Why does an orthodontist shave between teeth (interproximal reduction)?

More space for the teeth: the AAO’s goal and definition

The American Association of Orthodontists (AAO) describes interproximal reduction (IPR) from two sides. Its glossary gives the means, “Removal of a small amount of enamel from between the teeth to reduce their width,” and its FAQ gives the reason, more space for the teeth.

Narrower teeth take up less room in the row, and that is where the space comes from. Making room matters where room is short, as with crowded teeth, which have an answer of their own. Where teeth have room to spare, the question turns into one about gaps between teeth.

How much enamel: Align’s figure and one study’s medians

Align Technology and one study each put a figure on how much enamel interproximal reduction involves, and the two figures measure different things. The AAO’s FAQ and glossary say some and a small amount, and give no figure.

Align, describing IPR in Invisalign® treatment in an August 2026 article on severe bite problems and crowding, puts the enamel removed at “typically less than half a millimeter per contact point,” a contact point being where two neighboring teeth meet. That is Align’s statement of what is typical, not a limit.

A 2024 study in the American Journal of Orthodontics and Dentofacial Orthopedics (Abasseri, Weir and Meade), of the digital treatment plans of 242 Invisalign patients of 11 orthodontists, found a median of 1.1 mm of interproximal reduction prescribed per patient in the initial plan and 0.6 mm in refinement plans, with the lower front teeth the most common site.

Those medians are per patient and not per tooth, and they describe that cohort alone: they do not say how many patients have interproximal reduction, what most patients have, or what your plan would involve.

Cavities and sensitivity after enamel reduction: two reviews and their limits

Two systematic reviews report no increase in cavities after interproximal reduction, each with a limit. A 2022 systematic review of eight clinical studies (Gómez-Aguirre and colleagues, Orthodontics and Craniofacial Research) says “no demineralization of the enamel, no increase in caries incidence, no periodontal changes or dental sensitivity was found after IPR,” rates the overall quality of those studies between low and very low, and calls for more and better trials.

A 2014 systematic review (Koretsi and colleagues, also in Orthodontics and Craniofacial Research), whose caries finding rests on four studies followed for 1 to 7 years, says “the occurrence of caries on surfaces previously treated with IER was the same as that on intact surfaces.” IER is that review’s name for the same procedure, and caries is the clinical word for cavities.

Those are findings about groups of patients, each with the limit stated beside it, so neither is a promise about your teeth.

Who decides: the orthodontist’s treatment plan

Interproximal reduction is decided in the orthodontist’s treatment plan, as the 2024 study by Abasseri, Weir and Meade and Align both describe it. The study’s digital plans record it as prescribed, and Align’s August 2026 article says “Your ClinCheck treatment planning software will map exactly where IPR is planned and how much space it creates.”

The AAO’s glossary says enamel does not regenerate, in an entry about enamel broken away or worn down by a bad bite, and by plain reasoning the enamel removed here does not grow back either. That makes these fair questions for your orthodontist before a plan goes ahead: whether it would be used at all, where, how much and why.

The clear aligners page covers how aligners move teeth once there is room, and you can browse other questions about orthodontic treatment from the hub.