Tech tip: FAQ about IPR

We sent out a survey recently asking doctors for their questions about IPR.

DrMah.jpegIn this week's tip, we've consulted with our Chief Technology Officer, Dr. James Mah, to get answers to your questions.

IPR and the treatment setup

ClearCorrect's role is to help you create the treatment setup you want for your patient. We can offer recommendations for the course of treatment for your patient, but those recommendations are never absolute. It’s up to you to make any necessary changes to customize an ideal treatment plan for each individual patient.

We can adjust all preferences related to IPR (which teeth, when and how, no IPR, expansion, limited IPR, limited expansion, etc.) or engagers based on your specifications. Just let us know what you want when you submit your case or when you review your treatment setup.

Questions about how much IPR to perform

Why do your IPR instructions always call for 0.3 mm?

If we don’t receive specific instructions from you on the amount of IPR you want done, we will go with our default increment of 0.3 mm IPR per interproximal each step. In some situations, we may recommend smaller increments of 0.1 or 0.2 mm of IPR.

These 3 increments of space can be created predictably if the right tools are used:

  • 0.1 mm of space is predictably created with hand stripping.
  • 0.2 mm can be predictably created with a single-sided diamond disc.
  • 0.3 mm can be predictably created with a double-sided diamond disc.

Doing any more than 0.3 mm of IPR at once to one interproximal is prone to problems. We usually recommend IPR in 0.3 mm increments to account for potential accumulated errors, such as:

  • When IPR is not performed correctly, the diamond disc can flex and create a “V” shape space which appears to be larger than it actually is. 
  • Hand stripping requires some force applied to the strip towards the tooth that needs reduction.  This force will sometimes move the teeth, which will make the space bigger. This space makes it look like the required tooth reduction occurred, when in fact it did not. Instead the teeth just shifted around to create space. When the aligners are put on the teeth, the space will be smaller than what is needed. 
  • A similar problem also happens when doctors force an IPR gauge into a space. They may think there is proper amount of reduction when all they really did was just move the teeth around.

Is it better to do IPR up to a point to correct rotations or to flare out to the labial?

This depends on the patient and the specific teeth. Clinician and patient preferences play a key role in determining the course of treatment. The treatment setup is your treatment plan and you are at liberty to make specific requests related to your individual patient.

How do I know when to do more or less IPR than scheduled?

Again, it depends on the specific situation. When considering IPR and the patient in front of you, you must understand that you are dealing with a biological system as opposed to a manufactured part. There are anatomic, biologic and patient variations at play which produce varying results. You will need to continue to follow what is happening with the patient and oversee treatment to obtain optimum results.

Also, knowledge of dental anatomy is important. Incisors have less enamel than other teeth and do not allow for as much IPR. Intra-oral radiographs can be used to check the amount of available enamel before submitting the case or performing IPR.

How do you measure the amount of IPR?

gauges.jpgThere are a few ways to check the amount of IPR:

  • IPR gauges (such as the ones sold by ClearCorrect) are commonly used.
  • Some dentists use the thickness of the IPR strip as a gauge, knowing that it is 0.1 mm thick. If you fold the strip over, it produces a thickness of 0.2 mm and one more fold results in 0.3 mm.
  • Some dentists use the width of the disc in the same manner.

I occasionally have difficulty with angulation of cuts, overlap, rotated teeth, access, insufficient space and possible over-reduction of one approximal surface vs. another. What should I do about this?

In some situations, it may be necessary to slightly procline the teeth and improve alignment before performing IPR, so that the appropriate tooth surface is reduced. For this reason, some clinicians prefer to perform IPR over several visits.

Scenarios like this are why many doctors do not schedule IPR at the first aligner appointment. Orthodontic tooth movement results in minor tooth mobility which allows for easier IPR.

If access is an issue on posterior teeth, you can request no IPR in posterior areas when submitting your case or reviewing the treatment setup.

What do I do to get exactly the same amount of reduction along the whole interproximal space?

When performing IPR you need to make sure that the strip or disc is completely through and past the contact point, and that the strip or disc is applied uniformly during the process. One common error is excessive tooth reduction above the contact point, leading to a “V” shaped interproximal gap.

The goal of IPR is to reduce tooth size while maintaining the original morphology of the teeth. In other words, smaller contact points between incisors should remain as such and not be flattened into broad ones. If in doubt, it is easier to carefully go slower with a strip than it is with a rotary disc.

Tight contacts make it difficult to perform IPR and for this reason, some clinicians prefer to start moving the teeth and take advantage of the associated tooth mobility before performing IPR. Another option is to start the IPR with a strip to overcome the tight initial contact and subsequently use the burr or disc.

Do you keep track with the total amount of IPR being performed throughout a case? My only concern is that at times it seems IPR is being done on the same teeth, and I worry about the patient having sensitivity due to loss of enamel.

Screen_Shot_2016-03-11_at_11.55.21_AM.pngClearCorrect represents the amounts and locations of recommended IPR on the treatment plan and treatment setup.

Our technicians usually won't recommend more than 0.3 mm IPR mesial of the canines, or more than 0.6 mm IPR distal of the canines and mesial of the first molars, unless specifically requested by the doctor. We have found that those values are conservative enough to maintain the enamel structure and to satisfy most doctors that have concerns about reducing too much enamel.

