An in vitro study of needle force penetration comparing a standard linear insertion to the new bidirectional rotation insertion technique

Objective: The purpose of this study was to determine the effect of a bidirectional rotation insertion technique on the force necessary to puncture and advance a needle through a tissuelike substance. Method and materials: Two in vitro penetration test models were constructed using different tissuelike substances of different densities. Each tissuelike substance was tested with 30-gauge, 27-gauge, and 25-gauge needles of two brands commonly used in dentistry. The needles were placed to a standardized depth of 0.5 inch (1.27 cm) at a standardized rate of insertion. A customized dental surveyor allowed controlled forces to be applied. A linear insertion technique and a newly described bidirectional rotation insertion technique were tested. The force of puncture and penetration drag was recorded with an electronic digital scale. A total of 400 needle insertions were performed. Results: A multivariate analysis of technique, material, needle gauge, and needle brand revealed the data to be statistically significant, demonstrating no overlap. The post-hoc analysis of between-subject effects found that the needle insertion technique accounted for the most powerful effect in reducing force penetration. The bidirectional insertion technique had the greatest influence on reducing the force penetration irrespective of material, needle gauge, or needle brand tested in this study. Conclusion: The bidirectional rotation insertion technique required two to three times less force than did a standard linear insertion technique. A continuous rotation in a single direction would be expected to produce similar results. Needle gauge and needle design appeared to have a smaller effect on reducing force penetration than did the technique used during insertion. The in vitro model used in this study represents a reliable dynamic testing system that can be used for future evaluation of needles.