The effect of screwdriver angle variation on the off-axis implant abutment system and hexalobular screw

A recently introduced hexalobular screw system allows for off-axial screw channel access. The screwdriver angle input torque relative to the screw axis output torque has not been established.

The purpose of this in vitro study was to evaluate the effect of maximum angulation on the abutment-implant screw connection and torque values for a hexalobular screw system and to determine how input versus output varies with the angle of the screwdriver.

Twenty angulated abutments attached to implant fixtures were tightened to the manufacturers' prescribed torque at 2 different input angles: 0 and 28 degrees off axial (n=10/group). Input and reverse torque values were recorded by using calibrated torque sensor devices and compared for significant differences by using the Mann-Whitney U test. Fifty hexalobular screws were subjected to screwdriver angle variations of 0, 10, 15, 25, and 28 degrees (n=10/group). The input torque (screw head) and output torque (screw body) were recorded. The Kruskal-Wallis rank sum test and the post hoc Dunn test were used for statistical analysis of the output torque (α=.05).

Significant differences in mean reverse torque existed (P<.05) between the abutment-implant connection at the 2 angles measured. Significant differences were found at the output torque with varying angles of input torque (P<.05). No statistically significant differences were determined between 0 and 15 degrees. Torque values were significantly reduced for 25- and 28-degree angulations.

Angle changes may affect the screw torque and ultimate preload. At extreme angulation beyond 15 degrees, screw performance may be affected and have clinical relevance in areas with high occlusal load.