grown by both solution and gel methods. Small bunched hexagonal crystals, along with many other morphological crystals of size 0.3 mm across, were obtained. The crystals were analysed by X-ray diffraction and IR analyses.
Effect of TEGDMA content on staining of experimental bis-GMA-based resinsMatsumae, I.; Wakasa, K.; Satou, N.; Urabe, H.; Shintani, H.; Yamaki, M.
doi: 10.1007/BF00123440pmid: N/A
This study was to examine water uptake, contact angle and colour change vector in relation to the staining on the optically smooth surface in five experimental visible light-cured (VLC) bis-GMA-based resins. They were formulated from bis-GMA-based resins including 25 to 45 wt% TEGDMA which were accelerated by CQ/DMAEMA/BHT = 0.5/2/0.05 (wt%) to bis-GMA/TEGDMA resin matrix. Of the set resins including more than 25 wt% of TEGDMA, the resins including 30 to 45 wt% had less than 1.0% as bis-GMA residual monomer. Water uptake and solubility in bis-GMA-based resins including 35 wt% TEGDMA were the minimum of the resins tested. Contact angle decreased with increasing time over 70 days, from 67 to 62 degrees. Using the hydrophilic staining solution (food red 3), the values of colour change vector were 6 to 9 after immersing them for 70 days at 37 °C, whereas hydrophobic oil orange staining test had a range of 12 to 19. The change of water uptake with time of immersion correlated with that of the colour change vector. With the accelerated test, the minimum value was 4.55 in 65/35 (bis-GMA/TEGDMA) resin. Of the bis-GMA-based resins (25 to 45 wt% fraction of TEGDMA) the minimum value of water uptake and contact angle were obtained.
Thermal expansion of compositesMcCabe, J.; Wassell, R.
doi: 10.1007/BF00123441pmid: N/A
Coefficient of thermal expansion (CTE) has been determined for selected composite materials using differential thermal analysis. Variables evaluated were: type of material, with particular emphasis on filler content; annealing; thermal history, with particular attention being payed to the effects of multiple heating and cooling cycles; ageing in wet or dry conditions. Filler content was a major factor involved in controlling CTE, although clearly other factors such as the type of filler, resin and degree of conversion are important. For an inlay material, annealing at 120°C significantly reduced the value of coefficient of thermal expansion and this is most likely due to an increase in conversion of methacrylate groups. The findings of this study confirm those of previous studies regarding the reduction in CTE following an initial heating. This is most likely due to the relief of internal stress. New information reported here relates to the fact that stress release can occur slowly without heating and that rapid stress release can be achieved through water storage at mouth temperature. These results suggest that, clinically, internal stresses induced by polymerization will be dissipated rapidly. A further finding was that long-term water storage causes an increase in CTE, which may reflect changes at the resin-filler interface.
Double torsion testing of prescription lensesMcAuliffe, P.; Truss, R.
doi: 10.1007/BF00123442pmid: N/A
In previous work, a modified double torsion test was developed to measure the fracture toughness of polymeric ophthalmic lenses with parallel surfaces. The method used production lenses so that the toughness of the manufactured articles could be measured directly. This method has now been extended to measure the K
1c of powered lenses in which the thickness of the sample varied with both X and Y coordinates instead of being constant. A computer model of the sample's breaking load was constructed and the predicted values from this were compared to experimental results and a good correlation was obtained. In addition, the computer-generated correction factors were validated using the more rigorous compliance curve technique.
Fracture properties of fully cured acrylic bone cementHailey, J.; Turner, I.; Miles, A.
doi: 10.1007/BF00123443pmid: N/A
The fracture properties of bone cement are strongly influenced by the complex interactions between the residual monomer and components of the media surrounding the bone cement. The aim of this study was to eliminate the influence of the residual monomer by fully curing the cement prior to storage in air, water, lipid or Ringer's solution at room or body temperature for up to 18 months. Subsequent mechanical testing indicated that initially there was a significant increase in the work of fracture values for all the samples stored in the fluid media. With longer-term storage periods a decrease was observed; this was attributed to the process of physical ageing. The removal of the residual monomer eliminated the monomer: lipid interaction, consequently the effect of the storage in lipid was similar to that observed for the other fluid media.
Effect of bioactive glass granules and polytetrafluoroethylene membrane on repair of cortical bone defectTurunen, T.; Peltola, J.; Happonen, R.-P.; Yli-Urpo, A.
doi: 10.1007/BF00123444pmid: N/A
The effect of bioactive glass (BG) granules and nonresorbable polytetrafluoroethylene (PTFE) membrane on the repair of cortical bone defects was studied. Monocortical holes (diameter 3.0 mm) were drilled in rabbit tibia. Sixteen holes were filled with BG granules (diameter 630–800 μm). Twelve holes were left empty and covered with PTFE membrane. No material was used at ten control holes. All experiment areas were covered with periosteum attached to the soft tissue flap. Histomorphometric evaluation of resection specimens showed that new bone and glass particles formed a continuous bridge in the BG group at the upper part of the hole, occupying 73.6% and 61.7% of the defect at 6 and 12 weeks, respectively. If only the amount of bone but not glass particles was included in the measurements the corresponding figures were 31.4% and 41.5%. The bone repair in the PTFE group was 12.1% and 11.3% and in the control group 25.1% and 23.3% at 6 and 12 weeks, respectively. The results indicate that BG granules improve repair of cortical bone defects and PTFE membrane seems to impair bone formation in these defects.
