A Biomechanical Comparative Analysis of Abutment Screw Head Designs on Preload Stability Under Oblique Compressive Forces: An In Vitro Pilot Study

The purpose of this study was to examine the impact of abutment screw head sizes on preload stability when secured to a standard external hex implant under oblique compressive forces. Fifteen metal crowns were divided into 3 equal groups. The first group had 5 angulated cemented crowns connected to a 3-mm-tall straight hexagonal abutment with an external hex abutment screw. The second and third groups each had 5 straight cemented crowns attached to a tapered abutment with flat-slotted and internal hex abutment screws, respectively. Samples were subjected to a static cyclic load until failure. Kruskal-Wallis H, Dunn, and one-way analysis of variance with Tukey honestly significant difference tests were performed. Cemented straight crowns supported by an angled abutment connected to implants with flat-slotted and internal hex abutment screw heads failed at an average of 4.24 × 10⁶ cycles ± 3.31 SD and 12.67 × 10⁶ cycles ± 5.47 SD, respectively. Cemented angled crowns supported by a straight abutment connected to identical implants with an external hex abutment screw survived 18.02 × 10⁶ cycles ± 4.49 SD. The periotest value rate of change increased at a higher rate in crowns supported by angled abutments compared with straight abutments (p < .05). No cement failure was observed. Under the experimental conditions, larger abutment screw head sizes demonstrated greater stability of the abutment-abutment screw joint interface. Based on the in vitro findings, no cement failure was observed between the cemented crown and abutment connection. Future research with standardized comparative setups and larger sample sizes is needed.