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315
Consecutive Case Series of Monolithic and Minimally Veneered Zirconia Restorations on Teeth and Implants: Up to 68 Months Michael Moscovitch, DDS, CAGS1
The aim of this study was to evaluate the performance of monolithic zirconia in function and minimally veneered zirconia (feldspathic ceramic, not in function, on the facial surface to enhance tooth esthetics or replace gingival structures) on both teeth and implants. This open-ended consecutive case series involved 238 patients between the ages of 16 and 92 years, 1,022 restoration units, and 365 cases in all categories of tooth and implant restorations in a private practice clinical environment for up to 68 months. The restoration parameters monitored in the patient base were fracture, cracking, or chipping of the zirconia structure and/or the minimally veneered feldspathic ceramic. There were no observed complications with respect to these parameters associated with any of the restorations included in this study. (Int J Periodontics Restorative Dent 2015;35:315–323. doi: 10.11607/prd.2270)
Assistant Clinical Professor, Department of Restorative Sciences/Biomaterials, Goldman School of Dental Medicine, Boston University, Boston, Massachusetts, USA; Lecturer, Faculty of Dentistry, Dental Residency Program, Jewish General Hospital, McGill University, Montreal, Québec, Canada.
1
Correspondence to: Dr Michael Moscovitch, 4150 St Catherine St West, Suite 210, Montreal, Quebec, Canada H3Z 2Y5; fax: 514-935-5261; email: [email protected]. ©2015 by Quintessence Publishing Co Inc.
The basic indications for the use of an advanced high-strength ceramic is to avoid damage and wear and increase the esthetic and performance outcomes of dental restorations. The variability of function and support, ie, teeth and/or implants, underpins the use of the technical ceramic zirconia to circumvent the performance issues of weaker ceramics. Zirconia is a well-documented material of high strength and excellent biocompatibility in the scientific literature in both the dental and medical disciplines.1–4 Zirconia ceramics have been used in dentistry for implants, implant abutments, posts and cores, orthodontic brackets, as well as copings and frameworks for bilayered dental restorations with feldspathic ceramic.5–7 During the past decade, there has been a dramatic increase in the use of all-ceramic non-zirconia-based and zirconia-based restorations in fixed prosthodontics. Wang et al8 reported an overall 5-year fracture rate of 4.4% of teeth supported by single all-ceramic crowns (bilayered), irrespective of the materials used. Posterior segments showed higher veneer fracture incidences than anterior segments. Molars showed significantly higher crown fracture rates than premolars. This study did not include glass-ceramics because this material is no longer recommended for full crown use.3 The strength
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316
Table 1 Restorative materials used in the case series Restorative material
Number of restorative units
Monolithic zirconia
745
Monolithic zirconia with facial feldspathic veneer
277
Pink feldspathic ceramic (not in function)*
193
Total
1,022
*Not included in total; used in conjunction with the monolithic zirconia or monolithic zirconia + feldspathic ceramic veneer units.
of zirconia allowed its use in the fabrication of frameworks for fixed partial dentures. Breakage of the veneering feldspathic ceramic continued to plague this approach, especially in posterior segments.9–11 Conrad et al3 reported typical survival rates of 88% to 100% after 2 to 5 years in service and 84% to 97% after 5 to 14 years in service for allceramic restorations (bilayered), including fixed partial dentures. The frequent occurrence of breakage of the veneering feldspathic ceramic and substrate became a clinically unacceptable problem compared to bilayered metal restorations.12–14 These complications were generally the result of the greater forces of occlusion in posterior areas, varying parafunctional occlusal activity, and the rigid nature of dental implants.15–17 Historically, restoring patients with advanced wear or function with bilayered ceramics on both teeth and implants has been challenging without the prescription of a protective acrylic appliance or full-metal occlusion to prevent damage.18,19 In recent years, various shortterm clinical reports involving the use of monolithic and minimally veneered zirconia have shown prom-
ising results with respect to the performance of these restoration designs.20–22 In addition, several studies have indicated that monolithic or minimally veneered (ie, no feldspathic in function) zirconia would be the current choice for reliable ceramic dental restorations.5,7,23 The aim of this study was to evaluate the performance of monolithic zirconia in function (no feldspathic ceramic veneer) and minimally veneered zirconia (feldspathic ceramic on the facial surface, not in function, used to enhance tooth esthetics or to replace gingival structures with pink feldspathic ceramic; Table 1) on both teeth and implants, regardless of parafunctional occlusal activity. Klasser et al24 reported that this condition is a continuously variable event, and it would be challenging to determine the severity of bruxism activity at any given time.
