A simple removable appliance is better than clear aligners for crossbite correction!
Correcting an anterior crossbite in the mixed dentition is one of the simplest forms of orthodontic treatment. Traditionally, this has been achieved using a basic removable appliance with springs to procline the upper teeth or a sectional fixed appliance such as the 2 x 4. Recently, advances in clear aligner technology have indicated that aligners may be utilised for interceptive orthodontic treatment. The main benefit of this approach is that the appliances are aesthetic.
This new study examined the effectiveness of clear aligners and a straightforward removable appliance for correcting crossbites.
A team from Antalya, Turkey, did this trial. The Angle Orthodontist published the paper.
Buse Nur Gok et al
Angle Orthodontist. Advance access. DOI: 10.2319/022125-154.1
What did they ask?
They did the study to ask the following question.
“What is the effectiveness of clear aligners and Z spring appliances in correcting anterior crossbite during the mixed dentition”.
What did they do?
They did a single-centre randomised controlled trial with a one-to-one allocation. The PICO was
Participants.
30 orthodontic patients age 7 to 12 years with class one molar relationship and anterior crossbite involving at least one permanent incisor. They all had Class I molar relationships with a pseudo Class III anterior crossbite.
Intervention.
Customised clear aligners. These range from 7 to 12 aligners per patient.
Comparator
Z spring appliances with a spring to proline the upper incisor. Retention was provided with Adam’s claps and a passive labial arch.
Outcomes.
The duration of treatment was the primary outcome. The secondary outcome was quality of life data.
The patients were instructed to wear their appliances for at least 22 hours a day and remove them only during meals. The aligners were changed every 10 days during clinical visits. For the removable appliance, the springs were also activated every 10 days. Treatment continued until a positive overjet was established.
They carried out a sample size calculation that was nicely done and this suggested that they needed 15 participants per group.
They used a predetermined randomisation that was concealed using sealed envelopes. The same clinician performed the treatments and outcome measurements.
Data was collected at the start of treatment and at the end of treatment, which included cephalometric radiographs and analysis.
They analysed the data with simple parametric statistics
What did they find?
Both groups were similar at the start of treatment. The overall main age of the patients was 113 months with 33% female and 66.7 % male patients. All the patients completed treatment.
They presented a detailed cephalometric and model analysis.
However, the most important data concerned treatment duration and overall success rate. This showed that the overall treatment duration for the aligner group was 96.3 (SD = 22.7, 95% CI=84.812 , 107.788) days, whereas for the Z spring group it was 48.4 (SD = 27, 95% CI=34.73 , 62.06) days. This difference was both clinically and statistically significant with a mean difference of 53.1 days (95%CI=27.5-78.7).
They did not find many meaningful differences in the cephalometric or the quality of life evaluation.
Their overall conclusions were;
“Clear aligner and spring appliances were effective in treating anterior crossbite. Importantly, the clear aligner treatment took considerably longer than with the simple Z-spring removal appliance”.
What did I think?
This is the kind of study needed when evaluating the effectiveness of simple orthodontic treatment. Although the study was small, the effect size they reported was large and clinically significant. The study was well conducted and clearly reported. It is a good first step into providing more information about clear aligners.
There are, of course, issues with blinding of the operator, as this was not possible to achieve. As a result, there is a risk of bias in the findings because the operator set the endpoint of treatment.
It was also important to consider that the operator examined the patients every 10 days for appliance reactivation. While this may be the protocol for clear aligners, it is not applicable to removable appliances. Nonetheless, these regular visits seem suitable for removable appliance treatment and appeared to result in an effectively short treatment duration. This is illustrated by the lower 95% CI of 27.5 days, this is still clinically significant.
Nevertheless, it seems that the removable appliance is more effective than the clear aligner in achieving this straightforward tooth movement. This maybe because this form of malocclusion can be corrected by tipping methods and is suited to a simple removable appliance.
We can use the findings of this study to inform our patients that both treatments can be effective. While the clear aligner may be more aesthetic than the removable appliance, the “trade off” is a treatment that takes almost twice as long as the simple removable appliance. I know what I would recommend to my patients.
In fact, if we consider these results, I cannot think of any reason to suggest aligner treatment as opposed to a much simpler and cost-effective method using a removable appliance.
Emeritus Professor of Orthodontics, University of Manchester, UK.
