WHY REPLACE A MISSING BACK TOOTH?
 

If you fail to replace an extracted back tooth with a false tooth, you could
lose all of your teeth.  This article explains how.

This article contains general principles.  There are individual exceptions.

ANATOMY

Each tooth consists of two parts: the crown and the root(s).
Only the crown is visible in the mouth.  The roots are in the bone,
under the gums.
The gums are a protective type of skin that clings to the necks of the teeth
and covers the bone holding the teeth.
Molars are back teeth.  They have two or three roots.  Most other teeth have
one root.

LOSING TEETH "TWO-FOR-ONE"
 

Recent extraction of a lower molar has created space X.  
Upper tooth 6 is now useless because it no longer has a tooth to chew against. Therefore, losing one tooth can result in the loss of the use of two. Losing two teeth can result in the loss of the use of four, and so on.

A Series Of Problems Begins
 

OVERERUPTION

Back teeth have a tendency to erupt (move farther into the mouth).  Only the
presence of a tooth to chew against keeps a back tooth from overerupting.
This patient had a tooth extracted from space X.  Upper 6 has overerupted.
The resulting unevenness among the upper back teeth has created areas between these teeth that trap debris.  It is difficult to keep spaces between uneven teeth clean, despite your best efforts at brushing and flossing.
Unclean teeth usually cause inflammation of the surrounding gums.  They 
decay more readily too.

Lower molar 7 is jammimg food in between overerupted 6 and 7 during 
eating(arrow).
This pressure between upper 6 and 7 has caused upper 7 to move backward and separate slightly from upper 6.  It has created a space between these 
teeth(arrow). 
Food can pack into this space with great force during chewing.  This creates
a serious inflammation of the gum.
Note that overeruption of upper 6 has caused some of its root to become 
exposed.  Exposed root decays faster than the crown of a tooth, as we will see later.

TILT AND DRIFT

Back teeth have a lifetime tendency to tilt (lean over) towards the front 
of the mouth.  They also have the potential to drift (move) towards the front
of the mouth. Now that a tooth has been extracted from position X, a space is left.  This allows lower molar 7 to tilt and drift forward.
Lower 7 will tilt farther and farther over as you chew on it.

GUM POCKET FORMATION

A tooth tilted over will develop a gum pocket along its forward root, as shown
here.
Gum pockets are narrow, abnormal spaces or clefts that develop between the 
gums and the tooth root.  These pockets trap food debris and bacteria.
A gum pocket is a problem because you can never keep it clean, even with 
the best brushing and flossing.
The debris and bacteria that collect in a pocket lead to ever-worsening 
inflammation of the gums adjacent to the pocket.

LOSS OF BONE SUPPORTING THE TOOTH

When an area of the gums is constantly inflamed, as you see in this gum 
pocket, the bone immediately adjacent to it can become inflamed too.  Inflamed bone softens, and slowly begins to disappear.
This process of gum inflammation and loss of the bone holding a tooth is 
called Periodontal Diease.

DESTRUCTION SPREADS

Lower molar 7 has drifted and tilted so far forward that upper 7 no longer
bites on it. This allows upper 7 to overerupt too with advancing gum pockets, gum inflammation, and bone loss.
Decay has begun on upper teeth 6 and 7 , particularly on the exposed portion
of the roots of 6 and 7.  Exposed roots are especially prone to decay.
Both upper molars are deeply decayed.  Decay has also started on lower 7.
Periodontal disease -- gum pockets, gum inflammation, and loss of bone --
continues to worsen.

Deep decay has allowed bacteria to enter and infect the pulps ("nerves")
of upper 6 and 7.  These two teeth have abscessed (become seriously infected).
They are so badly damaged by decay that they must be extracted.
Because of inflammation from the gum pocket of lower 7, bone loss (outlined 
by arrows) has spread around the front root of this tooth and extended to part
of the back root too.  This tooth has lost so much bone support that it is now
loose and must be extracted.

Because all the molars on this side of the mouth have been removed, the upper and lower 5's have no support behind them and are forced backwards by the action of chewing .
Food jams between the separated teeth (arrows).  Gum inflammation has begun.  Gum pockets will follow, along with bone loss and decay.  Eventually the 5's will have to be extracted.
After the loss of the upper and lower 5s, the destructive process can move
farther forward.  The front teeth will start to spread apart, gum pockets will
form, decay begin.
Now the front teeth may be lost as well.

CONCLUSION

Failure to replace a single molar tooth may start a chain of events:
Overeruption, tilting, drifting, gum pockets, decay, bone loss. 
Over the years this chain of events can lead to the loss of all of your teeth.
Inserting a false tooth today will avoid grief and much greater expense
in the future.