Yang et al. prepared a Zn-HA coating on Ti plates by an electrochemical process, and the SEM examination showed irregularly shaped rod-like crystals with hexagonal cross-section; this corresponded well with the current study results. They also concluded that a Zn-HA coating improves proliferation and differentiation of osteoblasts and would enhance implant osseointegration [11].

Ceramic coatings must have good adhesion to the implant to act as a barrier and assure good protection to the substrate. The adhesion test was performed in this study to verify the adequacy of the coating thickness.

An improvement of coating adhesion occurs as their thickness decrease, although very thin coatings may not attain the protection requirements [33]. Contrariwise, it is recognized that thick ceramic coatings may develop cracks after the deposition procedure [34]. The adhesive tape test read the highest score (5A); this might be attributed to the fine homogenous, closely packed, coating particles that appear crack free and highly sintered, as proved by the SEM results in Figs. 4, 5, and 6.

Dental implants do exist with various geometries, different lengths and diameters, and features, such as, pits, pores, vents, and slots. Essentially, a highly rough surface produces better initial stability and anchorage. Moreover, a rough surface with a larger surface area facilitates particles exchange between the implant and surrounding tissues. It could be concluded that such coatings with an increased surface area could have better clinical performance [35]. This developed electro-deposition process, can be applied  to deposit a nano-HA-Zr coating to complex implant surfaces and thus increases their surface area, surface roughness, initial stability and clinical performance. 

Supplementary, biocompatibility, anti-bacterial activity, and in vivo investigations are required to correlate between the HA-Zn coating properties and their effect on bone formation and osseo-integration.