I'm a dentist on paleo diet and I brush and floss once a day. If your diet doesn't have sugar and refined carbohydrates the risk of cavities is minimal. Once a day brushing and flossing along with the improved diet will keep your gums in optimal health.

Many, though not all, toothpastes contain sodium lauryl sulfate (SLS) or another of the sulfate family. SLS is found in other personal care products as well, such as shampoo, and is largely a foaming agent although it also acts as a powerful antimicrobial. For some However, SLS may cause a greater frequency of mouth ulcers in some people as it can dry out the protective layer of oral tissues causing the underlying tissues to become damaged.

Many health food stores and specialty shops will carry SLS Free toothpastes, switching to one of these may help as well.

Are we making our gums more sensitive by brushing our teeth twice a day?

IMO, we are doing a disservice to our dental health by brushing twice a day...if you are eating Paleo. Our gums and teeth weren't designed such that be briskly "cleaned" twice a day. I personally think, if you eat Paleo, you can have great dental health and brush your teeth much less frequently. If you are bathing your mouth in sugars all day i.e. eating SAD -- you are probably better off brushing 2x daily.


and if so, is there any evidence to suggest that eating a paleo diet can help with teeth and gum sensitivity?

I don't know about sensitivity per se. But my experience with myself (n=1) is that eating Paleo has radically improved my dental and gum health.

Former "healthy eating" times (super low fat/tons of fruits aso.) I had always bleeding issues while flossing. My teeth are sensitive from grinding and extremely tender to everything acidic. So eating fruits like apples was no fun and brushing pure torture. This problems were fixed as soon as I went keto. Even switched from soft to middle toothbrush. I think gums benefits especially from fat soluble vitamins A/D/K. As you can see here: http://www.dentalgentlecare.com/new_page_41.htm http://wholehealthsource.blogspot.com/2008/06/more-fat-soluble-vitamin-musing.html
http://www.westonaprice.org/Weston-A.-Price-DDS.html
Most of the recommended micronutrients are widely presented in a primal diet.

Sensitivity: Use SLS-free and glycerin free toothpaste, or mix coconut oil with baking soda. Brush/floss gently. Eliminate sugars (including grains) from the diet. Take COQ10 and K2. Your gums/teeth will be less sensitive.

Twice a day: If our food was the same as in Paleo times, maybe it would be too much. In 2010, I don't know. I'll stick with 2X a day for now.

I know tooth decay is completely preventable and reversible. Good nutrition high in fat soluble vitamins and minerals and removal of sources of simple sugar, lectins and phytates helps a lot.

An emphasis should be put on vitamin D, K2 and A. Weston Price noticed that tooth remineralization didn't happen without adequate vit-D and k2 and that the k2 was necessary to activate the vit-D.

I wrote an article about it here: http://paleodietlifestyle.com/preventing-and-healing-tooth-decay/

My teeth used to hurt and started to become sensitive to cold liquids, but it stopped when cutting sugars. Cutting regular toothpaste has also helped, I now brush once in a while with coconut oil and baking soda.

sidenote: I remember some dental studies showing that things like bread and carbs stuck to your teeth for much longer than sugar /candy did