Interproximal Reduction: Benefits and Biological Implications

Interproximal reduction (IPR) is a dental procedure used to create space between teeth by selectively removing small amounts of enamel. It is commonly performed in orthodontics to improve alignment without extractions. While the technique has been used for decades, its benefits and biological effects remain areas of interest for both patients and professionals.

Understanding how IPR interacts with tooth structure and surrounding tissues is essential for evaluating its advantages and limitations.

Enamel Dimensions And Tooth Anatomy

Enamel, the outermost layer of the tooth, is the hardest and most mineralized tissue in the human body. Composed of approximately 96% hydroxyapatite, it provides structural integrity and resistance to mechanical forces. However, enamel lacks regenerative capacity due to the absence of living cells, making any removal permanent. Its thickness varies, with occlusal surfaces measuring between 2.5 to 3.0 mm and interproximal areas—where IPR is performed—ranging from 0.3 to 0.5 mm. This variation is critical when determining the extent of enamel removal to prevent excessive reduction that could compromise tooth integrity.

Tooth anatomy influences how much enamel can be safely removed. Incisors have relatively thin interproximal enamel, making them more susceptible to over-reduction, while premolars and molars have slightly thicker enamel. The shape of the contact points between adjacent teeth also affects the amount of space that can be created. Teeth with broad, flat contacts require more enamel removal than those with naturally tapered contacts. Understanding these differences allows clinicians to tailor the procedure to each patient’s dentition, ensuring safe reduction while achieving the desired orthodontic outcome.

Beyond enamel thickness, the underlying dentin must also be considered. Dentin, which comprises about 70% mineral content, is softer and more porous than enamel, making it more susceptible to wear and sensitivity if exposed. The proximity of the dentinoenamel junction (DEJ) to the interproximal surface varies among individuals, meaning that even small reductions in enamel thickness could inadvertently lead to dentin exposure. This is particularly relevant in patients with naturally thin enamel or pre-existing wear. Excessive interproximal reduction increases the risk of dentin hypersensitivity and caries development, reinforcing the need for precise measurement and controlled removal techniques.

Process And Instruments

IPR involves the controlled removal of enamel from the contact surfaces of adjacent teeth to create space for orthodontic alignment. The procedure requires precision to optimize tooth positioning while maintaining structural integrity. Instrument selection depends on factors such as the amount of enamel to be removed, tooth anatomy, and clinician preference. Traditional methods relied on hand-held abrasive strips, but modern approaches use rotary and oscillating systems for greater accuracy and efficiency.

Manual reduction with diamond-coated abrasive strips is effective for minimal enamel removal, typically 0.1 to 0.3 mm per contact. These strips allow controlled reduction but can be time-consuming when multiple interproximal contacts need adjustment. To improve efficiency, clinicians often use motor-driven systems such as diamond discs or oscillating segmental strips. Diamond discs, mounted on low-speed handpieces, facilitate uniform reduction but require careful angulation to prevent excessive removal. Improper disc positioning can lead to uneven enamel reduction, increasing the risk of exposing underlying dentin.

Oscillating systems, such as the EVA handpiece with reciprocating strips, minimize the risk of over-reduction by allowing more controlled movement. These systems are particularly useful in posterior regions where visibility and access are limited. Research comparing oscillating strips to diamond discs has shown that oscillating systems produce smoother enamel surfaces with fewer irregularities, reducing susceptibility to plaque accumulation. Surface roughness is a key consideration following IPR, as increased texture can facilitate bacterial adhesion. To mitigate this, polishing protocols use fine-grit finishing strips or fluoride-based remineralization agents to restore smoothness and enhance enamel resistance.

Accurate measurement of enamel removal is essential. Digital calipers and thickness gauges allow clinicians to verify reductions down to 0.05 mm. Advancements in intraoral scanning and artificial intelligence-driven software have enabled real-time monitoring of enamel reduction, improving procedural accuracy. A study in the Journal of Clinical Orthodontics found that digital scanning reduces variability in IPR measurements compared to traditional manual assessments, leading to more predictable outcomes.

Biological Response

The biological effects of IPR center on enamel integrity, dentin sensitivity, and periodontal adaptation. Since enamel does not regenerate, any removal permanently alters the tooth’s protective outer layer. While controlled reduction aims to stay within safe limits, post-IPR enamel surfaces exhibit increased roughness, which can affect bacterial adhesion and plaque retention. Surface irregularities may create microenvironments conducive to biofilm accumulation, increasing the risk of caries if proper oral hygiene is not maintained. To counteract this, clinicians implement polishing protocols or fluoride applications to enhance enamel remineralization and reduce surface porosity.

Dentin hypersensitivity is a potential consequence when reduction approaches the DEJ. While enamel lacks nerve endings, underlying dentin contains microscopic tubules that communicate with the pulp. If these tubules are exposed or become more permeable due to IPR, patients may experience transient sensitivity to thermal or mechanical stimuli. Research in the Journal of Oral Rehabilitation suggests that sensitivity following IPR is generally mild and self-limiting, resolving within a few weeks as tubular occlusion occurs naturally through salivary mineral deposition. However, individuals with pre-existing enamel wear or thin enamel layers may have a higher risk of persistent discomfort, necessitating the use of desensitizing agents such as arginine-based compounds or calcium phosphate pastes.

Periodontal tissue response also plays a role in biological adaptation to IPR. The reshaping of interproximal contacts can influence gingival contour and papillary architecture, particularly when significant space is created. A study in the American Journal of Orthodontics and Dentofacial Orthopedics found that minor reductions do not significantly alter gingival health when performed with proper technique and post-procedural care. However, excessive removal leading to increased interdental spacing may contribute to soft tissue recession or black triangle formation, especially in patients with thin gingival biotypes. Maintaining optimal oral hygiene and monitoring soft tissue response can help mitigate these effects.

Uses In Orthodontic Realignment

IPR is widely used in orthodontic treatment to address mild to moderate crowding without extractions. By selectively removing small amounts of enamel, clinicians create space to facilitate tooth movement while preserving a patient’s natural dentition. This approach is particularly beneficial in cases where arch length discrepancies exist but do not warrant the removal of entire teeth. Compared to extraction-based treatments, IPR offers a conservative alternative that maintains facial profile and occlusal stability while achieving alignment goals.

In cases of Bolton discrepancy, where the size ratio between upper and lower teeth is mismatched, IPR helps harmonize tooth proportions. A common example is mandibular anterior excess, where lower incisors are relatively larger than their maxillary counterparts, leading to improper occlusion. By reducing interproximal enamel in a controlled manner, orthodontists can balance tooth dimensions and improve intercuspation without restorative interventions. Studies show that addressing these discrepancies through IPR enhances long-term stability by reducing the likelihood of post-treatment relapse.