Is there an error in this paper? (modulus of elasticity vs. movement)

[swampwiz]

NOTE: I seem to have a dental implant in which there has been a mechanical failure of the abutment, which has piqued my interest in this.

The paper is here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4668729/

About 40% down, there is:

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The most commonly used retaining screws are either of gold or titanium. Gold screws are designed to be the most “flexible” portion of the implant assembly. Due to their higher modulus of elasticity than titanium, they permit an adequate micro movement to distribute force to the implant body.[37] Implant posts, that are retained with gold or gold coated screws, show a reduction of screw loosening and improved clamping force in comparison with titanium screws.[38,39,40]

Titanium alloy has four times the bending fracture resistance of grade 1 titanium. Therefore, abutment screws made of grade 1 titanium will deform and fracture more easily than the alloy. A higher torque magnitude can be used on the titanium alloy abutment screw and female component (implant body).[36] Titanium retaining screws are stronger than gold, but have a lower modulus of elasticity; metal fatigue will produce a gold screw fracture before the titanium retaining screw is affected.[37] The major disadvantage of titanium retaining screws is their tendency to cause galling, which results in excessive friction between the two mating surfaces there by causinga localized welding with a further roughening of the mating surfaces.[41] Galling occurs in the following manner: Titanium of the retainings crew slides in contact with the titanium of the implant body, the coefficient of friction increases whereby titanium molecules transfer from the mating surfaces.[42] This has been described as the adhesive wear mechanism[43] which causes slight damage to both the implant body and the retaining screw threads.

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This seems to make no sense. It would seem that a material with a higher modulus of elasticity would be less flexible and harder to have "micro movements". Also, looking up this property for the elements @ Wikipedia, gold is at 79 while titanium is at 116 (GPa), which seems to be completely contradictory to what is presented in the paper.

 

[JBA]

You are correct, higher modulus = lower strain per unit stress i.e. stiffer material. It appears the author has "inadvertently" used the term modulus of elasticity when flexibility was what he intended. It may have been, since he is writing "a review of current technology" he may have not technically understood what "modulus of elasticity" represented and assumed a higher modulus indicated more flexibility. If you clip on "more author information" you will see that all of the authors are from "Babu Banarasi Das College of Dental Sciences" so engineering terminology may not be their strong suit.