What is IPR? Simply put it is the removal of interproximal enamel to reduce the mesial-distal size of teeth.
Interproximal reduction became popular over the past years with the advent of bonding brackets on teeth which exposed the interproximal surfaces and created the option to gain space by modifying the enamel with slenderizing techniques. Prior to that, intra-arch space was solely created by extraction, expansion, proclination or surgery. IPR is commonly used with clear aligner treatments such as Essix Minor Tooth MovementTM and InvisalignTM.
Historically, Black described natural slenderization in 1902. Bullard in 1944 described the first clinical technique for narrowing teeth, followed by Sheridan (labial technique) and Fillion (lingual technique). Recently there are a slew of entrepreneurs that have developed equipment, and teach techniques, to facilitate the process.
Confusion exists because there are many names for similar procedures with slightly different twists. The term IPR was popularized by InvisalignTM (Align Technology). Prior to that ARS (Air Rotor Stripping) was the most common term, Dr. J Sheridan having wrote the book on ARS (Dentsply Raintree Essix). ERSTM (Electric Rotor Slenderization) is basically ARS with more control, safety and accuracy, getting disc revolutions down to between 100 and 500 rpms. (Spee Corporation- San Diego, Ca) Other terms new to the arena are Interproximal Reduction SystemTM (IRS-GAC), Cosmetic Tooth Contouring (CTC- Drs. Jaimee Morgan and Stan Presley) and Dr. David Galler has named what he is teaching the Galler Technique.
Why/WHEN DO YOU USE IPR?
Basically IPR is an adjunctive technique employed to reduce intra-arch crowding of up to 8mm and to increase stability by flattening contact surfaces. It is good to help with mild to moderate crowding and to reduce the amount of expansion, proclination and extraction required. It facilitates moving teeth shorter distances as opposed to extraction cases, and has further advantages of less relapse, more parallel roots and more stable contact points. Barrel shaped or triangular teeth provide more enamel, but, as in younger teeth the location of the nerve should be considered too. It should be avoided in patients with very poor hygiene or very rectangular teeth and teeth with little interproximal enamel. Although 8-9mm of space per arch can be achieved by removing interproximal enamel, Dr. Sheridan has recommended creating no more than 1mm shared posterior space and .5mm shared space in the anterior interproximal points. Crowding of 2.5mm in the anterior may be resolved without expansion just using IPR of the anterior 5 contact points.
PERIODONTIAL IMPLICATIONS OF IPR
Generally speaking, “the smaller the interproximal space, the less the predilection for intrabony defects and the larger the distance, the greater the tendancy. Data indicates that some wider, rather than narrower interradicular spaces may be more likely to experience bone loss.” In posterior areas it was found that “bone was apparent and healthy when root surfaces were as close as .3mm. When root surfaces were closer, interproximal bone was not observed.” In addition- “there is a physiologic adaptation to attenuated space in the absence of pathology”. One must be careful in doing IPR not to nick or gouge the cementum which could lead to loss of attachment.
ARMAMENTARIUM
Here are some of my preferred IPR collection of tools and toys.
Clear separators to wedge contacts open prior to beginning IPR. (34-000-35 GAC/ Dentsply Canada). If you do not have an orthodontic haemostat these can be placed using two pieces of floss as handles or a placement plier (Dentsply Raintree Essix) .
Hand help stripping devices: QwikStripsTM (mynydoc@aol.com), colour coded in the typical endo sequence i.e. white, yellow, red, blue, green and black and invented and patented by Dr. Louie Khouri. QwikStrips are my preferred workhorse, for initiating IPR and getting a contact point opened. They come in single sided, double sided and anatomical curved and can open a contact point to over 3mm. You should not gouge or ledge the enamel if you use this product, it has a non-cutting edge. They are reusable to some extent, very grippable, safe and reliable. They come with instructions and a sequence guide, to guide you through anterior and posterior contact point opening. They are marketed for multiple use if you follow manufacturers sterilization procedures. When they become very worn they can still be used for breaking open bonded contact points, polishing and removing stain from interproximal restorations and even calculus removal in areas that a scaler didn’t get to. Tip: get the white serrated ones to open contact points after bonding veneers- place them interproximally and gently seesaw them until the contact opens. ContacEzTM (ContacEZ, LLC Vancouver, Washington) is a recent copycat version of QwikStripsTM, the contact surface is smaller and more flexible.
Leaf Gauges for measuring space before and after IPR which should be accurately recorded. Different ones are available metal ones (Invisalign, Dentsply Raintree Essix and other suppliers), clear plastic .125 thickness (Great lakes Ortho, Tonawanda, NY). TIP: your periodontal probe can act as a measuring gauge, in general the flat surface is .25mm at the 1-3mm portion and .5mm at the 7-9mm portion.
