Some front teeth look short or square because extra gum covers part of a normal-length tooth. Aesthetic crown lengthening moves the gum line higher so more of each tooth shows. How well the new gum line holds depends a great deal on the bone underneath it, along with gum thickness and how each person heals. If the bone sits too close to where the new gum edge is placed, the gum can grow back towards the biting edge during healing, so planning starts with measuring the bone, not just the gum.
Short-looking teeth can be fully grown teeth under extra gum
After an adult tooth has come through, the gum edge normally moves back towards the neck of the tooth, where the enamel meets the root. In some people it stops short, and part of the enamel stays covered. In some of these cases the bone also sits higher than usual. Dentists call this altered passive eruption. The tooth itself may be a normal shape and length; it simply is not all on show.
It is one of several reasons gum can look prominent in a smile. In a study of 160 women aged 18 to 40 attending a dental clinic in Egypt, all of whom showed more than 2 mm of gum in a full smile, Amro and colleagues (ScientificWorldJournal, 2026) found altered passive eruption on its own was the most common single cause, at 29.4%, and that 44.3% had more than one cause, such as a short upper lip or a long upper jaw combined with extra gum. Results in other groups of people may differ. That is why a smile assessment looks at the lips, the jaw and the teeth before anyone talks about surgery. Our article on gum display at rest and in a full smile explains the measurements, and the gummy smile guide covers the other causes.
The tissue between the gum edge and the bone
Between the edge of the gum and the top of the bone there is a band of soft tissue attached to the tooth. It used to be called the biologic width. The 2017 World Workshop on the Classification of Periodontal and Peri-Implant Diseases and Conditions replaced that term with supracrestal tissue attachment, and its consensus report (Jepsen and colleagues, Journal of Periodontology, 2018) noted that placing restoration edges into this tissue is associated with inflammation or loss of supporting tissue.
This band is the reason the bone matters in a cosmetic procedure. If gum is trimmed but the bone stays too close to the new gum edge, the gum can creep back over the tooth as it heals. A 2026 article on aesthetic crown lengthening by Essadeq and colleagues (Cureus), which combines a literature review with a single patient case, describes this attachment as approximately 2 to 3 mm. In their case the surgeons reshaped the bone to leave at least 3 mm between the new gum edge and the bone crest.
Where the bone sits guides the type of procedure
A classification published by Coslet, Vanarsdall and Weisgold in 1977 is still widely used to plan treatment for altered passive eruption. It sorts cases by how much firm gum there is and where the bone sits relative to the enamel edge at the neck of the tooth (the cemento-enamel junction).
| Finding | What it means | Usual direction of treatment |
|---|---|---|
| Type I | A wider than normal band of firm gum | Combined with subgroup A or B below to guide the approach |
| Type II | A normal width of firm gum | Combined with subgroup A or B below to guide the approach |
| Subgroup A | Bone crest about 2 to 3 mm below the enamel edge | Repositioning the gum alone may be enough |
| Subgroup B | Bone crest at or near the enamel edge | Bone usually needs reshaping as well as the gum |
The table summarises the classification as described by Essadeq and colleagues (2026). In practice two front teeth can fall into different groups, which leads to the next point.
Measuring tooth by tooth
The bone level cannot be seen from the outside. It is usually checked by gently probing through the numbed gum to the bone (bone sounding), with X-rays, and in selected cases with a 3D scan. In a study of 30 people with altered passive eruption using a soft tissue technique for 3D scans, Gluckman and colleagues (International Journal of Esthetic Dentistry, 2026) measured an average of 4.2 mm from gum edge to bone crest, and found significant differences between matching teeth on the left and right sides. The authors recommended diagnosing and planning on a tooth-by-tooth basis.
The planned gum line is also designed against the face, not just the teeth. Tooth proportions, the smile line and the position of the upper lip all feed into where each new gum edge should sit. Our guides to digital smile design and the trial smile mock-up explain how a proposed shape can be previewed before treatment. Any preview is a guide, not a promised result.
