[Differential diagnosis within primary molar retention: Characteristics of primary eruption failure versus primary retention of a single tooth].

INTRODUCTION: While impaired eruption of permanent molars is a rare phenomenon, its prevalence appears to be increasing. Among these disorders, a distinction can be made between impactions, in which a tooth is blocked along its eruption path by a physical obstacle, and primary retention, in which eruption ceases in the absence of such a barrier. Within primary retention, primary failure of eruption (PFE) is a genetically determined condition that can severely affect one or more teeth and impact adjacent teeth. The clinical management of PFE is complex and multidisciplinary, and orthodontic traction is not recommended, as it often results in progressive ankylosis. Early identification of PFE is therefore essential to guide the therapeutic strategy.

MATERIALS AND METHOD: Clinical and genetic analyses were conducted in a cohort of patients presenting with primary molar retention. The objective was to propose clinical and radiological criteria to differentiate PFE from primary retention of a single tooth (PRST), in order to guide clinicians in treatment planning prior to genetic confirmation.

RESULTS: Thirty-four patients treated at the Orthodontics Department of La Pitié-Salpêtrière Hospital (Paris, France) were included. PFE cases were characterized by involvement of several teeth, posterior predominance with possible anterior involvement, posterior infraclusion, reduced alveolar bone height in the affected area, eruption arrest that typically occurred at the supra-crestal level, a positive family history, and an absent, abnormal, or pathological response to orthodontic treatment. PRST cases were characterized by involvement of a single tooth in a given area, predominantly posterior location, eruption arrest that most often occurred intraosseously, apical root curvature in contact with the cortical bone, absence of family history, no initial ankylosis, and a favorable response to orthodontic traction.

DISCUSSION: In patients with PFE, orthodontic treatment does not correct eruption but may in fact worsen the condition, notably by causing intrusion of adjacent teeth. In contrast, patients with PRST generally achieve gradual and effective eruption correction with orthodontic traction. Establishing precise clinical and radiological diagnostic criteria is therefore essential to avoid inappropriate treatment and to promptly refer patients to appropriate care, including genetic confirmation if necessary.