## 4 Discussion  
Numerous studies have used the FEM to analyze the biomechanical responses of the PDL during tooth movement due to orthodontic treatment. However, most such studies have used the FEM to develop partial jawbone models. The few studies that have created complete jawbone models have overlooked the occlusal force encountered in daily life. Therefore, we established partial and complete mandible models to analyze the effect of jawbone model integrity on the biomechanical reactions of the PDL by using the FEM. The simulation results suggested that the effects of the partial and complete mandible models on von Mises strain in the canine PDL were negligible when only orthodontic force was considered. However, the occlusal force that individuals exert in daily life had a substantial effect on the von Mises strain in the PDL. This effect was even larger when the PDL was assigned a linear elastic modulus. The FEM is an excellent method for evaluating tooth movement caused by orthodontic treatment because it can simulate orthodontic forces of different amounts and directions. The biomechanical responses of the PDL can be evaluated, and the direction and rate of tooth movement can be predicted according to pressure-tension theory. Numerous researchers have used the FEM to investigate tooth movement during orthodontic treatment, but most studies have created only partial jawbone models. Although some studies have established complete jawbone models, their goals were to analyze the effects of occlusal modes on jawbone biomechanical response [32] or on the PDL [33]. However, \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multicolumn{6}{c}{**Investigated Issue: Integrity of Mandible**} & \multicolumn{6}{c}{**Investigated Issue: Material**} \\ \hline  & **Model 1** & **Model 2** & **Model 3** & **Model 4** & **Model 5** & **Model 6** & **Model 7** \\ \hline [PERSON] strain & & & & & & & \\ on canine’s PDL & 0.461 & 0.394 & 1.811 & 6.047 & 2.594 & 0.887 & 1.811 \\ \hline [PERSON] stress & & & & & & & \\ on cortical bone & 0.498 & 0.765 & 7.5375 & 6.25 & 8.3067 & 14.343 & 7.5375 \\ around canine’s PDL & & & & & & & \\ \hline [PERSON] stress & & & & & & & \\ on cancellous bone & 0.0599 & 0.0794 & 0.6914 & 0.5622 & 1.2387 & 1.5905 & 0.6914 \\ around canine’s PDL & & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Finite-element simulation results. Figure 4: Distribution of von Mises strain in the canine PDL: models with (**a**) low linear elastic modulus, (**b**) moderate linear elastic modulus, (**c**) high linear elastic modulus, and (**d**) bilinear elastic modulus. whether occlusal force interferes with the mechanical response of the PDL during orthodontic treatment has remained unclear. Our simulation results suggest that the maximum von Mises strains in the canine PDL differed by 17.0% between the partial and complete mandible models. This difference was caused by the difference in method used for setting the boundary conditions. The partial mandible model involves a finite-element simulation for the mesial and distal sides. The proximal side of the mandible near the side incisors was a fixed surface that was too close to the canine tooth and was moving in the distal direction. Therefore, when the canine PDL exerted orthodontic force against the mesial side, the strain distribution differed substantially from that in the complete mandible model, which was subject only to orthodontic force. The distal side of the canine PDL was farther from the completely fixed partial mandible mesial side. Thus, the effect on strain distribution was weaker. This demonstrates that boundary conditions should be applied farther from the tooth requiring movement in future models of tooth movement due to orthodontic treatment. In other words, for a partial mandible, a larger area must be modeled to mitigate effects on the simulation results.