Machinable Glass Ceramics Research Articles

In Vitro Bioactivity Characterization of Machinable Glass Ceramics Containing 85wt% Na-mica and 15wt% Fluorapatite

In this study; in-vitro bioactivity characterization of machinable glass-ceramics having 85 wt% sodium mica (NaMg3AlSi3O10F2) and 15 wt% fluoroapatite has been carried out. Two different heat treatment procedures are applied to the machinable glass-ceramics. The first one is nucleation at 610°C for 2 hours and crystallization at 1000°C for 3 hours and the second is nucleation at 610°C for 2 hours and crystallization at 1000°C for 4 hours. It is observed that increasing the crystallization time to 4 hours resulted in the increasing the formation of hydroxyapatite layer on surface. According to the microstructural investigations, the morphology of the precipitated crystals are different. In addition, the speed of the precipitation of hydroxyapatite is higher in glass-ceramic B than A. Thin film XRD analysis supports these results.

Influence of alumina content on the nucleation crystallization and microstructure of barium fluorphlogopite glass-ceramics based on 8SiO2·YAl2O34MgO2MgF2BaO Part I Nucleation and crystallization behaviour

The effect of varying the aluminium oxide content on the nucleation and crystallization behaviour of barium containing glasses based on 8SiO2·YAl2O34MgO2MgF2BaO was investigated in order to develop novel, high strength, machinable glass-ceramics. Nine glasses were synthesized and characterized by Differential Scanning Calorimetry (DSC) Combined Differential Thermal Analysis Thermal Gravimetric Analysis (DTA/TGA), X-ray diffraction (XRD) and dilatometry.

“EDGE TOUGHNESS” AND MATERIAL PROPERTIES RELATED TO THE MACHINING OF DENTAL CERAMICS

Seven dental ceramic compositions, including zirconia, glass-infused alumina, polycrystalline alumina, porcelain and three different machinable glass ceramics (MGC's) were tested for edge flaking. The chosen load range encompassed the forces typically associated with machining operations for these materials. The results were examined with regard to material properties and the applicability of a parameter defined as “edge toughness” to machin-ability. It was determined that a non-linear low-load chipping relationship may be more relevant to machinability than the “edge toughness” parameter calculated from the high-load linear region.

ABRASIVE MACHINING OF GLASS-CERAMICS WITH A DENTAL HANDPIECE

Dental restorations are commonly prepared from machinable glass-ceramics using modern dental CAD/CAM systems. Unfortunately, little is understood about the influence of machining parameters on material removal rates and any damage which could be introduced into the restoration during the abrasive machining processes employed with these systems. These effects are investigated for three experimental machinable glass-ceramics with varying microstructure and one closely related commercial material. Abrasive machining is performed with dental burs containing coarse and fine diamond particles. The results show that the microstructure of the glass-ceramic, the size of diamond grit in the burs, and the load applied to the burs during machining have significant effects on the machining behavior. By increasing the size of the mica platelets within the glass-ceramics or by increasing the load on the burs, material removal rate increases. However, chipping damage at groove edges increases as either the load is increased or as the size of the mica platelets is decreased. The use of coarse burs does not necessarily result in high material removal rates but increases the extent of chipping damage. Surface roughness is found to be relatively independent of the microstructure or applied load but is strongly dependent upon coarseness of the diamond particles in the burs.

TEM study on the origin of cabbage-shaped mica crystal aggregates in machinable glass-ceramics

In micaceous glasses cabbage-shaped mica crystal aggregates are formed at certain compositions and distinct heat-treatment schedules. It is experimentally proved that a liquid–liquid phase separation is responsible for this peculiar behaviour. Based on transmission electron microscopy observations of glasses and glass-ceramics, a novel growth mechanism is proposed for cabbage-shaped mica crystal aggregates in machinable mica glass-ceramics. In this model, crystallization takes place along isocompositional lines at or not far from the surface of the liquid–liquid phase separation droplets. Due to high growth rates, diffusion has only little impact on the crystal growth. Finally, experimental reasons for earlier misinterpretations are discussed.

