Clear aligners versus conventional braces: what the evidence shows

If you are considering orthodontic treatment to straighten your teeth, you might be weighing different options. Two common choices are clear aligners and conventional fixed braces. Both can improve the alignment of your teeth, but they work in different ways.

Many people wonder if clear aligners are as effective as fixed braces. Research has explored this question by comparing the outcomes of these two treatment methods. This article will look at what systematic reviews, which summarize many studies, have found about their effectiveness.

How clear aligner treatment differs from fixed braces

Fixed braces use brackets that are glued to the front of your teeth. A wire connects these brackets and is adjusted periodically by your dental professional. The wire puts gentle, continuous pressure on your teeth to move them into their new positions. Brackets and wires are typically made of metal, but clear or tooth-coloured options are also available. Once placed, fixed braces stay on your teeth for the entire treatment period.

Clear aligners are a series of custom-made, clear plastic trays that fit snugly over your teeth. You wear each set of aligners for a specific period, usually one to two weeks, before switching to the next set in the series. Each new set is slightly different from the last, designed to move your teeth incrementally. You remove aligners to eat, drink anything other than water, and to brush and floss your teeth.

What the research shows

Several systematic reviews have looked at the effectiveness of clear aligners, often comparing them to fixed braces. A systematic review gathers all available studies on a topic, assesses their quality, and summarizes their findings.

How these reviews were built

Knowing what sits underneath a review's conclusions helps you weigh them:

• The largest of the three reviews included 22 studies: three randomized controlled trials (RCTs), 8 prospective studies, and 11 retrospective studies. The RCTs carried a low risk of bias, but 13 of the other studies were rated at moderate risk and 6 at high risk [1].
• A comparative review of aligners versus fixed appliances included 8 studies — two RCTs and six cohort studies — drawn from searches of five major research databases through August 2018 [2].
• The most recent of the three searched the literature from January 2014 to April 2019 and included 7 studies (one RCT and six retrospective cohorts). Six of the seven had a moderate risk of bias and one a high risk. The reviewers graded the certainty of the evidence for each outcome using the GRADE approach [3].

One detail matters more than it first appears: in the largest review, the studies were so different from one another — in design, methods, and treatment protocols — that the authors concluded a valid pooled estimate was not possible [1]. That is why this article reports patterns and directions rather than one headline number: the research itself does not support one.

Effectiveness for mild-to-moderate cases

For certain situations, clear aligners appear to be a viable option. One systematic review found that clear aligners can be an alternative to conventional braces for correcting mild to moderate teeth alignment issues in patients who are not still growing [1]. Another review also noted that clear aligners may lead to clinically acceptable results for mild to moderate malocclusions, particularly for the buccolingual (front-to-back) inclination of upper and lower front teeth [3].

Predictability of specific tooth movements

The ability of clear aligners to achieve certain tooth movements has been studied:

• Predictable movements: Clear aligners can predictably level, tip, and derotate teeth [1].
• Less predictable movements: Aligners show limited effectiveness in certain areas. This includes arch expansion through bodily tooth movement, closing spaces after extractions, correcting how upper and lower teeth meet (occlusal contacts), and fixing larger differences in how teeth align from front to back or up and down [1].
• Specific tooth types: While aligners can derotate teeth generally, they are less predictable for the rotation of cuspids (canine teeth) and premolars [1].
• Torque and transverse width: Clear aligners might not be as effective as braces in controlling the torque (the rotation of a tooth around its long axis) of teeth or in increasing the width of the dental arch [2].
• Overall predictability: Despite advances in technology, many tooth movements may not be predictable enough to be accomplished with just one set of aligner trays [3].

The overall-outcome comparison

The comparative review also looked at a summary measure of treatment results called the Objective Grading System (OGS) score, which grades how well the finished result meets orthodontic standards. On this overall measure, the difference between aligner-treated and brace-treated patients was not statistically significant (a weighted mean difference of 8.38, with a 95% confidence interval of −0.17 to 16.93; P = 0.05) [2]. In plain terms: when the end result was graded as a whole, the two approaches landed close enough that the studies could not confidently separate them — even though braces held clear advantages on specific components such as occlusal contacts, torque control, and retention [2].

