This study did have some limitations. The response rate for plaster models was quite low, at 48.3%, and it was likely influenced by the time of collection. In addition, the reliability of the results is low, since the questionnaire was only conducted with students from one dental school. However, the histograms of the three student groups showed the same frequency distribution and had the same median with the highest frequency; therefore, the samples were considered valid for statistical analysis. However, the results of this study should not be over-generalized, since high external validity is not likely with just one study. Therefore, the external validity of this field will increase as many researchers complement each other.