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Clinical performance and patient satisfaction obtained with tooth-supported ceramic crowns and fixed partial dentures
CLINICAL RESEARCH
Clinical performance and patient satisfaction obtained with tooth-supported ceramic crowns and fixed partial dentures Fiona Alena Forrer, Dr med dent,a Nicole Schnider, Dr med dent,b Urs Brägger, Prof Dr,c Burak Yilmaz, DDS, PhD, PD, Dr,d and Stefan Paul Hicklin, Dr med dente
ABSTRACT Statement of problem. Studies reporting survival rates along with patient-centered outcomes are necessary to select the appropriate restorative material for crowns and fixed partial dentures (FPDs). However, studies that report the survival and complication rates of lithium disilicate crowns and the performance of zirconia FPDs compared with metal-ceramic FPDs are lacking. Purpose. The purpose of this clinical study was to assess the failure and complication incidence of tooth-supported ceramic crowns and FPDs in function for at least 5 years. Groups included were pressed lithium disilicate crowns (CP), veneered pressed lithium disilicate crowns (CV), and computer-aided design and computer-aided manufacturing (CAD-CAM) lithium disilicate crowns (CC). Veneered zirconia-based FPDs (FPDC) were compared with metal-ceramic FPDs (FPDM). Outcomes were survival and failure, success and complications, periodontal conditions, and patient satisfaction assessed at 2 examinations (at baseline 1 year after delivery and at the follow-up examination 5 years of function). Material and methods. Eighty-two participants with 158 restorations (CP=39, CV=16, CC=20, FPDM=30, FPDC=53) were examined (2.38 ±0.96 years after delivery) to form the baseline data. For the prospective follow-up examination, 70 participants with 141 restorations (CP=39, CV=15, CC=16, FPDM=28, FPDC=43) were examined 4.08 ±0.36 years later. Results. At the follow-up, restorations were in function for a mean of 6.44 ±1.14 years. Survival rates for crowns were 97.1% (CP=97.4%, CV=100%, and CC=93.8%) and 98.6% for FPDs (FPDM=96.4%, FPDC=100%). Among the 68 crowns, 1 technical and 4 biological complications were recorded. FPDs had more biological and technical complications than crowns (15/149 abutment teeth and 11/71 restorations). Technical complications were seen in 9.3% of zirconia FPDs compared with 25% for metal-ceramic FPDs. Complications were commonly observed at the baseline examination (crowns: 12/75 biological and 1/75 technical; FPDs: 40/174 abutment teeth with biological and 8/83 FPDs with technical complications). The periodontal conditions improved significantly after baseline. The patients reported a high level of satisfaction with the esthetics and function of the crowns and FPDs. Conclusions. Survival rate for ceramic crowns and FPDs was 97.9% after a mean observation time of 6.44 ±1.14 years. Biological complications were more commonly observed than technical complications, and complications were more common in FPDs than in crowns. The complication rate was similar for zirconia FPDs and metal-ceramic FPDs. Adherence to strict maintenance measures may have reduced the risk of biological complications. (J Prosthet Dent 2019;-:---)
Newly developed dental materials and innovative production processes have been used to provide patients with esthetic fixed restorations.1,2 Currently, lithium disilicate and zirconium dioxide represent the most commonly used ceramics in fixed prosthodontics.3,4
Glass ceramics with a high lithium disilicate content demonstrated adequate stability to serve as a reliable material for crowns.5 The analysis of data obtained from 12 clinical studies for lithium disilicate crowns and FPDs revealed
This investigation was financed by the Department of Reconstructive Dentistry and Gerodontology, University of Bern. There are no other sources of funding. a Senior Lecturer, Department of Reconstructive Dentistry and Gerodontology, School of Dental Medicine, University of Bern, Bern, Switzerland. b Postgraduate student, Department of Reconstructive Dentistry and Gerodontology, School of Dental Medicine, University of Bern, Bern, Switzerland. c Professor and Chair, Department of Reconstructive Dentistry and Gerodontology, School of Dental Medicine, University of Bern, Bern, Switzerland. d Associate Professor, Division of Restorative and Prosthetic Dentistry, The Ohio State University College of Dentistry, Columbus, Ohio. e Senior Lecturer, Division of Fixed Prosthodontics and Biomaterials, University Clinics of Dental Medicine, University of Geneva, Geneva, Switzerland.
