# Martens Hardness of CAD/CAM Resin-Based Composites
## 2 Materials and Methods  
Eleven resin-based CAD/CAM materials (n = 6 per material) were investigated using instrumented indentation testing according to ISO 14577-1 [19]. Table 1 provides an overview over the tested materials, as well as some of their properties (modulus of elasticity E (GPa), filler content wt. (%), and fracture strength FS (MPa)) for the better interpretation of the results of this study. Rectangular specimens (10 \(\times\) 10 \(\times\) 2 mm) were produced in CAD/CAM dental milling machine (98 milling blank, Inlab MC X5, Dentsply Sirona, Germany) and polished (1000 grit sandpaper, Tegramin 25, Struers, Germany).  
The Martens hardness (HM) is the ratio of the maximum force to the associated contact area (N/mm\({}^{2}\)). Other material parameters, such as indentation modulus, indentation creep, and plastic and elastic work of deformation, can be characterized from a force-indentation depth curve. In this study, force, depth and time during the indentation of the diamond pyramid were continuously recorded. The contact area under load was calculated from the maximum indentation depth. The indentation depth was constantly monitored at a loading speed of 0.5 mm/min to a maximum force of F\({}_{\text{max}}\) = 10 N using a Vickers indenter and dwell-time of 10 s. Unloading was performed at 0.1 mm/min. The recorded force-indentation depth curves were used to calculate indentation depth (h\({}_{\text{r}}\)), Martens hardness (H\({}_{\text{M}}\)), indentation hardness (H\({}_{\text{IT}}\)), indentation modulus (E\({}_{\text{IT}}\)), the elastic part of indentation work (\(\eta_{\text{IT}}\)), and indentation creep (C\({}_{\text{IT}}\)) as defined in ISO 14577-1. The [PERSON]'s ratio of the diamond indenter was set to \(\
u_{\text{i}}\) = 0.07, and that of the resin-based composite materials was set to \(\
u_{\text{s}}\) = 0.3 [23]. The [PERSON]'s modulus of the indenter was E\({}_{\text{i}}\) = 1140 GPa.  
Calculations and statistical analyses were performed using SPSS 25.0 for Windows (IBM, Armonk, NY, USA). The normal distribution of data was controlled using the Shapiro-Wilk test. Means and standard deviations were calculated and analyzed using ANOVA  
\begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Material** & **Manufacturer** & **Abbr.** & **E [GPa]** & **wt. [\%] d** & **FS [MPa]** \\ \hline Cerasmart & GC Corp., Tokyo, JP & CS & 12.1 \({}^{\text{a}}\) & 66.9 & 231 \\ Brilliant Crios & Coltene Holding AG, Altsätten, CH & BC & 10.3 & 72.0 & 198 \\ Estelite & Tokuyama Dental, Chiyoda, JP & EL & 13.8 & 72.4 & 225 \\ Block HC & Shoft Dental GmbH, Ratingen, GER & BL & 9.5 \({}^{\text{b}}\) & 64.1 & 191 \\ Katana Avencia & Kuraray Nortiake, Tokyo, JP & KA & 12.4 & 58.6 & 190 \\ KZR CAD & Yamakin Co. Ltd., Kochi, JP & KC & 10.4 & 69.0 & 235 \\ \hline Experimental & & & & 20.0 & 78.3 & 200 \\ Lava Ultimate & 3M Deutsch GmbH, Neuss, GER & LU & 12.7 & 75.4 & 204 \({}^{\text{c}}\) \\ Grandio bloc & VOCO GmbH, Cuxhaven, GER & GB & 18.0 & 84.5 & 330 \\ VOCO Experimental & VOCO GmbH, Cuxhaven, GER & VO & n/a & 79.7 & n/a \\ \hline Vita Enamic & VITA Zahnfabrik, Bad Säckingen, GER & VE & 30.0 & 85.1 & 150–160 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Materials, manufacturers, abbreviations (Abbr.), modulus of elasticity (E), filler content (wt.), fracture strength (FS) according to manufacturer’s specifications or literature: \({}^{\text{a}}\)[20], \({}^{\text{b}}\)[21], \({}^{\text{c}}\)[22], and \({}^{\text{d}}\)[11]). Filler content classification: low-fill \(\leq\) 74% wt. \(\leq\) compact.  
Figure 1: (**a**) ZwickiLine Z2.5 and (**b**) schematic test procedure with maximum indentation depth (h\({}_{\text{max}}\)) at application of maximum force (F\({}_{\text{max}}\)) and residual indentation depth (h\({}_{\text{min}}\)) after stress relaxation.  
and the Bonferroni test for post-hoc analysis. Pearson correlations were calculated. The level of significance was set to \(\alpha\) = 0.05.