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Abstract
STATEMENT OF PROBLEM
Currently, many implant systems are developed and divided into two types according to their joint connection: external or internal connection. Regardless of the connection type, screw loosening is the biggest problem in implant-supported restoration.
PURPOSE
The purpose of this study is to assess the difference in stability of abutment screws between the external and internal hexagonal connection types under cyclic loading.
MATERIAL AND METHODS
Each of the 15 samples of external implants and internal abutments were tightened to 30 N/cm with a digital torque gauge, and cemented with a hemispherical metal cap. Each unit was then mounted in a 30° inclined jig. Then each group was divided into 2 sub-groups based on different periods of cyclic loading with the loading machine (30 N/ cm - 300 N/cm,14 Hz: first group 1 × 106, 5 × 106 cyclic loading; second group 3 × 106, 3 × 106 for a total cyclic loading of 6 × 106) The removal torque value of the screw before and after cyclic loading was checked. SPSS statistical software for Windows was used for statistical analysis. Group means were calculated and compared by ANOVA, independent t-test, and paired t-test with α= 0.05.
RESULTS
In the external hexagonal connection, the difference between the removal torque value of the abutment screw before loading, the value after 1 × 106 cyclic loading, and the value after 1 × 106, and additional 5 × 106 cyclic loading was not significant. The difference between the removal torque value after 3 × 106 cyclic loading and after 3 × 106, and additional 3 × 106 cyclic loading was not significant. In the internal hexagonal connection, the difference between the removal torque value before loading and the value after 1 × 106 cyclic loading was not significant, but the value after 1 × 106, and additional 5 × 106 cyclic loading was reduced and the difference was significant (P < .05). In addition, in the internal hexagonal connection, the difference between the removal torque value after 3 × 106 cyclic loading and the value after 3 × 106, and additional 3 × 106 cyclic loading was not significant.
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Fig. 1.
The specially customized metal cap; hemisphere shape in order to transmit the applied load to the center of abutment.
Fig. 2.
Digital torque gauge (MGT12.mark-10. corp. USA). All abutment screws were tightened to 30 N/cm ± 0.5 N/cm with this digital torque gauge and the removal torque values of the screws were recorded.
Fig. 3.
Schematic diagram of the specimen. The load was applied on the hemispheric metal cap at 30° and the distance was 11 mm from the exposed position of the fixture to the center of the hemisphere.
Fig. 4.
The specimen is mounted in the customized jig with 30° inclined plane to be loaded with load machine (Instron model 8871. USA).
Fig. 5.
Group A, B Group A: External hexagonal connection of the abutment and fixture (Left). Group B: Internal hexagonal connection of the abutment and fixture (Right).
Table I.
Materials of tested specimens
Table II.
Assessment of the removal torque value in Group A-a and Group A-b after cyclic loading
Table III.
Comparison of the removal torque value after total 6 × 106 cyclic loading between Group A-a and Group A-b
| Group | Cyclic loading | Mean removal torque value (N/cm) | SD | t/p value |
|---|---|---|---|---|
| A-a | 1 × 106, and additional 5 × 106 | 17.79 | 1.28 | |
| A-b | 3 × 106, and additional 3 × 106 | 18.78 | 0.25 | -1.673/.118 |
Table IV.
Assessment of the removal torque value in Group B-a and Group B-b after cyclic loading
| Group | Cyclic loading | Mean removal torque value (N/cm) | SD | t/p value |
|---|---|---|---|---|
| Before loading | 30.32 | 0.31 | .875/.397 | |
| B-a | 1 × 106 | 19.29 | 1.28 | -1.239/.223 |
| 1 × 106, and additional 5 × 106 | 11.40 | 1.25 | 14.096∗∗∗/.000 | |
| Before loading | 30.18 | 0.53 | 1.206/.236 | |
| B-b | 3 × 106 | 18.84 | 1.09 | -.278/.783 |
| 3 × 106, and additional 3 × 106 | 18.20 | 0.91 | .666/.510 |
Table V
. Comparison of the removal torque value after total 6 × 106 cyclic loading between Group A-a and Group A-b
| Group | Cyclic loading | Mean removal torque value (N/cm) | SD | t/p value |
|---|---|---|---|---|
| B-a | 1 × 106, and additional 5 × 106 | 11.4 | 1.25 | |
| B-b | 3 × 106, and additional 3 × 106 | 18.2 | 0.91 | -10.694∗∗∗/.000 |
Table VI.
Comparison of the removal torque value after cyclic loading between Group A and Group B
| Cyclic loading | Group | Mean removal torque value (N/cm) | SD | t/p value |
|---|---|---|---|---|
| 1 × 106 | A-a | 19.05 | 1.11 | -0.463 |
| B-a | 19.29 | 1.28 | /.654 | |
| 1 × 106, and additional 5 × 106 | A-a | 17.79 | 1.28 | 10.834∗∗∗ |
| B-a | 11.40 | 1.25 | /.000 | |
| 3 × 106 | A-b | 19.36 | 0.64 | .808 |
| B-a | 18.84 | 1.09 | /.465 | |
| 3 × 106, and additional 3 × 106 | A-b | 18.78 | 0.26 | 1.329 |
| B-a | 18.20 | 0.91 | /.255 |
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