Objective: Deflection of dental needles during tissue penetration has been associated with a failure to achieve successfui 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. Method and materials: 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-gauge, 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. Conclusion: 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. Palabras clave: computer-controlled drug delivery system, deflection, force penetration, insertion technique, local anesthesia, needle