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Guidelines for Interproximal Enamel Reduction (IPR)
Guidelines for Interproximal Enamel Reduction (IPR)
Sewon Yang, D.D.S.; Min Seok Kim, D.D.S.; Eugene H. Bass, D.M.D.
ABSTRACT
The purpose of this review is to present current guidelines for interproximal enamel reduction (IPR) safety and to provide clinical protocols for the practitioner to follow to conduct safe and effective IPR. This comprehensive step-by-step protocol for IPR, including pre-, intra- and postoperative safety measures, is proposed with further suggestions to assure the safety of the procedures and to minimize the potential iatrogenic side effects of IPR.
Interproximal enamel reduction (IPR), or air-rotor stripping, has been recognized as a popular space-gaining method in orthodontic treatment procedures. Various other space-gaining methods, such as extractions, arch expansions or molar distalization by using mini-implants, are also utilized by practitioners. In addition, IPR has been recognized as a standard of practice for clear aligner therapy that provides relatively conservative orthodontic treatment to patients.
IPR is usually indicated for mild-to-moderate crowding that requires less than 8 mm of space gaining. Other indications include the correction of Bolton Index discrepancies,[9] dental esthetics, the enhancement of retention and stability of orthodontic treatment, and the correction of the Curve of Spee.[6] The benefits of IPR include but are not limited to the following: 1) It is a less invasive procedure to attain space in a patient’s dentition compared to extraction therapy; 2) It provides the ability to create the precise amount of space necessary for tooth movement; 3) It results in a reduced incidence of post-extraction relapse following conventional appliance or fixed band removal.[5,9,11]
Even though IPR is recognized as a relatively safe/lowrisk procedure, the potential iatrogenic side effects of IPR include but are not limited to the following: 1) increased susceptibility to caries; 2) increased incidence of periodontal disease; 3) temperature sensitivity; 4) increased plaque accumulation; 5) residual furrows; and 6) soft-tissue trauma.[8] Therefore, it is important for the clinician to have a comprehensive understanding of the pre-, intra- and postoperative safety measures and to follow these guidelines in order to optimize patient outcomes.
This paper presents the currently available armamentarium for the practitioner to utilize to optimize patient outcomes.
Current Guidelines for IPR
A literature review was conducted to assess currently available guidelines pertaining to IPR. Articles were identified by searching databases (2023): PubMed and NYU Health Science Library. Keywords included: “Interproximal Enamel Reduction”; “IPR”; “Air-rotor stripping”; and “Nonextraction orthodontic treatment.” Articles not available in full text were excluded.
The current guidelines in the dental literature for IPR safety are the following: 1) Case Selection and Space Analysis; 2) Leveling and Alignment; 3) Ensuring Adequate Access to Interproximal Areas; 4) IPR with Soft-tissue Protection; 5) Finishing and Polishing; 6) Topical Application of Fluoride or Casein Phosphopeptide-amorphous Calcium Phosphate (CPP-ACP).[9] What follows is a more comprehensive set of guidelines for practitioners to follow, including pre-, intra- and postoperative considerations (Figure 1).
Preoperative
Case Selection
Acceptable oral hygiene, absence of dental disease, lack of previous proximal reduction, and adequate gingival retraction and visualization of contacts are prerequisites for successful IPR to be conducted.[9] The dentist should identify the complexity of the malocclusion and determine the proper sequence of treatment. If a multidisciplinary approach is required to address the malocclusion, a discussion with the specialists and the patient must be completed before the treatment, and informed consent for the comprehensive treatment plan should be obtained from the patient before proceeding with the IPR procedure.[8]
Space Analysis /Comprehensive Exam
A thorough space analysis should be conducted. A calculation of the exact amount of space required is necessary, as is a determination that the required space can be generated with IPR. IPR has a risk of causing irreversible enamel furrows, scratches and ledges, predisposing to plaque retention, and the risk of sensitivity if dentin is exposed.[9] Therefore, IPR should be planned only when necessary.
An adequate analysis is also required to maintain functional occlusion and to achieve the goals of Andrews Six Keys of Normal Occlusion.[1] Andrews Six Keys are the significant characteristics shared by all the nontreated orthodontic patients with normal occlusion. This includes consideration of the following: 1) molar relationship; 2) crown angulation; 3) crown inclination; 4) rotations; 5) spaces; 6) occlusal plane. One should ask if the space gained through IPR, followed by orthodontic alignment, would be sufficient to achieve Andrews Six Keys.
