Background: The diagnosis of sleep bruxism (SB) in children is difficult due to the lack of a polysomnographic protocol for this population. Moreover, the gold standard treatment [occlusal splint (OS) therapy] has limitations, as adequate use depends on the child's cooperation. The etiology of SB may include stress factors. Salivary cortisol is a biomarker used as a noninvasive method to evaluate the response to stress. Besides physiological aspects, it is also important to investigate morphological aspects, such as masticatory muscle strength. The aim of the present study was to determine the occurrence of bite marks on the buccal mucosa in children as a complementary sign for the diagnosis of SB and investigate and the effectiveness of photobiomodulation as an alternative treatment for this condition. Methods: Seventy-six children 6-12 years of age were divided into four groups: G1-with SB and submitted to laser therapy over acupuncture points (λ = 786.94 nm, 20 sec per point, fluency = 33.5 Jcm2, energy = 1 J, number of points = 12); G2-with SB, use of OS, G3-with SB and submitted to sham laser therapy; and G4-control group without SB. Clinical signs (bite marks on buccal mucosa and headaches), bite force (BF), and salivary cortisol (biomarker of stress) were evaluated before and after treatment. Statistical analysis involved the Kolmogorov-Smirnov, Shapiro-Wilk, and analysis of variance (ANOVA) tests. Results: Bite marks on the buccal mucosa were significantly associated with SB (p < 0.001). A statistically significant difference was found between the frequency of children with headache before and after treatment in G1 (p = 0.0005) and G2 (p = 0.0001), with no significant differences between the two groups (G1 and G2). The children in G1 had lower BF on both sides compared to the other groups. In the intragroup analysis after treatment, all groups exhibited an increase in salivary cortisol levels. Conclusions: Bite marks on the buccal mucosa can be used as a complementary sign for the clinical diagnosis of SB. Children with SB responded well to photobiomodulation therapy, as evidenced by the reduction in BF and reports of headache.