## 2 Materials and Methods  
A systematically conducted scoping review was utilized to summarize the currently available research on the cytotoxicity of 3D printable acrylic resins. The workflow followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement to identify, screen, elect, and include scientific papers in this review. MESH keywords were inserted into the databases to perform the search. The keywords selection obeyed the P (population), I (intervention), C (comparison), and O (outcome) question system to associate them with the advanced search option of each database portal. Table 1 describes the PICO keywords association. The scoping review search was conducted at the OVID Medline, EMBASE, and SCOPUS databases to compile papers evaluating topics related to the cytotoxicity of 3D printable resins. English-language peer-reviewed journal papers were selected from 2015 to 2023. Papers, such as dentures and occlusal nightguards, were included when investigating 3D-printed acrylic resin designs for long-term clinical use. Papers were excluded if they did not focus on 3D-printed acrylic materials used for prosthetic devices, if they studied temporary rehabilitation materials, if they investigated experimental non-commercially available materials, resin-based composite materials, ceramic and metallic materials, materials designed for biodegradable scaffolds or implant dentistry. These papers were compiled into Covidence for further review and selection, and a librarian removed duplicate entries. Two independent reviewers used the Covidence software (www.covidence.org accessed on 14 July 2023) to screen the titles and abstracts to filter out papers relevant to the topic, applying inclusion and exclusion criteria. To ensure consistency, both reviewers evaluated all article abstracts and voted \"yes\", \"no\", or \"maybe\" for the relevance of the articles, with ties broken by a third investigator. The reviewers performed another screen, now evaluating the full text, and finalized the selection of these papers, resulting in 24 papers included in this scoping review. Figure 4 states the PRISMA workflow from identification to the inclusion of papers. Both reviewers extracted data from the selected papers, considering the following criteria: author, year of paper publication, 3D-printed materials evaluated, 3D-printer device, post-processing method performed, variables tested in the experiment, cytotoxicity assay and cell lineage used, the mains results, and conclusion. All data were extracted independently, and the results from each reviewer were discussed with a third researcher when needed and merged into Table 2. \begin{table}
\begin{tabular}{l l} \hline \hline \multicolumn{1}{c}{**PICO**} & \multicolumn{1}{c}{**Keywords**} \\ \hline \multirow{2}{*}{Population} & 3D print\$4 OR 3-D print\$4 OR 3-dimensional print\$4 OR \\  & three-dimensional print\$4 \\ \hline \multirow{3}{*}{Intervention} & “dental night guard *” OR “oclusal split *” OR “night guard *” OR bruxism OR prosthodontic * OR “dental restoration *” OR denture * OR “artificial tooth” OR “artificial teeth” \\ \hline \multirow{2}{*}{Comparison} & “three dimensional print *” OR “three-dimensional print *” \\ \hline \multicolumn{1}{c}{Outcome} & Biocompatib * OR cytotoxic * OR genotoxic * \\ \hline \hline \end{tabular}  
* This is a key used by the librarian to decrease the chance of losing an important paper during the search.  
\end{table} 
Table 1: MESH Keyword. Figure 4: Flow chart describing the extraction and selection process of relevant papers. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Author/Year** & **Materials/n** & **Printer** & **Processing Method** & **Variables** & **Bio Method/Cell** & **Main Results/Conclusion** \\ \hline  & & & & & & & Extracts of uncured resin reduced cell \\  & & &