Influence of Different Undercut Depths of Clasp Fabricated by Selective Laser Melting on Retentive Force

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  • Keita Tomono
  • Yoshimitsu Kato
  • Juro Wadachi
  • Akinori Tasaka
  • Shinji Takemoto
  • Shuichiro Yamashita


Introduction: The purpose of this study was to investigate the influence of undercut depths on abutment teeth regarding the retentive force of clasps fabricated through selective laser melting (SLM), and to compare them with conventional cast clasps. Methods: Akers clasps made of cobalt chromium alloy were fabricated using the SLM method (SLM), and the retentive forces were compared with clasps made with the conventional cast method (Cast). Three undercut amounts (0.25 mm, 0.15 mm, and 0 mm) were applied on the abutment tooth. The specimens were subjected to 10,000 repetitive insertion/removal cycles.
Results: SLM-0.15 showed slightly lower initial retentive force than the Cast specimens, it remained within an acceptable range. During insertion/removal test, the SLM-0.15 specimen showed a significant difference between the initial retentive force and the retentive force after 5,000 cycles, indicating that SLM-0.15 was the least likely to change in retentive force within the parameters established in this study. The inner clasp surface on the SLM groups had higher surface roughness before testing compared to the Cast specimen. Conclusions: Akers clasps fabricated by SLM demonstrated optimal initial retentive forces with smaller undercuts than conventional Cast clasps, and the retentive forces changed less with repetitive insertion/removal.

Removable Partial Denture
Selective Laser Melting
Retentive Force
Insertion/Removal Test