This study compares clear aligners with a removable spring appliance for anterior crossbite correction, but it’s really apples vs pears. The spring appliance simply tips a tooth over the bite, while aligners usually include broader anterior alignment. Aligner movements are typically set at ~0.25 mm linear and 1–2° rotational movement per stage, with 7-day changes being standard — giving an expected correction time of around 60 days, although noted this study elected 10 day changes. Either way a few weeks’ difference is not clinically significant, and with mismatched endpoints and limited control for case severity or compliance, the study offers little meaningful evidence on aligner versus traditional appliance effectiveness.
As a final thought, a third group using a small blob of composite and an elastic might have achieved the result even faster!
well said – apples vs pears and apricots – the aligner appliance was not of a single “fruit”.
Let me try and reply as simply as possible. In a 40 year span of specialist orthodontics – the last 10 years have been spent treating 7-11 year olds purely with ALIGN’s – iFIRST and sometimes Express.
For anterior crossbites – I have always loathed the use of Hawleys with springs – they are grubby, accumulate plaque and it is kind of hit and miss activating the springs.
The lower incisor counterpart is often also proclined and needs some attention. In most of these cases I only use 7 aligners on a 5-7 day cycle. It works and fixes both arches and if smartly programmed can address some adjacent teeth as well!
Many of these kids have been reviewed 5-10 years later.
Hello John!
Excellent point regarding the ability of Invisalign First (not sure about any other aligner product) to correct multiple aspects of the malocclusion, rather than simply correcting crossbite. We may simultaneously reduce overjet, align arches, create space for canines, allocate E space, reduce overbites. (if programmed). When this is taken into account along with the absence of need for patients to take chair time during weekly (or 10 day activation as elected in this sample), compared to weekly necessity of chair time, and single malocclusion feature corrected (Anterior crossbite), the conclusion of decreased efficiency of the various brands of aligners (not Invisalign) used in this sample is erroneous, as efficiency was not tested, only treatment time. As you and Usman Qureshi alluded, the mean treatment duration difference was 47 days.
Efficiency? So let’s see; over the longest period they encountered of 12 weeks – 3 visits max aligners (being generous and adding 1 elective monitoring visit, or you could use virtual care), correct multiple aspects required to normalize development of the entire dentation (including allowing eruption and alignment of the teeth; erupting lateral incisor blocked by the Hawley bow in the picture in the article) versus scan, insertion, 11 visits every 10 days – poor parents – 12 visits for Z spring versus 3 max for aligners – I know which I would be recommending to parents – you don’t need to take chair, school and parent time to activate aligners – especially considering the minimal cost of the Phase 1 Invisalign First product. In fact, product cost was never measured or tested in this study- so to conclude anything but mean 47 days shorter treatment with equal clinical efficiency is not supported by this study. Aligners are more efficient, requiring no chair time to activate.
This study appears to be another nail in the coffin for treatment with Invisalign First.
While the study did not utilize Invisalign First, the correlation is hard to ignore.
Had the authors utilized Invisalign First and also considered the variable of cost to the patient, I expect that there would be an even more profound difference.
Yes, Invisalign First might sometimes correct a problem in need of interceptive or Phase I treatment. However, when we consider all variables, including cost to the patient, it seems to be very rarely the ideal treatment for interceptive or Phase I treatment. This study shows that inferior treatment efficiency is also a detriment to treatment with Invisalign First, for treatment of pseudo class III anterior crossbite.
My own opinion is that when we consider all alternatives, including cost to the patient and efficiency of treatment, Invisalign First is almost never the best Phase I treatment for a patient.
Sadly, I am starting to think that it is sometimes being chosen because it is the ideal treatment for the orthodontist, KOL, or Invisalign, despite what is best for the patient. Happily, I think that more and more of us are starting to realize that it is not appropriate for most Phase I patients, despite what we are sometimes told. It’s nice to see research support for this as well.
Thanks for sharing!
With due respect, this study in no way supported your desired hypothesis that Invisalign First “is not appropriate for most Phase I patients”, it was not even used, let alone these M&M supporting finding of such a conclusion.