Investigation on phase separation, nucleation and crystallization in bioactive glass-ceramics containing fluorophlogopite and fluorapatite

Apatite and mica-containing glass-ceramics in the system K 2OMgOCaOAl 2O 3B 2O 3 SiO 2P 2O 5F can be used to repair and reconstruct diseased or damaged bones and teeth, due to their biocompatibility and bioactivity. Like other glass-ceramics, the properties of these machinable glass-ceramics depend on composition, size and volumetric ratios of the crystalline phases in the materials. Phase separation, nucleation and crystallisation of these multi-phase glass-ceramics were investigated with DTA, SEM/EDAX, XRD and FTIR techniques. The phase relationships are discussed with regard to crystal chemistry, thermodynamics and kinetics.

Al2O3-and ZrO2-modified dental glass ceramics

Castable machinable glass-ceramics have been widely considered as aesthetic materials for dental restoration. In order to extend their applications to bridge-work fabrication, it is necessary to increase their fracture strength and fracture toughness. The effects of ziconia and alumina additions on the properties of glass-ceramics, especially on the mechanical properties were studied. It was found that appropriate addition of alumina increases the bending strength due to aluminium strengthening the glass-ceramic by means of incorporation into the glass network. However, additions of ziconia fail to show promising results on the mechanical property. The evolution of recrystallization and the associated microstructure were also studied and are discussed.

Time-dependent elastic modulus recovery measurement on thermally shocked SiC fibre-aluminosilicate composites, machinable glass ceramics and polycrystalline alumina

Time-dependent partial recoveries in Young's modulus were observed for thermally shocked specimens of three ceramic materials: an SiC fibre-aluminosilicate composite, a machinable glass-ceramic, and a polycrystalline alumina. The observed Young's modulus recovery is likely to be due to room-temperature microcrack healing. The room-temperature modulus recovery rates measured in this study are compared to the physical property recovery rates obtained from an analysis of data in the literature for other cracked ceramics.

Development of Glass-ceramics for Dental Applications to CAD/CAM System - Machinable Glass-ceramics -

Development of Glass-ceramics for Dental Applications to CAD/CAM System - Machinable Glass-ceramics -

Preparation of High-Strength Calcium-Mica-Containing Machinable Glass-Ceramics

New machinable glass-ceramics containing fine calcium-mica were prepared by crystallizing glasses in the system CaxK(1-2x)Mg3(Si3AlO10)F2. TEM observation suggested that the host glasses were separated into two fine phases, and the precipitating crystal size decreased with increasing the potassium content. The machinability were improved with increasing the calcium content. The mechanical strength and the machinability of the glass-ceramics depended on both the amount of calcium-mica precipitated and the crystal size. Because of its high bending strength (≈300MPa) and its hardness compatible with natural teeth, it has great potential for dental prostethic applications.

The effect of fluorine source and concentration on the crystallization of machinable glass-ceramics

Abstract Transparent and clear glasses were prepared from the MAS system (based on MgO-Al 2 O 3 -SiO 2 ) with different fluorine contents. Their crystallization behaviour to giving mica glass-ceramics upon heat treatment was studied as a function of the source of fluorine and its concentration. The predominant crystalline phase in these glass-ceramics is fluoborite, norbergite, or fluorphlogopite, depending on the heattreatment temperature, fluorine source, and concentration. An interlocking microstructure of fluorphlogopite in a glassy matrix is observed above 870°C.

