Spotlight on Invisalign: Pros and cons of treatment planning with clear aligners
For years the term “orthodontics” conjured images of metal wires, painful brackets and middle school chants of “brace face,” all of which are effective deterrents from the orthodontist’s office. However, with the 1998 introduction of Align Technology’s Invisalign came a comfortable, esthetic, and practical alternative to traditional fixed orthodontics. At its inception, many in the dental community dubbed Invisalign as a panacea for maloccluded teeth.
However, this is not necessarily the case, as orthodontic treatment with Invisalign presents benefits as well as drawbacks. It is this article’s intention to outline both the pros and cons of Invisalign treatment as well as the indications and contraindications of treatment planning for use of clear orthodontic aligners.
Through the integration of wireless, more esthetic aligners for the correction of malocclusion, Invisalign has permanently changed the landscape of contemporary orthodontics. This concept has not been credited to a formally trained orthodontist; rather, it has been credited to Zia Christie and Kelsey Wirth, two MBA students from Stanford University who founded Align Technology in 1997. By 1998, Align Technology received FDA approval; one year later commercial sales of the clear aligners commenced. Align Technology was greeted with open arms by the public and had sold its millionth pair of aligners by late 2011.
The Invisalign process begins, like all other orthodontic processes, with dental impressions, X-rays and photographs of the patient’s teeth. This diagnostic information is then sent to Align Technology. With the aid of a CT scan, technicians at Align create a three-dimensional diagnostic model of the patient’s teeth. These digital models are manipulated tooth by tooth, moving them to their final position as prescribed by the orthodontist. These movements are divided into a sequential progression, often corresponding to 11 or 12 discrete aligners given to the patient throughout treatment. This sequential treatment plan is presented to the orthodontist for approval. Once approved, a plastic aligner is manufactured for each of the proposed stages and shipped to the orthodontist.
When treatment planned and implemented properly, Invisalign is an effective alternative to traditional fixed appliances. Use of plastic aligners minimizes deleterious plaque accumulation, tissue inflammation, gingival recession and root resorption, characteristics that are often attributed to more traditional orthodontic approaches (Boyd, 2009). As it involves no metal components and allows for tooth bleaching during treatment, Invisalign presents an esthetic advantage over its metallic counterparts and is thus more readily accepted by patients. Invisalign generally produces less soft tissue irritation and myofascial pain (Boyd, 2009).
Dr. Robert Boyd, chair of orthodontics at the University of the Pacific and one of the early pioneers of Invisalign, is the first author of the first publication of Invisalign (Boyd et al. 2000). He discussed the pros and cons of clear aligners through a series of cases in his article “Periodontal and Restorative Considerations with Clear Aligner Treatment to Establish a More Favorable Restorative Environment” (Boyd, 2009, p.286-288). Clinical trails showed significant control of tissue inflammation, excellent plaque removal and decreased mobility after treatment in patients with severe periodontitis and horizontal bone loss, on all upper and lower incisors.
A patient presented with class I occlusion, deep overbite, 8 mm of overjet, posterior crossbite on the left side, 2 mm crowding on the lower arch, and 4 mm of spacing on the upper arch was treated for 29 months with clear aligners. The results demonstrated that anterior spaces were relieved and the posterior cross-bite and the deep overbite was corrected, both while maintaining excellent esthetics and good stability of the corrected occlusion.
In the cases presented by Boyd (2009), computer-aided (CAD/CAM) clear aligners either eliminate the need for certain restorative procedures or create more optimal periodontal health and tooth position for performing these procedures. A reduction in plaque accumulation and gingival inflammation was observed during orthodontic treatment with clear aligners (Boyd, 2009). In cases treated with traditional fixed appliances, increased plaque accumulation has often been associated with increased inflammation and mild periodontal breakdown, despite preventive measures performed during treatment. Invisalign appliances provide easier periodontal maintenance and greater access while brushing, attributing to a reduction in gingival inflammation.
