Interproximal Reduction, When, Why, and How | 9 MINUTE SUMMARY
In this episode, I dive into the fundamentals of interproximal reduction (IPR) when to use it, why it matters, and how to do it effectively.
We’ll cover how much IPR can safely be carried out, compare different clinical protocols and their pros and cons, and take a critical look at how aligner software plans IPR (and where it may fall short).
This summary is based on Dr. Flavia Artese’s insightful lecture at the recent American Association of Orthodontists Annual Session in Philadelphia, along with insights from my own clinical research and experience.
How much IPR is possible?
Recommended amount ½ to 1/3 of outer enamel
Estimate with periapical radiographs are inaccurate, under-estimate as well as over estimate Meredith 2017 Brine 2001
Quantity of the enamel each interproximal surface Kailasam 2021 systematic review, with an excellent table created by Bosio in 2022 highlighting the enamel present and hypothetical safe reduction, ranging from 0.3-0.7mm, with 5-10% greater enamel on the distal surfaces
Can all teeth have IPR?
· Triangular teeth are ideal
o Large interradicular distance, roots can approximate with no issue
· Square shaped teeth not ideal
o Reduced interradicular distance, root approximation of 0.8mm = loss of crestal bone Taera 2008
Are we accurate with IPR? Johner 2013 AJODO
· Manual strips Vs rotary disc Vs oscillating strips = all underperformed IPR by up to 0.1mm
Protocols:
Small Vs Large
· 0.1-0.2mm manual strips
· 0.3mm+ larger reduction
· Polishing required – If not = 25 um furrows retain plaque Jack Sheridan 1989
Separation posterior region
· Separator – Requires measuring of premolar before and after
· Bur – needle bur
o Parallel occlusal plane
o Recontour tooth surface to create contact point
· No separator – requires contact point to be broken, advantage is the measurement of the IPR site is accurate
Bolton’s analysis
· Based on excess, rather than tooth removal
Proportionality
· Width
o Canine 90% of central incisor
o Lateral 70% of central incisor
IPR planning
Bolton’s discrepancy + Tooth proportionality
= when to add or remove tooth structure
However
· “Don’t do pre-emptive stripping for balancing tooth mass ratios between arches. Chances are it will work out just fine” Jack Sheradin 2007 JCO
Vincent Kokich – “we need to establish the vision”: Use of digital planning
Method of use for 4 mm of IPR:
· Posterior to anterior – Jack Sheridan
o Posterior IPR first, followed by distalisation, e.g. 4-5 first, distalise 4
o Maintain arch length with stops etc, maintain anchorage
· Anterior to posterior – Farooq
o Anchorage preserving
o Tony Weir 2021 the most common site in clinical practice was the lower anterior segment
IPR on overlapping teeth
· Not possible to achieve ideal anatomy with motorised IPR instruments
· Posterior IPR first, distalise, followed by anterior alignment and IPR – Flavia
· Use of handstrips is possible on overlapping teeth – Farooq
Limits of IPR
· 4-5mm, although Sheridan described possible 8.9mm, technically challenging
· IPR is not a possibility for sagittal discrepancy:
· Correct posterior occlusion prior to resolution of discrepancy
Greater Bolton’s discrepancies in class 3 and class 2 malocclusions, SR 53 studies Machado 2020, greater in class 2 and 3 cases albeit a small difference of 0.3-0.8%
Retained primary 2nd molars
· Idealise occlusion
· Consider root morphology divergence, as post IPR space may not close
o If divergence greater than crown, reconsider as space closure unlikely
Why do we need to use IPR with aligners? Dahhas 2024
· Alogrythm reduces the number of aligners
· More IPR rather than saggital correction
· IPR staged inappropriately with large IPR whilst contact point overlap, which is difficult to perform adequate anatomical reduction
Figure from Bosio JA. Safe interproximal enamel reduction. Evidence-based orthodontics equals the author’s opinion. Am J Orthod Dentofacial Orthop. 2022 Aug;162(2):143-145. doi: 10.1016/j.ajodo.2022.04.007. PMID: 35933147.
