Successful retrieval of a separated instrument in the root canal of a primary molar using ultrasonic oscillation combined with H-File and barbed broach: a case reportLu Lidan1 Zhao Min1 Yao Qingting1 Qian Xukun1 Wu Yanhui21 Department of Stomatology, Xuchang Central Hospital, Xuchang, Henan, China (461000); 2 Songjiang Stomatological Hospital of the Ninth People’s Hospital Affiliated to Shanghai Jiaotong University School of Medicine, Shanghai, China (200000)[Abstract ] Instrumentation separation occurs when metal instruments, such as endodontic files or enlarging pins, fracture and remain in the root canal during treatment, often due to fatigue, mismanagement, or anatomical challenges. This risk is present in both primary and permanent teeth, with more frequent reports in permanent teeth. However, clinical cases involving primary teeth are less common, and successful removal of separated instruments has been documented. We present a case where an instrument was effectively extracted from the distal middle root canal of a lower right second molar using a combination of ultrasonic shock, H-file, and cotton twisting with an extraction needle.【Keywords】 Endodontics; Instrument Separation; Breast Molar; Ultrasonic Shock; H-File; Pulp Extraction Needle[Corresponding author] : Yanhui Wu, Attending Physician, Graduate Student, Email:wwwwuyanhui@126.com ，Tel:021-576119003002Root canal treatment in both primary and permanent teeth carries the risk of instrument fracture[1]. In primary teeth, a broken instrument can impede root resorption or lead to periapical lesions, potentially affecting the successor permanent teeth. Consequently, the standard approach often involves extracting the affected tooth and fitting a gap retainer[2]. However, primary teeth play a crucial role in occlusal function and the transition to permanent dentition. If technological methods can successfully remove the fractured instrument, preserving the affected tooth would be beneficial for maintaining both occlusal function and the natural development of the dentition[3].Instrument separation in permanent teeth often necessitates significant dentin removal, while in deciduous teeth, this process is constrained by the dentin’s inherent thinness and the preference for noninvasive or minimally invasive techniques. The ultrasonic technique, which employs ultrasonic vibrations, is a minimally invasive method for removing separated instruments[4]. Additionally, the friction created by an H-file wrapped in cotton twists, combined with an endodontic needle, enhances the likelihood of successful instrument retrieval. This paper presents a case involving the extraction of a broken needle from the root canal of a 6-year-old patient’s right mandibular second molar. By employing ultrasonic vibrations to loosen the instrument, a disinfected cotton twist was wrapped around the H-file and pulpotomizing needle to create an adhesive interface, facilitating the instrument’s removal. This case confirms the clinical efficacy of combining ultrasonic vibrations with the H-file and pulpotomizing needle wrapped in a cotton twist.