Mirrors used for intraoral photography are not all the same. There are several kinds of mirrors. Standard metal mirrors reflect 55-60% of light. Chromium coated mirrors reflect 65-70% of light and rhodium coated mirrors reflect 75% of light. The manufacturer of the mirror that I use claims that this mirror reflects 99.5% visible light. This increased light reflection is also due to the flatness of the mirror. I usually use a standard mirror, but when want a good photograph, I'll pull out a rhodium coated mirror.
Here is a standard mirror.
This is the exact same photograph using a rhodium plated mirror.
When taking intraoral photographs, the quality of the mirror can make a big difference in the quality of your images.