A considerable number of studies have shown that cells attach better to hydrophilic surfaces than to hydrophobic surfaces.1 But what, exactly, is hydrophilicity? Here, we explain what it is, how it works, and how it can benefit your implant treatment outcomes.

What is hydrophilicity?

Hydrophilicity refers to the affinity that a material has in relation to water. If the contact angle of a water droplet on the surface is less than 90 degrees, that material can be considered hydrophilic.2 Conversely, if the contact angle is more than 90 degrees, it is hydrophobic.

Some surface treatment procedures can make it ‘ultra-hydrophilic’, whereby a drop of water (or blood) spreads and wets the surface when it comes into contact with the surface at close to 0 degrees.3

 

What causes hydrophilicity?

Surface hydrophilicity is determined by surface chemistry, or chemical composition, and procedures exist whereby the chemical composition of a surface can be altered. One example is anodization.

Anodization, briefly put, involves submerging a titanium implant in an electrolytic fluid and applying an electric potential (voltage). This increases the thickness of the titanium oxide layer and alters the topography.4 During anodization, hydroxyl groups, which have been shown to promote bone formation when present on the surface,5 6 7 are formed in high density. Phosphates, which can increase osteoblastic cell attachment,8 9 can be added to the electrolyte to incorporate them into the oxide layer.

Figure 1: Phosphate from the electrolyte can be incorporated into the oxide layer during anodization. The amount of free hydroxyl groups on the surface is increased by anodization.

Research has found that, when compared to sand-blasted and acid-etched implants, anodized surfaces have the most hydroxyl groups.10 Furthermore, the surface charge has also been proven to enable higher thrombogenicity (blood clotting) than sand-blasted and acid-etched implant surfaces11; the first of a number of biological processes that enable bone healing.12

(A) Representative low magnification fluorescence images of stained sandblasted acid‐etched and anodized implants are shown. (B, C) Quantification of fibrin coverage and nuclei present on implant surfaces. Data are mean ± SD (n = 6). ** indicates P < 0.01 and **** indicates P < 0.0001 (Student’s t‐test) Clinical Implant Dentistry and Related Research, Volume: 21, Issue: S1, Pages: 8-14, First published: 28 February 2019, DOI: (10.1111/cid.12737)
Figure 2: Quantitative in vitro comparison of the thrombogenicity of sandblasted acid-etched and anodized dental implants

Implant surfaces and hydrophilicity

Increasing the hydrophilicity of an implant’s surface can lead to a better interaction between this surface and the surrounding biological environment.13 This increase in activity has a number of benefits for the implant, chief among them being fast osseointegration.14

 

Hydrophilicity and abutment surfaces

Of course, osseointegration is not the only factor that determines whether a dental implant is successful in the long term.15 Dense soft tissue attachment to the abutment surface is also important in this regard, having been shown to act as a protective seal for the underlying bone against bacterial irritation and inflammation.16 17 18 19 20

A number of studies have demonstrated that hydrophilic abutment surfaces may help to facilitate soft tissue attachment and cell adhesion,21 22 23 24 both of which are important factors for long-term implant survival.

Xeal™: A hydrophilic abutment surface for the Mucointegration™ process

Xeal is an anodized abutment surface that, through its surface chemistry and topography properties, has been designed to support soft tissue stability and attachment to the abutment.11 Introduced for the first time in 2019*, this anodized and nanostructured surface is already supported by a clinical study with two-years’ follow-up, the findings of which demonstrate a significant increase in keratinized soft tissue height and better general soft tissue outcomes when compared to a machined surface.25

TiUltra™: More than roughness

Introduced in parallel with the Xeal abutment surface, TiUltra is an ultra-hydrophilic implant surface, also anodized. The surface chemistry has been designed with the aim of positively influencing its interaction with cells and leading, ultimately, to early osseointegration and long-term bone stability.26 Its multi-zone topography gradually changes from a minimally rough and non-porous collar to a moderately rough and porous implant apex, a transition that respects the natural tooth’s own shift from hard, dense cortical bone to cancellous bone.27

Figure 3: Xeal and TiUltra are a synergy of anodized surfaces, designed to enhance tissue integration from abutment to implant apex.

A preclinical study of TiUltra showed that all areas of the implant surface osseointegrate equally, with high bone-to-implant contact.28

In order to preserve the condition of the surface, Xeal and TiUltra both have a Protective Layer that dissolves upon contact with a fluid, i.e. blood. This layer significantly decreases the amount of carbon build-up on these surfaces, maintaining the surface chemistry allowing for hydrophilicity to be maintained.29

More to explore

*Not available for use in all markets. Please contact your local sales rep for more information.

References

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  2. Albrektsson T, Wennerberg A. On osseointegration in relation to implant surfaces. Clin Implant Dent Relat Res 2019;21:4-7
  3. Albrektsson T, Wennerberg A. On osseointegration in relation to implant surfaces. Clin Implant Dent Relat Res 2019;21:4-7
  4. Albrektsson T, Wennerberg A. On osseointegration in relation to implant surfaces. Clin Implant Dent Relat Res 2019;21:4-7
  5. Fujibayashi S, Neo M, Kim HM, Kokubo T, Nakamura T. Osteoinduction of porous bioactive titanium metal. Biomaterials. 2004;25:443-450.
  6. Lai HC, Zhuang LF, Zhang ZY, Wieland M, Liu X. Bone apposition around two different sandblasted, large-grit and acid-etched implant surfaces at sites with coronal circumferential defects: an experimental study in dogs. Clin Oral Implants Res. 2009;20:247-253.
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  9. Park JW, Kim YJ, Jang JH, et al. Effects of phosphoric acid treatment of titanium surfaces on surface properties, osteoblast response and removal of torque forces. Acta Biomater 2010;6(4):1661-70.
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  11. Milleret V, Lienemann PS, Bauer S, Ehrbar M. Quantitative in vitro comparison of the thrombogenicity of commercial dental implants. Clin Implant Dent Relat Res. 2019;21:8–14
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  13. Sartoretto SC, Alves ATNN, Resende RFB, Calasans-Maia J, Granjeiro JM, Calasans-Maia MD. Early osseointegration driven by the surface chemistry and wettability of dental implants. J Appl Oral Sci 2015 May-June;23(3):279-297.
  14. Milleret V, Lienemann PS, Gasser A, Bauer S, Ehrbar M, Wennerberg A. Rational design and in vitro characterization of novel dental implant and abutment surfaces for balancing clinical and biological needs. Clin Implant Dent Relat Res 2019;21:e15-e24.
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  27. Milleret V, Lienemann PS, Gasser A, Bauer S, Ehrbar M, Wennerberg A. Rational design and in vitro characterization of novel dental implant and abutment surfaces for balancing clinical and biological needs. Clin Implant Dent Relat Res 2019;21:e15-e24
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  29. Milleret V, Lienemann PS, Gasser A, Bauer S, Ehrbar M, Wennerberg A. Rational design and in vitro characterization of novel dental implant and abutment surfaces for balancing clinical and biological needs. Clin Implant Dent Relat Res 2019;21:e15-e24

Posted by Chris Kendall