A missing tooth/teeth, are routinely replaced by means of a "bridge" which spans across the two adjacent teeth on either side of the gap attaching what is called a "pontic" to fill the void of the lost tooth. This procedure is commonly done, and can be effective for years.
The challenge of this procedure is the need to cut into/prepare the adjacent teeth to fit a crown on either sides of the gap. Although this treatment option can last up to a decade, eventually the crowns may require replacement due to decay of the underlying teeth.
Cleaning under a bridge can also be a challenge leading to the need for replacement after some years. An implant on the other hand, is a titanium pin/post placed in the site of the missing tooth and subsequently crowned with a ceramic/porcelain crown which essentially replaces the missing tooth. It does not require any preparation of the adjacent teeth and it is cleaned and flossed as a normal tooth.
It is important to note that after a tooth has been extracted, the bone will decrease in volume and density with time, therefore it is important to replace the tooth as soon as possible.
The consequences of losing teeth can result in many other problems in the mouth which include: movement of the adjacent teeth into the gap, and over-eruption/growth of the opposing tooth; increased function/loading of the adjacent teeth which accelerates the deterioration of those teeth; loss of bone where the tooth was which may mean requiring a bone graft later when wanting to replace the tooth with an implant.
