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REVIEW SCIENTIFIC ARTICLES Stomatologija, Baltic Dental and Maxillofacial Journal, 19:19-23, 2017 A review of PEEK ’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 (PEEK), its characteristics and use in prosthodontics. 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 . 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 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- candi- and dentition and pleases demanding patients. date for replacing 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 fi ber reinforced problems. According to World Health Organization PEEK (CF/PEEK), this new 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, – 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 -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, 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 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 ̴ 8.3 GPa Resistant to cor- Biocompatible Component parts of im- rosion 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 ; 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 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. the highest tensile bond strength when Heliobond Individual abutments on implants can be milled was used as adhesive (15). All these investigations of PEEK. They are usually used for temporary confirm that resin composites can be used as a restorations. Randomized controlled clinical trial covering material of the PEEK frames. However, showed, that there is no statistically signifi cant it is dangerous to use concentrated sulfuric acid in difference between PEEK and titanium abutments, clinical practice. causing bone resorption or infl ammation. Moreover, Mechanical properties of the PEEK are similar the attachment of oral microorganisms to PEEK to dentin and enamel. Thus it has superiority over abutments is comparable to those made of titanium, metal alloys and restorations. CAD-CAM zirconia and poly methyl methacrylate. Therefore, milled PEEK fi xed prostheses' resistance to fracture PEEK is a promising alternative to titanium abut- is 2354N. It has higher resistance than lithium disili- ments (4). Comparing to titanium, the polymer cate ceramic (950N), (851N) or zirconia could exhibit less shielding, but very limited (981-1331N) (19). However, there are no clinical inherent osteoconductive properties (4). This leads data about PEEK’s abrasion with other materials to negative in osseointegration process. such as metal alloys, ceramics, dentin or enamel. Nowadays, there are many combinations of Mastication cyclically loads the teeth with a 400 N PEEK with other materials such as , carbon force. As PEEK has high fracture load resistance it is or ceramics. Due to complexed chemical structure suitable for producing frames. High fracture resist- and poor wetting capabilities of PEEK it is hard to ance is also stated in Stawarczyk et al. publications. prepare its surface in order to increase bond strength A mean fracture relative load was 1383 N of 3-unit and bonding with composites. For good functioning, PEEK frameworks without veneering (16). the surface of PEEK restorations has to be covered Despite high fracture resistance, PEEK is by other material like resin composites or lithium relatively weak mechanically in homogenic form. disilicate. The best surface processing option is Tannous et al. (14) in vitro research showed that still not found. Moreover, composite as a coating clasps made of PEEK have lower resistance forces material of the PEEK may degrade with time. So than the ones made from cobalt - chrome. Scientists if the polymer frame remains stable, it is neces- have searched for combinations with other materi- sary to renew the coating material. These are extra als, to improve PEEK’s properties. Modifi ed PEEK expenses to the patient. Unfortunately, there was containing 20% ceramic fi llers known as BioHPP not enough clinical research made to prove PEEK’s superiority over other Table 2. Effect of sinus membrane perforations on the complications materials. There is still not enough information Author of the Year Preparation of PEEK surface stated about complica- article Surface condition- Adhesive system Shear bond tions, biofilm formation ing (prepare) strength (MPa) on PEEK surface and its Schmidlin PR et 2010 Sulfuric acid 96% Heliobond 18.2±5.4 resistance to compres- al. [17] Relyx™ Unicem 19.0±3.4 sion. Even so, PEEK is Sandblasting 50 μm Heliobond 13.5± 2.4 being used in manufac- Zhou L et al. [12] 2014 Sulfuric acid 98 % SE Bond/Clearfi l AP-X™ 8.7 ± 0.2 turing fixed restorations Relyx™ Unicem 7.4 ± 0.6 (18), dental implants, Hydrofl uoric acid SE Bond/Clearfi l AP-X™ 2.8 ± 0.2 individual abutments, 9.5% Relyx™ Unicem 0 removable prostheses Sandblasting 50 μm Relyx™ Unicem SE 1.4 ± 0.2 and their parts (4) and Bond/Clearfi l AP-X™ 5.3 ± 0.6 even maxillary obturator Sandblasting 100 μm Relyx™ Unicem 0 prostheses (20).

22 Stomatologija, Baltic Dental and Maxillofacial Journal, 2017, Vol. 19, No. 1 G. Skirbutis et al. REVIEW

CONCLUSIONS research is necessary to fi nd out the situation, because most of the studies have been carried out in vitro. PEEK is an attractive modern material to use in prosthodontics. Due to its favorable chemical, mechani- STATEMENT OF CONFLICTS OF INTEREST cal and physical properties it is used in producing fi xed and removable prostheses. However, more clinical The authors state no confl ict of interest.

REFERENCES

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Received: 29 05 2016 Accepted for publishing: 27 03 2017

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