Interproximal reduction, usually called IPR, is one of the most common steps in aligner treatment. It is also one of the most misunderstood. Done well, it creates just enough space to finish the case smoothly. Done poorly, it can cause tight contacts, gaps, sensitivity or wasted time.

This guide covers when IPR makes sense, where it is usually planned, how much is reasonable and what to check when you review a setup. The numbers and limits you use should always come from your training, the evidence and your aligner system’s guidance. This article gives a general framework, not fixed rules.

What is IPR?

IPR means removing a very small amount of enamel from the sides of teeth where they touch, to create space. It is also called slenderizing, stripping or reproximation. The space it creates can be used to relieve crowding, adjust tooth shape or help teeth move into a better position.

Why use IPR in aligner cases?

IPR is often planned to:

• Relieve mild to moderate crowding when there is not enough space in the arch
• Reshape triangular teeth to reduce dark gaps near the gum line, sometimes called black triangles
• Correct a small tooth size mismatch between the upper and lower arches
• Create space for rotations or other planned movements
• Help a planned change in tooth position, such as moving teeth back slightly

IPR is only one way to create space. Others include expanding the arch, tilting front teeth forward, moving back teeth backward and, in some cases, extractions. See our guide to clear aligners for crowded teeth for how these options compare.

When IPR is a good choice

IPR tends to suit cases where:

• Crowding or space need is mild to moderate
• The gums and bone are healthy
• There is enough enamel at the contacts that will be reduced
• The patient has good oral hygiene and a low risk of cavities
• Teeth are wide or triangular, so a small reduction is practical

When to be careful or avoid IPR

Take extra care, or choose another approach, when:

• The patient has a high risk of cavities, or active decay
• The enamel is thin, or the teeth are small
• There is bone loss or periodontal disease
• The patient already has sensitivity
• Fillings, crowns or other restorations sit at the contact
• Another method would solve the problem more safely

The patient’s consent is also part of good practice. Explain what IPR is, why it is planned and what it involves before you start.

Where IPR is usually planned

IPR is planned at the contacts between teeth, and the pattern depends on the case:

• Front teeth: common for relieving crowding and reshaping triangular teeth.
• Premolars and molars: used when more space is needed or to support movement of the back teeth.
• Contacts that will not move much: often better to avoid, unless there is a clear reason.

Choose contacts where enamel is available and where the space is really needed. Spreading small amounts across several contacts is generally gentler than taking a lot from one.

How much is reasonable?

The amount is planned per contact and in total for the arch. General principles are widely accepted:

• Keep amounts per contact small, usually a fraction of a millimeter, rather than removing large amounts at one point.
• Stay within the enamel. A commonly cited limit is to keep reduction well under half of the enamel thickness at a contact. Always check the evidence and your system’s guidance.
• Think about the whole arch. Several small amounts add up, so check the total.
• Consider the patient. Younger patients and those with larger teeth may tolerate more than those with thin enamel.

If a plan asks for a large total, ask whether another method of creating space would be better.

When in treatment to do IPR

IPR is usually planned in stages. It is not always done all at once at the start. Planned stages let the space be made just before teeth need it, which helps the aligners fit and reduces the chance of leaving open spaces for too long.

Your setup should show an IPR chart that lists which contacts to reduce, how much and at which stage. Make sure everyone on the team follows the same chart.

How IPR is done

Common methods include:

• Hand strips, thin abrasive strips used by hand
• Discs or burs in a handpiece, for faster reduction
• Oscillating or segmental systems, designed for controlled removal

After reduction, the surface should be smoothed and polished, and fluoride is often applied. Use a gauge to check the space you have made, because the amount removed should match the plan.

Common IPR mistakes

1. Doing all of the IPR at the beginning, instead of following the planned stages
2. Taking too much from a single contact
3. Reducing contacts that were not planned or that need no space
4. Not measuring, so the actual amount is a guess
5. Skipping polishing and aftercare
6. Ignoring tracking problems when IPR was not done as planned
7. Not explaining IPR to the patient before treatment

A checklist for reviewing IPR in a setup

Question	Yes	No
Is IPR really the best way to create this space?
Is the patient suitable, with healthy gums and low cavity risk?
Are the contacts chosen sensible, with enough enamel?
Are the amounts per contact small and reasonable?
Is the total for the arch reasonable?
Is the IPR staged, not all at the start?
Do attachments and IPR work together, not against each other?

For a full review of a setup, use our checklist of 7 signs a case needs a second look. For how attachments fit alongside IPR, read our guide to aligner attachment design.

When to ask for help

IPR planning affects tooth health and treatment time, so it is a good place for a second opinion. An independent QC review checks IPR amounts, staging, attachments and bite interference before you approve a setup. Read why every setup needs a QC check, and see which cases suit aligners in our guide to which cases clear aligners can treat.

How OrthoAlign Solution can help

Our aligner planning service includes attachment and IPR strategies as part of each treatment plan. You review the plan, ask for changes and approve it. You can see our full list of services or contact us to discuss a case.

Frequently asked questions

Is IPR safe? When it is planned carefully and done in small, measured amounts by a trained dentist, IPR is a common part of aligner treatment. Your dentist can explain the plan for your teeth.

Does IPR hurt? Most patients feel little or no pain, but some may feel mild sensitivity. Tell your dentist if you have concerns.

Does enamel grow back after IPR? No. Enamel does not regenerate, which is why the amount is planned carefully.

Will IPR increase the risk of cavities? When surfaces are smoothed and polished and the patient keeps good hygiene, the risk can be low. Your dentist will advise on care.

Do all aligner cases need IPR? No. Some cases have enough space or use other methods to create it.

Can IPR be done after the aligners are started? Yes. It is often done in stages during treatment, as shown in the IPR chart.

Get IPR checked before you approve

Send us a setup and we will review the IPR, attachments and staging with you. Contact OrthoAlign Solution to get started.