Electrical stimulation to promote osseointegration of bone anchoring implants: a topical review

Abstract

Electrical stimulation has shown to be a promising approach for promoting osseointegration in bone anchoring implants, where osseointegration defines the biological bonding between the implant surface and bone tissue. Bone-anchored implants are used in the rehabilitation of hearing and limb loss, and extensively in edentulous patients. Inadequate osseointegration is one of the major factors of implant failure that could be prevented by accelerating or enhancing the osseointegration process by artificial means. In this article, we reviewed the efforts to enhance the biofunctionality at the bone-implant interface with electrical stimulation using the implant as an electrode. We reviewed articles describing different electrode configurations, power sources, and waveform-dependent stimulation parameters tested in various in vitro and in vivo models. In total 55 English-language and peer-reviewed publications were identified until April 2020 using PubMed, Google Scholar, and the Chalmers University of Technology Library discovery system using the keywords: osseointegration, electrical stimulation, direct current and titanium implant. Thirteen of those publications were within the scope of this review. We reviewed and compared studies from the last 45 years and found nonuniform protocols with disparities in cell type and animal model, implant location, experimental timeline, implant material, evaluation assays, and type of electrical stimulation. The reporting of stimulation parameters was also found to be inconsistent and incomplete throughout the literature. Studies using in vitro models showed that osteoblasts were sensitive to the magnitude of the electric field and duration of exposure, and such variables similarly affected bone quantity around implants in in vivo investigations. Most studies showed benefits of electrical stimulation in the underlying processes leading to osseointegration, and therefore we found the idea of promoting osseointegration by using electric fields to be supported by the available evidence. However, such an effect has not been demonstrated conclusively nor optimally in humans. We found that optimal stimulation parameters have not been thoroughly investigated and this remains an important step towards the clinical translation of this concept. In addition, there is a need for reporting standards to enable meta-analysis for evidence-based treatments.

Keywords: Bone formation; Electrical stimulation; Osseointegration; Prostheses; Titanium implants.

Fig. 1

Endogenous vs exogenous electrode configurations for electrical stimulation. Created with BioRender.com

Fig. 2

Pulsed electrical current can have many different shapes and waveforms. A Examples of monophasic waveforms above the zero baseline. A pulse above the baseline is said to have a positive polarity and a pulse below the baseline is said to have a negative polarity. Examples of biphasic waveforms. The pulse crosses the zero baseline to appear both above and below the baseline. The pulse shape may be B symmetric and charged-balanced or C asymmetric and/or charged unbalanced

Fig. 3

Amplitude vs stimulation duration. Current controlled in vivo studies 1) Bins-Ely et al. (2017) [48] 2) Buch et al. (1984) [46], 3) Colella et al. (1981) [50], 4) Song et al. (2009) [9] 5) Shayesteh et al. (2007) [49], 6) Dergin et al. (2013) [10]. * = Stimulation duration and evaluation assessment time point(s) differ