Clinical outcome of single porcelain-fused-to-zirconium dioxide crowns: A systematic review Takuro Takeichi, DDS, PhD,a Joannis Katsoulis, DMD, Dr Med Dent,b and Markus B. Blatz, DMD, Dr Med Dent Habilc Aichi Gakuin University, Nagoya, Aichi, Japan; University of Pennsylvania School of Dental Medicine, Philadelphia, Pa; School of Dental Medicine, University of Bern, Switzerland Statement of problem. The increasing demand by patients for esthetic and metal-free restorations has driven the development of ceramic restorations with good esthetic and mechanical stability. Recent clinical studies have investigated the use of zirconium dioxide as a core material for complete crowns and computer-aided-design/computer-aided-manufacturing fabricated restorations. Purpose. The aim of this systematic review was to evaluate the clinical survival rates of porcelain-fused-to-zirconia (PFZ) single crowns on anterior and posterior teeth and to compare them with metal ceramic (MC) crowns. Material and methods. A systematic search was conducted with PubMed and manual research to identify literature written in English that refers to in vivo studies published from January 1, 1950 through July 1, 2011. Clinical trials that evaluated PFZ and MC single crowns on natural teeth were selected for further analysis. Titles and/or abstracts of articles identified through the electronic searches were reviewed and evaluated for appropriateness. In addition, a hand search of relevant dental journals was peformed, and reference lists of culled articles were screened to identify publications. Results. The search resulted in a total of 488 initial matches. Nineteen studies with a total of 3621 crowns met the inclusion criteria. The survival rates of PFZ crowns (total 300) ranged from 92.7% to 100% for a follow-up time of 24 to 39 months, whereas those of MC crowns (total 3321) ranged from 70% to 100% for a follow-up time of 12 to 298 months. Studies that reported long-term results were found only for the MC crown group. Conclusions. The scientific clinical data available to compare PFZ and MC crowns are limited. The survival rates may well be influenced by the selection and appropriate use of the veneering ceramic, and, therefore, additional prospective long-term clinical trials are necessary to draw reliable conclusions. (J Prosthet Dent 2013;110:455-461)
Clinical Implications Well-controlled prospective clinical studies are needed to compare the long-term survival rates of porcelain-fused-to-zirconia crowns and metal ceramic crowns. Computer-aided-design/computeraided-manufacturing technology allows for the production of precise coping
a
and frameworks.1 Different systems are currently commercially available that combine computer-aided-design/
computer-aided-manufacturing technology with ceramic materials.1 Metal ceramic (MC) crowns are often
Lecturer, Department of Fixed Prosthodontics, School of Dentistry, Aichi Gakuin University; and Adjunct Associate Professor, Department of Preventive and Restorative Sciences, Robert Schattner Center, University of Pennsylvania School of Dental Medicine. b Assistant Professor, Department of Prosthodontics, School of Dental Medicine, University of Bern; and Adjunct Assistant Professor, Department of Preventive and Restorative Sciences, Robert Schattner Center, University of Pennsylvania School of Dental Medicine. c Professor and Chair, Department of Preventive and Restorative Sciences, Robert Schattner Center, University of Pennsylvania School of Dental Medicine.
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Volume 110 Issue 6 recommended because of their strength and reliability because they have been in use for more than 50 years. A metal framework could provide the desired strength for an MC crown, but the dark metal framework and opaque oxides make it difficult to emulate the esthetics of a natural tooth.1,2 Currently, ceramic crowns are often preferred to MC crowns when maximum esthetics are needed. Ceramic crowns have several advantages: excellent esthetics, color stability, wear resistance, chemical resistance, and biocompatibility.3 In contrast, the most common failure of ceramic restorations is the chipping and fracture of the veneering porcelain.4 The increasing demand by patients for esthetic and metal-free restorations has driven the development of ceramic restorations with excellent esthetic and adequate mechanical stability. The use of zirconiumoxide (zirconia) as a core material for complete-coverage crowns provides better esthetic characteristics, mechanical properties, and biocompatibility.5
Table I.
Zirconia substructures distinguish themselves with a high flexure strength of more than 1000 MPa.6,7 Zirconia has several crystalline structure phases, which depend on temperature.8 Yittria or ceria are added to the crystalline structure to stabilize zirconia at room temperature. Both yttrium-oxide partially stabilized zirconia and yttriastabilized tetragonal polycrystals improve fracture toughness.9,10 The yttria-stabilized tetragonal polycrystal has better physical properties than other types of zirconia due to stressinduced transformation toughening of the materials. As a crack begins to transfer through the material, a highenergy state causes a change from the tetragonal form to the monoclinic form with a concomitant volumetric growth that exerts a compressive force at the crack tip, which prevents its progression; this is termed ‘transformation toughening.’11 Porcelainfused-to-zirconia (PFZ) crowns require almost the same clinical procedures as MC crowns because they are veneered
with a feldspathic porcelain for esthetic restoration.12 The clinical failures of zirconia-based partial-fixed dental prostheses have been evaluated and show a high complication rate, especially external ceramic chipping.1 Thus, the purpose of this study was to compare the clinical outcome of PFZ and MC single crowns on natural teeth.
