The adducted vocal folds do not close completely but instead remain partially open. The narrow opening between the folds is referred to as the glottis. As air moves through the glottis, it causes a distortion of the air particles which sets the vocal folds into vibratory motion. It is this vibratory motion that produces phonation or voice. In dysphonia, there is an impairment in the ability to produce an appropriate level of phonation. More specifically, it results from an impairment in vocal fold vibration or the nerve supply of the larynx. Diagnosis
The assessment and diagnosis of a dysphonic voice is completed by a multidisciplinary team, such as an otolaryngologist (ear, nose and throat doctor) and Speech-Language Pathologist, involving the use of both objective and subjective measures to evaluate the quality of the voice as well as the condition of the vocal fold tissue and vibration patterns. Definition
Dysphonia is a broad clinical term which refers to abnormal functioning of the voice. More specifically, a voice can be classified as "dysphonic" when there are abnormalities or impairments in one or more of the following parameters of voice: pitch, loudness, quality, and variability. For example, abnormal pitch can be characterized by a voice that is too high or low whereas abnormal loudness can be characterized by a voice that is too quiet or loud. Similarly, a voice that has frequent, inappropriate breaks characterizes abnormal quality while a voice that is monotone (i.e., very flat) or inappropriately fluctuates characterizes abnormal variability.
These causes can range from vocal abuse and misuse to systemic diseases. Causes of dysphonia can be divided into five basic categories, although overlap may occur between categories. (Note that this list is not exhaustive):

Employment
It has been suggested that certain occupational groups may be at increased risk of developing dysphonia due to the excessive or intense vocal demands of their work. Research on this topic has primarily focused on teachers and singers, although some studies have examined other groups of heavy voice users (e.g. actors, cheerleaders, aerobic instructors, etc.). At present, it is known that teachers and singers are likely to report dysphonia. Moreover, physical education teachers, teachers in noisy environments, and those who habitually use a loud speaking voice are at increased risk. The term clergymans throat or dysphonia clericorum was previously used for painful dysphonia associated with public speaking, particularly among preachers. However, the exact prevalence rates for occupational voice users are unclear, as individual studies have varied widely in the methodologies used to obtain data (e.g. employing different operational definitions for "singer"). Mechanism
Located in the anterior portion of the neck is the larynx (also known as the voice box), a structure made up of several supporting cartilages and ligaments, which houses the vocal folds. In normal voice production, exhaled air moves out of the lungs and passes upward through the vocal tract. At the level of the larynx, the exhaled air causes the vocal folds to move toward the midline of the tract (a process called adduction).