Articles - Forum Implantologicum

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Feature Article

May 25, 2021 // 25 min read

Surface Modifications of Dental Implants – A Review of Developments and Current Trends

Abstract

Since the pioneering discovery made by Professor P.I. Brånemark and coworkers that titanium achieves direct contact with bone, the replacement of missing teeth with dental implants has evolved into a routine procedure in dentistry. While the first dental implants were made of titanium with a turned surface, subsequent titanium implants had more textured surfaces with higher roughness values, corresponding to greater surface areas. These surface modifications were achieved by either additive or subtractive techniques. Next, chemical surface modifications produced titanium implants with a higher surface energy and hydrophilic properties. While surface modifications were first performed on titanium implants, modifications on the surface of titanium alloys and zirconia followed later. Preclinical and clinical research has shown that surface modifications have a profound effect on the process of osseointegration and implant stability; implants with a microrough surface accelerate bone apposition and increase mechanical stability, and hydrophilicity further accelerates osseointegration. It must be noted that only a vague picture exists of how physicochemical implant properties translate into cell responses. Nevertheless, macrophages, which are among the first cells to come in contact and to interact with a biomaterial, seem to be key players. Although excellent clinical long-term data exist for certain implant brands, it is of value to create an overview of how and why surfaces have evolved to where they are today and then discuss some of the more recently highlighted possible adverse effects of surface modifications on dental implants.

Introduction

Dental implants have become a predictable and effective treatment option for the replacement of missing teeth in completely and partially edentulous patients, provided that some guidelines are strictly followed. The greatest credit in implant dentistry goes to Professor P.I. Brånemark, who discovered that commercially pure titanium achieves direct contact with bone (Brånemark et al. 1969, 1977). Since then, titanium has been the material of choice for dental implants due to its proven biocompatibility and excellent mechanical strength and resilience. The first dental implants had a machined and therefore rather smooth (Sa < 0.5 µm) titanium surface and were used for decades, but required several months to achieve safe osseointegration (Albrektsson & Sennerby 1991). The next generation of dental implants had more textured surfaces with higher roughness values that were produced by various technologies. Preclinical studies have shown that increasing the surface roughness, within a certain roughness value range, accelerates the osseointegration process and results in higher removal torque values (Bosshardt et al. 2017). Clinically, these microrough (or moderately rough) surfaces with Sa = 1-2 µm reduce the healing time and allow earlier loading (Cochran et al. 2002; Cochran et al. 2007; Cochran et al. 2011). Furthermore, there is good evidence that this new generation of dental implants with a microrough surface also yields better clinical outcomes in terms of implant survival than the first generation of implants with a machined surface (Albrektsson et al. 2012; De Bruyn et al. 2017). Further surface modifications resulted in higher surface energy and in the formation of nanostructures and higher hydrophilicity/wettability. These third-generation implants further accelerated osseointegration, as shown in preclinical studies, and reduced the healing time (Buser et al. 2004; Lai et al. 2009; Lang et al. 2011; Oates et al. 2007). Currently, implants with a microrough surface may be regarded as the gold standard in implant dentistry. The aims of this review are 1) to summarize surface modification techniques for dental implants and 2) to describe the effect of surface modifications on osseointegration in preclinical models. The influence of surface modifications on soft tissue integration, albeit of interest and significance, will not be covered in this review, but information can be found in recent reviews (Atsuta et al. 2016; Sculean et al. 2014; Wang et al. 2016). Likewise, biomimetic coating with or without drugs or growth factors will not be discussed.

Fig. 1: Scanning electron micrograph of a machined titanium surface (kindly provided by Insititut Straumann AG, Basel, Switzerland)

Fig. 2: Scanning electron micrograph of a titanium plasma-sprayed (TPS) surface (from Buser et al. 1991)

Fig. 3: Scanning electron micrograph of a titanium implant sandblasted with large grit (kindly provided by Insititut Straumann AG, Basel, Switzerland)

Fig. 4: Scanning electron micrograph showing a titanium implant surface morphology using acid-etching (kindly provided by Insititut Straumann AG, Basel, Switzerland)

Fig. 5: Scanning electron micrograph of a zirconia surface after sandblasting and alkali etching (from Saulacic et al. 2012 with permission)

Fig. 6: Scanning electron micrograph of an SLA® titanium implant surface after sandblasting with large grit and acid etching (from Janner et al. 2018 with permission)

Fig. 7a: Low- (a) and high-magnification (b) scanning electron micrographs of a Roxolid® implant surface after sandblasting with large grit and acid etching followed by SLActive® treatment (from Saulacic et al. 2012 with permission)

Fig 7b: Low- (a) and high-magnification (b) scanning electron micrographs of a Roxolid® implant surface after sandblasting with large grit and acid etching followed by SLActive® treatment (from Saulacic et al. 2012 with permission)

