Why a bright mirror?
Did you know that a front surface Rhodium mirror reflects 76% of the light but even then, only 58% of the light is reflected back into your eyes?
When using front surface dielectric mirrors the result is far better: 98% of the lamp light is reflected. This is important for a micro dentists, who suffers from extra loss of light, due to the image being transported by plural mirrors.
As shown below, the use of UHR mirrors is extremely efficient. When using UHR mirrors, the luminance of your working field can be significantly less, which decreases your eye fatigue.