Case report and review of mechanical failure of eruption of the maxillary second primary molar with ectopic  eruption of the first permanent molar 

Abstract Objective: This case report presents a rare case of mechanical failure of eruption (MFE) of the maxillary second primary molar, combined with ectopic eruption of the first permanent molar. The aim is to explore early orthodontic intervention strategies and non-invasive techniques to correct eruption issues, prevent secondary impaction, and improve long-term outcomes. Case Summary: A 6-year and 11-month-old male patient presented in June 2023 with the complaint of "failure of eruption of the upper left molar." Six months prior, the patient had undergone "windowing for assisted eruption" of the left maxillary second primary molar (65), but the result was unsatisfactory. The patient had no family history of similar dental conditions, and clinical examination revealed ectopic eruption of both the second primary molar and the first permanent molar, as well as signs of impaction in tooth 25. Symptoms and Clinical Findings The patient was in the mixed dentition stage. The upper left second primary molar (65) exhibited distal impaction with incomplete eruption, while the first permanent molar (26) showed mesial ectopic eruption. Radiographic examinations revealed that tooth 65 was impacted against the cervical region of 26, and tooth 25 displayed palatal impaction, indicating mechanical obstruction. CBCT confirmed the abnormal positioning and impaction of these teeth. Diagnosis Based on clinical and radiographic findings, the diagnosis was: 1. Mechanical failure of eruption of the upper left second primary molar (65) 2. Mesial ectopic eruption of the first permanent molar (26) 3. Crowded dental arch 4. Misalignment Treatment Plan The following treatment plan was developed based on the diagnosis of mechanical failure of eruption: 1. A spiral expander was used to distalize 26, resolving its mesial impaction and creating space for 65 to erupt. 2. A parallel expander was employed to alleviate crowding and ensure proper tooth alignment. 3. A custom removable appliance was designed to guide the eruption of 65, preventing further impaction. Clinical Outcome After six months of orthodontic treatment, 65 successfully erupted, and the palatal impaction of 25 was improved, while the mesial ectopic eruption of 26 was resolved. Radiographic examination confirmed significant relief of dental crowding, with noticeable improvement in occlusal function and arch stability. This case demonstrates that non-invasive treatment methods can effectively address complex eruption issues, avoiding extractions and other surgical interventions. Conclusion: Early non-extraction intervention strategies can effectively manage complex eruption disorders, reduce trauma, and improve patient outcomes.