Lathe Cut Research Articles

Contact lens manufacturing technology

Currently, the following technologies are used in the production of contact lenses: lathe cut, polymerization in the form (cast molding) and centrifugal molding (spin cast). The last two technologies, due to the low cost of production, have been established in the mass production of soft contact lenses with standard parameters.Methods of production of contact lenses are constantly being improved to obtain products that better meet the requirements of patients in terms of safety, comfort and customization.The main methods of production of contact lenses are already localized in Russia and remain available to domestic consumers in conditions of geopolitical instability.

Characterisation of Ag–Sn–Cu Dental Amalgam Powder and Its Amalgam Triturated with Nominal and Higher Pressure

Ag–Sn–Cu lathe cut particles of dental amalgam powders are mixed with mercury with an approximate 1:1 ratio. Mercury and amalgam powder mixtures are triturated at nominal pressure and at higher pressure applied intermittently, and then condensed into an acrylic mould with reasonably higher condensation pressure as well, followed by setting at room temperature for different time period. The microstructural features of the amalgam alloy powders and its amalgams of various states are studied by FESEM, X-ray elemental mapping, X-ray diffraction, differential scanning calorimetry and by hardness measurement as well. Results showed that the amalgams triturated with higher pressure have yielded finer matrix γ1 (Ag2Hg3), presence of Ag-rich β1 and finer unreacted γ (Ag3Sn) phases with reduced porosity and higher hardness.

Examination of the Iraqi– product lathe–cut dental amalgam alloy by using Taha Indicator. Microscopic investigation

Examination of the Iraqi– product lathe–cut dental amalgam alloy by using Taha Indicator. Microscopic investigation

PENGARUH PENAMBAHAN PALADIUM TERHADAP PERILAKU THERMAL AMALGAM TEMBAGA TINGGI TIPE LATHE CUT

Effects of additing 1 percent (w/o) palladium (Pd) on the thermal behavior of a lathe cut type high copper amalgam (13 w/o copper) were studied. The identical alloys, with and without 1% Pd were fabricated. X-ray diffraction studies of the amalgams revealed the elimination of the γ 2 -phase by Pd addition DSC thermogram of non-Pd containing amalgam indicated the existence of two γ 1 -phaseone with the transition temperature (endothermic peak) at 88 ◦ C and the other at 109 ◦ C. The thermogram data of the Pd containing amalgam showed an endothermic peak at 110.7 ◦ C. The transition temperature of the n phase of the palladium containing amalgam is 4.9 ◦ C lower than the transition temperature of the n phase of the non Pd containing amalgam. This result indicates that the n phase of the Pd containing amalgam includes more of Tin (Sn) than the non-Pd containing amalgam. The thermogravimetri diagram showed that the phase decomposition occurred at about 390 ◦ C for the non-Pd containing amalgam and at about 410 ◦ C for the Pd containing amalgam. It is concluded that the addition of 1% Pd into a lathe cut type of high copper amalgam (13%) could eliminate the formation of γ 2 phase as well as an unstable γ 1 phase, promoting strong mercury bonding to Silver.

Lens prism in rgp manufacturing and its effect on edge quality

Unwanted prism in lathe cut RGP lenses is most frequently caused by misalignment when re-blocking the button for cutting the front surface. The geometrical relationships in three types of alignment errors and the resulting variations in edge thickness were mathematically analysed and experimentally confirmed. The edge thickness variations in a prismatic lens along the circumference follow a cosine function. For a typical tri-curve lens design, an eccentric offset 30 μm between the front and the back surface can lead to a difference in edge thickness of more than 50 μm Edge thickness variations are greatest for high power minus lenses with prominent lenticulation. The polished edge shape is significantly compromised by inconsistent edge thickness. Typically, the thinner side has a sharp and pointed edge, while the thicker side is blunt.

Experimental Study of Size Effects and Surface Damage in Closed-Cell Polymethacrylimide and Open-Cell Copper Foams

This article describes experimental investigations of size effects in torsion and bending of lathe cut closed-cell polymethacrylimide and open cell copper foams. Slender specimens were found to have a slightly smaller effective stiffness than thick ones. This behaviour is consistent with a model of surface damage to the outermost cells of the foam. The surface damage layer was inferred to be from 0.13 to 0.37 cell diameters for the polymethacrylimide, depending on the grade of foam, and from 0.3 to 0.4 cells in the copper foam. Effects of Cosserat (micropolar) elasticity, which would give rise to an effective stiffening of slender specimens, were not observed.

