[Strength of the In-Ceram system under mechanical loads and thermocycling in artificial saliva]

The mechanical strength of the new oxide ceramic system In-Ceram introduced by Vita (Bad Säckingen, Germany) was investigated by an in-vitro study for its mechanical strength and suitabilities for use as posterior three-unit bridges. The transverse strength value measured by a three-point bending test (DIN 13,927) is 320 MPa and the maximum vertical load on three-unit bridges until brittle failure occurs is in the range of 1000 to 1350 N. This is up to four times higher than corresponding values of other ceramics, e.g. Dicor (Dentsply) or Optec (Jeneric). The dental bridges were luted to metallic pontics, and a layer of silicon rubber simulating the periodontal membrane, separated the pontic from a resin base in the testing machine. Life value tests were performed before and after 10 days of thermocycling at temperatures alternating between 5 and 55 degrees C in artificial saliva. Although the pontics had a much higher mobility than normal teeth, the fatigue limit was found to be above 600 N which is much higher than the average biting forces acting on the first and second molars.