Use of a Polyetheretherketone Clasp Retainer for Removable Partial Denture: a Case Report

dentistry journal

Case Report Use of a Polyetheretherketone Clasp Retainer for Removable Partial Denture: A Case Report

Tetsuo Ichikawa * , Kosuke Kurahashi, Lipei Liu, Takashi Matsuda and Yuichi Ishida

Department of Prosthodontics & Oral rehabilitation, Tokushima University, Graduate School of Biomedical Sciences, 3-18-15 Kuramoto, Tokushima 770-8504, Japan; [email protected] (K.K.); [email protected] (L.L.); [email protected] (T.M.); [email protected] (Y.I.) * Correspondence: [email protected]; Tel.: +81-88-633-7346

Received: 27 November 2018; Accepted: 20 December 2018; Published: 3 January 2019

Abstract: Clasp retainers made of metal alloys may be esthetically unappealing or cause allergic reactions. To investigate alternative materials, we used the nonﬁller polyetheretherketone (PEEK) to fabricate the clasp retainer of a removable partial denture for the mandibular bilateral distal free-end abutment of an 84-year-old female. Two years later, few color and texture changes of PEEK were found macroscopically. The rest part and the clasp arm ﬁtted well without any deformation. There were no particular occlusal or periodontal problems. Subjective satisfaction was expressed by both the practitioner and the patient.

Keywords: polyetheretherketone (PEEK); clasp retainer; removable partial denture; nonmetal clasp

1. Introduction The clasp retainer is one of the requisite components of removable partial dentures (RPDs), which are currently used for partial edentulism. The clasp is conventionally made of metal alloys, but most wearers of these dentures show a strong dislike for the metallic color when the clasp is installed in the esthetic zone. In addition, metal allergies present a clinical problem [1,2]. It is therefore desirable to investigate the use of nonmetal materials as substitutes for these clasps. Materials used for nonmetal denture clasps include polyamide, polyester, polycarbonate, acrylic, and polypropylene, many of which are thermoplastic resins. Physical properties that contribute to the suitability of clasp material include bending strength, flexural modulus, adhesive strength, water absorption properties, abrasion resistance, surface hardness, impact resistance, color stability, compatibility, and ease of processing. However, substitute materials with more esthetic appeal compared with metals frequently do not meet the necessary physical criteria [3,4]. In particular, one problem is material degradation with color and texture changes. Another issue is deterioration in self-cleaning action is another problem for nonmetal denture clasps, which cover the cervical part of the abutment tooth in many cases [5]. Polyetheretherketone (PEEK) is a ketone-based semicrystalline thermoplastic that has been widely used for medical and industrial applications because of its excellent mechanical and chemical resistance properties. In the dental field, its use for crowns, implant superstructures, fixed partial dentures, and RPD frameworks is being investigated [6–9]. In this case report, we used PEEK to fabricate a clasp retainer for RPDs for the mandibular bilateral distal free-end abutment, although RPD components, such as denture base, retainer, and connector are generally composed of just a thermoplastic resin in the nonmetal clasp denture. After two years of use, we clinically assessed the attributes of this clasp including color and color changes, bacterial adhesion, and compatibility.

Dent. J. 2019, 7, 4; doi:10.3390/dj7010004 www.mdpi.com/journal/dentistry Dent. J. 2019, 7, 4 2 of 6 Dent. J. 2019, 7, x FOR PEER REVIEW 2 of 6

