U istraživanju su korišteni uzorci (N = 22) dimenzija 11 mm x 11 mm x 1.5 mm (± 5 %) monolitne translucentne cirkonij-oksidne keramike KATANA Zirconia (Super Translucent Multi Layered). Uzorci su, ovisno o načinu završne obrade površine, podijeljeni u dvije skupine: polirani (N = 10), glazirani (N = 10) te kontrolni (N = 2) bez završne obrade površine. Sva mjerenja provedena su u dvije faze: prije i poslije eksperimentalnih protokola starenja. Analizirani su kemijski sastav uzoraka EDXRF-analizom, fazni sastav uzoraka XRD-analizom, optička svojstva izražena kolorimetrijskim parametrima CIE LAB te translucencija, stanje površine izraženo sjajem i hrapavošću (profilometrija) i mehanička svojstva uzoraka (tvrdoća po Vickersu, savojna čvrstoća). Eksperimentalni protokoli starenja predstavljaju način ispitivanja svojstava materijala simulacijom uvjeta koji vladaju u usnoj
šupljini čime se može predvidjeti funkcijska trajnost nadomjeska. Provedeni su hidrotermalna degradacija u autoklavu: 134 °C, dva bara, 3 h te kemijska degradacija: 4 %-tna octena kiselina pH-vrijednosti 2.49, 80 °C, 16 h (ISO 6872). Nakon statističke obrade podataka (ANOVA, Bonferroni, HSD-test i LSD-test) rezultati su pokazali stabilnost kemijskoga sastava uz odsustvo tetragonsko-monoklinske transformacije. Kolorimetrijski parametri CIE ∆E, CIE ∆L i CIE ∆C pokazali su određeni stupanj promjene dok se translucencija uzoraka nije značajno promijenila. Sjaj uzoraka je značajno smanjen kod svih uzoraka. Hrapavost površine je povećana kod uzoraka svih podskupina, osim glaziranih starenih u autoklavu kod kojih je nastupilo smanjenje hrapavosti. Mehanička svojstva uzoraka nisu značajno promijenjena. Dobiveni rezultati ukazuju na postojanost materijala u agresivnome mediju. Materijal je prikladan za izradu pojedinačnih krunica i mostova kraćih raspona u frontalnoj te
u lateralnoj regiji zubnoga niza kod pacijenata bez parafunkcija i s umjerenim žvačnim silama.
|Abstract (english)|| |
The aim of this study is to examine the effect of aging protocols on the structure, composition, properties and surface state of a new-generation monolithic translucent zirconium-oxide ceramic – KATANA Zirconia Super Translucent Multi Layered (STML) (Kuraray Noritake Dental Inc., Tokyo, Japan), shade A2 – using two different methods of final surface treatment: glazing and polishing. Experimental aging protocols are a mode of examining material properties by simulating conditions in the oral cavity; they also serve to predict the behaviour of materials over a specific period of clinical application. MATERIALS AND METHODS: The materials employed in this study were tile-shape specimens (N = 22) of monolithic translucent zirconium-oxide ceramic KATANA Zirconia STML, dimensions 11 mm x 11 mm x 1.5 mm (± 5 %). With respect to the mode of final surface treatment, the specimens were divided into two groups – polished specimens (N = 10)
and glazed specimens (N = 10); control specimens (N = 2) were not subjected to a final surface treatment protocol. The chemical composition of specimens was examined using the EDXRF technique, while the XRD technique was employed for the analysis of phase composition. Optical properties were conveyed as CIE LAB colorimetric parameters and analysed alongside translucency. Surface state was assessed according to gloss and roughness (profilometry), with the mechanical properties of specimens (Vickers hardness, flexural strength) also being included in the analysis. Initial flexural strength measurements were administered on two glazed and two polished specimens, while the remaining specimens underwent experimental aging protocols and were divided into four subgroups (G1 - G4, G5 - G8, P1 - P4, P5 - P8). Specimens G1 - G4 and P1 - P4 were subjected to hydrothermal degradation in an autoclave at 134 °C and 2 bar pressure over a three-hour period, while specimens G5 - G8 and P5 - P8 were chemically degraded trough exposure to a corrosive medium (four-percent acetic acid (pH 2.49) at 80 °C over a sixteen-hour period) (ISO 6872). After all the analyses had been conducted, the results were statistically processed. Quantitative data were outlined as ranges, arithmetic means and standard deviations, i.e. medians and interquartile ranges in cases of non-parametric distribution. Intergroup differences were analysed using the Analysis of Variance (ANOVA) and the Bonferroni correction. The differences in categorical variables among tested groups were examined withTukey’s (HSD) test and Fisher’s (LSD) test. Graph charts (Box and Whisker plots) were employed together with numerical (table) charts. All P values under 0.05 were deemed to be