Does early extraction of first permanent molars disrupt eruption patterns?

I spent most of my career working in inner-city Manchester. Unfortunately, the dental health of the children living in the city was poor. As a result, paediatric dentistry colleagues often asked for my input on the decision to do early extraction of carious first molars. Most of the time, we followed traditional criteria for extracting these teeth when the children were about 8-10 years old, depending on their dental development. We believed this would allow reasonable spontaneous closure of any extraction space.

These practices were mostly based on clinical experience. However, we were not truly sure if our treatment was effective because it was very difficult to follow up with these children. This new trial investigates a similar issue of early molar loss with Molar-Incisor Hypomineralisation. 

We are all familiar with this condition, as early extraction of first molars with MIH is often the preferred choice. This new trial investigates the eruption patterns of teeth following early loss of first molars with MIH.

A team from Sweden did this trial. The EJO published their paper.

This is an open access paper.

What did they ask?

They did this study to:

“Evaluate panoramic radiographs to follow the eruption pattern of the second permanent molar and premolar, as well as the overeruption of the opposing first permanent molar, following the early extraction of the first permanent molar due to severe Molar Incisor Hypomineralisation at 11 years of age”.

What did they do?

The team evaluated a subset of participants involved in a large multicentre study called the “Gothenburg University Restoration or Extraction of first permanent molars due to severe MIH”. They selected a group of trial participants who had undergone unilateral extraction of first permanent molars because of MIH.

I would like to clarify the nature of this study. It is important to realise that this is not a standalone RCT. The best way to describe it is that it is a retrospective analysis of a cohort taken from a larger RCT.

The PICO was

Participants.

Children aged 6-9 years who had undergone unilateral extraction of first permanent molars (FPM) due to severe MIH.

Intervention

Extraction of first permanent molar

Comparison

No extraction of first permanent molar on the contra lateral side.

Outcomes

The tooth angulation and eruption length of the second permanent premolar and second permanent molar was derived from panoramic radiographs.

They collected data both before extracting the FPM and at a follow-up when the participants were 11 years old.

They analysed the data with univariate statistics and Pearson Correlation to find out if there was a relationship between the FPM root development and eruption positions.

The team did a sample size calculation based on the ability to detect a difference of 1.6mm in eruption length of the second permanent molars. This revealed that they needed to analyse 20 participants with unilateral extraction FPM for each jaw.

What did they find?

They analysed data from 47 patients. 20 were male and 27 female. 31 had unilateral extractions in the maxilla and 25 in the mandible.  The mean follow up was 3.2 years (SD=1.0). At the follow up 3 of the maxilla and 1 of the mandible group had fully erupted second permanent molars.

At T0, eruption length and angulation of SPMs and SPs were similar between sides.

When they looked at the data concerning the position of the teeth at follow up. They found that at “T1, maxillary SPMs erupted faster (13.5mm vs. 10.8mm, p < 0.001) and more upright (72.9° vs. 62.1°, p < 0.001) on the extraction side, while SPs showed increased mesial angulation (82.5° vs. 89.3°, p < 0.05). 

“Mandibular SPMs and SPs showed no differences. They did not observe overeruption of opposing FPMs”.

Furthermore, the stage of root development did not appear to be associated with tooth eruption.

Their overall conclusion was

“Early extraction of the first permanent molar (FPM) due to severe MIH at age 11 had different effects on eruption patterns in the upper and lower jaws. In the maxilla, the second permanent molar (SPM) and second premolar (SP) erupted perpendicularly, with the SPM erupting faster. However, in the mandible, their eruption patterns were not affected. No overeruption of the opposing FPM was observed”.

What did I think?

This was an interesting and clinically relevant study. Since the sample of patients was drawn from a larger RCT, we can assume that there was some minimisation of bias. However, the authors did not specify whether they had evaluated all the eligible participants who entered the study. Consequently, we must consider that potential bias could have been present. Nonetheless, this might be minimal.

We also need to recognise that this study does not address the more clinically relevant question of how much spontaneous space closure can be expected after the early loss of the first permanent molar. The results simply indicate that the teeth adjacent to the extraction site are in a “good position” for space closure. 

However, they do suggest that there is a minimal risk of overeruption of the opposing first permanent molar, which can prevent spontaneous lower molar space closure.  This is a useful clinical finding.

I contacted the authors to ask if they are continuing to follow up on the patients to observe the amount of spontaneous space closure. They do plan to present data on this important clinical finding in due course. However, this will involve a long-term follow-up. I hope they are successful with this aim. If so, it will be a valuable addition to the literature.