A Test For Comparing Functional Deflection Of Dental Anesthetic Needles

Objectives: To compare the functional deflection of five types of dental needles in vitro.

Method:

Five types of needles from different manufacturers were tested. All were 30 gauge; four (C1-C4) were of conventional tip morphology and one (C5) was a novel tip design. Experiments were carried out using a universal testing machine (model 5567, Instron, Bucks, UK.) A 0.4mm polyurethane membrane (Melab, Leonburg, Germany) was secured horizontally to a test jig platform. The needle was mounted with the tip 11mm above the membrane and advanced 13mm to penetrate the membrane at a rate of 50mm/min. The needle was then returned to its initial position. A 10mm block of heavy bodied silicon impression material was placed directly on top of the membrane. The same needle was then advanced 13mm at 50mm/min, passing through the silicon block before penetrating the membrane for a second time. After the needle was withdrawn the membrane was removed and the distance between the two penetration points measured using a micrometer by two researchers blinded to the randomization. The experiment was then repeated with a new needle and membrane. This was carried out 12 times for each needle type. Data were analyzed by ANOVA.

Results: The novel tip morphology needle (C5) deflected less than the four (C1-C4) conventional needles (F = 40.01; p<0.0001). Conventional needles did not differ in their deflection. (F = 1.5; p = 0.228).

Conclusions: The deflection of dental needles in vitro is influenced by their bevel design. This test method is capable of detecting the deflection differences.