Fig. 5

NAC-treated group experienced lower levels of pain, decreased sensitivity to cold and similar degrees of satisfaction of the bleaching outcome based on their exit interview responses. The levels of pain measured at a scale of 0–10, 10 being the most painful, in patients were collected after each of the three bleaching cycles and every 2 hours post-procedure for the first 10 h, and thereafter on a daily basis for 5 days. The mean values for each time point was plotted for both H2O and NAC-treated patients. A Wilcoxon Rank Sum Test (Mann-Whitney U Test) was performed for each time point to compare significant differences in patient responses. Higher pain levels were noted in H2O group with significant differences in cycle 2 (p = 0.012), cycle 3 (p = 0.005), and 2-h post-treatment (p = 0.048) (a) Exit interview response for overall levels of pain experienced by patients were recorded on a scale of 0–5 with 5 being the most painful, and plotted for both H2O and NAC groups. A Wilcoxon Rank Sum Test (Mann-Whitney U Test) was used to calculate statistical significance. Patients receiving bleaching and NAC experienced a lower resting pain level with a P-value of 0.0002 (n = 21) (b). Exit interview response was obtained for overall experience to sensitivity to cold on a scale of 0–5, with 5 being the most sensitivity to cold stimulus. A two-tailed, unpaired t-test showed a significantly higher sensitivity to cold in control patients, with a P-value of 0.0006 (n = 20) (c). Exit interview response was obtained for post-procedure satisfaction of bleach whitening esthetics according to a 0–5 scale, with 5 being the most satisfied. A two-tailed t-test showed that NAC patients were equally satisfied with their bleaching cosmetic outcome, with a P = value of 0.35 (n = 21) (d)