Leveling and Alignment
Along with the space analysis and comprehensive exam, a practitioner should plan a proper sequence for IPR. When access to the interproximal area is not possible for various reasons, such as crowding, IPR procedures on crowded teeth have to be carried out at a later stage after required leveling and alignment are achieved.[9]
Enamel Thickness
Enamel thickness is an important factor to consider when planning how much enamel can be safely reduced. The amount of enamel is generally greatest in the region of the contact point and decreases towards the cemento-enamel junction. It is unaffected by gender, but there are some racial variations. Pre-existing interproximal wear can also affect the magnitude of enamel that can be removed. It is widely accepted that approximately 50% of proximal enamel can be removed by IPR without causing dental and periodontal risks.[7]
Standardized radiographs may help quantify the amount of enamel present; however, these should be used with caution due to the risk of overestimating the amount of enamel present. Approximately 0.25 mm of enamel reduction in the anterior region and 0.8 mm on each proximal surface of posterior teeth is a safe rule of thumb.[3,7,9]
Contact Point Location
The ability to visualize the contact point is a critical part of the IPR procedure. The absence of proper access might cause the practitioner to inaccurately impart the proper amount and location of the proposed enamel reduction. Contact point locations can be influenced by a variety of factors. Such factors include the shape and size of teeth, the mesio-distal inclination of proximal teeth, their rotations and pre-existing restorations. Enamel reduction leads to the apical movement of the contact point. Apical relocation of the contact point may impinge upon the biologic width of the periodontium or affect the formation of “black triangles.”[9] It is critical to preoperatively assess the ability to visualize and enable proper access to the contact points, in order to assess how the final contact point will be positioned after the procedure. Therefore, it is important to communicate with the patient and obtain informed consent about how variations of crown morphology may lead to a higher risk of creating ledges and less-than-ideal interproximal contacts.
Intraoperative
Soft- and Hard-tissue Protection
Proper retraction of soft tissues is necessary to perform IPR. Such measures to achieve retraction can include using a rubber dam, bite blocks, cheek retractors, cotton rolls and mouth mirrors. Utilization of four-handed dentistry is recommended to accomplish this. The extraoral cheek retractor provides soft-tissue retraction and better visualization of the dentition (Figure 2J).
Steel indicators, coil springs or wedges can be placed gingival to the contact point to minimize the risk of soft-tissue damage and to gain better visual access.[3,7] Firm finger
rest is necessary to avoid unstable use of the instrumentation. A hallmark study suggests that increasing the temperature in the dental pulp by greater than 5.5 °C while using a high-speed handpiece may lead to irreversible damage to pulpal tissue.[10] Therefore, mechanical instrumentation should be water- or air-cooled to reduce the heat imparted on pulpal tissue. If performing IPR on multiple interproximal contacts, changing heated instruments could reduce the risk of thermal damage to the pulp.[7]
Possible Sources of Distraction
All sources of distraction should be reduced or eliminated to prevent accidental damage to the soft and hard tissue of the patient. The involuntary movement caused by the distraction of the patient or the dentist may lead to lacerations and irreversible damage to the intraoral and extraoral tissues. It is important to establish proper communication with the patient in advance to avoid excessive movement during the procedure.
Armamentarium
Manual and mechanical instruments are available for enamel reduction, finishing and polishing, and to avoid soft- and hard-tissue injuries. Interproximal diamond strips are manufactured in varying grits and sizes to allow a sequential increase of enamel reduction and are single or double-sided to allow specific surfaces to be reduced at a time (Figures 2 A,B,C). The manual diamond strips require greater time to accomplish enamel reduction. The mechanical diamond strips are faster but have a risk of causing thermal damage to the pulp tissue.
Safe-tipped diamond burs have non-cutting ends to prevent the formation of notches and allow for precise removal of enamel in the proximal surfaces (Figure 2D).
Rotary diamond discs are also manufactured in varying grits, sizes, and single or double-sided (Figures 2 E,F). These diamond discs are recommended for use in conjunction with the diamond disc guards to prevent any trauma to soft tissue (Figure 2G). New commercially available diamond discs with safe guides have non-cutting edges to prevent unwanted damage to soft and hard tissues (Figure 2F).
