Purpose:

To examine the impact of abutment screw head sizes on preload stability when secured to a standard external hex implant under oblique compressive forces.

Materials and method:

Fifteen metal crowns were divided into three equal groups. The first group had five 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 five 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's, and one-way ANOVA with Tukey HSD tests were performed.

Results:

Cemented straight crown supported by an angled abutment connected to implants with flat slotted and internal hex abutment screw heads failed at an average of 4.24 x 106 cycles ± 3.31 SD and 12.67 x 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 x 106 cycles ± 4.49 SD. Periotest value (PTV) rate of change increased at a higher rate in crowns supported by angled abutments compared to straight abutments (p < 0.05). No cement failure was observed.

Conclusion:

Under the experimental conditions, larger abutment screw head sizes demonstrated greater stability of the 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.

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