1223 Veneer Thickness Ratio and Layering Methodology Effect Layered Zirconia Strength

Saturday, March 24, 2012: 8 a.m. - 9:30 a.m.
Presentation Type: Oral Session
J. SORENSEN1, T. HILL2, and K. CHLOSTA2, 1Pacific Dental Institute, Portland, OR, 2Ivoclar Vivadent, Inc, Amherst, NY
Objectives:   Novel processing methodologies have been developed for veneering zirconia substructures attempting to reduce the incidence of chipping. We studied the biaxial strength of layered zirconia by varying veneer/substructure thickness ratio (VTR), testing mode, and material processing methodologies.

Methods: Zirconia disks 15mm in diameter were layered to 1.5mm total thickness (n=10/group). Veneer processing groups were: POW=fluorapatite powder handbuild-up (e.maxCeram, IvoclarVivadent), ZirLiner (0.1mm); CAD1=CAD/CAM low strength layering, feldspathic powder compact superstructure, (Lava DVS, 3M Espe), Fusion® (0.1mm); CAD2=CAD/CAM high strength layering, lithium disilicate glass ceramic superstructure (CAD-on, ZirCAD, IvoclarVivadent), Connect®(0.1mm).

Approximately 25%, 50%, 75% VTR groups (mm) were: A)0.4 veneer/1.0 zirconia; B)0.7 veneer/0.7 zirconia; C)1.0 veneer/0.4 zirconia. Testing mode groups were veneer loaded in: (T)=tension, (C)=compression. Specimens were loaded on universal testing machine in piston-on-three-ball test fixture (ISO 6872) at a cross-head speed of (0.5)mm/min recording first veneer cracks and catastrophic failure.

Results: Mean (sd) biaxial fracture loads (MPa) for test groups were: POW: AC=604(95), AT=398(54), BC=444(72), BT=208(18), CC=287(55), CT=111(18). CAD1: AC=746(193), AT=403(16), BC=529(79), BT=208(9.2), CC=400(29), CT=115(32). CAD2: AC=526(42), AT=442(58), BC=658(132), BT=436(35), CC=653(138), CT= 413(29).  ANOVA (p<0.001) showed no difference between POW and CAD1 and significant differences from CAD2 at 50%VTR and 75%VTR.   

Conclusions: Tested in tension, at 25%VTR all veneering methods had similar high strength values. At 50%VTR the two low veneer strength methods dropped by half, at 75%VTR the two low strength methods dropped by 75%. The high strength veneer method CAD2 maintained a high biaxial strength at all 3 VTR and at 75%VTR showed a significantly higher overall strength about 4x CAD1 and 4x POW. The lower strength veneer layer strength controls the overall strength of the layered zirconia structure. It appears the veneer-zirconia bond strength also makes a significant contribution. These results will be compared to composite beam theory.

Study partially sponsored by Ivoclar Vivadent. 

This abstract is based on research that was funded entirely or partially by an outside source: Partially funded by Ivoclar Vivadent

Keywords: CAD/CAM, Ceramics, Prosthodontics, Stress and Technology
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