Revolutionizing Interproximal Enamel Reduction
Technique can be applied to modern orthodontic tooth alignment.
The rise in popularity of adult orthodontics is an indication that the general population understands the benefits of a healthy bite and a straight, pretty smile. According to a recent study by American Association of Orthodontics posted on its Web site (http://www.braces.org), the number of adult patients receiving some form of orthodontic care has risen 37%.1,2 This jump is credited to increased self-esteem found in an attractive smile and the various alternatives to traditional “braces” available today. Clear or “invisible” braces that involve either a series of trays or “aligners” are very popular. These alternatives can correct spaces, straighten misaligned teeth, and alleviate crowding.
Several methods to alleviate crowding are employed in both conventional and “invisible” tray orthodontics. Arch expansion, tooth extraction, and proclination are often used to create room for crowded teeth; however, it is quite common to employ some form of interproximal reduction (IPR) or air-rotor stripping (ARS) to create space in many orthodontic situations.3 These slenderizing and reshaping teeth methods are quite common in adult orthodontics and are often employed with systems like Invisalign® (Align Technologies, http://www.invisalign.com) and Essix Minor Tooth Movement (DENTSPLY Raintree Essix, http://www.essix.com).
Guidelines for Interproximal Reduction
It is generally advised to remove approximately one half of the enamel thickness available on any interproximal surface.4 On average, premolars and incisors have 0.7 mm to 1 mm of interproximal enamel. Therefore, conservative interproximal reduction should not exceed 0.5 mm from any single interproximal surface. By using these guidelines, sufficient enamel should remain to resist decay and avoid sensitivity.
It is quite common for some orthodontic tray systems, such as Invisalign, to dictate IPR as part of the treatment protocol to correct crowded teeth. Though the amount of reduction may vary based on each specific case, typical reduction recommendations are standardized between 0.1 mm to to 0.5 mm with 0.05-mm increments in between.5,6 Metal reduction guides gauged to each thickness are used to ensure proper reduction.
The Danger of Rotary Discs
The use of flexible diamond-coated discs in a straight handpiece (Figure 1) or in a latch-grip attachment has been used in performing IPR by some clinicians. Because these discs rotate 360° (often at 35,000 to 40,000 rpms), if they become jammed in the contact, the risk of the disc rotating out of control and rapidly ejecting into the surrounding tissue is extremely high.
KOMET USA’s IPR Kit
A novel product designed specifically for safe, efficient, and accurate interproximal tooth reduction has been developed by KOMET USA (http://www.komet-usa.com). Featuring a series of diamond-coated OS (oscillating segment) discs that are designed to be used in conjunction with an KOMET OS30 electric handpiece, the IPR Kit 4594 (Figure 3) is the current state-of-the-art tool for creating interproximal space for orthodontic correction of crowded teeth.
What is unique about this IPR system is that each honeycombed-designed disc does not rotate 360°, but merely oscillates 30° (15° in each direction). The oscillating motion is superior to complete rotary movement in that binding or jamming in the interproximal contact is minimized and accidental rotation (catching and running) into the adjacent hard or soft tissue is less likely to occur.
The diamond-coated OS discs are arranged in increasing thickness (0.2 mm to 0.4 mm including reduction by subsequent polishing) and are sequentially used from the thinnest to the thickest until the target amount of enamel is reached. Furthermore, the kit contains discs that have diamond coating on one or both sides. Even though it is not recommended by KOMET USA, in the author’s practice, he has discovered that he can use a single-sided coated OS disc to carefully reduce a single tooth when mild overlap or rotation does not permit a straight pass interproximally.
The single-sided coating is available in 0.15-mm to 0.2-mm thickness on the outside (away from the shank) or the inside (toward the shank) so that either a “push” or “pull” motion may be used as dictated by the arrangement of the teeth to be reduced. Also included in the kit are discs in each thickness that are diamond-coated on both sides. These OS discs are best used when crowding is less severe and simultaneous interproximal reduction of both adjacent teeth is possible.
The OS30 handpiece should be used after the initial contact is opened with diamond-coated metal strips and should operate at a 1:1 setting. This setting permits an oscillating speed of 5,000 oscillations per second and should be used with sufficient water spray for heat reduction. The OS discs are designed to enter the contact from the occlusal aspect of the contact and the honeycombed design permits clear visibility as the reduction occurs.
The following case presentations demonstrate the clinical techniques and advantages of using the KOMET USA IPR Kit for interproximal enamel reduction.
