Brushing Your Teeth

There are several different motions. First, the hand squeezes toothpaste onto the toothbrush. This requires the pronation of the hand, in order to properly orient the toothpaste tube towards the toothbrush. To squeeze the toothpaste out of the tube, this pronation is followed by flexion of the proximal and distal interphalangeal joints. These joints enable movement of the proximal and intermediate phalanges. In flexion, the flexor digitorum profundus, flexor digitorum superficialis, and the flexor pollicis longus are all engaged, creating the strength and grip necessary to squeeze toothpaste out of its tube. These muscles are innervated by the median nerve. After the toothpaste is squeezed out of the tube, the toothbrush is gripped in the hand in the same manner that the toothpaste tube was gripped with.

Next, the arm raises so the toothbrush is near the mouth. This requires the abduction of the arm and forearm, combined with mild elevation of the shoulder and flexion of the forearm at the elbow. The joints involved in this motion are the elbow (consisting of the humeroulnar, humeroradial, and superior radioulnar joints) and the glenohumeral joint. The bones moved by these joints are the radius, ulna, humerus, clavicle, and scapula, along with all of the bones of the hand and wrist. The muscles associated with these movements are the levator scapulae, supraspinatus, deltoid, pectoralis major, coracobrachialis, and biceps brachii. The brachial plexus innervates the entire arm, and the axillary, musculocutaneous, lateral pectoral, suprascapular, and dorsal scapular nerves are the specific nerves that help this motion occur.

Next, the lips open to reveal the teeth. This requires no joint movement or bone movement, but there are several muscles that are engaged in the elevation of the upper lip and depression of the lower lip. These muscles include the depressor labii inferioris, depressor levator labii superioris, zygomaticus (major and minor), orbicularis oris, risorius, and buccinator. These muscles are innervated by the buccal branches of the facial nerve, except for the depressor labii inferioris, which is innervated by the marginal mandibular branch of the facial nerve.

During the promotion of dental health, the actual brushing motion consists of the rapid, repeated extension and flexion of the arm at the shoulder. Although the movement is slight, the glenohumeral joint of the brushing arm controls the motion, engaging the clavicle, scapula, and humerus while also moving the bones of the forearm, hand, and wrist. During this rapid extension and flexion, the muscles engaged include the deltoid, pectoralis major, coracobrachialis, latissimus dorsi, and teres major. These muscles are innervated by the suprascapular, axillary, and lateral pectoral nerves, which are all a part of the brachial plexus.

In order to properly brush children's teeth, the mouth must open in order for the molars and tongue to get cleaned. This requires the abduction of the jaw. This lowering motion is controlled by the temporomandibular joint, which is comprised of two bones: the upper temporal bone, and the mandible. The mandible does most of the work here, and the four muscles of mastication – masseter, medial pterygoid, lateral pterygoid, and temporalis – are all active during the opening of the mouth, which is also assisted by the digastricus muscle. The mastication muscles are innervated by the mandibular branch of the trigeminal nerve, and the digastricus is innervated additionally by the facial nerve. These same joints, bones, muscles, and nerves are all used at the end of brushing one’s teeth, when excess toothpaste is spit back into the sink.

Work Cited

Marieb, Elaine N. Essentials of Human Anatomy & Physiology. 8th ed. San Francisco: Pearson/Benjamin Cummings, 2006. Print.