MATERIAL AND METHODS This review was conducted with PubMed by using the following keywords: “single and zirconia crown,” “single and porcelain fused to metal crown,” “single and PFM crown,” and “single and metal ceramic crown.” Titles and abstracts of the searches were initially screened for possible inclusion in the review. The full text of all possibly relevant studies was then obtained for assessment by each researcher. In addition, a hand search of relevant dental journals was performed by a single researcher, and
Summary of complications and survival rates for PFZ crowns
No. Crowns
Year Published
Total
Anterior
Cehreli et al13
2009
15
14
2009
Study
Ortorp et al
Beuer et al15 Schmitt et al
16
Total
Posterior
Framework Material
Veneering Material
-
15
Cercon
NI
216
48
168
NobelProcera
2010
50
15
35
IPS e.max ZirCAD
IPS e.max ZirLiner
2010
19
19
-
Lava
Lava Ceram
300
82
218
Observation Time, mo Study
Luting Agent
Cehreli et al13 Ortorp et al
14
Glass ionomer cement Self-adhesive modified composite resin cement
Mean 24 NI
Vita Lumin, NobelRondo Zirconia
Survival Rate, %
Min
Max
Total
Anterior
Posterior
NI
24
93.3
-
93.30
NI
36
a
92.7
b
91.7
95.2b
Beuer et al15
Glass ionomer
35
NI
NI
100b
100b
100b
Schmitt et al16
Glass ionomer
39.2a
NI
NI
100b
100b
-
Total
24-39.2
92.7-100
91.7-100
93.3-100
Min, minimum; Max, maximum; NI, not indicated; PFZ, porcelain-fused-to-zirconia. a After period indicated for calculation of survival rate. b Cumulative survival rate (Kaplan-Meier).
The Journal of Prosthetic Dentistry
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December 2013 reference lists of culled articles were screened to identify publications. Eligible clinical trials that investigated single crowns on natural teeth made with a zirconia or metal framework were included if they were written in English and published in peer-reviewed journals from January 1, 1950 through July 1, 2011. Human in vivo studies published in peerreviewed journals, written in English, reporting on single crowns with natural teeth abutments, and providing survival rates were included in this review. In vitro studies, case reports, studies that reported on fixed dental prostheses and implant-supported restorations, and studies without information on clinical survival rates were excluded. Of 488 titles found, 340 articles were excluded based on these criteria. Extracted data included patient charcteristics, for example, age, and included restoration characteristics, for example, the anterior or posterior position of the single crown, the fabrication details, and information about the clinical procedure. Clinical outcome was defined as a failure if a biologic or technical complication occurred that required the replacement or repair of the crown or the extraction of the tooth. Technical complications included fracture of the framework, fracture of the veneering porcelain, marginal discoloration, excessive occlusal wear, and loss of retention. The estimated annual failure percentages (eaFP) per 100 restorations were calculated by dividing the indicated failure percentage by the total observation time. The estimated 3-year cumulative survival percentages were calculated based on the retrieved data of the studies.
RESULTS Of the 488 retrieved articles, a total of 4 studies13-16 met the inclusion criteria regarding PFZ crowns, and 15 studies17-31 met the inclusion criteria regarding MC crowns. The
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457 reviewed articles are presented in Tables I and II, which show the number of crowns (total, anterior, posterior), framework and veneering materials used, fabrication methods, luting agents, observation time, and clinical survival rates. The 4 studies13-16 that evaluated single PFZ crowns included in the present review were published in 2009 and 2010. The number of the participants studied ranged from 10 to 161. The age range of the participants was 25 to 85 years. A total of 300 single crowns, 82 in the anterior and 218 in the posterior jaw, were placed. The average observation time ranged from 24 to 39.2 months. The survival rates of PFZ single crowns ranged from 92.7% to 100%, with survival rates between 91.7% and 100% for anterior teeth and between 93.3% and 100% for posterior teeth (Table I). The mean eaFP for PFZ single crowns was 0% on anterior teeth, 1.5% on posterior teeth, and 1.35% on both combined. The estimated 3-year cumulative survival percentages was 100% on anterior teeth, 95.5% on posterior teeth, and 95.9% (range, 91.0% to 100%) in total (Table III). A total of 3321 MC crowns, 209 in the anterior region and 1290 in the posterior region, were evaluated in 15 studies published from 1991 through 2011.17-31 The number of participants ranged from 18 to 456. The age range of the participants was from 17 to 91 years. The mean observation time ranged from 33 to 298 months. Survival rates of MC single crowns were 92% for anterior and between 70% and 98.3% for posterior teeth and ranged from 70% to 100% in total (Table II). The mean of eaFP for the MC single crowns was 1.6% on anterior teeth, 1.5% on posterior teeth, and 1.1% on the total number teeth. The estimated 3-year cumulative survival percentage was 95.2% on anterior teeth, 95.7% on posterior teeth, and 95.4% (range 84.1% to 100%) in total (Table IV). The PFZ studies had observation times that ranged from 24 to 39.2 months; whereas, in the MC studies, participants
were seen from 12 to up to 25 years after placement of the restoration.
DISCUSSION The present review analyzed 19 clinical trials that focused on the survival rates of PFZ and MC single crowns on natural teeth. The 4 studies that evaluated PFZ crowns showed a median observation time of only approximately 3 years.13-16 The present clinical studies show good survival rates for tooth-supported zirconia crowns in the short term, but more trials are needed to compare with MC crowns in the long term. The survival rates of 92% to 100% for this time period are considered to be short term compared with the follow-up time of 18 to 25 years for several MC studies.18,22,26,29 Obviously, the longterm survival rates, 70% to 92%, in these studies were significantly lower. However, the MC studies with almost the same follow-up time as the PFZ studies (2 to 3 years) showed comparable survival rates of 85% to 100%.17,19,20,30 The estimated annual failures as the calculated mean events per year for 100 restorations were 1.35 (range, 0.0 to 3.0) for the PFZ crowns and 1.1 (range, 0.0 to 5.3) for the MC crowns. The calculated 3-year cumulative survival percentage was 95.9% for PFZ crowns and 95.4% for MC crowns. Analysis of these findings suggests that survival rates for tooth-supported zirconia crowns might be as predictable as for MC crowns, although only 4 PFZ trials were included in the present study. The failure percentage of posterior ceramic single crowns is reported to be 3% to 4% per year for other ceramic systems.32-36 In the present systematic review, the mean of eaFP for the PFZ single crowns was 0% on anterior teeth, 1.5% on posterior teeth, and 1.35% on the total number of teeth. An optimized zirconia substructure design with increased occlusal support and an even thickness of the veneering porcelain reduces the number and surface area of chipping
458
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Table II.