Fig. 8a: Low- (a) and high-magnification (b) field-emission-gun scanning electron microscopy of an ultrafine-grained titanium implant surface with SLActive® treatment (from Chappuis et al. 2018 with permission)

Fig. 8b: Low- (a) and high-magnification (b) field-emission-gun scanning electron microscopy of an ultrafine-grained titanium implant surface with SLActive® treatment (from Chappuis et al. 2018 with permission)

Fig. 9a: Scanning electron micrographs illustrating the surfaces of zirconia (a) and zirconia/alumina (b) implants after sandblasting and acid etching (from Chappuis et al. 2016 with permission)

Fig. 9b: Scanning electron micrographs illustrating the surfaces of zirconia (a) and zirconia/alumina (b) implants after sandblasting and acid etching (from Chappuis et al. 2016 with permission)

Fig. 10: Scanning electron micrograph of a zirconia implant after sandblasting and acid etching (ZLA® surface treatment) (from Janner et al. 2018 with permission)

Fig. 11: Scanning electron micrograph of a titanium TiUnite® implant with a surface produced by electrochemical anodization (kindly provided by Insititut Straumann AG, Basel, Switzerland)

Fig. 12a: Field-emission-gun scanning electron microscopy of a cp titanium surface with SLActive® treatment (a) and an ultrafine-grained titanium implant surface with SLActive® treatment (b) illustrating nanostructures (from Chappuis et al. 2018 with permission)

Fig. 12b: Field-emission-gun scanning electron microscopy of a cp titanium surface with SLActive® treatment (a) and an ultrafine-grained titanium implant surface with SLActive® treatment (b) illustrating nanostructures (from Chappuis et al. 2018 with permission)

Fig. 13a-b: Low- (a) and high-magnification (b) micrographs of a hollow-cylinder TPS implant explanted from a human. Both images show excellent bone-to-implant contact after 28 years in service

Fig. 14: Mean percentage of direct bone-to-implant contact (%BIC) of different implant surfaces at 3 and 6 weeks. E, electropolished; HA, hydroxyapatite-coated plasma-sprayed; SL, sandblasted with large grit; SLA, sandblasted with large grit and acid-etched; SMP, sandblasted with medium grit and acid pickling; TPS, titanium plasma-sprayed (from Buser et al. 1991; modified from Bosshardt et al. 2017 with permission)

Fig. 15: Diagram showing the degree of osseointegration (presented as percentage of bone-to-implant contact [% BIC]) from day 0 to 12 weeks at sandblasted and acid etched (SLA) and turned (T) titanium implants. Osseointegration – BIC% (entire intraosseous portion). *p<0.05 (from Abrahamsson et al. 2004 with permission)

Fig. 16: Graph illustrating the effect of implant surface chemistry on the percentage of bone-to-implant contact (%BIC) over time. SLA modified, treated with sandblasting and acid etching followed by chemical activation (from Buser et al. 2004; modified from Bosshardt et al. 2017)

Fig. 17: Graph illustrating the effect of implant surface chemistry on the percentage of new bone-to-implant contact (%BIC) over time. SLA, sandblasted and acid etched; SLActive, chemically activated and treated with sandblasting and acid etching (from Lang et al. 2011; modified from Bosshardt et al. 2017 with permission)

Fig. 18: Histogram illustrating the effect of implant surface chemistry on the percentages of new bone, old bone, bone debris and soft tissue covering the implant surface after 1, 2, 4 and 6 weeks of healing (from Bosshardt et al. 2011 with permission)

Fig. 19a-b: Low- (a) and high-magnification (b) micrographs of an ultrafine-grained titanium implant in the mandible of a miniature pig 8 weeks after installation. Note the excellent bone-to-implant contact (from Chappuis et al. 2018 with permission)

Fig. 20: Graph illustrating the effect of the implant materials on the percentage of bone-to-implant contact (%BIC) and the percentage of implant surface along the grooves covered with multinucleated giant cells (%MNGCs) over time (from Saulacic et al. 2012 with permission)

Fig. 21: Graph illustrating the effect of implant surface modifications on the percentage of bone-to-implant contact (%BIC) for sandblasted (SB), sandblasted and acid-etched (SB-AC), and sandblasted and alkaline-etched (SB-AL) zirconia implants (modified from Saulacic et al. 2014 with permission)

Fig. 22: Histogram illustrating the percentage of bone-to-implant contact (%BIC – median values) for titanium (Ti), alumina-toughened zirconia (ZrO2/Al2O3), and zirconia (ZrO2) implants after 4 and 8 weeks of healing in the maxillae of miniature pigs (modified from Chappuis et al. 2016 with permission)

Fig. 23: Osseointegrated (a) zirconia (ZrO2) and (b) alumina-toughened zirconia (ZrO2/Al2O3) implants after 4 weeks of healing and tissue integration in a miniature pig maxilla (from Chappuis et al. 2016 with permission)