Journal List > J Korean Acad Prosthodont > v.55(3) > 1034928

Kim, Park, Choi, Kim, Kim, Kim, Moon, and Lee: Influence of internal connection length on screw loosening in internal connection implants



The purpose of this study was to evaluate whether the internal abutment length affected screw stability in an internal connection implant.

Materials and methods

Twenty long internal connection implants (Replus system, 4.7 × 11.5 mm) were selected for this investigation. Abutments were assigned to four groups depending on the length of the internal connection (abutments with internal lengths of 1, 2, 3, and 4 mm, respectively). Each implant fixture specimen was embedded in resin medium and connected to an abutment with an abutment screw. A load of 100 N, applied at an angle of 30° to the long axis of the implant, was repeated for 1.0 × 106 cycles. Reverse torque values (RTV) were recorded before and after loading, and the change in RTV was calculated. Data were analyzed with the Kruskal-Wallis test.


The change in RTV was not significantly different among the groups (P>.05). Screw loosening and fractures were not observed in any groups, and joint stability was maintained.


The internal length of the abutment may not significantly affect the degree of screw loosening. (J Korean Acad Prosthodont 2017;55:251-7)


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Fig. 1.
Internal connection dental implant system. (A) From the left, abutments with internal lengths of 1, 2, 3, and 4 mm (a, b, c, and d, respectively); the abutment comprised double lobes, including an upper lobe and a lower lobe, (B) Longitudinal and cross sectional views of the implant fixture complex.
Fig. 2.
Implant crown fabrication. Crowns were cast with Ni-Cr; all crowns were of one size. A hole was made in the crown to measure the removal torque value of each specimen.
Fig. 3.
Crown refinement and fixation. (A) Schematic diagram of implant crown and loading direction (red arrows). (B) Schematic diagram of implant assembly embedded in clear resin. It was fixed at a 30° angle to the long axis of the implant.
Fig. 4.
Means and standard deviations of the differences between initial and final RTVs. The groups represent different lengths of internal abutment connections (see Fig. 1A).
Fig. 5.
SEM images of abutment screw surfaces (×200 original magnification). (A) Ti alloy abutment screw into 1 mm internal abutment, (B) Ti alloy abutment screw into 2 mm internal abutment, (C) Ti alloy abutment screw into 3 mm internal abutment, (D) Ti alloy abutment screw into 4 mm internal abutment.
Fig. 6.
SEM images of internal abutment connection surfaces (×150 original magnification). (A) The lobe surface of a 1 mm internal abutment, no damage was observed; (B) upper lobe and lower lobe surfaces of a 2 mm internal abutment, upper lobe showed some damage, and the lower lobe showed significant damage and scratches; (C) lower lobe surface of a 3 mm internal abutment was more scratched than the upper lobe; (D) lower lobe surface of a 4 mm internal abutment showed significant scratch marks compared to other surfaces.
Table 1.
Initial reverse torque value (RTV), post loading RTV, and the difference between the initial and post loading RTVs
Specimen no. Initial RTV (Ncm) Mean (SD) initial RTV (Ncm) Post loading RTV (Ncm) Mean (SD) post loading RTV RTV differences (Ncm)
Group A (1 mm)
1 24.0 25.7 (1.0) 20.5 22.4 (1.8) -3.5
2 26.4 20.6 -5.8
3 25.5 24.5 -1.0
4 26.0 23.7 -2.3
5 26.4 22.9 -3.5
Group B (2 mm)
1 24.4 25.3 (1.4) 20.8 22.7 (2.1) -3.6
2 24.2 22.3 -1.9
3 24.4 22.1 -2.3
4 25.7 22.3 -3.4
5 27.6 26.3 -1.3
Group C (3 mm)
1 26.0 25.3 (0.9) 24.7 23.6 (1.2) -1.3
2 24.0 21.7 -2.7
3 25.4 23.7 -1.7
4 26.3 23.1 -3.2
5 24.8 24.6 -0.2
Group D (4 mm)
1 24.5 24.8 (1.2) 24.3 23.5 (1.6) -0.2
2 24.6 22.3 -2.3
3 24.5 24.7 -0.8
4 23.5 21.2 -2.3
5 26.8 24.9 -1.9
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