Summary of complications and survival rates for MC crowns
Year Published
Study Cheung17 Palmqvist and Swartz
18
No. Crowns Total
Anterior
1991
48
28 NI
1993
16
Nilson et al19
1994
47
Kaus et al20
1996
69
NI
Martin and Bader21
1997
555
Smales and Hawthorne22
1997
Walton et al23 Lövgren et al24
Posterior
Framework Material
Veneering Material
NI
NI
20
NI
NI
Titanium
Procera ceramics, Ducera, Rosbach
NI
Titanium
Low-fusing experimental porcelain
-
555
Gold alloy
NI
174
-
174
NI
NI
1999
688
NI
NI
High-noble metal alloys
NI
2000
242
74
168
Titanium
Low-fusing porcelain
Marklund et al25
2003
42
42
-
Gold alloy, Titanium
Backer et al26
2006
1037
NI
NI
Gold alloy
NI
2006
190
-
190
Noble metal alloys
Duceram
NI
Reitemeier et al Eliasson et al
27
28
2
NI 45
Ivoclar classic, Procera ceramics
2007
12
NI
Cobalt-chromium alloy
VITA Omega 900
Napänkangas and Raustia29
2008
100
51
49
NI
NI
Boeckler et al30
2009
41
12
29
Titanium
VITA Titanium porcelain
Abou Tara et al31
2011
60
-
60
Cobalt-chromium alloy
Veneering ceramic (IPSd. Sign)
Total (excluding NI)
3321
209
1290
MC, metal ceramic; NI, not indicated.
incidents.37 In addition, the unique physical and thermal properties of zirconia require specific surface treatment procedures and adapted veneering porcelain layering, firing, and cooling protocols that substantially differ from the ones applied for metal-alloy copings and frameworks.38,39 More well-conducted clinical studies that investigate the long-term results and details of complications and failures are needed to give a comparable and successful predictability for tooth-supported PFZ crowns. Some studies on MC single crowns did not differentiate between anterior and posterior crowns or provide separate data regarding survival rates.17-20,23,24,26,28-30 Several studies were missing important
information, such as details regarding setting regions,18,20,23,26,28 framework materials,17,18,22,29 veneering materials,17,18,21-23,26,29 luting agents,17-22,25,29 and the mean observation time.18,19,23,26,27,30 One of the main limitations of this systematic review is the small number of relevant clinical studies reported in the literature. Any conclusions drawn from these data must be interpreted with caution. Some evidence exists that an excessive cement space may increase the veneering failures. Under actual circumstances (that is in vivo and loading), viscoplastic deformation of the adhesive material occurs and may increase stress concentrations on the tensile surface of the restoration, which causes failure of the veneering
The Journal of Prosthetic Dentistry
porcelain.40 Composite resin cements were reported to flow under repeated loading and thus increased the stress in the system.41,42 The veneering ceramics are different in each study and may, therefore, affect the clinical behavior of these restorations. In general, and this applies to both MC and PFZ restorations, veneering porcelains have to complement the properties of the framework material. The coefficient of thermal expansion of the veneering ceramic should be slightly lower than that of the framework material so to create favorable, internal compressive stresses during the cooling process.43 Other influencing factors include modulus of elasticity, flexural strength, and hardness of
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December 2013
459
(Continued) Summary of complications and survival rates for MC crowns
Table II.
Observation Time, mo Study
Luting Agent
Cheung17
Mean 3a
NI
Palmqvist and Swartz Nilson et al
18
19
20
Survival Rate, %
Min
Max
Total
Anterior
NI
NI
85.40
NI
NI
NI
NI NI
NI
NI
216
276
100
NI
NI
26
30
95.70
NI
b
NI
Posterior
NI
31
21
41
85
Martin and Bader21
NI
60a
NI
NI
84b
-
84b
Smales and Hawthorne22
NI
298
NI
NI
70
-
70
Walton et al23
Zinc-phosphate cement
NI
12
120a
97.0b
NI
NI
Glass ionomer cement, zinc-phosphate cement
60
a
NI
NI
99.60
NI
NI
NI
60a
NI
NI
92
92
-
NI
NI
Kaus et al
Lövgren et al
24
Marklund et al25 Backer et al
26
Zinc-phosphate cement 27
NI
NI
216
a a
NI
NI
NI
84
Eliasson et al28
Glass ionomer cement, zinc-phosphate cement
51
28
82
Napänkangas and Raustia29
NI
226
210
246
Boeckler et al30
Zinc-phosphate cement
NI
12
Reitemeier et al
Abou Tara et al
31
Glass ionomer cement
a
47
Total (excluding NI)
78
92.40
-
100 78b
36a
19
b
94.9b
62
98.3
12-298
b
92.40
NI
NI
NI
NI
NI
NI
-
70-100
NI
92
98.3b 70-98.3
MC, metal ceramic; Min, minimum; Max, maximum; NI, not indicated. a After period indicated for calculation of survival rate. b Cumulative survival rate (Kaplan-Meier).