The same review also noted, as background to why the question matters, that patients have tended to prefer aligners for comfort and appearance, while their effectiveness remained the debated question [2]. Preference and effectiveness are separate questions — which is exactly why the component-level findings above are worth reading closely.

Treatment duration and segmented movement

Some research suggests potential advantages for clear aligners in specific aspects of treatment:

• Shorter treatment duration: One systematic review found that patients treated with clear aligners had a statistically significant shorter treatment duration compared to those with braces — about 6.31 months shorter on average (95% confidence interval −8.37 to −4.24; P < 0.001) [2].
• Segmented movement: Clear aligners may have an advantage when it comes to moving individual teeth or small groups of teeth independently [2].

Where fixed appliances retain the edge

While clear aligners are effective for many cases, fixed braces still tend to be the preferred choice for more complex orthodontic issues.

• Complex cases: Fixed braces generally offer more precise control over tooth movement, making them better suited for severe malocclusions, significant bite problems, and cases requiring complex tooth rotations or movements [1].
• Occlusal contacts and retention: Fixed braces may be more effective in creating adequate occlusal contacts (how teeth meet when you bite down) and in achieving long-term retention of tooth positions [2].
• Larger discrepancies: For larger discrepancies in tooth alignment from front to back or up and down, fixed braces often provide more comprehensive correction [1].

Limitations of the evidence

It is important to understand the limitations of the current research on clear aligners and fixed braces:

• Heterogeneity of studies: Many studies included in systematic reviews vary widely in their design, methods, and the specific patient groups they examine. This "heterogeneity" makes it difficult to combine results from different studies for a clear, overall conclusion [1].
• Risk of bias: While some studies, particularly randomized controlled trials (RCTs), have a low risk of bias, many others have a moderate or high risk of bias. This means that their findings might be influenced by factors other than the treatment itself [1, 3].
• Level of certainty: The overall level of evidence regarding the effectiveness of clear aligners is often moderate, and the certainty level for specific tooth movements is described as "low to moderate" [1, 3]. This means that while findings exist, more high-quality research is needed to draw stronger conclusions.
• Evolving technology: Orthodontic technology, especially for clear aligners, changes quickly. Some reviews note that despite recent advances, not all clinical scenarios have been fully assessed in the included studies [3]. This rapid evolution means that new products and techniques are constantly emerging, and research may not always keep pace with the latest developments.
• Lack of standardized protocols: A lack of consistent treatment protocols across different studies also makes it challenging to compare results directly [1].

Due to these factors, researchers caution that results should be interpreted carefully, and clear clinical recommendations based on solid scientific evidence are currently limited to non-extraction treatment for mild to moderate malocclusions in non-growing patients [1].

Who these findings apply to — and who they don't

The populations studied shape how far the conclusions reach. The strongest, most consistent finding — that aligners are a viable alternative to braces — was specifically established for non-growing patients with mild to moderate malocclusions who did not need extractions [1]. If you are a teenager whose jaw is still developing, if your case requires extractions, or if your malocclusion is severe, the reviews do not extend their conclusions to you — those scenarios sit outside what the included studies established [1]. The most recent review is explicit that not all potential clinical scenarios have been assessed in the available studies [3].

It is also worth being clear about what these reviews set out to measure: tooth movement and treatment outcomes. Questions people reasonably care about when choosing — day-to-day comfort, appearance, the discipline of wearing removable trays as prescribed, and what treatment costs — were not the outcomes these reviews graded, and this article draws no conclusions about them. They are real considerations; they are simply ones to work through with your own dental professional rather than ones this evidence answers.

What this means for you

The choice between clear aligners and fixed braces largely depends on your specific needs and the complexity of your orthodontic condition. What the evidence shows is that clear aligners are a good option for mild to moderate alignment issues, and they may offer a shorter treatment time. However, fixed braces often provide more predictable results for complex movements, significant bite corrections, and achieving optimal occlusal contacts.

Case selection is the whole game. This means that determining which treatment option is right for you is the most critical step. A licensed dentist or orthodontist can assess your teeth and bite, discuss your treatment goals, and explain whether clear aligners or fixed braces would be more suitable for your individual situation. They can also explain the expected outcomes, potential challenges, and duration of each treatment option.

To learn more about dental care options in your area, you can explore resources like our guide to dentistry in Calgary.