2 is sometimes used when a smaller mirror is needed, such as when working on back teeth with a dental dam in place.
Three of its most important functions are allowing indirect vision by the dentist, reflecting light onto desired surfaces, and retraction of soft tissues.
The posterior (or lingual) surfaces of the anterior maxillary teeth is a notable area where mouth mirrors are often used.
Without the mouth mirror, poor body positioning would occur daily and lead to chronic postural problems, especially in the back and neck.
Dentist's mirrors are also commonly used by engineers to allow vision in tight spaces and around corners in equipment.