2. CaseDent. J. Presentation 2019, 7, x FOR PEER REVIEW 2 of 6 2. Case Presentation 2. AnCase 84-year-old Presentation female patient presented to Tokushima University Hospital with only three An 84-year-old female patient presented to Tokushima University Hospital with only three anterior residual roots in the maxilla and anterior teeth with a bilateral free end saddle in the anterior residualAn 84-year-old roots in female the maxilla patient and presented anterior to teeth Tokushima with a bilateral University free Hospital end saddle with in only the three mandible. mandible. Although the crowns in the lower jaw had poor esthetics, the patient was unwilling to Althoughanterior the residual crowns roots in the in lowerthe maxilla jaw hadand pooranterior esthetics, teeth with the a patientbilateral was free unwillingend saddle to in receive the a receivemandible. a revised Although prosthesis. the crowns A treatment in the lower plan jaw wa hads devisedpoor esthetics, that involved the patient fitting was ofunwilling a complete to revised prosthesis. A treatment plan was devised that involved fitting of a complete overdenture to overdenturereceive a revisedto the prosthesis.maxilla and A atreatment RPD to planthe mawandible.s devised Silicone that involved impressions fitting (Exadenture, of a complete GC theCorporation, maxillaoverdenture and Tokyo, ato RPD the toJapan)maxilla the mandible. usingand a individualRPD Silicone to the tray impressionsmasndible. and theSilicone (Exadenture,interocclusal impressions GCrecord (Exadenture, Corporation, were obtained GC Tokyo, Japan)accordingCorporation, using to individual conventional Tokyo, traysJapan) methods. and using the Afterindividual interocclusal trial atraypplication records and the wereof ainterocclusal wax obtained denture, accordingrecord the final were to denture conventionalobtained was methods.madeaccording (Figure After to trial1). conventional The application clasp retainermethods. of a was wax After made denture, trial of application nonfiller the final typeof denture a wax PEEK denture, was as follows. made the final (Figure First, denture we1). scanned The was clasp retainerthemade working was (Figure made model 1). of The with nonfiller clasp a dental retainer type scanner; PEEK was made asthen, follows. of we nonfiller designed First, type we the PEEK scanned clasp as retainer follows. the working withFirst, CAD we model scanned software with a dental(Geomagicthe scanner; working Freeform, then,model we with3D designed Systems, a dental South thescanner; clasp Carolina, then, retainer we USA) designed with and CAD usedthe clasp software a milling retainer (Geomagicmachine with CAD (RXP500 Freeform, software DSC, 3D Systems,Roeders(Geomagic South BmbH, Freeform, Carolina, Soltau, 3D USA)Germany) Systems, and Southto used shape Carolina, a milling the clasp USA) machine from and useda (RXP500 PEEK a milling disk DSC, machine(JUVORA Roeders (RXP500 Dental BmbH, DSC, Discs, Soltau, Germany)Lancashire,Roeders to BmbH, shapeUK) (Figure theSoltau, clasp 2). Germany) Details from a of PEEKto form shape disk were the (JUVORA claspmodified from Dentalusing a PEEK technical Discs, disk Lancashire,(JUVORA bars, and Dental polishing UK) Discs, (Figure was 2 ). DetailsperformedLancashire, of form with wereUK) silicone (Figure modified points 2). usingDetails (Shofu, technical of formKyoto, were bars, Japan) modified and and polishing ausing Robins technical wason performedbristle bars, brush and with polishing with silicone polishing was points performed with silicone points (Shofu, Kyoto, Japan) and a Robinson bristle brush with polishing (Shofu,paste. Kyoto, Japan) and a Robinson bristle brush with polishing paste. paste.

Figure 1. Complete upper denture and removable partial denture with nonfiller polyetheretherketone FigureFigure 1. 1.Complete Complete upper upper denture denture andand removable partial partial denture denture with with nonfiller nonﬁller polyetheretherketone polyetheretherketone (PEEK) clasps, at delivery. (PEEK)(PEEK) clasps, clasps, at at delivery. delivery.

Figure 2. PEEK clasp components milled in the PEEK disk. Dent. J. 2019, 7, x FOR PEER REVIEW 3 of 6 Dent. J.Dent.2019 J., 20197, 4 , 7, x FOR PEER REVIEW 3 of 6 3 of 6 Figure 2. PEEK clasp components milled in the PEEK disk. Figure 2. PEEK clasp components milled in the PEEK disk. The adhered surface of PEEK embedded in a resin base was treated using sand blasting with The adhered surface of PEEK embedded in a resin base was treated using sand blasting with Al2O3 50-Theµm adhered particles surface (HiBlaster of PEEK Ovaljet, embedded Shofu, in Kyoto,a resin Japan).base was The treated denture using was sand then blasting molded with using Al2O3 50-μm particles (HiBlaster Ovaljet, Shofu, Kyoto, Japan). The denture was then molded using Al2O3 50-μm particles (HiBlaster Ovaljet, Shofu, Kyoto, Japan). The denture was then molded using a heat-curinga heat-curing acrylic acrylic resin resin (Acron, (Acron, GC,GC, Tokyo,Tokyo, Japan)Japan) with a a conventional conventional flask ﬂask investment investment method method (Figurea heat-curing3). Although acrylic the resin clasp (Acron, apex was GC, primarily Tokyo, Japan) positioned with a conventional in the far zone flask of investment the abutment method teeth at (Figure(Figure 3). 3). Although Although the the clasp clasp apex apex was was primarily primarily positioned inin the the far far zone zone of of the the abutment abutment teeth teeth at at the fabrication, it was prepared slightly beyond the central line of the abutment at the denture delivery thethe fabrication, fabrication, it itwas was prepared prepared slightlyslightly beyondbeyond the centralcentral lineline ofof the the abutment abutment at atthe the denture denture because of the aesthetic problem. deliverydelivery because because of of the the aesthetic aesthetic problem. problem.

