dentistry journal Article Effect of Hand and Rotary Instruments on the Fracture Resistance of Teeth: An In Vitro Study Nisha Acharya 1,2 , Md Riasat Hasan 2, * , Dashrath Kafle 3 , Anil Chakradhar 1 and Takashi Saito 2 1 Department of Conservative Dentistry and Endodontics, Kathmandu University School of Medical Sciences, Dhulikhel Hospital, Dhulikhel 45200, Nepal; menishaacharya@gmail.com (N.A.); anil254413@gmail.com (A.C.) 2 Division of Clinical Cariology and Endodontology, Department of Oral Rehabilitation, School of Dentistry, Health Sciences University of Hokkaido, Hokkaido 061-0293, Japan; t-saito@hoku-iryo-u.ac.jp 3 Department of Orthodontics, Kathmandu University School of Medical Sciences, Dhulikhel Hospital, Dhulikhel 45200, Nepal; dashrath07@yahoo.com * Correspondence: riasat@hoku-iryo-u.ac.jp; Tel.: +81-133-23-1129; Fax: +81-133-23-1296 Received: 12 February 2020; Accepted: 27 April 2020; Published: 29 April 2020   Abstract: Objective: Endodontic treatment should be both conservative and effective. Endodontic instruments with a greater taper are used for coronal flaring, for proper debridement with efficient irrigation. However, increased taper of an instrument can remove a larger amount of pericervical dentin, compromising the strength of the tooth. The aim of this study was to determine the effect of hand files, ProTaper Universal, ProTaper Next, and V Taper rotary instrument systems on the fracture resistance of teeth. Materials and Methods: In total, 60 extracted human maxillary first premolars were divided into four groups—Group I (Hand Files; HF), Group II (ProTaper Universal; PT), group III (ProTaper Next; PTN) and Group IV (V Taper; VT) (N = 15). Each group was instrumented with the respective instrument system, irrigated, obturated, restored, and mounted in cold cure acrylic. A universal load-testing machine (Shimadzu, Japan) was used to apply a vertical compressive load. The maximum force was recorded in Newton. Analysis of variance (ANOVA) and Independent t-tests were applied to compare the maximum mean force required to fracture the tooth. Results: There was a statistically significant difference in fracture resistance between Group I (HF) and Group II (PT) and between Group II (PT) and Group IV (VT) (p < 0.001). Similarly, a significant difference was observed between Group II (PT) and Group III (PTN) (p < 0.01). Furthermore, a significant difference was observed between Group I (HF) and Group III (PTN), and between Group III (PTN) and Group IV (VT) (p < 0.05), too. However, there was no statistically significant difference between Group I (HF) and group IV (VT) (p > 0.05). Conclusion: Rotary files with more taper seem to remove more pericervical dentin than traditional manual and rotary files with less taper, thus altering the strength of the tooth. Keywords: endodontic treatment; fracture resistance; pericervical dentin; rotary instruments 1. Introduction Endodontically treated teeth are considered to have a lower survival rate compared to vital teeth. One of the various causes of failure of root-filled teeth is root/tooth fracture. According to Vire, nearly half of the failures of root-treated teeth are due to crown fracture (59.4%), which he describes as a prosthetic failure [1]. It has also been noted that endodontically treated teeth are extracted more frequently for non-endodontic rather than endodontic causes [2–4]. Moreover, the strength, integrity and manner of force distribution in the remaining tooth structure during mastication also has an influence on the long-term survival of the tooth [5]. Dent. J. 2020, 8, 38; doi:10.3390/dj8020038 www.mdpi.com/journal/dentistry