A<unk>  or dentist's<unk>  is an instrument in dentistry commonly used in the dental armamentarium. The head of the<unk>  is usually round, and the most common sizes used are the No 4 and No 5. A No. 2 is sometimes used when a smaller<unk>  is needed, such as when working on posterior teeth with a dental dam in place. The<unk>  has a wide range of uses. Three of its most important functions are allowing indirect vision by the dental health care provider, reflecting light onto desired surfaces, and retraction of soft tissues.
Indirect vision is needed in certain locations of the<unk>  where visibility is difficult or impossible.  The posterior (or lingual) surfaces of the anterior maxillary teeth is a notable area where<unk> s are often employed.  Other areas of the<unk>  can be viewed more readily with the<unk> , even though it would be possible to see them if the dentist or dental hygienist adjusted their body into a poor position. Without the<unk> , poor body positioning would occur daily and lead to chronic musculo-skeletal problems, especially of the back and neck.
There are other areas of the<unk>  where lighting is difficult, even with the over head lights used regularly in dental offices. In these instances, the<unk>  is used to reflect light onto those surfaces. This is especially useful if the<unk>  is simultaneously being used for indirect vision of an obscure area.
Additionally, the<unk>  is used to retract tissues, such as the tongue or cheeks, to gain better visualization of the teeth.
Dentist's<unk> s are also commonly used by engineers to allow vision in tight spaces and around corners in equipment. They are a common tool in optics and laser labs as well.
Mouth mirror
Ophthalmoscope
Contact lens
Audiometrist
Optometry
Eyeglass prescription
Visual routine
Ocular prosthesis