Torque decrement and screw loosening values resulting under different dynamic loadings on angled and straight titanium abutment with narrow diameter implants: An in-vitro investigation

The aim of this in-vitro study is to investigate straight and angled titanium abutments' torque relaxation and screw loosening values under different dynamic loading cycles for narrow diameter implants and to compare values after dynamic loadings and previous values. Material and methods: 40 samples of 3,5 mm diameter 10 mm length implants and as superstructure 20 samples of straight and 15° angled titanium abutment were used. Samples divided in to 4 groups: 1. Group: 3x105 dynamic load cycles on straight abutment (Group D3), 2. Group: 6x105 dynamic load cycles on straight abutment (Group D6), 3. Group: 3x105 dynamic load cycles on angled abutment (Group A3) and 4. Group: 6x105 dynamic load cycles on angled abutment (Group A6). Before dynamic load cycles, every abutment screws were fastened and loosed 3 times with 30 N.cm torque. The loosening torque values (GTD's) were measured and registered as 1. 2. and 3. GTD's. Then, samples were fastened again with new screws with 30 N.cm torque value and subjected to different dynamic load procedure. After dynamic cycles, GTD's remeasured as 4.GTD's. Finally, aged screw were subjected to one more time fastened-loosening cycles and obtained 5.GTD values. As a result, five GTD's were measured for every sample. These values were compared with repeated ANOVA, two-way ANOVA and Tukey HSD tests in groups and among the groups. Results: After dynamic load cycles, there were no significantly differences among the groups (p>0,05) (D3: 26,43±0,72, D6: 26,05±0,75, A3:26,40±0,73, A6:26,27±0,80). In all groups 4. GTS was significantly lower than 1. 2. and 3. GTD (p<0,05). No significant differences were observed on 4. GTD's among groups. For 5.GTD's only A6 group was significantly lower than 1. 2. and 3. GTD's (p<0,05), while there were no statistically significantly differences between D3 and D6 groups (p> 0,05). In A3 group, there were statistically significantly differences between 5.GTD and 2. GTD. Conclusion: GTD values were significantly decreased by dynamic loading procedures. Before dynamic loads, initial GTD values were measured and found that angled abutments have higher initial GTD values than straight abutments. According to 5.GTD results; while there were no significantly difference between 5.GTD's with 1. 2. and 3. GTD's on D3 and D6 groups, there were significantly difference between 5.GTD with 1. 2. and 3 GTD's on A6 group and between 5.GTD with 2.GTD on A3 group. Particularly, changing of aged screw to new screw could be more advantageous in angled abutment usage