This cross-sectional observational study aimed to identify the predictors of sleep bruxism (SB) in patients with temporomandibular disorder (TMD) and to comprehensively investigate its association with clinical, sleep-related, psychological, and hematological factors. Seventy-nine patients with TMD (69 females and 10 males; mean age 45.46 ± 14.46 years) were divided into two groups based on the presence or absence of SB: TMD_nonbruxer and TMD_bruxer. Descriptive statistics, correlation analyses, and multivariate stepwise logistic regression were conducted; p < 0.05 was considered statistically significant. In Cramer's V, SB was correlated with several clinical and sleep-related factors, including TMJ noise (r = 0.52), TMD pain (r = 0.48), craniomandibular index (r = 0.32), limited mouth opening (r = 0.29), tinnitus (r = 0.29), an increase in the Pittsburgh sleep quality index (PSQI) global score (r = 0.24), and poor sleep quality, defined as a PSQI global score ≥ 5 (r = 0.19) (all p < 0.05). SB was also associated with psychological distress. Regarding hematological factors, elevated levels of cortisol (r = 0.30), adrenocorticotropic hormone (ACTH) (r = 0.34), and cortisol/ACTH ratio (r = 0.35) were also associated with SB (all p < 0.05). The factors associated with an increased likelihood of SB ranked in terms of the odds ratio (OR) were: craniomandibular index (OR = 18.400, p = 0.006), poor sleep quality with a PSQI global score ≥ 5 (OR = 11.425, p = 0.027), depression (OR = 1.189, p = 0.014), cortisol/ACTH ratio (OR = 1.151, p = 0.007), anxiety (OR = 1.081, p = 0.040), and adrenocorticotropic hormone (OR = 1.073, p = 0.019). Notably, an increase in age was associated with a decreased likelihood of SB (OR = 0.905, p = 0.006), with a cut-off value of 50 years (AUC = 0.259, 95% CI: 0.149-0.368, p = 0.024), indicating a significant decrease in bruxism occurrence in individuals aged ≥ 50 years. Further analysis revealed complex interconnections between SB and its predictors. In conclusion, SB in TMD patients was associated with age < 50 years, various clinical factors, such as TMD pain and TMJ noise, poor sleep quality, psychological deterioration, and elevated cortisol and ACTH levels.