FigureFigure 3. PEEK 3. PEEK clasp clasp installed installed in in the the denture denture base.base. The The curly curly bracket bracket region region was was treated treated with withsand sand Figure 3. PEEK clasp installed in the denture base. The curly bracket region was treated with sand blastingblasting before before ﬂasking. flasking. blasting before flasking. FiguresFigures4–6 show 4–6 show the PEEKthe PEEK clasps clasps two two years years after afte delivery.r delivery. The The patient patient reported reported thatthat denturedenture had hadFigures been rinsed 4–6 show under the running PEEK waterclasps after two every years meal afte rand delivery. immersed The into patient a denture reported cleanser that for denture the been rinsed under running water after every meal and immersed into a denture cleanser for the night hadnight been at rinsed bedtime. under Few running color and water texture after changes every mealwere andfound immersed macroscopically, into a denture and denture cleanser plaque for the at bedtime. Few color and texture changes were found macroscopically, and denture plaque adherence nightadherence at bedtime. around Few the color clasp and appear textureed minimal. changes However, were found staining macroscopically, with a plaque-disclosing and denture agent plaque around the clasp appeared minimal. However, staining with a plaque-disclosing agent revealed clear adherencerevealed aroundclear denture the clasp plaque appear on bothed theminimal. inside andHowever, outside staining of the clasps. with a plaque-disclosing agent denturerevealed plaque clear ondenture both theplaque inside on both and outsidethe inside of and the clasps.outside of the clasps.

(a) (b)

(c)

Figure 4. Fit of the PEEK clasps to abutments. (a) just after delivery, (b) Labial view (two years later), and (c): Occlusal view (two years later). Dent. J. 2019, 7, x FOR PEER REVIEW 4 of 6 Dent. J. 2019, 7, x FOR PEER REVIEW 4 of 6 Figure 4. Fit of the PEEK clasps to abutments. (a): just after delivery, (b): Labial view (two years later), andFigure (c): 4. Occlusal Fit of the view PEEK (two clasps years to later).abutments. (a): just after delivery, (b): Labial view (two years later), and (c): Occlusal view (two years later). The rest part and the clasp arm still fitted well without any deformation, and the participant reportedThe norest particular part and problethe claspm with arm occlusal still fitted contact. well without any deformation, and the participant reportedNo specific no particular mobility proble of them withabutment occlusal teeth, contact. and no specific inflammation of the gingiva around the abutmentNo specific teeth mobility were found. of the Theabutment subjective teeth, oper andational no specific opinion inflammation of the practitioner of the gingiva about wearing around Dent.andthe abutment detaching J. 2019, 7, 4 teeth of the were denture found. was The also subjective reported oper as good.ational opinion of the practitioner about wearing4 of 6 and detaching of the denture was also reported as good.

(a) (b) (a) (b)

(c) (d) (c) (d) Figure 5. Bacterial adherence on PEEK clasps two years later. (a), (c): before staining and (b), (d): after Figurestaining. 5.5. Bacterial adherenceadherence on on PEEK PEEK clasps clasps two two years years later. later. (a, (ca)), before (c): before staining staining and (b and,d) after (b), ( staining.d): after staining.