Creating 0.5 mm of IPR between Mildly Rotated Teeth
In this case, Invisalign is being used to correct moderate anterior crowding by distalizing the premolars to create space. The Invisalign ClinCheck dictated that 0.5 mm of IPR between teeth Nos. 13 and 14 and 12 and 13. As seen in Figure 4, the preoperative condition displays only a mild rotation of tooth No. 13 and ample access to the contact from an occlusal approach. The first step in using KOMET USA’s OS discs is to lightly break contact with a fine diamond-coated abrasive strip (WS37EF, KOMET USA) (Figure 5). In cases where the contact is large and access is difficult, using progressively thicker strips to open the contact significantly is advantageous before beginning with the OS discs.
The next step is to decide whether to use the dual-coated diamond OS discs or the single-sided, diamond-coated OS discs. In this case, the amount of tooth rotation is minimal and the teeth are not overlapped. This presentation is ideal for using the dual-sided, diamond-coated OS discs for rapid removal of interproximal enamel on both adjacent teeth simultaneously.
Begin by attaching the thinnest OS disc (0.13-mm red-banded disc, not shown) to the oscillating handpiece. Place the electric handpiece setting on 1:1. With coolant spray, enter the contact area at the appropriate angle from the occlusal at 5,000 oscillations per second. Entering the contact at lower speeds does not facilitate a smooth pass. Using a firm finger rest, simply hold the handpiece still and allow the 30° oscillations to reduce the interproximal enamel as pressure is applied toward the gingival papilla. Once the contact has been breached, remove the OS Disc from the interproximal area and insert the next thickest disc into the handpiece. Figure 6 shows the final 0.5-mm, blue-banded disc finalizing the interproximal reduction. The completed interproximal reduction is shown in Figure 7 and the width of the space is checked with the 0.5-mm thickness gauge (Figure 8).
Interproximal Reduction between Overlapping Teeth
When interproximal reduction is necessary between overlapping teeth, removing the appropriate amount of enamel on each of the adjacent teeth can be more challenging. As seen in Figure 9, simply passing a dual-coated diamond disc between teeth positioned like these would result in uneven reduction and anatomically mutilated contours.
In clinical scenarios such as this, the single-sided, diamond-coated OS discs are appropriate. In this case, the amount of IPR indicated is 0.3 mm, which means that 0.15 mm needs to be reduced from each tooth. After breaking contact with a diamond-coated metal strip, simply insert the 0.15-mm OS disc with the diamond coating facing the shank and position it against the mesial aspect of tooth No. 9. With water coolant, use a sweeping motion to begin removing enamel and enter the contact area from the facial aspect (Figure 10 and Figure 11). The OS discs have the flexibility of common diamond discs and are optimal for shaping and contouring as well as interproximal slicing. The clinician should be careful not to jam the disc.
When the 0.15-mm disc can pass freely between the teeth at the appropriate angle, insert the 0.15-mm disc into the oscillating handpiece with the diamond coating facing away from the shank. Position it against tooth No. 8 and with a sweeping, pushing motion, begin reduction of the mesial enamel. Again, be sure to shape and contour the tooth as the contact is opened an additional 0.15 mm.
Figure 12 shows the view of the completed IPR from the patient’s right side. A 0.3-mm reduction gauge confirms the appropriate amount of reduction. Figure 13 shows the completed IPR from a straight-on facial view. Note that even though the IPR is complete, the teeth remain appropriately contoured and are smoothly polished with little to no need for diamond strips.
Though interproximal reduction is often used in traditional banded/bracket orthodontics, it is quite commonly used in tray aligner systems such as Invisalign and Essix Minor Tooth Movement. As the popularity of these “invisible” orthodontic options increases, more and more practitioners will need a safe and reliable system to create space for tooth alignment. KOMET USA’s IPR kit and OS30 electric handpiece not only offers a safe alternative to traditional 360° rotating discs, but also comes in the customary thicknesses often prescribed by these tray aligner systems. The 30° oscillating handpiece reduces the potential for running into adjacent soft tissue, facilitates the access to posterior teeth, and permits shaping and contouring while the reduction sequence is used. Fast, efficient, and easy to use, the IPR Kit revolutionizes the clinical technique for interproximal reduction and eliminates the need for free-hand improvisation at the chair.
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5. Data on file. Available at: http://www.invisalign.com. Accessed December 23, 2009.
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About the Author
Jeff T. Blank, DMD
Carolina Smile Center
Fort Mill, South Carolina
Chief Clinical Instructor
New Millennium Education, LLC