When a patient presents with a missing tooth, the best two options are usually a bridge or an implant. A bridge is when you use the teeth next to the missing tooth to support a prosthetic tooth. A bridge is essentially three crowns fused together and it is permanently cemented—it is not a removable device. An implant is simply a titanium cylinder that is placed in the bone where the missing tooth used to be. On top of that cylinder, a crown (prosthetic tooth) is attached.
All things being equal, an implant is usually a better option than a bridge. They tend to last a little longer, and there is no need to shave natural tooth structure down. The advantages of a bridge are usually related to cost, and the speed in which the procedure can be finished. Whereas an implant may take months to finish, a bridge can usually be done in two weeks.
Often, a bridge is actually a better option than an implant. If the teeth next to the space are ugly and need crowns anyway to make them look better, then a bridge is preferred. If the patient has a medical issue like diabetes that would make implants a poor option, then a bridge is preferred. If the space created by the missing tooth is too narrow or too wide to create proper symmetry, then a bridge could more easily mask the asymmetry.
In some situations, implants are clearly the better option over bridges. If the teeth next to the space are not strong enough (due to bone loss, large existing fillings, or decay), then a bridge is not a good option. Putting the extra weight of a missing tooth on adjacent teeth that are already compromised is not a good idea.
In summary, implants are usually better than bridges…but not all the time! You should always ask your dentist why he/she has decided on an implant or a bridge for your mouth.