Year : 2020 | Volume
: 12 | Issue : 7 | Page : 1--4
Clear aligner therapy––Narrative review
Aljazi H Aljabaa
Division of Orthodontics, Department of Pediatric Dentistry and Orthodontics, College of Dentistry, King Saud University, Riyadh, Saudi Arabia
Aljazi H Aljabaa
Assistant Professor, Division of Orthodontics, Department of Pediatric Dentistry and Orthodontics, College of Dentistry, King Saud University, Saudi Arabia, 8357 al buhayrat-ar rahmaniyah, Riyadh 12343-3664.
Clear aligners are gaining more popularity, as most patients, especially adults, dislike the appearance of fixed appliances. In 1997, Align Technology© (Santa Clara, CA) released the Invisalign® system. The company used both computer-aided design (CAD) and computer-aided manufacturing (CAM) to produce its orthodontic appliances. This technology, which allows for multiple tooth movements from a single impression, introduced the clear aligner as it is now known. At the beginning, the Invisalign® system was used to treat simple tooth movement. However, as it developed, the manufacturer began using attachments and intermaxillary elastics to obtain different movements, so Invisalign® became a viable alternative to fixed appliances. Different aligner systems similar to Invisalign®, such as ClearCorrect, etc., became available on the market, and they use the same principle to obtain the desired results. This review investigated the indications and contraindications of clear aligner therapy (CAT), including its efficiency and limitations; patient comfort and acceptance; and periodontal health, root resorption, and stability. In conclusion, CAT has been improved over the last 18 years and is still being improved. The treatment results depend on the clinician’s own experience, case selection, and patient adherence. The clinician should be clear about the advantages and disadvantages of CAT, and the patient should be made aware that he/she should wear the appliance for 22–23h/day and only remove it while eating. The limitations of this study are lack of comparison between available CAT systems, the types and mechanics of movement produced by different types of attachments, and the cost.
|How to cite this article:|
Aljabaa AH. Clear aligner therapy––Narrative review.J Int Oral Health 2020;12:1-4
|How to cite this URL:|
Aljabaa AH. Clear aligner therapy––Narrative review. J Int Oral Health [serial online] 2020 [cited 2020 Sep 26 ];12:1-4
Available from: http://www.jioh.org/text.asp?2020/12/7/1/276086
Clear aligners have become the treatment of choice, especially with the increasing number of adults seeking orthodontic treatment, as they are more comfortable and aesthetic as compared to conventional fixed appliances.,, Clear aligners were first introduced by Kesling, who developed a thermoplastic tooth positioner to progressively move teeth to improved positions. Pointz introduced an “invisible retainer,” based on the same principle as Kesling’s appliance, but only minor tooth movement can be produced with it. Sheridan proposed a method of using clear aligners with interproximal reduction (IPR), which also produces minor tooth movement and requires a new impression for each tooth movement, taken at almost every visit. Therefore, this method requires clinical and laboratory time. In 1997, Align Technology© (Santa Clara, CA) released the Invisalign® system. The company used both computer-aided design (CAD) and computer-aided manufacturing (CAM) to produce its orthodontic appliances. This technology, which allows for multiple tooth movements from a single impression, introduced the clear aligner as it is now known. At the beginning, the Invisalign® system was used to treat simple tooth movement. However, as it developed, the manufacturer began using attachments and intermaxillary elastics to obtain different movements, so Invisalign® became a viable alternative to fixed appliances. Different aligner systems similar to Invisalign®, such as ClearCorrect, etc., became available on the market, and they use the same principle to obtain the desired results.
The aim of this study was to investigate the indications and contraindications of clear aligner therapy (CAT), including its efficiency and limitations; patient comfort and acceptance; and periodontal health, root resorption, and stability.
Indications and Contraindications for Clear Aligner Therapy
CAT is indicated to be used in adults or adolescents with fully erupted permanent teeth. Although there is general agreement that CAT is not the treatment of choice for all types of orthodontic problems, there is still controversy about such aligners’ treatment indications. Some indicate that they should be used in patients with mild dental crowding; however, others suggest that they can be used in more complex orthodontic cases., Therefore, a systematic review concerning the indications and limitations of Invisalign® was conducted, and the literature was found to lack studies that quantified CAT treatment effects, as well as clinical indications or limitations to CAT treatment. Finally, the reviewers recommended that clinicians should rely on their own experience when making decisions about CAT.
As a general rule, the indications for CAT include mild crowding (1–5 mm), spacing problems (1–5 mm), deep overbites (Class II, div. 2), narrow arches requiring expansion, absolute intrusion (one or two teeth), severe crowding with lower incisor extraction, and molars requiring distal tipping. The contraindications are as follows: crowding or spacing problems of more than 5 mm, anteroposterior skeletal problems of more than 2 mm, centric relation and centric occlusion discrepancies, severely rotated and severely tipped teeth, open bite cases, cases requiring teeth extrusion, cases with multiple missing teeth, and teeth with short clinical crowns.
