The Strategic Importance of Interproximal Reduction (IPR) in Clear Aligner Therapy

Interproximal Reduction (IPR), also known as "stripping," is a widely misunderstood and sometimes controversial topic in orthodontics. However, when strategically and skillfully performed, IPR is a powerful and irreplaceable tool that enables the successful treatment of a broad range of cases with clear aligner therapy. For dental professionals, a deep understanding of IPR is not just beneficial it's essential for achieving predictable and stable outcomes. 

What is IPR and Why Is It Necessary? 

IPR is the controlled removal of a small, precise amount of enamel from the sides of teeth to create space. Unlike extractions, which are reserved for severe crowding, IPR is a conservative approach that addresses a fundamental challenge in orthodontics: a tooth-size and arch-length discrepancy. 

In the context of clear aligner therapy, IPR serves several critical functions: 

• Space Creation: The primary purpose of IPR is to generate the small amount of space necessary to resolve mild to moderate crowding. Clear aligners move teeth by a few millimeters at a time, and this movement often requires extra room that can be created with IPR. A study on Invisalign cases found that IPR was required in 71% of patients, highlighting its common use. 

• Correction of Bolton Discrepancy: This refers to an unequal ratio between the width of the upper and lower teeth, which can lead to an improper bite. IPR can be used to "fine-tune" the size of specific teeth to achieve a perfect fit and improve occlusal stability. 

• Midline Correction: By selectively reducing the enamel on one side of the dental arch, IPR can help shift the dental midline to align with the facial midline, enhancing esthetics. 

• Reduction of "Black Triangles": These are small spaces that can appear between teeth at the gum line after alignment. By making the teeth slightly more tapered, IPR can encourage the teeth to move closer together and reduce or eliminate these triangular spaces. 

Techniques, Tools, and Best Practices 

The success of IPR is highly dependent on the technique and tools used. Practitioners must be proficient to ensure patient safety and predictable results. 

• Techniques: 

• Manual Stripping: Involves the use of abrasive diamond strips, ideal for minimal adjustments and fine-tuning. 

• Mechanical Stripping: Uses oscillating handpieces with diamond-coated discs or saws. This method is more efficient for greater reductions and in posterior regions where access is limited. 

• Tools: The choice of tools includes manual strips, diamond-coated burs, and specialized oscillating instruments. For larger reductions, mechanical tools are often more predictable, while manual strips are excellent for finishing and polishing. 

• Precision is Paramount: IPR should be performed in a measured and planned manner. The amount of enamel removed per tooth contact is typically between 0.1mm and 0.5mm, with the total amount of reduction being carefully calculated and mapped out in the digital treatment plan. Following IPR, the treated surfaces must be polished to prevent plaque accumulation and maintain enamel health. 

Risks and Professional Consensus 

While IPR is a safe procedure, it is not without risk. Potential issues are almost always the result of improper technique. 

• Enamel Loss: By definition, IPR involves irreversible enamel removal. However, when performed within the recommended guidelines (up to 50% of the enamel thickness on the contact surface), it does not compromise the long-term health or integrity of the tooth. 

• Increased Sensitivity: A temporary increase in tooth sensitivity can occur after IPR, but this usually resolves quickly. Post-procedure fluoride application can help remineralize the enamel and reduce sensitivity. 

• Pulp Damage: This is an extremely rare and severe risk, typically only occurring if excessive or uncontrolled reduction damages the dentin, which is why a conservative and measured approach is critical. 

• Plaque Accumulation: If the treated surfaces are not properly smoothed and polished, they can become rough, making them susceptible to plaque retention. 

Conclusion

In conclusion, IPR is a fundamental procedure that complements the biomechanics of clear aligner therapy. For any dental professional aiming for excellence in their clear aligner cases, mastering IPR is a strategic investment that enables more predictable outcomes, enhances treatment stability, and expands the range of cases that can be successfully treated.