# Injection Molding of Biodegradable Deciduous Teeth Dental Post
## 3 Results and Discussion
### Comparison with Existing Dental Post Materials  
To better contextualize the flexural performance of the PLA/PCL/ACP composite, Table 9 summarizes its strength and modulus alongside representative values reported for conventional dental post materials, including biodegradable PLA-based systems [10], fiber-reinforced composite posts [11], and metallic posts [12]. The PLA/PCL/ACP composite exhibited a flexural strength of approximately 22 MPa and a modulus of 2.08 GPa, which are considerably lower than those of commercial fiber posts (1800-2000 MPa; 15 GPa [11] and stainless-steel posts (230 \(\pm\) 15 MPa; 200 \(\pm\) 10 GPa [12]. However, it is important to note that most of these reference data correspond to posts designed for permanent teeth, which experience greater functional loading demands due to higher occlusal forces. In contrast, deciduous teeth exhibit thinner dentin walls, shorter roots, and physiological resorption, necessitating more flexible and resorbable post systems to avoid excessive stress concentration and interference with natural exfoliation. Compared to natural primary dentin, which has a flexural modulus of \(\sim\)3.63 GPa [31], the PLA/PCL/ACP system's lower modulus may help reduce interfacial stress at the dentin-post junction, promoting better stress distribution and preservation of root integrity. This rationale aligns with modulus-matching strategies advocated for in pediatric endodontics [31; 32]. While biodegradable PLA-based posts have demonstrated moderately higher mechanical values (e.g., 64.2 \(\pm\) 7.9 MPa strength; 2.75 \(\pm\) 0.3 GPa modulus [10], the current composite remains compliant with structural requirements for primary teeth and demonstrates promising potential for pediatric endodontics. Notably, the inclusion of ACP provides biochemical benefits beyond mechanical reinforcement. As demonstrated in our \begin{table}
\begin{tabular}{c c c} \hline
**Category** & **Property** & **Value** \\ \hline \multirow{4}{*}{Material Properties} & Flexural Strength (MPa) & 21.90 \(\pm\) 2.70 \\  & Flexural Modulus (GPa) & 2.08 \(\pm\) 0.13 \\  & Glass Transition Temperature (\({}^{\circ}\)C) & 65.0 \\  & Melting Temperature (\({}^{\circ}\)C) & 172.6 \\  & Contact Angle (\({}^{\circ}\)) & 73.7 \(\pm\) 1.6 \\ \hline \multirow{4}{*}{Molding Performance} & Average Linear Shrinkage (\%) & 1.29 \\  & Length (mm) & 21.153 \(\pm\) 0.025 \\ \cline{1-1}  & Head Diameter (mm) & 2.452 \(\pm\) 0.011 \\ \hline \end{tabular}
\end{table} 
Table 8: Summary of key material properties and molding performance of the PLA/PCL/ACP composite. The table includes flexural properties, thermal transitions, wettability, shrinkage, and dimensional accuracy of the molded posts. \begin{table}
\begin{tabular}{c c c} \hline
**Dental Post System** & **Flexural Strength (MPa)** & **Flexural Modulus (GPa)** \\ \hline PLA/PCL/ACP (This study) & 21.94\(\pm\) 2.70 & 2.08\(\pm\) 0.13 \\ \hline PLA-Based Post [10] & 64.2 \(\pm\) 7.9 & 2.75 \(\pm\) 0.3 \\ \hline Fiber Post (D.T. Light-Post®) [11] & 1800–2000 & 15 \\ \hline Metal Post (Stainless Steel) [12] & 230 \(\pm\) 15 & 200 \(\pm\) 10 \\ \hline Natural Primary Dentin [31] & & \(\sim\)3.63 \\ \hline \end{tabular}
\end{table} 
Table 9: Comparative flexural properties of dental post systems. The PLA/PCL/ACP composite developed in this study is compared with PLA-based, fiber, and metal posts, as well as natural primary dentin, in terms of flexural strength and modulus. previous study [22], ACP neutralizes the acidic degradation by-products from PLA/PCL matrices, stabilizing the local pH and reducing the risk of inflammatory responses--an essential feature in pediatric applications. Although variations in testing parameters and filler dispersion may affect absolute values across studies, flexural performance remains a valid metric for benchmarking candidate materials.