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Purpose: The purpose of this study was to identify the source of specific pollutants in dental laboratory wastewater and to suggest management methods for wastewater in such settings. Methods: Test samples (81 types) were created from wastewater generated during prosthetic fabrication using plaster products. The water quality of these samples was tested three times by an authorized testing agency, and the results were categorized based on plaster manufacturer and the prosthesis-making method. Results: In the model plaster group and related samples, lead (Pb) was not detected. In the dental stone group, Pb was detected in sample 50 at 152 times more than the water quality standard, and in sample 51, Pb was detected at a level below the standard. In the highstrength stone group, Pb was detected in two out of three samples. In the high-strength stone test group, after trimming, the concentrations of copper (Cu) and Pb in the gypsum sludge increased. In the mixed gypsum group, after 30 days, the concentrations of mercury (Hg) and hexavalent chromium (Cr6+) increased. Conclusion: Some of the tested gypsum samples exceeded hazardous substance standards, indicating that these gypsum products should not be used in prosthetic fabrication. Additionally, the concentration of hazardous substances increases before and after plaster trimming, necessitating a thorough management of plaster trimming machines. Since the concentration of hazardous substances in wastewater from the plaster trap increases over time, it is critical to maintain cleanliness in the plaster trap at all times.