Tooth Broken at the Gum Line: How Dentists Decide If It Can Be Saved

When a tooth fractures at gum level, what remains looks like very little — a rim of tooth, some gum, and a root that is still firmly in place. The instinctive question is whether something can be built on top of it.

That is the wrong question, and understanding why is the key to the whole situation. Building a crown on a root is technically easy. The difficulty is that the assembly has to survive years of chewing, and whether it does depends almost entirely on a dimension most patients have never heard of.

Picture a wooden axe handle fitted into an iron head. What keeps the head on is not glue in the socket. It is the metal collar gripping the wood around its full circumference.

A crown works the same way. When a post is cemented into a root and a core built on it, the forces of chewing act sideways as well as downwards. A post is very good at resisting downward force and very poor at resisting the sideways wedging that tries to lever it out or split the root. What resists that is the crown extending down past the core and encircling a band of solid tooth structure below it.

That encircling band is the ferrule. Clinical research consistently indicates that roughly one and a half to two millimetres of sound tooth wall, all the way round, is what distinguishes a restoration that performs well over years from one that debonds or splits the root.

So the real question when a tooth breaks at gum level is: is there enough sound tooth remaining, and is it in the right place?

Our article on core build-up requirements for crowns covers what goes underneath, and our article on structural reinforcement of root-treated teeth covers why coverage is needed at all.

Even where sound tooth exists below the gum, the crown margin cannot simply be placed wherever it is found.

Between the top of the bone and the base of the gum sulcus is a band of tissue — connective tissue fibres and junctional epithelium — that attaches the gum to the tooth. It occupies a fairly consistent vertical dimension, historically called the biological width and now more precisely the supracrestal tissue attachment.

This zone is not negotiable. If a crown margin is placed into it, the body responds with persistent inflammation, bleeding, discomfort and eventually bone loss as it recreates the space it requires. The restoration may look correct on the day it is fitted and be causing ongoing damage for years. Our article on biological width and dental crowns covers this, and our article on how crown margin placement affects gum health covers the consequences.

So the requirement is not simply two millimetres of tooth. It is two millimetres of sound tooth for the ferrule, plus the supracrestal attachment zone, plus a small sulcus depth — all above the level of the bone.

That is why a tooth broken level with the gum is frequently not restorable as it stands, even though there appears to be tooth there.

Where the fracture is too deep, the tooth is not automatically lost. There are three approaches, and they trade off against each other.

Gum and a controlled amount of bone are removed around the tooth so that the bone level drops and the required dimensions become available above it.

It is predictable and done in a single procedure with a healing period before the crown is made. The costs are real: the tooth ends up looking longer, the adjacent teeth may need contouring so the gum line stays even, the root becomes partly exposed, and — importantly — removing bone from one tooth necessarily removes it from the neighbours too, because bone is continuous. In the front of the mouth this can be aesthetically significant.

An elastic force is applied to pull the root slowly upwards out of the socket over several weeks. Because the periodontal ligament is under tension, the bone follows the tooth up rather than staying behind, so sound tooth structure is brought above the bone without removing any.

It preserves bone and gum architecture, which makes it the preferred approach in the aesthetic zone. It is slower, requires an attachment to the adjacent teeth, and needs a stabilisation period afterwards to prevent the tooth dropping back. There is also a limit to how far a root can be extruded before it becomes too short in the bone to be stable.

Sometimes neither is appropriate, and this is not a failure of ambition. Extraction is the reasonable route where the fracture extends well down the root, where the root is vertically split, where the remaining root would be too short to support anything after lengthening or extrusion, where root canal treatment has previously failed, or where the outlay of time and money would be better directed at a replacement that will last longer.

Our article on choosing between a crown and extraction covers how that judgement is framed.

• A fracture running vertically down the root, which does not heal and is the most common reason a post-crowned tooth is eventually lost

• Fracture extending several millimetres below the bone level

• Insufficient root length remaining to keep the tooth stable after lengthening or extrusion

• Extensive decay into the root

• Advanced bone loss around the tooth from gum disease

• A root perforation

• A crown-to-root ratio that would leave the crown far longer than the supporting root

The examination establishes how much tooth remains, where the fracture edge sits relative to gum and bone, whether the tooth is mobile, and whether there are signs of infection. Radiographs are essential, because the fracture line and the bone level are below the surface. A cone beam scan may be used where a vertical root fracture is suspected, though these are often only confirmed on direct inspection.

Vitality testing establishes whether the nerve is still alive. Many gum-line fractures involve the pulp, which means root canal treatment is part of the plan if the tooth is to be kept. Our article on root canal treatment through an existing crown covers a related situation.

If the tooth is not restorable, extraction should be discussed alongside the replacement plan rather than as a separate event later — in particular whether the socket should be grafted at the time of extraction to preserve the ridge for a future implant. Our article on alveolar ridge preservation covers this, and our article on deciding between implants, bridges and dentures covers the options.

Do not chew on the tooth. Keep the area clean, gently, including the broken margin — it accumulates plaque readily. Cover a sharp edge with sugar-free gum or orthodontic wax if it is catching the tongue. Take analgesia as needed, and never place a tablet against the gum. If the break happened because a crown came off, keep the crown; it may be refittable. Our article on emergency care for a broken crown covers that.

Seek urgent care if there is facial swelling, fever, or severe pain. Our article on dental abscess symptoms covers the warning signs.

• The deciding factor is the ferrule — roughly one and a half to two millimetres of sound tooth encircled by the crown.

• The supracrestal tissue attachment above the bone cannot be encroached upon by a crown margin.

• Required space is therefore ferrule plus attachment plus sulcus, all above bone level.

• Crown lengthening creates space by lowering the bone; it is predictable but costs bone and aesthetics.

• Orthodontic extrusion brings the tooth and its bone upward; it preserves architecture but takes longer.

• A vertically fractured root, or a fracture well below the bone, generally means the tooth cannot be kept.

A tooth broken at gum level needs assessment promptly, as the exposed structure decays quickly and infection can follow. You can contact our team to arrange an assessment and discuss dental crowns, root canal treatment or dental implants.

This article is provided for general information only and does not constitute dental advice. Whether a fractured tooth can be restored depends on factors that can only be assessed through clinical examination and radiographs, and outcomes vary between individuals. All treatment options carry risks, which will be discussed with you beforehand.

Next review due: 13 August 2027