Mini Review Modifying an Implant: A Mini-review of Dental Implant Biomaterials Oliver K. Semisch-Dieter1, Andy H. Choi1, Besim Ben-Nissan1 and Martin P. Stewart1,* Abstract 1School of Life Sciences, Faculty of Science, University Dental implants have been used as far back as 2000BC, and since then have developed into highly sophisti- of Technology Sydney, Ultimo, cated solutions for tooth replacement. It is becoming increasingly important for the materials used in dental implants to exhibit and maintain favorable long-term mechanical, biological and more recently, aesthetic NSW, Australia properties. This review aims to assess the biomaterials used in modern dental implants, introducing their properties, and concentrating on modifications to improve these biomaterials. Focus is drawn to the promi- nent biomaterials, titanium (Ti) and zirconia due to their prevalence in implant dentistry. Additionally, novel coatings and materials with potential use as viable improvements or alternatives are reviewed. An effective *Correspondence to: dental biomaterial should osseointegrate, maintain structural integrity, resist corrosion and infection, and not Martin P. Stewart cause systemic toxicity or cytotoxicity. Current materials such as bioactive glass offer protection against bio- E-mail: martin.stewart@uts. film formation, and when combined with a titanium–zirconium (TiZr) alloy, provide a reliable combination edu.au of properties to represent a competitive alternative. Further long-term clinical studies are needed to inform the development of next-generation materials. Received: September 7 2020 Revised: December 7 2020 Keywords Accepted: January 4 2021 Biocompatibility, biomaterials, dental implant, titanium, zirconia. Published Online: March 19 2021 Significance Statement Available at: Biomaterials have become essential for modern implants. A suitable implant biomaterial integrates into the https://bio-integration.org/ body to perform a key function, whilst minimizing negative immune response. Focusing on dentistry, the use of dental implants for tooth replacement requires a balance between bodily response, mechanical structure and performance, and aesthetics. This mini-review addresses the use of biomaterials in dental implants with significant comparisons drawn between Ti and zirconia. Attention is drawn to optimizing surface modifi- cation processes and the additional use of coatings. Alternatives and novel developments are addressed, providing potential implications of combining biomaterials to form novel composites that combine and synergize the benefits of each material. Introduction situation, and optimizing the clinically rel- evant performance of that therapy” [2]. Biomaterials are crucial for modern med- The application of biomaterials as a ical applications, and in the last several dental implant is shown in Figure 1A; an decades, these materials have been refined endosseous fixture is used to replace the and improved for applications seen in root and support a dental prosthesis. Dental dentistry, orthopedics, drug delivery, and implants have become an evidence-based cardiology. Candidate materials include treatment for the replacement of missing polymers, metals (and their alloys), cera- teeth. Selecting a biomaterial for a den- mics, composites (e.g. carbon fiber), and tal implant requires additional considera- glass. For clinical use, the material must tions for biological, mechanical, and aes- not cause any adverse or damaging effects thetic properties. Modern dental implants to the patient [1]. This concept is known need to feature effective osseointegration as biocompatibility and was described by and maintain long-term stability of their Williams as, “the ability of a biomaterial favorable properties to maintain both the to perform its desired function with respect implant’s structure and the integrity of sur- to a medical therapy, without eliciting any rounding hard and soft tissue [3, 4]. undesirable local or systemic effects in the This review aims to assess the current recipient or beneficiary of that therapy, but state of biomaterials (Ti, zirconia, and generating the most appropriate beneficial novel materials) used in dental implants. cellular or tissue response to that specific Materials are assessed on their attributes, 12 BIOI 2021, Vol 2, No. 1, 12–21 https://bio-integration.org doi: 10.15212/bioi-2020-0034 © 2021 The Authors. Creative Commons Attribution 4.0 International License Mini Review BIOI 2021 AB Figure 1 (A) Illustrates a cross-sectional view of a dental implant and the surrounding oral tissue. (B) Selecting the appropriate material to use for the implant requires considerations of implant durability, cell adhesion, and physiological implications for implant biocompatibility, and