If a clinician wants better visualization of and access to the interproximal area, oscillating segment discs can be utilized (Figure 2H). These segment discs oscillate only par-
tially and help to achieve greater control over the reduction compared to the full 360° disc rotation. IPR gauges accurately measure the amount of enamel reduction, which enhances the precision of the procedure (Figure 2 I).
Postoperative
Topical Application of Fluoride or CPP-ACP
Under current guidelines for the postoperative treatment following IPR, in order to prevent caries development in the IPR sites, topical application of fluoride or CPP-ACP for facilitating remineralization of enamel should be prescribed. CPP-ACP is said to be effective in the regression of orthodontic white-spot lesions and was introduced to IPR protocols for postoperative protection of the reduced enamel.[2,4] Furthermore, proper oral hygiene regimens and plaque control are essential to prevent the potential side effects of IPR.
Proper Documentation of IPR
Comprehensive documentation of the IPR procedure and informed consent, including the sites treated, and the amount of enamel reduced in each site are necessary.
Conclusion
IPR has been recognized as a standard of practice for clear aligner therapy. It is acknowledged to be a safe/low-risk alternative to space-gaining for orthodontic teeth alignment compared to extraction therapy. However, even though the IPR has a low risk associated with the procedure, it is important for the clinician to have a comprehensive understanding of the preoperative, intraoperative and postoperative safety measures put forth in this article. Adherence to these proposed guidelines allows practitioners to deliver safe and effective IPR to their patients.
Queries about this article can be sent to Dr. Yang at sy2819@nyu.edu.
REFERENCES
1. Andrews LF. The six keys to normal occlusion. American Journal of Orthodontics 1972;62(3):296–309. https://doi.org/10.1016/s0002-9416(72)90268-0.
2. Chen H, Liu X, Dai J, Jiang Z, Guo T, Ding Y. Effect of re-mineralizing agents on white spot lesions after orthodontic treatment: a systematic review. Am J Orthod Dentofacial Orthop 2013;143:376-82.
3. Chudasama D, Sheridan JJ. Guidelines for contemporary air-rotor stripping. Journal Clinical Orthodontics: JCO 2007;41(6):315–320.
4. Giulio AB, Matteo Z, Serena IP, Silvia M, Luigi C. In vitro evaluation of casein phosphopeptide-amorphous calcium phosphate (CPP- ACP) effect on stripped enamel surfaces. A SEM investigation. J Dent 2009;37:228-32.
5. Gómez-Aguirre JN, Argueta-Figueroa L, Castro-Gutiérrez MEM, Torres-Rosas R. Effects of interproximal enamel reduction techniques used for orthodontics: a systematic review. Orthodontics & Craniofacial Research 2022;25(3):304–319.
6. Lapenaite E, Lopatiene K. Interproximal enamel reduction as a part of orthodontic treatment. Stomatologija 2014;16(1):19–24.
7. Livas C, Jongsma AC. Ren Y. Enamel reduction techniques in orthodontics: a literature review. The Open Dentistry Journal 2013;7:146–151. https://doi.org/10.2174/1874210601307010146.
8. Noar JH, Kneafsey LC. The ethics of interproximal reduction. Dental Update 2015;42(10):922–924.
9. Pindoria J, Fleming PS, Sharma PK. Inter-proximal enamel reduction in contemporary orthodontics. British Dental Journal 2016;221(12):757–763.
10. Zach L, Cohen G. Pulp response to externally applied heat. Oral Surg Oral Med Oral Pathol 1965;19:515-30.
11. Zhong M, Jost-Brinkmann PG, Zellmann M, Zellmann S, Radlanski R J. Clinical evaluation of a new technique for interdental enamel reduction. Journal of Orofacial Orthopedics = Fortschritte der Kieferorthopadie: Organ/official journal Deutsche Gesellschaft fur Kieferorthopadie 2000;61(6):432–439.
Sewon Yang, D.D.S., principal investigator on this paper, is a recent graduate of New York University College of Dentistry, New York, NY.
Min Seok Kim, secondary investigator on this paper, is a recent graduate of New York University College of Dentistry, New York, NY.
Eugene H. Bass, D.M.D., faculty advisor on this paper, is a group practice director and clinical assistant professor, Department of General Dentistry and Comprehensive Care, New York University College of Dentistry, New York, NY.
