IPR stands for interproximal reduction, a procedure where your orthodontist shaves a tiny amount of enamel from the sides of your teeth to create space. The amount removed is small, typically 0.3 to 0.5 mm per tooth surface, and the procedure is common in both braces and clear aligner treatments. You might also hear it called tooth slenderizing, stripping, or enamel reduction.
Why Orthodontists Use IPR
The most common reason for IPR is making room to straighten crowded teeth without pulling any. For adults with minor to moderate crowding (roughly 4 to 8 mm of space needed), shaving small amounts from several teeth can add up to enough room to bring everything into alignment. It’s especially popular for the front six teeth, sometimes called the “social six,” where crowding tends to be most visible.
IPR also corrects mismatches in tooth size between your upper and lower arches. Somewhere between 20% and 30% of people have a noticeable size difference in their front teeth alone. When upper and lower teeth don’t match in width, your bite can’t come together properly. Trimming the wider teeth slightly lets the orthodontist balance the proportions so your bite closes evenly.
A third use is cosmetic: eliminating or preventing black triangles. These are the small dark gaps that appear between teeth near the gumline when the gum tissue doesn’t completely fill the space. Black triangles sometimes show up after rotated teeth are straightened into line, because the contact points between teeth shift higher. By reshaping the sides of the teeth during IPR, the orthodontist moves the contact point closer to the gum, giving the tissue a better chance of filling the gap.
How IPR Works With Clear Aligners
If you’re using Invisalign or another clear aligner system, there’s a good chance IPR is part of your treatment plan. Aligners rely on precise, pre-programmed tooth movements, and they need somewhere for crowded teeth to go. Since aligners can’t expand the jaw the way certain braces can, IPR is often the primary method of gaining space. Your provider’s digital treatment plan will specify exactly which teeth get reduced, by how much, and at which stage of your aligner sequence the reduction should happen.
What the Procedure Feels Like
There are no nerves in tooth enamel, so IPR doesn’t hurt. Most people don’t need any anesthesia at all. You’ll feel slight vibrations from the instrument, but that’s typically the extent of it. Some people notice mild tooth sensitivity for a few days afterward, which resolves on its own.
The actual reduction takes only a few minutes. Your orthodontist may use one of several tools: thin diamond-coated strips that slide between the teeth like dental floss, small rotating diamond discs, or fine dental burs attached to a handpiece. The choice depends on the location of the tooth and how much enamel needs to come off. The orthodontist measures as they go, usually with a small gauge, to stay within the planned amount.
How Much Enamel Can Be Safely Removed
The general safety threshold is no more than half the enamel thickness on any given surface. In practice, that means up to 0.5 mm can be removed from each side of a back or upper front tooth (so about 1 mm total per contact point between two teeth). Lower incisors have thinner enamel walls, so the limit there is about 0.375 mm per surface, or roughly 0.75 mm at each contact point. These amounts are small enough that the remaining enamel still provides full protection for the inner layers of the tooth.
Protecting Teeth After IPR
When enamel is shaved, the freshly exposed surface is rougher than natural enamel and slightly more vulnerable to mineral loss. That’s why many orthodontists apply a fluoride varnish immediately after the procedure. Research shows that fluoride varnish acts as a physical barrier against acid attacks and significantly reduces demineralization of the reduced surface. Products containing casein phosphopeptide (a milk-derived protein found in some remineralizing pastes) and zinc-carbonate hydroxyapatite toothpastes have also shown effectiveness in promoting remineralization after enamel reduction.
Interestingly, final polishing of the stripped surface doesn’t appear to make a meaningful difference in preventing demineralization. The fluoride application matters more.
IPR vs. Tooth Extraction
IPR is generally the more conservative option. It’s preferred when crowding is mild to moderate, your facial profile looks balanced, your bite relationship is normal, and your teeth have a triangular shape (which responds well to side trimming). It’s also favored in patients with good oral hygiene and a low history of cavities, since the reduced enamel surfaces do need to stay clean.
Extraction becomes the better choice in different circumstances: when the size mismatch between upper and lower teeth is 4 mm or more, when a tooth is already structurally compromised or has periodontal problems, or when crowding is severe enough that shaving alone can’t free up sufficient space. The decision is always individualized, and orthodontists often use physical or digital models to test both approaches before committing to a plan.
Long-Term Stability
One concern patients sometimes have is whether results achieved with IPR hold up over time. A study comparing patients treated with and without IPR found that long-term alignment stability was similar in both groups. Both groups experienced some minor relapse in lower incisor crowding after retainers were discontinued, which is normal regardless of treatment method. The key finding: IPR patients’ dental arches held their width better over time than those who didn’t have the procedure. In other words, the slight narrowing of individual teeth didn’t make the overall result any less stable.