Effect Of Low-temperature Degradation Research Articles

Effect of low-temperature degradation and sintering protocols on the color of monolithic zirconia crowns with different yttria contents.

This study investigated the effects of low-temperature degradation (LTD) on the L*, a*, and b* values of highly translucent zirconia crowns. Four types of zirconia disks with different yttria contents (IPS e.max ZirCAD LT, IPS e.max ZirCAD MT, IPS e.max ZirCAD MT Multi, IPS e.max ZirCAD Prime, Ivoclar) and two shades (A2 and BL) were used. A crown was manufactured using four types of zirconia and LTD treated. Color measurements were performed, and the color difference (ΔE00) before and after LTD was calculated. The microstructure was determined through X-ray fluorescence and X-ray diffractometry. Highly translucent zirconia crowns showed greater changes in the a* and b* values than in the L* value after LTD, regardless of the shade. The Multi2 crowns exhibited a discernible color change due to the LTD treatment. The X-ray fluorescence results did not reveal any apparent change in the microstructure between sintering programs for all zirconia specimens.

Effect of low-temperature degradation on the fatigue performance of dental strength-gradient multilayered zirconia restorations

ObjectivesFatigue and low-temperature degradation (LTD) are the main factors contributing to zirconia restoration failure. This study evaluated the effect of LTD on the fatigue performance of the novel “strength & shade-gradient” multilayered zirconia restorations. MethodsDiscs (15 mm × 1.2 mm) of each yttria content layer from a newly developed strength-gradient multilayered zirconia were fabricated and under accelerated aging in an autoclave at 134℃ for 0 h, 32 h, and 64 h. Then, the phase transformation, microstructure, and mechanical properties after LTD were assessed. In addition, the crown samples, including the multi-Zir, 3Y-Zir, and 5Y-Zir were fabricated, and their monotonic and fatigue load before and after LTD, percentage of fatigue degradation (Sd) and the fracture morphology were investigated. Statistical analyses were performed using paired samples t-test (α′ = α/3 = 0.017), one-way ANOVA and Weibull analysis. ResultsAfter LTD, the phase transformation, surface roughness, depth of transformed zone, and residual stress were increased and inversely associated with the yttria content. The indentation elastic modulus and hardness after LTD decreased; however, there was no significant difference between the different yttria content layers. The monotonic and fatigue load of multi-Zir restorations decreased, but their Weibull modulus increased, and Sd decreased, similar to 3Y-Zir. The crack origin was associated with the cervical region. ConclusionThese results show that although LTD reduces the absolute fatigue strength of strength-gradient multilayered zirconia restorations, it also reduces the effect of cyclic fatigue itself on the strength of zirconia (relative to monotonic strength), which might be due to the increase of residual stress. Clinical significanceThe novel “strength & shade-gradient” multilayered zirconia restorations show a promising performance during in vitro LTD and fatigue test and their reliability to some extent is comparable to 3Y-Zir. Yet, further in vivo longitudinal studies are warranted to confirm their precise performance.

Antibacterial and osteogenic activities of thiolated and aminated yttria-stabilized tetragonal zirconia polycrystal with tolerance to low temperature degradation

