Delayed crack development in porcelain due to incompatibility stress

Area of Science:

• Materials Science
• Biomaterials Engineering
• Dental Materials Science

Background:

• Delayed failure in metal-ceramic restorations can occur due to static fatigue, even without intra-oral forces.
• Residual tensile stress in porcelain is a key factor in this delayed failure mechanism.

Purpose of the Study:

• To characterize the potential of incompatible metal-ceramic systems for delayed crack development.
• To compare the sensitivity of fixed-partial-denture (FPD) and semicircular arch specimens in monitoring incompatibility stresses.

Main Methods:

• Utilized two incompatible metal-ceramic systems with varying thermal contraction coefficients (nickel-chromium alloy and three experimental porcelains).
• Employed fixed-partial-denture (FPD) specimens and semicircular arch specimens with gapped cross-arch segments.
• Analyzed residual stresses by measuring gap changes and comparing experimental data with composite strip equations.

Main Results:

• Semicircular arch specimens were more suitable for residual stress analysis due to larger gap changes.
• FPD specimens showed earlier evidence of delayed crack growth when metal's thermal contraction exceeded porcelain's by 1.7 x 10^-6/°C or 2.2 x 10^-6/°C.
• Excellent agreement was found between experimental and predicted gap values for arch specimens under these incompatibility conditions.

Conclusions:

• Thermal contraction mismatch between metal alloys and porcelains is critical for metal-ceramic restoration longevity.
• FPD specimens can provide early detection of crack initiation related to material incompatibility.
• Composite strip equations accurately predict stresses in arch specimens, validating their use in material characterization.