Accuracy and Stability of Clear Aligner Treatment: A Systematic Review

ABSTRACT

This systematic review evaluates the long-term stability and retention of clear aligner treatment, focusing on factors like aligner compliance, attachment use, and treatment duration. Following PRISMA guidelines, we searched electronic databases and manual sources, identifying 112 records and narrowing down to six relevant studies. These studies compared clear aligners to traditional braces, highlighting their effectiveness, especially for mild crowding and anterior movements. Clear aligners, particularly Invisalign, showed benefits like shorter treatment times and higher patient satisfaction. However, variability in treatment accuracy and limited long-term follow-up indicate a need for further research. Overall, clear aligners offer a discreet, flexible, and effective orthodontic option.

INTRODUCTION

Clear aligners have revolutionized orthodontic treatment by providing a discreet and flexible alternative to traditional braces.[1,2] This review explores the evolution, benefits, and challenges of clear aligner therapy, emphasizing long-term stability and retention. Clear aligners are nearly invisible and adaptable, offering a customizable solution for various orthodontic needs.[3] Technological advancements, including improved software and materials, have enhanced treatment precision and patient comfort.[4,5]

Advanced digital models enable precise planning and forecasting, while innovations like Invisalign’s SmartTrack, SmartForce, and SmartStage technologies further optimize outcomes.[6] Despite their success, challenges remain, particularly in cases involving extractions.[7]

METHODS

The study adhered to PRISMA guidelines, with a structured selection and inclusion process shown in the PRISMA flowchart. It was registered with the International Prospective Register of Systematic Reviews (CRD42024531256).

Information sources and search strategy

The objective of this systematic review is to analyze the long-term stability and retention of clear aligner treatment, examining the impact of aligner compliance, attachment utilization, and treatment duration on treatment success and durability. Evidence was collected through electronic database searches (MEDLINE PubMed, Cochrane) and manual searches using institutional library resources. The search strategy utilized a comprehensive set of keywords and MeSH terms, including “clear aligners,” “orthodontic treatment,” “long-term stability,” “retention,” and “orthodontic appliances.”

Study criteria

Inclusion and exclusion criteria followed the SPICO framework [Table 1], covering RCTs, prospective clinical studies, and retrospective observational studies without date restrictions. Excluded were case reports, studies without control groups, non-clear aligner treatments, irrelevant interventions, and non-peer-reviewed literature. Only studies with relevant outcomes and high-quality evidence were included.

Table 1.

Comparison of study design and a sample of the included studies

Author and year of the studies	Population	Type of study	The age range of patients	Parameters checked
Hennessy and Al-Awadhi 2016[5]	67 participants	RCT	18 years old	Mean cephalometric change in mandibular incisor inclination to the mandibular plane at the end of treatment.
Li et al., 2015[6]	152 participants	RCT	27 to 35 years old	Discrepancy index (DI) and the objective grading system (OGS) for malocclusion severity.
Solano-Mendoza et al., 2015[7]	365 patients	Prospective clinical study.	Mean age of 36.57 years (SD±11.53)	Gingival and cuspid widths, depth, arch, and molar rotations and inclinations were assessed in orthodontic treatment using Invisalign®.
Kravitz et al., 2009[8]	37 participants	Prospective clinical study.	Mean age of 31 years	Gingival and cuspid widths, depth, arch, molar rotations, and inclinations.
Gu et al., 2017[9]	48 subjects	Retrospective case-control study.	26.0 years	Pretreatment and posttreatment scores.
Simon et al., 2014[10]	37 patients	Retrospective observational study.	13 and 72 years	Tooth movements include upper medial incisor torque and premolar derotation.

Study selection and data collection process

The process included four stages: 1) excluding irrelevant citations, 2) one reviewer assessing titles and abstracts, with further analysis for unclear cases, 3) independent review of eligible articles by two evaluators, and 4) detailed data extraction and evaluation of included studies. A total of 37 studies were excluded for not meeting the predefined criteria.

