## 4 Discussion  
Two major factors affecting impression quality are appropriate handling of the impression materials and the impression technique. Influencing the marginal fit of the cast restoration may determine the restoration's durability and abutment teeth survival [1; 2; 3; 4; 5; 6; 7]. Previous in vitro studies have shown that different mixing techniques have an effect on impression quality and machine mixing superiority [39; 40]. These findings are consistent with our in vivo study results, which emphasize the fact that mechanical mixing produced significantly more accurate metal framework restorations than hand mixing (\(p\) = 0.04). The clinical outcome shows that hand mixing led to twice as many metal frameworks misfits compared to machine mixing (31.1% vs. 14.1%). The mechanical mixing allows for better control of the amounts and proportions of the impression material used, facilitates polymerization reaction, reduces the number and the size of the bubbles incorporated in the impression material and avert contamination. Moreover, mechanical mixing is preferred by dental staff due to the ease of use [29; 32; 34; 38; 40]. Additional factors that influence the operator's decision to use the mixing technique for impression material is the accessibility of a mixing machine [36]. Similar to previous in vitro study results, the present study has shown a significant difference in PFD metal frameworks' fit accuracy when compared two common impression techniques. While the one-step technique has the benefits of being faster, it has also led to fabrication of twice as many ill-fitted metal frameworks compared to the two-stage impression technique (31.8% vs. 14.6%). Previous studies have found an association between the impression technique used and the metal framework fit accuracy of fixed partial dentures [19; 21; 25]. In the one-step technique, the viscous putty material tends to \begin{table}
\begin{tabular}{c c c c} \hline
**Mixing Technique** & **N** & **Misfit** & **Fit** \\ \hline Automatic mixing & 47 & 7 (14.9\%) & 40 (85.1\%) \\ Hand mixing & 45 & 14 (31.1\%) & 31 (68.9\%) \\ Total & 92 (100\%) & 21 (22.8\%) & 71 (77.2\%) \\ \hline \end{tabular}
\end{table} 
Table 2: Clinical result for mixing technique. \begin{table}
\begin{tabular}{c c c c c} \hline
**Impression Technique** & **Mixing Method** & **Misfit** & **Fit** & **Total** \\ \hline \multirow{2}{*}{One stage} & Automatic & 5 (11.4\%) & 17 (38.6\%) & 22 \\  & Conventional & 9 (20.4\%) & 13 (29.5\%) & 22 \\ \hline \multirow{2}{*}{Two stage} & Automatic & 1 (2.1\%) & 22 (45.8\%) & 25 \\  & Conventional & 6 (12.5\%) & 19 (43.2\%) & 23 \\ \hline \end{tabular}
\end{table} 
Table 3: Clinical result for combination of impression and mixing techniques. push the light body material away from the abutment teeth, and thus they are recorded by the less precise putty material. Uncontrolled impression ray pressure during setting may also lead to a significant effect on precision. Tray rigidity may also affect the accuracy of polyvinyl siloxane impressions. Metal trays produce more accurate impressions than plastic trays [20; 21; 22; 23; 24; 25]. Moreover, the uncontrolled wash bulk thickness causes dimensional changes (vertical and horizontal) due to impression material contraction towards the tray walls, resulting in distorted stone dies on the working models [45; 46; 47; 48]. While with the two-step putty-wash technique, the wash layer thickness is minimal and uniform, the critical details are copied precisely, with minimal distortion [13; 14], emphasizing the fact that the controlled wash bulk is the critical factor in fabricating accurate restorations [19]. The present in vivo results demonstrated the superiority of the two-step impression technique in terms of restoration accuracy while using a custom metal tray.