(a) (b) (a) (b) FigureFigure 6. 6. SurfaceSurface change change on on the the PEEK PEEK clasp. clasp. (a (a):) just just after after delivery and ( b):) twotwo yearsyears later.later. Figure 6. Surface change on the PEEK clasp. (a): just after delivery and (b): two years later. 3. DiscussionThe rest part and the clasp arm still fitted well without any deformation, and the participant reported3. Discussion no particular problem with occlusal contact. This case report on the PEEK clasp involved a follow-up of short duration (two years), but both No specific mobility of the abutment teeth, and no specific inflammation of the gingiva around patientThis and case practitioner report on werethe PEEK almost clasp satisfied involved with a thefollow-up outcome. of Fewshort color duration and texture(two years), changes but wereboth the abutment teeth were found. The subjective operational opinion of the practitioner about wearing observed,patient and reconfirming practitioner werethe chemical almost satisfied stability with and thebiocompatibility outcome. Few ofcolor PEEK, and althoughtexture changes it has werebeen and detaching of the denture was also reported as good. reportedobserved, that reconfirming such changes the in chemical other nonmetal stability clasp and biocompatibilitymaterials are occasionally of PEEK, found although several it has months been reported that such changes in other nonmetal clasp materials are occasionally found several months 3.after Discussion delivery. after delivery. This case report on the PEEK clasp involved a follow-up of short duration (two years), but both patient and practitioner were almost satisfied with the outcome. Few color and texture changes were observed, reconfirming the chemical stability and biocompatibility of PEEK, although it has been reported that such changes in other nonmetal clasp materials are occasionally found several months after delivery. Biofilm formation on the surface of PEEK has been reported to be equal to or lower than that on the surface of conventionally applied abutment materials, such as zirconia and titanium [10]. However, bacterial adherence is easily overlooked, because the colors of denture plaque and PEEK material Dent. J. 2019, 7, 4 5 of 6 are similar. Clinical examination revealed no periodontitis or gingivitis in relation to the abutment teeth. The clasp design of PEEK may be similar to that of nonmetal denture clasps considering the mechanical property of PEEK, while the PEEK clasp permits reduction of the coverage/proximity of the cervical part of abutment teeth. Therefore, the gingiva around the PEEK clasp should be monitored with regular check-ups. Clinical complications around the interface between the metal frame and denture base resin, such as fracture of the denture base and invasion of foreign objects into the gap, often occur in conventional RPDs [11]. In our case study, such complications were not found after two years. The difference in elastic modulus between PEEK and acrylic resin is smaller than that between metal and resin, reducing the likelihood of these interface problems, although there is no chemical adhesion between PEEK and acrylic resin [12]. Esthetically, the color of conventional nonmetal clasp materials is viewed as that of gingiva, while the color of PEEK is that of teeth. The slightly grayish, nontransparent white color of PEEK was more acceptable than the silver color of a metal clasp. Nonetheless, it did not match the tooth or crown color sufficiently. If the PEEK clasp is placed in the esthetic zone, the clasp apex had not better located in the far zone of the abutment teeth, but rather positioned slightly beyond the central line of the crown as we did in our case. Future development of PEEK that matches the tooth color more closely and is slightly more transparent will improve its esthetics. The elastic coefficient of PEEK is approximately 4 GPa [13], which is considerably less than that of gold alloy (100 GPa) and Co–Cr alloy (200 GPa) [14]. Appropriate retention force and bracing will need to be attained by increasing the thickness and width of the clasp arms in PEEK relative to those of conventional metal clasp. Clasp retentive force is directly proportional to these attributes, and also to elastic modulus and the degree of undercut, and is inversely proportional to the length of the clasp arm [15,16]. Therefore, the shortened and wide clasp arm, with the clasp apex slightly overlapping the center, contributed to improved aesthetics and to increased retentive force. In contrast, the lower flexural modulus than that of metal may be beneficial, because it reduces the risk of excessive force on the abutment tooth [17]. To date, it has not been reported that the PEEK clasp occlusal force distribution was unsatisfactory in this case. Clasp design without coverage of the cervical area, in contrast with conventional thermoplastic resins, is advantageous for periodontal disease and root caries. A PEEK clasp has the same disadvantages as other nonmetal clasp materials: difficulty of polishing and adjusting retention capacity. The appropriate polishing procedure of PEEK is under consideration; it is expected to have the same smoothness as that of acrylic resin. It is impossible to adjust the retention capacity due to clasp bending at delivery; therefore, preoperative designing is necessary for a PEEK clasp. In conclusion, we have presented a satisfactory outcome of an RPD case utilizing a PEEK clasp retainer over a short observation period. Standardizations of clasp design and laboratory and clinical work will be required in the near future.

Author Contributions: All dental treatment procedures: T.I., and K.K.; Writing—Preparation of Original Draft, T.I., Y.I., L.L., and T.M.; Writing—Review and Editing, T.I. and L.L. Funding: This work was partially supported by JSPS KAKENHI Grant Number JP16K11597. The subject gave her informed consent for inclusion before she participated in the study. The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of Tokushima University Hospital (No. 2413). Acknowledgments: We would like to express our gratitude to Shizuo Higuchi (Wada Precision Dental Laboratories, Osaka, Japan) for the fabrication of the PEEK clasps. Conﬂicts of Interest: PEEK material was kindly provided by InvibioTM Biomaterial Solutions. The authors declare no conﬂicts of interest. Dent. J. 2019, 7, 4 6 of 6

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