What Are Invisalign Braces and How Do They Work?

Invisalign is a brand of clear, removable plastic trays (called aligners) that gradually shift teeth into new positions, serving as an alternative to traditional metal braces. Each tray is custom-made from a digital scan of your mouth and is designed to apply gentle, controlled force to specific teeth. You wear a series of these trays in sequence, swapping to a new one every week or two, and each tray nudges your teeth a fraction of a millimeter closer to the target position mapped out by your orthodontist’s software. The system has been around since the late 1990s and has expanded considerably in what it can treat, though it still has real limits compared to fixed braces for certain types of tooth movement.

How the Treatment Starts

The process begins with a digital intraoral scan, which creates a three-dimensional model of your teeth and bite. Older workflows used physical impressions (the gooey molds you may remember from childhood dentistry), but most providers today use a handheld scanner that captures the geometry of each tooth in minutes. That 3D model gets uploaded to treatment-planning software, where the orthodontist maps out every intended movement from your current bite to the desired final position. The software lets the clinician preview the entire course of treatment on screen before a single tray is manufactured.

Once the plan is approved, a series of aligners is fabricated. Depending on case complexity, you might receive anywhere from a dozen trays for minor crowding to 50 or more for more involved corrections. Each tray is slightly different from the last, encoding the next small increment of movement. The trays are made from a medical-grade thermoplastic polymer and are nearly transparent when worn, which is a big part of their appeal.

Many treatment plans also call for interproximal reduction, a procedure where tiny amounts of enamel are shaved from the sides of certain teeth to create space for movement. The treatment software can automatically stage when and where this should happen, scheduling it for points in the sequence when the teeth are positioned to allow safe access to the contact surfaces between them.

The Biology Behind Tooth Movement

Aligners move teeth through the same biological process that braces do. When force is applied to a tooth, it compresses the periodontal ligament (the thin tissue connecting each tooth root to the surrounding bone) on one side and stretches it on the other. That compression creates a low-oxygen environment that triggers an inflammatory response, which in turn recruits cells that break down bone on the compressed side. On the tension side, other cells lay down new bone to fill the gap. The net result is that the tooth drifts through the bone in the direction it is being pushed.

1PubMed Central. Orthodontic tooth movement: The biology and clinical implications

This remodeling cycle is why orthodontic treatment takes months rather than days. Bone cannot be rebuilt overnight, and applying too much force too fast can damage the root or the surrounding tissue. Aligners are designed to deliver light, continuous pressure within the range that promotes healthy remodeling rather than tissue damage.

Why Attachments Matter

If you have seen someone wearing Invisalign and noticed small tooth-colored bumps on certain teeth, those are attachments. They are tiny composite resin shapes bonded directly to the enamel, and they serve as grip points for the aligner. Without them, a smooth plastic tray sitting over a smooth tooth can only push in limited directions. Attachments give the aligner something to grab onto, allowing it to deliver forces for more complex movements like rotation, extrusion (pulling a tooth down from the gum), and torque (tilting the root forward or backward).

2PubMed Central. Clear Aligner Attachments: A Comprehensive Review

Some treatment plans also use elastic bands hooked from the aligners to attachments or buttons on opposing teeth, functioning much the same way rubber bands work with traditional braces. These are common in cases that involve correcting the front-to-back relationship of the upper and lower jaws.

3PubMed Central. Camouflage Treatment of a Severe Hyperdivergent Class II Malocclusion by Posterior Interproximal Tooth Reduction and Clear Aligners: A Case Report

What Invisalign Does Well and Where It Struggles

Not all tooth movements are created equal when it comes to aligners. Research on how accurately Invisalign achieves the movements its software prescribes has consistently shown that some things are straightforward and others are stubbornly difficult. An early prospective study found that the average accuracy of tooth movement with Invisalign was about 41%, meaning teeth ended up only partway toward where the software said they would go. Extrusion was the least reliable movement, with upper central incisors reaching their target position less than 20% of the time. Rotation of canines was also significantly less accurate than for other teeth.