Estimated annual failure percentages (per 100 restorations) and survival percentages for PFZ crowns after 3 years
Table III.
eaFP (total) Estimated Annual Failure Percentages Estimated per Year and per 100 Estimated 3-y eaFP 3-y SP eaFP Estimated 3-y Restorations SP (total) (anterior) (anterior) (posterior) SP (posterior)
Study Cehreli et al13
3.0
91.0
-
-
3.0
91.0
Ortorp et al14
2.4
92.7
NI
NI
NI
NI
0
100
a
0
100
Schmitt et al16
0
100a
0
Mean total
1.35
0
Beuer et al
15
95.9
a
0
100a
100a
-
-
100.0
1.5
95.5
PFZ, porcelain-fused-to-zirconia; eaFP, estimated annual failure percentage; SP, survival percentage; NI, not indicated. a Actual survival rates.
the veneering porcelain. Clinical survival rates may well be influenced by the selection and appropriate use of the veneering ceramic. For clinical success and longevity,
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adequate material selection and handling are crucial to prevent veneering porcelain chipping.1 Currently, improvements in materials and technology have been geared
toward resolving these problems. Improvements in porcelain can enhance the bond strength between the porcelain and a zirconia framework.43
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Volume 110 Issue 6 Estimated annual failure percentages (per 100 restorations) and survival percentages for MC crowns after 3 years
Table IV.
eaFP (total) Estimated Annual Failure Percentages Estimated Estimated Estimated per Year and per 100 3-y SP eaFP 3-y SP eaFP 3-y SP Restorations (total) (anterior) (anterior) (posterior) (posterior)
Study Cheung17
5.3
Palmqvist and Swartz18
0
Nilson et al Kaus et al
19
NI
NI
NI
NI
NI
NI
NI
94.90
NI
NI
NI
NI
4.4
86.80
NI
NI
NI
NI
3.2
90.40
-
-
3.2
90.40
1.2
96.40
-
-
1.2
96.40
23
0.3
99.10
NI
NI
NI
NI
24
0.1
99.70
NI
NI
NI
NI
1.6
95.20
1.6
95.20
-
-
1.2
96.40
NI
NI
NI
NI
1.1
96.70
-
-
1.1
Martin and Bader
21
Smales and Hawthorne22 Lövgren et al
Marklund et al25 Backer et al
NI
1.7
20
Walton et al
84.10 100a
26
Reitemeier et al
27
28
NI
NI
NI
NI
1.1
96.70
NI
NI
NI
NI
Boeckler et al30
1.7
94.90
NI
NI
NI
NI
Abou Tara et al
31
Mean total
100
96.70
Napänkangas and Raustia29
Eliasson et al
0
a
0.3
99.10
-
-
0.3
99.10
1.1
95.4
1.6
95.2
1.5
95.7
MC, metal ceramic; eaFP, estimated annual failure percentage; SP, survival percentage; NI, not indicated. a Actual survival rates.
CONCLUSIONS The available scientific clinical data to compare PFZ and MC crowns are limited. The survival rates may well be influenced by the selection and appropriate use of the veneering ceramic, and, therefore, additional long-term clinical trials are necessary to draw definitive conclusions.
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461 29. Näpänkangas R, Raustia A. Twenty-year follow-up of metal-ceramic single crowns: a retrospective study. Int J Prosthodont 2008;21:307-11. 30. Boeckler AF, Lee H, Stadler A, Setz JM. Prospective observation of CAD/CAM titanium ceramic single crowns: a three-year follow up. J Prosthet Dent 2009;102:290-7. 31. Abou Tara M, Eschbach S, Bohlsen F, Kern M. Clinical outcome of metal-ceramic crowns fabricated with laser-sintering technology. Int J Prosthodont 2011;24:46-8. 32. Fradeani M, Aquilano A. Clinical experience with Empress crowns. Int J Prosthodont 1997;10:241-7. 33. Fradeani M, D’Amelio M, Redemagni M, Corrado M. Five-year follow-up with Procera all-ceramic crowns. Quintessence Int 2005;36:105-13. 34. Fradeani M, Redemagni M. An 11-year clinical evaluation of leucite-reinforced glass-ceramic crowns: a retrospective study. Quin tessence Int 2002;33:503-10. 35. Malament KA, Socransky SS. Survival of Dicor glass-ceramic dental restorations over 14 years. Part II: effect of thickness of Dicor material and design of tooth preparation. J Prosthet Dent 1999;81:662-7. 36. Malament KA, Socransky SS. Survival of Dicor glass-ceramic dental restorations over 16 years. Part III: effect of luting agent and tooth or tooth-substitute core structure. J Prosthet Dent 2001;86:511-9. 37. Rosentritt M, Steiger D, Behr M, Handel G, Kolbeck C. Influence of substructure design and spacer settings on the in vitro performance of molar zirconia crowns. J Dent 2009;37:978-83.
