Improving the predictability of clear aligners Steven Jay Bowman Once limitations of clear aligner treatments were identified, conceptualizing techniques to improve the predictability in producing desired results was the next logical step. The present communication offers a variety of concepts methods to enhance the efficiency and effectiveness of clear aligners. (Semin Orthod 2017; 23:65–75.) & 2017 Elsevier Inc. All rights reserved. like predictability because I know what I’m esthetic zone. Predictable, consistent, and com- I getting into. pleted results without adverse effects were —Actress Katherine Heigl requirements. First and foremost was a justified concern for patient compliance in wearing removable devices during the course of possibly Addressing limitations of clear aligner years of treatment. As Buzz Behrents cautioned, treatment compliance is the single most important factor in treatment success. The advent of using a series of clear aligners Cooperation in wearing aligners differs from came at the turn of the 21st century, despite the that of fixed braces in that wires and brackets basis for this concept originating over 55 years cannot be taken off and disregarded by the earlier.1 Although, the original fanfare of plastic patient, so the treatment might proceed toward aligners equitably replacing traditional metal at least “straighter” teeth. In contrast, if aligners braces quickly tarnished as early adopters are not worn as prescribed, the patient receives became painfully aware of limitations of the – no result. Consequently, an alternative track for concept.2 9 Some practitioners vacated, some the non-compliant patient must be a part of vacillated, and others simply dug-in to doggedly informed consent. invent ways to improve this innovation. Patients 10 The introduction of so-called Compliance desire “braceless” correction of their smiles and s Indicators for the Invisalign (Align Technology, thus far, the efforts to give them what they want San Jose, CA) product was evaluated during testing has led to continual advances and increasing of their Teen product (targeted for the audience number of applications and adjuncts for aligners – with the highest concerns for adherence to wear). in orthodontics.11 23 The soluble, color-fading dots were found to rea- sonably demonstrate if patients had been con- Compliance, consequences, and quality of sistently wearing their aligners.24 If used as a life with clear aligners “policing” device, however, much like embedded timers in headgears or functional appliances, their If treatment with aligners was to be seen as effectiveness in actually eliciting cooperation is still completely successful, it was not enough to in question.24 More importantly, compliance by occasionally straighten some teeth just in the orthodontic patients with either braces or plastic is, on average, favorable and comparable.25 Non- Kalamazoo Orthodontics, Portage, MI; Adjunct Associate compliant patients likely suffer consequences of Professor, Saint Louis University, Saint Louis, MO; Instructor, The University of Michigan, Ann Arbor, MI; Assistant Clinical prolonged or compromised results no matter the Professor, Case Western Reserve University, Cleveland, OH; Visiting treatment method chosen. Clinical Lecturer, Seton Hill University, Greensburg, PA In terms of adverse effects, although there are Address correspondence to S. Jay Bowman, DMD, MSD, still concerns for decalcification, gingivitis, root Kalamazoo Orthodontics, 1314 West Milham Ave, Portage, MI. resorption, etc., with either fixed braces or E-mail: [email protected] & removable aligners, the oral hygiene advantage 2017 Elsevier Inc. All rights reserved. fi 1073-8746/12/1801-$30.00/0 for removable appliances is signi cant; however, http://dx.doi.org/10.1053/j.sodo.2016.10.005 the trade-off is the risk of patients failing to Seminars in Orthodontics, Vol 23, No 1, 2017: pp 65–75 65 66 Bowman re-insert their aligners after eating and brushing. material and its conformation from the incisal All in all, it was not surprising that the quality-of- edge to the gingival margin of individual teeth, life satisfaction of teen aligner patients was found combined with the necessary duration of forces to be quite high.25 applied to specific teeth, can be problematic. It seems there must be a compromise between Aligner tracking heavier forces from thicker or less pliable plastic versus thinner or more resilient materials.27,28 In A common concern running consistently any event, some tooth movements (extrusion, throughout the history of aligner treatments has torque, and rotations) especially for certain teeth been that of teeth not following the predicted or (maxillary laterals and cuspids) have been clearly desired movement. This is despite