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The assessment of abutment screw stability between the external and internal hexagonal joint under cyclic loading
Tae-Sik Lee, Jung-Suk Han, Jae-Ho Yang, Jae-Bong Lee, Sung-Hun Kim

STATEMENT OF PROBLEM: Currently, many implant systems are developed and divided into two types according to their joint con-
nection: 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 inter-
nal hexagonal connection types under cyclic loading. MATERIAL AND METHODS: Each of the 15 samples of external implants and in-
ternal 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 × 106cyclic loading; second group 3 × 106, 3 × 106for a total cyclic load-
ing 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 × 106cyclic loading, and the value after 1 × 106, and additional 5 × 106cyclic loading was not significant. The
difference between the removal torque value after 3 × 106cyclic loading and after 3 × 106, and additional 3 × 106cyclic 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 × 106cyclic 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 × 106cyclic loading was not significant. CONCLUSION: The external hexag-
onal connection was more stable than the internal hexagonal connection after 1 × 106, and additional 5 × 106cyclic loading (t = 10.834, P
< .001). There was no significant difference between the two systems after 3 ×106, and additional 3 × 106cycles.

* Keywords: Screw loosening, External hexagonal connection, Internal hexagonal connection, Cyclic loading

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