An Overview of the Mechanical Integrity of Dental Implants

Abstract

With the growing use of dental implants, the incidence of implants' failures grows. Late treatment complications, after reaching full osseointegration and functionality, include mechanical failures, such as fracture of the implant and its components. Those complications are deemed severe in dentistry, albeit being usually considered as rare, and therefore seldom addressed in the clinical literature. The introduction of dental implants into clinical practice fostered a wealth of research on their biological aspects. By contrast, mechanical strength and reliability issues were seldom investigated in the open literature, so that most of the information to date remains essentially with the manufacturers. Over the years, implants have gone through major changes regarding the material, the design, and the surface characteristics aimed at improving osseointegration. Did those changes improve the implants' mechanical performance? This review article surveys the state-of-the-art literature about implants' mechanical reliability, identifying the known causes for fracture, while outlining the current knowledge-gaps. Recent results on various aspects of the mechanical integrity and failure of implants are presented and discussed next. The paper ends by a general discussion and suggestions for future research, outlining the importance of mechanical considerations for the improvement of their future performance.

Figure 1

Implant components: (a) implant body, (b) abutment screw, and (c) abutment.

Figure 2

Macroscale photographs of retrieved fractured implants and implant's components: (a) fractured implant, (b) fractured abutment screw, and (c) fractured abutment.

Figure 3

Failure analysis of retrieved fractured Ti-6Al-4V implant (a) and CP-Ti implant (b). (A1) and (B1) are macroscopic views of the fracture surface of the implant. (A2) and (B2) show fatigue striations on retrieved fractured implants. (A3) and (B3) show fatigue striations on dental implants fractured in laboratory conditions in room air. Note the high resemblance of the in vivo and in vitro fracture surface topographies.

Figure 4

Typical surface topography of dental implants that were fractured and retrieved from the oral cavity. Note the numerous secondary cracks, arrowed in yellow. Embedded foreign particles (arrowed in red) are associated with the crack path; (a), (b), and (d) originate from grit-blasted and etched implants, while (c) originates from an as-machined surface. Reprinted with permission from [35].

Figure 5

The involvement of embedded ceramic particle in fatigue crack initiation in dental implants. The origin of the fatigue crack was traced to the implant surface. The connection to the embedded particle left behind during the surface treatment can be easily observed.

Figure 6

Metallographic section from in vitro fatigue testing of 3.3 mm implant diameter. The length and width of the implant and abutment are indicated. The upper red arrow indicates testing force applied to the implant abutment and the force direction at an angle of 30° off-axis. The red circles indicate the different fracture location found for this implant diameter. The magnified picture shows the fracture location and the corresponding metal width at the fracture location. Reprinted with permission from [46].

Figure 7

Embedded foreign particles on full cracks and crack-like defects, as identified on grit-blasted (with or without etching) implants. The white arrows mark the defects (full cracks or crack-like defects) and the white circles mark embedded foreign particles. Reprinted with permission from [49].