Why the jawbone shrinks after tooth loss

The bone depends on the tooth it holds

The bone that holds a tooth behaves differently from the rest of the jaw. A thin layer of fibres sits between the root and the bone, and every time you chew, the force spreads through those fibres into the bone around the root. Bone rebuilds itself according to the load it takes, so that part keeps its shape because a tooth is standing in it.

The first months after an extraction

Once a tooth is out, the socket fills with a clot and, over the following weeks, with new bone. The outer wall of the ridge, the thin plate of bone on the cheek side, is the part that thins the most. That is why the area loses width before it loses height: the ridge grows narrow and sharp along the top.

• The ridge narrows and the gum line sinks inwards.
• Neighbouring teeth tilt into the gap and the tooth in the opposing jaw drifts towards it.
• As the gap widens the bite changes and chewing shifts to the other side.

The change slows down but does not stop

Most of the visible change happens in the first 3–6 months. After that the pace drops, though the ridge keeps changing quietly for years. How much bone goes varies from person to person: how the extraction went, whether the area had been inflamed beforehand, how thick the bone was to begin with and general health all shift the picture.

The bone under a removable denture

A denture does not stand in for a root. It presses on the gum and loads the surface of the bone rather than its inside, so the ridge underneath keeps flattening year after year. In time the denture loosens, moves while you speak and lets food underneath. Needing a reline is often the first sign that the bone under it has changed shape.

Why less bone makes later decisions harder

An implant sits inside the bone and needs a certain width and height to hold. If the ridge has thinned, bone may have to be added first, and at the back of the upper jaw the floor of the sinus may have to be raised. Every extra step means more healing time. An implant planned while the bone is still there usually takes the shorter route.

The hard part about bone loss is that it does not hurt; most people only notice it when a denture stops sitting still.

How the remaining bone is measured

A ridge cannot be judged by looking at the gum. A panoramic X-ray gives the general view, and when the width of the ridge or its distance from the sinus matters, a three dimensional image is taken. The measurement says nothing about how long the gap has been there; it shows how much bone is left today, and the plan follows that figure.

What can slow the change down

Filling the socket with a bone graft at the time of the extraction reduces how much the ridge shrinks. An implant placed in the gap sends chewing force back into the bone and helps to hold the volume at that spot. For anyone wearing a denture, regular checks and a reline at the right time keep it from pressing on one point. Which route suits a particular mouth depends on what is found in it.

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