4PubMed. How well does Invisalign work? A prospective clinical study evaluating the efficacy of tooth movement with Invisalign

More recent evidence broadly confirms this hierarchy. Movements with high predictability, meaning the teeth generally reach more than three-quarters of the planned position, include arch expansion and pushing upper back teeth further back. Moderate predictability applies to tipping and incisor rotation. Low predictability, where teeth reach less than half of where they were planned to go, still applies to extrusion, canine and premolar rotation, and root torque.

5Seminars in Orthodontics. The predictability of tooth movement with clear aligner systems

The biggest discrepancies between planned and actual movement tend to show up in angular adjustments and in rotating teeth with round-shaped crowns, where the aligner has less surface area to grip. One study found the ratio was roughly 0.4 degrees of achieved rotation for every degree prescribed.

6PubMed Central. Predictability of orthodontic tooth movement with aligners: effect of treatment design

Orthodontists compensate for this by “over-prescribing” movements in the software, programming the aligner to attempt more movement than is actually needed, knowing teeth will only get partway there. Refinement rounds, where new scans and additional trays are ordered partway through treatment, are routine for anything beyond mild crowding.

Aligners Versus Traditional Braces

The question most people want answered is whether Invisalign works as well as metal braces. The answer depends on what you mean by “works.” For overall finish quality in straightforward cases, multiple studies have found no statistically significant difference. One study comparing finished cases found no meaningful difference in total occlusal grading scores at the end of treatment or after six months of retention, though the braces group finished about five months faster.

7PubMed Central. Differences in finished case quality between Invisalign and traditional fixed appliances

Other research has found the opposite on timing. A comparative analysis reported that Invisalign cases averaged about 18 months of treatment versus 24 months for conventional braces, with both achieving success rates around 88 to 90%.

8PubMed Central. Comparative Analysis of Braces and Aligners: Long-Term Orthodontic Outcomes

A broader review found that aligners tended to have statistically shorter treatment durations than braces overall, but that braces may still have an edge in producing good bite contacts, controlling root angulation, and expanding the arch.

9PubMed Central. A comparison of treatment effectiveness between clear aligner and fixed appliance therapies

The honest summary is that for mild to moderate crowding and spacing, the final results are comparable. For complex cases involving significant vertical correction, large rotations, or major bite discrepancies, traditional braces still have more mechanical control. Many orthodontists use both systems and choose based on the specifics of each case.

How Much You Need to Wear Them

Invisalign’s standard recommendation is 20 to 22 hours per day, removing the trays only for eating, drinking anything other than water, and brushing your teeth. Compliance is the single biggest variable in treatment success, and it is also the system’s most obvious drawback compared to braces: you cannot forget to wear braces, but you can absolutely leave your aligners in their case all evening.

A randomized clinical trial tested whether a reduced wear protocol of 12 hours daily could still produce adequate results. For the upper jaw in cases of very mild crowding, the 12-hour protocol worked reasonably well. But for lower teeth, correction was significantly less efficient compared to the 22-hour group.

10European Journal of Orthodontics. Evaluation of the effectiveness of orthodontic treatment with Invisalign in different wear time protocols: Randomized Clinical Trial

In practice, this means the 22-hour guideline is not arbitrary. Cutting wear time significantly, even if it feels manageable, can mean your teeth do not track with the trays and the whole treatment plan drifts off course. When that happens, the fix is usually a mid-course correction scan and a new set of trays, which adds time and cost.

Gum Health and Plaque During Treatment

One area where aligners consistently outperform braces is oral hygiene. Brackets and wires create nooks and crannies that trap food and plaque, making cleaning harder and gum inflammation more common during treatment. Because aligners are removable, you can brush and floss normally.

Studies have borne this out. A three-month evaluation found that Invisalign patients had better periodontal health and lower total biofilm mass compared to those with fixed braces, with a statistically significant difference in biofilm accumulation.