Method and materials Patient selection
This consecutive case series included 1,022 restorative units (all categories) in 365 cases involving 238 patients (38% male, 62% female)
between the ages of 16 and 92 years (mean age, 61.9 years; Table 2 and Fig 1). The inclusion criteria of this study were all patients who were planned for restorative treatment involving fixed restorations on teeth and/or implants in a private practice clinical environment. These restorations ranged from single crowns to multi-unit fixed partial dentures (Table 3). The selection process was sequential, except for patients requiring only custom esthetics with fully veneered zirconia restorations in the anterior maxilla.
Clinical approach
Patient histories were taken, followed by complete diagnosis and treatment planning procedures. Supportive implant, periodontal, endodontic, and orthodontic treatment was provided by the appropriate dental specialists in a team approach.25 Informed consent was obtained with respect to procedures, choice of materials, and outcomes. Each patient in the study entered into the normal clinical workflow of the author’s private practice.
Restorative workflow
Initially, the workflow to produce the provisional restorations, prototypes, and definitive zirconia restorations was managed with analog technology. Subsequently, digital technologies were included in the workflow (Fig 2). These technologies comprised in-laboratory scanning of the master casts and computer-aided
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317
Parameter
Number
Total patients
238
Total cases* (tooth- and implant-supported)
365
Tooth-supported restorations (units)
422
Implant-supported restorations (units)
600
Total restorations (units)
140 120 Number of patients
Table 2 Number of patients, cases, and restorative units included in case series
100 80 60 40 20
1,022
0
*A case refers to a restored segment; there may be more than one case per patient.
10s
20s
30s 40s 50s 60s 70s Age range of patients (y)
80s
90s
Fig 1 Age distribution of patients.
design/computer-assisted manufacturing (CAD/CAM) software, along with computer numerical controlled (CNC) machinery. The zirconia restorations were equally precise irrespective of the technique.26 All intraoral impressions were taken with traditional materials: alginate (Jeltrate, Dentsply) for study casts and opposing casts and polyvinyl siloxane (Aquasil, Dentsply) for all master casts. These impressions were poured with high-quality die stone (Fujirock EP, GC) and scanned. Diagnostic mock-ups were accomplished for each patient situation. This information was scanned into the design software and further modified as necessary. The completed design was then used to generate a polymethyl methacrylate (PMMA; Vipi Block PMMA, Vipi) provisional and/or prototype restoration to be used as a blueprint for the zirconia design.27,28 Master casts for multi-unit tooth-supported restorations were verified intraorally with the prototype restoration. Master casts for multi-unit implantsupported restorations were veri-
Table 3 Case categories Location and type of unit
Tooth-supported
Single anterior and posterior (units)
Implant-supported
236
91
61
98
Multi-unit anterior, posterior, and full-arch (at least one pontic; units)
125
411
Total
422
600
Multi-unit splinted anterior, posterior, and full-arch (units)
Scanned diagnostic setup Data input merged
Design modifications
Phase 1 Digital milled data input
Provisional restoration PMMA
Scanned provisional and cast Data input merged
Design modifications
Phase 2 Digital milled data input
Prototype restoration PMMA
Scanned prototype Data input merged
Design modifications
Phase 3 Digital milled data input
Definitive restoration Zirconia
Fig 2 Digital restorative workflow.
fied intraorally with either the fixed provisional or prototype restoration. The prototype was adjusted intraorally, then scanned and merged with the master cast. Further minor virtual modifications were carried out as necessary, eg, contour, occlusal form, and facial cutbacks for white or pink feldspathic ceram-
ics in the nonfunctioning anterior facial surfaces or gingival areas (to meet patient-specific esthetic requirements). The completed file was then used with the CAD/CAM software to mill the definitive zirconia restoration29 according to the manufacturer’s specifications (Prettau, Zirkonzahn).
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318
a
b
c
d
e
f
Fig 3 Case presentation: Maxillary implantsupported screw-retained restoration (Astra Tech Implant System, Dentsply). (a) Virtual design for the provisional (PMMA), prototype (PMMA), and definitive (zirconia with pink gingival feldspathic ceramics) restorations. (b) Pretreatment intraoral frontal view with eight implants. (c) Completed definitive restoration. (d) Posttreatment intraoral frontal view with definitive restoration in place. (e) Occlusal view of the virtual design. (f and g) Posttreatment occlusal view of zirconia restoration with open (f) and sealed (g) screw access channels. (h) Posttreatment full smile view. (i) Posttreatment radiograph of the maxillary restoration.