Stainless steel diamond coated strips are available alone or with handles. The strips are flexible and leave rounded and smooth edges Most of them can be sterilized and reused keeping in mind that the thickness and efficiency will be altered. Many suppliers sell these, the perforated ones are great for vision, but, do not last as long as the solid ones. These are great for finishing too. Strip holders include Stainless Steel Strip HolderTM (Spee corp.) and CeristripTM (DenMat),
Mechanical strip systems include Intensive Ortho Strip SystemTM (GAC Dentsply) and Ideal StripsTM (Dentsply Raintree Essix) both sold with reciprocating handpieces. Ideal strips have been used manually without the handpiece, they are more expensive and less controlled than hand held Qwik StripsTM mentioned earlier. Ideal Strips are also marketed for single use.
Discs: to be used with caution as often cause ledging , are hard to control, and produce heat and the ones with cutting edges are sharp. They can bind and bend. Discs often gauge the enamel and leave rough surfaces.
There are lots of options here and lots of sizes and thickness to choose from. They are most useful when you need to create a lot of space. Discs can be necessary and they tend to last a long time but a word of caution because discs and burs are the leading cause of ledging! Ledging can be avoided completely with proper technique and caution- open the contact point with something like a QwikStrip first and then use the discs to get you to the desired size. Having a good set of discs around is invaluable. The thinner the disc the more flexible it is and they can deform permanently. I’ve tried discs from Axis, Brassler, Dentsply Raintree Essix, Komet, and Invisilign. They look like they might come from a similar source and are great.
Disc Guards: If you are ordering one of these make sure that it fits on the hand pieces that you have. They are available in plastic (clear) or metal. It is highly recommended that you use one of these to protect the inadvertent nicking of soft tissue, especially the lip and tongue. The clear version allows for better
vision. Some guards allow you to grip closer to the tooth surface for better tactile sense. Discs are scary for the dentist and the patient, and a disc guard might alleviate that somewhat.
Mechanical disc systems: Often come with their own handpieces and disc systems. They are air/electric powered slow speed motors with discs that have non-cutting edges for safety. ERSTM discs (Spee), IDEAL IRSTM and the new comer from Kavo (Patterson , Komet). I recently demoed the Kavo unit and the discs are triangular and perforated for better vision. They come in a number of widths, but, it is difficult to know what width you are using without going by the flexibility of the disc. Although it is a bit pricey, the discs can be reused a lot and as long as you open the contact point prior to using this system, you can avoid getting it jammed in the contact point. With this type of system, it is recommended to insert the moving disc/strip into the slightly opened contact point and swing it “like a violin” to the desired space. Swing it in a buccal/lingual motion and do not force it or use it as a lever. When it jams it is very awkward as your hand will swing and not the disc…not appearing very good to the patient.
ARS Burs: to use with caution as they are rigid and unforgiving and can cause ledging, taking off a lot of enamel quickly.
The mosquito bur is probably my favourite for making larger IPR spaces, especially in the posterior segments. The Mosquito bur allows for easier access of the smaller anterior teeth. This bur is ubiquitous and can be purchased from most of the larger manufacturers. Use caution as the bur is flared and you want parallel proximal surfaces.
The best technique to use this bur is to place it below the contact point (protect the gingival with a wedge) from the buccal and travel toward the occlusal surface. Get a non-cutting end and ask for the measurement of the width of the bur. If you are entering from the buccal or lingual- consider entering from the lingual first to retain better esthetics.
Finishing burs to smooth and shape surfaces are the operator’s preference, but should be at hand. They’re used to reduce ridges and grooves produced by IPR to ~15 microns. Function will continue to smooth the surfaces close to the texture of unaltered enamel.(Radlanski)
Fluoride or remineralization products: This is a controversial subject, some operators recommend it and others do not. In fact, the enamel is said to be stronger after IPR once it remineralizes than the untouched surface! I might look at the caries potential of the individual that you are working on and decide on an individual basis.
TECHNIQUE
There is no one technique for every situation- but there are a number of common sense systems that facilitates getting the job done.
1. Diagnose and plan ahead: You should never IPR in a false contact point where you are not adjusting interproximal enamel. Determine the amount of space you need and where to get it from best and then decide on the IPR technique to get you there. This can be done with a Bolten Analysis ( Spee article) , measuring each tooth width and comparing it to the space required; x-ray analysis of the teeth will tell you where the enamel is thickest…look for bell shaped teeth rather than rectangular. Check for black triangles and the length of the contact points. Sound to bone from the base of the contact point if you are concerned with a black triangle you want 4.5-5mm to allow for the papilla to fill the space (D. Tarnow). Also, IPR should allow the vertex of the papilla to be in line with the contact point vertically, so plan the IPR to allow for this. You never want to IPR a crowded contact point, you may have to IPR adjacent teeth and then shift them to get the space in the right spot, or “round house” by doing expansion first then employing IPR (only on interproximal enamel) and then pull the teeth back again…worthwhile not to misshape the teeth. Also, be careful to keep the central incisors symmetric and the same width and to respect the facial midlines. In the same line of thought, try not to slenderize the laterals so much that they start to look like peg laterals. Consider recontouring over dimensioned restorations before touching enamel. Plan to remove at the contact point and avoid flattening other rounded contours…a flexible cutting tool facilitates this as do finishing tools.
