Is oral hygiene influenced by Invisalign or self ligating brackets?

We are all concerned about the oral hygiene of our patients, but is it influenced by our choice of orthodontic appliances?  This new trial sheds some light on this problem.

Some people have suggested that the choice of appliance may influence the ability of our patients to maintain their oral hygiene.  This may be particularly relevant to removable appliances as they can be removed to make tooth brushing easier.  As a result, claims are being made that aligner treatment reduces oral hygiene/periodontal problems. This was the subject of this trial.

A team from Connecticut did this study. The AJO-DDO published the paper in February.

Which orthodontic appliance is best for oral hygiene? A randomized clinical trial

Aditya Chhibber et al

Am J Orthod Dentofacial Orthop 2018;153:175-83

They did the study to answer this question

“Is there an effect of clear aligners, self ligating brackets and conventional brackets on oral hygiene”?

What did they do?

They did a three arm randomised trial with a 1:1:1 allocation. The PICO was

Participants: Patients having orthodontic treatment in the permanent dentition.

Intervention:  Invisalign

Comparator: Self ligating brackets or conventional brackets

Outcome: Periodontal measurements. The primary outcome was Plaque Index (PI), The secondary outcomes were the gingival index (GI) and papillary bleeding index (PBI).

They collected this data from the maxillary second premolars before treatment (T0), after 9 months (T2) and after 18 months (T3).

They did a sample size calculation and pre-prepared a block randomisation. When a patient consented to take part in the trial, the investigators phoned or texted a person who let them know the treatment allocation. Therefore, the investigators were independent of allocation etc.

It was not possible to blind the treating orthodontist to the intervention. Importantly,  the person recording the periodontal measures was not done blinded. This is important and I shall return to this later.

They did a complex intention to treat statistical analysis which took confounders into account.

What did they find?

They entered 71 patients into the study. Unfortunately, they did not always allocate the correct intervention to the patients. Consequently, they lost 10 patients from the study. This loss was unbalanced and resulted in 5 of the patients in the self ligating group not receiving self ligating brackets.

They found that there were differences in all the outcome measures between the brackets and Invisalign after 9 months. However, after 18 months there were no differences.  They showed this in these nice graphs.




Overall, they concluded that there was no significant difference in the oral hygiene level between clear aligners, self-ligated brackets and conventional brackets after 18 months of orthodontic treatment.

What did I think?

This was an ambitious and difficult study. I think that the authors did a good job and the results are interesting. They also clearly outlined the limitations of their study and did not make extreme claims about their findings.

We now need to consider whether this study provides us with high quality clinical information. As usual, I will start this discussion with the good points of the trial. Firstly, they carried out most aspects of the trial such as randomisation, enrolment and allocation well. They did an appropriate ITT statistical analysis.

I then looked for issues that may influence bias. The most relevant was that they did not blind the examiners to the treatment allocation when they recorded the outcome measures. This is important, because the examiners may have internal bias towards an intervention and may measure the outcomes differently accordingly. However, it is also difficult to see how they could blind the plaque recordings as this was a clinical measurement and the examiner was bound to see the bracket/aligners.

Another important factor was that the participants knew that their oral hygiene was being monitored because they were in a trial. This is a common issue in trials and is called the Hawthorne effect. I am not as concerned about this because we monitor the oral hygiene of all our  patients.  As a result, the Hawthorne effect may not have a large influence.

Finally, I am not clear about the reasons for 10 of the participants not receiving the correct treatment allocation. This could be a simple error. Alternatively, the operator may not have been in equipoise and they decided to prescribe their own choice of treatment rather than the treatment allocated by the randomisation. This could result in bias.


I have thought about these factors and I feel that there were problems with blinding and treatment allocation. These introduce uncertainty into the results. As a result, we should bear this in mind when we interpret this study.

I was surprised to see that the oral hygiene measures were not better for Invisalign. However, the authors pointed out that their finding was similar to other studies. This does suggest that aligner treatment does not make it easier to practice good oral hygiene.

As with many studies I cannot help feeling that “the person wearing or adjusting the appliance has a greater effect than the appliance”.

What is faster for space closure?  Ni-Ti springs or powerchain?

Those of us who still diagnose malocclusion and extract teeth will want to know which is the best method of force application for sliding mechanic space closure.  This systematic review gives us the answer.

Several trials have been done to help answer this question. This team of authors from Scotland and Australia did this systematic review to pool the results of these trials.

Effectiveness of nickel-titanium springs vs elastomeric chains in orthodontic space closure: A systematic review and meta-analysis

H. Mohammed et al

Orthod Craniofac Res. 2017;1–8. DOI: 10.1111/ocr.12210

They wanted to answer the following question;

“How effective are Ni Ti coil springs and elastomeric chains in orthodontic space closure”?

What did they do?

They carried out a standard systematic review. The PICO was

Population: Orthodontic patients of any age treated with conventional ligation fixed appliances and requiring space closure secondary to premolar extraction.

Intervention: Orthodontic space closure with NiTi springs

Comparison: Orthodontic space closure with elastomeric power chain

Outcome: Primary outcome was the rate of space closure.

They only included human randomised trials and excluded all other study designs.  They did a standard electronic search with no language limitations and assessed bias using the Cochrane Risk of Bias Tool.

What did they find?

They obtained a final sample of 4 RCTs to include in the review.  Two of these used a split mouth design and two were parallel group trials.  All trials reported the rate of space closure per month.

When they looked at risk of bias, one study was low risk, one had unclear risk and the remaining two had high risk of bias. I have interpreted this as suggesting that the evidence that we can obtain from this review is of moderate strength.

When they included the data in a meta analysis they found that space closure with Ni Ti springs was faster than with elastomeric chain by 0.2 mm/month (95% CI 0.12-0.28).

What did I think?

This was a nicely carried out systematic review that showed a statistically significant difference between the two methods of force application. When we interpret this data we need to consider several important factors.

Firstly, the strength of evidence was moderate. However, most orthodontic systematic reviews report this level of bias.  We also need to consider that the risk of harm with either intervention is low. As a result, I am not too concerned about this level of bias.

Then, we need to consider whether the difference is clinically significant.  The difference of 0.2mm/month is small. I have calculated that if we wanted to completely close a first upper premolar space with Ni Ti we would save one month.  I am not sure that I would regard this as clinically significant.

However, we still need to consider the different properties of the two methods.  I find it easier to use Ni Ti springs as they do not always need adjusting at every appointment.  Importantly, I do not like power chain because it accumulates plaque that tends to flick off into my face when I remove the chains. This means that I favour coil springs.  There is  a difference in cost but I accept that with the advantages of Ni Ti.

My final point, is that none of the papers included any information on the way that the patients felt about the interventions.  For example, did they find it easier to clean their teeth with either of the methods of force application?  These are also important questions and it would be great if they could be included in future studies.


I feel that the results of this review reinforce my current practice. I will continue to use Ni Ti springs the next time that I need to close space following the “amputation of premolars”…