Interproximal reduction (IPR) / Teeth stripping (shaving). -

What is it? Case applications. | How is the procedure performed? How much enamel is trimmed off? Does it hurt? | Procedure timing (with Invisalign® vs. conventional braces.) | Risks and side effects. | Illustrations and pictures.

Picture showing lower front teeth that have had interproximal reduction (IPR) performed.

Stripping teeth creates room for realigning them.

What is teeth stripping / interproximal reduction?

"Stripping" (teeth shaving) refers to a procedure where your dentist trims a small thickness of tooth enamel from the sides of selected teeth (at that point where they would normally touch against each other if in regular alignment).

What is accomplished?

The purpose of this procedure is to narrow the width of the teeth, so there is available space in which to orthodontically realign them.

Other terms.

Equivalent terms used to refer to this process include teeth shaving, interdental reduction, interproximal reduction (IPR) and, most precisely, interproximal enamel reduction.

With this last term, the word enamel is included in the phrase as an indication that the trimming is confined to just the enamel layer of a tooth. As we explain below on this page, this is an important stipulation for this procedure.


We've subdivided our coverage of this subject into the following topics.

 


When is interproximal reduction technique used?

There are a number of applications where just slicing a minute portion of several individual teeth off can cumulatively provide all of the room that's needed for a person's planned orthodontic work.

Your dentist should be able to tell you if they expect that IPR will be needed before your treatment is begun.

Applications for teeth shaving.

a) Correction of tooth crowding.

Probably the most-used application for IPR is the obvious one. It's used as a part of the treatment plan in correcting cases involving tooth-crowding issues (crooked and otherwise misaligned teeth).

Animation showing how crowded teeth can be stripped (reduced in width) and then realigned.

The teeth are first stripped (narrowed), then realigned.

The plan.
Interproximal reduction is first performed to create the additional space that the case requires.

Then, some type of orthodontic appliance (conventional braces, Invisalign® aligner, etc...) is used to reposition and correct the alignment of the teeth. (See animation.)

Types of cases.
  • When tooth stripping can provide enough space, it might be used with a person's initial/original orthodontic treatment.
  • This technique is often ideally suited for correcting orthodontic relapse that has occurred with a patient's lower front teeth following their original treatment. (Like when a person has not worn their retainers as directed.)

 

b) Tooth size and teeth length discrepancies.

The corresponding teeth on a person's left and right sides are usually mirrored images of each other. In cases where they're not, the size discrepancy that exists between matching tooth pairs can interfere with producing an acceptable treatment outcome.

Additionally, the combined length of a person's upper and lower teeth must be of comparable proportions. If one is substantially larger than the other, producing an acceptable orthodontic outcome may not be possible.

Using interproximal reduction to file down the width of individual teeth to more normal and expected dimensions can resolve these issues.

c) Black triangle reduction.

Due to the (normal, natural) shape of their teeth, some people's smiles show "black triangles" (spaces between their teeth that are not filled with gum tissue). This appearance is often caused by or amplified by gum recession that has occurred.

By filing down and flattening out the contact point of the teeth and then realigning them, these spaces can be closed in to some degree.

d) An aid in making other alignment improvements.

Interproximal reduction can sometimes be used with treatment plans that attempt to camouflage (not fully correcting but only improving the appearance of) some dental abnormalities. Although, using this type of approach isn't always appropriate.

a) Overjet correction.

Overjet refers to the situation where a person's upper teeth protrude forward (their lower teeth occupy a position some distance to the rear of the uppers). With some cases, tooth shaving might be used to narrow the width of the upper teeth, so they can be pulled back into a more normal-looking alignment.

b) Proclined incisors.
This condition refers to the situation where the patient's center front teeth (their incisors) are flared out forward. Narrowing the teeth may make it possible for the orthodontist to pull them back into a more normal-looking arrangement.

Section references - Noar, English


How much of a tooth is trimmed away?

The precise amount that's sliced off will vary according to the specifics of the patient's case. (As you'll learn below, that's a prime advantage of using IPR. Only the actual amount of space that's needed is created.)

General rules that apply to the amount of interproximal reduction that's possible.

  • To avoid harming a tooth, the amount that's sliced off is never greater than the thickness of its enamel covering. (A dentist can get an idea of this thickness from x-rays that have been taken.) And preferably, on the order of no more than about 50%. (Pindoria)
  • For front teeth, even small lower ones, it's usually possible to remove on the order of 0.3 mm, possibly more, from each side of a tooth. For back teeth, this number can usually be 0.6 mm or more. (Proffit, English)

    (As a point of comparison, a credit card is usually just slightly less than 0.8 mm in thickness. So, the amount shaved off between two touching teeth is right about this same amount.)

 

  • Of course, it's the cumulative amount of space that can be generated that's important. So generally, IPR technique is considered a viable option for tooth-crowding cases that require 8mm or less of additional space (generally categorized as mild to moderate tooth crowding) (Pindoria).