Bonding characteristics of a phosphonated anaerobic adhesive to amalgam

The shear bond strength of a phosphonated anaerobic resin dental adhesive (Panavia-Ex) to amalgam was determined and clinically important parameters affecting the bond strength: amalgam type, surface finish and corrosion, were investigated. It is possible to bond to high copper set amalgam using this adhesive with a clinically useful shear bond strength. Three copper-enriched, single composition alloys were studied. One was a spherical alloy and two were lathe cut. The bond strength to one of the lathe-cut alloys was significantly lower than to the other two alloys. A significantly higher bond strength to aged lathe-cut amalgam than to fresh amalgam was found. However, Weibull analysis indicated that these latter changes were less consistent and indicated patchy, localized changes in the amalgam surface. The bond strength to the spherical alloy was significantly reduced by polishing with a finishing bur or Prophy-Jet. Therefore when bonding to a large amalgam restoration with such a phosphonated anaerobic adhesive, no polishing of the amalgam should be undertaken.

Application of rapid solidification for production of dental amalgams

Abstract A technique of direct strip casting and rapid solidification has been used to produce high capacity melts of silver based powder alloys for dental amalgam. The properties of the amalgam were compared with those of conventional lathe cut or spherical powder amalgams. It was found that by optimising the size distribution and heat treatment, properties can be obtained to meet or excel international standards. The high cooling rate during rapid solidification produces a chemically homogeneous amalgam and its flake morphology gives superior workability in the mouth. The dimensional change (contraction) of in situ fillings is much reduced.MST/1520

A five year study of the clinical performance of a posterior composite resin restorative material

Five-year results from four centres of the multicentre clinical trial of the posterior composite Occlusin are reported. Data is presented in respect of 256 restorations of Occlusin and 69 restorations of a conventional lathe cut amalgam. It is concluded that more than 90 per cent of the restorations under investigation should be rated as clinically acceptable after five years in clinical service, that the wear resistance of the restorations of Occlusin, as assessed by the clinicians, was similar in preparations of different sizes and to that of the amalgam controls, and that similar clinical results were obtained irrespective of the technique used to achieve moisture isolation.

Manufacture of epikeratophakia lens.

Epikeratophakia lenses may be manufactured from donor cornea either with a lathe or using devices that make flat cuts on to previously deformed cornea. Details are given of a manufacturing technique using a cryolathe, including the storage and preparation of donor corneas and derivation of the formulae used to determine the radius of lathe cut.

The clinical evaluation of hydrogel lens back optic zone radius according to 3 commercially available procedures

Using three commercially available procedures for measuring the back optic zone radius of hydrogel lenses, we investigated four series of lathe cut lenses (each series of common labelled B.O.Z.R.) to see if the measure of back optic zone radius related to lens power. Analysis of variance shows: 1. the three procedures produced significantly different measurements of back optic zone on any single lens and 2. the lenses of a given series do not appear to be of the same back optic zone radius. No obvious trend between stated power and measured back optic zone radius was found.

Effect of Soft Lens Power on Peripheral Corneal Edema

The effect of soft lens design (lathe cut, spun cast) and power (-0.75 to -9.00 D) on central and peripheral corneal swelling was analyzed by measuring the change in corneal thickness after 3 h of eye closure and at mid-day during extended wear. Peripheral swelling was less than central for both lathe cut- and spun cast-type lenses. Significant correlations were found between spun cast lens power and central (r = +0.48) or peripheral (r = +0.32) swelling during eye closure. Small differences in swelling occurred with different power lathe cut lenses (r = -0.19). Correlations of mid-day (open eye) central corneal swelling with lens power were significant for both the spun cast (r = +0.43) and lathe cut (r = -0.53) lenses. However, correlation of peripheral swelling with power was weak. These results indicate that significant lateral diffusion of oxygen and/or epithelial metabolites may be occurring in the cornea between areas of high and low oxygen tension.

Protein adsorption on soft contact lenses: III. Mucin

Adsorption of bovine submaxillary mucin (BSM) on three different soft contact surfaces, lathe cut (LC) and spin cast (SC) crosslinked poly-2-hydroxyethylmethacrylate and spin cast poly(2-hydroxyethylmethacrylate/methacrylic acid) (PHEMA/MAA), was studied. The in vitro process was followed by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). A three-layer structure is envisaged for the adsorbed BSM: a very thin surface layer of strongly bound and conformationally altered mucin constitutes the surface layer. A random to β-sheet structural transition activated by the hydrogel surface is proposed for this layer. Glycoprotein hydrogen-bonding with the polymer hydroxyls and interaction of charged and hydrophobia groups with hydrogel surfaces are important in stabilizing this layer. Most of the adsorbed BSM (99%) is found in the middle and top layers which are formed by a different degree of associated BSM (their conformation is minimally changed or not changed at all, respectively) and are weakly adsorbed to the lens surfaces. Surface morphololgy and chemical composition of the lenses are important adsorption parameters only for the reversibly adsorbed BSM.

Protein adsorption on hydrogels: II. Reversible and irreversible interactions between lysozyme and soft contact lens surfaces

Lysozyme was adsorbed on spin cast and lathe cut soft contact lenses of poly-2-hydroxyethylmethacrylate (PHEMA) and on poly-HEMA-methacrylic acid (PHEMA/MAA). The in vitro adsorption process was followed by ATR-FTIR. Lysozyme adsorbs both, reversibly and irreversibly, on the surfaces. While the reversible bound lysozyme experiences only minor changes in its secondary structure, conformational changes occur for the irreversibly adsorbed protein. The type and extent of structural changes depend on the degree of protein coverage on the lens surface, as well as the chemical structure and surface morphology of the lenses. PHEMA/MAA lenses adsorbed thirty times more lysozyme than either of the PHEMA lenses. Fabrication processes appear to induce different adsorption behaviour, PHEMA lathe cut lenses adsorb twice the amount of protein compared with PHEMA spin cast lenses.

