Objectives: The root morphology of the maxillary first premolar differs from the other premolars by presenting a high incidence of separated roots. This study addressed the spatial conditions during root development as a possible influencing factor. Therefore, maxillary computed tomographic (CT) scans of patients with regularly erupted or impacted permanent canines were evaluated on the root morphology of the premolars.
Methods: The following parameters were retrospectively analysed in 250 maxillary CT scans (100 patients with regular erupted permanent canines, 150 patients with at least one impacted permanent canine): sex, status of the canines (erupted/impacted), position of the impacted canines (buccal/palatal; vertically inclined inside/outside the dental arch/horizontally inclined) and root morphology of the premolars.
Results: Of the patients, 68% with at least one impacted canine were female; the canine was impacted palatally in 75.6% and in a horizontally inclined position in 58.4%. In patients with an impacted canine, the number of first and second premolars with separated roots was significantly reduced on the ipsilateral as well as on the contralateral side (all p values < 0.01).
Conclusions: The present study detected an influence of maxillary canine impaction on the root morphology of all premolars, in that impaction and the associated surplus of space resulted in decreased root separation. This supports the hypothesis that root development is at least partly influenced by increased spatial conditions of the dental arch. However, root development can be regarded as a multifactorial event, influenced by space, direct mechanical interferences, as well as genetic predetermination. The retrospective nature of this observational study did not allow for conclusive differentiation between these factors. Alternatively, root separation and the mesial concavity of the first premolar may represent a path for canine eruption similar to the lateral incisor.
Clinical relevance: A single-rooted maxillary first premolar might represent an additional risk factor for canine impaction.