    More commonly, this technique is utilized with cases requiring only 1 to 5 mm of additional space. (Like the case of mildly irregular lower incisors.) (English)

  • The idea of tooth stripping isn't usually considered until all of the teeth involved have erupted and can be evaluated collectively. (Proffit)

Section references - English, Proffit, Pindoria


The rationale for interproximal reduction.

You might be concerned that your dentist plans to shave off a portion of your misaligned, but otherwise healthy, teeth.

Our risks and side effects section below discusses why that's not usually a concern. But also, when compared to other options it's often obvious why filing off a little bit of tooth enamel frequently makes the better, more conservative, choice.

Possible alternatives to IPR.

As an example of what we mean, take the usual case where a patient's teeth are crowded and the dentist must find a way to gain the extra space needed to realign them. With this situation, the dentist only has a few options.
a) Tooth extraction.
A common way of gaining space for orthodontic purposes is to remove teeth. Of course, that involves surgery for the patient, with usually at least two teeth being extracted (one on each side so the person's dentition remains bilaterally symmetrical).

There's also the issue that there's no such thing as removing 1/2 of a tooth. The dentist always gains a whole tooth's width, whether they needed that much or not. (In comparison, with tooth stripping, very small, precise amounts of needed space can be created.)

b) Teeth flaring.

The additional space needed for tooth realignment can sometimes be made by flaring the patient's teeth forward, or slanting them backward or to the side. But making these types of changes can result in an alignment that is inherently unstable and therefore placing the patient at risk for case relapse (post-treatment tooth shifting).

So, in comparison to both of these alternatives, and especially in situations where just a small amount of space is needed, tooth stripping may prove to be the most practical and predictable, and possibly even the most conservative, solution.

A unique benefit of interproximal reduction.

The way the contact points between teeth are shaved down with IPR and therefore are less rounded and flatter helps to aid in the inherent stability of the patient's teeth as a unit.

In simpler terms, that means that at the completion of their orthodontic treatment, the alignment of teeth that have been stripped is less inclined to relapse (post-treatment tooth shifting).

Section references - Proffit


Risks, side effects and concerns associated with IPR.

Does stripping your teeth damage them?

Obviously, when interproximal reduction is performed, some thickness of the tooth's enamel is lost. The question then becomes, does shaving off this amount of enamel damage a tooth?

a) IPR approximates normal (acceptable) wear.

As an explanation for why it's OK to strip teeth, the idea is that the amount filed off (ideally no more than about 1/2 the thickness of enamel that exists) is on the order of the amount of wear evolution has prepared our teeth to accommodate.

Background.
  • Every tooth is anchored in your jawbone by a ligament. And this ligament allows for small amounts of tooth movement.
  • As movement takes place continuously over time, like when we eat or clench our teeth, some tooth-to-tooth wear occurs. And in fact, it's normal for the contact points of teeth to wear flatter as we age.
  • This effect was especially noticeable in primitive humans who had a coarse diet. In comparison, modern humans typically maintain a comparatively much softer diet, and therefore experience much less interproximal wear.
  • As a result, the enamel covering of teeth is much thicker than is expected to ever wear away naturally over a person's lifetime. And therefore some of this enamel can be sacrificed (shaved away) without resulting in tooth harm.

Section references - English

b) Are stripped teeth more likely to experience problems or side effects?

Interproximal reduction technique has been used by orthodontists for decades. And over the years, many dental researchers have evaluated its long-term effects in search of associated risks and problem issues.

Concerns include the potential for increased levels of tooth decay, problems in maintaining periodontal (surrounding gum and bone) health, pulpal (nerve tissue) irritation or damage, and increased thermal (hot/cold) sensitivity.

Research findings.

A study by Zachrisson found no increased incidence of side effects (tooth decay, periodontal or pulpal problems) in a group of subjects that had had tooth stripping performed more than ten years previously.

However, 2 of the 61 subjects did report having thermal sensitivity. Although, this is a multifaceted complication and couldn't be conclusively attributed to the teeth having been shaved.

In passing, we'll also mention that the vast majority of resources cited on this page also include statements that interproximal reduction has not been shown to adversely affect dental or periodontal (gum and bone tissue) health.

Section references - Zachrisson


Animation showing methods a dentist uses for tooth interproximal reduction (stripping).

Teeth can be filed using either a dental drill or an abrasive strip.

Interproximal enamel reduction - How is it performed.

What tools are used?
A dentist has various protocols they can use to perform IPR.
  • Mechanical methods - Using a dental drill, teeth are trimmed using a spinning diamond-coated bur or disk.
  • By hand - Diamond coated abrasive strips are worked back and forth in a sawing motion between the teeth.

