A Voice in the Arena: The Importance of Timing IPR by Dr. Chad Foster

Categories: Orthodontics;
A Voice in the Arena: The Importance of IPR   

by Chad Foster, DDS, MS, editorial director

Interproximal reduction (IPR) is a really nuanced technique that deserves our thoughtful attention. I’m not granted the word count here to properly express the deep love in my heart for IPR, but let’s nerd out for just a bit on one important aspect.

Strategic timing of IPR plays an important role in its multifaceted effectiveness. In anticipation of significant IPR, it is important that ideal alignment is achieved first (after pano/repo is completed). This is for two reasons that have to do with posttreatment relapse.
  1. It’s important that first-order rotation issues are normalized so the new interproximal contacts are as close to 90-degree abutments as possible. IPR done before this, when rotations still remain, is very likely to create angled contact points that are readymade for relapse of the original rotation. I have defined the term “relapse contacts” to describe this.
  2. If root position (tip/second order) is not ideal and IPR contacts are created in this position, there is a tendency for these roots to naturally attempt to upright to their ideal positions after treatment, which could unfavorably alter the aesthetic contacts of the anterior teeth. If early IPR before ideal alignment and root position is necessary, it’s important to consider performing it again later (after ideal alignment) to address that issue. [Editor’s note: For greater detail on this subject, read “A Protocol for Inverting Upper Incisor Brackets,” an article Dr. Foster wrote before he became editorial director of Orthotown.]

When early IPR makes sense
However, there are some circumstances where early IPR can be very important. I find that adult patients who are periodontally compromised or sensitive can benefit greatly here. One useful tactic in these types of patients is to employ early IPR to avoid what I call “round-tripping” crowded teeth within the compromised/sensitive periodontal housing.

For how “round-tripping” teeth can impact dark-triangle formation, I highly recommend a great presentation from the 2018 AAO Annual Session by Dr. Olivier Sorel titled “Diagnosis, Prognosis and Control of Adult Orthodontic Treatments Focused on Taking Into Account the Shape of the Teeth.” He did a fantastic job talking about this concept as it relates to dark triangles.

Sorel explains that in aesthetic areas of concern with significant crowding, as alignment occurs, there is a tendency for the roots to be displaced mesial-distal (M-D) from each other at a distance that is equal to the crowding that overlaps the contact points. The larger the distance of initial displacement, the more significant risk there is of papillary tissue recessing and dark triangles forming.

So, what happens if you just align the crowding as-is and perform IPR later, after alignment? Beware that the papilla’s response to the large M-D displacement of the roots will have already occurred before your postalignment IPR. In this scenario, papillary recession and the expression of dark triangle formation has likely been maximized. IPR can be done at this point (after alignment), but there will now likely be greater total amount of IPR required to compensate for the greater disturbance of papilla and maximized dark triangle.

Sorel’s suggestion was to perform IPR before alignment in aesthetic areas that are susceptible to dark triangle formation. When this is done, the initial M-D root displacement upon alignment is less than if IPR was done after alignment. The papillary response is more favorable and most often, less total IPR is required because dark triangle formation has not been maximized.

In my view, the concept of round-tripping of roots within a compromised/sensitive periodontal housing relates not just to the papillary response and dark triangle formation like Sorel discussed so well; it also directly affects the important relationship of the roots to the alveolar housing.

Case study discussion
Fig. 1: Initial records.
Fig. 2: Pre-treatment CBCT.
Fig. 3: Lowers at bonding
Fig. 4: Five-week progress photo.
Fig .5: Eight-week progress photo.
Fig. 6: 12-week progress photo. 
Fig. 7: Lower 12-week comparison
Fig. 8: Final records, after 14 months. 
Fig. 9: Comparison of pre- and posttreatment CBCTs.

The patient shown in these included records is a male in his early 40s with significant crowding. It’s a great case to discuss at length, but for the sake of brevity I’ll keep it short and to the point.

I didn’t think extractions were necessary in the upper arch for ideal maxillary aesthetics, and I also generally do not like the occlusal compromise in lower incisor extraction cases except for very unique scenarios. My plan here definitely relied on IPR. However, an important diagnostic CBCT finding for this patient was that he had what I would consider to be a relatively thin and unfavorable alveolar housing in the area of his lower incisors (as well as recession of gingiva on his L3s). Because of that finding, strategic early IPR was employed to attempt to minimize round-tripping of the lower incisor roots within the compromised alveolar housing.

IPR of approximately 0.1 mm between each contact L4–4 was done immediately after placing braces. The patient was then seen back approximately every four weeks during the first 12 weeks of treatment for me to lightly IPR the proximal surfaces of these teeth again (0.1 mm or less each contact L4–4 each time) to make sure the teeth were not heavily binding during this time as they fought to achieve alignment. Light IPR was again performed in this area (as well as the upper) after pano/repo to idealize the “relapse contacts” that likely occurred from the early IPR. The case finished in just under 14 months and with very minimal change to the relationship of the lower incisor roots within the alveolar housing.

Key takeaway #1: Early IPR can often create “relapse contacts” that will tend to favor relapse of those affected teeth to exact original crowding/ misalignment. So try to do IPR only after ideal alignment has been achieved. If early IPR is needed, consider again performing IPR later after ideal alignment is reached to idealize the proximal contact surfaces.

Key takeaway #2: Avoid “round-tripping” crowded teeth in periodontally compromised/ sensitive patients. For these cases, consider IPR early to limit the initial and often unfavorable M-D displacement of the roots within the periodontal housing.

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