g
h
i
The zirconia restoration was colored with water-based (Colour Liquid Aquarell, Zirkonzahn) or acid-based (Colour Liquid Prettau, Zirkonzhan) stains before the sintering and glazing cycles. Feldspathic
white and pink ceramics (VITA VM9, VITA Zahnfabrik) were added to the nonfunctioning facial surfaces where required for esthetics (Figs 3 and 4). Post-delivery minor occlusal adjustments were performed
with fine high-speed diamonds (ET Series Fine, Brasseler) and copious water spray. In all cases, the glaze was polished from the functional surfaces to minimize wear of opposing structures.30 The adjusted
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319 Fig 4 Case presentation: Four maxillary anterior tooth–supported single crowns. (a) Pretreatment maxillary anterior view. (b to d) Definitive tooth preparations. (e to g) Posttreatment radiographs. (h to j) Posttreatment facial views of definitive zirconia crowns (minimally veneered; no feldspathic ceramic in function). Note that the maxillary canines were restored with direct composite. (k and l) Virtual design of definitive zirconia restorations with facial cutbacks. (m) Posttreatment full smile.
e
f
g
a
b
c
d
h
i
j
k
l
surfaces were finished with a zirconia polishing system (Dialite, Brasseler). All tooth- and implantsupported cement-retained restorations were sandblasted with aluminum oxide (50 μm) at 2 bars
m
and luted with resin ionomer (RelyX, 3M). Screw-cement-retained implant-supported restorations were secured with a combination of temporary cement (TempBond, Kerr) and titanium-alloy fixed par-
tial denture screws to allow for future retrievability. Screw access channels were sealed with poly tetrafluoroethylene tape (white) and a suitable composite shade (Filtek Supreme Ultra, 3M; Fig 3).31
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320 Results
350
Number of restorations
300 250 200 150 100 50 0
0–12
12–24
24–36 36–48 Time in function (mo)
48–60
60–68
Fig 5 Distribution of restorations in function over time.
Table 4 Distribution of restorations lost to follow-up Number of restorations Cause of loss
ToothImplantsupported supported
Months in function
Replacement months in function
Abutment fracture*
0
1
1.9
49.1
Root fracture
1
0
10.5
44.8
Root fracture
1
0
1.5
10.3
‡
Root fracture
1
0
9.4
N/A
Root fracture‡
1
0
14.0
N/A
Root fracture‡
1
0
31.4
N/A
Root fracture
1
0
20.3
N/A
Deceased
0
4
10.6
N/A
Deceased
0
9
13.4
N/A
Deceased
0
4
45.4
N/A
Deceased
3
5
45.4
N/A
Total (11 patients)
9
23
N/A
N/A
†,‡ †,‡
‡
N/A = not applicable. *Zirconia abutment fracture; replaced with screw-retained crown with titanium base. †Replaced with an implant-supported restoration. ‡All root fractures were associated with endodontically treated teeth.
Table 5 Number of restorative units with clinical complications at 68 months Complication
Zirconia structure*
Feldspathic veneer†
Fracture
0
0
Chipping
0
0
Cracking
0
0
*All units have zirconia in occlusal function. †No feldspathic ceramic in function.
Within the patient population of the study, 1,022 restorative units were completed over a period of 68 months (Fig 5). A total of 755 units of restoration have been in function between 1 day and 36 months. A total of 267 units of restoration have been in function between 36 and 68 months. All patients in the study were followed by the author in his private practice continuing care program. The distribution of restorations lost to follow-up is shown in Table 4. One cement-retained implant-supported restoration was lost to zirconia abutment fracture (not a failure of the zirconia restorative material) and replaced with a single screw-retained implant-supported zirconia restoration with a titanium base. Six tooth-supported restorations were lost as a result of root fracture (not a failure of the zirconia restorative material); two of these were replaced with single-crown restorations each supported by two implants.32 Four patients with 22 implant-supported and 3 toothsupported restorations passed away during the follow-up period. There were no observed complications with respect to fracture, cracking, or chipping of the zirconia structure and/or the minimally veneered feldspathic ceramic to date (Table 5). This is in agreement with case reports by Rojas-Vizcaya,21 Thalji and Cooper,22 and Marchack et al.33 However, these results vary from previous studies using zirconia with feldspathic ceramic in function9–11 as well as all other bilayered ceramic or metal-based restorations.12–14
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321 Discussion In the present study, the zirconia restorations exhibited a 100% success rate at 68 months. No fractures, cracks, or chipping of the monolithic zirconia structure with or without a minimally veneered feldspathic ceramic component (not in function) have been observed to date (see Table 5). Acrylic occlusal guards were not used to protect any of the restorations in the study because of the strength of zirconia and the fact that all function was only on this material.23 However, it should be noted this practice has been routinely used with traditional bilayered ceramic restorations.18 This is of particular importance going forward in terms of being able to create esthetic restorations with a time-efficient workflow that results in outcomes with a level of success not previously reported in the literature.9–11,15,16 The use of zirconia to produce dental restorations as described requires a milling protocol. Previously, milling with analog machinery made this a tedious and time-consuming process. As CNC machinery and associated software became available, it allowed for an increase in the time efficiency of producing zirconia restorations. These new digital protocols for milling zirconia also provided a collateral benefit in the ability to create surgical guides, provisional restorations, and prototype restorations with PMMA. Studies supporting the biologic and strength characteristics of zirconia over other ceramic materials resulted in zirconia being used as
the restoration substructure with fully veneered feldspathic ceramic.1–6 This bilayered approach led to a high percentage of chip-off fractures of the veneering ceramic.9–11 Some of these studies surmised that the use of monolithic zirconia would be likely to produce the results that are reported in this clinical study.5,6 The restorative community continues to seek solutions to the clinical challenges using bilayered zirconia restorations. In an effort to solve the chip-off fracture problem, Fabbri et al34 suggested the use of reinforced feldspathic ceramic (lithium disilicate) cemented over a zirconia substructure, and some have suggested various modifications to the technical management of applying feldspathic ceramic to the zirconia substrate.35,36 However, limited data are available for these techniques. Realistically, all bilayered designs of zirconia restorations with material other than the zirconia in function continue to create complications that affect outcomes.9–11 All restorations in this study, whether supported by teeth and/ or implants, have only zirconia in function against opposing restorations or natural teeth. The opposing restorative materials included precious alloys, nonprecious alloys, feldspathic ceramics, reinforced feldspathic ceramics, amalgams, and composites. As reported by Park et al,30 zirconia is minimally abrasive to opposing structures, and this property is maximized by leaving the occlusal surfaces polished after definitive intraoral occlusal adjustments.
