Monolithic zirconia crowns – wall thickness, surface treatment and load at fracture

Abstract

Purpose: The aim of this study was to evaluate the effect of wall thickness on load at fracture of monolithic zirconia dental crowns after aging. Materials and Methods: Seventy translucent monolithic zirconia crowns (DD Bio ZX 2 , Dental Direkt GmbH) were produced to fit a second upper premolar preparation with a circumferential shallow chamfer. Thirty crowns had a minimum wall thickness of 0.4 mm and 40 had 0.8 mm. TwentyAQ4 of the thick-walled crowns were glazed. The remaining crowns were polished. Ten crowns from each group functioned as controls, while the remaining were subjected to an aging procedure of alternation between dynamic loading and autoclaving. The surviving crowns were assessed for margin damages and surface wear before beeing subjected to quasi-static loading until fracture. All fractures were analyzed by fractographic methods. Results: There were statistically significant differences among the test groups concerning the effects of aging and surface wear. All thick-walled and eight of the thin-walled crowns survived the aging procedure. All fracture origins both from dynamic and quasi-static loading were located in the cervical margin with crack propagation corresponding to cervical hoop stress as observed in clinical failures. Conclusions: Thin-walled translucent monolithic zirconia crowns were more affected by the aging procedure than thick-walled crowns.

Effect of artificial aging on high translucent dental zirconia: simulation of early failure

“…However, 'aging' test periods should not be so long as to be clinically unrealistic, which may be the case with autoclave treatments with long durations (38). The reported early clinical failures of zirconia restorations most likely have explanations other than aging, such as poor damage tolerance, insufficient design parameters of the restoration or preparation, undesirable load distribution in the oral cavity, or existing flaws in the zirconia material (26,49).…”

“…All sixty crowns were subsequently subjected to axial loading until fracture (23,(26)(27)(28). The crowns were loaded centrally at the occlusal fossa with a horizontal cylindrical steel indenter (⌀ = 13 mm), cushioned with a 2 mm thick ethylene propylene diene rubber disc of hardness 90 Shore A (EPDM 90) to avoid contact damage.…”

Effect of Marginal Designs on Fracture Strength of High Translucency Monolithic Zirconia Crowns

“…This material demonstrates high strength levels, and it has been used increasingly in dental practices, especially for chair-side fabrications of zirconia restorations. However, it has been detected that the origin of failure for the zirconia crown fracture during clinical usage was reported to have been generated from the crown margin [ 13 ]. The margin is a crucial area of restoration that is closely adapted to the definite finishing area of the prepared abutment.…”

“…The source of the failure originating in the margin of the zirconia restoration may relate to the margin design, as well as the thickness of the margins. Several investigations have been carried out with regard to the effect of the margin design on the load-bearing capacity of zirconia restoration in relation to occlusal thickness and wall thickness [ 13 , 18 – 21 ]. Some investigations into the fracture resistance of all ceramic restorations were carried out by applying an occlusal load, either longitudinally or obliquely, on anatomical crowns until fracture, indicating that the fracture was possibly influenced by the design of the margin in the restoration [ 22 – 24 ].…”

Marginal fit of full contour monolithic zirconia in different thicknesses and layered zirconia crowns

“…It is particularly, helpful in confined interocclusal space, and in preparation on the root surface. [ 12 13 14 ] In addition, monolithic zirconia has better translucency in lower thicknesses and in proper case selection a better esthetic result can be achieved. [ 15 ]…”