Characterization of protein adsorption on soft contact lenses: I. Conformational changes of adsorbed human serum albumin

Adsorption of human serum albumin on three different soft contact lens surfaces (lathe cut and spin cast crosslinked PHEMA and spin cast PHEMA/MAA) was studied. Using ATR-FTIR spectroscopy the spectra of the adsorbed protein were obtained at different times of adsorption. Structural changes were detected, initially characterized by an increase in hydrogen bonding and after that by involvement of the protein hydrophobic side chain residues. At long adsorption times, the protein becomes denatured, its α-helix content is drastically reduced and the amounts of random coil and β-sheet conformations are increased. ATR-FTI R and circular dichroism studies of albumin solutions reveal similar conformational changes to those experienced by the adsorbed protein. Differences in the adsorption behaviour for the hydrogel surface, indicate the importance of the hydrophilicity, surface regularity and the chemical composition of the contact lens surfaces as the controlling parameters in the protein adsorption phenomena.

Identification of mercury-containing phases in dental amalgams by differential scanning calorimetry

Differential scanning calorimetry was used to differentiate between γ1 and γ2 phases in dental alloys. Four different types of dental amalgams were examined: conventional lathe cut alloy, conventional spheralloy, non-γ2 dispersalloy and ternary alloy (sybralloy).The results showed that the non-γ2 alloy produced a characteristic endotherm around 105°C, which is 20–30°C higher than that of the conventional alloys.This method is not only a simple means of identifying the presence of dominant γ2 phases in dental amalgams, but also serves to check the homogeneity of phase distribution in alloy particles.

Optiflex angle fixation lens.

The Optiflex anterior chamber lens was implanted in 153 eyes of 150 patients. This lens was selected because it was lathe cut, with a good surface finish as demonstrated by scanning electron microscopy, had an open haptic and required a simple implantation technique. The surgeon's standard intracapsular or extracapsular technique was used and adjunctive agents, such as Healon, were not required. Observations made over an 18-month period revealed no corneal decompensation, which was probably an advantage of the lens design and insertion technique. Corneal astigmatism was the principal disadvantage.

Properties of Ag-Cu-Pd dispersed phase amalgam: compressive strength, creep, and corrosion.

Dental amalgams fabricated from a dispersion phase consisting of 62%Ag-28%Cu-10%Pd, combined with traditional lathe cut and spherical Ag3Sn alloys, were investigated and compared with commercial Cu-enriched amalgams. High one-hour compressive strength, reduced creep, and significant improvements in corrosion resistance of dispersant and resultant amalgams were obtained.

アマルガム組織の腐食による変化

Conventional lathe cut and spherical amalgams were fully covered with heavily protuberant corrosion products when placed in saline solution for a six-month period. The products were mostly composed of two distinct layers : the inner consisting primarily of Sn and Cl, and the outer primarily of Sn or Sn with small amount of Cu. Cl was detected together with Sn from the traces of corroded γ_2 phase in the specimen, indicating that γ_2 phase was selectively attacked in succession inward. Residual γ alloy particles were also attacked to a lesser extent than γ_2 phase. High-copper amalgams composed of lathe cut Ag_3Sn and admixed spherical Ag-Cu alloys did not yield so marked corrosion products as the conventional ones by virtue of the absence of γ_2 phase. Their surfaces were mostly covered with Cu-rich small, angular crystals and newly grown-up curly γ_1 crystals. Cl was detected together with Sn from the traces of corroded Cu_3Sn phase and from the vicinity of the residual γ alloy particles. Cl was also found in the γ particles. On the contrary, another system of high-copper amalgam composed of spherical Ag-Sn-Cu ternary alloy including a small amount of In yielded big protuberant corrosion products on the surface regarded as verdigris. Most of the original alloy particles within a 1000μm depth from the surface were severely destroyed leaving In together with Cu and/or Cl and many microcracks. The presence of In seems to induce the corrosive attack in the amalgam after three months. Cl penetration into the amalgam specimen was generally deeper in Zn free amalgams than in Zn containing amalgams.

SOFT LENS POWER AND CURVATURE

Determining the concave curve by a projection method, 350 spin cast lenses were compared with information published by the manufacturer. The power was also determined, using Sarver's method, to establish the clinical reliability of label powers. An equal number of lathe cut lenses were subjected to the same tests. Results indicated that spin cast lenses are very nearly as described in the manufacturer's published information. The lathe cut lenses involved in this study were not as dependable. Variations in the power of "C" series lenses and other related observations are also reported.