PEEK

The Use of a Modified Poly-Ether-Ether-Ketone (PEEK) as an Alternative Framework Material for Removable Dental Prostheses. A Clinical Report Panagiotis Zoidis, DDS, MS, Dr Dent, Ioannis Papathanasiou, DDS, & Gregory Polyzois, DDS, MScD, Dr Dent Department of Prosthodontics, Dental School, National and Kapodistrian University of Athens, Greece

Keywords BioHPP; distal extension; high-performance polymer; PEEK; removable dental prosthesis. Correspondence Panagiotis Zoidis, Department of Prosthodontics, Dental School, National and Kapodistrian University of Athens, 2 Thivon Street, 11527, Athens, Greece. E-mail: [email protected] This paper was completed as part of the postgraduate program co-financed by the “Scholarships Programme of the State Scholarships Foundation (IKY Scholarships) with an individualized assessment process of the Academic Year 2012 to 2013” Act from the resources of the operational program, “Education and Lifelong Learning,” of the European Social Fund (ESF), NSRF 2007 to 2013.

Abstract This clinical report presents a modified poly-ether-ether-ketone (PEEK) as an alternative material for the fabrication of distal extension removable dental prosthesis (RDP) frameworks. This material can be used for patients allergic to metals, or who dislike the metallic taste, the weight, and the unpleasant metal display of the denture framework and retentive clasps. This modified PEEK material, known as BioHPP, is a biocompatible, nonallergic, rigid material, with flexibility comparable to bone, high polishing and low absorption properties, low plaque affinity, and good wear resistance. It has been used for years in orthopedics and medical technology. BioHPP frameworks can be constructed either via CAD/CAM manufacturing or via the conventional lost wax technique. The clinical use of a BioHPP RDP framework is presented as an alternative for the treatment of a distal extension case.

The authors declare no conflicts of interest with respect to the authorship and publication of this article. Accepted March 13, 2015 doi: 10.1111/jopr.12325

Traditional removable dental prostheses (RDP) with chromecobalt frameworks and clasps have been an inexpensive and predictable treatment option for the rehabilitation of partially edentulous patients.1 The esthetically unacceptable display of metal clasps, the increased weight of the prosthesis, the potential for metallic taste, and allergic reactions to metals led to the introduction of a number of thermoplastic materials in clinical practice such as nylon and acetal resins. Nylons provide improved esthetics and reduction of rotational forces on the abutment teeth due to their low elastic modulus. The major disadvantage of a nylon RDP is the inability for a reline procedure and the lack of occlusal rests as well as rigid frameworks, that could lead to occlusal instability and sinking, especially in Kennedy class I and II cases. On the other hand, acetal

resins present adequate mechanical strength to form a framework more rigid than nylon with retentive clasps, connectors, and supportive elements; however, the acetal resin material lacks natural translucency and vitality.2-5 An alternative restoration material (poly-ether-ether-ketone [PEEK]) has been successfully used over the last years in the medical field, and orthopedics, specifically. A modified PEEK material containing 20% ceramic fillers is a high performance polymer (BioHPP; Bredent GmbH, Senden, Germany), which presents high biocompatibility, good mechanical properties, high temperature resistance, and chemical stability.6-8 Due to a 4 GPa modulus of elasticity, it is as elastic as bone and can reduce stresses transferred to the abutment teeth. Furthermore, the white color of BioHPP frameworks provides a different

C 2015 by the American College of Prosthodontists Journal of Prosthodontics 0 (2015) 1–5

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Figure 2 Existing RDP lingual bar, occlusal rest seats, and clasps.

Figure 1 Existing RDP with conventional Roach clasps, buccal view.

esthetic approach than the conventional metal framework display does. Additional advantages of this polymer material are elimination of allergic reactions and metallic taste, high polishing qualities, low plaque affinity, and good wear resistance.9-12 Although PEEK in general has been successfully used for years in orthopedics and medical technology,13 it has only recently been used in dentistry. Thus, studies evaluating the properties of this material are limited.14-22 The existing reports on this material are generally in vitro, emphasizing the need for further clinical tests. The purpose of this clinical report was to present an alternative treatment approach using a BioHPP framework in combination with the traditional denture base acrylic resins for the fabrication of a mandibular RDP.

Figure 3 BioHPP framework, lingual plate.

