Introduction

Dental implants increase the quality of life for many patients with tooth loss.¹ The material of choice for oral endosseous implants is pure titanium, introduced at the end of the 1960s by Branemark.² Although implants based on titanium and titanium alloys, such as Ti-6Al-7Nb and Ti- 6Al-4V,^{3, 4} are well evidence-based, it was demonstrated that their use can be correlated with a range of problems. One problem is a potential hypersensitivity to titanium.^{5, 9} Another problem could occur due to the gradient difference in the elastic moduli of a titanium implant and its surrounding bone. This may cause stress in the implant-bone interface during load transfer,^{10, 11} probably resulting in peri-implant bone loss.^{12, 13} Also, titanium can cause esthetic problems due to its lack of light transmission.¹⁴ This can provoke a dark shimmer of the peri-implant soft tissue in cases of thin biotype mucosa and / or mucosa recession around a titanium implant. This can be problematic especially in the presence of a high smile line.^{15, 16} Additionally, an increasing number of patients are demanding dental reconstructions of completely metal-free materials.¹⁵ As an alternative to titanium, ceramic implants are proposed, which were first introduced about 40 years ago and were made from aluminum oxide.^{17, 22} Due to frequent fracture incidence, this material was substituted by titanium.²³ Nowadays, ceramic dental implants are made of zirconia, which seems to be a better suitable alternative to titanium because of its tooth-like color, mechanical properties, biocompatibility, and low plaque affinity.²⁴ But a systematic review of the literature by Andreiotelli et al¹⁵ from 2009 concludes that the scientific clinical data are not yet sufficient to recommend ceramic implants for routine clinical use. This corresponds to a grade C recommendation of the definitions of types of evidence originating from the US Agency for Health Care Policy and Research.¹⁵ Furthermore, the stress distribution of a zirconia implant to the surrounding bone could be associated with even higher stress peaks compared to titanium, due to the higher elastic modulus of zirconia of 210 GPa.²⁵

Another biocompatible material with an elastic modulus of 3.6 GPa, which is closer to that of bone, is polyetheretherketone (PEEK).²⁶ Its modulus can be modified by reinforcing it with carbon fibers, for example, to achieve a modulus of 18 GPa, similar to that of cortical bone.²⁷

Since PEEK showed resistance to degradation in vivo, it was offered commercially in April 1998 as a biomaterial for long-term implants (Invibio Ltd, Thornton-Cleveleys, UK).²⁸ Since then, PEEK has demonstrated to be a high-performance thermoplastic polymer able to replace metallic implant components in the field of orthopedics^{29, 30} and traumatology.^{31, 32} Also, calvarial reconstructions with PEEK implants were described.³³ These findings suggest that PEEK could substitute titanium as material for dental endosseous implants.

The current review pertains to literature published prior to December 1, 2010. The aim was to figure out whether there are existing studies about dental implants from PEEK, which probably underline the theory that PEEK could be considered as a viable alternative material for dental implants.