Hisbergues et al2 have indicated that soft tissue response and plaque adhesion to zirconia is as good as or better than natural tooth structure. At this time, the high cost of gold alloys is influencing the restorative community to consider alternative metal alloys such as titanium for substructures, combined with various veneering materials. Ko et al37 have shown that titanium has been implicated in inducing localized hypersensitivities as well as severe systemic allergic reactions. Gökçen-Röhlig et al38 indicated that dental zirconia has no reported allergic reactions and has proven to be nontoxic and nonirritating, enhancing the desirability of using zirconia as a substrate for restorations. Finally, recent studies by Alghazzawi et al39 and Flinn et al40 have indicated that previous concerns regarding low-temperature degradation of zirconia at oral temperatures is not a long-term concern for the residual strength of zirconia restorations. The results of this study indicate that there is a new paradigm possible in fixed prosthodontics that allows for the use of an advanced high-strength ceramic (zirconia) to enhance the overall esthetics, biocompatibility, performance, efficiency, and cost-benefits41 to the restorative community and patients in a manner not previously possible.
Conclusions After an observation time of 68 months, monolithic and minimally veneered zirconia in the restoration
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322 of teeth and implants shows promising results as a reliable material for the wide variety of clinical applications described in this study. More studies of this category of restoration will be helpful in establishing this treatment modality as a possible new benchmark in restorative dentistry.
Acknowledgments The author would like to thank Hiam Keren, MDT, for the laboratory support in the production of all restorations in this study and Jacques Geleyn and Danae Sandoval for their technical assistance in the preparation of this manuscript. The author reported no conflicts of interest related to this study.
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19. Moshaverinia A, Kar K, Aalam AA, Takanashi K, Kim JW, Chee WW. A multidisciplinary approach for the rehabilitation of a patient with an excessively worn dentition: A clinical report. J Prosthet Dent 2014;111:259–263. 20. Keren H, Caro S. Das beste material. Dental Labor 2009;57:1056. 21. Rojas-Vizcaya F. Full zirconia fixed detachable implant-retained restorations manufactured from monolithic zirconia: Clinical report after two years in service. J Prosthodont 2011;20:570–576. 22. Thalji GN, Cooper LF. Implantsupported fixed dental rehabilitation with monolithic zirconia: A clinical case report. J Esthet Restor Dent 2014;26: 88–96. 23. White SN, Miklus VG, McLaren EA, Lang LA, Caputo AA. Flexural strength of a layered zirconia and porcelain dental all-ceramic system. J Prosthet Dent 2005;94:125–131. 24. Klasser GD, Greene CS, Lavigne GJ. Oral appliances and the management of sleep bruxism in adults: A century of clinical applications and search for mechanisms. Int J Prosthodont 2010;23: 453–462. 25. Cohen M (ed). Interdisciplinary Treatment Planning: Principles, Design, Implementation, vol 1. Chicago: Quintessence, 2008. 26. Kapos T, Evans C. CAD/CAM technology for implant abutments, crowns, and superstructures. Int J Oral Maxillofac Implants 2014;29(suppl 1):117–136. 27. Güth JF, Almeida E Silva JS, Beuer FF, Edelhoff D. Enhancing the predictability of complex rehabilitation with a removable CAD/CAM-fabricated long-term provisional prosthesis: A clinical report. J Prosthet Dent 2012;107:1–6. 28. Moscovitch MS, Saba S. The use of a provisional restoration in implant dentistry: A clinical report. Int J Oral Maxillofac Implants 1996;11:395–399. 29. Jing Z, Ke Z, Yihong L, Zhijian S. Effect of multistep processing technique on the formation of micro-defects and residual stresses in zirconia dental restorations. J Prosthodont 2014;23:206–212. 30. Park JH, Park S, Lee K, Yun KD, Lim HP. Antagonist wear of three CAD/CAM anatomic contour zirconia ceramics. J Prosthet Dent 2014;111:20–29.
