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This study investigated the surface characteristics and biocompatibility of ultrafine-grain pure titanium (UFG Ti) after sandblasting and acid etching (SLA) treatment to determine an effective method for modification of UFG Ti dental implants. The UFG Ti was processed by equal-channel angular pressing (ECAP). The micromorphology, roughness, and wettability of its surface were studied after SLA modification in different conditions. Rat bone marrow mesenchymal stem cells were subsequently seeded onto the specimens to evaluate the biocompatibility of cell adhesion, proliferation, and differentiation compared with commercially pure titanium (CP Ti). The results showed that surface characteristics of UFG Ti were affected by the pressure of sandblasting and acid etching time in addition to material properties. The favorable hierarchical porous structure that would benefit cell adhesion was formed on the UFG Ti surface when the pressure of sandblasting was 0.6 MPa and the acid etching time was 5 min; at this time, UFG Ti promoted proliferation and differentiation to a greater extent than CP Ti because of its excellent wettability. From this study, it could be seen that UFG Ti can be used as a dental implant material after proper surface modification.

Osseointegration is the key to implant stability and occlusal support. Biomechanical response and remodeling of peri-implant bone occurs under impact loading. Sclerostin participates in bone formation and resorption through Wnt and RANKL pathways. However the mechanism of microdamage and expression of sclerostin in peri-implant bone under impact load is still unclear. In present study, specific impact forces were applied to the implants with favorable osseointegration in rabbits. The microdamage of peri-implant bone and the expression of sclerostin, β-catenin and RANKL during the process of bone damage and remodeling were investigated by micro-CT, histology, immunofluorescence and RT-qPCR analysis. Interface separation and trabecular fracture were found histologically, which were consistent with micro-CT analyses. Throughout remodeling, bone resorption was observed during the first 14 days after impact, and osseointegration and normal trabecular structure were found by 28 d. The expression of sclerostin and RANKL increased after impact and reached a maximum by 14 d, then decreased gradually to normal levels by 28 d. And β-catenin expression was opposite. Results indicated that sclerostin may involve in the peri-implant bone damage caused by impact and remodeling through Wnt/β-catenin and RANKL/RANK pathways. It will provide a new insight in the diagnosis and treatment for patients suffering impact.

The aim of this in vitro and in vivo study was to evaluate the fracture strength and osseointegration of an ultrafine-grained pure titanium (UFG-Ti) mini dental implant, prepared by equal channel angular pressing (ECAP) after macro-morphology optimization. UFG-Ti was prepared by ECAP using four passes in route Bc with the internal channel angle of 120°at room temperature. Furthermore, its microstructure and mechanical properties were studied. In optimization, a three-dimensional finite element model (FEM) composed of an UFG-Ti mini implant and alveolar bone was established to improve the implant surface area and decrease the stress distribution. Then, optimized mini implants were fabricated using UFG-Ti, and a fracture strength test was performed. For the in vivo study, UFG-Ti mini implants were inserted into rabbit femurs. A histological assessment and a pullout test were performed to evaluate its osseointegration ability. The results show that the ultimate tensile strength of UFG-Ti (685 ± 35 MPa) was significantly higher than that of commercial pure titanium (CP-Ti grade 4, 454 ± 27 MPa). After optimization, the surface area of the 2.5 mm diameter mini implant was 19% higher than that of the standard-thread mini implant, and the maximum equivalent stress (Max EQV stress) decreased by 28% in cortical bone and by 33.1% in cancellous bone, when the thread height was 0.3 mm and the pitch was 0.67 mm. The fracture strength of the UFG-Ti mini implants (328 ± 21 N) was significantly higher than that of CP-Ti grade 4 mini implants (197 ± 11 N). The in vivo study showed favorable osseointegration in both the UFG-Ti and CP-Ti groups, but the osseointegration strength of the optimized mini implants was higher than that of the standard-thread mini implants. In conclusion, the fracture and osseointegration strength had been significantly improved for UFG-Ti mini dental implant after optimization. The excellent mechanical properties and osseointegration of the UFG-Ti mini implant suggest its feasibility for clinical application.