Masticatory muscle activity and oral health-related quality of life in patients wearing clear thermoplastic versus wrap-around retainers : A randomized controlled trial.

Aim: To evaluate the surface electromyography (sEMG) activity of the superficial masseter and anterior temporalis muscles at rest, during maximum voluntary clenching (MVC), and mastication, over 6 months of wearing clear thermoplastic or wrap-around retainers. Furthermore, the patients' oral health-related quality of life was assessed using the Oral Impacts on Daily Performance (OIDP) index at 6 months.

Materials and methods: Sixty patients aged 14-39 years (19 males/41 females) who received upper and lower retainers after finishing orthodontic treatment were recruited. The patients were randomly divided into a clear thermoplastic retainer group (n = 30) or a wrap-around retainer group (n = 30). The sEMG activity was recorded at retainer delivery (T0), after 3 months (T1), and after 6 months of wearing (T2). The OIDP index was evaluated at T2.

Results: None of the sEMG parameters for the masseter and temporalis muscles were different between the two groups at T0, T1, or T2. Over the period of 6 months, both masticatory muscles in both groups demonstrated increased sEMG activity during MVC and mastication; however, only the temporalis muscle demonstrated decreased normalized sEMG activity at rest (P < 0.05). The frequency and severity of the OIDP in the eating aspect at T2 was low and similar in both groups.

Conclusions: sEMG activity of the two masticatory muscles tended to increase during MVC and mastication, while temporalis muscle activity tended to decrease at rest during the observation period, regardless of retainer type. Notably, these sEMG changes did not affect the patients' subjective masticatory function.