REVIEW SCIENTIFIC ARTICLES Stomatologija, Baltic Dental and Maxillofacial Journal, 19:19-23, 2017 A review of PEEK polymer’s properties and its use in prosthodontics Gediminas Skirbutis1, Agnė Dzingutė2, Viltė Masiliūnaitė2, Gabrielė Šulcaitė2, Juozas Žilinskas1 SUMMARY Objective. The aim of this study is to review polyether ether ketone (PEEK), its characteristics and use in prosthodontics. Material and methods. Information search for articles about PEEK and it’s use in prosthodon- tics between January 2010 and April 2017 was conducted in Medline via PubMed, Science direct, Wiley online library as well as the Web search Google Scholar sources. Twelve full text articles were selected and used in this review. Results. 143 articles were found in the database using keywords: PEEK, prosthodontics, den- tistry. Data on the suitability of PEEK polymer were organized according to mechanical, chemical, physical properties and PEEK surface preparation. Conclusions. PEEK polymer is suitable to use in prosthodontics. However, there are not enough statements about complications, biofi lm formation on PEEK surface and its resistance to compres- sion. More research should be done to fi nd out the results. Key words: PEEK, prosthodontics, dentistry. INTRODUCTION Advance in dentistry and development of tech- PEEK (-C6H4-OC6H4-O-C6H4-CO-)n is a semi- nologies can be reached by improving materials. crystalline linear polycyclic aromatic polymer. In Biocompatibility, low plaque affi nity, good aes- 1978 it was developed by a group of English scien- thetics and characteristics close to dental structure tists. Later PEEK was commercialized for industrial are essential to modern materials used in advanced applications. By the late 1990s, PEEK became an dentistry. It helps to rebuild the defects of the teeth important high-performance thermoplastic candi- and dentition and pleases demanding patients. date for replacing metal implant components, in ver- Insuffi cient oral hygiene and a lack of preven- tebral surgery as a material of the interbody fusion tion cause increase of dental caries and periodontal cage. With the emergence of carbon fi ber reinforced problems. According to World Health Organization PEEK (CF/PEEK), this new composite material was (WHO) 2012 data 60-90% of school children and exploited for fracture fi xation and femoral prosthesis nearly 100 % of adults have dental cavities which in artifi cial hip joints (2). untreated may destroy dental tissues (1). Dental PEEK is white, radiolucent, rigid material with defects can be restored by using fi xed or removable great thermal stability up to 335.8° C (3). It is non restorations. For the best rehabilitation of mastica- allergic and has low plaque affi nity (4-6). Flexural tory function it is indicated to use scientifi cally modulus of PEEK is 140-170 MPa, density – 1300 approved and safe materials. This article reviews kg/m3 and thermal conductivity 0.29 W/mK (4, 6, one of the new dental materials - polyether ether 7). PEEK's mechanical properties do not change ketone (PEEK), its characteristics and use in pros- during sterilization process, using steam, gamma thodontics. and ethylene oxide (2, 8). Young’s (elastic) modulus of PEEK is 3-4 GPa (7, 9). Young’s modulus and 1Clinic of Dental and Maxillofacial Orthopedics, Medical Acad- tensile properties are close to human bone, enamel emy, Lithuanian University of Health Sciences, Kaunas, Lithuania and dentin (10). Polyether ether ketone is resistant 2 Faculty of Odontology, Medical Academy, Lithuanian University to hydrolysis, non-toxic and has one of the best bio- of Health Sciences, Kaunas, Lithuania compatibility (11, 12). Special chemical structure of Address correspondence to Agnė Dzingutė, Faculty of Odontology, PEEK exhibits stable chemical and physical proper- Medical Academy, Lithuanian University of Health Sciences, A. Lukšos - Daumanto g. 6, LT-50106 Kaunas, Lithuania. ties: stability at high temperatures (like sterilization E-mail address: [email protected] processes), resistance to most substances apart from Stomatologija, Baltic Dental and Maxillofacial Journal, 2017, Vol. 19, No. 1 19 REVIEW G. Skirbutis et al. Fig. Diagram of the literature search strategy concentrated sulfuric acid and wear-resistance (2). manufacture, surface modifi cations, the kind of Lieberman et al. (13) in vitro research comparing investigation (in vitro or in vivo), type of scientifi c PEEK, poly methyl methacrylate (PMMA) and articles (case reports, original researches, review composite resin showed that PEEK has the lowest articles). The period of selected articles was from solubility and water absorption values. As PEEK is January 2010 until April 2017. quite new material in dentistry comparing to com- Exclusion criteria: articles not related to pros- posite, ceramics or zirconia, it is important to fi nd thodontics, articles written not in English language, out and summarize its properties. articles older than seven years. The aim of this review is to evaluate PEEK polymer and its use in dentistry. RESULTS MATERIAL AND METHODS 143 articles were found in the database using keywords: PEEK, prosthodontics, dentistry. The The literature search covered the following da- studies over 7 years old were not included. 