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OBJECTIVE: This investigation evaluated the effect of two sintering modes of a translucent zirconia (Y-TZP) on its surface roughness, topography, phase-transformation (t â m), translucency and biaxial flexure fatigue strength. MATERIALS AND METHODS: To do so, 50 Y-TZP discs (Ø = 15 mm; thickness = 1.2 mm; IPS e.max ZirCAD LT) were prepared and divided into two groups: Standard mode (SM) and Fast mode (FM). Staircase fatigue testing was performed (piston-on-three balls set-up, ISO 6872:2015), as well as surface roughness, profilometry, scanning electron microscopy (SEM-FEG), energy dispersive X-ray spectroscopy (EDX), phase transformation (t â m) using X-ray diffraction analysis (XRD), translucency parameter analysis (TP and TP00 ) and fractography. RESULTS: The results showed no statistical significant differences for roughness parameters (p > 0.05, SM: Ra = 0.13 ± 0.02, Rz = 1.21 ± 0.26 and RSm = 24.91 ± 2.19; FM: Ra = 0.14 ± 0.03, Rz = 1.32 ± 0.25 and RSm = 24.68 ± 2.16) or flexural fatigue strength (SM: 512 (464-560) MPa; FM: 542 (472-611) MPa) between the groups. In addition, similarity in surface morphological features (SEM and profilometry), composition and phases (EDX and XRD) was observed between the firing protocols. Fractography showed that the failure origin occurred on the tensile side. Sintering mode did not affect the TP (F = 0.001, p = 0.97) and TP00 (F = 0.12, p = 0.72). CONCLUSIONS: Therefore, the fast-sintering mode is suggested as a viable alternative to the standard mode since it does not influence the evaluated surface morphology, microstructure, fatigue strength and translucency of a translucent monolithic zirconia. CLINICAL SIGNIFICANCE: The fast sintering mode is a viable alternative for zirconia without compromising its topography, microstructure, mechanical performance or translucency.
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Cerâmica , Ítrio , Ítrio/química , Cerâmica/química , Teste de Materiais , Propriedades de Superfície , Zircônio/química , Materiais Dentários/químicaRESUMO
BACKGROUND: Endocrown restorations as a conservative approach to restore endodontically treated teeth still need in vitro investigation under fatigue and made in different materials. This study evaluated the effect of restorative material and restoration thickness on the maximum fracture load of endocrowns subjected to cyclic loading. MATERIAL AND METHODS: Sixty (60) third molar teeth received an endocrown preparation with three different heights of remaining dental tissue (1.5, 3.0 or 4.5 mm). A leucite-based ceramic (LEU) and a lithium disilicate (LD) based ceramic were selected to manufacture the CAD/CAM endocrown restorations, totaling 6 groups (n=10). The specimens were subjected to fatigue loading (200N, 2 x 106 cycles, water) and then to the single load to failure test (1 mm/min crosshead speed). Data were analyzed by using two-way ANOVA and Tukey tests (p< 0.05). RESULTS: All endocrowns survived the fatigue test. The thickness did not influence the restoration's fracture load (p=0.548) instead the restorative material (p=0.003). LD showed higher mean values (1714.43 N)A than LEU (1313.47 N)B. CONCLUSIONS: Endocrowns manufactured with CAD/CAM lithium disilicate blocks showed superior fracture load than the leucite-based blocks after mechanical fatigue. Nevertheless, both materials presented acceptable survival and fracture load as long as the material's minimum thickness and the enamel adhesion are respected. Key words:Endocrown, CAD/CAM, Endodontically treated teeth, Failure load, Minimal intervention dentistry.
