Delayed ceramic fracture of the ceramic crown in molar is due to cyclic loading of

Ceramic orthodontic brackets and activated wires within the brackets represent a clinical system that can exhibit static fatigue failure. The delayed fracture of molar ceramic crowns that are subjected to periodic cyclic forces may be caused by dynamic fatigue failure. The failure begins as a flaw that propagates until the catastrophic fracture occurs. Stresses well below the ultimate tensile strength can produce premature fracture of a dental prosthesis because microscopic flaws grow slowly over many cycles of stress. This phenomenon is called fatigue failure. Normal mastication induces several thousands of stress cycles per day within a dental restoration. For glasses and certain glass containing ceramics, the induced tensile stress and the presence of an aqueous environment further reduce the number of cycles to cause fatigue failure. Phillip’s 12th edition page 60