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35. Canullo L, Micarelli C, Bettazzoni L, Magnelli A, Baldissara P. Shear bond strength of veneering porcelain to zirconia after argon plasma treatment. Int J Prosthodont 2014;27:137–139. 36. Tan JP, Sederstrom D, Polansky JR, McLaren EA, White SN. The use of slow heating and slow cooling regimens to strengthen porcelain fused to zirconia. J Prosthet Dent 2012;107:163–169. 37. Ko N, Mine A, Egusa H, et al. Allergic reaction to titanium-made fixed dental restorations: A clinical report. J Prosthodont 2014;23:501–503. 38. Gökçen-Röhlig B, Saruhanoglu A, Cifter ED, Evlioglu G. Applicability of zirconia dental prostheses for metal allergy patients. Int J Prosthodont 2010;23: 562–565.
39. Alghazzawi TF, Lemons J, Liu PR, Essig ME, Bartolucci AA, Janowski GM. Influence of low-temperature environmental exposure on the mechanical properties and structural stability of dental zirconia. J Prosthodont 2012;21:363–369. 40. Flinn BD, deGroot DA, Mancl LA, Raigrodski AJ. Accelerated aging characteristics of three yttria-stabilized tetragonal zirconia polycrystalline dental materials. J Prosthet Dent 2012;108: 223–230. 41. Walton TR. Making sense of complication reporting associated with fixed dental prostheses. Int J Prosthodont 2014; 27:114–118.
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315
Consecutive Case Series of Monolithic and Minimally Veneered Zirconia Restorations on Teeth and Implants: Up to 68 Months Michael Moscovitch, DDS, CAGS1
The aim of this study was to evaluate the performance of monolithic zirconia in function and minimally veneered zirconia (feldspathic ceramic, not in function, on the facial surface to enhance tooth esthetics or replace gingival structures) on both teeth and implants. This open-ended consecutive case series involved 238 patients between the ages of 16 and 92 years, 1,022 restoration units, and 365 cases in all categories of tooth and implant restorations in a private practice clinical environment for up to 68 months. The restoration parameters monitored in the patient base were fracture, cracking, or chipping of the zirconia structure and/or the minimally veneered feldspathic ceramic. There were no observed complications with respect to these parameters associated with any of the restorations included in this study. (Int J Periodontics Restorative Dent 2015;35:315–323. doi: 10.11607/prd.2270)
Assistant Clinical Professor, Department of Restorative Sciences/Biomaterials, Goldman School of Dental Medicine, Boston University, Boston, Massachusetts, USA; Lecturer, Faculty of Dentistry, Dental Residency Program, Jewish General Hospital, McGill University, Montreal, Québec, Canada.
1
Correspondence to: Dr Michael Moscovitch, 4150 St Catherine St West, Suite 210, Montreal, Quebec, Canada H3Z 2Y5; fax: 514-935-5261; email: [email protected]. ©2015 by Quintessence Publishing Co Inc.
The basic indications for the use of an advanced high-strength ceramic is to avoid damage and wear and increase the esthetic and performance outcomes of dental restorations. The variability of function and support, ie, teeth and/or implants, underpins the use of the technical ceramic zirconia to circumvent the performance issues of weaker ceramics. Zirconia is a well-documented material of high strength and excellent biocompatibility in the scientific literature in both the dental and medical disciplines.1–4 Zirconia ceramics have been used in dentistry for implants, implant abutments, posts and cores, orthodontic brackets, as well as copings and frameworks for bilayered dental restorations with feldspathic ceramic.5–7 During the past decade, there has been a dramatic increase in the use of all-ceramic non-zirconia-based and zirconia-based restorations in fixed prosthodontics. Wang et al8 reported an overall 5-year fracture rate of 4.4% of teeth supported by single all-ceramic crowns (bilayered), irrespective of the materials used. Posterior segments showed higher veneer fracture incidences than anterior segments. Molars showed significantly higher crown fracture rates than premolars. This study did not include glass-ceramics because this material is no longer recommended for full crown use.3 The strength
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Table 1 Restorative materials used in the case series Restorative material
Number of restorative units
Monolithic zirconia
745
Monolithic zirconia with facial feldspathic veneer
277
Pink feldspathic ceramic (not in function)*
193
Total
1,022
*Not included in total; used in conjunction with the monolithic zirconia or monolithic zirconia + feldspathic ceramic veneer units.
