Radiographic prognostic factors determining spontaneous space closure after loss of the permanent first molar

Permanent first molars (PFM) with a poor prognosis are routinely extracted in children throughout the United Kingdom. National guidelines suggest that to achieve spontaneous closure for the mandibular arch, the PFM should be extracted at 8 to 10 years of age, during bifurcation formation of the second molar. The literature is of limited quality and has suggested alternative variables that may be associated with successful space closure. Our aim was to investigate the radiographic prognostic factors associated with space closure after extraction of PFM. Two objectives of the research are reported in this article: to determine factors that might predict space closure of the second molar after extraction of the PFM, and to develop a tool kit to aid clinical decision making.

We assessed 148 maxillary and 153 mandibular PFM extracted from 81 participants retrospectively. Dental age, second molar developmental stage, second premolar and second molar angulations, and presence or absence of the third molar were assessed on the preextraction orthopantomograms. Outcome was assessed via visual examination, study models, or radiographs.

Closure occurred in 89.9% of the maxillary and 49.0% of the mandibular quadrants. Dental age was statistically, but not clinically, significant in the maxillary arch (P <0.05). For the mandibular arch, presence or absence of the third molar and second molar angulation were statistically and clinically significant (P <0.01 and P <0.05, respectively). A tool kit was developed in relation to the mandibular arch variables.

These findings are contradictory to the Royal College of Surgeons guidelines and suggest that the presence of the third molar and a mesially angulated second molar are favorable for space closure. The developed tool kit requires further validity testing.