Cyclic contact fatigue resistance of ceramics for monolithic and multilayer dental restorations.

OBJECTIVE

To evaluate the cyclic contact fatigue resistance and failure mode of ceramics for monolithic and multilayer restorations.

METHODS

Ceramic structures (10 mm × 1.8 mm) were fabricated as follows (n = 28): (1) CAD-on- trilayer structure composed of Y-TZP (yttria stabilized tetragonal zirconia polycrystal- IPS e.max ZirCAD) infrastructure, fusion glass-ceramic (IPS e.max CAD Crystall/Connect) and lithium disilicate-based glass-ceramic (IPS e.max CAD); (2) ZFC- bilayer structure composed of Y-TZP infrastructure veneered by a fluorapatite glass-ceramic (IPS e.max Ceram); (3) LDC- monolithic lithium-disilicate glass-ceramic (IPS e.max CAD); and (4) YZW- monolithic Y-TZP (Zenostar Zr Translucent). All ceramics structures were bonded to a dentin analog substrate (G10). Specimens were submitted to cyclic contact fatigue test in a pneumatic cycling machine with 80 N load and 2 Hz frequency in distilled water at 37 °C. Test was interrupted after 10, 10, 5 × 10 and 10 cycles and the presence or absence of failure was recorded. Fatigue data were analyzed using Kaplan-Meier (log rank) and Holm-Sidak tests (α = 0.05). The relationship between the type of crack leading to failure and the experimental group was analyzed using chi-square test (α = 0.05).

RESULTS

There was no statistical difference between CAD-on and YZW groups (p = 0.516), which presented the highest survival rates after cyclic loading, followed by ZFC and LDC groups (p < 0.01). There was a significant relationship between type of crack and experimental group (p < 0.001). LDC specimens showed the greatest frequency of radial cracks, while cone cracks were more prevalent for ZFC and CAD-on specimens.

SIGNIFICANCE

Monolithic Y-TZP (YZW) showed similar fatigue resistance to CAD-on multilayer specimens, but different failure mode. Monolithic lithium disilicate glass-ceramic (LDC) and Y-TZP conventionally veneered by glass-ceramic (ZFC) showed lower survival time under fatigue.