I salivate a lot at night, and my teeth are whitening unevenly. Are they related, and what should I do?

If whitening trays are soft and flexible, they can feel somewhat bulky and flare out at the gumline (allowing saliva to get in and leave teeth yellow near the gums).  The flaring and bulk can stimulate saliva flow, so superior methods (like the KöR system) will help.  The rigid trays are also much thinner, so more comfortable and they do not allow saliva to infiltrate.

Whitening trays can increase saliva. You may want to try whitening for a couple of hours before bed. The darkness towards the gumline is due to the enamel being thinner there and tooth structure being naturally darker.