of zirconia allowed its use in the fabrication of frameworks for fixed partial dentures. Breakage of the veneering feldspathic ceramic continued to plague this approach, especially in posterior segments.9–11 Conrad et al3 reported typical survival rates of 88% to 100% after 2 to 5 years in service and 84% to 97% after 5 to 14 years in service for allceramic restorations (bilayered), including fixed partial dentures. The frequent occurrence of breakage of the veneering feldspathic ceramic and substrate became a clinically unacceptable problem compared to bilayered metal restorations.12–14 These complications were generally the result of the greater forces of occlusion in posterior areas, varying parafunctional occlusal activity, and the rigid nature of dental implants.15–17 Historically, restoring patients with advanced wear or function with bilayered ceramics on both teeth and implants has been challenging without the prescription of a protective acrylic appliance or full-metal occlusion to prevent damage.18,19 In recent years, various shortterm clinical reports involving the use of monolithic and minimally veneered zirconia have shown prom-
ising results with respect to the performance of these restoration designs.20–22 In addition, several studies have indicated that monolithic or minimally veneered (ie, no feldspathic in function) zirconia would be the current choice for reliable ceramic dental restorations.5,7,23 The aim of this study was to evaluate the performance of monolithic zirconia in function (no feldspathic ceramic veneer) and minimally veneered zirconia (feldspathic ceramic on the facial surface, not in function, used to enhance tooth esthetics or to replace gingival structures with pink feldspathic ceramic; Table 1) on both teeth and implants, regardless of parafunctional occlusal activity. Klasser et al24 reported that this condition is a continuously variable event, and it would be challenging to determine the severity of bruxism activity at any given time.
Method and materials Patient selection
This consecutive case series included 1,022 restorative units (all categories) in 365 cases involving 238 patients (38% male, 62% female)
between the ages of 16 and 92 years (mean age, 61.9 years; Table 2 and Fig 1). The inclusion criteria of this study were all patients who were planned for restorative treatment involving fixed restorations on teeth and/or implants in a private practice clinical environment. These restorations ranged from single crowns to multi-unit fixed partial dentures (Table 3). The selection process was sequential, except for patients requiring only custom esthetics with fully veneered zirconia restorations in the anterior maxilla.
Clinical approach
Patient histories were taken, followed by complete diagnosis and treatment planning procedures. Supportive implant, periodontal, endodontic, and orthodontic treatment was provided by the appropriate dental specialists in a team approach.25 Informed consent was obtained with respect to procedures, choice of materials, and outcomes. Each patient in the study entered into the normal clinical workflow of the author’s private practice.
Restorative workflow
Initially, the workflow to produce the provisional restorations, prototypes, and definitive zirconia restorations was managed with analog technology. Subsequently, digital technologies were included in the workflow (Fig 2). These technologies comprised in-laboratory scanning of the master casts and computer-aided
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317
Parameter
Number
Total patients
238
Total cases* (tooth- and implant-supported)
365
Tooth-supported restorations (units)
422
Implant-supported restorations (units)
600
Total restorations (units)
140 120 Number of patients
Table 2 Number of patients, cases, and restorative units included in case series
100 80 60 40 20
1,022
0
*A case refers to a restored segment; there may be more than one case per patient.
10s
20s
30s 40s 50s 60s 70s Age range of patients (y)
80s
90s
Fig 1 Age distribution of patients.
design/computer-assisted manufacturing (CAD/CAM) software, along with computer numerical controlled (CNC) machinery. The zirconia restorations were equally precise irrespective of the technique.26 All intraoral impressions were taken with traditional materials: alginate (Jeltrate, Dentsply) for study casts and opposing casts and polyvinyl siloxane (Aquasil, Dentsply) for all master casts. These impressions were poured with high-quality die stone (Fujirock EP, GC) and scanned. Diagnostic mock-ups were accomplished for each patient situation. This information was scanned into the design software and further modified as necessary. The completed design was then used to generate a polymethyl methacrylate (PMMA; Vipi Block PMMA, Vipi) provisional and/or prototype restoration to be used as a blueprint for the zirconia design.27,28 Master casts for multi-unit tooth-supported restorations were verified intraorally with the prototype restoration. Master casts for multi-unit implantsupported restorations were veri-
Table 3 Case categories Location and type of unit
Tooth-supported
Single anterior and posterior (units)
Implant-supported
236
91
61
98
Multi-unit anterior, posterior, and full-arch (at least one pontic; units)
125
411
Total
422
600
Multi-unit splinted anterior, posterior, and full-arch (units)
Scanned diagnostic setup Data input merged
Design modifications
Phase 1 Digital milled data input
Provisional restoration PMMA
Scanned provisional and cast Data input merged
Design modifications
Phase 2 Digital milled data input
Prototype restoration PMMA
Scanned prototype Data input merged
Design modifications
Phase 3 Digital milled data input
Definitive restoration Zirconia
Fig 2 Digital restorative workflow.
fied intraorally with either the fixed provisional or prototype restoration. The prototype was adjusted intraorally, then scanned and merged with the master cast. Further minor virtual modifications were carried out as necessary, eg, contour, occlusal form, and facial cutbacks for white or pink feldspathic ceram-
ics in the nonfunctioning anterior facial surfaces or gingival areas (to meet patient-specific esthetic requirements). The completed file was then used with the CAD/CAM software to mill the definitive zirconia restoration29 according to the manufacturer’s specifications (Prettau, Zirkonzahn).
