Nicoleta Ilie1. 1. Department of Conservative Dentistry and Periodontology, University Hospital, LMU Munich, Goethestr. 70, D-80336, Munich, Germany. Electronic address: nilie@dent.med.uni-muenchen.de.
Abstract
OBJECTIVES: The study aimed to find a relationship between the most common standards used in testing resin-based materials (RBC) in a three-point bend test - ISO 4049 and NIST 4877 - using a size-strength relationship defined by the Weibull model. The direct comparison of calculated and measured data is used for validation. METHODS: 280 (n = 20) specimens were prepared from seven different light-cured RBCs. The flexural strength, FS, and modulus, E, were measured with a span of 12 mm (NIST) or 20 mm (ISO). A fractographic analysis determined the origin of fracture. One and multiple-way analysis of variance (ANOVA), the Tukey honestly significant difference (HSD) post-hoc tests (α = 0.05), Weibull statistics and Pearson correlation analysis were used for data analysis. RESULTS: Calculated data approximate the measured data very well. FS measured according to ISO is 11 % lower and E is 17 % higher than the NIST data. The test method influenced the properties measured, but not the material ranking or the fracture mode. Fractures originated from volume defects (sub-surface) were the most common type of fracture. CONCLUSIONS: Weibull analysis is successful to predict the scaling of strengths to other configurations in RBCs. CLINICAL SIGNIFICANCE: The need to limit the sample size of RBCs up to the dimensions of their clinical use can benefit from the use of Weibull statistics. Weibull size-strength relationship and fractographic analysis can help to better assess the clinical behaviour of the RBCs, calculate the reliability of a restoration, and assess the nature of the flaws in the material.
OBJECTIVES: The study aimed to find a relationship between the most common standards used in testing resin-based materials (RBC) in a three-point bend test - ISO 4049 and NIST 4877 - using a size-strength relationship defined by the Weibull model. The direct comparison of calculated and measured data is used for validation. METHODS: 280 (n = 20) specimens were prepared from seven different light-cured RBCs. The flexural strength, FS, and modulus, E, were measured with a span of 12 mm (NIST) or 20 mm (ISO). A fractographic analysis determined the origin of fracture. One and multiple-way analysis of variance (ANOVA), the Tukey honestly significant difference (HSD) post-hoc tests (α = 0.05), Weibull statistics and Pearson correlation analysis were used for data analysis. RESULTS: Calculated data approximate the measured data very well. FS measured according to ISO is 11 % lower and E is 17 % higher than the NIST data. The test method influenced the properties measured, but not the material ranking or the fracture mode. Fractures originated from volume defects (sub-surface) were the most common type of fracture. CONCLUSIONS: Weibull analysis is successful to predict the scaling of strengths to other configurations in RBCs. CLINICAL SIGNIFICANCE: The need to limit the sample size of RBCs up to the dimensions of their clinical use can benefit from the use of Weibull statistics. Weibull size-strength relationship and fractographic analysis can help to better assess the clinical behaviour of the RBCs, calculate the reliability of a restoration, and assess the nature of the flaws in the material.