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OBJECTIVE: Using Fourier transform infrared analysis (FTIR) in vitro, the effects of varying radiant exposure (RE) values generated by second and third generation LED LCUs on the degree of conversion (DC) and maximum rate of polymerization (Rpmax) of an experimental Lucirin TPO-based RC were evaluated. MATERIAL AND METHODS: 1 mm or 2 mm thick silicon molds were positioned on a horizontal attenuated total reflectance (ATR) unit attached to an infrared spectroscope. The RC was inserted into the molds and exposed to varying REs (18, 36 and 56 J/cm2) using second (Radii Plus, SDI) and third generation LED LCUs (Bluephase G2/Ivoclar Vivadent) or a quartz tungsten based LCU (Optilux 501/SDS Kerr). FTIR spectra (n=7) were recorded for 10 min (1 spectrum/s, 16 scans/spectrum, resolution 4 cm-1) immediately after their application to the ATR. The DC was calculated using standard techniques for observing changes in aliphatic to aromatic peak ratios both prior to, and 10 min after curing, as well as during each 1 second interval. DC and Rpmax data were analyzed using 3-way ANOVA and Tukey's post-hoc test (p=0.05). RESULTS: No significant difference in DC or Rpmax was observed between the 1 mm or 2 mm thick specimens when RE values were delivered by Optilux 501 or when the 1 mm thick composites were exposed to light emitted by Bluephase G2, which in turn promoted a lower DC when 18 J/cm2 (13 s) were delivered to the 2 mm thick specimens. Radii Plus promoted DC and Rpmax values close to zero under most conditions, while the delivery of 56 J/cm2 (40 s) resulted in low DC values. CONCLUSIONS: The third generation LCU provided an optimal polymerization of Lucirin TPO-based RC under most tested conditions, whereas the second generation LED-curing unit was useless regardless of the RE.
Assuntos
Resinas Compostas/efeitos da radiação , Lâmpadas de Polimerização Dentária , Cura Luminosa de Adesivos Dentários/métodos , Fosfinas/efeitos da radiação , Análise de Variância , Teste de Materiais , Transição de Fase , Fotoiniciadores Dentários/química , Polimerização/efeitos da radiação , Doses de Radiação , Valores de Referência , Reprodutibilidade dos Testes , Espectroscopia de Infravermelho com Transformada de Fourier , Fatores de TempoRESUMO
Abstract Alternative photoinitiators with different absorption wavelengths have been used in resin composites (RCs), so it is crucial to evaluate the effectiveness of light-curing units (LCUs) on these products. Objective Using Fourier transform infrared analysis (FTIR) in vitro, the effects of varying radiant exposure (RE) values generated by second and third generation LED LCUs on the degree of conversion (DC) and maximum rate of polymerization (Rpmax) of an experimental Lucirin TPO-based RC were evaluated. Material and Methods 1 mm or 2 mm thick silicon molds were positioned on a horizontal attenuated total reflectance (ATR) unit attached to an infrared spectroscope. The RC was inserted into the molds and exposed to varying REs (18, 36 and 56 J/cm2) using second (Radii Plus, SDI) and third generation LED LCUs (Bluephase G2/Ivoclar Vivadent) or a quartz tungsten based LCU (Optilux 501/SDS Kerr). FTIR spectra (n=7) were recorded for 10 min (1 spectrum/s, 16 scans/spectrum, resolution 4 cm-1) immediately after their application to the ATR. The DC was calculated using standard techniques for observing changes in aliphatic to aromatic peak ratios both prior to, and 10 min after curing, as well as during each 1 second interval. DC and Rpmax data were analyzed using 3-way ANOVA and Tukey’s post-hoc test (p=0.05). Results No significant difference in DC or Rpmax was observed between the 1 mm or 2 mm thick specimens when RE values were delivered by Optilux 501 or when the 1 mm thick composites were exposed to light emitted by Bluephase G2, which in turn promoted a lower DC when 18 J/cm2 (13 s) were delivered to the 2 mm thick specimens. Radii Plus promoted DC and Rpmax values close to zero under most conditions, while the delivery of 56 J/cm2 (40 s) resulted in low DC values. Conclusions The third generation LCU provided an optimal polymerization of Lucirin TPO-based RC under most tested conditions, whereas the second generation LED-curing unit was useless regardless of the RE.