The incidence of complex crown-root fractures is high, and the prognosis is poor. It mainly refers to the simultaneous fracture of the tooth crown and root caused by external forces, involving dental pulp and periodontal tissues, with an incidence rate of approximately 5%, predominantly occurring in individuals aged 11 to 18 years old [2]. Complex crown-root fractures account for 97.3% of all crown-root fractures [8]. Due to the involvement of dental pulp, tooth structure, and periodontal tissues, treatment methods for complex crown-root fractures are controversial, and the prognosis is often poor. A variety of dental trauma types including complicated crown fracturewith pulp exposure, uncomplicated crown-root fracture, complicated crown-root fracturewith pulp exposure and root fracture may involve endodontic injury. Most previous studies have proposed differentiated treatment options according to the type of trauma as well as different developmental stages. The latest guidelines point out that vital pulp should be preserved and tooth should be preserved as much as possible after trauma in both young permanent teeth and mature permanent teeth [4,5,6,7].

According to the IADT guidelines, treatment options for complex crown-root fractures of varying severity include root canal therapy, crown restoration, orthodontic or surgical traction, intentional replantation, and extraction, all aiming to elevate the subgingival fracture line to a supragingival position. This repositioning helps restore and reconstruct the biological width, which is essential for maintaining periodontal health [4,5,6,7]. However, when the fracture line extends below the alveolar ridge, achieving an above-gingival plane restoration with an appropriate crown-root ratio becomes impractical, presenting significant treatment challenges. Given the variability in patient conditions, individualized treatment plans are necessary but can carry periodontal health risks. In the short term, restorative techniques such as resin bonding, full crown placement, or autogenous fragment reattachment can preserve affected teeth and partially restore aesthetics and function. However, these approaches often lead to periodontal issues, including gingival inflammation, periodontal pocket formation, alveolar bone loss, and gingival recession [9]. Furthermore, for children in developmental stages, additional factors—such as their physical and psychological development, time, and financial costs—add complexity to the treatment of complex crown-root fractures in anterior teeth, making outcomes less predictable [10, 11]. In this case, a multidisciplinary approach, with the involvement of periodontists, led to a more favorable outcome.

In response to the periodontal health issues encountered during the treatment of pediatric complex crown-root fractures, the authors conducted a literature review and analysis. Firstly, considering factors such as the crown-root ratio, the insufficient movement distance of orthodontic traction therapy for tooth 11 in the child affected the subsequent restoration process [12]. Orthodontic restorative therapy involves removing the coronal fragment and then using orthodontic methods to pull the subgingival fracture surface toward the crown before restoration, aiming to place the fracture surface as much as possible above the gingiva while preserving physiological periodontal membrane attachment. Generally, after traction, gingival and alveolar bone morphology adjustment is often necessary [3, 13]. However, in this case, due to the deep fracture position of the affected tooth and considering the crown-root ratio and long-term prognosis, the movement distance of the crown was insufficient. Also, due to the uncontrollable aesthetics and future prognosis of anterior teeth, crown lengthening surgery is not suitable for pediatric patients in the developmental stage. Consequently, difficulties arose in polishing the subgingival repair body surfaces, adversely affecting periodontal health. Periodontal tissues attachment cannot form with adhesive materials alone [14], but in combination with the epithelium, they can form attachment in the form of hemidesmosome, playing a certain role in periodontal sealing. The smoothness of the adhesive material surface and oral hygiene also affect this [15]. Adhesive materials (usually glass ionomer cement or composite resin used clinically) have poor biocompatibility, and prolonged contact of the subgingival portion with periodontal tissues affects healing [16, 17]. Specifically, complex crown-root fractures, due to their deep fracture position and surrounding tissue occlusion, are prone to incomplete resin curing, resulting in excessive residual monomers and cytotoxicity [17,18,19,20]. Additionally, subgingival resin materials are difficult to achieve high levels of polishing, accelerating plaque accumulation, stimulating periodontal tissues, disrupting the balance of the periodontal microbiota, and affecting periodontal tissue health [15]. During the retreatment, flap surgery was performed under local anesthesia to expose the fracture surface of tooth 11, followed by subgingival repair body polishing and suturing of the gingiva. The 8-year follow-up results post-surgery showed good periodontal health in the patient, indicating the stability of the retreatment measures. Furthermore, the patient underwent permanent restoration treatment at the age of 18, and the current status is stable. We reviewed radiographic images and clinical assessments of the affected areas, which revealed no observable signs of root resorption or ankylosis at this stage. However, given the susceptibility of these conditions to late manifestations, especially in cases of extended orthodontic treatment, we have noted the importance of monitoring the patient closely through periodic radiographic evaluation. In terms of future treatment, we recommend regular follow-up visits every 6–12 months to monitor any signs of root resorption or ankylosis.

The treatment of complex crown-root fractures often presents significant risks to periodontal health. This case illustrates that with appropriate periodontal management, subgingival resin repairs, following thorough polishing, can maintain healthy gingival conditions, providing an effective transitional restoration before permanent treatment for pediatric and adolescent patients. This case highlights the periodontal challenges encountered when managing pediatric complex crown-root fractures across disciplines, including pediatric dentistry, orthodontics, and restorative dentistry, and demonstrates effective strategies for addressing these issues. It underscores the essential role of periodontists throughout the entire treatment planning process, advocating for an integrated approach that comprehensively includes pediatric dentistry, orthodontics, restorative dentistry, and periodontics. Such a holistic approach aims to minimize periodontal complications, reduce both treatment time and costs, and support the overall physical and mental well-being of pediatric patients.