Orthodontic space closure in a patient with congenitally missing mandibular second premolars and compromised first molars: a case report and focused literature review

An 18-year-old female with skeletal Class I malocclusion, hyperdivergent growth pattern, bimaxillary crowding, compromised permanent first molars, and bilateral congenital absence of mandibular second premolars was treated with fixed mechanotherapy following strategic extraction of the compromised first molars. Maxillary molar mesialization was performed using NiTi closed-coil springs, while mandibular mesialization employed reverse helical loops with tip-back bends. Complete extraction space closure and sequential posterior tooth substitution were achieved without skeletal anchorage, resulting in a functional therapeutic Class III molar and Class I canine relationship, improved alignment, dental midlines, incisor inclination, and soft tissue profile. No significant root resorption or periodontal compromise was observed. The case demonstrates that controlled molar mesialization and sequential posterior substitution can provide a conservative alternative to prosthetic rehabilitation in selected patients with congenitally missing mandibular second premolars and compromised first molars.