20 stud- tabases: Medline via PubMed, Science direct, Wiley ies included reading titles and abstracts. Twelve full online library as well as the Web search Google text articles were selected and used in this review. Scholar sources dated between January 2010 and The selected studies were divided into groups ac- April 2017. The titles and abstracts were reviewed. cording to the type of the study: properties and it's Some study subjects were not suitable for this re- suitability in prosthodontics and PEEK’s surface view, others were mentioned in different databases. conditioning using various adhesive systems. The In the end, twelve full text articles fulfi lled the analysis of the articles shows PEEK's characteristics inclusion criteria (Figure 1). and its suitability in prosthodontic treatment. Data Inclusion criteria: exclusively English articles were systematized in assessing kind of mechanical, about dental prostheses from PEEK or modifi ed chemical, biological properties (Table 1). Data of PEEK were included, despite of the methods of evaluation of shear bond strength of PEEK to den- 20 Stomatologija, Baltic Dental and Maxillofacial Journal, 2017, Vol. 19, No. 1 G. Skirbutis et al. REVIEW tal tissues using various surface conditioning and brown color PEEK is not suitable for monolithic adhesive systems (Table 2). aesthetic restorations of anterior teeth (16). More aesthetic material like composite should be used DISCUSSION for coating to get an aesthetic result. In literature many surface conditioning methods of PEEK are PEEK is quite new material in prosthodontics. offered to improve bonding with resin composite Comparing to the metals used in dentistry, PEEK crowns. Air abrasion with and without silica coating is more aesthetic, stable, biocompatible, lighter creates wettable surface, but etching with sulfuric and has reduced degree of discoloration (14, 15). acid makes rough and chemically processed sur- This makes it more attractive to patients with high face (4, 17). Low energy of PEEK surface creates aesthetic requirements. However, due to its grayish- resistance to chemical processing. Uhrenbacher et Table 1. Data associated with the lateral (direct) sinus fl oor elevation surgery Author of the Year Properties Applications of PEEK in article Mechanical Chemical Biological prothodontics Ma R et al. [2] 2014 Elastic modulus ̴ 8.3 GPa Resistant to cor- Biocompatible Component parts of im- rosion plants Najeeb S et al. 2016 Tensile strength 80 MPa; - Non allergic; Has Implant abutments; Fixed [4] Young’s modulus 3-4 GP; low plaque affi nity crowns, fi xed bridges; CFR-PEEK 120 MPa Removable dentures and components Vaezi M et al. [5] 2015 - Resistant to hy- Non allergic; Has Component parts of im- drolysis low plaque affi nity plants Zoidis P et al. [6] 2015 - - Non allergic; Has An alternative framework low plaque affi n- material for removable ity; Biocompatible partial dentures Garcia-Gonzalez 2015 Elastic modulus 3.6 GPa; Thermal conduc- - Component parts of im- D et al. [10] Density 1300 kg/m³ tivity 0.29 W/mK plants Sheiko N et al. 2016 - - Biocompatible Component parts of im- [8] plants Schmidlin PR et 2010 - - Biocompatible Fixed prosthesis: tempo- al. [17] rary abutment for im- plants, crowns Tannous F et al. 2012 Tensile strength 97 MPa; - - Partial removable den- [14] Elastic modulus 4 GPa. tures: thermoplastic resin clasps Monich PR et 2017 - The glass transi- Biocompatible Component parts of im- al. [3] tion temperature plants 143°C; The crystalline melt transition temperature 343 °C Schwitalla A et 2013 Elastic modulus 3,6 GPa; - - Component parts of im- al. [9] Carbon fi ber–reinforced plants PEEK (CFR-PEEK) obtain an elastic modulus of 17.4 GPa similar to that of cortical bone Xin H et al. [7] 2013 Flexural yielding strength - - Component parts of im- 165 MPa; plants Young’s modulus 3.7 GPa Zhou L et al. [12] 2014 - - Biocompatible Component parts of im- plants : abutments, healing caps; Fixed protheses. Stomatologija, Baltic Dental and Maxillofacial Journal, 2017, Vol. 19, No. 1 21 REVIEW G. Skirbutis et al. al. (18) investigated the modification of the surface (Bredent GmbH Senden, Germany) is non allergic strength of PEEK crowns adhesively bonded to and has high biocompability. Possibility of correc- dentin abutments. The highest values were found tions, excellent stability, great optimal polishable for the airborne-particle abrasion and sulfuric etched properties and aesthetic white shade of BioHPP help groups, and crowns adhesively pretreated with Sig- to produce high-quality prosthetic restorations (4). num PEEK bond and "visio.link" adhesive system. BioHPP has a great potential as framework mate- The results of Hallmann et al. research show that rial. This is a good alternative to Cr-Co frames for abraded PEEK surface with 50 μm alumina particles the patients with high aesthetic requirements. But followed by etching with piranha solution lead to in clinical situations the results might be different.