CONTROL ID: 2603669
CONTACT: Jeremy Pitman
Abstract Details


Preload Developed in a TiN-Coated Screw Driven by an Elliptical Driver for Angled Channels

AUTHORS: Pitman, Jeremy D.

Introduction: Omnidirectional screwdrivers provide an elegant solution for accessing retention screws in restorations with screw-channel angulations of up to 25° (Garcia-Gazaui et al. 2015). However, screw channels with large angulations are at risk of developing a reduced preload in the prosthetic screw as a result of the angulation of the driver relative to the screw axis, as torque is affected by magnitude and direction (The Physics Classroom, 2016).

An investigation was conducted to determine the effect of angulation on the developed preload in TiN-coated (TiN) Titanium dental screws under a range of input torque values, using an omnidirectional driver.

A secondary aim was to compare preloads generated in uncoated Titanium (Ti), TiN, and Gold screws over a range of input torque values.

Preload was measured in TiN test screws (IPD/AA-TR-52, IPD, Barcelona, Spain) during the application of input torques ranging from 20-40Ncm (in 5Ncm increments). At each input torque, the driver was angulated relative to the screw axis at set positions between 0-30°, in increments of 5°, using custom designed guide rings. Preload measurements were repeated 5 times with new screws at each angulation.

When compared to the 0° case, an increase in the developed preload of 1% was found in the TiN screws for the 5° case, whereas decreases of 3%, 8%,6%, 15% and 22% were found for the 10°, 15°, 20°, 25° and 30° cases respectively.

Compared with a Ti screw at the 0° angulation condition, the TiN screw developed a 2% higher preload at 20Ncm and a 28% lower preload at 40Ncm, whereas the Gold screw achieved a 146% higher preload at 20Ncm and a 77% higher preload at 40Ncm.

The drop of less than 10% in developed preload for the 5°, 10°, 15° and 20° cases indicates that omnidirectional drivers may be useful for small angle corrections. However, the large preload drop for the 25° and 30° cases indicates that screw channels with angulations of over 20° degrees, result in a reduced preload. A reduced prosthetic screw preload could lead to micromotion, the development of microgap and failure of the restoration.

The TiN coating was found to have almost no effect on developed preload performance at any input torque. The performance of the Gold screw under identical testing conditions shows that Gold screws provide vastly higher preloads than both TiN and uncoated Titanium screws at the same applied torques.

Jeremy AO abstract
Figure 1: Average screw preload developed when angulating the driver relative to the screw axis

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