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.
Abutments: frontal view of (1a) straight abutment and (1b) angled abutment each connected to an external hex threaded Ti implant fastened by (1a) an external hex abutment screw, (1b) flat-slotted abutment screw head or internal hex abutment screw head. (1-2) Crown wax-up: frontal view of (2a) crown wax-up for a straight abutment and a 15° angled crown that is 11 mm in height from the gingival margin to loading point. (2b) Crown wax-up of a 15° angled abutment and a straight crown 10 mm in height from the abutment margin. (1-3) Metal crowns: frontal view of a metal crowns (3a) 11 mm 15° angled crown cemented onto a straight abutment, (3b) 10 mm straight metal crown cemented onto a 15° angled abutment.
Cross-sectional view depicting the lateral resistance and preload areas of Ti abutment and abutment screw connected to external hex threaded implants. (a) A straight hexagonal abutment connected to an external hex threaded implant via an external hex abutment screw. (b) A 15° angled abutment connected to an external hex threaded implant via a flat-slotted abutment screw head. (c) A 15° angled abutment connected to an external hex threaded implant via an internal hex abutment screw. (a) Lateral resistive area = 15.08 mm2 and preload area = 3.71 mm2. (b) Lateral resistive area = 7.54 mm2 and preload area = 1.98 mm2. (c) Lateral resistive area = 13.59 mm2 and preload area = 1.98 mm2.
Front view of a 3-mm-thick silicon mask mimicking gingival mucosa superior to the implant-abutment junction, crown margins, and angled part depicting identical crown trajectories. (a) Cemented angled metal crown and (b) cemented straight metal crown. Both metal crowns are aligned with the required 15° angulation.
Side view of an 11-mm-tall and 15° angled crown cemented onto a 3-mm-tall straight hexagonal abutment connected to an external hex threaded implant fastened via an external hex abutment screw embedded in an acrylic resin block positioned 30° to the 30 kg static cyclic vertical load.
Side view of a 10-mm-tall and 0° straight crown cemented to a 7-mm-tall 15° angled abutment connected to an external hex threaded implant that was fastened with a flat-slotted or internal hex abutment screw head embedded in an acrylic resin block positioned 30° to the 30 kg static cyclic vertical load.
Mean number of cycles until a failure endpoint was detected for a 10-mm-tall straight crown cemented onto a 7-mm-tall 15° angled abutment fastened by a flat-slotted abutment screw head, 10-mm -tall, straight crown cemented onto a 7-mm-tall 15° angled abutment fastened by an internal hex abutment screw and 11-mm-tall, angled crown cemented onto a 3-mm-tall straight hexagonal abutment fastened by an external hex abutment screw (* p < .05).
The profile of the rate of crown mobility and trendlines of crown and abutment setups fastened by either a flat-slotted, internal hex, or external hex abutment screw head subjected to a 30 kg static cyclic vertical load.
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