aesthetic concerns for patient satisfaction. characteristics, comparison of strengths and weaknesses, deterring biofilm formation. Current surface topographies biocompatibility, and new advancements in addressing any include anodization, sandblasting, and polishing, however, issues or concerns. conclusive evidence on which specific surface topographies are optimal and why remains undetermined [9]. Titanium Alternative alloys Ti is widely used for medical applications and is currently It is known that Ti can form alloys to solve reactivity concerns the most commonly used material for dental implants. The [1]. Vanadium (V) and aluminum (Al) are common alloying popularity is in part due to the combination of its tensile elements for Ti (seen in Ti6Al4V alloy). Individually each strength, biocompatibility, ability to osseointegrate, density, element has shown potential adverse effects in high concen- corrosion resistance, and inert properties. Pure Ti, while trations, causing carcinogenicity and neurotoxicity [10–12]. being safe for most clinical use, has been observed to form However, reports on V also demonstrate antidiabetic effects an accumulation of Ti ions around the implant site. While and resulted in reduced weight gain and gastrointestinal dis- no material is entirely bioinert, such ions released from an comfort [1, 13]. Attempts are being made to replace these implant that fails to osseointegrate may induce proinflam- alloying elements with less toxic elements such as niobium matory responses from sensitization. Such failure occurs (Nb), tantalum (Ta), and palladium (Pd), to improve biocom- when there is a lack of biomechanical stability due to inad- patibility; however, Ti6Al4V remains a common choice [14]. equate osseointegration. Stability can be promoted by mod- When comparing a Ti alloy to surgical stainless steel and ifying the implant’s physiochemical properties and surface cobalt alloys, the superior quality of Ti is its corrosion resist- topography. Observations from failed Ti implants show an ance. The ability for Ti alloys to withstand corrosive environ- increased lymph node Ti ion concentration by 7.4–9 times ments and develop an oxide layer with a shorter repassiva- and lung Ti ion concentration by 2.2–3.8 times when com- tion time compared to other metal alloys, aids in preventing pared to a successfully integrated implant [5, 6] (Table 1). a release of ions which can potentially be toxic (cobalt) or Ti dental implants have been occasionally observed to result cause allergic reactions (nickel, found in stainless steel) [15]. in an allergic reaction. However, the exact mechanism for Ti A unique alloy, TiZr has shown clinical success in the past ion release and systemic effects remains unclear [7]. decade. Under the trade name Roxolid, Institut Straumann Surface modifications of Ti implants are performed to AG, Basel, Switzerland (a 15% Zr, 85% Ti composition), the improve osseointegration and modulate cell adhesion. The TiZr alloy was designed for dental implants, becoming a via- largest post-operative issue with such implants is biofilm-in- ble alternative to zirconia and other Ti-based implants [16]. duced mucositis, inflammation of mucous membranes, TiZr offers enhanced osseointegration compared to Ti6Al4V which can further develop into peri-implantitis, the inflam- and pure Ti and avoids the use of toxic alloying elements. mation of the gum and the surrounding bone structure. The Additionally, corrosion resistance can potentially reduce first generation of surface modification was developed in problems associated with peripheral Ti ion concentrations the 1960s, where machined Ti (smooth surface) was used [17–19]. A recent study observed that TiZr retains the ability to promote osseointegration by leaving a small degree of for surface enhancement without compromising the mechan- roughness. Second generation surface modifications have ical strength of the implant [20]. While TiZr dental implants been widely available since the 1990s and improve on the do not offer the aesthetic qualities of zirconia, they demon- first generation by creating a microscopically rough surface strate highly preferable qualities among clinically available topography. Finally, the current third generation (also known Ti alloy options. as bioactive surfaces) maintains similar roughness to the sec- TiNb is another alloy with favorable properties and ond generation and are modified chemically or topographi- provides a low elastic modulus similar to human cortical cally to promote osseointegration [8]. Most surface topogra- bone. It is clinically significant as it reduces the issue of phies minimize vertical deviation to 1 μm or less, effectively stress concentration between the implant and bone, thus Oliver K. Semisch-Dieter