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. 2025 Jan 23;18(3):506.
doi: 10.3390/ma18030506.

Factors Influencing the Screw Stability of Implant-Supported Single Crowns: An In Vitro Study

Shaza Bishti  1 , Mohamad Shams Eddin Alsagher  1 , Martin Homa  1 , Stefan Wolfart  1 , Taşkın Tuna  1
Affiliations

Factors Influencing the Screw Stability of Implant-Supported Single Crowns: An In Vitro Study

Shaza Bishti et al. Materials (Basel). .

Abstract

The aim is to investigate the impact of retention type, implant/abutment angulation, and the presence of sealant/antimicrobial agents on screw loosening of implant-supported restorations. Fifty dental implants along with their respective abutments and screws were allocated to five groups (n = 10). The groups were categorized based on type of crown retention (screw-/cement-retained), implant/abutment angulation (0°/20°), and type of disinfectant/sealant as follows: Cem_control (cemented/0°/none), Cem_GP (cemented/0°/gutta-percha), Cem_CHX (cemented/0°/chlorhexidine), Cem_Ang (cemented/20°/none), and Screw (screwed/0°/ none). Abutment screws were tightened (20 Ncm), and CAD/CAM zirconia crowns were fabricated. Glass ionomer cement was used for crown cementation in the cemented groups. Samples were subjected to dynamic loading in a chewing simulator (1,200,000 cycles/98 N). After loading, the reverse torque values (RTVs) of the abutment screws were determined (Ncm) using an electronic screwdriver, and the reverse torque difference (RTD) was subsequently calculated. The lowest RTD was reported in group Cem_GP (-2.22 ± 1.03), whereas the highest RTD was seen in group Screw (-4.65 ± 1.79). Group Screw showed a statistically significant difference from all other groups (p < 0.05). No statistically significant difference between the cemented test groups Cem_GP, Cem_CHX, and Cem_Ang and the control group was found. Screw-retained restorations exhibited significantly greater RTD values compared to cement-retained ones. Implant/abutment angulation and the sealant/disinfectant appeared to have no notable effect on the screw stability of single-implant restorations.

Keywords: cement-retained; crown; disinfectant; implant-supported; screw loosening; screw-retained; sealant.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
(A) Holding device with adjustable alignment across three axes (1: horizontal, 2: vertical, 3: angulation) used for embedding the implants in the holders in a standardized manner; (B,C) embedded straight and angulated implant in the sample holder filled with acrylic resin (implant shoulder 2 mm above resin level); (D,E) tested crown placed onto its corresponding straight/angulated implant abutment. (F) A sample screwed to its implant using an electronic screwdriver to a torque of 20 Ncm.
Figure 2
Figure 2
A: Schematic image showing the different study groups. Group Cem_control (cemented, straight abutment, empty screw chambers), group Cem_GP (cemented, straight abutment, gutta-percha in the screw chamber of the abutment), group Cem_CHX (cemented, straight abutment, chlorohexidine gel in the screw chamber of the implant), group Cem_Ang (cemented, 20° angulated abutment, empty screw chambers), and group Screw (screwed, straight abutment, empty screw chambers). Arrows between the implant crowns and antagonists represent the load in the vertical and lateral direction.
Figure 3
Figure 3
Different parts of the investigated cemented straight implant restoration samples.
Figure 4
Figure 4
(A) Tested samples loaded into the universal testing machine; (B) a closer image of the investigated implant crown with its antagonist; (C) steatite balls after loading showing two wear facets due to the excessive lateral forces.
Figure 5
Figure 5
Boxplots representing the reverse torque differences within the tested groups. (*) represents significant differences between the groups (p < 0.05).
See this image and copyright information in PMC

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