## 4 Discussion  
This study was designed to determine the efficacy of a computer-based 3D visualization and simulation method for knowledge acquisition on the occlusal adjustment compared with a conventional paper-based 2D presentation method. In the questionnaire survey on the expected effects of the 3D simulation method, most of the participants rated this method as highly appropriate for occlusion education, and especially effective for visualizing anatomical structures as well as memorizing occlusal adjustment concepts. Meanwhile, in the examination for evaluating students' learning effects, the difference in scores between the groups was significant (i.e., in the questions for occlusal adjustment  
Figure 5: Grading of examination scores. Figure 6: Scatterplot showing the association between survey and examination. in centric relation). The difference was, however, not significant in the questions for the occlusal adjustment in eccentric relation. The mean score of the test was higher in the 3D simulation group than in the 2D presentation group. Based on the findings, the proposed first null hypothesis (i.e., there is no difference in learning effects between the two methods) was partially rejected. The correlation between the survey and the examination results was also investigated and no statistical association was found. This result implies that the feedback from the students and the actual learning effect on knowledge acquisition could not be directly related. Thus, the second null hypothesis (i.e., learner response on the education method and the actual examination results would not be correlated) was not rejected. The distribution of examination scores for each student was visualized by classifying the scores in grades. An asymmetry in the score distribution was observed in the 2D presentation group, and it shows a large portion of the scores were in the low ranks. Conversely, in the 3D visualization group, scores were generally higher compared to the 2D presentation group, and a more symmetrical distribution of scores was observed. The bell-shaped curve might be recommended in grading academic achievements of students because this distribution fits well the normal distribution of natural learning ability in humans. Accordingly, based on the score distribution, it is thought that the 3D visualization method would be a more suitable method than the 2D presentation method in conveying the principles of occlusal adjustment in dentistry. Despite the fact that teacher-oriented lectures with 2D images are still mainstream, this conventional method might be less effective for teaching manual skills and inducing critical reasoning required in higher education, especially in clinical courses in medicine [26; 27]. Moreover, student participation would also be low in paper-based education systems [28; 29]. Clinical dentistry is largely manual. Hence, conventional demonstrative lectures clearly have limitations as a teaching technique [30; 31]. It is a challenge to understand the positional relationship of maxilla and mandibles in dynamic occlusion. It is also difficult to figure out occlusal disharmony that is topographic and its relationship with antagonistic teeth in cusp, fossa, and ridges. Recent studies in dental education revealed that mental training with 3D imagery could improve the in-depth perception for objects and had beneficial effects in acquiring clinical skills [32; 33]. Training for manual skills coupled with decision-making can be achieved efficiently in environmental settings mimicking clinical situations. Thus, computer-based 3D visualization and simulation may be relevant in training occlusal adjustment in pre-clinical courses because students are provided spatial and visual aids to estimate distances, sizes, and shapes of anatomical subjects. In the present study, the use of 3D dental mesh models and computer software providing color-coded occlusal analysis and functions for design modification motivated students to participate in the class.