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

Abstract

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 10⁴, 10⁵, 5 × 10⁵ and 10⁶ 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.

Keywords: Ceramic; Failure; Fatigue; Multilayer structures; Structural reliability.