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CLINICAL REPORT
aAssociate PrbChief Techn
166
Use of ceria-stabilized zirconia/alumina nanocomposite forfabricating the frameworks of removable dental prostheses:
A clinical report
Yoshiyuki Hagiwara, DDS, PhDa and Kiyoshi Nakajima, CDTbABSTRACTCeria-stabilized zirconia/alumina nanocomposite (Ce-TZP/A) exhibits an elasticity equivalent to thatof cobaltechromium alloy and a flexural property that is superior to that of yttria-tetragonal zirconiapolycrystal. Therefore, the use of Ce-TZP/A for the fabrication of removable dental prosthesisframeworks is being studied. However, the current English literature does not include anyclinical report on the use of Ce-TZP/A for the fabrication of the entire framework. This clinical reportdescribes the process and outcomes of fabricating a mandibular implant-supported overdentureand a maxillary complete denture with Ce-TZP/A as the framework material. (J Prosthet Dent2016;116:166-171)
An implant-supported over-denture (IOD) is an effectivetreatment option for patientswith edentulism. Comparedwith a complete denture (CD),the IOD achieves superiorretention through attachmentsand minimizes implant lossafter loading, resulting in highpredictability.1-3 In addition,
the IOD provides greater patient satisfaction by facilitatingimprovements in food intake because of increasedmasticatory function, comfort, and sense of confidence.4-7However, IOD use has been associated with severalcomplications, including the loss of attachment retentionor fracture of the denture base.2,8,9 Therefore, regularmaintenance is essential to enhance the predictability ofIODs and ensure comfortable, long-term use.10,11 Ac-cording to past reports, a robust metal frameworkincreases the fracture resistance of the base or the upperportions of attachments in IODs.12,13
Titanium (Ti) and cobaltechromium (CoeCr) arecommonly used in the frameworks of removable dentalprostheses (RDPs), including IODs, which are conven-tionally fabricated by casting procedures. However,fabrication through milling has become possible with thedevelopment of computer-aided design and computer-aided manufacturing (CAD-CAM) technologies, whichhave gradually simplified technical operations, particu-larly those involved in the fabrication of Ti and CoeCrframeworks.14,15 This technology has also facilitated the
ofessor, Department of Fixed Prosthodontics, Nihon University School of Dician and President, KN Dental Laboratory, Hitachi City, Japan.
use of ceria-stabilized zirconia/alumina nanocomposite(Ce-TZP/A), a recently developed material with highstrength, for RDP frameworks. Ce-TZP/A incorporatesalumina nanoparticles with a size of several hundrednanometers into ceria-stabilized zirconia crystals. Thevolume ratio is approximately 30%, and this materialexhibits extremely high fracture toughness (19 MPa.m1/2)and bend strength (1400 MPa).16-18 In addition, theincreased resistance to low-temperature degradationsuggests the material will have long-term reliability.19
Therefore, apart from fixed dental prostheses (FDPs), theuse of this material in implant bodies and abutments andframeworks of RDPs has been considered feasible.20,21
Ce-TZP/A exhibits poor light-transmitting properties andis white in color; consequently, it can only be used as anFPD framework and necessitates the use of porcelainveneers. The disadvantages of CoeCr frameworks forRDPs include unacceptable esthetics because of themetallic color and the possibility of metal allergy.21
Several studies have reported the use of Ce-TZP/A inFDP and implant abutments.22-26 However, to our
entistry, Tokyo, Japan.
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Figure 1. A, Occlusal view of maxillary arch. B, Occlusal view of mandibular arch with healing abutments.
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knowledge, only 1 study has reported an actual clinicalapplication.27 As an RDP framework, Ce-TZP/A exhibitsan elasticity equivalent to that of CoeCr and a flexuralproperty superior to that of yttria-tetragonal zirconiapolycrystal (Y-TZP). Therefore, its use in the fabrication ofclasps included in the framework of partial removabledental prostheses is being studied.21 This clinical reportdescribes the process and outcomes of fabricating amandibular IOD and a maxillary CD using Ce-TZP/A asthe material for the base frameworks.
CLINICAL REPORT
A 65-year-old, completely edentulous Asian womanpresented at Nihon University Dental Hospital. Thepatient’s medical history was unremarkable. On the basisof clinical and radiographic examinations and the pa-tient’s expectations, a treatment plan was developed tofabricate an IOD supported by 4 implants for themandible and a CD for the maxilla. For implant place-ment in the mandible, a surgical guide was fabricated,followed by the placement of 4 threaded, 4×10-mm im-plants (Osseotite; OSS 410; Biomet 3i). After 3 months,the implants were uncovered and healing abutments(One-piece Healing Abutment; Biomet 3i) were seated(Fig. 1).
