Objectives: This study was to investigate whether the interim rotational strain affects the bone contact rate and removal torque of osseointegrated implant.  Methods: Ninety male rats were randomly divided into five groups; NoR, 2wR, 4wR, 8wR, and 12wR.  A implant made of pure titanium (f1.6mmx4.0mm) was inserted in 1/4 of proximal tibia.  The NoR group as control received no strain, while 2wR, 4wR, 8wR, and 12wR groups received the interim rotational strain (ninety degrees) at 2, 4, 8, and 12 weeks after the implantation, respectively.  The removal torque of implants (N·cm) was measured in vivo and the bone contact rate (%) were calculated histomorphologically.  The data was analyzed with one-way ANOVA, and Scheffé method (p<0.05).  Results: In the NoR, the removal torque and the bone contact rate gradually increased with time.  A similar tendency of increase in the removal torque was observed in the strained category.  At 16-week stage, the torque in the 2wR, 4wR, 8wR, and 12wR was 4.16±1.47, 4.73±1.46, 4.22±1.34, and 4.10±1.48N·cm, respectively, and had no significant difference from the NoR (4.90±1.20N·cm).  The bone contact rate in the strained category except the 4wR did not increase from 8-week stage, and with significant difference from the NoR at 16-week stage (p<0.05).  The 4wR accelerated the bone formation at 8-week stage and maintained the high value (61.1±11.26%) until 16-week stage without significant difference from the NoR (72.0±5.24%).  Conclusion: The removal torque would receive no adverse effect by the interim rotational strain, while the bone contact rate showed a different change with the strained time of interim strain. The appropriate time for the interim rotational strain might exist to achieve the acceleration of bone formation.

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