Clinical report Pretreatment

A 70-year-old female patient presented with a conventional Cr-Co mandibular distal extension RDP. The major connector was a lingual bar; traditional roach clasps engaged the lower left second premolar and the lower right first premolar, which served as abutment teeth. Minor connectors emerged from the lingual bar engaging rest seats lingual to mandibular left canine, mesial to mandibular right first premolar as well as distal and mesial to the left first and second mandibular premolar, respectively (Figs 1 and 2). The patient complained of the metallic taste, the weight, and the unpleasant display of the metal clasps of her existing Cr-Co RDP and demanded an alternative material for the construction of a new RDP. She presented no history of allergy to metal or acrylics. Treatment plan

The treatment plan consisted of a modified PEEK material (BioHPP) distal extension RDP framework with regular acrylic denture teeth and conventional heat-cure acrylic resin bases, employing the existing design.

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Figure 4 BioHPP framework, C clasps.

Treatment

The initial impression was performed with irreversible hydrocolloid impression material (Blueprint Cremix; Dentsply DeTrey GmbH, Konstanz, Germany), and the diagnostic cast was constructed with stone (Moldadur; Heraeus Kultzer GmbH & Co KG, Hanau, Germany). A custom tray was constructed on this diagnostic cast using a light-cured resin material (Fastray LC; Harry J. Bosworth Company, Skokie, IL). Border molding with green stick compound (Kerr Corporation, Orange, CA)


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Figure 5 Heavy, conventional Cr-Co distal extension RDP.


investment (Brevest; Bredent GmbH). The mold was heated between 630°C and 850°C to melt the wax, and then cooled at 400°C. In that temperature, BioHPP melted and was vacuum pressed into the mold under 5.5 to 6 bar pressure. The usual devesting procedure was followed as soon as the mold had cooled down (35 minutes), and the framework was fitted to the definitive cast. The major connector design was a lingual plate instead of the conventional lingual bar to better withstand the torsional forces from the distal extension RDP (Fig 3). Conventional C clasps were constructed, engaging a 0.5 mm undercut on the abutment teeth (Fig 4). Centric relation records were performed using bite registration wax (Aluwax; Aluwax Dental Products Company, Allendale, MI), and the final try-in confirmed treatment position validity and tooth setup. Conventional acrylic denture teeth (Bioblend Trubyte; Dentsply International, York, PA) were used, and the heat-cured acrylic resin (Trevalon; De Trey Division, AD International Ltd, Weybridge, Surrey, UK) was processed according to the manufacturer’s instructions. A clinical remount followed by occlusal adjustments was performed to accommodate processing discrepancies. The distal extension RDP was delivered, and sore spots were relieved at the 48-hour recall appointment. The patient was very pleased with the “negative weight” of her new RDP and the white “healthy shade” of the framework and the retentive parts (Figs 5 and 6). Clasp retention was evaluated as equal and more “gentle” compared with the old Cr-Co RDP.

Discussion

Figure 6 BioHPP distal extension RDP, 27.5% lighter.

was performed for the edentulous areas, and polysulfide impression material (Permlastic; Kerr Corporation) was used for the final impression. Type IV dental stone (Prima-rock; Whip Mix Corporation, Louisville, KY) was used for the fabrication of the definitive cast. The BioHPP framework was constructed with the conventional lost wax technique using a vacuum press device (2 press; Bredent GmbH) especially designed for this material. The wax model was invested in a mold using a special

The choice of the material for the construction of RDPs should be based on clinical examination, patient’s demands, and scientific evidence. Behr et al,1 in a retrospective study evaluating the clinical performance of Co-Cr RDPs, estimated a 10-year survival rate of 90%; however, traditional RDPs do not always comply with the patient’s esthetic demands for a metal-free restoration. A modified PEEK high performance polymer (BioHPP) combined with regular acrylic denture teeth and conventional heat-cured denture base acrylic resin was used as an alternative RDP framework material. Due to its white color and high strength, BioHPP permits the fabrication of metal-free clasps and occlusal rests, providing occlusal stability and metal-free esthetics. Due to the viscoelasticity of the edentulous ridges, distal extension RDPs exhibit a greater rotation around the supporting rests under occlusal loading. This could lead to creation of distal torque on the abutment teeth. In our case, the use of BioHPP for the construction of the framework of a Kennedy class I RDP was thought to be beneficial for the periodontal health of the abutment teeth. The elasticity of this material might reduce the distal torque and the stress on the abutment teeth. Therefore, it could be hypothesized that BioHPP would be a viable alternative for abutments with reduced periodontal support when restoring distal extension cases. The retentive force of BioHPP clasps could be a matter of concern. According to Tannous et al,21 PEEK clasps offer a lower retentive force than metal clasps; however, properly


