A few months ago, I wrote an article detailing why it would be necessary for a child to get a space maintainer. A space maintainer is commonly referred to as simply a spacer.
In the picture to the left, you can see how the lower teeth of a six year old child might appear with a missing baby tooth — the first molar. Let’s say that this kid didn’t brush his teeth a lot and ended up needing his first molar extracted because of a large cavity that couldn’t be fixed.
If the dentist simply removed that tooth and sent the child home, that kid’s permanent tooth would probably never come in!
Under normal circumstances, all of the teeth in the mouth exert pressure on each other, which holds them in their proper position. When a tooth is lost, the teeth next to the lost tooth will move into the lost space since the lost tooth can no longer exert its pressure on the adjacent teeth. Also, the teeth above the lost tooth will erupt a little more to fill in the space below.
The picture below shows what happens if a space maintainer is not placed after a baby tooth gets extracted.

Why Teeth Move
Many people wonder why teeth want to move to fill in the gap when a neighboring tooth is extracted. Here’s an analogy to illustrate why teeth move.
Let’s say there’s a giant crowd of people waiting in line for the chance to read the latest article on Oral Answers. Now suppose that one person decides he’s sick and tired of waiting and decides to leave. When he leaves, there is a small opening in the crowd where he used to be excitedly waiting. Does the crowd leave that space open? No! The people that were waiting right next to the space where that guy used to be waiting move to fill it in the empty space that he left behind.
That’s pretty much how it works in the mouth. When there’s an empty space, teeth move to fill it in.
A Space Maintainer Maintains The Old Space
A space maintainer will conserve the space left by the extracted tooth. That way, when the permanent tooth starts to grow into the mouth, there will be lots of room for it to fit in perfectly.
Here’s a space maintainer that I made during my pediatric dentistry lab earlier this year.

Here’s another view:

Conclusion
If a space maintainer is not used, the jaw may never grow to its full potential and consequently it might not have room for all of the permanent teeth, necessitating the removal of some teeth along with orthodontic treatment (braces).
Do you have any questions or comments about space maintainers (spacers)? Leave them in the comments below and I’ll get back with you!