11PubMed Central. Periodontal health status in patients treated with the Invisalign® system and fixed orthodontic appliances: A 3 months clinical and microbiological evaluation

Another study found significantly better gingival health in Invisalign patients based on standardized gingival and bleeding indices, while plaque levels were lower with aligners but not by a statistically significant margin.

12PubMed Central. Braces versus Invisalign®: gingival parameters and patients’ satisfaction during treatment: a cross-sectional study

On plaque specifically, at least one study found a significantly lower plaque index in the Invisalign group compared to those with fixed appliances.

13PubMed. A comparison of the periodontal health of patients during treatment with the Invisalign system and with fixed orthodontic appliances

For root resorption, a small amount of root shortening is a known side effect of any orthodontic treatment. A retrospective study comparing Invisalign and fixed appliances found that both groups experienced external root resorption at similar rates, with no statistically significant difference between them.

14JOURNAL OF CLINICAL AND DIAGNOSTIC RESEARCH. Risk of root resorption between Invisalign and fixed orthodontic treatment: A retrospective study

Keeping the Aligners Clean

The trays themselves need regular cleaning. Aligners sit against your teeth for most of the day, and bacteria colonize their inner surfaces just as they colonize your teeth. Research has found that combining mechanical cleaning (brushing with a soft toothbrush) with a chemical agent is the most effective strategy. Brushing alone helps, but adding a cleaning solution, whether a dissolvable tablet or a mild antiseptic, reduces viable bacteria significantly more than either method alone.

15PubMed Central. Effects of cleaning methods on the removal efficacy of Streptococcus mutans biofilm and material properties of thermoplastic aligner materials

A systematic review of aligner hygiene found that the best-performing protocols involved either a sodium-carbonate-based effervescent tablet followed by brushing, or immersion in chlorhexidine or cationic detergent solutions. Ultrasonic cleaners showed partial effectiveness but were not consistently better than manual brushing.

16PubMed Central. Biofilm Management in Orthodontic Aligners: A Systematic Review

Since each tray is worn for only one to two weeks before being replaced, long-term buildup is less of a concern than with appliances that stay in place for months. Still, neglecting daily cleaning can produce odor, discoloration, and a higher bacterial load pressed against your enamel all day.

Pain and Day-to-Day Comfort

Discomfort is part of any orthodontic treatment, and aligners are no exception. A narrative review of the literature found that pain and discomfort peak at the beginning of treatment and with each new tray, then decrease as you progress through the series. Temporary speech difficulties (a slight lisp, mainly) and some awkwardness while eating are commonly reported but tend to be mild and short-lived.

17PubMed Central. Pain, discomfort and oral health-related quality of life in clear aligner therapy: a contemporary narrative review

Compared to the soreness from wire adjustments with traditional braces, many patients report that aligner discomfort is less intense and more manageable. The review also noted that aligners tend to improve quality-of-life measures related to appearance and reduce psychological burden during treatment, which makes sense given that the appliance is nearly invisible.

What Happens After Treatment Ends

Teeth have a tendency to drift back toward their original positions once active treatment stops. This is true regardless of whether you had braces or aligners. Retainers are not optional. A study evaluating retention protocols found that permanent (bonded) retainers were the most effective at preventing relapse, with a mean anterior relapse of just 0.2 mm compared to about 0.8 to 1.0 mm with removable retainer types.

18PubMed Central. Effectiveness of Different Retention Protocols in Preventing Posttreatment Relapse After Comprehensive Orthodontic Treatment

Relapse rates after aligner treatment appear broadly similar to those after braces. One review found that both methods showed small amounts of relapse over a two-year follow-up, with no significant difference between the groups. The mandibular arch (lower teeth) tended to relapse slightly more than the upper in both groups.