38. Fischer J, Stawarzcyk B, Trottmann A, Hämmerle CH. Impact of thermal misfit on shear strength of veneering ceramic/zirconia composites. Dent Mater 2009;25:419-23. 39. Fischer J, Stawarczyk B, Tomic M, Strub JR, Hämmerle CH. Effect of thermal misfit between different veneering ceramics and zirconia frameworks on in vitro fracture load of single crowns. Dent Mater J 2007;26:766-72. 40. Rekow D, Thompson P. Near-surface damageda persistent problem in crowns obtained by computer-aided design and manufacturing. Proc Inst Mech Eng H 2005;219:233-43. 41. Ferracane L, Matsumoto H, Okabe T. Timedependent deformation of composite resinsdcompositional considerations. J Dent Res 1985;64:1332-6. 42. Hirano S, Hirasawa T. Compressive creep of posterior and anterior composite resins in water. Dent Mater J 1994;13:214-9. 43. Blatz M, Bergler M, Ozer F, Holst S, Phark J, Chiche G. Bond strength of different veneering ceramics to zirconia and their susceptibility to thermocycling. Am J Dent 2010;23:213-6. Corresponding author: Dr Takuro Takeichi Department of Preventive and Restorative Sciences Robert Schattner Center University of Pennsylvania School of Dental Medicine 240 S 40th Street Philadelphia, PA 19104 E-mail: [email protected] Copyright ª 2013 by the Editorial Council for The Journal of Prosthetic Dentistry.
Clinical Implications Well-controlled prospective clinical studies are needed to compare the long-term survival rates of porcelain-fused-to-zirconia crowns and metal ceramic crowns. Computer-aided-design/computeraided-manufacturing technology allows for the production of precise coping
a
and frameworks.1 Different systems are currently commercially available that combine computer-aided-design/
computer-aided-manufacturing technology with ceramic materials.1 Metal ceramic (MC) crowns are often
Lecturer, Department of Fixed Prosthodontics, School of Dentistry, Aichi Gakuin University; and Adjunct Associate Professor, Department of Preventive and Restorative Sciences, Robert Schattner Center, University of Pennsylvania School of Dental Medicine. b Assistant Professor, Department of Prosthodontics, School of Dental Medicine, University of Bern; and Adjunct Assistant Professor, Department of Preventive and Restorative Sciences, Robert Schattner Center, University of Pennsylvania School of Dental Medicine. c Professor and Chair, Department of Preventive and Restorative Sciences, Robert Schattner Center, University of Pennsylvania School of Dental Medicine.
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Volume 110 Issue 6 recommended because of their strength and reliability because they have been in use for more than 50 years. A metal framework could provide the desired strength for an MC crown, but the dark metal framework and opaque oxides make it difficult to emulate the esthetics of a natural tooth.1,2 Currently, ceramic crowns are often preferred to MC crowns when maximum esthetics are needed. Ceramic crowns have several advantages: excellent esthetics, color stability, wear resistance, chemical resistance, and biocompatibility.3 In contrast, the most common failure of ceramic restorations is the chipping and fracture of the veneering porcelain.4 The increasing demand by patients for esthetic and metal-free restorations has driven the development of ceramic restorations with excellent esthetic and adequate mechanical stability. The use of zirconiumoxide (zirconia) as a core material for complete-coverage crowns provides better esthetic characteristics, mechanical properties, and biocompatibility.5
Table I.
Zirconia substructures distinguish themselves with a high flexure strength of more than 1000 MPa.6,7 Zirconia has several crystalline structure phases, which depend on temperature.8 Yittria or ceria are added to the crystalline structure to stabilize zirconia at room temperature. Both yttrium-oxide partially stabilized zirconia and yttriastabilized tetragonal polycrystals improve fracture toughness.9,10 The yttria-stabilized tetragonal polycrystal has better physical properties than other types of zirconia due to stressinduced transformation toughening of the materials. As a crack begins to transfer through the material, a highenergy state causes a change from the tetragonal form to the monoclinic form with a concomitant volumetric growth that exerts a compressive force at the crack tip, which prevents its progression; this is termed ‘transformation toughening.’11 Porcelainfused-to-zirconia (PFZ) crowns require almost the same clinical procedures as MC crowns because they are veneered
with a feldspathic porcelain for esthetic restoration.12 The clinical failures of zirconia-based partial-fixed dental prostheses have been evaluated and show a high complication rate, especially external ceramic chipping.1 Thus, the purpose of this study was to compare the clinical outcome of PFZ and MC single crowns on natural teeth.
MATERIAL AND METHODS This review was conducted with PubMed by using the following keywords: “single and zirconia crown,” “single and porcelain fused to metal crown,” “single and PFM crown,” and “single and metal ceramic crown.” Titles and abstracts of the searches were initially screened for possible inclusion in the review. The full text of all possibly relevant studies was then obtained for assessment by each researcher. In addition, a hand search of relevant dental journals was performed by a single researcher, and
Summary of complications and survival rates for PFZ crowns
No. Crowns
Year Published
Total
Anterior
Cehreli et al13
2009
15
14
2009
Study
Ortorp et al
Beuer et al15 Schmitt et al
16
Total
Posterior
Framework Material
Veneering Material
-
15
Cercon
NI
216
48
168
NobelProcera
2010
50
15
35
IPS e.max ZirCAD
IPS e.max ZirLiner
2010
19
19
-
Lava
Lava Ceram
300
82
218
Observation Time, mo Study
Luting Agent
Cehreli et al13 Ortorp et al
14
Glass ionomer cement Self-adhesive modified composite resin cement
Mean 24 NI
Vita Lumin, NobelRondo Zirconia
Survival Rate, %
Min
Max
Total
Anterior
Posterior
NI
24
93.3
-
93.30
NI
36
a
92.7
b
91.7
95.2b
Beuer et al15
Glass ionomer
35
NI
NI
100b
100b
100b
Schmitt et al16
Glass ionomer
39.2a
NI
NI
100b
100b
-
Total
24-39.2
92.7-100
91.7-100
93.3-100
Min, minimum; Max, maximum; NI, not indicated; PFZ, porcelain-fused-to-zirconia. a After period indicated for calculation of survival rate. b Cumulative survival rate (Kaplan-Meier).