2. Break the contact point carefully: The most precise way to get an accurate amount of enamel removed is with a single sided reduction one proximal surface at a time. On most occasions I will reach for my QwikStripsTM and sequentially open the contact point until I can utilize something in my armamentarium that will speed up the process. Protect the patient’s tongue, lips and gingiva at all times if you are using mechanical systems. Use an assistant and cooling water. Eye protection is recommended for patients and operators. Read and follow manufacturer’s directions until you find a way to use the product that works better for you. Most of the systems lay out which disc to use and how to use it fairly well in their information sheets.
3. Finishing IPR surfaces: You need to be able to bend the disc or strip to be concave in order to contour to final anatomy. IPR tends to flatten and roughen up tooth surfaces. Finishing gives you the opportunity to round and smooth them. Fine strips are very useful for this purpose. It has been demonstrated that IPR does not predispose to caries, but, rather to a period of demineralization followed by remineralization. (El-Mangoury et al.)
There is a rapid remineralization of enamel that leaves the surface more resistant to caries (Brudevold). The loss of a layer of fully reacted surface enamel, with surface porosities and increased surface area for interaction with remineralization agents leads to stripped enamel having more potential than unaltered surfaces. (Hanachi, Sheridan). Knowing this and the patient’s predilection for caries, it is up to the operator to decide if anti-caries or remineralization agents should be prescribed after IPR.
4. Goughed surfaces: This is rare, but, it eventually happens to everyone when we get a bit aggressive or misjudged the contact point or angle of approach. I highly suggest getting over it, and telling the patient that you are placing a resin restoration to seal and protect the tooth. It is not a big deal unless you are an orthodontist rather than a restorative dentist. If you are really nervous about ledging a tooth, stick with using the manual, sequentially larger QwikStripsTM and you will not have a problem.
5. Measure, record and date the amount of space interproximally that you have created. Use a perio probe or a number of gauges previously mentioned in the armamentarium section. There are a number of forms available to do this on: Invisilign or Dentsply Raintree Essix have downloads. I find recording it on the patient’s chart works for me. Be consistent in how you record measurements so that they are accurate and easily found.
6. Flouride and remineralization agents: It has been demonstrated that IPR does not predispose to caries, but, rather to a period of demineralization followed by remineralization. (El-Mangoury et al.) There is a rapid remineralization of enamel that leaves the surface more resistant to caries (Brudevold). The loss of a layer of fully reacted surface enamel, with surface porosities and increased surface area for interaction with remineralization agents leads to stripped enamel hav
ing more potential than unaltered surfaces. (Hanachi, Sheridan). Knowing this and the patient’s predilection for caries, it is up to the operator to decide if anti-caries or remineralization agents should be prescribed after IPR.
Conclusion
This article is a summary of personal opinions on techniques and materials with regards to performing interproximal reduction for the purpose of slenderizing teeth to create intra-arch space. There is a fair amount of anxiety that is associated with the procedure for both dentists and patients. If the technique is planned and done in stages to open the contact point in a less crowded location and then sequentially taken to the size needed, this anxiety should be allayed. OH
Janice Goodman graduated from University of Toronto Dental School in 1979. She teaches Essix Minor Tooth Movement, was on the advisory board for Dentsply Raintree Essix and practices general practice dentistry in Toronto. She is on the editorial board of Oral Health Journal.
Oral Health welcomes this original article.
REFERENCES
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2. The demineralization and remineralization potential of stripped enamel surfaces. Hanachi, F. s.l. : Thesis, Department of Ortho, Louisianna State University School of Dentistry, 1992.
3. Hug, H.U. Periodontal Status and its relationship to variations in tooth position: An analysis of the findings reported in literature. s.l. : Helv. Odont. Acta. 26:11-24, 1982.
4. Air-rotor stripping and proximal sealants: an SEM evaluation. Sheridan, JJ and PM, Ledoux. s.l. : J. Clin. Orthod. 23:790-794, 1989.
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6. Air-rotor stripping and lower incisor extraction treatent. Sheridan, JJ and Hastings.J. s.l. : J Clin. Orthod. 26: 18-22, 1992.
7. Relationship between the roots and the prevalence of intrabony pockets. Tal, H. s.l. : J Periodontal; 55:604-607, 1984.
8. Enamel thickness of the posterior dentition: It’s implications for nonextraction treatment. Stroud, JL, English J,Buschang PH. s.l. : Angle Orthod. 68:141-45, , 1998.
9. Air-rotor stripping and enamel demineralization in vitro. Twesme, DA and al., et. s.l. : Am J. Orthod. Dentaofac. Orthoped. 101:142-152, 1994.
10. Radlanski.RJ, et al. Plaque accumulations caused by interdental stripping. s.l. : Amer. Journal Orthod. 94:416-420, 1988.
11. Peck, H and Peck, S. Reproximation (enamel stripping) as an essential orthodontic treatment ingredient pp 513-22. St. Louis : Mosby, 1975.