19PubMed Central. Comparison of relapse of orthodontic treatment following aligner versus conventional fixed appliance treatment

A separate study using a standardized scoring system found that aligner treatment results were stable after about 10 months of retention, with no significant change in scores between the end of active treatment and follow-up.

20PubMed. Evaluation of effectiveness and stability of aligner treatments using the Peer Assessment Rating Index

Aligners for Teenagers and Growing Patients

Invisalign now offers products specifically designed for adolescents, including a version with a built-in mandibular advancement feature meant to guide lower jaw growth forward in teens with a receded lower jaw. This is roughly analogous to what functional appliances (like Herbst or Twin Block devices) do in traditional orthodontics, but packaged into a clear aligner system.

A retrospective study of growing patients treated with Invisalign’s mandibular advancement feature found significant skeletal and dental changes in both the teen group and a younger “first phase” group. The teens showed greater forward movement of the lower molars, while the younger group showed more backward movement of the upper molars. Both groups saw meaningful reductions in malocclusion severity scores.

21PubMed Central. Retrospective Evaluation of Invisalign Mandibular Advancement in Growing Patients: Cephalometric, PAR and 3D Molar Displacement Outcomes

Another study focused on adolescents with a receded lower jaw found that the mandible moved forward about 3 mm on average and grew in length by about 4 mm after treatment. The overjet (horizontal gap between upper and lower front teeth) decreased by about 4.3 mm, with roughly 60% of the correction attributable to skeletal change and the remainder to dental tipping.

22PubMed Central. Efficacy of invisible advancement correction for mandibular retraction in adolescents based on Pancherz analysis

The compliance challenge is amplified with teenagers, though. An appliance that can be removed will be removed, and adolescents are not always the most disciplined about putting it back. Many orthodontists factor this into their decision when recommending aligners versus braces for younger patients.

Microplastic Concerns

A newer area of research involves whether clear aligners shed microplastics into saliva during wear. A systematic review found that aligners may cause microplastic particles to disperse in saliva during therapy, raising questions about potential health effects from absorbing or ingesting these particles.

23PubMed Central. Can Clear Aligners Release Microplastics That Impact the Patient’s Overall Health? A Systematic Review

A laboratory study simulating seven days of mechanical friction in artificial saliva tested aligners from multiple manufacturers and confirmed microplastic detachment from all brands, though the amounts varied. Invisalign-brand aligners released the lowest number of particles among the brands tested.

24PubMed. A spectroscopic study on orthodontic aligners: First evidence of secondary microplastic detachment after seven days of artificial saliva exposure

The clinical significance remains unclear. Microplastic ingestion is an emerging area of environmental health research in general, and humans already ingest microplastics from food packaging, water bottles, and many other sources. Whether the additional load from orthodontic aligners is meaningful for health is something researchers are still working to quantify. It is worth being aware of, but there is no evidence yet linking aligner wear to specific health outcomes from microplastic exposure.

The Risk of Direct-to-Consumer Aligners

The success of Invisalign spawned a wave of direct-to-consumer (DTC) aligner companies that promise straighter teeth without in-person orthodontist visits. These services typically have you take impressions at home or visit a scanning kiosk, then mail you a series of trays. The appeal is convenience and lower cost.

The risks are real, though. A study of the FDA’s adverse event database for DTC aligners found that about 41% of reported events involved bite problems, about 30% involved facial or oral pain, and about 27% involved periodontal complications like gum recession or tooth loosening. Nearly 70% of people who experienced an adverse event followed up with a dentist not associated with the DTC company.

25PubMed Central. Adverse Events Related to Direct-To-Consumer Sequential Aligners—A Study of the MAUDE Database

The fundamental issue is not that the plastic trays are different. It is the absence of professional oversight. Orthodontic treatment involves forces applied to living tissue inside a complex biomechanical system. Without regular in-person monitoring, problems like teeth not tracking with the trays, root damage, or worsening bite relationships can go undetected until they require expensive corrective treatment. The FDA database findings suggest this is not a theoretical risk but a documented pattern of real complications.