statistically significant. STATISTICA 12.0 and XLSTAT statistical software packages were utilized in the analysis. RESULTS: The results of this study point to a stability in chemical composition following aging protocols due to a high share of yttrium-oxide stabilizer (11 % - 12 %). The aging of materials, i.e. tetragonal-to-monoclinic phase transformation was not proven. Colorimetric parameters CIE ΔE, CIE ΔL and CIE ΔC displayed a certain degree of change, especially in polished specimens. Statistically, average colour change ΔE is significantly greater in polished specimens subjected to hydrothermal degradation in an autoclave (ΔEavg = 2.75), polished specimens subjected to chemical degradation in a corrosive medium (ΔEavg = 2.65) and glazed specimens subjected to chemical degradation in a corrosive medium (ΔEavg = 2.87) than in glazed specimens that underwent hydrothermal degradation in an autoclave (ΔEavg = 1.64). In comparison with other subgroups, polished specimens subjected to hydrothermal degradation in an autoclave displayed a statistically more significant decrease in lightness ΔL (ΔLavg = -1.16). Light yellowing was observed in specimens subjected to aging protocols; it
was not statistically significant in any specimens subgroup, although it was more pronounced in polished specimens than in glazed specimens (polished specimens in autoclave and corrosive medium: ΔC avg = 1.25 and 0.43, respectively; glazed specimens in autoclave and corrosive medium: ΔC avg = 0.28 and 0.73, respectively). In general, glaze on specimens
reduces the magnitude of colour changes ΔE, ΔL and ΔC, i.e. glazed specimens manifest a greater stability of colour parameters than polished specimens. No significant changes occurred in terms of specimen translucency, which can be explained by the presence of a cubic structure and the absence of a monoclinic phase. A greater reduction in translucency
(ΔTP), albeit statistically insignificant, occurred in polished specimens subjected to hydrothermal degradation in an autoclave (ΔTPavg = -0.93) and polished specimens subjected to chemical degradation in a corrosive medium (ΔTPavg = -0.5), when compared to glazed specimens after hydrothermal degradation in an autoclave (ΔTPavg = -0.07) and chemical
degradation in a corrosive medium (ΔTPavg = -0.42). Significant surface gloss reduction was observed across all specimens, with average gloss reduction being somewhat greater in polished specimens exposed to hydrothermal degradation in an autoclave (ΔGavg = -4.65 GU) and chemical degradation in a corrosive medium (ΔGavg = -4.97 GU) than in glazed specimens exposed to hydrothermal degradation in an autoclave (ΔGavg = -3.06 GU) and chemicaldegradation in a corrosive medium (ΔGavg = -4.38 GU). Gloss reduction in specimens, especially polished ones, points to possible repercussions on the aesthetic qualiy of restorations over a longer period of clinical application. An increase in surface roughness was recorded across all specimen subgroups, except in glazed specimens, the surface roughness of which was decreased by an aging protocol in an autoclave. The mechanical properties of specimens did not display significant changes; the values for Vickers hardness remained exceptionally high even after experimental aging protocols (≥1430 HV). The mean value for the flexural strength of glazed specimens at the beginning of the study was ~340 N/mm2. After the experimental aging protocols, there was a reduction in the mean values for the flexural strength of glazed specimens subjected to hydrothermal degradation in an autoclave (~290 N/mm2) and to chemical degradation in a corrosive medium (~287 N/mm2), but it was statistically insignificant. The mean value for the flexural strength of polished specimens was
~420 N/mm2 at the start of the research. Polished specimens subjected to hydrothermal degradation in an autoclave also evinced a reduction in the mean value of flexural strength (~366 N/mm2), just like polished specimens subjected to hemical degradation in a corrosive medium (~355 N/mm2), albeit without statistical significance. The measured values are similar to the values for the flexural strength of glass ceramics. CONCLUSION: Monolithic translucent zirconium-oxide ceramic is a material that will remain constant over a longer period of a restoration’s application in oral cavity. It is recommended to be used for single crowns and short-span fixed partial dentures (up to three crowns) in the anterior and posterior area of the dental arch for patients without parafunctions. Glaze on the surface of specimens facilitates better aesthetic, tribological and hygienic effects of material.