Gums keep moving for months afterwards
Healing is not finished when the stitches come out. Pontoriero and Carnevale (Journal of Periodontology, 2001) followed 30 patients (84 teeth) for 12 months after crown lengthening surgery that included bone removal, done to expose more tooth for fillings or crowns. On average the gum edge moved back towards the biting edge by about 3 mm over the year, and this was more marked in people with thick gum tissue. That study was not about cosmetic cases, but it shows why the gum position is watched over time.
It is also why veneers or crowns planned after crown lengthening are usually made only once the gum line has settled. A systematic review by Nobre and colleagues (Clinical Oral Investigations, 2017) found measurable changes in gum measurements not only at treated teeth but at nearby teeth too, although it included only four case series, all at high risk of bias. Our general guide to crown lengthening covers the day of treatment and the first weeks.
When it is not the answer
Crown lengthening only changes how much tooth the gum covers. It does not change how high the lip lifts or how long the upper jaw is. If extra gum shows mainly because the lip rises a long way, other approaches may be discussed, such as those in our article on lip repositioning. If the teeth are short because they are worn, the plan usually involves rebuilding the teeth rather than only moving the gum.
Questions about aesthetic crown lengthening
Is it the same as gum contouring?
Not always. Gum contouring usually means trimming gum only. Aesthetic crown lengthening may include reshaping bone as well, depending on where the bone sits. Our article on gum contouring describes the gum-only approach.
Will the gum grow back?
It can move during healing, which is why the bone level is measured before treatment and the gum line is reviewed afterwards. In the study by Pontoriero and Carnevale, regrowth over 12 months was greater in thicker gum tissue.
Can it be planned from interstate?
Photos and existing X-rays can be sent first, followed by a video or phone call for an initial discussion, but the bone level usually needs to be measured in person before a plan is final. Our guide to travelling interstate for dental treatment explains how visits are usually arranged.
Talking it through
If your teeth look short or your smile shows more gum than you would like, a free cosmetic consult at Lumi Dental in Melrose Park is a starting point. The dentist can take clinical photographs and, where needed, a 3D X-ray, explain what may be causing the look, and discuss whether gum treatment, tooth treatment or both would be involved and who would carry out each step.
Sources
- Coslet JG, Vanarsdall R, Weisgold A. Diagnosis and classification of delayed passive eruption of the dentogingival junction in the adult. Alpha Omegan. 1977;70(3):24-8. PubMed 276255
- Jepsen S, Caton JG, Albandar JM, et al. Periodontal manifestations of systemic diseases and developmental and acquired conditions: consensus report of workgroup 3 of the 2017 World Workshop. J Periodontol. 2018;89 Suppl 1:S237-S248. PubMed 29926943
- Pontoriero R, Carnevale G. Surgical crown lengthening: a 12-month clinical wound healing study. J Periodontol. 2001;72(7):841-8. PubMed 11495130
- Nobre CM, de Barros Pascoal AL, Albuquerque Souza E, et al. A systematic review and meta-analysis on the effects of crown lengthening on adjacent and non-adjacent sites. Clin Oral Investig. 2017;21(1):7-16. PubMed 27515522
- Essadeq Z, Elhouari B, Kissa J. Esthetic crown lengthening: a case report and literature review. Cureus. 2026;18(8):e113868. PubMed 42688832
- Gluckman H, Rossi R, Moreira Rodrigues D, et al. Soft tissue CBCT for diagnosing and planning treatment of altered passive eruption. Int J Esthet Dent. 2026;21(2):146-162. PubMed 42145243
- Amro LA, Abdalwahab MM, Zazou N, Amr AEH. Prevalence of different etiologies of excessive gingival display: identifying diagnostic patterns. ScientificWorldJournal. 2026;2026:8869911. PubMed 41767215
This article is general information only and is not a substitute for advice about your own situation from a dentist.
