Lifetime-limiting Strength Degradation from Contact Fatigue in Dental Ceramics

Abstract

The hypothesis under examination in this paper is that the lifetimes of dental restorations are limited by the accumulation of contact damage during oral function; and, moreover, that strengths of dental ceramics are significantly lower after multi-cycle loading than after single-cycle loading. Accordingly, indentation damage and associated strength degradation from multi-cycle contacts with spherical indenters in water are evaluated in four dental ceramics: "aesthetic" ceramics-porcelain and micaceous glass-ceramic (MGC), and "structural" ceramics-glass-infiltrated alumina and yttria-stabilized tetragonal zirconia polycrystal (Y-TZP). At large numbers of contact cycles, all materials show an abrupt transition in damage mode, consisting of strongly enhanced damage inside the contact area and attendant initiation of radial cracks outside. This transition in damage mode is not observed in comparative static loading tests, attesting to a strong mechanical component in the fatigue mechanism. Radial cracks, once formed, lead to rapid degradation in strength properties, signaling the end of the useful lifetime of the material. Strength degradation from multi-cycle contacts is examined in the test materials, after indentation at loads from 200 to 3000 N up to 10(6) cycles. Degradation occurs in the porcelain and MGC after approximately 10(4) cycles at loads as low as 200 N; comparable degradation in the alumina and Y-TZP requires loads higher than 500 N, well above the clinically significant range.

Analysis of subcritical crack growth in dental ceramics using fracture mechanics and fractography

“…SCG of various dental ceramics has been investigated using cyclic, static, and dynamic loading methods [7,[19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Analyzing the SCG for both veneer and core components of the same all-ceramic system would enable lifetime prediction using finite element models.…”

Fracture Strength of Minimally Prepared Resin Bonded CEREC Inlays

“…30 In terms of in vivo loading, the masticatory cycle consists of a combination of vertical and lateral forces, subjecting the restoration to a variety of off-axis loading forces. 31 However, it was the intention of the current study to give an indication as to whether or not the proposed minimal design would provide inlays with a similar structural integrity to traditionally prepared CEREC inlays.…”

Material degradation due to moisture and temperature. Part 1: mathematical model, analysis, and analytical solutions

“…In general, the degradation mechanisms can be divided into four categories: mechanical processes, chemical reactions, biological degradation [Gu et al, 1998], and radiation [Kaplan, 1989]. For mechanical processes, the performance of materials can be affected adversely by fatigue [Jung et al, 2000], pressure loading [Rajagopal et al, 2007], and swelling of solid mixtures [Buonsanti et al, 2011]. Examples of chemical degradation include humid and alkaline effects [Björk et al, 2003], exposure to chlorides and carbon-dioxide [Glasser et al, 2008], and calcium leaching [Gawin et al, 2009].…”