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318
a
b
c
d
e
f
Fig 3 Case presentation: Maxillary implantsupported screw-retained restoration (Astra Tech Implant System, Dentsply). (a) Virtual design for the provisional (PMMA), prototype (PMMA), and definitive (zirconia with pink gingival feldspathic ceramics) restorations. (b) Pretreatment intraoral frontal view with eight implants. (c) Completed definitive restoration. (d) Posttreatment intraoral frontal view with definitive restoration in place. (e) Occlusal view of the virtual design. (f and g) Posttreatment occlusal view of zirconia restoration with open (f) and sealed (g) screw access channels. (h) Posttreatment full smile view. (i) Posttreatment radiograph of the maxillary restoration.
g
h
i
The zirconia restoration was colored with water-based (Colour Liquid Aquarell, Zirkonzahn) or acid-based (Colour Liquid Prettau, Zirkonzhan) stains before the sintering and glazing cycles. Feldspathic
white and pink ceramics (VITA VM9, VITA Zahnfabrik) were added to the nonfunctioning facial surfaces where required for esthetics (Figs 3 and 4). Post-delivery minor occlusal adjustments were performed
with fine high-speed diamonds (ET Series Fine, Brasseler) and copious water spray. In all cases, the glaze was polished from the functional surfaces to minimize wear of opposing structures.30 The adjusted
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319 Fig 4 Case presentation: Four maxillary anterior tooth–supported single crowns. (a) Pretreatment maxillary anterior view. (b to d) Definitive tooth preparations. (e to g) Posttreatment radiographs. (h to j) Posttreatment facial views of definitive zirconia crowns (minimally veneered; no feldspathic ceramic in function). Note that the maxillary canines were restored with direct composite. (k and l) Virtual design of definitive zirconia restorations with facial cutbacks. (m) Posttreatment full smile.
e
f
g
a
b
c
d
h
i
j
k
l
surfaces were finished with a zirconia polishing system (Dialite, Brasseler). All tooth- and implantsupported cement-retained restorations were sandblasted with aluminum oxide (50 μm) at 2 bars
m
and luted with resin ionomer (RelyX, 3M). Screw-cement-retained implant-supported restorations were secured with a combination of temporary cement (TempBond, Kerr) and titanium-alloy fixed par-
tial denture screws to allow for future retrievability. Screw access channels were sealed with poly tetrafluoroethylene tape (white) and a suitable composite shade (Filtek Supreme Ultra, 3M; Fig 3).31
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320 Results
350
Number of restorations
300 250 200 150 100 50 0
0–12
12–24
24–36 36–48 Time in function (mo)
48–60
60–68
Fig 5 Distribution of restorations in function over time.
Table 4 Distribution of restorations lost to follow-up Number of restorations Cause of loss
ToothImplantsupported supported
Months in function
Replacement months in function
Abutment fracture*
0
1
1.9
49.1
Root fracture
1
0
10.5
44.8
Root fracture
1
0
1.5
10.3
‡
Root fracture
1
0
9.4
N/A
Root fracture‡
1
0
14.0
N/A
Root fracture‡
1
0
31.4
N/A
Root fracture
1
0
20.3
N/A
Deceased
0
4
10.6
N/A
Deceased
0
9
13.4
N/A
Deceased
0
4
45.4
N/A
Deceased
3
5
45.4
N/A
Total (11 patients)
9
23
N/A
N/A
†,‡ †,‡
‡
N/A = not applicable. *Zirconia abutment fracture; replaced with screw-retained crown with titanium base. †Replaced with an implant-supported restoration. ‡All root fractures were associated with endodontically treated teeth.
Table 5 Number of restorative units with clinical complications at 68 months Complication
Zirconia structure*
Feldspathic veneer†
Fracture
0
0
Chipping
0
0
Cracking
0
0
*All units have zirconia in occlusal function. †No feldspathic ceramic in function.
