# Injection Molding of Biodegradable Deciduous Teeth Dental Post
## 3 Results and Discussion
### Injection Molding Parameter Study and Taguchi Results
#### 3.2.2 The Results of the Taguchi Experiment  
Before each set of experiments in the Taguchi experiment, the parameters were set, and the machine was preheated for 30 min to ensure stable operating conditions. For each parameter combination, five finished products were molded, and their dimensions were measured after resting for one day to account for material stabilization. Data pertaining to the axial (length) and radial (head diameter) shrinkage, as well as the combined total shrinkage, are listed in Table 6, along with the S/N ratios of the total shrinkage. The factor response graph (Figure 13) identified A1B2C3 as the optimal parameter combination. A verification experiment using this parameter set (melt temperature: 180 \({}^{\circ}\)C, injection speed: 60 mm/s, holding speed: 30 mm/s) resulted in a minimum average radial shrinkage of 2.09% and an average axial shrinkage of 0.485%. According to Table 6, the total shrinkage rate of 2.575% yielded an S/N ratio of 31.786, outperforming the 3.907% shrinkage rate and 28.163 S/N ratio observed in Taguchi's best L3 level, thus confirming the robustness of the selected parameters. Figure 14 displays the deciduous tooth root canal posts molded under the optimized settings. The use of Taguchi's experimental design (L9 orthogonal array) to optimize injection molding parameters aligns with findings from prior studies. [PERSON] et al. [30] demonstrated that molding shrinkage serves as a key performance index in plastic injection molding, with orthogonal arrays improving process stability. Similarly, [PERSON] et al. [29] examined the impact of melt temperature, injection speed, and holding speed on shrinkage, highlighting melt temperature as the most dominant factor--consistent with the present study's ANOVA results. Figure 11: Melt temperature distribution after 6 s of cooling at **(a)** 180 \({}^{\circ}\)C and **(b)** 200 \({}^{\circ}\)C. In both cases, the temperature difference within the cavity stabilizes within 10 \({}^{\circ}\)C, reducing the risk of warpage due to uneven cooling. This analysis supports the selection of a 6 s cooling time. Figure 12: Moldex3D analysis of gate solidification at 180 \({}^{\circ}\)C and 200 \({}^{\circ}\)C under various holding times. The gate fully solidifies after 2.558 s at both temperatures, beyond which additional holding pressure has no effect. A holding time of 3 s was selected accordingly. Figure 14: Injection-molded PLA/PCL/ACP dental posts for deciduous teeth, produced using the optimal processing parameters (A1B2C3). A ruler is included for scale. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Shrinkage (\%) = (Mold Size \(-\) Post Size)/Mold Size \(\times\) 100\%** \\ \hline
**Group** & **Axial** & **Radial** & **Sum** & **S/N** \\ \hline L1 & 0.427 & 7.202 & 7.628 & 22.351 \\ L2 & 0.260 & 5.777 & 6.038 & 24.383 \\ L3 & 0.140 & 3.767 & 3.907 & 28.163 \\ L4 & 0.469 & 8.919 & 9.388 & 20.549 \\ L5 & 0.248 & 4.992 & 5.240 & 25.614 \\ L6 & 0.560 & 7.095 & 7.655 & 22.321 \\ L7 & 0.463 & 8.613 & 9.076 & 20.843 \\ L8 & 0.597 & 9.372 & 9.969 & 20.027 \\ L9 & 0.704 & 9.957 & 10.662 & 19.444 \\ \hline Optimal & 0.485 & 2.090 & 2.575 & 31.786 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Results of the Taguchi experiment showing dimensional shrinkage and signal-to-noise (S/N) ratios for each parameter set. The optimal combination minimized total shrinkage and maximized the S/N ratio. Figure 13: Main effects plot showing the influence of melt temperature (A), injection speed (B), and holding speed (C) on the selected response. The optimal parameter combination was A1B2C3. To determine the significance of each process parameter in injection molding, ANOVA was conducted. As shown in Table 7, melt temperature was the most influential factor, contributing 52.932% to molding shrinkage, followed by holding speed at 33.575%, whereas injection speed had a relatively smaller impact. Upon examining the radial and axial shrinkage, it was observed that radial shrinkage was significantly greater than axial shrinkage.