Palatogingival groove (also known as the radicular-lingual groove or disto-lingual groove) is a developmental anomaly of the oral and maxillofacial region, with a reported prevalence ranging from 1.01% to 18% across different populations (1). This anomaly arises from the infolding of the inner enamel epithelium and Hertwig's epithelial root sheath during tooth development, leading to the formation of irregular depressions or grooves on the tooth surface (2). These grooves provide an ideal niche for bacterial accumulation, predisposing the tooth to caries and combined periodontal-endodontic lesions (3).

The palatogingival groove is categorized into three types based on its length, depth, and the complexity of the root canal system: Type I, a short groove confined to the coronal third of the root with normal root canal morphology; Type II, a long but shallow groove extending beyond the coronal third of the root, associated with a normal or relatively simple root canal configuration; and Type III, a long and deep groove penetrating beyond the coronal third of the root, characterized by a complex root canal system (4).

Managing palatogingival groove lesions requires a precise and personalized treatment approach based on the lesion's severity (5). Non-surgical interventions such as mechanical cleaning, medicated irrigation, and resin fillings may suffice for mild cases (6). For severe infections or cases with significant clinical symptoms like combined periodontal-endodontic lesions or periapical inflammation, multidisciplinary treatment is advocated. In cases where the lesion infects the pulp, root canal treatment is necessary. For teeth with significant periapical and periodontal destruction, apical and periodontal surgeries can promote healing of the periapical and periodontal tissues (7). Anderegg et al. reported 10 cases of palatogingival groove with significant periodontal destruction treated with guided tissue regeneration (GTR) using bio-bone materials and membranes, showing superior long-term outcomes (8). Tan et al. suggested intentional replantation for complex Type II or higher palatogingival groove cases, where the invaginated groove is reshaped and sealed with bio-materials ex vivo, isolating the groove from the pulp and periodontal tissues, achieving good coronal sealing, effectively controlling infection, and preserving the affected tooth (9). In summary, the treatment of palatogingival groove requires a comprehensive consideration of the lesion's severity, patient's age, and physical condition to develop a personalized treatment plan (10).

The treatment of Type III palatogingival groove is particularly challenging, requiring precise surgery to fill deep grooves and restore normal tooth morphology while considering post-treatment stability and aesthetics. This case report details the use of root canal treatment combined with intentional replantation to treat a maxillary lateral incisor with Type III palatogingival groove, with a 3-year follow-up to verify the efficacy and mid-term stability of this method, providing reference for similar cases.

Palatogingival groove, a complex dental anomaly, presents significant challenges in dentistry. It may result from genetic factors, developmental abnormalities, or early trauma (11). Type III palatogingival groove is particularly challenging, leading to periodontal tissue loss, deep periodontal pockets, and an ideal environment for bacterial growth, which can result in pulp necrosis, periapical infection, and periodontal disease (12, 13). Early diagnosis is essential, with CBCT playing a critical role in identifying the groove and its relationship with surrounding tissues, enabling precise treatment planning (14, 15). When combined with microscopy and ultrasonic technology, CBCT acts as a digital navigation tool, minimizing surgical risks and improving treatment outcomes (16). Although case reports on palatogingival groove have increased in recent years, medium- to long-term follow-up studies are lacking. This study provides mid-term follow-up on a Type III palatogingival groove case, providing insights into its pathogenesis, treatment challenges, and management strategies.

This case describes a type III maxillary lateral incisor with a palatogingival groove, presenting combined periodontal and endodontic lesions. Preoperative CBCT revealed narrow bone width, an unfavorable location of the labial sinus tract, severe palatal bone resorption, and uncertain long-term implant stability. Given the patient's desire to retain the tooth, root canal treatment combined with intentional replantation was performed. The dual infection source in the root canal and invaginated groove had rendered single-method treatments ineffective, often leading to extraction within 5–6 months (17). Some scholars have attempted to preserve such teeth using microsurgical apicoectomy combined with guided tissue regeneration (GTR), but in cases like this, where the root surface groove extends to the apex and severe bone defects are present, the increased surgical difficulty and trauma from extensive bone removal pose significant risks (3). Intentional replantation has shown favorable clinical outcomes, standing out compared to periodontal flap surgery, GTR, or apical surgery (9). It allows thorough debridement and repair under direct vision, effectively eliminating the infection source and promoting tooth healing. The technique minimizes contamination risks by controlling the extraoral operation time within 15 min and maintaining root moisture with Hank's balanced salt solution, significantly reducing root resorption. Long-term success rates (>93%) and healing outcomes (72%–91%) are comparable to non-surgical retreatment and apicoectomy (18, 19).

Effective control of periodontal and periapical infection is critical for successful tooth replantation. In this case, preoperative use of chlorhexidine mouthwash reduced the bacterial load, while thorough root canal disinfection eliminated potential infection sources. The choice of root canal filling material is crucial for restoring tooth structure and controlling infection. iRoot BP Plus was selected to seal the root surface groove due to its excellent marginal sealing, stability, and biocompatibility. Upon contact with body fluids, it forms a hydroxyapatite-like layer, creating a favorable environment for osteoblast and periodontal ligament growth (20). Flowable resin was applied to seal defects above the enamel-dentin junction, ensuring effective sealing and minimizing plaque accumulation (21). The C-shaped root canal was thoroughly cleaned using microscopy and ultrasonic irrigation to preserve tooth structure and remove intracanal infections (22). Although a secondary canal near the malformed groove may have been overlooked, the external sealing remained intact. Regular follow-up is necessary, and if the external sealing is compromised in the future, intervention through root canal retreatment or flap surgery may be required.

Periodontal tissue recovery is a key indicator of treatment success, as it relates to the tooth's function and stability. In this case, the patient experienced mild pain on the second day post-surgery, with no subsequent discomfort during follow-up, indicating a favorable initial response. Over 3 years, periodontal probing depth and tooth mobility remained stable, with no signs of ankylosis or pathological root resorption, demonstrating good periodontal health. At the 1-year follow-up, minor gingival papilla recession (∼1 mm) and mild black triangle formation were observed (Figure 3D), likely due to alveolar bone remodeling after replantation (23). These issues remained stable at the 2- and 3-year follow-ups, and the patient reported no aesthetic concerns. For further improvement, membrane graft surgery or veneer restoration could be considered if necessary. Discoloration of the affected tooth, caused by pulp necrosis and blood decomposition, was another concern (24). The patient expressed a desire to improve the aesthetics of the affected tooth at the initial visit. Internal bleaching with 35% hydrogen peroxide successfully improved tooth color and restored smile aesthetics, aligning with studies showing comparable outcomes between 35% hydrogen peroxide and carbamide peroxide after 14 days (25). However, the risk of discoloration recurrence due to marginal leakage or permeability remains, necessitating regular follow-up to maintain optimal outcomes (26).

This case report presents a complex case of palatogingival groove. Through mid-term follow-up, we have gained a deeper understanding of the pathogenesis, treatment challenges, and effective methods for managing Type III palatogingival groove. The extended follow-up confirmed the stability and reliability of this treatment approach. We believe that in future practice, we will be able to offer more comprehensive, precise, and personalized treatment plans for patients with palatogingival groove, helping them overcome the condition and restore a healthy oral state.