Crown lengthening: gum and bone reshaping before crowns

Two very different people end up hearing the words "crown lengthening". One has a back tooth that has broken off at the gum line, and the dentist cannot get a crown to sit on it. The other has a gummy smile, with front teeth that look short and square, and wants crowns or veneers to fix it. In both cases the issue is the same: not enough tooth is showing above the gum. Crown lengthening deals with that by moving the gum, and sometimes the bone, rather than adding more to the tooth.

What crown lengthening is

Crown lengthening is a periodontal (gum) procedure. Depending on the case, it may involve:

• Gingivectomy or gingivoplasty: trimming and reshaping excess gum when there is plenty of space between the gum edge and the bone.
• An apically positioned flap: lifting the gum, moving it to a new, lower position on the tooth and stitching it there.
• Bone reshaping (osseous resection): removing a small amount of bone around the tooth so the gum has room to heal at its new level.

A review in the Journal of the American Dental Association describes all three as standard crown-lengthening techniques, used either to make restorative treatment possible or for appearance (Hempton and Dominici, 2010).

Why the bone matters: the space the gum needs

Between the edge of the gum and the bone, the body keeps a band of soft tissue that attaches to the tooth. It used to be called the "biologic width" and is now often called the supracrestal tissue attachment. If a crown edge is pushed down into that band, the gum often becomes inflamed, bleeds or shrinks back. A review of how gums interact with crown edges discusses this and explains that crown lengthening is one way to make room for a healthy margin (Padbury, Eber and Wang, 2003).

So for a tooth broken below the gum, simply cutting the gum back is often not enough. The bone may need to be moved too, so that the crown edge can sit on sound tooth with the soft tissue band intact above the bone. Our article on crown margins explains why the position of the crown edge matters.

Reason one: a tooth broken or decayed below the gum

For a crown to hold and seal, it needs sound tooth all the way round its base. On root-filled teeth this collar is called the ferrule, and a literature review concluded that 1.5 to 2 mm of it improves resistance to fracture (Juloski and colleagues, 2012). If decay or a fracture runs below the gum, there may be no sound tooth to give that collar. Crown lengthening can expose more, so the crown has something to grip.

It is not always the best answer. Removing bone around one tooth can affect the neighbours, shorten the root support and leave a gap or a longer-looking tooth. The same review suggested that, in teeth with no structure above the gum, pulling the tooth up with orthodontics (orthodontic extrusion) should be considered before surgery. Sometimes the honest conclusion is that the tooth is too short in the root to be worth saving. Our article on root-filled teeth, posts and crowns covers how those decisions are made.

Reason two: a gummy smile

A gummy smile, or excessive gingival display, has several possible causes, and the cause decides the treatment. A recent review identified two main soft-tissue causes: altered passive eruption, where the gum and sometimes bone never moved back to their usual position as the teeth came in, and a hypermobile upper lip, which lifts higher than usual when you smile (Tatakis and Silva, 2023). Other causes include the upper jaw itself being long and teeth that are worn short.

For altered passive eruption, aesthetic crown lengthening is the established surgical treatment, according to the same review. Another review describes the aim as restoring the normal relationship between the gum edge, the bone and the junction where enamel meets root, which helps appearance and may help gum health too (Mele and colleagues, 2018). For a hypermobile lip, lip repositioning surgery is the established option, and crown lengthening would not solve it.

Why crowns alone can make a gummy smile worse

If your teeth are normal size but the gum covers part of them, crowning them will not show more tooth. It may give you crowns that look square and short, or tempt a dentist to make them longer at the biting edge, which can look odd and affect your bite. Getting the cause right first is what makes the difference between a natural result and an awkward one. For a full smile plan, see full-mouth crowns.

