Objective To explore the effect of SonicFill sonic resin restoration on restoration effect and periodontal health in patients with extensive tooth defect after root canal therapy. Methods A total of 479 patients with extensive tooth defect after root canal therapy treated in Wuxi Stomatological Hospital from January 2024 to December 2025 were selected, and they were divided into group A (n =149), group B (n =195) and group C (n =135) according to different treatment methods. Group A was restored with Grandio nanocomposite resin, group B was restored with 3M Z350XT nanocomposite resin, and group C was restored with SonicFill sonic resin. The restoration effect, periodontal health indicators and complication rate were compared among the three groups. Results The excellent and good rates of integrity, marginal adaptation and marginal discoloration in group C were higher than those in group A and group B (P <0.05). At 6 months after restoration, the scores of gingival index and plaque index in group C were lower than those in group A and group B (P <0.05). The incidence of complications in group C was lower than that in group A and group B (P <0.05). Conclusion SonicFill sonic resin restoration for patients with extensive tooth defect after root canal therapy can improve restoration effect, optimize periodontal health, and reduce the incidence of complications.