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1.
J Clin Exp Dent ; 11(11): e969-e977, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31700569

RESUMO

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.

2.
J Mech Behav Biomed Mater ; 91: 326-334, 2019 03.
Artigo em Inglês | MEDLINE | ID: mdl-30639981

RESUMO

The aim of this study was to evaluate the effect of sequential usage (milling order) of CAD/CAM diamond burs on the surface roughness, topography and fatigue performance of a lithium disilicate glass-ceramic. Seventy-two (72) ceramic discs (Ø= 13.5 mm; thickness= 1.2 mm; IPS e.max CAD) were milled using four pairs of burs and allocated into three groups (n = 24) according to the milling sequence: 1 through 6 (1-6), 7 through 12 (7-12), and 13 through 18 (13-18). The burs were evaluated under SEM at the different milling stages to depict any degradation generated by the milling sequence. Fatigue performance was assessed by a stepwise approach (initial strength of 20 MPa for 5000 cycles; incremental steps of 20 MPa for 20,000 cycles each until fracture; frequency of 20 Hz) using the ISO 6872:2015 recommendation for piston-on-three-balls biaxial flexure strength tests. Surface roughness, topography analysis and fractography of the failed discs were also performed. Survival analysis (Kaplan-Meier and Mantel-Cox post hoc test) showed that the milling sequence had no effect on the fatigue strength (190 - 201 MPa) or the number of cycles until fracture (174,958 - 180,087 cycles). Ceramic topography and roughness (Ra, Rz and RSm parameters) were similar among the groups, even though SEM analysis depicted CAD/CAM diamond burs degraded over time. Fractography evidenced all failures starting from surface defects introduced by milling at the samples' tensile side. The sequential usage of CAD/CAM diamond burs (milling order) does not affect the lithium disilicate surface roughness, topography or fatigue performance.


Assuntos
Cerâmica , Desenho Assistido por Computador , Porcelana Dentária , Diamante , Teste de Materiais , Desenho de Equipamento , Estresse Mecânico , Propriedades de Superfície
3.
Dent Mater ; 34(10): 1466-1473, 2018 10.
Artigo em Inglês | MEDLINE | ID: mdl-29935769

RESUMO

OBJECTIVE: The goal of this study was to evaluate the stress distribution in a tooth/restoration system according to the factors "amount of dental remnant" (3 levels) and "restorative material" (2 levels). METHODS: Three endodontically treated maxillary molars were modeled with CAD software for conducting non-linear finite element analysis (FEA), each with a determined amount of dental remnant of 1.5, 3, or 4.5mm. Models were duplicated, and half received restorations in lithium disilicate (IPS e.max CAD), while the other half received leucite ceramic restorations (IPS Empress CAD), both from Ivoclar Vivadent (Schaan, Liechtenstein). The solids were imported to analysis software (ANSYS 17.2, ANSYS Inc., Houston, TX, USA) in STEP format. All contacts involving the resin cement were considered no-separation, whereas between teeth and fixation cylinder, the contact was considered perfectly bonded. The mechanical properties of each structure were reported, and the materials were considered isotropic, linearly elastic, and homogeneous. An axial load (300N) was applied at the occlusal surface (triploidism area). Results were determined by colorimetric graphs of maximum principal stress (MPS) on tooth remnant, cement line, and restoration. RESULTS: MPS revealed that both factors influenced the stress distribution for all structures; the higher the material's elastic modulus, the higher the stress concentration on the restoration and the lower the stress concentration on the cement line. Moreover, the greater the dental crown remnant, the higher the stress concentration on the restoration. Thus, the remaining dental tissue should always be preserved. SIGNIFICANCE: In situations in which few dental remnants are available, the thicker the restoration, the higher the concentration of stresses in its structure, protecting the adhesive interface from potential adhesive failures. Results are more promising when the endocrown is fabricated with lithium disilicate ceramic.


Assuntos
Coroas , Porcelana Dentária/química , Restauração Dentária Permanente/métodos , Análise do Estresse Dentário , Silicatos de Alumínio/química , Desenho Assistido por Computador , Falha de Restauração Dentária , Módulo de Elasticidade , Análise de Elementos Finitos , Humanos , Técnicas In Vitro , Teste de Materiais , Dente Molar , Dente não Vital
4.
J Appl Oral Sci ; 25(2): 140-146, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28403354

RESUMO

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 , Luzes de Cura 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 Tempo
5.
J. appl. oral sci ; 25(2): 140-146, Mar.-Apr. 2017. tab, graf
Artigo em Inglês | LILACS | ID: biblio-841182

RESUMO

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.


Assuntos
Fosfinas/efeitos da radiação , Resinas Compostas/efeitos da radiação , Cura Luminosa de Adesivos Dentários/métodos , Luzes de Cura Dentária , Doses de Radiação , Valores de Referência , Fatores de Tempo , Teste de Materiais , Reprodutibilidade dos Testes , Análise de Variância , Espectroscopia de Infravermelho com Transformada de Fourier , Transição de Fase , Fotoiniciadores Dentários/química , Polimerização/efeitos da radiação
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