مقالات

BACKGROUND

Significant vertical space which has not been corrected with vertical ridge augmentation, may necessitate selection of longer abutments which would lead to an increased vertical cantilever

PURPOSE

This study investigated the influence of different heights of abutment collar on screw loosening of single-unit dental implants after cyclic loading.

MATERIAL AND METHODS

Fifteen implant-abutment assemblies each consisted of an internal hexagonal implant were randomly assigned to three groups. Three groups were arranged, Group1 consisted of five abutments with 1.5 mm gingival height (GH); Group2, five abutments with 3.5 mm gingival height, and Group3 consisted five abutments with 5.5 mm gingival height. Each specimen was mounted in transparent auto-polymerizing acrylic resin block and abutment screw was tightened to 35 N.cm with an electric torque wrench. After 5 minutes, Initial Torque Loss (ITL) was recorded for all specimens. Metal crowns were fabricated with 45oocclusal surface and were placed on the abutments. A cyclic load of 75 N and frequency of 1HZ was applied perpendicular to the long axis of each specimen. After 500000 cycles, Secondary Torque Loss (STL) was recorded. One way ANOVA analysis was used to evaluate the effects of abutment collar height before and after cyclic loading.

RESULTS

One-way ANOVA showed that ITL among the groups was not significantly different (P=.52), while STL was significantly different among three groups (P=.008). Post Hoc Tukey HSD Tests showed that STL values were significantly different between the abutments with 1.5 mm GH (Group1) and with 5.5 mm GH (Group3) (P=.007). Also, Paired comparison t-test showed that cyclic loading significantly influenced the STL in comparison with the ITL in each group.

CONCLUSION

Within the limitation of this study, it can be concluded that increase in height of abutment collar could adversely affect the torque loss of abutment screw.