Impacted lower second molars

When she was 12 1/2, I started cosmetic treatment to align her upper front teeth (for those of you not in the dental field, the dental development shown above is severely delayed for someone this age) and create space for the eruption of her permanent teeth. Her lower second molars appear to developing relatively normally. I used partial upper braces (2x4) and a lower lip bumper.

When she was 15, all of her permanent teeth that could erupt on their own had come in, and I began full treatment with braces. (The upper primary second molars did fall out on their own and the second premolars did not need to be exposed). There is some controversy regarding whether lower lip bumpers impact second molars. I can't say for certain whether this was the case, but I would think in her case it is more likely than not that the lip bumper contributed to the impaction of the second molars.

Her lower right third molar was extracted (by convention, when we view patients' images, right and left are reversed so that it appears that you are standing in front of the person looking at them) and lower second molars uprighted. Her upper right second premolar came in rotated 180 degrees, and they declined my offer to correct it due to the increase in treatment time required. Because of her late dental development and the fact that she had braces on at such a late age, she and her mother requested that I remove the braces before I could complete her case fully (thus the non-parallel roots evident on the xray above).

The other options in her case regarding the impacted lower second molars would be:

  1. extracting the lower third molars and having the surgeon surgically upright the second molars. In general, I prefer not to do this because of the questionable long term effect this has on the surgically uprighted teeth.
  2. extract the second molars and hope the third molars erupt into position. In some cases where the third molars are well inclined, they can migrate forward on their own and replace the extracted second molars. In general, I prefer not to rely on this approach for a couple of reasons:
    1. the biting surfaces of third molars are usually less regular in form than second molars. Third molars typically have unusual dental anatomy with very deep grooves that are prone to cavities and their root structure can be highly variable, with multiple roots or even multiple canals per root. Should the third molars ever need a root canal (since they are more susceptible to cavities), their root structure makes this very difficult. If a patient had all of their molars present and needed a root canal on a third molar, it is frequently recommended that the third molar be extracted rather than trying to save it with root canal treatment. If the only viable option was to extract the third molar in a patient for whom the second molar was previously extracted, this would leave the patient with only one molar to chew with. This is not the best scenario for the remaining first molar since this tooth now has to contend with biting forces that are normally distributed over more teeth. These forces that are now relatively excessive could damage the first molar (increased wear, increased risk of gum problems, etc.).
    2. what if the third molar does not completely drift forward, or comes forward but is tipped. Since it takes such a long time for the third molar to come forward, the braces have likely long since been removed. You now have to consider putting the braces back on to correct the positions of the third molars at additional expense, or leave the third molars in a compromised position which may lead to gum problems in this area and eventual loss of these teeth. Especially since in the patient's case above, since the lower third molars were tipped forward, extracting the second molars was not a good option.

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