How much relapse occurs after 40 years?
We all know that orthodontic treatment relapses to a degree. This new study looked at orthodontic relapse over 40 years. I thought that the results were interesting and clinically relevant.
Most research suggests that orthodontic relapse is inevitable. However, longitudinal studies also show that arch dimensions in untreated people change over several years. Therefore, we could consider that relapse is part of the normal ageing process that we cannot stop! In many ways, it is surprising that only a few researchers have looked at this critical area. As a result, I thought that this new study was fascinating.
A team from Bauru, Brazil, did the study. The AJO-DDO published the paper.
Karina Maria Salvatore Freitas, et al. AJO on line. https://doi.org/10.1016/j.ajodo.2020.05.027
What did they ask?
The aim of their study was
“To compare the ageing changes of the dental arches in orthodontically treated and untreated subjects after a four-decade follow up”.
What did they do?
They looked at the dental casts of orthodontic patients and an untreated group.
The orthodontic sample.
They collected the records for the 29 orthodontic patients from the files of the graduate clinic at Bauru Dental School. The main inclusion criteria were:
- Class I or Class II Division 1 malocclusion
- Fixed appliance treatment with the extraction of four first premolars.
They took the records at the start and end of treatment and at least 25 years after the end of treatment. Notably, the patients had stopped retention at less than 3.3 years after treatment.
The untreated group
These were 22 people who had not received orthodontic treatment. They collected the initial records from 1967 to 1974. They took final records from April 2015 to May 2016. Unfortunately, the authors did not state where they obtained this sample of people.
In the treated group, the only teeth that were missing were the first premolars. However, in the untreated group, most subjects had some teeth missing.
The primary outcome was Little’s Index for incisal crowding. The study team also used the PAR index for treatment change and measured other dental dimensions. For example, arch width at the canines and molars, arch length, etc.
What did they find?
The paper contained a large amount of detailed data. Unfortunately, I do not have the space to go into this all here. So, I am going to concentrate on what I feel are the main findings.
At the start of the study, the groups were similar for their age and sex distribution. But, unfortunately, the groups were different in follow-up times. The authors addressed this problem by annualising the changes for the untreated group. I thought that this was reasonable.
The important findings were
- The treated group was followed for 36.4 years after the end of retention. The follow-up for the untreated subjects was 43.12 years.
- In the treated group, crowding was corrected with treatment. However, it then significantly relapsed in the long term. For example, the mean Little’s Index change for mandibular crowding was 4.28 (SD=2.79) compared to 1.29 (1.05) in the untreated group. When they looked at maxillary crowding, the difference for the treated group was 3.11(1.49) and 0.68 (0.9) for the untreated subjects.
- At the final data collection, the treated group had Little’s Index scores of 4.0 in the maxilla and 5.3 in the mandible. At the start of the treatment, the LI score for the maxilla was 10.0 and 8.9 for the mandible.
- In the treated group, intercanine width increased with treatment and decreased with time. This was not the case for the untreated sample.
- Overjet and overbite were corrected with treatment and remained stable.
Their conclusions were:
“Treated patients showed a relapse of crowding and a decrease in arch form. However, the long-term changes in the untreated group were different from the treated group”.
What did I think?
I thought that this was an ambitious project that must have taken a great deal of effort. The authors wrote a very detailed paper, and I hope that I have extracted sufficient information from the large amount of data they produced.
As with all research work, there are some deficiencies that I feel I should mention. Most importantly, I could not find any information on the source of the untreated subjects. As a result, we need to be careful in assuming that the two groups came from similar sources. This problem means that there may be some bias. However, we do not know the direction of the bias.
We also need to consider the reasons for people taking part in studies of this nature. For example, was it possible to take the records because the participants were pleased with the results of their treatment, or were they disappointed? Again, this may introduce bias.
Nevertheless, I think that I am being very critical. It is an outstanding achievement to obtain information over such a long period. I know that the expansionists, magic bracket users, mandible growers, breathing physicians, and myofunctional orthodontists will say that the investigators did this study wrong, and the findings do not apply to their patients. I simply suggest that they research their treatment and not merely quote the “Pyramid of Denial”.
This paper adds to our knowledge and reinforces that orthodontic treatment relapses to a clinically important degree. I cannot help feeling that orthodontic relapse is something that we should accept. Perhaps, we should explain that this is a feature of ageing and we cannot stop time?
Emeritus Professor of Orthodontics, University of Manchester, UK.