A marked difference between Invisalign aligners and traditional fixed techniques exists in the amount of root resorption that is caused (Boyd, 2009). Traditional fixed orthodontic appliances are often attributed to increased instances of bone resorption (approximately 1 mm for every millimeter of apical displacement). The torque with which Invisalign produces the desired orthodontic movements is less than that of fixed orthodontics, thus resulting in decreased tooth mobility and root resorption (Boyd, 2009). For this reason, treatment of extreme cases, in which larger movements are desired, are better served with traditional cemented brackets and wires.
While effective, Invisalign appliances do present some disadvantages. Treatment efficiency lies in the hands of the patient, as the appliances can easily be removed. Another significant limitation involves tooth movement, which requires bodily movement of roots, such as premolar extraction cases where root paralleling and space closure is desired. Bollen (2003) stated that Invisalign aligners are best suited for tipping movements, thereby necessitating fixed appliances at some point during treatment.
Although Invisalign presents a more esthetic alternative to the patient, treatment time with clear aligners is often longer than fixed treatment, due to laboratory fabrication time. There is an estimated two-month lag-time between the initial treatment planning appointment to delivery of the first aligners (Womack, 2002). Additionally, if modifications are needed, treatment must be stopped and the newly modified aligners must be fabricated, adding to the treatment time.
While some drawbacks do still exist, many of the shortcomings that had limited treatment with Invisalign aligners have been mitigated through a series of new treatment protocols. Boyd (2007) outlines these protocols through four case demonstrations in which many previously thought drawbacks to Invisalign were refuted. Prior to this new treatment protocol, it was thought that treatment of anterior open-bite with inter-arch forces such as class II and class III elastics was nearly impossible with Invisalign aligners and that treating these cases with clear aligners often results in relapse and tooth malposition. However, through his case presentations, Boyd (2007) describes multiple cases in which inter-arch forces had been used to correct anterior open bite and notes that clear aligners may be better indicated for treatment of anterior open-bites than traditional fixed appliances as the fixed approach may lead to an increase in extrusion during treatment and ultimately increase the amount of open-bite (Boyd, 2008).
After weighing the pros and cons of both clear Invisalign aligners and traditional fixed orthodontic appliances, it is important to discuss combined treatment, utilizing the benefits of both disciplines to achieve optimal orthodontic results. Boyd (2009) presented a patient presenting with: class I occlusion, spacing on upper arch due to congenitally missing maxillary lateral incisors, normal overbite, normal overjet, slight crowding on the lower arch, implant desired to replace congenitally missing #7 and #10 who was treated for 24 months, 18 of which were with clear aligners and the remaining six with fixed, clear brackets. Here, clear aligners were used for the majority of orthodontic movement. However, due to Invisalign’s limitations in regards to root paralleling, the maxillary canines and central incisors required movement using a traditional fixed appliance.
In conclusion, with the introduction of the Invisalign aligner in 1999, Align Technology has added yet another suitable option for the orthodontist to consider during treatment planning. While standard fixed appliances are better suited to control difficult tooth movement in three planes of space, clear aligner orthodontic treatment afford the orthodontist a more comfortable and esthetic option, indicated for patients with mild to moderate cases of malocclusion. These clear aligners also allow for superior oral hygiene, thus maintaining the stability of the periodontium. However, while these clean aligners do provide an esthetic alternative to traditional fixed orthodontic appliances, they are limited in the amount and the velocity with which they may reposition teeth. The pros and cons of Invisalign treatment point to the consideration of combined treatment, using both traditional fixed appliances and Invisalign to optimally correct malocclusion.
Moreover, it is most important to realize that the onus of proper treatment planning and modification falls flatly onto the practitioner.
The author would like to thank Dr. Robert L. Boyd, whose feedback and research was invaluable to the publishing of this article and without whom the article would have never been written and published.
(Note: A complete list of references is available from the publisher.)