THE SCIENTIFIC JOURNAL
Broken or Decayed Below the Gum: Does the Tooth Have to Come Out?
By Dr. Khalid Aletaibi11 min readQUICK ANSWER
Not necessarily. A tooth broken off at the gum line, or decay running below it, is harder to restore, but harder and hopeless are different things. What decides it is how far the defect sits relative to the bone, how much sound tooth remains around it, and whether the margin can be brought back up to where a restoration can be sealed and cleaned. Two established techniques, deep margin elevation and selective crown lengthening, exist precisely to make otherwise awkward teeth restorable.
Why a margin below the gum gets a tooth written off
Three practical problems arrive at once when a margin drops below the gum, and it is worth being precise about which of them are real constraints and which are simply difficult.
The first is access. Bonding needs a dry, clean, isolated field, and a margin sitting in a sulcus that bleeds when touched is the opposite of that. Rubber dam isolation, together with tissue retraction where it is needed, is what turns that field back into a workable one.
The second is the impression or scan. You cannot record a margin you cannot see. Once the field is isolated and dry, a modern intraoral scanner will capture a margin that a conventional impression would have missed.
Those two are questions of technique and equipment. They are demanding, and they take longer than working on a straightforward tooth, but they are solvable, and a tooth is not hopeless because a step is inconvenient.
The third is different, because no amount of technique removes it. Around every tooth sits a band of soft tissue attached to the root above the bone. The 2017 World Workshop renamed it the supracrestal tissue attachment, retiring the older term biologic width [3]. Placing a restoration margin inside that band is associated with inflammation and loss of supporting tissue [3].
So of the three reasons a tooth gets written off at this point, two are surmountable and one is a genuine biological limit. Which is why everything now turns on a measurement.
The measurement that actually decides it
Here is where the usual rule of thumb goes wrong.
Most of us were taught that the attachment is about 2 mm, so leave 3 mm between the margin and the bone. It is a tidy number, and the evidence does not support it as a universal rule.
A systematic review that screened 615 papers and meta-analysed six found mean values between 2.15 and 2.30 mm, but an individual range of 0.2 mm to 6.73 mm, and concluded that no universal dimension appears to exist [1]. A separate clinical study measured a mean of 3.98 mm, significantly greater than the classic histologic figure [2].
The same review recorded a smallest individual value of 0.2 mm. The spread, not the average, is the clinically useful finding.
Two consequences follow, and they point in opposite directions.
In a mouth at the low end of that range, a margin placed 2 mm below the gum can end up level with the bone or beneath it, and no amount of careful restorative work will settle that tooth down.
In a mouth at the high end, the same margin leaves several millimetres of attachment untouched, and a tooth that looked doomed is entirely restorable.
There is a further wrinkle. In that clinical study, the sites with the shallowest probing depths had the greatest attachment, meaning they stand to lose the most if bone is removed [2]. The tooth that looks easiest to operate on can be the one that pays most for it.
This is why measurement comes before a verdict, and why a proper examination with radiographs is not a formality.
Deep margin elevation: raising the margin instead of cutting the gum down
Deep margin elevation, also called cervical margin relocation, does something simple. Under rubber dam, a carefully placed layer of composite is bonded into the deepest part of the box, lifting the margin from below the gum to a level that can be isolated, scanned and sealed. The definitive onlay or partial-coverage restoration is then bonded on top of that new margin, using the same adhesive technique the rest of the tooth depends on.
It turns a problem below the gum line into one above it by adding material rather than removing tissue.
That reversal is the whole of the conservative case, and it is the principle behind biomimetic and minimally invasive restorative work: the tooth you were born with outperforms anything built to replace it, so the aim is to remove as little of it, and as little of what holds it in, as the job actually requires.
What the evidence says, including the unsettled parts. A systematic review of ten clinical studies, followed between six months and twelve years, found pocket depths and bleeding within normal limits in every treated tooth and no deleterious effect on pulp or periodontium, while rating its own level of evidence as low [4]. A more recent meta-analysis found the technique did not adversely affect periodontal outcomes in periodontally healthy or stabilised patients [5].
A third review is the useful one, because it found where the technique runs out of room: bleeding on probing increased when the distance between the restorative margin and the bone was under roughly 2 mm [6]. That review concluded the overall periodontal impact remains inconclusive.
Read together, those three say something precise. Elevation works, in the right tooth, with enough distance to the bone, done under isolation. It is not a way to ignore the anatomy.
| Deep margin elevation | Surgical crown lengthening | |
|---|---|---|
| What it does | Adds bonded material to raise the margin | Removes tissue and bone to expose sound margin |
| Tooth structure removed | None | None from the crown |
| Supporting bone | Untouched | Reduced |
| Practically reversible | Yes | No |
| Waiting time before the final restoration | None | Weeks to months |
| Suits | A defect shallow enough to reach and isolate | A defect at or below the bone |
When crown lengthening is the right answer
Sometimes the defect really is too deep to elevate, and the honest move is to reposition the tissue rather than pretend otherwise.