The chemical immobilization of silane on yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) surface is promising in improving both osseointegration and antibacterial activity, however, the effect of low temperature degradation (LTD)-induced the tetragonal (t) to monoclinic (m) phase transformation on the chemical bonding and continuous bioactivity remains unclear. In this study, 3-aminopropyltriethoxysilane (APTES) and 3-mercaptopropyltrimethoxysilane (MPTS) were grafted on the Y-TZP surface. Quantum chemistry revealed that Zr–O–Si bonds formed by t/m-ZrO2 both had a strong tendency to undergo hydrolysis in acidic or neutral environments, but were stable in alkaline environments. Inductively coupled plasma mass spectrometry showed that the release of Si increased during weeks 1–3 on both APTES- and MPTS-grafted surfaces, then decreased rapidly on MPTS-grafted surface while maintained a sustain release on APTES-grafted surface until week 4; in particular, the hydrolysis of Zr–O–Si bonds did not accelerated by LTD. X-ray photoelectron spectroscopy showed that LTD-induced reductions in Zr–O–Si bond contents on APTES- and MPTS-grafted surfaces were 0.63% and 1.79%, respectively. In vitro MC3T3-E1 cell experiments confirmed that APTES- and MPTS-grafted Y-TZP surfaces maintained similar adhesion and proliferation before and after LTD. Scanning electron microscopy, laser confocal scanning microscopy, and spread plate assay findings showed favorable anti-Porphyromonas gingivalis (P. gingivalis) effects induced by APTES- and MPTS-grafted t/m-ZrO2 surfaces. Thus, APTES and MPTS both provide LTD-stable and hydrolysis-stable chemical bonding for Y-TZP implants, and t-m phase transformation does not cause detectable effects on Y-TZP bioactivity.

Effect of Low-Temperature Degradation, Ph-Cycling and Simulated Tooth Brushing on Surface Roughness, Topography, and Polish Retention of Yttrium-Stabilized Tetragonal Zirconia.

Surface roughness of zirconia is an important parameter that determines the success of zirconia restorations. When zirconia surfaces are left rough, higher susceptibility to hydrothermal aging, plaque accumulation and color changes would occur. Therefore, polish retention of these restorations is considered as a challenge. The purpose of this in vitro study was to determine the effect of hydrothermal degradation, pH- cycling, and simulated tooth brushing on surface roughness, topography, and polish retention of an yttrium-stabilized monolithic zirconia. In this experimental study, 64 specimens of yttria-stabilized tetragonal zirconium oxide (20×4×2mm) were prepared (ZirKonzahn, Steger, Ahrntal). The specimens were wet- polished (standard polishing), and divided into 8 groups (n=8). Four control groups were assessed in non-aged condition while in 4 experimental groups the artificially ageing was done. Different finishing and polishing procedures were performed in 8 groups. The surface roughness values including mean surface roughness (Ra) and mean height of surface roughness (Rz) was measured by a profilometer. The results were analyzed using two-way ANOVA and Tukey's HSD test (α=0.05). One representative specimen of each group was inspected under a scanning electron microscope (SEM) for assessment of surface topography. The effects of surface treatments on Ra (p<.001) and Rz (p<.001) parameters were significant. Ageing had no significant effect on Ra (p=.086) and Rz (p=.067) values. Maximum Ra and Rz parameters were recorded following grinding (p<.001) and minimum values were recorded after glazing, which were significantly lower than the values in grinding group (p<.001). Polishing and glazing diminished the surface roughness (Ra) of ground zirconia similarly (p=.995). Aging had no significant effect on surface roughness of zirconia, irrespective of surface treatment type. Grinding yielded maximum surface roughness. Intra oral polishing yielded a surface roughness comparable to standard polishing and glazing.

Influence of low-temperature degradation on the wear characteristics of zirconia against polymer-infiltrated ceramic-network material

