Introduction
Interproximal reduction (IPR) is a common adjunct to contemporary orthodontic treatment. This study aimed to carry out a quantitative analysis of IPR prescribed in the refinement phases of clear aligner therapy with the Invisalign appliance (Align Technology, San Jose, Calif).
Methods
The digital treatment plans (DTPs) of a total of 330 patients treated by 11 orthodontists were evaluated. Relevant data regarding patient age, gender, and prescription of IPR in the initial and refined DTPs were obtained from Align Technology’s digital interface, ClinCheck. Computational analyses included descriptive statistics, Mann-Whitney U, and Kruskal-Wallis tests.
Results
Most (n = 182; 75.2%) of the 242 patients who satisfied inclusion criteria were females. The median (interquartile range [IQR]) age was 29.2 (22.1-40.2) years. More than 60% of the contact sites prescribed IPR related to the initial DTP (n = 1312; 60.4%), with 39.6% (n = 859) recorded in the refinement DTPs. A median (IQR) of 1.1 (0.6-2.1) mm of IPR was prescribed per patient in the initial DTP compared with a median (IQR) of 0.6 (0.3-1.3) mm in the refinement DTPs. The most common site for prescribed IPR in all DTPs was the mandibular anterior region. Almost half (n = 108; 44.6%) of the patients were prescribed IPR at the same contact point site more than once during treatment.
Conclusions
Almost 40% of the contact points that were prescribed IPR were in the patients’ refinement DTPs. Most IPR was prescribed for the anterior region of the mandible. Almost half of the patients had IPR repeatedly prescribed at the same sites during treatment.
Highlights
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The prescription of interproximal reduction (IPR) with the Invisalign appliance was evaluated.
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Almost 40% of contact points that were prescribed IPR were in the refinement phases.
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The most common site for prescribed IPR was in the anterior teeth of the mandible.
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Approximately 44.6% were prescribed IPR at the same site more than once during treatment.
Clear aligner therapy (CAT) has become an integral part of contemporary orthodontics, and its use has increased over the last 2 decades. , This is partly credited to a greater proportion of adult patients seeking orthodontic treatment and demanding more comfortable and esthetic alternatives to fixed appliances. , The popularity of CAT can also be attributed to the rise of digital dentistry, in which the increased use of extraoral and intraoral scanners has influenced the ease and efficiency by which patient data can be acquired and evaluated by the clinician.
The Invisalign appliance (Align Technology, San Jose, Calif) appears to be one of the most commonly prescribed CAT appliances globally. Align Technology’s proprietary software (ClinCheck Pro) is used by the clinician to formulate a digital treatment plan (DTP), which enables the manufacture of a series of aligners intended to address specific treatment objectives.
ClinCheck Pro provides numerical data related to various dental, intraarch, and interarch characteristics, such as mesiodistal tooth widths. After treatment with the initial series of aligners, ≥1 additional or refinement phase may be needed. This involves the manufacture of ≥1 additional series of aligners from ≥1 new DTP to obtain the desired treatment outcomes. Several studies have shown that ≥1 refinement phases are routinely required during Invisalign CAT.
Interproximal reduction (IPR) is an adjunctive technique commonly employed during CAT. , , It involves the permanent removal of proximal enamel from the contact points between the teeth. Purported reasons for its use include the need to gain space for the relief of crowding and tooth reshaping in addition to the management of open gingival embrasures and tooth size discrepancies. IPR has also been used as an adjunct to increase the stability of incisor alignment after orthodontic treatment. Current evidence suggests that up to half of the enamel thickness may be removed without adverse side effects. This equates to approximately 0.3 mm for each single maxillary incisor interproximal contact point or surface, 0.2 mm for each single mandibular incisor interproximal contact point or surface, and 0.6 mm for a single contact surface of a posterior tooth.
The ClinCheck Pro software can be used to identify relevant sites and time and quantify the amount of IPR required in the DTP. The IPR recorded within the software is for each contact area and not for the individual teeth associated with each contact area. A 2022 study reported that IPR was prescribed in 71% of 500 patients in the initial DTP of Invisalign treatment. Furthermore, respondents in a recent survey of orthodontists reported that they routinely prescribed IPR in a mean of 55% of their annual caseload in the initial accepted DTP and 31% of their annual caseload in the additional refinement plans. However, the evidence also indicated that the quantity of IPR carried out is less than that prescribed in the initial DTP for treatment with the Invisalign appliance, with less than half of the planned amount of IPR being carried out. , , This may be of clinical relevance, as shortfalls in this regard may have a deleterious impact on treatment efficacy and patient and clinician satisfaction.
To date, research regarding IPR in the refinement phases of CAT is limited. One recent prospective study evaluated the accuracy of IPR with the Invisalign appliance, but direct evaluation of the refinement phase was lacking. This study aimed to quantitatively analyze the IPR prescribed in the refinement phases of CAT with the Invisalign appliance. A secondary aim was to compare the characteristics of IPR prescribed in the refinement phase with those in the initial phase.
Material and methods
Institutional ethical approval was granted by the University of Adelaide Human Research Ethics Committee.
