IADR Abstract Archives
Effect of Crown Height on Screw Stability of Screw-Retained Crowns
Objectives: Clinically, the increase in stresses on the restoration can cause loosening of the screw and fracture, abutment and crown fracture, or fracture of the implants. Thus, it is important to consider the loosening of the prosthetic screw because it occurs frequently. The use of a suitable crown height could reduce the incidence of biologic and biomechanical complications. The aim of this in vitro study was to evaluate the effect of crown height on the screw stability of screw-retained implant crowns.
Methods: Twenty-one internal connection implants (4.7 mmx10 mm) were used with screw-retained implant crowns. Maxillary first molar crowns were CAD-CAM fabricated in titanium in 3 different heights (6 mm, 10 mm and 14 mm). The screws were tightened to 30 Ncm by using a mechanical torque driver as recommended by the manufacturer. Cyclic loading was applied with 120 N load at 2Hz frequency with 30-degree angle to the long axes of the crowns. The crown stability on their implants was checked after each million cycles and the crowns that were not loose had their screw detorque value measured using a torque measuring device after 5 million cycles. The detorque values were analyzed using one-way ANOVA (alpha=.05) for the effect of crown height on the screw detorque values.
Results: The mean detorque value and standard deviation(±) was 21.07±2.08 Ncm for 6-mm crowns, was 19.49±3.94 Ncm for 10-mm, and was 18.08±3.28 Ncm for 14-mm crowns. The average percentage torque loss calculated was 29.78±6.93 for 6-mm crowns, was 35.03 ±13.14 for 10-mm crowns and was 39.74±10.93 for 14-mm crowns. No statistically significant differences were found among the 3 different height groups (P>.05).
Conclusions: Under 120 N cyclic loading simulating over a 5-year clinical use, crown height didn’t have a significant effect on the screw stability and didn’t influence the percentage torque loss of screw.
Methods: Twenty-one internal connection implants (4.7 mmx10 mm) were used with screw-retained implant crowns. Maxillary first molar crowns were CAD-CAM fabricated in titanium in 3 different heights (6 mm, 10 mm and 14 mm). The screws were tightened to 30 Ncm by using a mechanical torque driver as recommended by the manufacturer. Cyclic loading was applied with 120 N load at 2Hz frequency with 30-degree angle to the long axes of the crowns. The crown stability on their implants was checked after each million cycles and the crowns that were not loose had their screw detorque value measured using a torque measuring device after 5 million cycles. The detorque values were analyzed using one-way ANOVA (alpha=.05) for the effect of crown height on the screw detorque values.
Results: The mean detorque value and standard deviation(±) was 21.07±2.08 Ncm for 6-mm crowns, was 19.49±3.94 Ncm for 10-mm, and was 18.08±3.28 Ncm for 14-mm crowns. The average percentage torque loss calculated was 29.78±6.93 for 6-mm crowns, was 35.03 ±13.14 for 10-mm crowns and was 39.74±10.93 for 14-mm crowns. No statistically significant differences were found among the 3 different height groups (P>.05).
Conclusions: Under 120 N cyclic loading simulating over a 5-year clinical use, crown height didn’t have a significant effect on the screw stability and didn’t influence the percentage torque loss of screw.