Retentive forces of repaired Akers clasps using laser welding

Purpose: Titanium is very compatible for laser welding of metals used in prosthetic treatment. The purpose of this study was to evaluate the stability of clasp retention of repaired clasps using laser welding. Materials and Methods: Using 18-8 stainless steel tooth die, an Akers clasp with a 0.25 mm undercut was fabricated using three metals: CP titanium (CP; JIS grade 3, T-ALLOY H, GC), a Ti-6Al-7Nb alloy (6-7; T-ALLOY TOUGH, GC), and a cobalt-chromium alloy (Co-Cr; Wisil, Dentsply-Sankin). After a measurement of the retentive forces at the initial time and up to 10,000 insertion/removal times, one of the clasp arms was cut and rejoined using laser welding. For CP, the clasp with a 0.5 mm undercut was also prepared, and the following three joining methods were performed: 1. A new clasp arm without gap distance was remade and joined to the broken clasp; 2. A clasp arm was cut after 10,000 insertions/removals, and a broken clasp arm was rejoined; 3. A clasp arm was cut without any 10,000 insertion/removal, and a broken clasp arm was rejoined. After repairs, the retentive forces were also measured at the initial time and up to 10,000 insertion/removal times. All data were analyzed by ANOVA/Tukey's test (a=0.05). Results: CP and 6-7 indicated constant similar retentive forces before and after repair. The retentive force of the 0.5 mm undercut tended to decrease more than that of the 0.25 mm undercut both before and after repair. There were no significant differences of retentive forces in the three methods of joining. Conclusion: A clasp with a 0.25 mm undercut made with CP should be used for long-term stability of the retentive forces. A new clasp arm without any gap distance should be remade and joined using laser welding for clasp repair after having failed.