Statement of problemLow-temperature degradation may affect zirconia restorations during their clinical service. Concerns have been raised about the effect of low-temperature degradation on the wear behavior of zirconia. Moreover, the wear resistance of this novel polymer-infiltrated ceramic-network material needs to be better evaluated. PurposeThe purpose of this in vitro study was to investigate the influence of aging on the wear resistance of zirconia opposing polymer-infiltrated ceramic-network material. Material and methodsTwelve specimens for 2 newly developed polymer-based materials (a polymer-infiltrated ceramic-network material VITA ENAMIC and a resin nanocomposite material Lava Ultimate), 2 commonly used glass-ceramic materials (IPS e.max CAD and VITABLOCS Mark II), and 2 conventional composite resin materials (VITA CAD-Temp and PMMA Disk) were tested; human enamel was used as a control group. The wear simulator used was a ball-on-disk type with zirconia balls, with and without autoclaving (134°C, 200 kPa, 20 hours) as antagonists. The vertical loss and volume loss of specimens and the roughness average of zirconia antagonists were measured with a 3-dimensional optical profilometer. Vickers hardness values were determined using a micro-Vickers hardness tester. Data were statistically analyzed with a mixed-model ANOVA for wear loss (vertical loss [μm] and volume loss [mm3]) and roughness average (μm) of zirconia antagonists and with the Kruskal-Wallis test for Vickers hardness values (α=.05). The Spearman correlation coefficient was used to determine the relationship between wear loss and hardness. ResultsResults showed that specimens opposing the non-aged zirconia balls demonstrated significantly higher wear than those opposing the aged ones (P<.001). The polymer-infiltrated ceramic-network material VITA ENAMIC group (vertical loss=27.44-33.53 μm, volume loss=0.0198-0.315 mm3) and the resin nanocomposite material Lava Ultimate group (vertical loss=24.42-27.83 μm, volume loss=0.0159-0.0233 mm3) showed lower vertical loss and volume loss than the conventional composite resin groups (vertical loss=43.95-61.87 μm, volume loss=0.0395-0.0593 mm3) but higher wear than the glass-ceramic groups (IPS e.max CAD and VITABLOCS Mark II; vertical loss=8.95-11.47 μm, volume loss=0.0072-0.0094 mm3) and human enamel (vertical loss=9.95-12.32 μm; volume loss=0.0089-0.0103 mm3). The aged zirconia antagonists indicated greater roughness average values than the aged zirconia balls after the wear test (P<.001). Distinct abrasion-induced tracks were observed on the contact surfaces of the aged zirconia antagonists. ConclusionsEven though zirconia ceramic subjected to low-temperature degradation exhibited increased roughness after the wear test, it was still nonabrasive toward opposing materials. The polymer-infiltrated ceramic-network material showed intermediate wear resistance compared with glass-ceramic and conventional composite resin.

The effect of low temperature degradation on color stability of two types of monolithic translucent zirconia crowns

Objective: To investigate the effect of artificial aging on the shade of two types of monolithic translucent zirconia crowns, manufactured using two different CAD/CAM systems.Materials and methods: A sound human maxillary first premolar was selected to receive all ceramic crown preparation. The prepared premolar was then duplicated to produce twenty epoxy dies divided into two groups (n=10) according to the constructed crowns.. Twenty Standardized monolithic translucent zirconia (10 Prettau, & 10 Incoris TZI crowns) were CAD/CAM fabricated onto the epoxy dies and cemented using Panavia F 2.0. Vita Easy-Shade digital spectrophotometer was used to measure the color shade differences (ΔE) value between the selected color shade (A3 classical shade) and the color shade of the cemented CAD/CAM crowns before and after aging. The samples were aged under standard autoclave conditions for ten hours. XRD analysis was used to analyze the microstructure of both ZrO2 types before and after accerlated aging. SEM was done to examine the surface changes before and after aging. Results were tabulated and statistically analyzed using Kruskal-Wallis test and post hoc analysis .Results: The results showed that the Prettau crowns had higher ΔE (4.26 ± 0.51) values than that of Incoris TZI crowns before (3.56 ± 0.28) aging. Also after aging Prettau showed higher ΔE (5.6 ± 0.47) than that of Incoris TZI (4.36 ± 0.34). Statistical analysis showed statistical significant difference between the groups.Conclusions: This study concluded that Incoris TZI crowns better color shade results than Prettau crowns before and after aging.

Effect of Low Temperature Degradation on Scratch Behaviour of 3Y-TZP

Effect of low-temperature degradation of 3Y-TZP ceramics (polycrystalline zirconia stabilized by 3mol% of yttria) on contact damage resistance has been studied applying scratch testing technique. Friction properties and damage mechanisms have been investigated for various degrees of hydrothermal ageing, i.e. for different grain sizes and crystallography, and for different thickness of the degraded surface layer. The onset of plastic damage, catastrophically cracking, grain pull-out, spalling and chipping due to top layer debonding have been identified. The contact damage micromechanisms corresponding to various degrees of degradation have been studied in detail by interferometry and microscopy.