Background: The declaration of COVID-19 as a pandemic by the World Health Organization in 2020 led to the suspension of several clinical practices globally, including dentistry. This study investigates the impact of these restrictions on dental caries experience. Methods: A retrospective cross-sectional study was conducted at Egas Moniz University’s dental hospital in the Lisbon Metropolitan Area from June 2019 to June 2021. The study involved 3380 participants who were divided into two cohorts: after and before COVID-19 restrictions. Data collection included a questionnaire, full-mouth clinical examinations, and radiographs (panoramic X-rays, bitewings). Results: Before the COVID-19 restrictions, the prevalence of dental caries was 91.8%, with an average DMFT (decayed, missing, and filled teeth) index of 12.13. Post-restrictions, the prevalence decreased to 84.5%, with a DMFT index of 10.99. There was an increase in missing teeth and a decrease in decayed and filled teeth. Additionally, the frequency of toothbrushing declined among participants. Conclusions: The COVID-19 pandemic restrictions have significantly impacted dental caries experiences and oral health, highlighting a decrease in dental caries, but also a concerning reduction in oral hygiene practices. These results emphasize the importance of customized dental healthcare during public health emergencies to reduce impacts and maintain oral health.