Heat-pressed ionomer glass-ceramics. Part I: an investigation of flow and microstructure.
OBJECTIVE
This study investigated a series of ionomer glasses based on the formula: 4.5SiO(2)-1.5P(2)O(5-)(X)Al(2)O(3)-4.5CaO-0.5CaF(2), where X was varied from 3.0 to 1.5. The possibility of processing ionomer glasses using a heat-pressing method for dental restorations was investigated.


METHODS
A simple flow test was designed to measure the amount of flow the glasses underwent as a result of heat-pressing at 1150 degrees C for different times. Heat-pressed samples of the X=3.0, 2.8, 2.4 and 2.0 glass were further heat-treated for 1 and 4 h at 1150, 1200 and 1250 degrees C to promote crystal growth. Scanning electron microscopy was used to investigate the microstructure of the glass-ceramics. X-ray diffraction was used to identify the crystalline phases in the glass-ceramics.


RESULTS
The ionomer glasses exhibited excellent flow ability. Crystallization could not be suppressed during heat-pressing. Very fine scale fluorapatite crystals were present in all of the samples after heat-pressing. Mullite and/or anorthite formed as a second crystal phase. On further heat-treatment of the samples, changes in crystal phases took place.


CONCLUSIONS
Apatite was the main crystalline phase produced in the glass-ceramics; this factor is of clinical significance. In conclusion these glass-ceramics could be suitable for all-ceramic dental restorations.
Gorman
Catherine M
CM
Department of Restorative Dentistry and Periodontology, School of Dental Science, Trinity College Dublin, Lincoln Place, Dublin 2, Ireland. cgorman@dental.tcd.ie
Hill
Robert G
RG
D000180:Acrylic Resins / Q000737:chemistry; D000538:Aluminum Silicates; D001031:Apatites; D002152:Calorimetry, Differential Scanning; D002516:Ceramics / Q000737:chemistry*; D003460:Crystallization; D018360:Crystallography, X-Ray; D003776:Dental Porcelain / Q000737:chemistry*; D003793:Dental Restoration, Permanent; D006358:Hot Temperature; D008855:Microscopy, Electron, Scanning; D012212:Rheology; D012822:Silicon Dioxide / Q000737:chemistry; D014783:Viscosity
D000180:Acrylic Resins; D000538:Aluminum Silicates; D001031:Apatites; C015897:glass ionomer; D003776:Dental Porcelain; C074225:anorthite; C049037:aluminosilicate; D012822:Silicon Dioxide; C023506:Glass ceramics; C025105:fluorapatite