RESULTS

Out of 112 initial records, 85 unique studies remained after removing duplicates. After screening and evaluating full-text articles, six studies were included in the systematic review. Hennessy and Al-Awadhi[5] (2016) conducted a randomized controlled trial comparing clear aligners to fixed appliances in 60 non-extraction cases, finding clear aligners effective for achieving desired tooth movements, particularly for mild mandibular crowding.

Li et al.[6] (2015) compared Invisalign and traditional braces in 152 extraction cases, finding similar outcomes based on the discrepancy index (DI) and objective grading system (OGS) over 1.5 to 2 years. Solano-Mendoza et al.[7] (2015) assessed Invisalign in 365 patients, highlighting its effectiveness and predictability in achieving orthodontic outcomes from March 2005 to November 2012. Kravitz et al.[8] (2009) reported a 41% mean accuracy for Invisalign in anterior tooth movements over 2 years, with variability by tooth type and movement direction. Gu et al.[9] (2017) found similar PAR score improvements for fixed appliances and Invisalign in 48 subjects, but Invisalign had significantly shorter treatment times. Simon et al.[10] (2014) showed that Invisalign with auxiliaries like attachments and Power Ridges achieved tooth movements that closely matched predictions over 2 years.

DISCUSSION

The systematic review examines six studies on the effectiveness of clear aligners, especially Invisalign, as an alternative to traditional braces. With increasing interest in the cosmetic and effective nature of clear aligner therapy, this review provides key details on study design, participant characteristics, interventions, and outcomes. Each study offers valuable insights into the efficacy and reliability of clear aligner treatment.

Hennessy and Al-Awadhi (2016) found that clear aligners and fixed braces were equally effective for mild mandibular crowding, making aligners a viable alternative.[5] Li et al.[6] (2015) reported similar outcomes for Invisalign and braces over 1.5 to 2 years in extraction cases, indicating both are effective for treating malocclusion. Solano-Mendoza et al.[7] (2015) conducted a prospective clinical study exclusively focusing on Invisalign aligner treatment. Their investigation evaluated various parameters such as gingival and cuspid widths, arch depth, and molar rotations. The study highlighted the effectiveness and predictability of Invisalign treatment in achieving desired orthodontic outcomes over an extended period, emphasizing its reliability and efficacy in orthodontic practice.

Kravitz et al.[8] (2009) conducted a prospective clinical study assessing the accuracy of Invisalign aligners in achieving tooth movements. Their findings, based on anterior Invisalign treatment in 37 participants, revealed a mean accuracy of 41% for all tooth movements over a 2-year period. While variability was observed based on tooth type and movement direction, the study provides valuable insights into the effectiveness and limitations of Invisalign treatment in achieving desired orthodontic outcomes. Gu et al.[9] (2017) found that Invisalign and fixed braces had similar PAR score improvements, but Invisalign offered shorter treatment times. Simon et al.[10] (2014) demonstrated that Invisalign with auxiliaries achieved accurate and predictable tooth movements.

Strengths and limitations

The systematic review evaluates clear aligner treatments, especially Invisalign, across various study designs. It provides insights into treatment effectiveness, precision, duration, and patient satisfaction. The diversity in methodologies and participant demographics strengthens the findings and enriches the analysis. Despite the strengths of the included studies, limitations include variability in study designs, small sample sizes, and potential biases from retrospective methods. Self-reported measures of compliance and satisfaction may impact data accuracy, and the lack of long-term follow-up limits the assessment of treatment stability. These issues highlight the need for further research to address gaps and enhance understanding of clear aligner treatment.

CONCLUSION

Clear aligners, notably Invisalign, are effective for treating mild mandibular crowding and anterior tooth movements, showing comparable efficacy to traditional braces. They offer benefits like shorter treatment times and increased patient satisfaction. However, further research is needed to address issues such as treatment accuracy, small sample sizes, and limited long-term follow-up.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.