In Vitro Evaluation of the Effects of Multiple Oral Factors on Dental Implants Surfaces
Presence of metal ions and debris resulting from corrosion processes of dental implants in vivo can elicit adverse tissue reactions, possibly leading to peri-implant bone loss and eventually implant failure. This study hypothesized that the synergistic effects of bacterial biofilm and micromotion can cause corrosion of dental implants and release of metal ions in vivo. The goal is to simulate the oral environment where an implant will be exposed to a combination of acidic electrochemical environment and mechanical forces. Four conditions were developed to understand the individual and synergistic effects of mechanical forces and bacterial biofilm on the surface of dental implants; In condition 1, it was found that torsional forces during surgical insertion did not generate wear particle debris or metal ions. In condition 2, fatigue tests were performed in a wet environment to evaluate the effect of cyclic occlusal forces. The mechanical forces applied on the implants were able to cause implant fracture as well as surface corrosion features such as discoloration, delamination, and fatigue cracks. Immersion testing (condition 3) showed that bacteria (Streptococcus mutans) were able to create an acidic condition that triggered surface damage such as discoloration, rusting, and pitting. A novel testing setup was developed to understand the conjoint effects of micromotion and bacterial biofilm (condition 4). Surface damage initiated by acidic condition due to bacteria (condition 3), can be accelerated in tandem with mechanical forces through fretting-crevice corrosion. Permanent damage to surface layers can affect osseointegration and deposition of metal ions in the surrounding tissues can trigger inflammation.
Figure 1. Process involved in designing a quasi-static test: (a) Whole view of the Materials Testing System (MTS) and implant fixture. (b) Fractured implant at end of the quasi-static test. Figure 2. Axial force versus axial displacement curve generated from quasi-static test. Figure 3. (a) Dental implant cemented in sawbone material with a spacer placed at the bottom to provide a 30° inclination. (b) Implant fixture clamped at the base of the MTS system with load applied from the top. (c) Fatigue test in PBS-containing environment.
(a) A sketch explaining the dimensions of the custom made chamber. (b) Whole view of the 3D printed chamber. (c) Top view sketch displaying circular port of entry for mechanical forces and a rectangular slot for placing implant fixture. (d) Top view picture of the fabricated chamber. (e) Modified sawbone block used to make implant fixture that will snug-fit into the rectangular slot.
Low magnification images of implants post-fatigue test: (a) I1. (b) I2. (c) I3. (d) I4. Fracture observed with only I1.
Qualitative analysis of the surface post-fatigue test: (a) Control. (b) Discoloration at the implant-abutment interface of I1. (c) Yellow purple discoloration of the rough surface of I2. (d) Delamination of the top surface of I1. (e) Black taints at the rough surface I2. (f) Surface crack and propagation of fatigue crack in the smooth-rough interface of I3.
Control Implant (I5): (a) Whole view of the implant. (b) Flawless junction of smooth-rough surface of I5. (c) 3D depth up analysis showing a deformation free surface with uniform color distribution. (d) SEM image demonstrating an intact surface oxide layer. (e through h) Implant immersed in bacteria (I6). (e) Whole view of the implant with visible color change throughout the surface. (f) Surface color change from grey to yellow and blue. (g) Surface deformation in the form of micropits. (h) SEM image displaying surface deformation.
Novel chamber setup to study the synergistic effects of micromotion and bacterial biofilm. (a) An overview of the custom made setup placed inside the Envirobath chamber. (b) A closer view displaying the inlet and outlet. (c) Top opening of the chamber to facilitate mechanical loading.
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