# Influence of Printing Angulation on the Flexural Strength of 3D Printed Resins: An In Vitro Study
## 4 Discussion  
Flexural strength is one of the fundamental characteristics of a restorative material, and high values will reduce the risk of restoration fractures under the masticatory forces [33]. Due to the results obtained in the present in vitro study, the null hypothesis was partially rejected since no statistically significant differences were reported on the flexural strength between the studied 3D-printed resin groups, but they were found for the built angles evaluated. All tested samples showed high values of flexural strength, higher than the minimum requirement of ISO 4049:2019 standard [34]. The mean value of flexural strength for each resin was double the minimum requirement of flexural strength reported in ISO 10477:2020 standard [35] of 50 Mpa for interim restorations. Thus, as reported by a previous study by [PERSON] et al. [36], all the tested materials can be considered suitable for performing temporary restorations. Even if the 90\({}^{\circ}\) printing orientation allows an optimization of the printing procedure, the results obtained suggest that it produces lower values of flexural strength compared to 0\({}^{\circ}\) or 45\({}^{\circ}\)[37]. As shown in Table 4, printing angulation plays a fundamental role for some of the tested materials. However, Varseo smile teeth (Bego GmbH & Co., Bremen, Germany) and Sprintray Crown (SprintRay, Los Angeles, CA, USA) flexural strength values seem to be not statistically influenced by the printing angulation. Instead, for V-print C&B temp (Voco GmbH, Cuxhaven, Germany), flexural strength values were statistically significantly lower when the samples were printed at a 90\({}^{\circ}\) angulation respect to 0\({}^{\circ}\) or 45\({}^{\circ}\), while for Bego Triniq (Bego GmbH & Co. KG, Bremen, Germany), samples printed with an inclination of 45\({}^{\circ}\) were statistically significantly stronger than the ones printed at 0 or 90\({}^{\circ}\). Therefore, when selecting the material for future restorations, clinicians and technicians should take \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Materials** & **Inclination** & **Mean** & **SD** & **Sig. \(p\) **< 0.05** \\ \hline \multirow{3}{*}{Bego Varseo Smile teeth} & 0\({}^{\circ}\) & 132.52 & 35.25 & A \\ \cline{2-5}  & 45\({}^{\circ}\) & 133.04 & 22.12 & A \\ \cline{2-5}  & 90\({}^{\circ}\) & 134.24 & 14.94 & A \\ \hline \multirow{3}{*}{V-print C\&B temp} & 0\({}^{\circ}\) & 156.56 & 25.58 & A \\ \cline{2-5}  & 45\({}^{\circ}\) & 130.46 & 12.33 & A \\ \cline{2-5}  & 90\({}^{\circ}\) & 116.97 & 34.87 & B \\ \hline \multirow{3}{*}{Bego trinQ} & 0\({}^{\circ}\) & 113.37 & 31.93 & A \\ \cline{2-5}  & 45\({}^{\circ}\) & 148.91 & 21.23 & B \\ \cline{2-5}  & 90\({}^{\circ}\) & 100.96 & 16.66 & A \\ \hline \multirow{3}{*}{Sprintray Crown} & 0\({}^{\circ}\) & 110.41 & 36.13 & A \\ \cline{2-5}  & 45\({}^{\circ}\) & 136.33 & 15.38 & A \\ \cline{1-1} \cline{2-5}  & 90\({}^{\circ}\) & 114.85 & 17.72 & A \\ \hline \hline \end{tabular} Legend: N: number of samples for each group, SD: standard deviation, Sig.: significant differences. Same letters per table denote no statistically significant differences (_p_ > 0.05).  
\end{table} 
Table 4: Mean flexural strengths (Mean), standard deviations (SD), and significant differences (Sign.) for Bego Varseo smile teeth, V-print C&B temp, Bego Triniq, and Sprintray Crown. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Inclination** & **N** & **Mean** & **SD** & **Sig. \(p\) **< 0.05** \\ \hline
0\({}^{\circ}\) & 40 & 137.19 & 18.92 & B \\
45\({}^{\circ}\) & 40 & 128.21 & 36.37 & B \\
90\({}^{\circ}\) & 40 & 116.75 & 24.74 & C \\ \hline \hline \end{tabular} Legend: N: number of samples for each group, SD: standard deviation, Sig.: significant differences.  
\end{table} 
Table 5: Mean flexural strengths (Mean), standard deviations (SD), and significant differences (Sign.) for printing orientation. into consideration that the printing angulation, for some materials, has important effects on the durability of the future restoration.