The rehabilitation of an edentulous mandible with a CAD/CAM zirconia framework and heat-pressed lithium disilicate ceramic crowns: A clinical report

Youngwook Cho, DMD, MSD, PhDa and Ariel J. Raigrodski, DMD, MSb School of Dentistry, Kyung Hee University, Seoul, Republic of Korea; School of Dentistry, University of Washington, Seattle, Wash

This clinical report describes a complete arch, implant-supported prosthesis with a zirconia framework and monolithic lithium disilicate crowns. The design of the computer-aided design/computer-aided manufacturing zirconia framework with cemented crowns with screw access is useful in facilitating retrievability and adequate fit, and may reduce the likelihood of porcelain chipping. (J Prosthet Dent 2014;111:443-447)

Dental implants are considered to prostheses (FDP). Suggested causes abutment screw access that are bonded be a predictable treatment for restor- include a lack of compatibility in terms onto a zirconia framework to restore ing edentulous mandibular arches.1-3 of the coefficient of thermal expansion the edentulous mandible while de- Computer-aided design/computer-aided between the zirconia core and the creasing the risk of veneering porcelain manufacturing (CAD/CAM) systems veneering porcelain,18-21 a framework fracture and facilitating retrievability. have been used for restoring edentulous design that does not provide proper arches with implant-supported fixed support for the veneering porcelain,22 CLINICAL REPORT restorations4,5 because they facilitate rapid cooling rates, and relatively low the fit between implants and super- fracture toughness and low flexural A 49-year-old man presented to structures better than conventional strength of the veneering porcelain.23-25 the prosthodontic clinic of Gowoon metal alloy castings.6,7 Various meth- To address these concerns, new layering Guide Dental Hospital with generalized ods for fabricating these types of res- porcelains with an adequate coefficient advanced chronic periodontitis and torations have been reported. Some of thermal expansion and adequate missing teeth in the right posterior suggest acrylic resin and denture teeth mechanical properties have been de- mandible and multiple teeth missing in processed onto a CAD/CAM milled veloped.26,27 However, the veneering the maxilla (Fig. 1). His chief complaint titanium framework,8 and others re- porcelain may still chip, and the repair was difficulty in masticating. His med- commend the use of a screw or cement- process may become complicated ical history was noncontributory, with retained 1-piece zirconia framework and time consuming. In addition, por- the exception of controlled hyperten- with veneering porcelain.9,10 celain chipping is the most frequently sion. A clinical evaluation revealed class A zirconia framework is superior reported prosthesis-related technical II to class III mobility (according to to a metal alloy or titanium framework complication of implant-supported the Miller classification) of the man- in terms of esthetics and biocom- ceramic FDPs.28-30 To reduce the like- dibular teeth and gingival swelling with patibility.11-14 However, concerns have lihood of defects in veneering ceramics, probing depths that exceeded 5 mm. been reported regarding long-term alternative techniques such as mono- The maxillary remaining teeth were in degradation, aging, and veneering por- lithic zirconia restorations or pressing good condition except for wear due to celain chipping.15,16 Even though long- the veneering porcelain to the zirconia sleep bruxism. A panoramic radiograph term degradation is known to decrease framework have been introduced.31-33 showed an edentulous atrophic poste- the flexural strength of zirconia, the Another frequent implant-related tech- rior maxilla with pneumatization and fracture of zirconia infrastructures has nical complication is abutment screw significant alveolar bone resorption rarely been reported and is unlikely to loosening.34 The purpose of this clini- in the mandible (Fig. 2). Because of cause clinical catastrophic failure.17 cal report was to describe the use financial concerns, the patient wanted Veneering porcelain chipping has been of lithium disilicate monolithic heat- to have the mandible treated first with reported with zirconia-based fixed dental pressed ceramic crowns with holes for an implant-supported complete fixed aPrivate practice; and Affiliate Professor, Department of Prosthodontics, Kyung Hee University. bProfessor, Department of Restorative Dentistry, University of Washington, School of Dentistry; Adjunct Professor, Department of Materials Sciences and Engineering University of Washington, College of Engineering. Cho and Raigrodski 444 Volume 111 Issue 6

