Background: In the last years an increasing number of patients have sought for comfortable and aesthetic alternatives to fixed appliances. Aligners, due to the protection against tooth wear, can be compared to occlusal splints used in patients suffering from sleep bruxism (SB). The aim of the study was to analyze the effects of clear aligners on SB episodes using a validated portable device (Bruxoff®, OTBioelettronica, Torino, Italy) allowing a simultaneous recording of electromyographic signals from both the masseter muscles as well as heart frequency to evaluate variation on SB activity. Methods: Forty patients were analyzed for the study. Twenty of them were assigned to orthodontic treatment with clear aligners (Invisalign®, Align Technology). The other twenty patients were used as control group observed for a period of twelve months. Intra-group and inter-group variances were analyzed by using a two-way ANOVA test. For each analysis a P < 0.05 was set. Results: After the first month of clear aligners therapy, all patients in the case group showed a significant reduction in the number of SB episodes (P < 0.05). However, after three months SB values returned to baseline levels. The number of tonic contractions were reduced even after three months of orthodontic treatment (P < 0.05). Conclusions: While clear aligners seem to be capable to reduce clenching, i.e. occlusal load, in SB patients, the grinding activity seems to be not influenced by those appliances at least in the short term of the present investigation.