Background: The COVID-19 pandemic resulted in the strengthening of the earlier stressors and the appearance of new pandemic-related stressors. Many students of dentistry fit the profile of a group who are particularly susceptible to stress related to the pandemic. Thus, it was necessary to implement preventive activities, reducing their stress perception. This was understood as a means of significantly influencing the student’s well-being, thus improving the quality of education. Therefore, the aim of the study was to assess the impacts of implemented preventive activities on stress perception among students of dentistry during the pandemic, as well as their influence on this assessment of the selected students’ personal experiences regarding the pandemic. Methods: The study was performed one year after the outbreak of the pandemic on students of dentistry at Jagiellonian University Medical College, Krakow, Poland. It consisted of the completion of a self-designed, voluntary, anonymous, online questionnaire. The respondent’s task was to assess the influences of implemented preventive activities on stress perception using a five-point scale. The activities were divided into external (national, global) and internal (institutional). The material was statistically analysed for all students, including pre-clinical and clinical groups. Additionally, the impact of the selected students’ personal experiences regarding the COVID-19 pandemic on the assessment was studied. Results: All preventive activities (in total) significantly reduced stress perception (p ≤ 0.001), but the intensity of their impacts (mean rank) was different. The most highly assessed activities were all external preventive activities, with the greatest intensity belonging to the prospect of receiving vaccination against SARS-CoV-2. The remaining external activities were the prospect of developing an effective COVID-19 treatment and the increase in knowledge about SARS-CoV-2. The internal activities were assessed and ascribed lower positions, with the exception of the theoretical classes held online. This activity was placed slightly lower than the highest-rated activity, the prospect of receiving vaccination. Conclusions: The studied preventive activities reduced stress perception with different levels of intensity. The highest-ranked activities were external activities. One exception was the theoretical classes held online, an internal activity. Due to the lower impact of the internal activities and the ability to modify them by the educators, there is a need to strengthen their effectiveness. The possibility of monitoring and tailoring some preventive activities to the students’ needs was the practical aspect of the conducted study. Students’ personal experiences related to the COVID-19 pandemic influenced their assessment of the preventive activities, in some cases significantly.