Abstract
In orthodontics and pedodontics, parafunction including oral breathing and tongue thrusting are considered to be factors that lead to malocclusion including maxillary protrusion and open bite. In order to correct these parafunction, oral myofunctional therapy (MFT) is commonly used.
There are several MFT training regimens for lips, which include button pull exercises (pulling a button with the lips closed tight) and the use of the Patakara, a mouth rehabilitation instrument. However, there has been limited research to objectively evaluate training methods to improve the strength and endurance of the orbicularis oris muscle.
Our previous studies measuring oxygenation dynamics in the orbicularis oris muscle by using near-infrared spectrometry indicated that performing 5 or 10 sets of 5 seconds load at 80% 1-RM (1 repetition maximum) and 5 seconds rest was effective for the orbicularis oris muscle to enhance muscle strength as a result of the hypoxic conditions in the muscle. These studies also indicated that repetition of 15 sets of 5 seconds load at 50% 1-RM and 5 seconds rest was effective as the endurance of the orbicularis oris muscle as a result of the aerobic conditions in the muscle. The aim of this study was to validate the effectiveness of hypoxic and aerobic conditions for improving the strength and endurance of the orbicularis oris muscle, respectively.
Subjects consisted of 15 adults from both sexes with normal stomatognathic function and no interference with lip closure. Traction plates were inserted in the upper and lower oral vestibules, and 1-RM was measured by pulling against the plates using a universal testing machine. Subjects were assigned to three groups: Group A subjects completed 20 sets comprised of load of 50% 1-RM for 5 seconds and rest for 5 seconds; Group B subjects completed 5 sets comprised of load of 80% 1-RM for 5 seconds and rest for 5 seconds; and Group C subjects completed 5 sets comprised of load of 50% 1-RM for 5 seconds and rest for 5 seconds. Maximum tension and duration of contraction of the orbicularis oris muscle were measured 14 and 28 days after the loading. The results revealed that for orbicularis oris muscle training, 5 sets with load of 80% 1-RM was more effective for improving muscle strength, whereas 20 sets with load of 50% 1-RM was more effective for improving endurance.
