A Comprehensive Review of Clear Aligner Therapy

In the realm of modern orthodontics, new technologies, including three-dimensional photography, artificial intelligence (AI), digital impressions, and clear aligner therapy (CAT), have marked a transformative juncture in the pursuit of achieving ideal dental esthetics, occlusion, and symmetry.¹ In the quest for enhancing the patient experience and treatment outcomes, CAT has emerged as a prominent alternative to traditional fixed appliances. This systematic review seeks to provide a comprehensive and evidence-based summary of this therapy.^2,3

In the late 1990s, a groundbreaking approach to straightening teeth using a series of removable, transparent aligners was introduced. Over the years, clear aligner technology has evolved, harnessing computer-aided design and 3D printing to tailor treatment plans with precision.^2,4,5

One critical aspect of orthodontic treatment is its influence on periodontal health. Clear aligners offer benefits such as easier oral hygiene maintenance and reduced risk of enamel demineralization. This paper will also investigate how clear aligners can positively and negatively impact periodontal health.⁶

Methodology and results

The major databases, including PubMed/MEDLINE and Google Scholar, were searched from 2015 to 2023, including randomized control trials (RCTs), cohorts, and in vitro studies, which showed 60 initial results. All articles with incomplete information in the title or abstract were excluded to facilitate an informed conclusion. After review of article titles only, a set of 38 relevant papers was chosen. In the second stage, the list was reduced to 20 by eliminating irrelevant articles based on their abstracts. Then, researchers reviewed the full content of the remaining articles on the list, excluding in vitro and systematic review studies, which left 12 results. Out of the 12 articles considered, six RCTs.^2,3,6–9 One nonrandomized group study was included¹⁰ and two were retrospective studies.^11,12 One double-centered cohort study¹³ and one prospective observational study⁴ were reviewed.

All articles were written in English and collectively explored the effectiveness of clear aligners in various treatment scenarios. These investigations encompassed a range of areas, including evaluating periodontal health and microbial changes, analyzing alveolar bone transformations, assessing the severity of orthodontically induced inflammatory root resorption, gauging the impact of CAT on oral health-related quality of life, examining the accuracy and predictability of clear aligners, comparing outcomes with fixed appliances and clear aligners, studying the effects during the retention period, assessing oral health impacts before and after CAT, and exploring potential relationships with personality traits. See Table 1 for a review of the included studies.

Clinical Case

This case report features a 26-year-old patient who underwent clear aligner treatment, under the care of the Advanced Eduction in General Dentistry Clinic at the University of California San Francisco School of Dentistry. The treatment spanned over 2 years and aimed to correct an anterior crossbite and achieve overall dental alignment.

The initial consultation occurred on June 17, 2021, where we presented a detailed treatment plan, supported by a digital representation of the expected final outcome (Figure 1). Initial photos and a panoramic X-ray of the patient were documented (Figures 2 and 3). He was then scheduled for a clear aligner tray delivery after 6 weeks. The next appointment was set for 2 months later; the first set of trays was changed every 2 weeks for 2 months. This schedule then switched to changing trays weekly. The two sets of additional trays were changed every 2 weeks.

During the third visit, that patient was informed that we were making space on the left side of the lower jaw before teeth #28-29 could be engaged. After 3 months, the patient was concerned about inadequate teeth movement, so we informed him we also needed to create space on the right side of the mandible to help tooth #29 move. We scheduled to check after tray #30 to see if there was adequate space and if new impressions and revisions were required. The patient was provided with comprehensive instructions on the use of the clear aligner trays, with a specific alteration to frequency from 2 weeks to 1 week for trays 13 to 26 due to his anterior crossbite. Regular follow-up appointments were conducted to ensure proper fit of the trays and to address any the patient concerns, such as issues with tray fit on the lower right side and feelings of inadequate tooth movement. Chewies (small appliances made of styrene copolymer designed to eliminate air gaps between the clear aligner tray and the dentition) were not recommended.

The need for new impressions, cutting the trays, and additional trays became apparent, particularly to address a posterior open bite and to continue the alignment process. Posterior open bite could have developed due to improper tray fitting, or a biological factor when a tooth is resistant to move or there is a lack of space to move the tooth. Throughout the treatment, the patient reported high compliance with tray usage and follow-up appointments, a factor that significantly contributed to the progress noted. However, he did express concerns at various stages, ranging from issues with tray fit to a desire for further adjustments to specific teeth, such as wanting tooth #7 to be more facially aligned. These concerns were addressed through adjustments to the treatment plan and additional trays. This led to an interproximal reduction procedure and the delivery of new trays (Figure 4).

To achieve active control of teeth movement, attachments were placed using packable composite in June 2022 to complete the refinement and improve the overall result. The treatment culminated with the delivery of overcorrection trays in April 2023 and a final series of follow-ups to ensure the successful alignment of the patient’s teeth. By the end of the treatment, the patient expressed satisfaction with the outcomes, particularly the alignment of tooth #7, which had been a point of concern for him.

This case underscores the effectiveness of CAT, the importance of patient compliance, and the value of regular follow-up examinations and open communication in achieving successful treatment outcomes. It also suggests potential limitations due to the issues on the lower right and the lack of movement of tooth #29.