1 Preoperative photographs: frontal view. 2 Preoperative panoramic radiograph.

(Vertex Light Curing Trayplates; Vertex Dental) and open-tray impression cop- ings (Impression Coping Pick-up; Den- tium Corp). The impression was poured with Type IV gypsum material (Fujirock EP; GC America Inc) to fabricate the definitive cast. Six yellow abutments for direct milling (Dual Milling abutment; Dentium Corp) with titanium nitride coating were connected to the implant replicas on the definitive cast. These were milled with a 2-degree milling bur to fabricate a cement-type zirconia superstructure. Subsequently, all the 3 Panoramic radiograph after connecting interim abutments to implants. abutments were transferred to the oral cavity, and their positions were con- firmed with an abutment positioning prosthesis and then to have the maxilla 1 week, 6 impression copings (Impres- device. A centric relation record was treated with a partial removable den- sion Coping Pick-up; Dentium Corp) made with a recording device (GC tal prosthesis. An interim mandibular were connected to the implants Pattern Resin; GC America Inc), and complete denture was inserted and re- and used as interim screw-type abut- casts were mounted in a semiadjustable lined with tissue-conditioning material ments (Fig. 3). The prefabricated fixed articulator (Hanau modular articulator; (Soft-liner; GC Corp) immediately after detachable interim prosthesis made Whip Mix Corp). An anatomic contour extraction of the remaining teeth and by duplicating the interim complete waxing was made and converted into was used for evaluating esthetics, denture, with access holes for the an acrylic resin prosthesis (GC Pattern phonetics, and the occlusal vertical interim abutments, was placed and resin; GC America Inc) by using putty dimension. A clear acrylic resin surgical evaluated for proper occlusion and index (Lab Putty; Coltène/Whaledent, template (Vertex Rapid Simplified; Ver- clearance between each access hole Inc). Light-polymerized composite resin tex Dental) was made with a duplicate and its corresponding interim abut- (Rigid Transparent þ Blue; Zirkonzhan) of the interim denture. ment. Successively, autopolymerized was used free hand to correct each Three months after extraction, 6 acrylic resin (Jet denture repair resin; tooth shape. This complete contour endosseous dental implants, 10 mm Lang Dental Mfg Co) was applied to simulation was inserted intraorally to in length and 4.3 mm in diameter the holes, and an interim fixed pros- verify the occlusal vertical dimension (Implantium; Dentium Corp) were thesis was placed for 4 months until a and soft-tissue support (Fig. 4). Each placed with the 1-stage approach. maxillary partial removable dental tooth of the simulated restoration was Because of patient fatigue and reduced prosthesis was fabricated. cut back approximately 2.0 mm to treatment compliance and because of Subsequently, a definitive man- permit the fabrication of the definitive the length of surgery, an early loading dibular impression was made with restoration, with the silicone matrix as a interim denture was planned. After a custom light-polymerized open tray reference. The acrylic resin framework The Journal of Prosthetic Dentistry Cho and Raigrodski June 2014 445

4 Vertical dimension and soft-tissue support evaluation. 5 Scanning of acrylic resin framework.

6 Zirconia framework before final sintering. 7 New centric relation record. was scanned (Optical scanner S600; was etched for 30 seconds with hydro- restorative material (Fermit; Ivoclar Zirkonzhan), and the CAD/CAM zirco- fluoric acid, and a primer (Z-Prime Vivadent), and composite resin restor- nia framework was fabricated (Prettau; plus; Bisco Inc) was applied on the ative material (Filtek P60; 3M ESPE) Zirkonzahn). The intaglio was also cut abutment margin. The crowns were (Figs. 9, 10). The occlusion was refined, back for gingival porcelain addition, and etched for 20 seconds with hydrofluoric and the patient expressed his satisfac- the framework was sintered (Figs. 5, 6). acid and silanated. Self-etching, self- tion with the esthetic and functional Once sintering was completed, the adhesive resin cement (Unicem; 3M outcomes. The patient was scheduled zirconia framework was veneered with ESPE) was used to bond each mono- for recall at 6-month intervals and feldspathic gingival porcelain (Creation lithic lithium disilicate crown to the presented with satisfactory oral hygiene Zi-F; Creation Willi Geller Intl GmbH). zirconia framework extraorally. After and no mechanical complications at After verifying the fit of the zirconia connecting the custom abutments with the 9-month follow-up. framework on the abutments intra- the implants in the oral cavity, the orally, a new centric relation record was CAD/CAM zirconia framework was DISCUSSION made (Fig. 7) and used for remounting. cemented onto the abutments with A complete-contour waxing was per- provisional implant cement (Implant In this clinical treatment, each formed on each tooth preparation Cement; Premier). To ensure the com- crown was fabricated from monolithic simulation of the zirconia framework. plete removal of residual cement, each lithium disilicate and cemented onto Subsequently, lithium disilicate mono- abutment screw was loosened and the framework. Lithium disilicate was lithic crowns (Emax; Ivoclar Vivadent) the restoration was removed; then it chosen for esthetics and strength.35 were heat pressed to fit each abutment was reseated, and all the abutment Clinical studies on monolithic lithium (Fig. 8). screws were tightened to 35 Ncm. disilicate crowns and FDPs have shown The gingival ceramic around each Finally, the access holes were filled with promising results in terms of structural margin of the zirconia tooth simulation cotton pellets, interim composite resin integrity.36-38 If chipping or fracture of Cho and Raigrodski 446 Volume 111 Issue 6

8 Complete contour waxing and monolithic lithium disilicate crowns.

9 Complete mandibular prosthesis in process of bonding 10 Intraoral occlusal view of complete prosthesis. individual lithium disilicate crowns.

the crowns occurs, then the prosthesis Because crowns on this prosthesis be more costly than conventional design allows the removal and replace- can be easily replaced compared with prostheses. ment of the crown intraorally, or a monolithic zirconia prosthesis, er- extraorally by removing the restoration. rors such as deficient occlusal con- SUMMARY Another prospective complication with tactsonanindividualcrowncanbe complete arch implant-supported FDPs corrected. The possible disadvantage This technique combines the CAD/ is screw loosening or screw fracture. of this prosthesis is the risk of failure CAM fabrication of a zirconia frame- This type of prosthesis enables retriev- in the bond between the zirconia work for precision with heat-pressed ability and screw management because framework and the veneering gingival monolithic lithium disilicate crowns each access hole is maintained as part porcelain. Using individual crowns, for esthetics and function. This type of of the crown. as with this prosthesis, may also prosthesis may reduce the likelihood of The Journal of Prosthetic Dentistry Cho and Raigrodski June 2014 447

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