The study used data from the Australasian Aligner Research Database (AARD). As of October 2023, the AARD contained the relevant Invisalign treatment information related to approximately 17,000 patients treated by 17 orthodontists between 2013 and 2023. At the time of data acquisition, the database included patients from 11 orthodontists.
Before commencing their Invisalign treatment, all patients had provided consent for their records to be used for research purposes. The orthodontists are required to make the records of all patients treated with the Invisalign appliance available to AARD.
The last 30 consecutive patients treated to completion by each of the orthodontists with the appliance were selected. After selection, the patients were screened with reference to the selection criteria. The inclusion criteria entailed: (1) patients aged ≥18 years undergoing nonextraction, dual arch CAT with the Invisalign appliance; (2) patients who required ≥1 refinement phase; (3) the availability of ClinCheck Pro files after completing the initial phase, and the completion of the refinement phase; (4) IPR prescribed after the initial phase, to have been completed by the end of the refinement phase; (5) minimum 1-mm IPR in total per patient; and (6) minimum of 2 sites for IPR per patient.
Patients with missing teeth and IPR prescribed to the second and third molars only were excluded from the study.
The age, gender, and number of refinement phases of patients satisfying inclusion and exclusion criteria were recorded. The resultant patient files were opened with the ClinCheck Pro facility, and millimeter values for prescribed IPR between tooth contacts were recorded.
The prescribed IPR sites were recorded and grouped according to the following DTP categories: initial DTP (I), first refinement DTP (R1), second refinement DTP (R2), third refinement DTP (R3), fourth refinement DTP (R4), combined refinement DTPs (R1-4), and total (I + R1-4).
The categories were classified into the following subgroups: maxillary (anterior and posterior), mandibular (anterior and posterior), anterior (incisors and canines), posterior (premolars and first molars), maxillary anterior, maxillary posterior, mandibular anterior, and mandibular posterior.
The contact area between the first premolar and canine was classified as a posterior contact. Consequently, the anterior subgroup contained 5 contact points, and the posterior subgroup contained 6 contact points. All data were entered into a Microsoft Excel spreadsheet (Microsoft, Redmond, Wash).
Statistical analyses
Statistical analysis was conducted via SPSS software (version 29; IBM, Armonk, NY). The significance was set to P <0.05. The Shapiro-Wilk test was performed to determine the normality of the distribution of the data. The test indicated that the results did not follow a normal distribution. Frequencies were presented in medians and percentages. The Mann-Whitney U test and the Kruskal-Wallis H test were carried out to determine whether the differences between the medians of groups and subgroups were significant.
Results
A total of 242 (73.3%) patients were evaluated after the exclusion of 88 patients who did not satisfy the selection criteria. The sample comprised 182 (75.2%) females and 60 (24.8%) males. The median (interquartile range [IQR]) age for the overall sample was 29.2 (22.1-40.2) years, with no significant differences in the median ages of males and females ( P >0.05).
More than 60% of the contact sites prescribed IPR related to the initial DTP (n = 1312; 60.4%), with 39.6% (n = 859) recorded in the refinement DTPs.
Table I outlines the location of IPR sites according to the DTP in which the IPR was prescribed. IPR was prescribed for a total of 2171 contact point sites. The maximum number of refinement DTPs requiring IPR was 4. Overall, 15 patients required 4 refinement DTPs, and 22 patients required 3 refinement DTPs.
| Group | Total | DTP | |||||
|---|---|---|---|---|---|---|---|
| Initial | R1 | R2 | R3 | R4 | R1-4 | ||
| Mx + M d | 2171 (100) | 1312 (60.4) | 600 (27.6) | 223 (10.3) | 32 (1.5) | 4 (0.2) | 859 (39.6) |
| Mx | 728 (100) | 408 (56.1) | 214 (29.4) | 96 (13.2) | 10 (1.4) | 0 (0.0) | 320 (44.0) |
| M d | 1443 (100) | 904 (62.7) | 386 (26.8) | 127 (8.8) | 22 (1.5) | 4 (0.3) | 539 (37.4) |
| Mx + M d anterior | 1608 (100) | 941 (58.5) | 471 (29.3) | 170 (10.6) | 22 (1.4) | 4 (0.3) | 667 (41.5) |
| Mx + M d posterior | 563 (100) | 371 (65.9) | 129 (22.9) | 53 (9.4) | 10 (1.8) | 0 (0.0) | 192 (34.1) |
| Mx anterior | 527 (100) | 284 (5.0) | 170 (32.3) | 68 (12.9) | 5 (1.0) | 0 (0.0) | 243 (46.1) |
| Mx posterior | 201 (100) | 124 (61.7) | 44 (21.9) | 28 (13.9) | 5 (2.5) | 0 (0.0) | 77 (38.3) |
| M d anterior | 1081 (100) | 657 (60.8) | 301 (27.9) | 102 (9.4) | 17 (1.6) | 4 (0.3) | 424 (39.2) |
| M d posterior | 362 (100) | 247 (68.2) | 85 (23.5) | 25 (6.9) | 5 (1.4) | 0 (0.0) | 115 (31.8) |
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