Screw stability of CAD‐CAM titanium and zirconia abutments on different implants: An in vitro study

Abstract

Background Limited information is available regarding the removal torque values (RTVs) of screws of different abutment materials when used with different implants. Purpose To evaluate the effect of implant type and abutment material (zirconia; Zir and titanium; Ti) on the RTVs of abutment screws after cyclic loading. Materials and methods Internal conical connection implants (CC, OsseoSpeed TX) and modified internal conical connection implants (MCC, OsseoSpeed EV) (n = 10) were clamped in resin dies. Zir and Ti (N = 20) custom abutments were tightened to implants (20 Ncm for CC and 25 Ncm for MCC) as specified by their manufacturers. The abutments were cyclically loaded by using a sequentially increased loading protocol; 2‐million cycles under 100 N, 3‐million cycles under 200 N, and 2‐million cycles under 300 N loads with 2 Hz. After 7 million cycles, RTVs (Ncm) were measured by using a torque gauge. The data were analyzed with ANOVA by using the restricted maximum likelihood estimation method. Tukey–Kramer adjustment was used for any significant interaction of implant‐abutment pairs (α = 0.05). Results Two CC implants, 1 with Ti and 1 with Zir abutment, fractured during cyclic loading (under 300 N loads within the 6th and 7th million cycles) and discarded for statistical analysis. Only implant type had a significant effect on RTVs (p <0.001). Screws of Ti abutments on MCC implants had significantly higher RTVs than the screws of Ti (p = 0.003) and Zir (p = 0.005) abutments on CC implants. Conclusions Implant type affected the RTVs, however, the RTVs were higher than the initial torque values for all groups. Screws of Ti abutments on implant, which required greater initial torque values had higher RTVs than the screws of Ti and Zir abutments on the implant that required smaller initial torque values. RTVs were similar for Zir and Ti abutment screws within each implant type.

Monolithic zirconia single tooth implant‐supported restorations with CAD/CAM titanium abutments in the posterior region: A 1‐year prospective case series study

“…Loosening of the restoration occurred in 4.1% of the cases which is similar to Derksen et al who reported that loosening of the restoration occurred in 4.6% of the cases (screw loosening, n = 1; de‐cementation from the abutment, n = 1). A recent in vitro study showed that the stability of CAD/CAM titanium abutment screws tightened on implants with a conical connection is very high when inserted with a torque of 25 Ncm 30 . In the present study, both screw loosening cases had a relatively high anatomical restoration, making it hard to tighten the restoration to the implant as the screwdriver was only just long enough.…”

“…A recent in vitro study showed that the stability of CAD/CAM titanium abutment screws tightened on implants with a conical connection is very high when inserted with a torque of 25 Ncm. 30 In the present study, both screw loosening cases had a relatively high anatomical restoration, making it hard to tighten the restoration to the implant as the screwdriver was only just long enough. The 25 Ncm insertion torque value might have not been reached in those cases which could have contributed to the loosening of the restorations.…”

The effect of the digital manufacturing technique of cantilevered implant-supported frameworks on abutment screw preload

“…Furthermore, it can be due to micromovements at the implant abutment connection when the prosthesis is loaded. 11 12 17 18 45 The literature stated that when screw is tightened to the recommended value, the RTV will be lower than the applied torque by 7 to 10%. 18 46 After cyclic loading, the RTV was lower than the applied torque in most literature, which is in accordance with the results of the present study.…”

“… 1 5 8 9 10 Loss of preload is a major cause of screw loosening as it is stated that only 10% of the initial torque is transformed to preload while the other 90% is used to overcome the friction between the irregular surfaces of the implant abutment connection. 11 12 Achieving adequate preload results in a clamping force that secures the implant abutment connection. 13 14 With time, screw loosening leads to an unstable superstructure that irritates soft tissues and causes unequal force distribution.…”

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.…”