A gap in teeth can be an embarrassing cosmetic feature to have. There are many different ways to close gaps in teeth. The methods of correction depend upon the individual, his or her budget, other teeth and jaw problems, and the pain or embarrassment he or she is willing to undergo in order to correct the problem.
A veneer is a common solution, especially for those who cannot afford braces. Usually they are made out of porcelain and require little in terms of an installation process. The fit directly over the tooth and cap it. These can be used exactly the same way as regular teeth--they will not fall out or be able to be removed easily. You can chew with the perfectly fine.
The one major draw-back is that if the gap is extremely large, they would look funny. Because they cap your teeth, the veneers would have to be big enough to cover your whole tooth and cover the space in between your teeth. This can give people the appearance of having huge front teeth.
A better option for huge gaps would be to wear a manner of braces or orthodontic devices. Braces can be expensive and embarrassing for adults to wear. They are the most effective, though, and can sort out a great number of dental problems. They will slowly push your teeth together over a long-enough period to make the roots settle in those locations and stay there.
For adults who dislike the idea of pubescent looking braces, they can get clear ones that may take a little longer to close the gap. They will not be quite as noticeable. There are also ones available that connect to the back of your teeth instead of the front.
There are also plenty of retainers to use. Retainers are taken from molds of your teeth and are slightly adjusted to sit tightly on your teeth. The retainer will get more comfortable as your teeth shift. Many people just wear retainers at night and take them out in the morning. Retainers, because they are not fixed structures like braces, will have to be worn indefinitely.
There are also clear aligners that fit over teeth. They are essentially the same as retainers, only they deal less with your jaw and roof of your mouth and more directly with the teeth. You would leave them on all the time, since they are completely transparent and would not be noticed. After a while, when the teeth have shifted, you would get an updated one that would further tighten and shift things in your mouth.
One should not be overly hasty to close up gaps in teeth. This is especially true for children. Children's teeth will shift drastically on their own as they grow. It may be a waste of money and a lot of unnecessary pain for the child if his or her teeth are going to close up anyway. You may also want to check with an orthodontist for further problems before you start trying to move things around.