the fact that the demonstrated to be less predictable and require – – – forces and moments produced with plastic are extra attention.1 3,11 13,29 32 These types of con- comparable to those generated with fixed braces.26 cerns led directly to the creation of bonded For instance, Chisari et al.13 found that just 57% of composite attachments with the intent to the tooth movement programmed for a single increase the surface area for plastic aligners to incisor was actually realized in a period of an 8- “grip” onto teeth. week investigation. In addition, researchers from More importantly, the design of the sequence the University of Illinois11 reported only a 41% and velocity of the movement of teeth during mean accuracy of predicted tooth movement. The treatment requires the greatest consideration. reasons for these frustrations are multi-factorial Sequential or simultaneous tooth movement and require a variety of responses to resolve. For plans are desirable in different situations. Simply example, specific teeth oft times do not remain expecting teeth to move from start to a finished seated within the confines of the plastic aligner occlusion without a specific plan in-between for trays as treatment progresses. This may produce an how these teeth will overcome obstacles (i.e., air gap between tooth and plastic termed “lag” or collisions, contact points, occlusal and muscular “tracking error.” Strategies to reduce “tracking forces, insufficient force, or contacts from the errors” will be described below. plastic) is unrealistic at best.9 Rohit Sachdeva has described the process of One of the earliest adjuncts to help seat aligner orthodontic finishing as “reducing the errors that trays, attempt to maintain “tracking,” and increase have accumulated during treatment.” These occlusal forces to elicit tooth movement was the errors can crop up quickly during the sequence introduction of aligner “chewies” (Chewies Aligner of aligners, resulting in a loss of tracking and Tray Seaters, Dentsply Raintree Essix, York, treatment “running off the rails.” These errors PA).15,19 These plastic “cotton rolls” are prescribed may include those of diagnosis and treatment for patients to use at least the first few days after planning, but with aligners these accrue at the changing to each new pair of aligners. Like the outset. They include issues with impression tak- concept of a tooth positioner, the patient places ing, laboratory scanning of those impressions, the device in a site where teeth are not tracking (i. tolerances in the creation of laboratory models e., a visible “air” gap is seen between the occlusal or (poured or printed), tolerances in the process of incisalofatoothandthealigner).Thepatientthen the molding of plastic over said models, limi- bites and holds onto the chewies repeatedly, over a tations of the plastic materials themselves, and, of few minutes of time daily, with their aligners in course, inconsistent compliance. place.15,19 The intent is to help seat the aligner on Much like issues in manufacturing of metal the teeth that are not tracking, slightly intrude the wires and braces, there are tolerances permitted teethadjacenttoatoothinquestion,andthe in fabrication that may limit the accuracy of tooth added perturbations may help to accelerate the movement. The same situation occurs in molding remodeling in that site to stimulate the tooth to plastic trays, especially when “simulated/pre- move as prescribed. dicted tooth movements” are involved. In addi- tion, thin plastic may mold around the undercuts Lack of space and interproximal spaces between teeth but might provide insufficient force to achieve the Crowded dentitions offer only two options for desired tooth movement. The flexibility of the resolution: create more space (expand) or Clear aligners 67 reduce tooth mass (IPR or extraction). Expan- rotation), tipping (bodily movement), and ensur- sion implies either development or growth of ing interproximal contacts are created at the – new bone in the buccal alveolus. This may end.35 38,44,45 The application of intramaxillary – potentially position teeth into less stable locations or intramandibular elastics to miniscrews,41 43 due to change in equilibrium in the facial mus- intermaxillary elastics, and the increase in size culature and an associated potential loss of bone and type of composite attachments may be as teeth are pushed beyond the envelope of the needed to increase predictability.16 alveolus. Certainly, some modicum of expansion Predictable sequencing of space closure or appears to be tolerable or at least “retainable.” pushing individual teeth into alignment for any Unfortunately, aligners tend to expand a most of the previous scenarios may be best handled in unstable site: the mandibular intercanine