I ned serious dental work. What can I eat /take in order to maintain my weight.?

Protein shakes. If you go to the grocery store or a nutritional supplements store, you can ask for protein shakes or meal replacement shakes. They contain the nutrients usually found in an average meal and can provide the needed nutritional requirements that would otherwise be difficult to obtain via regular food.
Liquid or soft foods. Of course getting your teeth fixed if possible would be a good start, but i'll bet you are aware of that. Getting calories in when teeth are bad is a challenge. Healthy foods that are liquid or soft and have substantial calories are best; yogurt, fruit sauces, bananas, soups, soft breads - you just have to try and see what works for you. Protein shakes like ensure can also help.