Martin Dipl Ing Frank

A comparison of the microstructure and properties of the IPS Empress®2 and the IPS Empress® glass‐ceramics

The aim of this report is to analyze the microstructures of glass-ceramics of the IPS Empress 2 and IPS Empress systems by scanning electron microscopy. The main properties of the glass-ceramics were determined and compared to each other. The flexural strength of the pressed glass-ceramic (core material) was improved by a factor of more than three for IPS Empress 2 (lithium disilicate glass-ceramic) in comparison with IPS Empress (leucite glass-ceramic). For the fracture toughness, the K(IC) value was measured as 3.3 +/- 0.3 MPa. m(0.5) for IPS Empress 2 and 1.3 +/- 0.1 MPa. m(0.5) for IPS Empress. Abrasion behavior, chemical durability, and optical properties such as translucency of all glass-ceramics fulfill the dental standards. The authors concluded that IPS Empress 2 can be used to fabricate 3-unit bridges up to the second premolar.

Surface crystallization of leucite in glasses

Abstract The aim of this paper was to study surface crystallization of leucite in glasses derived from an SiO 2 -Al 2 O 3 -K 2 O base glass in a comparative study with another glass based on SiO 2 -Al 2 O 3 -MgO. Monolithic samples and glass powder of SiO 2 -Al 2 O 3 -K 2 O glass were studied and phase formations were determined by using scanning electron microscopy. Heterogeneous nucleation was promoted by seeding the surface of the monolithic glass samples with glass dust to produce a highly disordered crystal as the primary phase. In addition to leucite formation, growth of a highly symmetric, flat, almost two-dimensional crystal phase with controlled diffusion was also observed. In glass granules, leucite demonstrated rapid, almost dendritic growth, from the nucleating centers. Use of leucite ceramic as a restorative dental product is considered.

Mechanisms of nucleation and controlled crystallization of needle-like apatite in glass-ceramics of the SiO2-Al2O3-K2O-CaO-P2O5 system

Abstract Apatite containing glass-ceramic was prepared of the composition 61.5 mol% SiO2, 9.4 Al2O3, 9.2 Na2O, 7.7 K2O, 6.0 CaO, 0.5 ZrO2, 0.2 TiO2, 1.9 P2O5, 0.3 CeO2, 0.5 Li2O, 0.3 B2O3 and 2.5 F. The glass was melted at 1480°C for 1 h and 40 min. The cooling rate was 3–6 K/min in the transformation range. Heat treatment of the glass was carried out in the temperature range 700–1050°C and from 15 min to 8 h. Scanning electron microscope investigations (SEM) clearly demonstrated phase separation in the base glass. However, needle-like apatite did not precipitate in the droplet phase. This result revealed that phase separation leads to the formation of a primary crystal phase of NaCaPO4. This phase was determined by X-ray diffraction. Furthermore, another, unknown crystal phase may be precipitated prior to apatite formation. Fluoroapatite, Ca10(PO4)6F2, precipitated as a third crystalline phase, but not in a needle-like habit. The nucleation of these apatite crystals may be based on two mechanisms, a heterogeneous reaction of the primary NaCaPO4 crystals with the glassy matrix and an interface reaction of the glass droplet–glass matrix. The formation of needle-like apatite was observed by X-ray diffraction and SEM at 950°C. The driving force for the crystal growth of needle-like apatite can be described as a controlled diffusion process in which a region of diffusion is formed around the crystals. This diffusion region should show a higher solubility in aqueous HF than that of the other glassy matrix. This was demonstrated by SEM after etching the sample (10 s, 2.5% HF). The crystal growth of needle-like apatite was controlled by an Ostwald ripening mechanism. This was determined by investigating the number and length of the crystals as function of time at constant temperature of 1000°C.