Laser Peening of Endosseous Implants With a Trilobe Internal Connection

Objective: To investigate the effect of laser peening on the fatigue resistance of a 3.5-mm diameter implant with an internal trilobe connection (Replace Select, Nobelbiocare, Yorba Linda, CA). Methods: Eighteen implants were embedded into acrylic resin blocks (Palapress Vario, Heraeus Kulzer) with 3.0 mm of the implant above the acrylic to simulate the worst case clinical scenario for crestal bone loss as per ISO 14801. Half of the specimens were laser-peened circumferentially around the 1.5-mm polished collar with argon shielding using a dental Nd:YAG laser welding machine (Neolaser L, Girrbach) with a 0.8-mm spot diameter, a 3.0-ms pulse duration, and an excitation voltage of 150 V. The control specimens were taken directly from the manufacturer's sterile packaging and embedded into the acrylic resin. Implants were fatigue tested in 37^oC deionized water using a servohydraulic test machine (Minibionix II, MTS) with a 2 Hz sine wave and 0.1 min/max load ratio. Two time-load profiles were used. The load amplitude started at 1.8 N and increased by 1.8 N every 30 (n=10) or 60 (n=8) cycles until fracture. The fracture surfaces were observed using SEM. Step-stress statistical analysis with a Weibull lifetime distribution and an inverse power law load-life relation was used to estimate the median lifetime under a constant load amplitude of 600 N. Results: Failure originated from the internal trilobe platform in all specimens. Median cycles to failure and 95% confidence intervals were 2,907 (1,523-5,548) for control specimens and 3,310 (1,093-10,027) for laser-peened specimens. Laser-peened specimens had longer estimated lifetime, but this difference was not statistically significant (P>0.05). Conclusion: Step-stress analysis with nine specimens per group was not able to detect an effect of laser peening on the in vitro fatigue lifetimes of dental implants.