RESUMO
OBJECTIVES: Although ultra-short pulsed laser (USPL) microstructuring has previously improved zirconia bond-strength, it is yet unclear how different laser-machined surface microstructures and patterns may influence the material's mechanical properties. Therefore, the aim of this study was to assess the flexural strength of zirconia after different USPL settings creating three different geometrical patterns with structures in micrometer scale. METHODS: One hundred sixty zirconia bars (3Y-TZP, 21 × 4 × 2.1 mm) were prepared and randomly divided into five groups (n = 32): no surface treatment (negative control-NC); sandblasting with Al2O3 (SB); and three laser groups irradiated with USPL (Nd:YVO4/1064 nm/2-34 J/cm2/12 ps): crossed-lines (LC), random-hatching (LR), and parallel-waves (LW). Bars were subjected to a four-point flexural test (1 mm/min) and crystal phase content changes were identified by X-ray diffraction. Surface roughness and topography were analyzed through 3D-laser-profilometry and SEM. Data were analyzed with parametric tests for roughness and Weibull for flexural strength (α = 5%). RESULTS: LR (Mean[95%CI]: 852.0 MPa, [809.2-894.7]) was the only group that did not show a significantly different flexural strength than NC (819.8 MPa, [796.6-842.9]), (p > 0.05). All laser groups exhibited higher Weibull moduli than NC and SB, indicating higher reliability and homogeneity of the strength data. An increase of monoclinic phase peak was only observed for SB. CONCLUSION: In conclusion, USPL created predictable, homogeneous, highly reproducible, and accurate surface microstructures on zirconia ceramic. The laser-settings of random-hatching (12 ps pulses) increased 3Y-TZP average surface roughness similarly to SB, while not causing deleterious crystal phase transformation or loss of flexural strength of the material. Furthermore, it has increased the Weibull modulus and consequently material's reliability. CLINICAL SIGNIFICANCE: Picosecond laser microstructuring (LR conditions) of 3Y-TZP ceramic does not decrease its flexural strength, while increasing materials realiability and creating highly reproducible and accurate microstructures. These features may be of interest both for improving clinical survival of zirconia restorations as well as enhancing longevity of zirconia implants.
Assuntos
Resistência à Flexão , Ítrio , Cerâmica , Materiais Dentários , Lasers , Teste de Materiais , Reprodutibilidade dos Testes , Propriedades de Superfície , ZircônioRESUMO
The aim of this study was to systematically review the literature of in vitro studies comparing the mechanical properties of teeth restored after selective caries excavation (SCE) and complete caries excavation (CCE). The PubMed/MEDLINE and EMBASE electronic databases were searched systematically. In vitro studies investigating the mechanical properties of teeth restored after SCE, were independently checked by two authors. Inclusion criteria were: (1) performing SCE (2) mentioning the teeth were later restored, and (3) evaluating mechanical properties of the restored teeth. Meta-analysis was performed with and without discriminating between shallow and deep lesions. From 1,859 potentially eligible studies, 14 were selected for full text analysis and 5 were included in the meta- analysis. Fracture resistance was significantly lower after SCE than after CCE in overall analysis (SMD[95%CI]=-1.62[-3.04,-0.20]) and for deep lesion (SMD[95%CI]=-1.62[-2.62,-0.61]), whereas cuspal deflection at 200 and 400N was significantly higher after SCE than after CCE for discriminated and non- discriminated analyses. Furthermore, for shallow lesions the risk of catastrophic fracture was significantly lower after SCE than CCE (RR[95%CI]=0.58[0.43,0.78]). The included studies presented low and medium risk of bias. The mechanical behavior of restored teeth seems to be affected by the excavation strategy. Although there is a tendency for lower fracture resistance and higher cuspal deflection after SCE, there is a lower risk of catastrophic failure when compared to CCE. However, this conclusion is based on very few in vitro studies.
El objetivo de este estudio fue revisar sistemáticamente la literatura de estudios in vitro que comparan las propiedades mecánicas de los dientes restaurados después de la excavación selectiva de caries (ESC) y la excavación de caries completa (ECC). Se realizaron búsquedas sistemáticas en las bases de datos electrónicas PubMed / MEDLINE y EMBASE. Los estudios in vitro que investigan las propiedades mecánicas de los dientes restaurados después de la ESC fueron verificados de forma independiente por dos autores. Los criterios de inclusión fueron: (1) realizar ESC (2) mencionar que los dientes fueron posteriormente restaurados y (3) evaluar las propiedades mecánicas de los dientes restaurados. El metanálisis se realizó con y sin discriminación entre lesiones superficiales y profundas. De 1.859 estudios potencialmente elegibles, se seleccionaron 14 para el análisis de texto completo y 5 se incluyeron en el metanálisis. La resistencia a la fractura fue significativamente menor después de ESC que después de CCE en el análisis general (DME [IC del 95 %] = - 1,62 [-3,04, -0,20]) y para la lesión profunda (DME [IC del 95 %] = - 1,62 [-2,62, - 0,61]), mientras que la deflexión de las cúspides a 200 y 400 N fue significativamente mayor después de ESC que después de CCE para análisis discriminados y no discriminados. Además, para las lesiones superficiales, el riesgo de fractura catastrófica fue significativamente menor después de ESC que de CCE (RR [IC 95 %] = 0,58 [0,43,0,78]). Los estudios incluidos presentaron riesgo de sesgo bajo y medio. El comportamiento mecánico de los dientes restaurados parece verse afectado por la estrategia de excavación. Aunque existe una tendencia a una menor resistencia a la fractura y una mayor deflexión de la cúspide después de la ESC, existe un menor riesgo de falla catastrófica en comparación con la CCE. Sin embargo, esta conclusión se basa en muy pocos estudios in vitro.