Crown lengthening removes a small, planned amount of gum and bone so that sound tooth structure sits above the attachment again, with room for a restoration that can be kept clean. Done selectively, on the surfaces that need it rather than all the way around, it gives up a little support and keeps the whole tooth. Most people would take that trade over losing it.
The two techniques are less rivals than different answers to different depths, and the distinction between them is the additive one against the subtractive one. The authors who set them side by side framed it in exactly those terms, arguing that crown lengthening remains a valuable procedure while predicting that its indications should narrow over time as additive techniques become better understood [7].
A third route is worth knowing about: slow orthodontic extrusion, in which the tooth is drawn gently upward over weeks so the sound margin comes with it. It takes longer and needs planning alongside an orthodontic colleague, but it can bring a margin within reach without removing any bone at all.
What happens at the visit
- 1
Map the defect
Radiographs and direct inspection establish how far the decay or fracture extends and where the bone sits.
- 2
Assess what is left
How much sound wall remains matters as much as how deep the defect goes.
- 3
Clean out and look
Decay is removed under isolation. Only then is the true margin visible.
- 4
Choose the route
Elevate, lengthen, extrude, or occasionally accept that the tooth cannot be kept.
- 5
Rebuild the margin
If elevating, composite is bonded into the base of the box under rubber dam.
- 6
Restore and review
A bonded restoration is fitted, and the gum around it is monitored over time.
When the tooth genuinely cannot be kept
Being conservative is not the same as being unrealistic.
A vertical root fracture cannot be repaired, and no elevation technique changes that. Neither does decay that has tracked so far down the root that nothing sound remains to bond to, nor a tooth whose remaining structure will not carry a restoration under load.
That last point deserves a caveat, because it gets overstated. The surrounding band of remaining wall, the ferrule, does help. But an in-vitro meta-analysis of seventeen studies found that a partial ferrule, which is what you have when a defect destroys one wall and leaves the others, gave substantially better fracture resistance than no ferrule at all, and remains a viable option where a complete one cannot be achieved [8]. Laboratory conditions are not mouths, and that limitation is real. Even so, the absence of a ferrule all the way around is not on its own a reason to remove a tooth.
When a tooth truly cannot be kept, planning the replacement properly, whether an implant or another option, is the right work rather than a consolation.
If you have been told the tooth has to come out
Ask what the alternative would involve before agreeing to the extraction, and bring the radiographs, or ask for copies. They are your records.
Three questions are worth asking directly: how far the defect extends relative to the bone, how much sound tooth is left, and whether the margin could be elevated or the tissue repositioned instead.
A second opinion on a treatment plan is a reasonable step before anything irreversible, and an extraction is as irreversible as dentistry gets.
COMMON QUESTIONS
What patients ask most.
- I was told the cavity is below the gum and the tooth has to come out. Is that always true?
- No. It depends on how far below, how much sound tooth remains, and where the bone sits relative to the defect. Some subgingival margins can be raised with bonded composite, others need a small amount of tissue repositioned. Extraction is the answer for some of these teeth, not all of them.
- Is deep margin elevation safe for the gum?
- Published clinical studies followed between six months and twelve years found pocket depths and bleeding within normal limits and no harmful effect on the surrounding tissue, though the authors rate the strength of that evidence as low [^4]. One review found more bleeding when the margin sat within about 2 mm of the bone, which is precisely the situation where elevation is the wrong choice [^6].
- Does crown lengthening damage the tooth?
- It removes no tooth structure. It removes a planned amount of gum and bone so a restoration margin sits above the attachment. What it gives up is a little support around that tooth, weighed against keeping it at all.
- Is crown lengthening painful, and how long before the tooth is finished?
- It is done under local anaesthetic, so the procedure itself is not painful. The gum is tender for a few days afterwards, and the tissue then needs weeks to settle before the margin position is stable enough for a final impression. That waiting period is the main practical difference from elevating the margin, which needs no healing time at all.
- Why might two assessments of the same tooth reach different conclusions?
- Often because the defect was measured differently, or because the amount of attachment varies enormously between people. Recorded values range from 0.2 mm to 6.73 mm, so two teeth that look alike can genuinely warrant different treatment [^1].
- My molar broke off at the gum line. Is that different from decay under the gum?
- The same three questions decide it, but a fracture adds one more: whether the crack runs down the root. A crack confined to the crown often leaves a restorable tooth, while one extending vertically down the root does not, and no elevation technique changes that.
- Should I just have an implant instead?
- An implant is a good answer for a tooth that genuinely cannot be kept, and a poor answer for one that can. A natural tooth keeps its own attachment, its own ligament, and the bone that ligament maintains, none of which an implant reproduces. So the order matters: establish whether the tooth is restorable first, and plan a replacement only once it is not.
- How long does the tooth last afterwards?
- Studies of elevated margins report follow-up out to twelve years with the surrounding tissue healthy [^4]. As with any restoration, that depends on the quality of the seal, the bite, and how it is maintained.