The maxillary custom impression tray was bordermolded with modeling plastic impression compound(Impression compound type I; Kerr Corp) and animpression made with polyvinyl siloxane impressionmaterial (Take 1; Kerr Corp). The impression was pouredwith Type IV dental stone (New Fujirock; GC Corp). Thesame technique was used for the mandible. Then, thehealing abutments were replaced with implant impres-sion copings (IIC 12; 3i Implant Innovations Inc), and animplant-level impression was recorded using polyvinylsiloxane impression material (Take 1; Kerr Corp). Theimplant-level replicas (ILA 20; 3i Implant InnovationsInc) were attached to the impression copings in the
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impression. The impression was poured with Type IVdental stone (New Fujirock; GC Corp). Subsequently,wax occlusion rims were fabricated for both jaws, and thelip support and facial profile were evaluated. The occlusalvertical dimension (OVD) was determined on the basis ofthe OVD in the patient’s existing prostheses. The castswere mounted in a semiadjustable articulator (DenarMark II Articulator; Whip Mix Corp) in a centric relationrecord. Artificial teeth were selected according to thepatient’s existing CD (Duradent; GC Corp) and arrangedon the occlusion rims used for registration, which werethen evaluated in the oral cavity for pronunciation,appearance, and occlusion. Before the design and fabri-cation of the Ce-TZP/A framework, the definitive den-ture forms were determined using the wax trial dentures.This allowed an estimate of the denture space whiledesigning the Ce-TZP/A framework and created anappropriate framework.
The maxillary definitive cast and wax trial denturewere scanned with a laser scanner (Noritake DentalScanner SC-3; Kuraray Noritake Dental Inc), and thescanned data were overlaid on a personal computer (PC)screen using CAD software (Katana; Kuraray NoritakeDental Inc). An IOD using stud-type attachments wasfabricated for the mandible. Locator attachments(Locator implant attachment; Zest Anchors) weremounted on the definitive cast and read by a dentalscanner. The scanned data for the mandibular definitivecast and wax trial denture were overlaid on a PC screenusing CAD software (Katana; Kuraray Noritake DentalInc). The Ce-TZP/A framework was designed using CADsoftware (Katana; Kuraray Noritake Dental Inc), withfocus on the following considerations: the design of themaxillary framework was similar to that of conventionalTi and CoeCr frameworks; holes were included for theLocator attachments (Zest Anchors) in the mandibularframework to facilitate the use of the direct technique,wherein the retaining caps (Denture cap; Zest Anchors)are assembled inside the oral cavity at the time of delivery
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Figure 2. A, Optical scan of maxillary definitive cast. B, Digital design for CAD-CAM-fabricated Ce-TZP/A framework for maxillary complete denture.C, Optical scan of mandibular definitive cast with Locator implant attachments (Locator, Zest Anchors). D, Digital design for CAD-CAM-fabricatedCe-TZP/A framework for mandibular implant-supported overdenture.
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of the definitive IOD, and tissue stops were included onthe mucosal side of each framework (Fig. 2).
For the fabrication of the Ce-TZP/A framework,special CAM software (WorkNC Dental; Vero) was used.Milling operations were performed after determiningdetails such as the positions and heights inside thedisk, sizes, and lengths of the support pins, and the sizeof the stabilizer using a special template for the frame-work. The ceramic material was milled (C-Pro Nano-zirconia; Panasonic Healthcare) using a dedicatedmilling machine for Ce-TZP/A (imes-icore 250i 5-axisCAD-CAM milling machine; imes-icore GmbH). Then,the material was sintered for 15 hours in a dedicatedsintering furnace (Austromat mSiC; Dekema), and thebases were cut from the ceramic disks for dental millingand fitted to the definitive casts (Fig. 3). Wax trial den-tures were fabricated, again using an index on thecompleted Ce-TZP/A framework, followed by the finaltrial fitting in the oral cavity. The wax trial dentureswere invested in special flasks (Palajet duoflask; HeraeusKulzer GmbH).
As a preparation for resin packing and polymerizationafter wax elimination, the following pretreatments were
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performed for the mesh-type retention area for the resindenture base on the Ce-TZP/A framework. This area wasairborne-abraded with 0.11-mm particles (Rocatec Plus;3M ESPE). A bonding agent (Ceraresin Bond; Shofu Inc)was applied after primer (AZ Primer; Shofu Inc) appli-cation and photopolymerized. Finally, opaque material(Ceramage Pre-Opaque; Shofu Inc) was used for themesh-type retention area.
