Comparison of screw loosening, rotation, and deflection among
three implant designs
Donna L. Dixon, DMD, MA~ a Larry C. Breeding, DMD, MSEd, b
J. Peter Sadler, PhD, c and Matthew L. McKay, BS d
University of Alabama at Birmingham, School of Dentistry, Birmingham, Ala., and University of
Kentucky, College of Dentistry, Lexington, Ky.
A common problem associated with single tooth implant restorations is abutment screw
loosening. Manufacturers of implants have attempted to overcome this problem by
incorporating anti-rotational design characteristics into their systems. Micro-movement
and torque levels required to loosen abutment screws for straight and angled anti-
rotational screw-retained abutment/implant combinations from three different
manufacturers were examined in this in vitro investigation. A custom-built machine was
used and each sample was subjected to compressive horizontal reciprocal movements
over a 25-degree incline for a simulated 1-month period. Data were generated that
showed movements of the crown/abutment complex during force application. The
amount of torque necessary to loosen the abutment screws before and after testing was
also recorded and compared for each system. The results indicated no significant
differences (p < 0.05) among all the straight and angled abutments for the variables
studied. (J PROSTHET DENT 1995;74:270-8.)