Factors influencing dental cartridges aspiration and plunger movement

Objective: The aim of this work was to investigate the influence of the needle length and the type of cartridge - plastic (PC) or glass (GC) in the forces required to aspirate (FA), to initiate (FI) and to maintain (FM) the plunger movement. Methods: For each test 20 cartridges were placed in the same self-aspirating syringe. Three brands of needles were tested: BD® (BD), Unoject® (U) and Septoject® (S) in short and long lengths. All tests were performed in EMIC machine. The FA was measured using 1N incremental forces with needle immerged in blue ink until the ink was detected inside the cartridge. Both FI and FM were measured with 25mm/min speed. All data were analyzed by Kruskal-Wallis test (alpha=5%). Results: There were no statistical significant differences (p>0.05) among brands considering FA and FI for short needles in both PC and GC. BD long needles (PC and GC=2.4±0.6N) induced lower (p<0.05) FA when compared to the other needles in PC (S=3.55±0.76N; U=3.4±0.6N) and GC (S=3.2±0.95N; U=3.35±0.67N). All long needles induced higher FA than the short needles in both PC and GC (p>0.05). FI was higher (p<0.05) for PC than GC considering short needles. The FI for U long-needles (20.3±1.98N) in PC was higher (p<0.05) than the other needles (between 15.9±2.4N and 17.6±2.89N) in both PC and GC. Higher FM was observed for U short-needles (7.6±2.16N) in comparison to the other brands (BD= 5.9±1.46N; S= 5.3±2.36N). No differences among brands considering FM were found for long needles in both PC and GC (p>0.05). However, higher FM was required for GC (between 11.1±2.98N and 11.9±2.06N) than PC (between 5.9±1.04N and 6.5±1.7N). Conclusion: The forces necessary to aspirate, initiate and maintain the plunger movement are significantly influenced by the dental-needle length and the type of cartridge.