Treatment outcome with orthodontic Aligners and fixed appliances: A systematic review with meta-analyses

The increasing demand for more aesthetic and comfortable orthodontic alternatives has fostered the development of clear aligner therapy (CAT). Ever since Align Technology, Inc. released the Invisalign® system back in 1999, clear aligners have become more popular than ever.

At first, these aligners were used to correct milder cases of malalignment like anterior crowding or spacing. With the progression of material and software design as well as auxiliaries like attachments and elastics, clear aligners can now be used to treat more complex cases and severe malocclusions.

Fixed appliances, on the other hand, have been in use for over a hundred years. Due to their brilliant treatment outcomes and high success rates, they have earned a spot as the most reliable dental device in treating orthodontic malocclusion.

However, with clear aligners being more aesthetically pleasing, more and more individuals today are seeking CAT instead of fixed appliance therapy. Some experts claim that clear aligners today are able to treat almost everything from mild to severe malocclusions. Does this mean that clear aligners could essentially be a viable alternative for braces? This study may give us a better insight into this ongoing discourse.

This study was conducted by a team from Europe and published in the European Journal of Orthodontics.

Treatment outcome with orthodontic aligners and fixed appliances: a systematic review with meta-analyses.

Papageorgiou SN(1), Koletsi D(1), Iliadi A(2), Peltomaki T(3)(4)(5), Eliades T(1).

Eur J Orthod. 2020 Jun 23;42(3):331-343. doi: 10.1093/ejo/cjz094.

What they asked

The authors aimed:

“To assess the efficacy of aligners and fixed appliances for comprehensive orthodontic treatment.”

What they did

Systematic searches were made through eight databases without restrictions for publication date, language, or type from inception up to 25 April 2019. They included randomized as well as non-randomized trials on patients irrespective of age, sex, ethnicity, or malocclusion comparing full-arch orthodontic treatment with aligners and fixed appliances. Study selection and data extraction were done independently in triplicate.

They also assessed the risk of bias for the included studies using the Cochrane guidelines with the RoB 2.0 tool for randomized trials and the ROBINS-I tool for non-randomized trials. They also conducted random-effects meta-analyses of mean differences (MDs) or relative risks (RRs) with their 95% confidence intervals (CIs). They followed it with sensitivity analyses and GRADE analysis of evidence quality.

The primary outcome of this systematic review was the outcome of comprehensive orthodontic treatment judged using the PAR index and the ABO’s Objective Grading System (ABO-OGS). Secondary outcomes included treatment duration, as well as adverse effects like loss of periodontal support, External Apical Root Resorption (EARR), gingival recession, and proclination of the lower incisors during treatment.

What they found out

Through electronic search, they yielded 1376 results while another 7 were manually identified from reference or citation lists of identified papers. After checking them against the eligibility criteria, 11 papers were finally included, out of which 4 were randomized studies and 7 were retrospective non-randomized trials.

A total of 446 aligner patients and 443 fixed appliance patients were included, with a median total sample of 66 patients per study. The mean age of patients in the study was 28.0 years (male 33%).

Evidence from meta-analyses of overall ABO-OGS (American Board of Orthodontics Objective Grading System) scores indicated that treatment with aligners was associated with worse treatment outcomes as compared with braces (3 studies; MD = 9.9, 95% Cl = 1.2 – 2.0).

On the other hand, the PAR index revealed that there were no significant differences between aligners and braces, with the exception of an almost significant difference in PAR reduction (P = 0.06) for fixed appliances. There were also significant differences in the PAR components for upper anterior and overbite (P < 0.05) in the favour of braces.

No significant differences were identified for treatment duration. The main limitations of existing evidence were attributed to the risk of bias, inconsistency, and imprecision of included studies.

What we can conclude

According to existing clinical evidence, it seems that orthodontic treatment with aligners is associated with worse treatment outcomes compared to fixed appliances. Treatment duration, however, does not seem to be defined by appliance alone. Other related factors may come into play.

As for adverse outcomes like EARR, proclination of lower incisors, and development of gingival recessions, very limited data exists to support either narrative. Current evidence does not support the clinical use of aligners as a treatment modality especially when directly compared to fixed appliances. For now, traditional braces remain the gold standard of orthodontic treatment.