Effect of furnace type and ceramming heat treatment conditions on the biaxial flexural strength of a canasite glass-ceramic

Abstract

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°C for 1 h and then cerammed at 860°C using four heat soak times (0.5, 1, 2 and 3 h). The DLF furnace had a rate of climb of 13°C /min and the PF furnace had a rate of climb of 5°C /min to 520°C and 3°C /min to 860°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≤0.05). Individual differences were seen between results obtained from each furnace type/heat soak times evaluated (p≤0.05). Significance: 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.