Clear aligners, when they are the right choice.

Clear aligner therapy uses a series of custom-made, removable thermoplastic trays, each one slightly different from the last, to move teeth in controlled increments toward a digitally planned final position. The patient wears each tray for one to two weeks, removing it only to eat, drink, brush, and floss, then switches to the next tray in the sequence. The total number of trays depends on the complexity of the case: a simple spacing closure might require twelve to sixteen trays over four to six months, while a moderate crowding case could need twenty-five to forty trays over twelve to eighteen months.

The process starts with a digital intraoral scan, not a traditional impression. The scan is used to create a three-dimensional treatment simulation that maps every tooth movement from the current position to the target position. I review this simulation carefully before approving it, adjusting the staging, the speed of movement, and the sequencing of corrections. Small tooth-coloured attachments, bonded to specific teeth, act as handles that help the aligner grip the tooth and deliver the right force vector for certain movements, particularly rotations and extrusions that a smooth plastic tray cannot achieve on its own.

The most comprehensive overview of existing systematic reviews, published by Yassir and colleagues in 2022, pooled the findings of multiple prior reviews and concluded that clear aligners are effective for mild to moderate malocclusions but that fixed appliances remain superior for achieving precise outcomes in complex cases, particularly in controlling buccolingual inclination and achieving tight posterior occlusal contacts ^[1]. This matches the clinical reality I see in practice: aligners are genuinely good at resolving crowding, closing small spaces, and correcting mild rotations, but they struggle with large anteroposterior corrections, deep bite intrusion, and bodily movement of roots.

A dedicated systematic review by Rossini and colleagues specifically evaluated the effectiveness of clear aligner therapy and found that while aligners achieved predictable outcomes in alignment and levelling, their efficacy in producing significant anteroposterior or vertical changes was limited ^[2]. The more recent 2024 systematic review by AlMogbel and colleagues reinforced these findings, concluding that clear aligners show comparable efficacy to fixed appliances in controlling most orthodontic movements but that fixed appliances still hold an advantage in specific movement types such as torque and extrusion ^[3].

The single biggest difference between fixed braces and clear aligners is not the mechanics, it is the compliance demand. Fixed braces work twenty-four hours a day because they are bonded to the teeth; the patient cannot remove them. Aligners work only when they are in the mouth. Clinical guidelines recommend 20-22 hours of wear per day, leaving the trays out only for meals and oral hygiene. Every hour of non-wear slows the planned tooth movement and can cascade into tracking errors that compound over the course of treatment.

Research on compliance factors shows that this is not a trivial concern. Al-Abdallah and colleagues found that patient compliance varies significantly and that factors like age, motivation, and lifestyle all influence whether the aligners are actually worn enough hours to work ^[4]. This is why case selection is inseparable from patient selection. A technically perfect aligner plan will fail if the patient leaves the trays in a drawer for six hours a day. I discuss this candidly at the consultation: if the patient's lifestyle or habits suggest compliance will be a challenge, fixed appliances may be the more predictable path even if the case is technically suitable for aligners.

One area where clear aligners consistently show an advantage over fixed appliances is the incidence of external root resorption, a shortening of the tooth root that can occur with any orthodontic treatment. The systematic review and meta-analysis by Li and colleagues found that root resorption during clear aligner treatment was significantly lower than that observed with fixed braces ^[5]. This does not mean root resorption cannot happen with aligners; it means the risk is reduced, likely because the intermittent forces and the ability to remove the tray briefly reduce the sustained stress on the periodontal ligament.

Periodontal health during orthodontic treatment is also consistently better with aligners than with fixed brackets, and the reason is straightforward: the patient can remove the aligners to brush and floss normally. Fixed brackets create dozens of new surfaces for plaque to accumulate around, and even motivated patients struggle to maintain perfect oral hygiene. With aligners, there are no brackets, no wires, and no bonded auxiliaries blocking the toothbrush. The systematic review by Jiang and colleagues confirmed that patients treated with clear aligners showed significantly better periodontal outcomes than those treated with fixed appliances ^[6].

I am an Invisalign provider, and I use clear aligners regularly in my practice, but only for cases where the evidence supports a predictable outcome. That means mild to moderate crowding, small gaps, minor rotational corrections, and cases where the patient's compliance profile is reliable. I do not use aligners for cases that require significant vertical correction, large anteroposterior changes, or complex root movements, because the literature is clear that fixed appliances perform better in those situations.

The consultation starts with a comprehensive examination including a full digital scan, photographs, and radiographs. If aligners are appropriate, I walk the patient through the 3D treatment simulation so they can see exactly what will move, how far, and in what order. If aligners are not appropriate, I say so, and I explain why, even if the patient came in specifically asking for them. Recommending a treatment that will underperform is not a service, it is a compromise that costs the patient time and money. The conservative principle applies to orthodontics the same way it applies to restorations: use the right tool for the problem, not the most popular one.