Dental cutting behaviour of mica‐based and apatite‐based machinable glass‐ceramics

Some recently developed industrial ceramics have excellent machinability properties. The objective of this study was to evaluate the dental cutting behaviour of two machinable glass-ceramics, mica-containing Macor-M and apatite- and diopside-containing Bioram-M, and to compare them with the cutting behaviour of a composite resin typodont tooth enamel and bovine enamel. Weight-load cutting tests were conducted, using a diamond point driven by an air-turbine handpiece, While the transverse load applied on the point was varied, the handpiece speed during cutting and the volume of removal upon cutting were measured. In general, an increase in the applied load caused a decrease in cutting speed and an increase in cutting volume. However, the intensity of this trend was found to differ between four workpieces. Cutting Macor-M resulted in the second-most reduced cutting speed and the maximum cutting volume. Cutting Bioram-M gave the least reduced cutting speed and the minimum cutting volume. It was suggested that two machinable glass-ceramics could be employed as typodont teeth. This study may also contribute to the development of new restorative dental ceramic materials, prepared by machining.

ChemInform Abstract: Preparation and Characterization of Machinable Mica Glass‐Ceramics by the Sol‐Gel Process.

AbstractMica glass‐ceramics are prepared by the sol‐gel process using KF, MgSiF6, Al(OiPr)3, Si(OEt)4, and Mg(OMe)2 as starting materials.

Formation and Crystallization in the Glasses Containing Shirasu, Yttria-Concentrate, Calcium Oxide and Zinc Oxide, and Application of the Glass to the Machinable Glass Ceramics

We have investigated the formation of the glasses containing Shirasu, yttria concentrate, calcium oxide and zinc oxide from melts. Densities, thermal expansion coefficients and Vickers hardnesses were measured for some glasses. Linear relation between some physical properties and glass composition has been discussed. The agreement between observed values of density is satisfactory. On the contrary, observed values of thermal expansion coefficient are smaller than calculated values for yttria containing glasses. In a specific compositional region, crystals with needle-like habit were observed by SEM, which were identified as Ca4Y6O(SiO4)6 by XRD. The crystallized glass was able to be machined by lathe, and it is applicable to the machinable glass ceramics. This glass ceramics has a higher Vickers hardness than usual machinable glass ceramics.

化学切削用感光性ガラス

化学切削用感光性ガラス

Growth of fibroblasts and epithelioid cells on a new machinable bioactive glass ceramic in comparison with non-reactive materials

In this study scanning electron microscopy (SEM) was used to investigate the substrate attachment, cell spreading and growth properties of fibroblasts and epithelioid cells on a newly developed machinable bioactive glass ceramic. The morphogenetic reactions of cell cultured on bioactive ceramic were compared with those of identical cells cultured on non-reactive glass and vitreous carbon. The adhesion, subsequent spreading and the growth appearance of fibroblasts and epithelioid cells on the surface of machinable glass ceramics are similar to those on nonreactive materials. Our findings concerning the behaviour of cell populations in vitro on the surface of a new machinable glass ceramic allow the conclusion that this implant material is adhesive for cells and biocompatible.

Turning of Machinable Glass Ceramics with an Ultrasonically Vibrated Tool

Machining with an additional ultrasonic super position is known to be one possibility of influencing the chip formation process in metals. The degree of influence depends on the direction of the ultrasonic vibration of the tool relative to the work, the ultrasonic power as well as the mechanical properties of the material to be machined. Research into the turning of plain carbon steel with a carbide tool yielded hardly any practical results. The application of ultrasonics to the turning of machinable glass ceramics will, however, greatly facilitate the chip formation. Unlike the machining of metals chip removal in glass ceramics is primarily effected by fractures in the layers near the material surface. These fractures are caused by the vibrating tool. This results in an increase in the life of carbide tools by up to 20 times. Thus the acoustic analysis during machining proved to be a suitable method of detecting the wear of the tool and the end of tool life.

Vacuum compatibility of machinable glass ceramics

The thermal outgassing and helium permeation characteristics of Code 9658 machinable glass–ceramic are discussed. Up to 600° C, it is shown that this material can be treated like glass vacuum system components. The quantities of outgassing constituents under vacuum conditions are given and the need for vacuum baking freshly machined material is demonstrated. Although the material can be used up to 1000° C, between 600° and 1000° C some fluorine evolution from the material takes place and could present a corrosion problem to some systems. Helium permeability of this material is an order of magnitude lower than for Code 7740 glass.