Effect of furnace type and ceramming heat treatment conditions on the biaxial flexural strength of a canasite glass-ceramic.
OBJECTIVE
To assess the effect of different heat treatment conditions when using two different furnace types on the biaxial flexural strength (BFS) of a fluorcanasite castable glass-ceramic.


METHODS
Two furnace types, one a programmable furnace (PF), the other a dental laboratory burnout furnace (DLF), were used with various ceramming times to determine their effect on the BFS of a fluorcanasite castable glass-ceramic. The glass-ceramic material was cast to produce discs of 12 mm diameter and 2 mm thickness using the lost wax casting process (n = 80). After casting, both furnace types were used to ceram the discs. Half the discs were not de-vested from the casting ring before ceramming but cerammed in situ (DLF) and half were de-vested before ceramming (PF). All the discs were given a nucleation heat treatment at 520 degrees C for 1 h and then cerammed at 860 degrees C using four heat soak times (0.5, 1, 2 and 3 h). The DLF furnace had a rate of climb of 13 degrees C/min and the PF furnace had a rate of climb of 5 degrees C/min to 520 degrees C and 3 degrees C/min to 860 degrees C. After ceramming the discs were de-vested and the BFS determined using a Lloyd 2000R tester.


RESULTS
The maximum BFS values seen for both furnace types were almost identical (280 MPa), but were achieved at different heat soak times (1 h DLF, and 2 h PF). The only significant differences in BFS values for the two furnaces were between the 0.5 and 2 h heat soak times (p < or = 0.05). Individual differences were seen between results obtained from each furnace type/heat soak times evaluated (p < or = 0.05).


CONCLUSIONS
Already available dental laboratory burnout furnaces can be used to ceram fluorcanasite glass-ceramic castings to the same BFS values as more expensive and slower specialist programmable furnaces.
Johnson
A
A
Department of Restorative Dentistry, School of Clinical Dentistry, University of Sheffield, Claremont Crescent, Sheffield S10 2TA, UK. a.johnson@sheffield.ac.uk
Shareef
M Y
MY
van Noort
R
R
Walsh
J M
JM
D000704:Analysis of Variance; D002516:Ceramics / Q000737:chemistry*; D003734:Dental Casting Investment / Q000737:chemistry*; D003735:Dental Casting Technique / Q000295:instrumentation*; D005898:Glass / Q000737:chemistry*; D006358:Hot Temperature; D006801:Humans; D007754:Laboratories, Dental; D008422:Materials Testing; D018583:Pliability; D013223:Statistics as Topic; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors
D003734:Dental Casting Investment; C113305:fluorocanasite