title: Low-temperature degradation of Y-TZP ceramics: A systematic review and meta-analysis.
abstract: The aim of this study was to systematically review the literature to assess if low-temperature degradation (LTD) simulation in autoclave promotes deleterious impact on the mechanical properties and superficial characteristics of Y-TZP ceramics compared to the non-aged protocol. The MEDLINE via PubMed electronic database was searched with included peer-reviewed publications in English language and with no publication year limit. From 413 potentially eligible studies, 49 were selected for full-text analysis, 19 were included in the systematic review with 12 considered in the meta-analysis. Two reviewers independently selected the studies, extracted the data, and assessed the risk of bias. Statistical analysis was performed using RevMan 5.1, with random effects model, at a significance level of p<0.05. Descriptive analysis of monoclinic phase content data showed that aging in autoclave promotes an increase in m-phase content (ranging from 0% up to 13.4% before and 2.13% up to 81.4% after aging) with intensity associated to the material susceptibility and to the aging parameters (time, pressure and temperature). Risk of bias analysis showed that only 1 study presented high risk, while the majority showed medium risk. Five meta-analyzes (factor: aging×control) were performed considering global and subgroups analyzes (pressure, time, temperature and m-phase % content) for flexural strength data. In the global analysis a significant difference (p<0.05) was observed between conditions, favoring non-aging group. Subgroup analysis revealed statistical difference (p<0.05) favoring non-aging, for aging time >20h. However, for shorter aging times (≤20h), there was no difference between groups. Pressure subgroup analysis presented a statistical difference (p<0.05) only when a pressure ≥2bar was employed, favoring non-aging group. Temperature subgroup analysis showed a statistical difference (p<0.05) only when temperature=134°C was used, favoring the non-aging group. M-phase % content analysis presented statistical difference (p<0.05) when more than 50% of m-phase content was observed, favoring non-aging group. High heterogeneity was found in some comparisons. Aging in autoclave promoted low-temperature degradation, impacting deleteriously on mechanical properties of Y-TZP ceramics. However, the effect of LTD depends on some methodological parameters indicating that aging time higher than 20h; pressure ≥2bar and temperature of 134°C are ideal parameters to promote LTD effects, and that those effect are only observed when more than 50% m-phase content is observed.
authors.affiliation: Dental Science Graduate Program, Federal University of Santa Maria, Santa Maria, Rio Grande do Sul, Brazil. Electronic address: gabrielkrpereira@hotmail.com.
authors.forename: G K R
authors.initials: GKR
authors.lastname: Pereira
authors.affiliation: Dental Science Graduate Program, Federal University of Santa Maria, Santa Maria, Rio Grande do Sul, Brazil. Electronic address: andressa.venturini@hotmail.com.
authors.forename: A B
authors.initials: AB
authors.lastname: Venturini
authors.affiliation: School of Dentistry, Federal University of Santa Maria, Santa Maria, Rio Grande do Sul, Brazil. Electronic address: taissilvestri@yahoo.com.
authors.forename: T
authors.initials: T
authors.lastname: Silvestri
authors.affiliation: School of Dentistry, Federal University of Santa Maria, Santa Maria, Rio Grande do Sul, Brazil. Electronic address: kiara_s_d@hotmail.com.
authors.forename: K S
authors.initials: KS
authors.lastname: Dapieve
authors.affiliation: Dental Science Graduate Program, Federal University of Santa Maria, Santa Maria, Rio Grande do Sul, Brazil. Electronic address: animontag@gmail.com.
authors.forename: A F
authors.initials: AF
authors.lastname: Montagner
authors.affiliation: Department of Restorative Dentistry, Federal University of Santa Maria, Santa Maria, Rio Grande do Sul, Brazil. Electronic address: fzovico@hotmail.com.
authors.forename: F Z M
authors.initials: FZM
authors.lastname: Soares
authors.affiliation: Department of Restorative Dentistry, Federal University of Santa Maria, Santa Maria, Rio Grande do Sul, Brazil. Electronic address: lfvalandro@gmail.com.
authors.forename: L F
authors.initials: LF
authors.lastname: Valandro
mesh_terms: D002516:Ceramics / Q000737:chemistry*; D055595:Mechanical Phenomena; D011312:Pressure; D013696:Temperature; D013997:Time Factors; D015019:Yttrium / Q000737:chemistry*; D015040:Zirconium / Q000737:chemistry*
chemical_list: C499362:yttria stabilized tetragonal zirconia; D015019:Yttrium; D015040:Zirconium
keywords: Aging in autoclave; Dental materials; Dental prosthesis; Hydrothermal degradation; Zirconium oxide partially stabilized by yttrium