The Journal of Prosthetic Dentistry
Takeichi et al
December 2013 reference lists of culled articles were screened to identify publications. Eligible clinical trials that investigated single crowns on natural teeth made with a zirconia or metal framework were included if they were written in English and published in peer-reviewed journals from January 1, 1950 through July 1, 2011. Human in vivo studies published in peerreviewed journals, written in English, reporting on single crowns with natural teeth abutments, and providing survival rates were included in this review. In vitro studies, case reports, studies that reported on fixed dental prostheses and implant-supported restorations, and studies without information on clinical survival rates were excluded. Of 488 titles found, 340 articles were excluded based on these criteria. Extracted data included patient charcteristics, for example, age, and included restoration characteristics, for example, the anterior or posterior position of the single crown, the fabrication details, and information about the clinical procedure. Clinical outcome was defined as a failure if a biologic or technical complication occurred that required the replacement or repair of the crown or the extraction of the tooth. Technical complications included fracture of the framework, fracture of the veneering porcelain, marginal discoloration, excessive occlusal wear, and loss of retention. The estimated annual failure percentages (eaFP) per 100 restorations were calculated by dividing the indicated failure percentage by the total observation time. The estimated 3-year cumulative survival percentages were calculated based on the retrieved data of the studies.
RESULTS Of the 488 retrieved articles, a total of 4 studies13-16 met the inclusion criteria regarding PFZ crowns, and 15 studies17-31 met the inclusion criteria regarding MC crowns. The
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457 reviewed articles are presented in Tables I and II, which show the number of crowns (total, anterior, posterior), framework and veneering materials used, fabrication methods, luting agents, observation time, and clinical survival rates. The 4 studies13-16 that evaluated single PFZ crowns included in the present review were published in 2009 and 2010. The number of the participants studied ranged from 10 to 161. The age range of the participants was 25 to 85 years. A total of 300 single crowns, 82 in the anterior and 218 in the posterior jaw, were placed. The average observation time ranged from 24 to 39.2 months. The survival rates of PFZ single crowns ranged from 92.7% to 100%, with survival rates between 91.7% and 100% for anterior teeth and between 93.3% and 100% for posterior teeth (Table I). The mean eaFP for PFZ single crowns was 0% on anterior teeth, 1.5% on posterior teeth, and 1.35% on both combined. The estimated 3-year cumulative survival percentages was 100% on anterior teeth, 95.5% on posterior teeth, and 95.9% (range, 91.0% to 100%) in total (Table III). A total of 3321 MC crowns, 209 in the anterior region and 1290 in the posterior region, were evaluated in 15 studies published from 1991 through 2011.17-31 The number of participants ranged from 18 to 456. The age range of the participants was from 17 to 91 years. The mean observation time ranged from 33 to 298 months. Survival rates of MC single crowns were 92% for anterior and between 70% and 98.3% for posterior teeth and ranged from 70% to 100% in total (Table II). The mean of eaFP for the MC single crowns was 1.6% on anterior teeth, 1.5% on posterior teeth, and 1.1% on the total number teeth. The estimated 3-year cumulative survival percentage was 95.2% on anterior teeth, 95.7% on posterior teeth, and 95.4% (range 84.1% to 100%) in total (Table IV). The PFZ studies had observation times that ranged from 24 to 39.2 months; whereas, in the MC studies, participants
were seen from 12 to up to 25 years after placement of the restoration.
DISCUSSION The present review analyzed 19 clinical trials that focused on the survival rates of PFZ and MC single crowns on natural teeth. The 4 studies that evaluated PFZ crowns showed a median observation time of only approximately 3 years.13-16 The present clinical studies show good survival rates for tooth-supported zirconia crowns in the short term, but more trials are needed to compare with MC crowns in the long term. The survival rates of 92% to 100% for this time period are considered to be short term compared with the follow-up time of 18 to 25 years for several MC studies.18,22,26,29 Obviously, the longterm survival rates, 70% to 92%, in these studies were significantly lower. However, the MC studies with almost the same follow-up time as the PFZ studies (2 to 3 years) showed comparable survival rates of 85% to 100%.17,19,20,30 The estimated annual failures as the calculated mean events per year for 100 restorations were 1.35 (range, 0.0 to 3.0) for the PFZ crowns and 1.1 (range, 0.0 to 5.3) for the MC crowns. The calculated 3-year cumulative survival percentage was 95.9% for PFZ crowns and 95.4% for MC crowns. Analysis of these findings suggests that survival rates for tooth-supported zirconia crowns might be as predictable as for MC crowns, although only 4 PFZ trials were included in the present study. The failure percentage of posterior ceramic single crowns is reported to be 3% to 4% per year for other ceramic systems.32-36 In the present systematic review, the mean of eaFP for the PFZ single crowns was 0% on anterior teeth, 1.5% on posterior teeth, and 1.35% on the total number of teeth. An optimized zirconia substructure design with increased occlusal support and an even thickness of the veneering porcelain reduces the number and surface area of chipping
458
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Table II.