 

The method that's chosen will most likely depend on how much tooth structure needs to be sliced off.

If it's just a very small amount, the dentist will probably work by hand because that method gives them the most control over how much enamel is shaved away. For larger reductions, they'll probably use their dental drill.

The steps of the IPR procedure.

The trimming process is pretty much as easy as you might imagine. The dentist simply uses their chosen tool(s) (drill and/or abrasive strips) and incrementally files down and slices away small amounts of each tooth's enamel until the needed amount of reduction has been accomplished.

a) Specifics about the trimming process.
  • Since the filing is entirely confined to a tooth's enamel covering (a layer that has no association with its nerve tissue inside), an anesthetic is not usually administered.
  • If the teeth being trimmed are especially crooked, the dentist may "separate" the teeth so they have less obstructed access.

    To do so, they'll place some type of wedging device (wooden wedge, wedging clamp, etc...) in between the teeth that just pushes them slightly out of contact.

  • It's paramount that the dentist doesn't heat a tooth excessively as they trim it. Especially when using a drill for this process, air or water spray will be applied to the tooth to keep it cool.

 

b) Your dentist will take care not to trim too much.

From time to time during the stripping process, your dentist will stop and fit a small thickness gauge (leaf gauge or dental probe) between your teeth and measure the gap they've created so far.

Once they've widened the gap enough, they'll document this width in your dental chart. Any future stripping will be documented too, so no tooth has too much enamel removed.

c) Polishing the trimmed surfaces.

Once the needed amount of tooth reduction has been accomplished, the dentist will polish each tooth's filed surfaces so they are as smooth as possible.

This might be accomplished via the use of a strip or bur, disk or wheel placed in a dental handpiece. But this time the instrument used will have a much finer grit.

d) Protective measures for the shaved surfaces.
A dentist will want to help to protect the tooth's freshly-trimmed surfaces. Fluoride or some other compound that helps to promote tooth enamel remineralization will be applied at the completion of the stripping process.

Section references - Noar, Pindoria, Zachrisson

What's it feel like when interdental reduction is performed?

Does it hurt?

Don't worry, having your teeth shaved isn't that big of a deal and shouldn't hurt at all.

As stated above, the portion of your tooth that's being sliced down is 100% enamel. And since a tooth's enamel covering has no association with its nerve tissue inside, no pain should be felt (no dental anesthetic should be required).

What will you notice?

It's expected that you'll feel the tug of the diamond strip between your teeth or the vibration of the drill as it does its work. If some type of wedging device has been placed, you'll feel the minor pressure it creates too. But generally, the whole process should just be a minor event.

Picture showing lower front teeth that have had interproximal reduction (IPR) performed.

After IPR.

After they've been stripped, will you notice gaps between your teeth?

Sure, after IPR has been performed you should expect to see small gaps between your teeth. After all, creating spaces is the whole idea of the procedure.
But these spaces should be quite small, and probably not all that obvious to others. And, of course, as your treatment progresses, your gaps will become smaller and smaller until they're finally fully closed in.
 

Timing of the IPR procedure.

How many times/how frequently will your teeth need to be shaved down?

a) Interproximal reduction as a part of the Invisalign® treatment process.

Due to advances with the Invisalign® system's software, the timing of case IPR has evolved.

Historically.

When the Invisalign® system was first introduced, there was a need to perform a case's needed tooth shaving before the patient's aligners were fabricated.

However, having to perform IPR before any tooth movement had been accomplished often left the dentist with a difficult task. If their patient's teeth were especially overlapped, performing the trimming without damaging adjacent teeth could be difficult.

Nowadays.
With advances in the Invisalign® system, a process referred to as "staging" can now be used. This simply means that tooth trimming is delayed (staged) until that point during the patient's treatment process when the dentist has their best, or at least better, access to the tooth surfaces that need to be filed.

Section references - Boyd

b) IPR with conventional braces.

As opposed to the situation where the dentist's treatment actions must conform to the shape/design of their patient's previously fabricated Invisalign® aligners, with conventional braces the dentist can perform tooth stripping at any point during the treatment process.

In contrast to conventional thought, the amount of interproximal reduction that's performed with either traditional wire braces or Invisalign® treatment is generally about the same.

Section references - English

 

 Page references sources: 

Boyd RL. Esthetic Orthodontic Treatment Using the Invisalign Appliance for Moderate to Complex Malocclusions.

English JD, et al. Mosby's Orthodontic Review. Chapter: The Invisalign system.

Noar JH, et al. The Ethics of Interproximal Reduction.

Pindoria J, et al. Inter-proximal enamel reduction in contemporary orthodontics.

Proffit WR, et al. Contemporary Orthodontics. Chapter: Retention.

Zachrisson B, et al. Dental health assessed more than 10 years after interproximal enamel reduction of mandibular anterior teeth.

All reference sources for topic Straightening Teeth.

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