Effect of Crown Height on the Screw Stability of Titanium Screw‐Retained Crowns

Abstract

Purpose The aim of this in vitro study was to evaluate the effect of crown height on the screw stability of screw‐retained titanium implant crowns subjected to cyclic loading conditions. Materials and methods Twenty‐one implants with internal hex connections were placed in epoxy resin holders. Mandibular first molar screw‐retained titanium implant crowns with UCLA type, crown‐abutment connections were CAD/CAM fabricated. Seven crowns of 3 different heights (6 mm, 10 mm, and 14 mm) were made. The crowns were seated onto the implants and screws were tightened to 30 Ncm. The implants were clamped into holders and stepwise cyclic loads were applied to the occlusal surface at 30‐degree angles to the long axes of the crowns. The detorque values were measured after each 5 million cycles. Before increasing the applied load, the crowns were secured with new screws and tightened to 30 Ncm. Failure times, survival estimates and detorque values were then analyzed. (alpha = 0.05). Results Crown height did not significantly affect detorque values. However, five 14‐mm crowns failed with varying fractures during the 475 N loading condition. Overall, a significantly lower survival for 14 mm crowns was found compared to 6 mm and 10 mm crowns (p = 0.004). Conclusions Crown heights of one‐piece screw‐retained titanium implant crowns did not significantly affect detorque values. Screw fracture, however, was greater for crown height of 14 mm than those of 6 mm and 10 mm.

Effect of internal connection type and screw channel angle on the screw stability of anterior implant‐supported zirconia crowns

“…The crown–implant pairs were then mounted on mastication (Hernandez et al, 2008; Jacobs et al, 2022; Mulla et al, 2021; Nasrin et al, 2018; Yilmaz, Batak, et al, 2021; Yilmaz, Çakmak, et al, 2021; Yilmaz, Gouveia, et al, 2021) simulator at a 30‐degree off‐axis from the loading direction (ISO 14801:2007, 2007; Figure 3). A software program (Excel, Microsoft Corp) was used to randomize the specimen positions on the mastication simulator.…”

“…Optimal preload is achieved when the stress exerted on the screw reaches 60–75% of the screw material's yield strength (Lang et al, 2003). However, when the external force exceeds the preload, mechanical complications, such as instability, micro‐movement, screw loosening, and screw fracture occur (Delben et al, 2011; Yilmaz, Batak, et al, 2021; Yilmaz, Gouveia, et al, 2021). In addition, even if optimal values are reached, 2–10% of the initial preload is lost due to the embedment relaxation of the implant screw (Jaarda et al, 1994; Winkler et al, 2003), which may also lead to screw loosening (Kim & Lim, 2020).…”

Effect of Dynamic Cycles and Abutment Angle on The Screw Stability of Standard and Narrow Implants: An In vitro Study

“…Cyclic loading can result in a gradual decrease in clamping force and rotational movement of the crown or titanium base (18). Additionally, it has been observed that cyclic loading can affect the resistance to rotation of abutment screws (9). These findings highlight the importance of considering the effects of cyclic loading when evaluating the stability and longevity of dental implant restorations.…”

“…(7). However, mechanical complications such as instability, micro-movement, screw loosening, and screw fracture occur when the external force exceeds the preload (5,8,9).…”