A thick frame decreases the fracture toughness of veneering ceramics used for zirconia-based all-ceramic restorations

Shinobu Yamauchi, Shoko Miura, Shin Kasahara, Jirun Sun, Hiroshi Egusa

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)

Abstract

Purpose: To investigate the influence of firing condition and thickness of a yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) frame on the fracture toughness of veneering ceramics. Methods: Layering and pressable ceramics without frames or on 0.8- and 1.2-mm-thick Y-TZP frames were fired with 5 schedules (normal and 4 customized conditions). The fracture toughness of the ceramics was measured at 0.5–2.5 mm from the frame by the indentation fracture method. Crystal structures at the measurement points were evaluated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results: Under customized firing conditions, the fracture toughness of the layering ceramic significantly decreased, particularly near the frame. Use of a 1.2-mm-thick frame significantly decreased the fracture toughness of both layering and pressable ceramics compared to ceramics without the frame. The decreased fracture toughness only occurred close (0.5 and 1.0 mm) to the frame. XRD analysis showed identical diffraction patterns between points near and far from the frame, suggesting that the decreased fracture toughness was not due to crystal defects or impurities. SEM revealed many microcracks and large crystals in layering ceramic near the 1.2-mm-thick frame, possibly resulting from the thermal properties of the zirconia frame, such as large heat capacity and low thermal conductivity. Conclusions: Modification of the firing conditions from the manufacturer's instructions and inclusion of a thick Y-TZP frame decreased the fracture toughness of veneering ceramics at the interface, suggesting that a thick frame would pose a potent fracture risk in veneering ceramics used for zirconia-based all-ceramic restorations.

Original languageEnglish
Pages (from-to)184-192
Number of pages9
JournalJournal of Prosthodontic Research
Volume63
Issue number2
DOIs
Publication statusPublished - 2019 Apr

Keywords

  • Firing schedule
  • Fracture toughness
  • Frame thickness
  • Veneering ceramic
  • Y-TZP

ASJC Scopus subject areas

  • Oral Surgery
  • Dentistry (miscellaneous)

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