# Surface Morphology of Three-Dimensionally Printed Replicas of Upper Dental Arches
## 3 Results
### Surface Structure Analysis  
Surface quality is directly connected not only to the printing process, but also to different types of filament (SLA, FDM, PJ) or thermoplastic powder (SLS) (Figure 3). The FDM model showed clear lines of individual layers of the material, but at higher magnification some cuts which can influence the future durability of the material were observed. The SLS microscopic image presented a grainy structure with quite big and round grains. It was visible that this model was formed from powder. Material layering led to the creation of some holes in the structures and pits on the surface of the model. PJ material had a fibrous structure with connections of each layer. In the SLA sample, grained structures were found, but the surface was homogenous.  
Figure 2: Precision of models in cross-section among 3D printers: stereolithography (**SLA**), selective laser sintering (**SLS**), fused-deposition modeling (**FDM**) and polyjet technology (**PJ**).  
Scanning electron microscope (SEM) surface analysis showed differences in the surfaces which were directly connected to the 3D printing technology and the printing material (Tables 2 and 3). The curve surface profilometry of SLA is smooth due to laser application. FDM is a method where the filaments prepare clear curves of individual layers of the material. SLS and PJ created irregular layers with small defects.  
Mechanical profilometry was utilized to determine surface roughness. The measurement took place on an Alphastep IQ device with a scan length of 5 mm, stylus force of 14.5 mg and scan speed of 20 \(\upmu\)m/s\({}^{-1}\). The stylus diamond tip has a 5-\(\upmu\)m radius and 60\({}^{\circ}\) angle. Roughness average (Ra) and root mean square (Rq) values were calculated in accordance with ISO 4288, with Gaussian filters of different cutoff values (25/80/250/800 \(\upmu\)m). To obtain reproducible results, scans were made in two places in each of two perpendicular directions (in the tooth growth/print direction and perpendicular to that) and each line was measured three times.  
The smoothest and most homogeneous sample was SLA. The FDM sample was obviously printed by technology different from the others, as it was possible to observe each layer of thickness between 100 and 150 \(\upmu\)m with the naked eye. SLS and SLA samples showed the most similar results when comparing perpendicular directions (homogeneity). FDM and PJ materials exhibited significantly  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Cutoff**} & \multicolumn{4}{c}{**Ra (nm) in Direction of Printing**} \\ \cline{2-5}  & **SLA** & **SLS** & **FDM** & **PJ** \\ \hline
25 & 0.19 & 0.69 & 1.09 & 1.80 \\
80 & 0.65 & 4.30 & 4.78 & 5.35 \\
250 & 1.31 & 10.20 & 8.74 & 12.10 \\
800 & 2.37 & 19.35 & 12.80 & 14.00 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Roughness average (Ra) measured in direction of printing.  
Figure 3: Surface of 3D print. (**SLA**) stereolithography; (**SLS**) selective laser sintering; (**FDM**) fused-deposition modeling; (**PJ**) polyjet technology.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Cutoff**} & \multicolumn{4}{c}{**Ra (nm)**} & **Perpendicular to the Direction of Printing**} \\ \cline{2-5}  & **SLA** & **SLS** & **FDM** & **PJ** \\ \hline
25 & 0.08 & 1.15 & 0.05 & 0.33 \\
80 & 0.31 & 4.10 & 0.33 & 0.63 \\
250 & 1.35 & 10.30 & 0.65 & 4.09 \\
800 & 3.66 & 16.95 & 4.33 & 11.45 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Roughness average (Ra) measured in direction of printing.  
greater roughness in the printing direction than in the perpendicular one, which is most likely caused by the technology selected and/or print parameters.