# Preparation and Characterization of Hybrid Nanocomposites for Dental Applications
## 2 Materials and Methods
### Characterization Methods  
The dispersion of nanofillers and the nanofillers themselves were observed by scanning electron microscopy (SEM, Hitachi SU-70, Naka, Japan). The samples for SEM analysis were cryofractured in liquid nitrogen and subsequently coated (2-5 nm) in a vacuum with a thin silver film before the tests. FTIR spectrums were made (Thermo Nicolet 380 apparatus, Thermo Fisher Scientific, Waltham, MA, USA) in the range of wave numbers from 400 to 4000 cm\({}^{-1}\) using KBr pellet procedure. The thermo-oxidative stability of the nanofillers used in this study was evaluated by thermogravimetry (TGA 92-16.18 Setaram, Caluire, France) using the system measuring simultaneously TG-DSC. Measurements were carried out in an oxidizing atmosphere (i.e., dry, synthetic air (N\({}_{2}\):O\({}_{2}\) = 80:20 vol.%)). The study was conducted at a heating rate of 10 \({}^{\circ}\)C/min in the temperature range of 20-700 \({}^{\circ}\)C.  
The tensile properties of the prepared composites were measured according to ISO 527 using Autograph AG-X plus (Shimadzu, Kyoto, Japan) tensile testing machine (class 1.0 according to EN 10002-2, ISO 7500-1, BS 1610, ASTM E4, JIS B7721), equipped with a 1 kN Shimadzu load cell, an optical extensometer (class 0.5 according to ISO 9513), and the TRAPEZIUM X computer software (version 1.4.5, Shimadzu, Kyoto, Japan), operated at a constant crosshead speed of 1 mm/min. Measurements were performed at room temperature on the dumbbell samples with the grip distance of 30 mm. Seven measurements were conducted for each dumbbell-shaped sample (type A3), and the results were averaged to obtain a mean value. Results, taking into account standard uncertainty of measurement (according to Guide to the Expression of Uncertainty in Measurement, OSO, Switzerland 1995), for chosen qualities of researched materials are presented in Tables 1 and 2. The flexural properties were measured according to ISO 178 using Autograph AG-X plus (Shimadzu) testing machine (class 1.0 according to EN 10002-2, ISO 7500-1, BS 1610, ASTM E4, JIS B7721), equipped with a 1 kN Shimadzu load cell, operated at a constant crosshead speed of 1 mm/min. Measurements were performed on the samples with the dimensions of: l = 80 \(\pm\) 2 mm, b = 10 \(\pm\) 0.2 mm, h = 4 \(\pm\) 0.2 mm. The impact strength was determined by Charpy method according to the standard ISO 179-1/1 eV), type of the sample: 1 (l = 80 \(\pm\) 2 mm, b = 10 \(\pm\) 0.2 mm, h = 4 \(\pm\) 0.2 mm), edge impact (e), no notch (U). Hardness was determined by Shore method according to a standard EN ISO 868:2003 on a Zwick 3100 Shore D tester (Zwick GmbH, Ulm, Germany). Determination of abrasion resistance was carried out using a Schopper-Schlobach (VEB Thuringer Industriewerk, Thuringer, Germany) with a rotating drum in accordance with ISO 4649: 2002 (E). Test samples: cylinder with a diameter of 16 mm \(\pm\) 0.2 mm and a height of at least 6 mm. The method B was used, with the sample rotating, the pressing force to the barrel 10 N \(\pm\) 0.2 N. The density necessary to calculate the volume loss of mass was determined by the hydrostatic method (according to ISO 2781). Distilled water was used as an immersion liquid. The results are presented as the relative volume loss (\(\Delta V_{rel}\)) expressed in mm\({}^{3}\), calculated according to the formula:  
\[\Delta V_{rel}=\frac{\Delta m_{t}\times\Delta m_{const}}{\rho_{t}\times\Delta m _{r}} \tag{1}\]  
where:  
\(\Delta m_{t}\)**--mass loss of the tested rubber sample, in mg; \(\Delta m_{const}\)--determined value of mass loss of a rubber sample made of a reference composition, in mg; \(\rho_{t}\)--the density of the tested rubber, in mg/mm\({}^{2}\); \(\Delta m_{r}\)--mass loss of a rubber sample made of a reference composition, in mg (212 mg). The absorption testes were carried out in accordance with the standard ISO 62. Six materials were subjected to the study (4 samples each).