Background <p>Root fractures occurring close to the bone margin have a poor prognosis. Although conservative treatment is preferred, it presents considerable challenges. This report describes the successful use of two types of mineral trioxide aggregate materials for conservative treatment of horizontal cervical root fractures.</p> Case presentation <p>A 25-year-old Japanese woman experienced root fractures of the mandibular central incisor due to trauma. At the initial visit, the crown of the tooth on the labial side was fractured above the gingival margin, and the root on the lingual side was fractured near the bone margin. The fractured tooth structure was bonded with methyl methacrylate-based resin cement, and the gap was filled with a mineral trioxide aggregate material, a resin-modified mineral trioxide aggregate material, and a methyl methacrylate-based adhesive resin cement. The tooth was successfully preserved through the use of multiple fiber post reinforcements, minimal periodontal surgery, bleaching, and composite resin filling.</p> Conclusion <p>The treatment approach applied in this study, using appropriate materials and surgical procedures, successfully preserved the tooth with horizontal root fractures near the alveolar bone, which are considered difficult to treat. This case suggests that appropriate material selection and meticulous treatment procedures can enable successful tooth preservation.</p>