A patient showing inability to close the right corner of the mouth is most probably suffering from:
Myasthenia gravis
Bell's palsy
TMJ dysfunction syndrome
Multiple sclerosis
Bell's palsy is manifested by drooping of corner of mouth, drooling of saliva, watering of eye, inability to blink the eye. The patient has a typical mask-like or expressionless appearance. The patient will have speech diﬃculty and occasionally the taste sensation to anterior portion of tongue is lost or altered.
In supranuclear lesions of facial nerve, only the lower part of the face is paralysed. The upper part (frontalis and part of orbicularis oculi) escapes due to bilateral representation in the cerebral cortex.
In infranuclear lesions of facial nerve (Bell's palsy) half of the whole of face is paralysed. The face becomes asymmetrical, and any attempt to smile draws the mouth to the NORMAL SIDE.