Misinterpretation of ISO 4049 standard recommendations: Impact on Young's modulus and conversion degree of dental composites.

Objectives: The purpose of this study was to study the effects on Young's modulus and conversion degree of variations in polymerization conditions during the 3-point bending test of composite samples in accordance with the ISO 4049 standard.

Methods: Three nanocomposites were used in the 3-point bending test based on the conditions described in the ISO 4049 standard. Samples of 2 mm × 2 mm x 25 mm were fabricated and tested with a different number of irradiation points and irradiation time. Conversion degree of the samples were also measured by micro-Raman spectroscopy and correlated with the Young's modulus values obtained for each one.

Results: The variations in curing protocol during specimen's realization influenced the Young's modulus and degree of conversion of all composites. These two properties correlated well. The ISO 4049 standard defines the conditions for performing the properties tests of composites to allow reproducibility and comparison of different studies. Concerning the 3-point bending test, even a minimal change in the state causes differences in the results obtained. The standard should thus clarify the tools that can be used when producing samples in order to minimize discrepancies.

Significance: The influence of the parameters surrounding the design of the samples should be controlled and defined so as not to include bias in the studies carried out. This will allow literature studies to be compared with more accuracy.