an armrest for dental chairs and the like can be rotated 90 ° in a horizontal plane about a vertical axis to permit easier entry and exit of a patient to and from the chair . the armrest is automatically locked at either the forward position or the 90 ° position and is unlocked simply by lifting vertically on the armrest . a single set screw for connecting the armrest to the dental chair not only makes the armrest operable but also allows the armrest to be offered as an optional feature of the dental chair .