Orthodontic Retention: Counting the Cost of Stability?

Variation in operator preferences is widespread in orthodontics. Retention is an excellent example of this, with many of us being avowed users of a particular type of wire, adhesive, or technique. It is the part of my treatment that I have tinkered with most over the years.

I am now using fixed retainers far more than I did historically. This change reflects concerns around compliance with the long-term wear of removable retainers. It also relates that my failure rates with fixed retainers are a fraction of what they used to be. However, retainers do fail from time to time.

I try to plan retention on a case-by-case basis, considering the presenting malocclusion, the treatment-induced changes, and my (often incorrect) forecast as to how well they might fare with either fixed or removable retainers. One thing that I do not consider is cost. However, perhaps I should?

A team based in Malmo, Sweden, did this study. The EJO published the paper.

This is the second part of a series of papers about this study. Unfortunately, I managed to miss the first paper in which the team discussed the effectiveness of these retainers. I will catch up when I can!

In this part of their study, they looked at the important variable of the cost of treatment. The authors pointed out that economic appraisal of intervention costs is commonly done in medical research. However, this has rarely been done for orthodontic trials. The cost of treatment is relevant to both state/insurance-funded provision and private practice.

What did they ask?

They did this study to

“Discover if there was a difference in the costs of between vaccumm formed and fixed retainers after 2 years of retention”.

What did they do?

They did a single centre RCT with three parallel arms with a sample size of 90. The PICO was

Participants:

Adolescent patients treated with fixed orthodontic appliances in both arches

Intervention:

Bonded retainer from maxillary canine to canine (Group A)

Comparator 1:

Bonded retainer to the maxillary four incisors. (Group B)

Comparator 2:

Vacuum-formed retainer covering all maxillary teeth. (Group C)

Outcome:

The total cost of each treatment. Post-treatment change in irregularity using Little’s Index.

They calculated the cost of the retainers by obtaining information on the material costs, lab costs, and the cost of surgery time.

The team used remote pre-prepared block randomisation. They concealed the allocation using sealed envelopes. Before the study started, they calculated that they needed to enroll 28 participants in each group.

Three experienced orthodontists indirectly placed the bonded retainers.  These were 0.0195-inch in diameter and were bonded with Transbond Supreme LV. The VFRs were formed from 1.5-mm Essix blanks fitted within 24 hours of debonding. They were prescribed nearly full-time for 4 weeks before nighttime wear was recommended. They recommended wear on alternate nights after 1 year of retention.

What did they find?

They recruited 30 patients for each intervention. These included 54 females and 36 males with a mean age of 15.9 years. They followed them for two years and collected data at the start of retention and two years of follow-up.

Their main findings were:

• Group A, 9 patients had 16 emergency visits, and 1 patient lost the retainer twice.
• In group B, 5 patients had 7 emergency visits
• In group 6, 16 patients had 19 emergency visits.
• The mean total cost per patient was €734.00 for the maxillary four incisors bonded retainer; for the canine-to-canine retainer, this was €674.00, and for the VFR, the cost was €778. There was no statistical difference between these costs.
• There was no difference in costs in treatment time between the retainers. However, the material cost for the VFR was higher (€83.00) than the bonded retainers (€51.00 and @49.00).
• The mean emergency costs were €31.00 for the incisor retainer, €49.00 for the canine-to-canine retainer and €116.00 for the VFR. The costs for the VFR were significantly higher for the VFR.
• In another paper, they reported on the effectiveness of the retainers in preventing relapse. But, again, there were no significant differences.

Their overall conclusion was

“Although the material and emergency costs for the VFR were higher than the bonded retainers. There were no statistically significant differences for the total costs between the three retention methods”.

What did I think?

This was a well done and reported RCT. We certainly need more studies of this standard in our speciality. The good points of this study were that it was well planned, the randomisation and concealment were good, and the data analysis was relevant. I was particularly pleased to see that they did an intention to treat analysis. This means that all the data was analysed regardless of the outcome.

The results suggest that retention costs are unlikely to differ markedly based on retainer type. However, it is important to note that the follow-up period was relatively short (at 2 years).

The authors correctly acknowledge that the increasing possibilities around in-house, software-based approaches to the fabrication of fixed and removable retainers may change the direct costs of retainer production in time. In time, it would be interesting to see further analyses using 3-D printed wires.

I also think it would be helpful to perform a longer follow-up of these participants. In my opinion, there is every reason to expect that the pattern observed (of higher breakage and replacement rates with removable retainers) is likely to be perpetuated over time. In fact, the only logical reason why this might not occur is if the patients stop wearing the removable retainers altogether or become more sporadic with wear. Therefore, I wonder whether a cost-related benefit of fixed retention might become more apparent over time.

A final problem is the local nature of the evaluation, with the research being carried out within a single public clinic. However, single-centre studies involving universities or public hospitals are the norm in orthodontics. It would be great to see the research undertaken more frequently in orthodontic offices.

What can we conclude?

There was no meaningful difference in costs incurred with fixed retainers terminating on either the canines or lateral incisors and vacuum-formed retainers over a. 2-year period. However, higher emergency costs were found with vacuum-formed retainers.