An in vitro investigation of the effect of bevel design on the penetration and withdrawal forces of dental needles.

Objectives: To compare the effect on insertion and withdrawal forces using needles with a standard atraumatic bevel to those with a novel asymmetrical bevel in vitro.

Methods: Maximum needle penetration forces were measured using a 10N load cell mounted on an Instron universal testing machine. Forces were determined during insertion through a 0.4mm polyurethane membrane mounted at 90° (n=30 of each design), 30° (n=16 of each design) and 150° (n=16 of each design) to the needle bevel and during a 10mm insertion into a polyvinyl siloxane block mounted at 90° to the bevel (n=16 of each design). In all tests the rate of insertion was 50mm/min.

Results: The novel design required less force to penetrate the membrane at 30° and 150° compared to the standard design (mean forces at 30° being 0.75N and 0.98N for novel and standard designs respectively [p<0.001] and at 150° 0.52N and 0.66N respectively [p<0.001] but more force at 90° penetration tests (0.60N and 0.46N respectively [p<0.001]). The novel design required less force to insert 10mm into the polyvinyl siloxane (1.80N and 2.54N respectively [p<0.001]).

Conclusion: The novel design needed less force than the standard version to penetrate a thin membrane when used at 30° and 150° to the surface and to penetrate a polyvinyl siloxane block to a depth of 10mm but required more force to penetrate a thin membrane at 90°.

Clinical Significance: Needle bevel design affects the penetration and withdrawal forces of dental needles in vitro.