As you correctly pointed out, aligners used were a mix of, from what I can tell, 2 brands ” Crystal Aligner, registered in Pakistan and OrthoClear Antalya. I could find very little information regarding the manufacturing, activation programmed by the clinician or programmable by the company, if indeed it is directly computer programmed or simply computer simulated, material and recommended wear duration. All I can see is that the protocol as pointed out is not that typically used with Invisalign First, the aligner shown fits poorly and has attachments that are generic and likely unnecessary. In addition, this study cannot support “inferior treatment efficiency” as chair time and other aspects were not taken into account; only treatment duration that has no relevance to Invisalign First protocols or ability to be used efficiently and effectively in Interceptive Orthodontics.
The Z springs used in this study were made of SS. They differ from 3D axial springs in the DNA appliance that are made from a superior orthodontic wire and have a vertical (compressible) component. Finger springs have been available for over a century but they need to be combined with other components of the device to provide 6 degrees of freedom for comprehensive correction.
Disclosure: Professor Singh is the inventor of in the DNA appliance, the first palatal expander to be FDA cleared for the treatment of mild, moderate and severe OSA in both children and adults.
Once again Kevin, the bias that is on display is disheartening. I don’t see a place for prejudice emanating from an academic blog; let alone anywhere on earth.
1. Your title: “A simple removable appliance is better than clear aligners for crossbite correction!” Really? I did not see that statement corroborated by this study, others, nor concluded by the authors. Clinical equivalence was found with the 2-product 10 day change aligner group 49 (48.9) days mean difference in treatment time; without mention or measure of up to 9 additional clinical visits necessary to activate such appliances, when compared to aligners. That’s a significant parent, patient, staff and clinician time difference, totally unaccounted.
Additionally; if an aligner product such as Invisalign First were used, protocol is as JM above pointed out, 7 days- if that protocol had been used – very much within our biological benchmark of 1mm a month (bodily canine movement) – the treatment duration difference detected would fail to be statistically significant. Combined with in-office appointments needed when activating such Z spring appliances, I am finding it most difficult to envisage or support a belief of treatment efficiency superiority in clinical practice. I am not sure why the authors chose that 10 day change-over protocol that slows treatment, – obviously increases treatment duration – is difficult for patients to remember and varies from our benchmark of 1mm a month that arises from bodily movement of canines – not tipping! I could not find the activation used by any of the aligner companies used to treat the patients in the study, nor if the clinician then chose to alter that activation.
CONCLUSIONS
• Both aligners and z-spring appliances effectively corrected AC, achieving normal overjet relationships. Dentoalveolar changes were observed during treatment, whereas skeletal relationships and natural growth remained unaffected.
• Clear aligners required a significantly longer treatment duration than ZS appliances, with an average
difference of 47.9 days. Longer treatment durations in removable appliances may negatively affect patient
compliance and increase the risk of treatment discontinuation. Treatment selection should be made in collaboration with parents and clinicians.
• The impact of age on treatment duration was not statistically significant. However, younger patients
(7–10 years) showed greater variability, whereas older patients (.10 years) had a more consistent
but slightly longer duration.
• This study compared treatment outcomes and OHRQoL, showing that clear aligners offer esthetic
and comfort benefits, whereas ZS appliances provide a cost-effective, efficient alternative. Treatment
selection should consider patient preferences and clinical needs.
2. This study had as much to do with Invisalign First as – nothing.
Please stop the unsubstantiated assumption that all aligner systems are equivalent in safety, activation, comfort, occlusal and alignment outcome and treatment duration. Only 1 is largely tested in the literature. Basic differences such as activation per aligner, change-over protocols, material, attachment design- force vs displacement driven mechanics exist. To pass 1 off as equivalent to another to patients is bad enough for our profession to naively save a buck; but to assume equivalence of all aligners and then to apply findings to all aligner products from studies not even testing the product is at best, shall we say; unsound.
Would you conclude efficacy of Damon brackets when a study cohort was treated using an Andrews prescription? I think not.
3. You conclude: “We can use the findings of this study to inform our patients that both treatments can be effective. While the clear aligner may be more aesthetic than the removable appliance, the “trade off” is a treatment that takes almost twice as long as the simple removable appliance. I know what I would recommend to my patients.” ….As long as you inform the parents that there is currently only 1 evidence-based aligner system that uses a 7 day protocol, negating any significant treatment duration difference. The products used in this study are not evidence based; in fact, we know and can find very little about their efficacy or safety. There is however; 1 aligner system that when using the benchmark, evidence-based protocol of 1mm or less a month of activation, has equivalent or shorter treatment duration for mild to moderate malocclusions, requires fewer visits by yourself and your child compared to such z -spring appliances and we may correct many additional aspects of your child’s bite if required, for similar (or higher treatment fee, depending on clinician) – would that not be informed consent?
