IADR Abstract Archives
Comparison of in-vitro testing modalities to predict reliability and identify failure modes in porcelain veneered Y-TZP copings
Objectives: To determine types of failure modes of Y-TZP copings subjected to two fatigue protocols.
Methods: Copings machined from fully sintered blocks (hard state machined n=21) and from partially sintered Y-TZP blocks and later sintered (soft state machined n=21) (Renishaw plc, UK) were veneered with dental porcelain (VM9, Vitadent, US), by a single trained dental technician. Samples from both subgroups (n=12 each) were subjected to a uniaxial fatigue test protocol (3 step stress profiles in a ratio of 3:2:1) (Bose Enduratec elf 3300, Bose, USA), and (n=9 each) tested in bi-axial test or chewing protocol, using the bi-axial controllers on the fatigue tester. Each sample was visually examined (Meiji EMZ-TR stereo microscope, Meijo Techno Co. Ltd, Japan) and photographed at the end of predetermined time point.Testing was terminated for a sample when any crack opening was detected before the final end point. Failed sample surfaces and sections were later examined using a scanning electron microscope (Hitachi High-Technologies Europe GmbH, UK).
Results: For both protocols, master weibull curves and reliability for completion of 1,00,000 and 250,000 cycles (2 and 5 year clinical service) at 100N load (95% reliability) were calculated using a reliability software package (ALTA 7 PRO, Reliasoft, US). The results showed weibull modulus β of 1.7 (soft state machined) and 1.6 (hard state machined), for uniaxial test protocol; 4.49 (soft state machined) and 2.34 (hard state machined), for biaxial test protocol. All failures were within the porcelain itself, supported by previous work (Santana et al., 2009; Coelho et al., 2009). For uniaxial loading, failures were Hertzian contact failures and in bi-axial or mouth motion simulation these involved porcelain chipping.
Conclusions: β modulus values for uniaxial fatigue testing indicated that failures were distributed over large number of load cycles and that fatigue was not a strong acceleration factor, whereas for mouth motion fatigue seems a significant acceleration factor for soft state, whilst not so for hard state samples. Damage modes in bi-axial protocol is closer to in-vivo conditions, compared to uniaxial fatigue testing. The failure modes seen were delamination for bi-axial or chewing simulation, and were more realistic and comparable to in-vivo failure modes.
Methods: Copings machined from fully sintered blocks (hard state machined n=21) and from partially sintered Y-TZP blocks and later sintered (soft state machined n=21) (Renishaw plc, UK) were veneered with dental porcelain (VM9, Vitadent, US), by a single trained dental technician. Samples from both subgroups (n=12 each) were subjected to a uniaxial fatigue test protocol (3 step stress profiles in a ratio of 3:2:1) (Bose Enduratec elf 3300, Bose, USA), and (n=9 each) tested in bi-axial test or chewing protocol, using the bi-axial controllers on the fatigue tester. Each sample was visually examined (Meiji EMZ-TR stereo microscope, Meijo Techno Co. Ltd, Japan) and photographed at the end of predetermined time point.Testing was terminated for a sample when any crack opening was detected before the final end point. Failed sample surfaces and sections were later examined using a scanning electron microscope (Hitachi High-Technologies Europe GmbH, UK).
Results: For both protocols, master weibull curves and reliability for completion of 1,00,000 and 250,000 cycles (2 and 5 year clinical service) at 100N load (95% reliability) were calculated using a reliability software package (ALTA 7 PRO, Reliasoft, US). The results showed weibull modulus β of 1.7 (soft state machined) and 1.6 (hard state machined), for uniaxial test protocol; 4.49 (soft state machined) and 2.34 (hard state machined), for biaxial test protocol. All failures were within the porcelain itself, supported by previous work (Santana et al., 2009; Coelho et al., 2009). For uniaxial loading, failures were Hertzian contact failures and in bi-axial or mouth motion simulation these involved porcelain chipping.
Conclusions: β modulus values for uniaxial fatigue testing indicated that failures were distributed over large number of load cycles and that fatigue was not a strong acceleration factor, whereas for mouth motion fatigue seems a significant acceleration factor for soft state, whilst not so for hard state samples. Damage modes in bi-axial protocol is closer to in-vivo conditions, compared to uniaxial fatigue testing. The failure modes seen were delamination for bi-axial or chewing simulation, and were more realistic and comparable to in-vivo failure modes.