In vitro predegradation at elevated temperatures of poly(lactide)Bergsma, J.; Rozema, F.; Bos, R.; Boering, G.; Joziasse, C.; Pennings, A.
doi: 10.1007/BF00123445pmid: N/A
In this study in vitro predegradation at elevated temperatures, used to obtain an increased degradation rate, was investigated. The in vitro degradation was followed by mass loss, molecular weight loss and changes in thermal properties. Two biodegradable polymers, the homopolymer PLLA and a copolymer PLA96 (96% L4%D lactide), were hydrolytically degraded at 90°C in a phosphate buffered solution. Both polymers, PLLA and PLA96, showed an initial linear degradation rate, but with longer implantation periods the degradation rate decreased and total degradation was best described as an asymptotic. Mass loss of the copolymer PLA96 was twice that of PLLA. The chemical analysis of the in vitro predegraded polymers coincided for both the decrease in molecular weight and the thermal properties with physiologically degraded poly(lactide). The results of this study show that although the degradation temperature is well above the glass transition temperature and not comparable to physiological temperatures, there seems to be good correlation between the in vitro degraded material and physiologically degraded material. In vitro predegradation enables investigation of the entire degradation process of a polymer in a short-term study. Moreover, in vitro predegradation allows direct comparison of the degradation rate of various polymers.
Characterization of some proprietary soft lining materialsKalachandra, S.; Minton, R.; Taylor, D.; Takamata, T.
doi: 10.1007/BF00123446pmid: N/A
The physical and mechanical properties of a series of commercial denture soft lining materials have been investigated. The materials were selected to provide a representative sample of the materials widely used for this application. A total of seven products were evaluated including established and widely used acrylic and silicone materials as well as newer polyphosphazine and fluoroelastomer materials. The objective of the study was to determine minimally acceptable and desirable levels for each property which could be used as criteria or standards for the selection of proposed new materials. The results identified several areas requiring attention and future work. In particular, the importance of using fully-water-equilibrated specimens was emphasized for acrylic polymers where large property changes occurred between wet and dry conditions, and in the case of the polyphosphazine materials where the long time required for full equilibration may lead to understimates of the changes involved. Based upon the properties as measured, recommendations for appropriate standard level for each property are offered.
Further studies of calcium phosphate growth on phosphorylated cotton fibresMucalo, M.; Yokogawa, Y.; Suzuki, T.; Kawamoto, Y.; Nagata, F.; Nishizawa, K.
doi: 10.1007/BF00123448pmid: N/A
Further studies using scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX), micro-Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and solid state magic angle spinning nuclear magnetic resonance (MAS NMR) techniques of calcium phosphate growth on Ca(OH)2-treated urea/H3PO3- and urea/H3PO4-modified cotton fibres are reported. In the case of the Ca(OH)2-treated urea/H3PO3-modified fibres which have been reported in an earlier paper, further experiments subjecting the urea/H3PO3-modified cotton to alternative soaking treatment procedures to Ca(OH)2 as well as different calcium phosphate growth media such as the alkaline phosphatase-catalysed hydrolysis of disodium p-nitrophenylphosphate to free phosphate have reaffirmed the importance of the Ca(OH)2 treatment step for the stimulus and growth of calcium phosphate growth on the fibres. Studies on cotton phosphorylated by a slightly different method using urea/H3PO4 instead of urea/H3PO3 show that a phosphorylated cotton with similar properties to the urea/H3PO3-modified fibres can be produced. Soaking of these fibres in saturated Ca(OH)2 solution leads to cotton coated with thin layers of calcium phosphate formed by partial hydrolysis of the PO4 functionalities in the phosphorylated cotton which are believed to act as nucleation layers for further calcium phosphate deposition when the fibres are subsequently soaked in 1.5×SBF solution. SEM/EDX studies of the calcium phosphate coatings formed on the Ca(OH)2-treated urea-H3PO4 fibres as a function of soaking time in 1.5 × SBF show that coatings deposit and become noticeably thick after approximately 9 days. XPS studies indicated the presence of carbonate species in the calcium phosphate coating deposited. In common with the calcium phosphate coated Ca(OH)2-treated urea/H3PO3-modified fibres studied earlier, the average EDX-measured Ca: P ratios of the coatings formed on the Ca(OH)2-treated urea/H3PO4 fibres are ∼ 1.60 and give very similar micro-FTIR spectra with evidence of carbonate which suggests that amorphous calcium deficient apatite has deposited.