الفهرس 
Kim & Shin classified Cement retained abutment into two typesOnly 14 pages are availabe for public view
 |  | from | 155 |  |  |
| | | from | 155 | | |
Abstract
The connection between the implant and the abutment, implant diameter, and abutment types may be of great importance when it comes to long-term stability and the successful outcome of implant restoration. Therefore, several studies have been conducted and implant companies attempt to reduce screw loosening by achieving an accurate and stable connection between the components of implant systems through the fabrication of mechanical pieces with a high degree of precision, thereby decreasing both its mechanical and biological draw-backs . It was discovered that conical connection is better than internal hex connection because it provide perfect fixture abutment fit preventing and minimizing screw loosening and mechanical problems. This in-vitro study was carried out to evaluate screw loosening by measuring the removal torque value (Nm) of abutment screw for two different implant abutment connections, two implant diameter, and two abutment types before and after cyclic loading by using digital torque gauge. Twenty implants were selected for this in-vitro study and divided into two equal groups (conical hybrid, and internal hex), 10 each according to types of implant/abutment connection. Each group was divided into 2 subgroups according to implant diameters (3.3, 4.2 mm). For each subgroup, two types of abutment were used (stock titanium abutment, castable abutment). Data analysis was performed in several steps. The removal torque loss ratio before and after cyclic loading and between before and after cyclic loading were analyzed using the SPSS statistical analysis . ANOVA and Tukey’s post hoc test at 0.05 level of significance were performed to compare initial and postload removal torque loss ratio and percentage of difference in removal torque loss for subgroups. It was found that the difference between the two different implant/abutment connection groups in initial and postload removal torque loss ratio and percentage of difference in removal torque loss was statistically significant as indicated by T test (p=<0.0001) . The interaction between variables before and after cyclic loading showed that Gr I ( conical hybrid ) recorded the lowest removal torque loss ratio while the highest removal torque loss ratio was recorded by Gr II (internal hex ). ANOVA test was performed to compare mean of initial and postload removal torque loss ratio and % difference in removal torque loss for GIA, GIB, GIIA, GIIB. The test revealed significant difference between groups (F=7.52 p=<0.0001), (F=137.99 p=<0.0001), (F=27.30 p=<0.0001). Pairwise Tukey’s post-hoc test showed non significant difference between (GIA, GIB) also between (GIIA, GIIB). ANOVA test was performed to compare mean of initial and postload removal torque loss ratio and % difference in removal torque loss for prefabricated and castable abutment in GIA, GIB, GIIA, GIIB. The test revealed significant difference between groups (F=11.18p=<0.0001), (F=79.77p=<0.0001), (F=12.95p=<0.0001). Pair-wise Tukey’s post-hoc test showed non significance difference between abutment types in the same group.