February 01, 2021

A really useful paper on retained primary teeth.

When we see a patient with a retained primary tooth, we do not know how long this tooth will last in the mouth.  This paper provides us with excellent, clinically relevant information.

One clinical problem with retained primary teeth is to estimate the time that they will remain viable.  This decision is important because if a primary tooth’s prognosis is poor, then we may intervene early. Alternatively, if we are confident that the long-term prognosis is good, we may develop a treatment plan involving long-term retention of the tooth.  This decision, of course, also depends upon the characteristics of any malocclusion.

As a result, information on the long term prognosis of retained primary teeth benefits treatment planning and patient information.

The European Journal of Orthodontics published the paper.  A team from Oslo, Norway, did the study.

The long-term fate of persisting deciduous molars and canines in 42 patients with severe hypodontia: a 12-year follow-up

Christina L. Hvaring and Kari Birkeland

EJO: doi:10.1093/ejo/cjz090

What did they ask?

They did the study to ask this question.

“What was the ten-year prognosis of retained primary teeth”? and

“Were there any predictive factors for prognosis”?

What did they do?

They did a longitudinal observational cohort study.  The authors initially took 212 patients with non-syndromic hypodontia who attended their clinic between 1998 and 2010.  Then they approached 70 of these patients and asked them to take part in the study. Of these, 50 could take part.  The patients’ average age at the first appointment was 13.9 years, and at the follow-up, it was 25.6 years.  Forty-four of the participants had at least one persisting primary molar at follow up.

They reviewed the radiographs and assessed the retained tooth’s condition at the initial and the follow-up visit. They did this by evaluating the retained primary teeth for infraocclusion, root resorption and whether someone had restored them.

This information enabled them to classify the condition of the retained tooth as poor or good.

What did they find?

They provided a large amount of information, and I do not have space to go into it.  Hopefully, I have managed to highlight the significant findings of this paper.

At the first presentation, the mean number of retained primary teeth was 6.3. However, at the follow-up, this had reduced to 2.6.  The tooth types that had the greatest tendency to remain were the primary canines and second molars.

When they looked at the condition of the teeth at baseline, there were 183. At the follow-up, 101 were still present.

When they looked at the baseline condition of these teeth, they classified 112 as good, and 86 (77%) were still present at follow up.  Most of the teeth that they classified as poor at baseline had been replaced.

It appeared that infraocclusion was related to tooth loss.

Their overall conclusions were:

  • Retained primary canines and molars have the best long-term prognosis. Preserving these teeth if they are good condition is a good treatment choice.
  • Early infraocclusion is likely to lead to tooth loss.
  • Teeth with short roots may be more stable over time.
What did I think?

I thought that this was an interesting and highly detailed paper.  The study was ambitious, and the authors came to clinically relevant conclusions.  While these conclusions were beneficial, I was hoping to identify some strong predictors of long term survival. However, I was overoptimistic as it became clear to me that there was a marked variation in the initial presentation of the retained teeth. As a result, there needed to be a larger sample for accurate prediction.

I do not want anyone to think that this is a criticism of the study. I believe that it was an outstanding achievement to follow so many patients over this long period.  Nevertheless, we also have to look closely at the response rate to the study. Significantly, their initial sample of 212 patients was reduced to 50. This drop out rate was 75%. This was not surprising. However, we need to consider whether this resulted in bias.  There is no doubt that it does. Nevertheless,  we do not know the direction of this bias.

Final thoughts.

This paper gives us the best information on the long-term prognosis of retained primary teeth.  The overall conclusions are useful and allow us to provide information to our hypodontia patients as we plan for their long-term management.

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Have your say!

  1. Why teeth with short roots may be more stable over time.
    I question whether teeth with a longer root would last longer

  2. Good information! I too was surprised about the short roots, it will influence my tx recommendations in the future.

    Just a note, I really appreciate when you find good articles from reputable journals that are not AJO/DO or Angle. If I don’t see them here, they don’t cross my radar screen. To that effect, have you considered posting articles that you found were of good design/had relevant findings but did were not quite as relevant as the article you choose to “spotlight” on the blog. Kind of an “Other articles worth taking a look at” kind of list. Maybe you all ready cover everything that is worth while but I am guessing there are others you would want to share. Members of the AAO can easily get copies of articles from other journals thru the library, we just have to know to ask.

    Something to consider, unless there is just not that much more good stuff out there.

  3. The idea that infraocclusion, perhaps secondary to premature maturation of periodontal stem cells associated with a PTH1R mutation, is associated with deciduous tooth loss dovetails with the spatial matrix hypothesis (unlike the functional matrix hypothesis and equilibrium hypothesis)

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