Efficacy of Clear Aligner Therapy in Controlling Orthodontic Tooth Movement
Rossini et al. conducted a systematic review to assess the efficacy of CAT for controlling tooth movement. They included 11 related studies—six with a moderate risk of bias and five that were unclear—and they mentioned that most of the included studies had methodological problems (e.g., small sample size, bias, lack of blinding, etc.). Therefore, they concluded that CAT was effective in aligning and leveling dental arches in nongrowing patients; anterior intrusion with CAT was comparable to that with fixed appliances; and CAT was effective in molar bodily movement (distalization of 1.5 mm). However, CAT was not effective in anterior extrusion movement or for controlling rotated teeth. Regarding posterior vertical control, the selected studies reported contrasting results, and no conclusions were drawn. Rossini et al., therefore, mentioned that, to improve tooth movement auxiliaries, such as attachments and interdental elastics, interproximal reduction (IPR) should be used along with CAT. Another systematic review concluded that Invisalign® is able to alter intercanine, interpremolar, and intermolar width in the presence of crowding. Moreover, incisors tend to procline and protrude when crowding is >6 mm. Vertical movement and derotation are difficult movements to accomplish with aligners and IPR is recommended, especially in canines.
Zhou and Guo investigated the arch expansion among 20 Chinese patients who underwent Invisalign® treatment. Records (digital models and cone-beam computed tomography [CBCT]) were taken at the beginning of treatment (T0) and at the end of expansion phase (T1). They concluded that Aligners could increase the arch width, but expansion was obtained by tipping movement.
Limitations of Clear Aligner Therapy
When orthodontists plan to use CAT, they must rely on their own clinical experience or on weak, published evidence (expert opinions or poorly designed studies). Buschang et al. reported that CAT levels the dental arches; it was also predictable in anterior intrusion and for controlling the posterior buccolingual inclination, whereas its effects in extrusion of anterior teeth, rounded teeth rotations, and anterior buccolingual inclination were unpredictable.
A high degree of accuracy of anterior teeth buccolingual inclination was reported by Castroflorio et al. However, their study had several methodological weaknesses.
Studies have shown that CAT is the treatment of choice for adult patients at risk of periodontitis. Karkhanechia et al. ran a one-year study, comparing the periodontal status between patients treated with fixed appliances and those treated with CAT. They found that patients treated with CAT had increased periodontal status and decreased periodontopathic bacteria as compared to patients treated with fixed appliances. Another study compared the periodontal health of 67 orthodontic patients—32 treated with CAT, 35 treated with fixed appliances, and 10 control patients. The researchers found that better periodontal status P < 0.05 (plaque index, periodontal depth, and bleeding point index) was found in the CAT group, and periodontal pathogenic bacteria were absent. Rossini et al. also conducted a systematic review to assess periodontal health during CAT. Five articles matched their criteria, and they concluded that, during CAT, there is a significant improvement in periodontal indices, especially as compared to treatment with fixed appliances. However, they mentioned that their results should be interpreted cautiously, as few studies were included in their review, and these studies had various methodological problems, such as bias, heterogeneity, and a lack of blinding and proper randomization methods.
Orthodontic treatment with CAT could lead to root resorption, with an average percentage of <10% of the original root length. Its incidence is similar to that described for orthodontic light forces. Using CBCT, Aman et al. investigated the root resorption of 160 orthodontic patients, who had been given comprehensive orthodontic treatment with CAT. They found that there was minimal root resorption in patients undergoing CAT and that the percentage of change in root length is affected mainly by gender, malocclusion, crowding, and posttreatment approximation to the cortical plates. However, they did not include a control group in their study—i.e., patients treated with fixed appliances. Another pilot study compared 11 orthodontic patients treated with CAT (smart track) to patients treated with two different types of fixed appliances (11 treated with Damon brackets and 11 with regular, fixed brackets). They found that root resorption was lower in patients treated with CAT compared to those treated with regular, fixed appliances (P < 0.05). A further systematic review on root resorption with CAT was also conducted, and the researchers concluded that root resorption with CAT is comparable to that with light-force fixed appliances and better than that with heavy-force fixed appliances. However, the study only included two articles, which matched the researchers’ criteria.
Patient Comfort and Acceptance of Clear Aligner Therapy
Aesthetics were found to be the main concern and motive for adult and adolescent patients selecting CAT treatment., Miller et al. compared the first week of orthodontic treatment with CAT and fixed appliances, reporting that the aesthetics, removability, and small size of the aligners resulted in significant pain reduction and better functional and psychosocial differences as compared to patients treated with fixed appliances.
Retention and stability of the outcome is the most challenging part of orthodontic treatment. Using dental casts and panoramic radiographs, the postretention treatment outcomes of patients treated with CAT were compared to those of patients treated with regular, fixed appliances. The records were taken immediately after removal of the appliances (T1) and three years later (T2) and were measured by the American Board of Orthodontics Objective Grading System (ABO OGS). The results showed greater relapse in patients treated with CAT compared to those treated with fixed appliances (P < 0.05). However, this study cannot be generalized because of its small sample size (11 in each group).
The limitations of the current study are lack of comparison between available CAT systems, the types and mechanics of movement produced by different types of attachments, and the cost. This can be used as a suggestion for future studies.
CAT has been improved over the last 18 years and is still being improved. If patients—especially adults—seek CAT treatment, the clinician should be clear about the advantages and disadvantages of CAT, and the patient should be made aware that he/she should wear the appliance for 22–23h/day and only remove it while eating. The treatment results depend on the clinician’s own experience, case selection, and patient adherence. Effects of treatment with CAT must be evaluated using well-designed, randomized, controlled trials. There is a lack of scientific evidence concerning the indications and limitations of CAT, which is why clinicians should rely on their own experience, in addition to the limited available evidence.
The data set used in this study is available (option as appropriate) a. repository name b. name of the public domain resources c. data availability within the article or its supplementary materials d. available on request from (Dr.Aljazi Aljabaa, email: email@example.com) e. dataset can be made available after embargo period because of commercial restrictions
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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