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How much is too much IPR?

Interproximal reduction has been performed for over 70 years, and it can make clear aligner treatment more predictable and effective. 

But how much IPR is actually safe? Is it the same for everyone?

How much space can be gained?

It is widely acknowledged that removal of up to 50% of the proximal enamel is possible without dental and periodontal risks. In the anterior and buccal segments this can create between 2.5mm and 6.4mm of space respectively. 

Later studies have suggested that even more space can be created posteriorly, reducing the need for extractions by creating up to 9.8mm of space(!). 

The maximum amount of IPR suggested today is 0.5mm from each proximal surface in the buccal segment (1mm between each contact point), and a maximum of 0.75mm total from the lower incisors. 

Strategic IPR for extra space

Tooth shape can also determine how much space IPR can create- a small reduction in enamel at the contact point of a very triangular-shaped tooth can create a disproportionate amount of space! So be sure to consider this when doing your IPR plan.

Strategic IPR can win you a lot of space

Clear those contacts!

This also works in reverse! Not clearing the contact could really limit the amount of space you create, so make sure to check with a gauge.

Incomplete IPR can have the reverse effect, and limit the movement of teeth, increasing the chance of refinements

What other factors impact IPR and space creation?

Ethnicity impacts enamel thickness, with studies showing that black patients have on average slightly thicker enamel. 

Generally, wider teeth also have thicker enamel but there is no evidence for a difference between males and females.

The bottom line

IPR is a powerful technique which can really enhance the range of movements which can be achieved with clear aligners without relying on extractions or excess proclination. 

Carefully planned IPR can create extra space (for free!), reduce the risk of black triangles while having no detrimental impact on the teeth.

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