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Evaluation of implant abutment screw tightening protocols on reverse tightening values: An in vitro study

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Abstract

Statement of problem

Implant abutment screw loosening is a common prosthetic complication of implant-supported crowns. However, reports that have objectively evaluated the effectiveness of different tightening protocols on reverse tightening values are sparse.

Purpose

The purpose of this in vitro study was to determine the optimal tightening protocol for implant abutment screws.

Material and methods

Fifty Neoss implants were randomly distributed to 5 groups (n=10). The implants received a cover screw and mounted, and the impression coping was tightened. Tightening was measured by using a digital measuring device. Then, the implant abutments were placed and tightened to 32 Ncm by using a Crystaloc screw. In Group 2T10I, the screws were tightened twice with an interval of 10 minutes between the first and second tightening. In Group 2T0I, the screws were tightened twice with no interval time. In Group 1T, the screws were tightened 1 time only. In Group TCT, the screws were tightened, counter-tightened, and then tightened again. In Group TCTCT, the abutment screws were tightened, counter-tightened, tightened, counter-tightened, and then tightened again. All the mounted implants were left in the same environment for 3 hours, and the reverse tightening values were then measured.

Results

The mean reverse tightening values of the first 4 groups ranged from 21.49 Ncm to 22.57 Ncm, whereas the reverse tightening value for the fifth group was 25.51 Ncm. A significant difference was found among the groups (P<.05) with reverse tightening data.

Conclusions

No significant difference was found in tightening the abutment screw 2 times with a 10-minute interval time, no interval time, or tightening it 1 time only. However, a significant difference was found in reverse tightening in the 3-time tightening and counter-tightening group.

Section snippets

Material and methods

Fifty 4-mm diameter implants (ProActive; Neoss) were used in this study. Each specimen was assigned a number from 1 to 50, then the website (Randomizer.org) was used to randomly distribute the implants into 5 groups (Table 1); each group was assigned 10 implants (n=10). The implants were embedded in a light-polymerized composite resin (Triad Trutray; Dentsply Sirona) to ensure the implant would be perpendicular to the applied tightening force during the tests. The angulation of the implants was

Results

The mean screw initial tightening values recorded for the 5 groups were not statistically different (P>.05) (Table 3) and ranged from 32.00 to 32.45 Ncm. The RTVs for the 5 groups after 3 hours are shown in Table 4 and Figure 1, along with mean values; the lowest was Group 1T tightened 1 time with RTV (21.49 Ncm) and the highest Group TCTCT (25.51 Ncm) (Table 2). Group TCTCT was significantly higher than all other groups, and no difference in RTV was seen between any other pairs (P>.05).

Discussion

The null hypothesis that no significant difference would be found in tightening protocol with regard to the RTV was rejected. The results of this study indicate that in the first 3 abutment-screw tightening protocols (Group 2T10I, Group 2T0I, and Group 1T), there was no relation between either the time interval between tightening or retightening the screw a second time with regard to RTV. Moreover, tightening a screw 1 time made no significant difference in RTV compared with Group 2T10I and

Conclusions

Based on the findings of this in vitro study, the following conclusions were drawn:

  • 1.

    No significant difference was found in the time intervals between the tightening of implant abutment screws.

  • 2.

    To obtain optimum RTV, implant abutment screws should be tightened, counter-tightened, tightened, counter-tightened, and then tightened.

Acknowledgments

The authors thank Neoss Company for providing the implants components to conduct this research.

References (15)

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