The effects of a nonthermal atmospheric plasma jet with argon and argon/oxygen (Ar/O<sub>2</sub>) gases on live human dental pulp stem cells (hDPSCs) were studied to verify tooth vitality in the pulp-capping process. Using MTT assay, the surviving hDPSCs after plasma jet exposure for 1, 2, and 3 min were counted. First, for the pulsed plasma jet the frequency varied from 10 to 50 kHz for 5 groups with Ar and 5 groups with Ar/O<sub>2</sub> plasma jet. Later, with the alternating current (AC) plasma jet, the voltage was changed between 5.5 and 16.05 kV for 13 groups. The cells in the control group were only exposed to Ar and Ar/O<sub>2</sub> gases. To control thermal damage to hDPSCs, optical emission spectroscopy was used. For data analysis, the ANOVA repeated measure was used. There were significant differences between the various frequencies and exposure durations (<i>p</i> < 0.05) for the Ar plasma. For the Ar/O<sub>2</sub> gas, there were significant differences between frequencies (<i>p</i> < 0.001). For the AC plasma jet with Ar gas, there were significant differences between voltages (<i>p</i> < 0.001). At the higher pulsed jet frequencies, temperatures increased. Eventually, the suitable durations for root canal disinfection and hDPSC survival with the Ar pulsed jet were 2 and 3 min at 10 and 30 kHz, respectively. Since cold plasma disinfection keeps hDPSCs alive, it can be helpful in promoting tooth survival and durability for pulp capping in clinical treatments.