You also state:
“In fact, if we consider these results, I cannot think of any reason to suggest aligner treatment as opposed to a much simpler and cost-effective method using a removable appliance”…. Unfortunately we cannot conclude anything about cost effectiveness / laboratory fee from the study as it is not measured or tested. It should not even be mentioned in conjunction with these M&M’s. Maybe its paper 2, or they forgot that patients don’t need to attend the clinic to activate their aligner appliances, or in case of loss. I would be surprised if there would be a significant difference in cost effectiveness considering the aligners used. Even the Invisalign First product fee is modest compared to other products sold by the same company, and likely cheaper than the Z spring when you consider support, quality, number of activation visits, chair time saved and the other digital tools included in the “lab” fee.
Why not conclude only what is valid; in this study, clinical equivalence was found between z spring and the 2 aligner products tested – with patients in the 2-aligner product cohort taking mean of 49 days longer treatment time, with a 10-day change-over protocol?
VV provides sponsored lectures by Align Technology.
Thanks for your comments. Firstly, it is a shame that you decided to accuse me of bias. I simply critically analysed this paper, and this showed that a simple removable appliance was better than aligners because of the markedly different duration of treatment. Perhaps I was influenced by the UK philosophy of orthodontics, which is treating the patient’s problem to a high standard as quickly and effectively as possible.
In your next comment, I assume that you are suggesting that the operators did not use the appliances correctly. This is a common, redundant criticism that people often make about orthodontic research when the findings do not agree with their personal opinion.
Secondly, I have checked my text and I have not mentioned Invisalign First, so I am unclear of your argument here. Your other statements about Invisalign are not supported by science; they may be your opinion, but I am not sure what this is based upon other than clinical experience.
Your final conclusion was similar to mine. So I am not sure about the point you are trying to make.
Thanks also for clarifying that you are paid by Invisalign and are an Invisalign KOL.
Hi Kevin, Can you clarify the guidelines about putting a full name on posted comments please? Are initials OK or are full names required.
Hi John, thanks. I do not really apply policies to the comments. But I do take the point that you are making. I have decided that we need full names to accept comments. Thanks for raising this. Best wishes Kevin
Hello Dr McDonald – I have been using initials as I was unaware that I may not, and Dr O’Brien knows my identity. My name is lengthy; however, I am more than happy to oblige:)
Hi Kevin
One source of bias is demonstrated, perhaps inadvertently, by the unsupported title of your blog. I have addressed that above. It is not corroborated by the study, nor was it a conclusion of the authors. Treatment duration is a single variable we may take into account when evaluating appliance choice; it is not the variable that determines appliance superiority- for me. In that case we would all use forceps.
Regarding “redundant criticism”, in no way did I suggest the authors used the appliances incorrectly. I mentioned that I knew and could find little about the brands used. Along with other bloggers, we pointed out that the protocol used directly influenced and increased the treatment duration – a major variable being measured – and that the protocol was not one that is used for all aligner products.
Next point you raised; you typically refer to aligners generically. These products are not equivalent – or are they? If you feel that it is in fact valid and scientifically rigorous to assume that all aligners are of equivalent capability, (I do not, we do not know); then that includes Invisalign First. The product was also raised by fellow bloggers. Nov 3rd blog, you asked for studies in high quality journals.
Finally, when I blog re aligners, as you know, I disclose that I provide sponsored lectures for Align Technology. Nov 3 I also spoke to your bias against the inherent bias of KOL’s. No need to thank me!
Vicki Vlaskalic provides sponsored lectures for Align Technology for the last 27 years
Dear Kevin, I don’t think we have a different standard of care in this part of the world. To me it comes down to diagnosis. Is there lower incisor involvement with rotation or eversion, then aligners do a good job in correcting the cross-bite and the lower irregularities. If it is only one incisor a plate does a good job, but I never activated every 10 days. More like every 3 to 4 weeks. Both therapies have their own indication, that is where the apples and pears come in. Kind regards Ronald