Abstract
Objective: To evaluate the removal torque values on abutment screws after different torque application techniques. Materials and methods: Thirty specimens of an external hexagon implant, a prefabricated abutment and a titanium screw were distributed randomly in three groups. In group 1, the screws received a torque of 30 N.cm; group 2 received a torque of 30N.cm and a second torque after 10 min, in accordance with the technique proposed by Brending et al. and Dixon et al.; in group 3, a torque of 30 N.cm was applied and maintained for 20 s, in accordance with the technique recommended by Sella et al. The specimens were attached to a universal testing machine and a digital key was coupled to the load cell in order to control the torque value at a velocity of 1 N.cm/s. Removal torque was performed 10 minutes after torque application. Values were statistically analysed using one-way ANOVA and Tukey’s HSD test (? = 0.05). Results: The mean and standard deviations (±SD) of removal torque values found were 27.95±0.99N.cm for group 1, 28.32±0.68N.cm for group 2 and 26.89±1.03N.cm for group 3. Groups 1 and 2 exhibited statistically higher values of torque than group 3 (p ? 0.05). Conclusion: The technique recommended by Breeding et al. and Dixon et al. seemed to be the best option when considering the removal torque values of external hexagon implants. Keywords: Abutment screw; Dental implants; Removal torque.
Highlights
A lthough rehabilitation with implants has a 98% success rate [1], the literature has been emphatic in researching and reporting the main causes of failure and biological or mechanical complications [2,3,4,5,6]
Screw loosening occurs when separation forces are greater than the clamping force, thereby compromising the stability of the screw joint, which is the unit formed by the two components [16,17,18]; this mechanical complication can occur in two stages: 1 – external transverse or lateral forces are applied on the screw joint during chewing, leading to a reduction in the surface friction of the threads, which contributes to preload loss; and 2 – there is a continuous loss of preload to critical levels, threatening the stability of the system and causing screw loosening [16,19]
Changes in the final stability of the screws could be found, and prefabricated abutments generated larger preloads and the highest values in the loosening torque [10]. This current study aims to research the removal torque values of customized titanium abutments on external hexagon implants, comparing three techniques of torque application: the conventional technique, the technique proposed by Breeding et al [25] and Dixon et al [2], and the technique proposed by Sella et al [18]
Summary
A lthough rehabilitation with implants has a 98% success rate [1], the literature has been emphatic in researching and reporting the main causes of failure and biological or mechanical complications [2,3,4,5,6]. The mechanism for obtaining appropriate preload involves the application of torque, with removal torque indirectly proportional to the amount of preloading. This means that the value of the applied torque will not always generate the same preload value due to the coefficient of friction which acts on the screw head, abutment, screw threads and the internal threads of the implant, creating a loss of initial force (torque). The coefficient of friction depends on the hardness of the material of the surface finish of the threads, the quantity and quality of the lubricant, and the tightening speed [15]
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