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designed PEEK clasps with an undercut of 0.5 mm could provide adequate retention for clinical use. BioHPP clasps are gentler to the enamel and the porcelain restorative materials than conventional Cr-Co clasps are. The phenomenon of porcelain scoring caused by Cr-Co clasps during RDP insertion is absent when using BioHPP clasps, due to the material’s elastic properties. Also, clasps made of BioHPP result in healthy periodontium, especially in cases of tissue proximity, due to the material’s low plaque affinity properties.22 Due to its insolubility in water and low reactivity with other materials, BioHPP could be suitable for patients allergic to Cr-Co, or sensitive to the metallic taste of conventional Cr-Co frameworks. Another important advantage of this type of restoration is that it could be easily relined if resorption occurs since conventional heat-cured acrylic resin is used as a denture base material. The weight of a removable prosthesis may affect patient satisfaction. BioHPP has a low specific weight that permits the fabrication of lighter prostheses providing high patient satisfaction and comfort during function. In our case, the BioHPP RDP weighed 27.5% less than its Cr-Co predecessor, although it used a lingual plate instead of a lingual bar. According to Zlataric et al,23 proper design of an RDP is important for the maintenance of periodontal health. Compared to nylon RDPs that cover a great part of soft tissues, BioHPP RDPs provide a hygienic design that simplifies oral hygiene. As already mentioned, BioHPP is a material recently introduced in dentistry. Unfortunately, there is lack of studies evaluating the clinical behavior of this material. Stain resistance and color stability have been described in the literature,22 but through laboratory tests. In vitro tests by the University of Jena22 show that BioHPP can be polished to a roughness of 0.018 µm Ra following a strict polishing protocol. Clinical long-term tests are required to prove good stain resistance and color stability. Another matter of concern is the fatigue resistance of BioHPP. Although in vitro studies regarding a three-unit fixed partial denture provide breaking values greater that 1200 N under fatigue stress10 (1.2 million cycles), there is no scientific evidence of how this material behaves under fatigue stress when it is used as an RDP framework. This, combined with the lack of long-term clinical follow-up, suggest careful use of BioHPP, as an alternative material for RDP frameworks in case of metal allergies, complying with the literature for other thermoplastic resins,4,24 until there is enough clinical evidence to support its use as a substitute material. The above distal extension RDP presents a short-term, 1-year clinical follow-up, presenting no framework breakage and good clasp retention. There has been no sign of change in the BioHPP framework, apart from the high-gloss surface appearing to have lost some of its shine, in accordance with the literature.12 Shortterm recall appointments are required to record clinical status.

framework material for patients with taste sensitivity or allergies to conventional Cr-Co frameworks. Further longterm clinical evidence is needed to consolidate the scientific data.

Conclusion Due to the lack of solid clinical evidence, BioHPP should not be considered as a substitute framework material for a well-designed Cr-Co RDP. Under the present conditions, BioHPP should probably be considered as an alternative RDP 4

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19. Karan M, Dua JS, Chawla S, et al: Poly-etheretherketone (PEEK) dental implants: a case for immediate loading. Int J Oral Implantol Clin Res 2011;2:97-103 20. Costa-Palau S, Torrents-Nicolas J, Brufau-de Barberà M, et al: Use of polyetheretherketone in the fabrication of a maxillary obturator prosthesis: a clinical report. J Prosthet Dent 2014;112:680-682 21. Tannous F, Steiner M, Shahin R, et al: Retentive forces and fatigue resistance of thermoplastic resin clasps. Dent Mater 2012;28:273-278

22. Rzanny A, Gobel F, Fachet M: BioHPP summary of results for material tests. Research Report. Jena, Germany, University of Jena, Department of Materials and Technology, 2013 23. Zlatarić DK, Celebić A, Valentić-Peruzović M: The effect of removable partial dentures on periodontal health of abutment and non-abutment teeth. J Periodontol 2002;73:137-144 24. Fueki K, Ohkubo C, Yatabe M, et al: Clinical application of removable partial dentures using thermoplastic resin-Part II: material properties and clinical features of non-metal clasp dentures. J Prosthodont Res 2014;58:71-84


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