Background: Nocturnal bruxism patterns after orthodontic treatment have not yet been studied, even though they are important to understand issues of retention. Purpose: To compare, using BruxChecker®, nocturnal bruxism patterns that occur in patients who use two types of thermoformed retainers. Methods: The sample consisted of three-per-patient type III plaster models of 45 post-orthodontic treatment patients, mean age 30.5 years. The models were classified as: model 1 no plate plus BruxChecker®; model 2 Essix ACE® hard plate plus BruxChecker®; model 3 Essix C+® soft plate plus BruxChecker®. The sums of marks in the BruxChecker® were analyzed through the Klonk Image Measurement software and the wear patterns were described through a modification of Onodera’s classification. Results: The predominant guidance was group function (77.04%). Increased presence of anterior guidance and anterior plus premolar guidance was found in patients without plaque (4.44%). The biggest wear on mediotrusive side was associated with thickness and type of plate, with more wear on the hard plate (28.1%) and higher in mediotrusive contacts without plaque (14.8%). The median per plate shows statistically significant differences between hard and soft plates and without plate. Conclusions: Important changes in the sleep bruxism pattern were related to the use of retainers Essix C+® and Essix ACE®. Group function was the most common working guidance. The hard plate significantly increased mediotrusive contacts as compared to the soft plate and no plate groups.KEYWORDSorthodontics; occlusal guidance; sleep bruxism; BruxChecker®; group function; retainers