These types of injuries are most common in young adult males.Traumatic brachial plexus injuries may arise from several causes, including sports, high-velocity motor vehicle accidents, especially in motorcyclists, but also all-terrain-vehicle (ATV) and other accidents. Injury from a direct blow to the lateral side of the scapula is also possible. The severity of nerve injuries may vary from a mild stretch to the nerve root tearing away from the spinal cord (avulsion). "The brachial plexus may be injured by falls from a height on to the side of the head and shoulder, whereby the nerves of the plexus are violently stretched… The brachial plexus may also be injured by direct violence or gunshot wounds, by violent traction on the arm, or by efforts at reducing a dislocation of the shoulder joint".Brachial plexus lesions can be divided into three types:

An upper brachial plexus lesion, which occurs from excessive lateral neck flexion away from the shoulder. Most commonly, improper use of forceps during delivery or falling on the neck at an angle causes upper plexus lesions leading to Erbs palsy. This type of injury produces a very characteristic sign called Waiters tip deformity due to loss of the lateral rotators of the shoulder, arm flexors, and hand extensor muscles.
Gingival recession, also known as receding gums, is the exposure in the roots of the teeth caused by a loss of gum tissue and/or retraction of the gingival margin from the crown of the teeth. Gum recession is a common problem in adults over the age of 40, but it may also occur starting in adolescence, or around the age of 10. It may exist with or without concomitant decrease in crown-to-root ratio (recession of alveolar bone). Classification
Various classifications have been proposed to classify gingival recession, Miller’s classification system being the one that is most widely followed. Many cases which are encountered in daily clinical practice cannot be classified according to the criteria of the present classification systems. Kumar & Masamattis classification system gives a comprehensive depiction of recession defect that can be used to include cases that cannot be classified according to present classifications. A separate classification system for palatal recessions (PR) has been given. A new comprehensive classification system classifies recession on the basis of the position of interdental papilla and buccal/lingual/palatal recessions. Kumar & Masamattis classification system tries to overcome the limitations of Millers classification. Causes
There are many possible causes for gingival recession:

By far the most common cause is gum disease (periodontal disease). Overaggressive brushing also causes gum recession. One systemic review of the literature concluded that "The data to support or refute the association between tooth brushing and gingival recession are inconclusive," although aggressive or forceful brushing was not specifically addressed.