A great new trial on hemisection vs extraction to intercept missing mandibular second premolars?
Congenital absence of mandibular second premolars is relatively common. One treatment option when permanent tooth extractions are not needed as part of orthodontic treatment is to extract the deciduous molar and allow for spontaneous closure of the space. This has the advantage of promoting spontaneous space closure without orthodontic appliances.
An alternative treatment involves dividing the second molar and extracting the medial and distal segments at different time points. It has been suggested that this leads to better or more controlled spontaneous space closure.
Nevertheless, this treatment method has yet to be examined through randomised trial methodology, and I found this new trial highly interesting.
A team from Gothenburg, Sweden, did this study. The European Journal of Orthodontics published the paper. It is great to see that this paper is open access.
What did they ask?
They did this study to ask.
“Are there any differences in space closure, angulation of the adjacent teeth, complications or in cost between conventional extraction or hemi-section”?
What did they do?
They conducted a single-centre, single-blind, split-mouth randomised controlled trial. The team registered the trial prior to its commencement.
The PICO was.
Participants.
Orthodontic patients from nine public health clinics in Sweden participated in the study. The participants were aged between 9 and 12 years and had a bilateral absence of the mandibular secondary models with retained second mandibular molars.
Intervention
Hemisection of the second primary mandibular molar.
Control
Extraction of the second primary mandibular molar
Outcomes.
The primary outcome was the amount of space closure. Secondary outcomes were angulation of adjacent teeth, complications, and cost-effectiveness.
They conducted a sample size analysis based on previous investigations, which indicated that 30 patients were required. To compensate for possible dropouts, they increase the sample size to 40 patients
This was a split-mouth study, and they used stratified randomisation to assign the extraction method for each patient. They prepared a randomisation sequence before the trial, and allocation consignment was carried out using sealed envelopes.
They did the extractions prior to the eruption of the permanent second mandibular molars.
In the hemisection group of teeth, they divided the deciduous tooth with a surgical burr, and extracted the distal parts of the tooth. The operator left the remaining portion of the tooth without surgical dressing or endodontic treatment. They then reviewed the patients were scheduled every eight weeks to measure the residual space. When the space was less than 2 mm, they extracted the remaining part of the deciduous tooth.
They collected data at baseline and four years later.
What did they find?
All patients completed the study. When they measured the space between the surface of the first molar and the distal surface of the canine, it was found that for the hemisection group, this distance was 3.84 mm. For the extraction group, the total space was 3.95 mm. The 95% confidence interval for the difference was (-0.572 to -0.36), which was not statistically significant.
When they examined the economic analysis, they found that the total societal cost for the section was €361.38. For conventional extraction, the cost was €102.66. This was statistically significant.
When they examined pain and discomfort, they discovered that pain from the remaining root segment following bisection was reported by 22% of the patients, compared to 5% of patients who experienced symptoms after conventional extraction. This finding was again statistically significant.
They did not find any other differences in any of the other outcome measures.
The overall conclusion was
“There were no clinically significant differences in space closure or changes in angulation between conventional extraction and hemi-section. However, hemi-section was associated with more symptoms and complaints from patients, and it incurred higher direct and indirect costs than conventional extraction”.
What did I think?
This was a very interesting and well-conducted randomised trial carried out by a research team with a strong reputation for high-quality clinical studies. They addressed a common clinical scenario, and the study is highly relevant to our clinical practice. Their conclusions are compelling and provide evidence suggesting that simply extracting the primary second molar results in a positive outcome in terms of spontaneous space closure.
Some of you may have spotted that the team did not make measurements before treatment. This is good statistical practice because if the randomisation was done correctly we can assume that there were no pre-treatment differences between the groups.
Notably, the team did the study in the real-world setting of clinical practice. As a result, the study has generality.
This is an excellent example of how effective study teams can conduct clinically relevant trials with minimal resources, yet still provide us with valuable information. I highly recommend reading this paper.
Emeritus Professor of Orthodontics, University of Manchester, UK.
Allowing that previous studies including Valencia, 2004, Northway, 2004 and Sarver, 2015 advocate hemisection, this current study is very useful.
Hemisection still is very useful. It depends on the parameters one is looking at. The current study is looking at bilateral agenesis. This bilateral variant of agenesis of lower 5s seen in less than 10% of all lower 5 agenesis cases. In more than 90% only one side is affected which changes the anchorage needs significantly. In these unilateral agenesis cases, a hemisection is a simple tool to treat these patients with a space closure approach. Unfortunately, the authors of the study focussed only on the speed of tooth movement and the amount of tipping of the lower 1st molar.
So the conclusion is don’t bother with hemi-section as makes no difference regarding spontaneous space closure and is more uncomfortable for the patients! I wonder if any orthodontists in the UK actually carry out Hemi-sections?
Dear Dr O’Brien
A colleague recently commented on this excellent research and raised a very interesting point. The study follows a split-mouth design in a case of bilateral agenesis. However, in clinical practice, this condition is often unilateral. If we are dealing with unilateral agenesis and we extract the deciduous tooth instead of performing a root hemisection, we might end up causing significant midline deviation. I believe this is an important point to consider for clinical decisions. What do you think?
Hi Sergio, thanks for the comments. We are in the process of publishing a further blog post on this study and we will answer your question then. Best wishes: Kevin
The decision to extract the mesial fragment when there was 2 mm of space between the molar and the mesial fragment was surprising. This is not something I had heard of and I wonder why this approach was chosen. In my cases, I allow the molar to drift all the way to the mesial fragment and even slice more from the mesial fragment to allow continued mesial drift. I don’t have the mesial fragment removed until I am ready to complete space closure in full braces. In fact, in this study, time between extraction of mesial and distal fragment was 10 months +/- 4 months while time between T1 and T2 was 4 years or more. That means that for 3 out of the 4 years of the measured period, both sides were essentially the same, that is extraction of the tooth. Not surprising that the results showed no difference over that time period. I am not sure this study closes the door on the viability of the Hemi section procedure.
John, I thank you for pointing out this important aspect. In my cases I follow the same protocol you described.