Summary of complications and survival rates for MC crowns
Year Published
Study Cheung17 Palmqvist and Swartz
18
No. Crowns Total
Anterior
1991
48
28 NI
1993
16
Nilson et al19
1994
47
Kaus et al20
1996
69
NI
Martin and Bader21
1997
555
Smales and Hawthorne22
1997
Walton et al23 Lövgren et al24
Posterior
Framework Material
Veneering Material
NI
NI
20
NI
NI
Titanium
Procera ceramics, Ducera, Rosbach
NI
Titanium
Low-fusing experimental porcelain
-
555
Gold alloy
NI
174
-
174
NI
NI
1999
688
NI
NI
High-noble metal alloys
NI
2000
242
74
168
Titanium
Low-fusing porcelain
Marklund et al25
2003
42
42
-
Gold alloy, Titanium
Backer et al26
2006
1037
NI
NI
Gold alloy
NI
2006
190
-
190
Noble metal alloys
Duceram
NI
Reitemeier et al Eliasson et al
27
28
2
NI 45
Ivoclar classic, Procera ceramics
2007
12
NI
Cobalt-chromium alloy
VITA Omega 900
Napänkangas and Raustia29
2008
100
51
49
NI
NI
Boeckler et al30
2009
41
12
29
Titanium
VITA Titanium porcelain
Abou Tara et al31
2011
60
-
60
Cobalt-chromium alloy
Veneering ceramic (IPSd. Sign)
Total (excluding NI)
3321
209
1290
MC, metal ceramic; NI, not indicated.
incidents.37 In addition, the unique physical and thermal properties of zirconia require specific surface treatment procedures and adapted veneering porcelain layering, firing, and cooling protocols that substantially differ from the ones applied for metal-alloy copings and frameworks.38,39 More well-conducted clinical studies that investigate the long-term results and details of complications and failures are needed to give a comparable and successful predictability for tooth-supported PFZ crowns. Some studies on MC single crowns did not differentiate between anterior and posterior crowns or provide separate data regarding survival rates.17-20,23,24,26,28-30 Several studies were missing important
information, such as details regarding setting regions,18,20,23,26,28 framework materials,17,18,22,29 veneering materials,17,18,21-23,26,29 luting agents,17-22,25,29 and the mean observation time.18,19,23,26,27,30 One of the main limitations of this systematic review is the small number of relevant clinical studies reported in the literature. Any conclusions drawn from these data must be interpreted with caution. Some evidence exists that an excessive cement space may increase the veneering failures. Under actual circumstances (that is in vivo and loading), viscoplastic deformation of the adhesive material occurs and may increase stress concentrations on the tensile surface of the restoration, which causes failure of the veneering
The Journal of Prosthetic Dentistry
porcelain.40 Composite resin cements were reported to flow under repeated loading and thus increased the stress in the system.41,42 The veneering ceramics are different in each study and may, therefore, affect the clinical behavior of these restorations. In general, and this applies to both MC and PFZ restorations, veneering porcelains have to complement the properties of the framework material. The coefficient of thermal expansion of the veneering ceramic should be slightly lower than that of the framework material so to create favorable, internal compressive stresses during the cooling process.43 Other influencing factors include modulus of elasticity, flexural strength, and hardness of
Takeichi et al
December 2013
459
(Continued) Summary of complications and survival rates for MC crowns
Table II.
Observation Time, mo Study
Luting Agent
Cheung17
Mean 3a
NI
Palmqvist and Swartz Nilson et al
18
19
20
Survival Rate, %
Min
Max
Total
Anterior
NI
NI
85.40
NI
NI
NI
NI NI
NI
NI
216
276
100
NI
NI
26
30
95.70
NI
b
NI
Posterior
NI
31
21
41
85
Martin and Bader21
NI
60a
NI
NI
84b
-
84b
Smales and Hawthorne22
NI
298
NI
NI
70
-
70
Walton et al23
Zinc-phosphate cement
NI
12
120a
97.0b
NI
NI
Glass ionomer cement, zinc-phosphate cement
60
a
NI
NI
99.60
NI
NI
NI
60a
NI
NI
92
92
-
NI
NI
Kaus et al
Lövgren et al
24
Marklund et al25 Backer et al
26
Zinc-phosphate cement 27
NI
NI
216
a a
NI
NI
NI
84
Eliasson et al28
Glass ionomer cement, zinc-phosphate cement
51
28
82
Napänkangas and Raustia29
NI
226
210
246
Boeckler et al30
Zinc-phosphate cement
NI
12
Reitemeier et al
Abou Tara et al
31
Glass ionomer cement
a
47
Total (excluding NI)
78
92.40
-
100 78b
36a
19
b
94.9b
62
98.3
12-298
b
92.40
NI
NI
NI
NI
NI
NI
-
70-100
NI
92
98.3b 70-98.3
MC, metal ceramic; Min, minimum; Max, maximum; NI, not indicated. a After period indicated for calculation of survival rate. b Cumulative survival rate (Kaplan-Meier).
