Dilators used by urologists are called urethral dilators. These dilators are used to increase the size of the urethra to allow insertion of instruments, such as a cystoscope, which is used to visualize the interior of the urinary bladder. The most common style of urethral dilators are called van buren of which there are two basic types like the female style is a straight dilator and the male style is curved at the tip.