American journal of dentistry Feb;20(1):21-6 Park Jae Young

 Masticatory fatigue was assumed to cause early fractures of ceramic partial coverage restorations by development of micro-crack growth.  To determine the reliability and fracture resistance of adhesively luted all-ceramic partial ceverage restorations (PCR) on natural upper molars after masticatory fatigue loading. American journal of dentistry Feb;20(1):21-6

 64 mx. Molars (NP- 16 teeth, PCR- 48)  Tooth preparation (MOD inlay cavity) - 3mm occlusal box - 2mm isthmus width - 2mm occlusal reduction - 1.2mm palatal shoulder American journal of dentistry Feb;20(1):21-6

 NP – control (unprepared)  EM - IPS Empress, staining technique  EX - IPS e.max Press (lithium disilicate)  PC - ProCAD (leucite-reinforced glass- ceramic), CAD/CAM (Cerec 3) American journal of dentistry Feb;20(1):21-6

 PCR - Cleaned with 99% isopropanol - 4.9% hydrofloric acid (IPS ceramic etching gel) ; EM, PC for 60s, EX for 20s - Silane (monobond S)  Tooth - Cleaned with synthetic rotary brushes and fluoride-free polishing paste (Pell-ex) - Etched (enamel for 60s, dentin for 15s) with 37% phosphoric acid (Total Etch) and conditioned with Syntac Primer (15s) - Adhesive for 10s, Heliobond (light curing for 20s) - Luted with a dual polymerizing resin composite (Variolink II) American journal of dentistry Feb;20(1):21-6

 1.2 million masticatory cycles (F=49N, 1.6 Hz)  5,500 thermal cycles of 5 ℃ and 55 ℃  The masticatory process was simulated through horizontal(0.5mm) and vertical (6mm) movements.  Mesial-palatal cusp of the occlusal surface of the test specimen. American journal of dentistry Feb;20(1):21-6

 Failure was defined by bulk fracture of a specimen.  Subcritical crack patterns were observed.  Survived specimens were loaded until fracture in a universal testing machine.  The force was applied axially to the central fissure. American journal of dentistry Feb;20(1):21-6

 All specimens survived mastication simlation.  Superficial micro-cracks were identified in all groups in those places where the load was concentrated during the fatigue simulation, but especially in leucite-reinforced glass-ceramic restorations of Group EM. American journal of dentistry Feb;20(1):21-6

 The load-to-fracture values of Groups NP and PC in paticular were significantly higher than those of Groups EM and EX.  ProCAD restoratin demonstrated th best predictability of failure.  Most main final fracture propagation in the center of the occlusal plane in MD direction  Separate bulk fractures of the proximal areas ~40%  Delamination was not recognized. American journal of dentistry Feb;20(1):21-6

 Variability in strength is a consequence of the distribution in crack size, and the time dependency of strength results from the slow growth of these flaws to dimensions critical for catastrophic failure. American journal of dentistry Feb;20(1):21-6

 If the restorations are subjected to preliminary masticatory fatigue and thermal cycling, the fracture resistance may decrease by up to 50% compared with the baseline values.  Superficial and deep micro-cracks are responsible for this decline. American journal of dentistry Feb;20(1):21-6

 ProCAD PCR showed a similar fracture resistance when compared with natural teeth.  The majority of IPS e.max Press and ProCAD restorations survived loads within the range of physiological mastication forces, both materials appeared to be suitable for the predictable use of posterior partial crowns. American journal of dentistry Feb;20(1):21-6