title: Effect of Instrumentation Length and Instrumentation Systems: Hand Versus Rotary Files on Apical Crack Formation - An In vitro Study.
abstract: BACKGROUND
  Stresses generated during root canal instrumentation have been reported to cause apical cracks. The smaller, less pronounced defects like cracks can later propagate into vertical root fracture, when the tooth is subjected to repeated stresses from endodontic or restorative procedures.
  
  
  OBJECTIVE
  This study evaluated occurrence of apical cracks with stainless steel hand files, rotary NiTi RaCe and K3 files at two different instrumentation lengths.
  
  
  METHODS
  In the present in vitro study, 60 mandibular premolars were mounted in resin blocks with simulated periodontal ligament. Apical 3 mm of the root surfaces were exposed and stained using India ink. Preoperative images of root apices were obtained at 100x using stereomicroscope. The teeth were divided into six groups of 10 each. First two groups were instrumented with stainless steel files, next two groups with rotary NiTi RaCe files and the last two groups with rotary NiTi K3 files. The instrumentation was carried out till the apical foramen (Working Length-WL) and 1 mm short of the apical foramen (WL-1) with each file system. After root canal instrumentation, postoperative images of root apices were obtained. Preoperative and postoperative images were compared and the occurrence of cracks was recorded. Descriptive statistical analysis and Chi-square tests were used to analyze the results.
  
  
  RESULTS
  Apical root cracks were seen in 30%, 35% and 20% of teeth instrumented with K-files, RaCe files and K3 files respectively. There was no statistical significance among three instrumentation systems in the formation of apical cracks (p=0.563). Apical cracks were seen in 40% and 20% of teeth instrumented with K-files; 60% and 10% of teeth with RaCe files and 40% and 0% of teeth with K3 files at WL and WL-1 respectively. For groups instrumented with hand files there was no statistical significance in number of cracks at WL and WL-1 (p=0.628). But for teeth instrumented with RaCe files and K3 files significantly more number of cracks were seen at WL than WL-1 (p=0.057 for RaCe files and p=0.087 for K3 files).
  
  
  CONCLUSIONS
  There was no statistical significance between stainless steel hand files and rotary files in terms of crack formation. Instrumentation length had a significant effect on the formation of cracks when rotary files were used. Using rotary instruments 1 mm short of apical foramen caused lesser crack formation. But, there was no statistically significant difference in number of cracks formed with hand files at two instrumentation levels.
authors.affiliation: Postgraduate Student, Department of Conservative Dentistry and Endodontics, AECS Maaruti College of Dental Sciences , Bengaluru, Karnataka, India .
authors.forename: Madhuri R
authors.initials: MR
authors.lastname: Devale
authors.affiliation: Professor, Department of Conservative Dentistry and Endodontics, AECS Maaruti College of Dental Sciences , Bengaluru, Karnataka, India .
authors.forename: M C
authors.initials: MC
authors.lastname: Mahesh
authors.affiliation: Professor, Department of Conservative Dentistry and Endodontics, AECS Maaruti College of Dental Sciences , Bengaluru, Karnataka, India .
authors.forename: Shreetha
authors.initials: S
authors.lastname: Bhandary
keywords: Apical limit; NiTi files; Root stresses; Stainless steel files; Vertical root fracture