Estimated annual failure percentages (per 100 restorations) and survival percentages for PFZ crowns after 3 years
Table III.
eaFP (total) Estimated Annual Failure Percentages Estimated per Year and per 100 Estimated 3-y eaFP 3-y SP eaFP Estimated 3-y Restorations SP (total) (anterior) (anterior) (posterior) SP (posterior)
Study Cehreli et al13
3.0
91.0
-
-
3.0
91.0
Ortorp et al14
2.4
92.7
NI
NI
NI
NI
0
100
a
0
100
Schmitt et al16
0
100a
0
Mean total
1.35
0
Beuer et al
15
95.9
a
0
100a
100a
-
-
100.0
1.5
95.5
PFZ, porcelain-fused-to-zirconia; eaFP, estimated annual failure percentage; SP, survival percentage; NI, not indicated. a Actual survival rates.
the veneering porcelain. Clinical survival rates may well be influenced by the selection and appropriate use of the veneering ceramic. For clinical success and longevity,
Takeichi et al
adequate material selection and handling are crucial to prevent veneering porcelain chipping.1 Currently, improvements in materials and technology have been geared
toward resolving these problems. Improvements in porcelain can enhance the bond strength between the porcelain and a zirconia framework.43
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Volume 110 Issue 6 Estimated annual failure percentages (per 100 restorations) and survival percentages for MC crowns after 3 years
Table IV.
eaFP (total) Estimated Annual Failure Percentages Estimated Estimated Estimated per Year and per 100 3-y SP eaFP 3-y SP eaFP 3-y SP Restorations (total) (anterior) (anterior) (posterior) (posterior)
Study Cheung17
5.3
Palmqvist and Swartz18
0
Nilson et al Kaus et al
19
NI
NI
NI
NI
NI
NI
NI
94.90
NI
NI
NI
NI
4.4
86.80
NI
NI
NI
NI
3.2
90.40
-
-
3.2
90.40
1.2
96.40
-
-
1.2
96.40
23
0.3
99.10
NI
NI
NI
NI
24
0.1
99.70
NI
NI
NI
NI
1.6
95.20
1.6
95.20
-
-
1.2
96.40
NI
NI
NI
NI
1.1
96.70
-
-
1.1
Martin and Bader
21
Smales and Hawthorne22 Lövgren et al
Marklund et al25 Backer et al
NI
1.7
20
Walton et al
84.10 100a
26
Reitemeier et al
27
28
NI
NI
NI
NI
1.1
96.70
NI
NI
NI
NI
Boeckler et al30
1.7
94.90
NI
NI
NI
NI
Abou Tara et al
31
Mean total
100
96.70
Napänkangas and Raustia29
Eliasson et al
0
a
0.3
99.10
-
-
0.3
99.10
1.1
95.4
1.6
95.2
1.5
95.7
MC, metal ceramic; eaFP, estimated annual failure percentage; SP, survival percentage; NI, not indicated. a Actual survival rates.
CONCLUSIONS The available scientific clinical data to compare PFZ and MC crowns are limited. The survival rates may well be influenced by the selection and appropriate use of the veneering ceramic, and, therefore, additional long-term clinical trials are necessary to draw definitive conclusions.
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13. Cehreli MC, Kökat AM, Akça K. CAD/CAM zirconia vs. slip-cast glass-infiltrated alumina/zirconia all-ceramic crowns: 2-year results of a randomized controlled clinical trial. J Appl Oral Sci 2009;17:49-55. 14. Ortorp A, Kihl ML, Carlsson GE. A 3-year retrospective and clinical follow-up study of zirconia single crowns performed in a private practice. J Dent 2009;37:731-6. 15. Beuer F, Stimmelmayr M, Gernet W, Edelhoff D, Güh JF, Naumann M. Prospective study of zirconia-based restorations: 3-year clinical results. Quintessence Int 2010;41: 631-7. 16. Schmitt J, Wichmann M, Holst S, Reich S. Restoring severely compromised anterior teeth with zirconia crowns and feather-edged margin preparations: a 3-year follow-up of a prospective clinical trial. Int J Prosthodont 2010;23:107-9. 17. Cheung GSP. A preliminary investigation into the longevity and causes of failure of single unit extracoronal restorations. J Dent 1991;19:160-3. 18. Palmqvist S, Swartz B. Artificial crowns and fixed partial dentures 18 to 23 years after placement. Int J Prosthodont 1993;6:279-85. 19. Nilson H, Bergman B, Bessing C, Lundqvist P, Andersson M. Titanium copings veneered with Procera ceramics: a longitudinal clinical study. Int J Prosthodont 1994;7:115-9.
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December 2013 20. Kaus T, Probster L, Weber H. Clinical followup study of ceramic veneered titanium restorations-three-year results. Int J Prosthodont 1996;9:9-15. 21. Martin J, Bader J. Five-year treatment outcomes for teeth with large amalgams and crowns. Oper Dent 1997;22:72-8. 22. Smales R, Hawthorne WS. Long-term survival of extensive amalgams and posterior crowns. J Dent 1997;25:225-7. 23. Walton TR. A 10-year longitudinal study of fixed prosthodontics: clinical characteristics and outcome of single-unit metal-ceramic crowns. Int J Prosthodont 1999;12:519-26. 24. Lövgren R, Andersson B, Carlsson GE, Odman P. Prospective clinical 5-year study of ceramic-veneered titanium restorations with the Procera system. J Prosthet Dent 2000;84: 514-21. 25. Marklund S, Bergman B, Hedlund SO, Nilson H. An intraindividual clinical comparison if two metal-ceramic systems: a 5year prospective study. Int J Prosthodont 2003;16:70-3. 26. Backer HD, Maele GV, Moor ND, Berghe LVD, Boever JD. An 18-year retrospective survival study of full crowns with or without posts. Int J Prosthodont 2006;19:136-42. 27. Reitemeier B, Hänsel K, Kastner C, Walter MH. Metal-ceramic failure in noble metal crowns: 7-year results of a prospective clinical trial in private practices. Int J Prosthodont 2006;19:397-9. 28. Eliasson A, Arnelund CF, Johansson A. A clinical evaluation of cobalt-chromium metal-ceramic fixed partial dentures and crowns: a three- to seven-year retrospective study. J Prosthet Dent 2007;98:6-16.
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