Mouth Motion Fatigue and Durability Study
Petra C Guess*, Ricardo Zavanelli+, Nelson Silva and Van P Thompson, NYU
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Porcelain veneered zirconia crowns and monolithic lithium disilicate crowns were tested Mouth-motion-step-stress-fatigue was used to examine reliability and failure modes Failure was considered to be chip-off fracturesor fracture through the crown Three step-stress profiles were used up to failure or up to 900 N and 180K cycles after which a staircase fatigue method was implemented to a load at which 50% of specimens could be expected to survive 1 million cycles
Veneered zirconia crowns resulted in limited reliability - approximately 90% of specimens would fail from veneer chip-off fracture by 100kcycles at 200 N. These results are similar to previous findings for other veneered zirconia systems (LAVA, Cercon, Vita) tested using this methodology (Coelho PG, Silva NR, Bonfante EA, Guess PC, Rekow ED, Thompson VP. Fatigue testing of two porcelain-zirconia all-ceramic crown systems. Dent Mater. 2009 Apr 21. [Epub ahead of print]
Approximately 90% veneered zirconia specimens failed by 350 Nindependent of the number of cycles
None of the e.max CAD lithium disilicate specimens failed below 900 N and 180k cycles independent of loading profile
The e.max CAD lithium disilicate specimens survived r ratio fatigue of 1 million cycles at loads of 1000 N. There appears to be a threshold for damage/fracture for the lithium disilicate in the range of 1100-1200 N.
* VisitingScientist from the Department of Prosthodontics University of Freiburg, Freiburg, Germany + Visiting Scientist from the Department of Prevention and Oral Rehabilitation, Federal University of Goias School of Dentistry, Goiania, Brazil.
NYU Crown Fatigue Study
While Y-TZP core ceramic exhibits a high stability as a framework material in short-  and medium-term studies onfixed partial dentures [2- 3] chip fractures within the veneering ceramic are the most common clinical failure mode of all-ceramic Y-TZP based restorations . Hence attempts have been made to find all-ceramic alternatives for full crown application. As high survival rates with no chip failures within the veneering ceramic have been reported for lithium disilicate IPS Empress 2 crowns [5, 6] theexploration of the recently developed monolithic CAD/CAM fabricated lithium disilicate crown system IPS e.max CAD is expected to be promising. Since no study so far has been published on the clinical performance of Y-TZP based or CAD/CAM fabricated lithium disilicate crowns, a preclinical investigation of the vitro longevity and micro-structural fatigue is expected to be most enlightening for theevaluation of long-term behavior of the described allceramic systems. Objective: To evaluate the effect of on mouth-motion-step-stress-fatigue on reliability and failure modes of monolithic lithium disilicate full crowns (IPS e.max CAD) and to compare these results with hand-layer veneered Y-TZP based crowns (IPS e.max ZirCAD/Ceram). Methods: An anatomical correct 3D model of a mandibular firstmolar full crown was generated. Monolithic lithium disilicate full crowns (IPS e.max CAD, n= 19) and hand-layer veneered Y-TZP based crowns (IPS e.max ZirCAD/Ceram, n= 21) were tested. Full-anatomically shaped IPS e.max CAD and IPS e.max ZirCAD cores were designed and milled with a CAD/CAM system (Cerec InLAB, Sirona, Germany). IPS e.max ZirCAD cores were veneered using the hand-layering technique(IPS e.max Ceram) according to the manufacturer’s instruction. Figure 1: CAD/CAM crown configuration IPS e.max CAD: Full anatomic design (occlusal reduction: 2 mm, axial 1.5 mm, IPS e.max ZirCAD/Ceram (0.5 mm Y-TZP core; 1-1.5 mm veneering ceramic)
All crowns were cemented to aged resin-based composite dies (Tetric EvoCeram A2) with Multilink Automix. Prior to cementation, a layer of metal...