Factors related to maxillary expander loss due to anchoring deciduous molars exfoliation during treatment in the mixed dentition phase

Summary Objectives The aim was to identify factors associated with maxillary expander loss due to anchoring deciduous molars exfoliation and assess the diagnostic accuracy of the upper second premolar cusp position as a prognostic factor for the exfoliation of its corresponding deciduous molar. Materials/methods Ninety-two subjects aged 8.4 ± 1.1 years, treated with a Haas or hyrax expander, and using the same expansion protocol and deciduous teeth as anchorage were included. The position of the upper second premolar cusp, according to the half pulp chamber (HPC) line of the ipsilateral upper first permanent molar, was assessed on pre-treatment panoramic radiographs. Results A significant association between anchoring deciduous molar exfoliation and the position of the upper second premolar cusp according to the HPC line (P = 0.002; odds ratio = 5.7) was seen, while there was no association with gender, age, treatment duration, and type of expander. The median survival time for an anchoring deciduous molar, when the underlying premolar cusp was touching/crossing the HPC line, was 13.0 (11.7; 14.2) months. The upper second premolar cusp position to the HPC line showed high accuracy (at least 76.11 per cent) and substantial repeatability (at least 0.7) as a prognostic factor for the corresponding second deciduous molar exfoliation. Limitations Applicability in the mixed dentition phase with fully erupted upper first permanent molars. Conclusions The probability of a second deciduous molar to be successfully used as maxillary expander anchorage for at least 16 months is above 94 per cent; when at baseline, the corresponding premolar cusp is apical to the HPC line.