Within the patient population of the study, 1,022 restorative units were completed over a period of 68 months (Fig 5). A total of 755 units of restoration have been in function between 1 day and 36 months. A total of 267 units of restoration have been in function between 36 and 68 months. All patients in the study were followed by the author in his private practice continuing care program. The distribution of restorations lost to follow-up is shown in Table 4. One cement-retained implant-supported restoration was lost to zirconia abutment fracture (not a failure of the zirconia restorative material) and replaced with a single screw-retained implant-supported zirconia restoration with a titanium base. Six tooth-supported restorations were lost as a result of root fracture (not a failure of the zirconia restorative material); two of these were replaced with single-crown restorations each supported by two implants.32 Four patients with 22 implant-supported and 3 toothsupported restorations passed away during the follow-up period. There were no observed complications with respect to fracture, cracking, or chipping of the zirconia structure and/or the minimally veneered feldspathic ceramic to date (Table 5). This is in agreement with case reports by Rojas-Vizcaya,21 Thalji and Cooper,22 and Marchack et al.33 However, these results vary from previous studies using zirconia with feldspathic ceramic in function9–11 as well as all other bilayered ceramic or metal-based restorations.12–14
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321 Discussion In the present study, the zirconia restorations exhibited a 100% success rate at 68 months. No fractures, cracks, or chipping of the monolithic zirconia structure with or without a minimally veneered feldspathic ceramic component (not in function) have been observed to date (see Table 5). Acrylic occlusal guards were not used to protect any of the restorations in the study because of the strength of zirconia and the fact that all function was only on this material.23 However, it should be noted this practice has been routinely used with traditional bilayered ceramic restorations.18 This is of particular importance going forward in terms of being able to create esthetic restorations with a time-efficient workflow that results in outcomes with a level of success not previously reported in the literature.9–11,15,16 The use of zirconia to produce dental restorations as described requires a milling protocol. Previously, milling with analog machinery made this a tedious and time-consuming process. As CNC machinery and associated software became available, it allowed for an increase in the time efficiency of producing zirconia restorations. These new digital protocols for milling zirconia also provided a collateral benefit in the ability to create surgical guides, provisional restorations, and prototype restorations with PMMA. Studies supporting the biologic and strength characteristics of zirconia over other ceramic materials resulted in zirconia being used as
the restoration substructure with fully veneered feldspathic ceramic.1–6 This bilayered approach led to a high percentage of chip-off fractures of the veneering ceramic.9–11 Some of these studies surmised that the use of monolithic zirconia would be likely to produce the results that are reported in this clinical study.5,6 The restorative community continues to seek solutions to the clinical challenges using bilayered zirconia restorations. In an effort to solve the chip-off fracture problem, Fabbri et al34 suggested the use of reinforced feldspathic ceramic (lithium disilicate) cemented over a zirconia substructure, and some have suggested various modifications to the technical management of applying feldspathic ceramic to the zirconia substrate.35,36 However, limited data are available for these techniques. Realistically, all bilayered designs of zirconia restorations with material other than the zirconia in function continue to create complications that affect outcomes.9–11 All restorations in this study, whether supported by teeth and/ or implants, have only zirconia in function against opposing restorations or natural teeth. The opposing restorative materials included precious alloys, nonprecious alloys, feldspathic ceramics, reinforced feldspathic ceramics, amalgams, and composites. As reported by Park et al,30 zirconia is minimally abrasive to opposing structures, and this property is maximized by leaving the occlusal surfaces polished after definitive intraoral occlusal adjustments.
Hisbergues et al2 have indicated that soft tissue response and plaque adhesion to zirconia is as good as or better than natural tooth structure. At this time, the high cost of gold alloys is influencing the restorative community to consider alternative metal alloys such as titanium for substructures, combined with various veneering materials. Ko et al37 have shown that titanium has been implicated in inducing localized hypersensitivities as well as severe systemic allergic reactions. Gökçen-Röhlig et al38 indicated that dental zirconia has no reported allergic reactions and has proven to be nontoxic and nonirritating, enhancing the desirability of using zirconia as a substrate for restorations. Finally, recent studies by Alghazzawi et al39 and Flinn et al40 have indicated that previous concerns regarding low-temperature degradation of zirconia at oral temperatures is not a long-term concern for the residual strength of zirconia restorations. The results of this study indicate that there is a new paradigm possible in fixed prosthodontics that allows for the use of an advanced high-strength ceramic (zirconia) to enhance the overall esthetics, biocompatibility, performance, efficiency, and cost-benefits41 to the restorative community and patients in a manner not previously possible.
Conclusions After an observation time of 68 months, monolithic and minimally veneered zirconia in the restoration
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322 of teeth and implants shows promising results as a reliable material for the wide variety of clinical applications described in this study. More studies of this category of restoration will be helpful in establishing this treatment modality as a possible new benchmark in restorative dentistry.
Acknowledgments The author would like to thank Hiam Keren, MDT, for the laboratory support in the production of all restorations in this study and Jacques Geleyn and Danae Sandoval for their technical assistance in the preparation of this manuscript. The author reported no conflicts of interest related to this study.
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