May 19 2011
Superior zirconia-based dental restorations can be produced with a microwave sintering furnace, according to a research report in the April 2011 issue of Ceramic Industry magazine. The cover story, "Industrial-Scale Microwave Sintering", focuses on technology advances made by Spheric Technologies, a Phoenix, Arizona, company. A batch-type microwave sintering furnace has been specially designed for dental labs.
Microwave sintering of ceramics offers significant advantages over conventional sintering methods. Research conducted at Arizona State University showed that microwave-sintered zirconia samples had increased flexure strength compared to those sintered in a conventional furnace. This was attributed to a reduced grain size and rapid densification in the zirconia samples due to microwave-driven enhanced sintering kinetics. Microwave sintering also produces a more natural and translucent appearance in dental restorations.
Samples tested in a steam environment at 125°C and 200 kPa pressure for 75 hours showed a reduction of flexure strength by 43% for conventionally sintered samples and only 14% for microwave-sintered samples. It was estimated that this corresponded to 10 years of simulated testing in the mouth, after which microwave-sintered zirconia does not deteriorate significantly and is nearly 50% stronger than conventionally sintered zirconia.
Advanced microwave sintering furnaces specially designed for dental labs are now available. The ADS (private labeled as the MicroSinterWave A1614) microwave batch furnace is air-cooled; offers an effective uniform heating volume of approximately 100 x 100 x 60 mm; has a maximum microwave power output of 1.1 kW; and features computerized temperature programming and control in the range 250-1650°C. The system includes factory preset programs for automatic mode operation that complete zirconia sintering runs in as little as 90 minutes. Various operator-defined temperature ramp-up rates, temperature hold stages (up to about 1550°C) and hold times may also be programmed.
For labs with higher throughput requirements, the Spheric AMPS continuous microwave furnace is available.