These default values are smaller for anterior teeth, because they have less enamel than posterior teeth. These values also take into consideration how the tooth will look at the end of treatment. 0.3 mm of IPR in the anterior is only 0.15 mm on one tooth, if a double-sided diamond disc is used. 0.6 mm of IPR in the posterior is only 0.3 mm on one tooth, if a double-sided diamond disc is used. Since posterior teeth can have more enamel removed, you can go back and round out the square corners by contouring after using the diamond disc.

Besides our recommendations, you should also keep track of the IPR that is actually performed on each patient. We have an IPR Tracking Chart that can help you monitor this. Each time you perform IPR it should be recorded and correlated with specific patient tooth morphology (check intraoral radiographs for thickness of enamel). 

Questions about IPR and spacing

The majority of the time you ask for a 0.3mm reduction but every time I create the 0.3mm, I end up with spaces and have to ask for more trays to close that space. Why is this?

There are several possible reasons that you may have ended up with spacing after doing IPR:

  1. Patient non-compliance.
  2. Teeth can shift unpredictably in treatment. Always be aware of this and only do IPR when it appears necessary, using the treatment plan amounts as a guideline. Your technical expertise and judgment takes precedence over any IPR recommendations.
  3. Technicians are working with digital images vs. the actual patients, so the instructions are an imperfect estimate of the amount of IPR that will actually be needed.
  4. Space closure in deep/heavy bite patients is difficult.
  5. Problems in impressions can result in inaccurate digital images.
  6. More than the required amount of IPR may have been erroneously performed.

Before performing IPR at any stage of treatment, you should check the patient’s mouth to see if treatment has been progressing as planned.

Interproximal contacts should be checked with dental floss at every visit and if the contact is not closing, you can request a digital power chain to close residual spaces.

What if I'm sure I opened the space to the prescribed amount, and when I get a notation to check for closed contacts, it's still open? If patient compliance is not the issue, should we go on to the next step, or try the current aligner for a longer period?

If patient cooperation and aligner fit are not issues, continue with treatment. The periodontal tissues are still remodeling and the residual gap may close later in treatment. Check the contact often and if it remains after alignment is achieved, request a digital power chain to close up residual spaces. 

I am concerned about creating a narrower interproximal space with less space for gingival tissue on some teeth. I still don't find any of the methods to do IPR perfect. They all present risks of iatrogenia and don't allow us to preserve the ideal tooth anatomy.

Generally interproximal tissues will remodel to accommodate the new tooth positions and there will not be any gingival excess. However, in some situations, such as the maxillary midline, this may be an issue requiring gingivectomy. 

However, these issues are all according to your preference. You can specify less IPR or no IPR when you submit the case or evaluate the treatment setup.

The hand system wears out pretty quickly and doesn't always create enough space. Some teeth can be stubborn to move and need more space, especially when the teeth are really crowded. What do I do when this happens?

This could be the result of clinical technique. Reviewing the different IPR techniques might be helpful. It could also be affected by the choice of which strip to use (course/medium/fine). These variables should be considered when performing IPR.

Questions about contouring and IPR

How do I create a natural contour instead of just a flat side?

When contouring, knowing the various IPR techniques available to you and using the one most applicable for the case at hand is important to achieve the desired result. Using hand strips after use of a diamond disc can help with rounding out some corners.

It also may be necessary to slightly procline the teeth and improve alignment before performing IPR so that the appropriate tooth surface is reduced, and then perform IPR over several visits.

General concerns about performing IPR

I get worried about the accuracy of the proposed design.

This is why it is important to see patients on a regular basis to oversee their treatment progression. Additionally, this is a concern of many doctors when first performing IPR. With more cases, treatment, and experience, this concern fades.

I find using diamond saws very scary. It’s easy to create a bloody mess in a blink of an eye. The patients really dislike the sound of the diamond blade hacking away at their dentition. It takes a lot of effort to even start the pass thru. The feel of grit and the taste of blood make them want to run.

Knowing the various IPR techniques available to you and using the one most applicable for the case at hand is important in scenarios where you have a nervous or scared patient. There are multiple available techniques for IPR (manual strips, discs) that doctors can choose from. Dentists have varying levels of comfort with each system. The choice to perform IPR or not is entirely up to you. You can always make custom requests regarding IPR when you submit your case or review the treatment setup.

How do I reassure my patient I'm not hurting or damaging the teeth when I do IPR?

Discuss enamel thickness and dental anatomy with the patient. You can let the patient know that occlusal enamel reduction through everyday chewing is a normal occurance that happens as the patient gets older. If this is a significant issue for the patient, one alternative is arch expansion to reduce or eliminate IPR. However, there are also compromises and risks involved in arch expansion.

I would like to know more about when it is appropriate to do a little unscheduled IPR to help prevent teeth from getting off track.

During every visit you can check for excessively tight contacts with dental floss. If you find that tight contacts are an issue, you can perform a little hand stripping to help keep treatment from going off track.

Should the IPR gauge fit tightly or passively?

It should be fairly passive as a tight fit will result in compression of the PDL and natural tooth mobility may be confused with available space.

We hope you found this information helpful! There's lots more where this came from—check out our Help Center, which is filled with useful information for treating your patients with clear aligners.

Also, don't miss our upcoming advanced training webinar on IPR or our advanced training series of webinars on various topics related to clear aligner treatment.

Until next time…

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