IPR and ARS are acronyms that are commonly used in conjunction with orthodontic treatment, but they are generally unknown outside of orthodontics. Just like in the acronym filled military, orthodontists have their own language and acronyms. So what are IPR and ARS? IPR stands for Inter-Proximal Reduction and ARS comes from Air Rotor Stripping. They are very similar, but distinctly different. The purpose of both IPR and ARS is to make the teeth smaller, creating space so that the there is less crowding, a reduced need for extractions, and the teeth can be moved easier. The amount of tooth enamel removed with either IPR or ARS depends on several factors. The amount of crowding, the tooth shape and contours, location of the contact points, aesthetic goals and needs, in addition to other individualized needs all influence what is done and how much natural tooth structure is removed. In almost every case, the natural tooth structure that is removed is healthy and would normally be retained, unless there is a need for IPR/ARS that outweighs the normally detrimental removal of healthy tooth structure.
Inter-Proximal Reduction is a process that removes enamel between the front teeth, making the sides flat, the teeth skinnier, and providing long flat contacts in place of the natural contours and contacts of the teeth. IPR may be done using a long, thin diamond coated strip that is pulled between the teeth by hand, or it may be done with a slow speed handpiece that drives a thin diamond coated disc. The diamond coated strips and discs come in different levels of courseness from ultra-fine to extra-coarse. The coarser strips and discs remove enamel from the teeth more aggressively than the fine, and the discs remove enamel faster and more aggressively than the strips. If coarser strips/discs are used, the IPR will usually progress from the use of the coarse to the fine so that the tooth surface is polished to a more natural finish.
The strips are all the same size and thickness, but the discs can vary from thin and flexible to thick and ridgid. The thicker the disc, the more enamel it will remove and the more space it will create. There are varying thicknesses that correspond to the amount of space needed, so guess work is pretty much eliminated and only the amount of space needed is created. With IPR, both the size and the shape of the teeth are changed and the natural contours are eliminated to some degree, based on how much of the tooth structure is removed and ground away. The goal is to make the teeth skinnier and flatten the contacts.
With ARS, the goal is to maintain the natural tooth contours, but make the size of the tooth smaller. ARS is usually done on the back teeth; the molars and premolars. Oftentimes, these teeth are not crowded like the front teeth, and it can be very difficult to move them further back in the mouth to make more room at the front so the front teeth can be straightened. If these back teeth are made smaller, the spaces can be closed by sequentially moving the teeth towards the back, into the spaces that were created by making the teeth smaller. In essence, the spaces are being shifted to the front of the mouth where the crowding is. The space is then used to align the front teeth and eliminate the crowding.
With ARS, the sides of the teeth are ground down and polished so the teeth are thinner. However, unlike IPR where the goal is to modify the natural tooth contours, once the space is made, the sides of the teeth are not usually left flat. Initially, the teeth are made smaller by using a disc to break the contact, and a thicker disc may be used to remove additional tooth structure and create a bigger space. Once the desired amount of space is created, the teeth are re-contoured to a more natural form and the contacts remain more natural. There are different burs and discs used to make it possible to contour the teeth after the spaces are created by reducing tooth size. How much recontouring and enamel removal takes place is dependent on the treatment objectives, tooth shape, space requirements, and bite coordination.
Since both IPR and ARS remove natural tooth structure, they need to be used judiciously. Because enamel is being removed from healthy teeth, there is always a concern that this will adversely affect the health of the teeth. As a result, there have been many studies done to see if IPR or ARS has a detrimental effect. Studies have shown that the limited amount of enamel removed does not increase the risk of cavities, or the overall health of the teeth. However, there are risks of tooth sensitivity, unnatural contours, periodontal concerns, and aesthetic dilemmas. If ARS or IPR are done judiciously, the risks are minimal. If they are not done well, irreversible complications can occur. If complications occur, there is a way out; thanks to modern materials. If too much tooth material is removed, the natural contours or excess removal can be restored and cosmetics enhanced.
IPR and ARS came about because extraction of permanent teeth became very prevalent in orthodontic treatment. If it was not considered feasible to create the space and keep all the permanent teeth, teeth were extracted to create space to straighten the front teeth and fix the bite. The problem with extractions is that the amount of space needed was often significantly less than the amount of space created with the extractions. The ideal scenario in many cases would be to remove some portion of a tooth, but not a whole tooth. If the space of half a tooth was needed in treatment, a whole tooth would be extracted, the teeth aligned and the bite fixed, then the remaining excess space was basically wasted and would need to be closed.
If fractional tooth removal were possible, extractions could be reduced and the amount of space needed could be coordinated with the amount of space created. Fractional tooth removal is what IPR and ARS accomplish by making the teeth smaller by removing some of the enamel on the sides of the teeth. The main problem is that there is only a limited amount of enamel thickness on the tooth. Therefore, the amount of space that can be created without harm to the tooth is limited.
IPR and ARS have limited capacity to prevent tooth removal, but they have a place in orthodontic treatment and are a viable treatment option that should be used judiciously. It may be better to remove some healthy tooth structure on multiple teeth, rather than remove a whole tooth. Some believe that flattening the contacts has the benefit of enhancing long-term alignment of the front teeth. In some cases, there can be a nice aesthetic benefit to IPR/ARS. Some tooth shapes are considered more cosmetic than others, and the shape can be modified by recontouring by removal of enamel in specific areas. Although not a part of IPR or ARS, the edges of the teeth can be adjusted or restored to improve cosmetics and tooth shape. This may be referred to as manicuring the teeth, similar to manicuring the finger nails so the edges look better and have an improved contour. Manicuring can do a lot to enhance cosmetics, but if tooth wear is significant, restoring the lost tooth structure may be a better option.
IPR and ARS are just a couple of the many tools in the orthodontists tool box. They can be very helpful in reducing the need for extractions and can do a lot to enhance smile aesthetics when used properly. There is definitely a time and a place for using IPR and ARS in orthodontic treatment. It may not be much fun, but it might be better than extracting a tooth.