Biomechanical and biological factors can co-dependently influence the establishment of implant-tissue integration; thus, concurrent evaluation of these factors should provide a better understanding of osseointegration. This study aimed to establish and validate an in vivo rat model frequently used in molecular/cellular biology for implant biomechanical studies. We tested the hypotheses that the implant push-in test assesses the degree of osseointegration by the breakpoint load at the implant-tissue interface and that it sensitively differentiates between the effects of different implant surface topographies. The implant push-in test, which produces a consistent load-displacement measurement, was used to test miniature cylindrical titanium implants placed at the distal edge of the adult rat femur. The push-in test values obtained at each post-implantation healing point (weeks 0, 2, 4, and 8) significantly increased in a time-dependent manner. The implant surface after the push-in test was associated with remnant tissues containing host-derived elements, such as calcium, phosphate, and sulfate. In this model, acid-etched implants (average roughness, 0.159 microm) showed significantly greater push-in test values than did turned implants (average roughness, 0.063 microm) throughout the experimental period (p < 0.0001). These results support the validity of the push-in test in rats, which may be used as a rapid and sensitive biomechanical assay system for implant osseointegration research.

Objectives To investigate the role of different levels of pH of artificial saliva under simulated oral environment on the corrosion behavior of commercially pure titanium (cp‐Ti) and Ti‐6Al‐4V alloy. Special attention is given to understand the changes in corrosion kinetics and surface characterization of Ti by using electrochemical impedance spectroscopy (EIS). Materials and methods Fifty‐four Ti disks (15‐mm diameter, 2‐mm thickness) were divided into six groups (n = 9) as a function of saliva pH (3, 6.5, and 9) and Ti type. Samples were mechanically polished using standard metallographic procedures. Standard electrochemical tests, such as open circuit potential, EIS, and potentiodynamic tests were conducted in a controlled environment. Data were evaluated by two‐way ANOVA, Tukey multiple comparison test, and independent t‐test (α = 0.05). Ti surfaces were examined using white‐light‐interferometry microscopy and scanning electron microscopy (SEM). Results Saliva pH level significantly affected the corrosion behavior of both Ti types. At low pH, acceleration of ions exchange between Ti and saliva, and reduction of resistance of Ti surface against corrosion were observed (P < 0.05). Corrosion rate was also significantly increased in acidic medium (P < 0.05). Similar corrosion behavior was observed for both Ti types. The white‐light‐interferometry images of Ti surfaces show higher surface changes at low pH level. SEM images do not show detectable changes. No pitting corrosion was observed for any group. Conclusions The pH level of artificial saliva influences the corrosion behavior of cp‐Ti and Ti‐6Al‐4V alloy in that lower pH accelerates the corrosion rate and kinetics. The corrosion products may mitigate the survival rate of dental implants.

Despite reports of CpTi being electrochemically stable down to pH 2.0, this study suggests degradation peaks at near neutral pH values in the presence of motion. At pH 6.0, the passive film layer, typically protecting the surface of titanium may not be reformed cohesively, resulting in more tribocorrosion products at the surface, which are easily sheared off. These findings elevate concern with regard to dental implants because the average pH of the oral cavity is 6.3.

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To treat impairments in hard tissues or overcome pathological calcification in soft tissues, a detailed understanding of mineralization pathways of calcium phosphate materials is needed. Here, we report a detailed mechanistic study of hydroxyapatite (HA) mineralization pathways in an artificial saliva solution via in situ liquid cell transmission electron microscopy (TEM). It is found that the mineralization of HA starts by forming ion-rich and ion-poor solutions in the saliva solution, followed by coexistence of the classical and nonclassical nucleation processes. For the nonclassical path, amorphous calcium phosphate (ACP) functions as the substrate for HA nucleation on the ACP surface, while the classical path features direct HA nucleation from the solution. The growth of HA crystals on the surface of ACP is accompanied by the ACP dissolution process. The discoveries reported in this work are important to understand the physiological and pathological formation of HA minerals, as well as to engineer the biomineralization process for bone healing and hard tissue repairs.

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C(dl), capacitance of double layer; E(corr), corrosion potential; EIS, electrochemical impedance spectroscopy; I(corr), corrosion current density; I(pass), passivation current density; LPS, lipopolysaccharide; OCP, open circuit potential; R(p), polarization resistance; Ti, titanium.

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