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Microstructural evolution of cold-worked titanium dental implants following clinically relevant insertion torque
Mahmoud Elkahly1, Mohamed Elshewy1, Rafael Rocha Pacheco1
1Department of Restorative Sciences, Dental College of Georgia, Augusta University, Augusta, Georgia, USA.
Purpose:
This study evaluated whether single-direction torsional insertion at 30, 60, and 80 Ncm induces microstructural changes in cold-worked CP Grade 4 titanium dental implants compared with as-manufactured controls.
Materials And Methods:
Implants were inserted into polyurethane cortico-cancellous bone analogs using a standardized guided protocol. Three torque groups (30, 60, and 80 Ncm) were created, each comprising eight test implants and two controls. Recovered implants were sectioned and prepared metallographically through sequential grinding, polishing, and chemical etching. Five regions across each implant were examined using light microscopy (5×-100×). Deformation features, including intragranular planar bands, grain distortion, and localized microcrack initiation, were qualitatively assessed.
Results:
Control implants and those inserted at 30 Ncm retained their equiaxed grain structure with no observable cracking. At 60 Ncm, intragranular planar deformation features consistent with twinning were observed, indicating the onset of plastic deformation. At 80 Ncm, deformation banding became more pronounced, and microcracks appeared in highly stressed regions, exhibiting both intergranular and transgranular characteristics. No macroscopic deformation of the implant body or internal connection was observed at any torque level.
Conclusion:
Clinically relevant insertion torque influences the microstructure of CP Grade 4 titanium implants. Minimal changes occurred at 30 Ncm, while 60 Ncm produced early plastic deformation and 80 Ncm generated pronounced deformation banding with evidence of localized microcrack initiation. These findings suggest that high insertion torques, even when not causing visible deformation, may introduce subsurface plastic damage with potential implications for long-term mechanical behavior under cyclic loading. Moderate insertion torques were most consistent with preserving the as-manufactured microstructure in this implant configuration.
