New clear aligners differences with conventional fixed appliances

Invisalign technique VS Fixed orthodontic appliances

In 1946 Kesling first introduced the concept of clear orthodontic appliances to move misaligned teeth . In 1998, Align Technology, Inc. released Invisalign®. The initial cases were minor crowding or spacing. With development of material and computer design of tooth movement, the indication of clear aligners has been greatly enlarged. Many researchers reported successful cases to prove that the clear aligners today have been able to treat almost everything from mild to severe malocclusions . Fixed braces have been the conventional and effective orthodontic appliance for over a hundred years. While in recent years, increasing numbers of patients demanding for a more esthetic and comfortable orthodontic treatment technique has fueled the concerns on clear aligners. Whether clear aligners could be a viable alternative to braces was still not clear . Thus clinicians could only rely on the clinical experience and low-quality evidence when making treatment plans.

Compared with conventional fixed braces, clear aligners allowed for improved esthetics, comfort and oral hygiene to patients . On the other hand, clear aligners had some shortages in controlling tooth movement . However, few high-quality evidences were found to reveal the treatment effectiveness of clear aligners compared with conventional appliance, which left clinicians relying more on experience when making treatment decision and increased the risk of treatment. A recent systematic review published in 2015 concluded that clear aligners were effective in controlling anterior intrusion and posterior buccolingual inclination but not in anterior buccolingual inclination . Extrusion was the most difficult movement (30% of accuracy), followed by rotation. Bodily distalization of upper molar within 1.5 mm revealed the highest predictability (88%). Thus, clear aligners were recommended in simple malocclusions . 

There is review utilized eight studies. Four of them verified that clear aligners could not treat malocclusion as well as braces . Another four included studies did not found the statistically significant difference between two appliances . The result from meta-analysis illustrated that there was no significant difference between two appliances in orthodontic effectiveness evaluated by methods from the ABO Phase III examination.

The eight included researches studied on various treatment effects of clear aligners. A qualitative result was extracted from eight studies that both clear aligners and braces were able to improve the malocclusion, but clear aligners might not be as effective as braces in achieving great improvement , especially in producing adequate occlusal contacts and controlling posterior buccolingual inclination , which related to a poorer clinical outcome in increasing transverse dento-alveolar width . On the other hand, clear aligners had a good control of keeping teeth inclination during alignment in nonextraction cases . During postretention time, patients treated with clear aligners relapsed more than those treated with braces in alignment .

Braces were able to make precise wire adjustments within 0.5 mm to intrude or extrude teeth as necessary. While it was difficult for aligners to extrude a tooth and aligners covering the occlusal surfaces of the teeth, prevented settling of the occlusion. Thus clear aligners could not produce adequate occlusal contacts as well as braces did. Through the use of rectangular archwires, braces aligned and expanded arches by not only tipping teeth but also torquing roots. Moreover, as clear aligners were removable, clinicians must rely on patients’ motivation and dependability to complete the treatment. It was hard to guarantee the desired results.

On the other hand, braces placed a force coronal and buccal to the center of resistance of teeth . This could result in tipping and proclination during alignment. Clear aligners could align teeth individually with one aligner moving one or several teeth. This gradual, segmented movement might minimize the proclination of teeth. It could be postulated that clear aligners were suitable for patients with thin gingival biotypes to limit the risk of developing gingival recession.

Alveolar bone resorption required 7–14 days with equal time needed for periodontal tissue regeneration. Thus, orthodontic appliances should not be reactivated more frequently than three weeks  . Cutting short the repair process would produce damage to the teeth and alveolar bone. So it could be postulated that the 2-week interval of clear aligners was too short for alveolar bone to repair and led to more relapse than the braces adjusted usually every 4–6 weeks.

In terms of treatment duration, the result from meta-analysis found that treatment with clear aligners was more efficient than treatment with brace for nonextraction cases. For extraction cases, the treatment duration of clear aligners was 44% longer than that of brace.

Clear aligner technique was continually evolving owing to the development in materials, auxiliaries, and computer programming. 

Clear aligners had advantage in segmented movement of teeth and shortening treatment duration. While braces were more effective in achieving great improvement, producing adequate occlusal contacts, controlling teeth torque, increasing transverse width and retention than aligners. Therefore, clinicians should consider the characteristics of these two orthodontic appliances when making treatment decision.

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