Discussion

The results of our study demonstrate that clear aligner treatment can be effective in the management of various orthodontic issues, including correcting a mandibular incisor proclination, treating a patient undergoing a complex triple-jaw orthognathic surgery, and addressing a mild Class II malocclusion, with outcomes comparable to traditional fixed appliances in certain scenarios.^2,12 Our findings align with the systematic review conducted by Robertson et al,¹⁴ which analyzed seven eligible articles between 2014 and 2019, indicating the success of CAT in specific fields as well as highlighting challenges. Due to significant variations and high heterogeneity among the studies, a meta-analysis was not performed.

Studies have shown CAT’s capability to achieve substantial orthodontic improvements, particularly in adults, and maintain treatment stability over time.^2,4,12,13 However, CAT may present challenges in achieving certain tooth movements, for instance, clear aligners make control of root position extremely difficult, and it also is challenging to correct rotations and extrude teeth.¹⁵ However, there are techniques to overcome the limitations involving absolute rotations and extrusions, such as allowing button cutouts and using buttons with elastics to overcome deficiencies of extrusions. If these limitations are not important in a particular case, CAT can be then considered.¹⁵

Bilello et al⁴ determined that the rotational movements of canines, premolars, and lateral incisors were relatively unpredictable. On the other hand, vestibulo/lingual tipping was found to be a more predictable orthodontic movement. Similarly, in a prospective clinical study conducted by Kravitz et al,¹⁶ extrusion was identified as the movement with the lowest accuracy, reported at 29.6%.

Simona et al¹² mention that the biomechanics of CAT allow the clinician to plan and obtain a different range of dental movements, such as molar distalization, molar derotation, and incisor torque. This study investigated the effects of two orthodontic treatments — CAT and fixed multibracket therapy with intermaxillary elastics — on Class II malocclusion in growing patients. The two treatments achieved similar results, but CAT presented a better control in the proclination of the lower incisors.¹²

Leyva et al⁷ noted that patients were concerned about dentofacial deformities as caused by discrepancies in the shape and size of the jaws, leading to dental malocclusions and facial disharmony. They conducted an RCT and concluded that CAT use in postsurgical orthodontic treatment following orthognathic surgery shows promising results, providing comparable outcomes to conventional appliances.⁷ Furthermore, when compared to fixed appliances, clear aligners offer distinct advantages in terms of esthetics and comfort, which contribute positively to patient quality of life during treatment.^2,3,8

In terms of periodontal health, clear aligners tend to fare better, resulting in less plaque accumulation and gingival inflammation. Plus, fixed orthodontic appliances make tooth cleaning slower and more difficult.^3,6,7 Considering the proper case selection, aligners can be associated with less severe orthodontically induced inflammatory root resorption and alveolar bone changes.¹¹

The impact of clear aligners on patients’ oral health-related quality of life and overall experience is generally positive.^8,17 Patients report high levels of satisfaction and comfort, although temporary discomfort can occur at the onset of treatment.^3,10 Clear aligners also appear to positively impact patients’ self-perceived oral health and quality of life following orthognathic surgery.⁷ On the other hand, many adults feel apprehensive about wearing brackets in public.^7,18

The relationship between personality traits and patient perception of oral health CAT is complex and warrants further investigation.⁹ It is clear, however, that patients’ psychological profiles can influence their experience of orthodontic treatment, underscoring the need for a holistic approach that considers both clinical and psychological aspects of therapy.

The case report we presented accentuates the efficacy of CAT in addressing anterior crossbite and teeth crowding. It highlights the benefits of meticulous treatment planning, the importance of responding to patient concerns during treatment and follow-up, the key role of patient compliance, and points to the advantage of facilitating improved oral hygiene maintenance.

Conclusion

Clear aligners represent a significant advancement in orthodontic treatment, offering an esthetic and comfortable alternative to traditional braces. They are effective in treating various orthodontic conditions, with potential advantages in maintaining periodontal health, reducing root resorption, and enhancing patient satisfaction. Challenges, such as the precision of certain tooth movements and initial discomfort, however, must be carefully managed. Also, not all potential clinical scenarios have been assessed in the included studies.

The positive impact on quality of life, coupled with comparable clinical outcomes to fixed appliances, positions clear aligners as a viable option for many patients. A patient-centered approach, considering both clinical outcomes and patient experience, is essential to optimize treatment success and patient satisfaction. Thus, selecting the appropriate cases is crucial for the successful application of CAT. We recommend comparing the use of lingual braces to CAT in different cases, as the efficacy of lingual braces has been described more recently.¹⁹

Future Challenges

Our systematic review indicates that while various studies on different facets of clear aligner treatment exist, there is a notable lack of research dedicated to each area. We advocate for further research on periodontal considerations, appropriate case selection, specific teeth movements, efficacy of CAT attachments, and the psychological pros and cons associated with the treatment. Despite our current broad understanding of the benefits and challenges of CAT, there is room for improvement in this area.

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From Decisions in Dentistry. March 2024; 10(2):36,39-41