The pretreated Ce-TZP/A frameworks were returnedto the definitive casts, and resin packed by mixing a pour-type autopolymerizing resin at room temperature (Pal-aXpress vario; Heraeus-Kulzer GmbH) and pouring itinto flasks using a compressed air injection unit (Palajet;Heraeus-Kulzer GmbH) at a pressure of 414 kPa, whichwas held for 10 minutes. Subsequently, the resin waspolymerized using a multimode-type pressure polymer-ization unit (Palamat Elite; Heraeus-Kulzer GmbH) un-der a pressure of 200 kPa and at a constant temperatureof 55�C. The dentures were removed from the casts,finished, and polished (Fig. 4).
The definitive CD was delivered after clinicalremounting and occlusal equilibration. The definitive IODwas inserted, and the healing abutments were replaced by
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Figure 3. A, Complete CAD-CAM-fabricated Ce-TZP/A framework seated on maxillary definitive cast. B, Complete CAD-CAM-fabricatedCe-TZP/A framework seated on mandibular definitive cast. Four holes placed for Locator attachments.
Figure 4. A, Occlusal view of definitive prostheses with Ce-TZP/A framework. B, Intaglio surface view of definitive prostheses with Ce-TZP/A framework.
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Locator attachments (Zest Anchors) exhibiting a cuffheight of 4 mm. The male components (Denture caps;Zest Anchors) were incorporated into the IOD using thedirect technique with an autopolymerizing resin (Patternresin; GC Corp). The red plastic nylon insert (Extended
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Range Male; Zest Anchors) was inserted into the matrixhousing. The overdenture was polished and deliveredafter making minimal occlusal and fit adjustments (Fig. 5).
The patient was given oral hygiene and prostheticmaintenance instructions and was recalled at 24 hours, 1
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Figure 5. A, Occlusal surface view of mandibular arch with attachments (Locator; Zest Anchors). B, Intraoral facial view of definitive prostheses.
Figure 6. Intraoral facial view of definitive prostheses at 3-yearfollow-up visit.
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week, and 3 weeks. Each appointment involved theevaluation of occlusion, masticatory efficiency, oral hy-giene, and patient satisfaction and comfort. No clinicalproblems such as loosening or loss of the denture re-tainers, decreased retention, or loosened screws wereencountered. The patient’s satisfaction level and masti-catory function were improved by the IOD. The patienthas been undergoing regular follow-ups every 4 monthsfor 3 years and has not complained of the metallic tastethat is common with CoeCr metal bases (Fig. 6). How-ever, dark stains appeared on the palatal portion of thewhite Ce-TZP/A framework over time, which wereprobably caused by consuming approximately 3 cups ofcoffee each day, considering she was a nonsmoker. Thesestains were easily removed by chairside polishing.
DISCUSSION
Ti and CoeCr are commonly used for metal RDPframeworks, and the fabrication of frameworks usingthese materials by milling procedures instead of con-ventional casting procedures has become possiblethrough the advancement of CAD-CAM technologies.For this patient, Ce-TZP/A was used, which is not aconventional metal framework material. Ce-TZP/A ex-hibits higher strength and fracture toughness than Y-TZP, which is widely used for the fabrication of FDPs andcrowns. However, this material has almost never beenused for RDP frameworks, including IOD.
However, although Ce-TZP/A has better physicalproperties than Y-TZP, its applicability is limited becauseof its color. Nevertheless, it can be useful for the fabri-cation of RDP frameworks because of excellent biocom-patibility, resistance to low-temperature degradation, adensity lower than that of CoeCr, ability to accommodatea base thickness decrease of up to 0.55 mm, minimalimpact on the sensitivity to temperature inside the oralcavity, and the same fabrication process using CAD-CAM, as that for Ti and CoeCr frameworks.
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In this clinical report, the Ce-TZP/A framework forthe maxillary CD and the mandibular IOD was fabricatedusing the same clinical and technical procedures used forTi and CoeCr frameworks.
SUMMARY
This clinical report introduces the use of Ce-TZP/A forthe fabrication of CD and IOD frameworks. Both themaxillary CD and mandibular IOD are following an un-remarkable course without significant clinical problems;furthermore, the degree of patient satisfaction was high.However, the use of Ce-TZP/A as an RDP frameworkmaterial is relatively new; therefore, further studiesevaluating the responses to various issues are necessary.
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Corresponding author:Dr Yoshiyuki HagiwaraNihon University School of Dentistry1-8-13 KandasurugadaiChiyoda-ku, Tokyo 101-8310JAPANEmail: [email protected]
Copyright © 2016 by the Editorial Council for The Journal of Prosthetic Dentistry.
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