Healing: the gum comes back up

This is the part that most affects timing, especially if you are planning treatment abroad. After crown lengthening, the gum does not stay exactly where it was placed. A 12-month study of 84 teeth found that surgery gained an average of about 3.7 to 4.1 mm of tooth length, but as healing went on, the gum grew back up by around 3 mm. By 12 months the extra exposed tooth had fallen to about 0.5 mm between teeth and 1.2 mm on the cheek and tongue sides (Pontoriero and Carnevale, 2001).

The JADA review summarised wound-healing research in similar terms: about 3 mm of soft tissue rebounds above the bone, taking at least three months, and it advised waiting at least three months, and possibly up to six months in visible areas, before final crowns (Hempton and Dominici, 2010).

In practice, that usually means crown lengthening and final front crowns are not done in the same short trip. Temporary crowns can cover the gap while the gum settles. Our page on the crown trip explains how a standard crown visit runs; treatment that includes gum surgery normally needs extra planning.

Other ways to show more tooth

Crown lengthening is one tool among several, and the right one depends on the cause. If the teeth are worn short from grinding or erosion, length is often added at the biting edge with bonding, veneers or crowns rather than taken away at the gum. If the upper lip lifts unusually high, the lip is the issue, and lip repositioning is the established treatment for that according to the review mentioned above. If the upper jaw itself is long, the gum line may look excessive even with normal teeth and normal gums, and the options are more limited.

Often there is more than one cause in the same smile, for example slightly short teeth together with some extra gum. A good plan explains which part each treatment is fixing, so you know what to expect from each step. Photos of your smile at rest and in a full smile help a dentist start that diagnosis, but an examination and X-rays are needed to see where the bone sits.

Is it right for you?

• If a tooth is broken below the gum, ask whether crown lengthening, orthodontic extrusion or an implant gives the best long-term result for that tooth.
• If your smile looks gummy, ask what is causing it: tooth size, gum position, lip movement or jaw length.
• Ask how long you would need to wait after surgery before final crowns.
• Ask what the neighbouring teeth and gums will look like afterwards.

Any decay or infection is treated before crowns, and crown lengthening is planned only when the cause has been diagnosed. Ask us whether it is right for you; send photos of your smile, relaxed and smiling widely, plus any recent X-rays through our contact page, and we will reply with a free written plan that says what we recommend.

Common questions

Is crown lengthening painful?

It is done under local anaesthetic, so you should feel pressure rather than pain during it. Afterwards the gums are sore for some days. Your dentist or periodontist will give aftercare instructions.

Can I have crown lengthening and crowns on the same trip?

Usually not for final crowns in the smile zone, because the gum keeps changing for at least three months. Temporary crowns are often used during healing, then final crowns are made once the gum has settled.

Will my gummy smile be fixed with crowns alone?

Only if the cause is short or worn teeth. If the gum is covering normal-sized teeth, crowns alone would just make long teeth sit under long gum. The cause has to be diagnosed first.

Is there an alternative to surgery for a broken tooth below the gum?

Sometimes the tooth can be pulled up slightly with orthodontics, called orthodontic extrusion. In other cases the tooth is not worth saving and an implant is better. It depends on the root and the bone.

Do you do crown lengthening?

Ask us whether it is right for you. Your free written plan says what we recommend, including if gum treatment is needed before crowns.

Sources

1. Hempton TJ, Dominici JT (2010). Contemporary crown-lengthening therapy: a review. J Am Dent Assoc
2. Pontoriero R, Carnevale G (2001). Surgical crown lengthening: a 12-month clinical wound healing study. J Periodontol
3. Padbury A Jr, Eber R, Wang HL (2003). Interactions between the gingiva and the margin of restorations. J Clin Periodontol
4. Tatakis DN, Silva CO (2023). Contemporary treatment techniques for excessive gingival display caused by altered passive eruption or lip hypermobility. J Dent
5. Mele M et al. (2018). Esthetic treatment of altered passive eruption. Periodontol 2000
6. Juloski J et al. (2012). Ferrule effect: a literature review. J Endod

Checked October 2026. Where we give our own view as a clinic, we say so.