title: In vitro study of needle deflection: a linear insertion technique versus a bidirectional rotation insertion technique.
abstract: OBJECTIVE
  Deflection of dental needles during tissue penetration has been associated with a failure to achieve successful anesthesia. The purpose of this study was to determine whether needle deflection in a tissuelike substance could be minimized through the use of a bidirectional rotation insertion technique.
  
  
  METHODS
  Three in vitro deflection test models were constructed, each incorporating a different tissuelike substance of a different density. Each substance was tested with 3 different needle sizes (30-guage, 27-gauge, and 25-gauge). A customized dental surveyor allowed for standardized needle insertions to a standardized depth of 20 mm. Two different insertion techniques, a linear insertion technique and a newly described bidirectional rotation insertion technique, were tested. Radiographic analysis was performed after each insertion.
  
  
  RESULTS
  The bidirectional rotation insertion technique described was consistently more effective in minimizing needle shaft deflection for 30-, 27-, and 25-gauge needles. The differences were statistically significant. Each of the different tissuelike substances consistently demonstrated this reduction in needle deflection.
  
  
  CONCLUSIONS
  The factor that most greatly affects the path taken by a needle through a tissuelike substance is the force vectors that act on the needle's beveled surface. The use of a bidirectional rotation insertion technique minimized needle deflection, resulting in a straighter tracking path for 30-, 27-, and 25-gauge dental needles, in 3 different tissuelike substances tested in this study.
authors.affiliation: Department of Implant Dentistry and Department of Orthodontics, New York University, College of Dentistry, New York, New York, USA. PerioOrtho@aol.com
authors.forename: M N
authors.initials: MN
authors.lastname: Hochman
authors.forename: M J
authors.initials: MJ
authors.lastname: Friedman
mesh_terms: D000766:Anesthesia, Dental / Q000295:instrumentation*; D000772:Anesthesia, Local / Q000295:instrumentation*; D003102:Colloids / Q000737:chemistry; D003238:Connective Tissue / Q000033:anatomy & histology; D004867:Equipment Design; D005152:Facial Muscles / Q000033:anatomy & histology; D005205:Fascia / Q000033:anatomy & histology; D006801:Humans; D007267:Injections / Q000295:instrumentation / Q000379:methods; D008953:Models, Anatomic; D009061:Mouth Mucosa / Q000033:anatomy & histology; D009339:Needles; D009407:Nerve Block / Q000295:instrumentation; D018583:Pliability; D012399:Rotation; D013314:Stress, Mechanical; D013499:Surface Properties; D014885:Waxes / Q000737:chemistry
chemical_list: D003102:Colloids; D014885:Waxes