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Clinical Implications Clinicians may confidently consider the use of pressed or CAD-CAM lithium disilicate crowns and veneered zirconia-based FPDs given the promising 6-year outcomes found in this study, as well as the reported high patient satisfaction with respect to function and esthetics.
promising survival rates with 100% at 1 year, 97.8% at 5 years, and 96.7% at 10 years for the crowns.6 Approximately, 50% of the 849 included crowns were fabricated out of a recently introduced material (IPS e.max; Ivoclar Vivadent AG), and, of those, approximately 50% were in use for a follow-up time of 18 months.6 Studies comparing the survival of lithium disilicate crowns processed with different techniques (CAD, press technique, monolithic, or veneered) and reporting detailed complication rates and patient-centered outcomes such as patient satisfaction are lacking, and the need for clinical studies for these comparisons has been noted.7 The clinical outcomes of the initial zirconia restorations did not match the results obtained with conventional metal-ceramic FPDs.8-10 However, a randomized clinical trial (RCT)11 with newer zirconia materials and improved fabrication methods revealed improved outcomes comparable with those of metal-ceramic FPDs. At 5 years, the survival rates were 100% in both groups.11 At the 10-year examination, a survival estimate of 91.3% was reported for the zirconia FPDs compared with 100% for the metal-ceramic FPDs. A higher rate of framework fracture, debonding, major fracture of the veneering material, and poor marginal adaptation were also noted for the ceramic FPDs.12 A recent systematic review13 concluded that more studies are needed to compare the clinical performance of newly introduced materials with that of metal-ceramic FPDs. The purpose of this clinical study was to assess the incidence of failure and complications with toothsupported ceramic crowns and FPDs in function for at least 5 years. The included groups were pressed lithium disilicate crowns (CP), pressed lithium disilicate crowns with a veneer (CV), and CAD-CAM lithium disilicate crowns (CC). Veneered zirconia-based FPDs (FPDC) were compared with conventional metal-ceramic FPDs (FPDM). Outcomes were survival and failure, success and complications, periodontal conditions, and patient satisfaction assessed at 2 examinations, the first being the baseline 1 year after delivery and the follow-up examination 5 years of function. The null hypothesis was that ceramic crowns and FPDs would show similar THE JOURNAL OF PROSTHETIC DENTISTRY
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survival and complication rates to those of metal-ceramic FPDs. MATERIAL AND METHODS The participants included in this study were retrospectively recruited from a pool of patients in the former Division of Fixed Prosthodontics at the University of Bern, Switzerland. The study protocol was accepted by the Ethics Committee Bern (KEK-Nr. 020/13). Inclusion criteria were defined as insertion of at least 1 of the following: a lithium disilicate crown, a zirconiabased FPD, and/or a metal-ceramic FPD in the predoctoral clinic or the postgraduate program between January 2009 and November 2013. All patients received an initial dental prophylaxis treatment before the restorative phase. The abutment teeth were not prepared if the patients’ oral hygiene level indicated a complete-mouth plaque index,14 if a BOP of >20% was observed, or if probing pocket depths (PPDs) of 5 mm were found on abutment teeth. The restorations were cemented with a glass-ionomer (Ketac Cem; 3M ESPE AG) or composite resin (RelyX Unicem [3M ESPE AG], Variolink II [Ivoclar Vivadent AG], or Panavia 21 [Kuraray Dental GmbH]). The baseline clinical examination took place between June 2013 and May 2014, and the follow-up examinations were performed between September 2017 and May 2018. Data on the type of material; date of insertion; location; number of replaced teeth; number of abutment teeth, pontics, and cantilever; cement applied; vitality at the date of cementation; and provider were retrieved from the patients’ charts. According to a standardized procedure, one examiner scored the parameters for all patients. Four of the authors were involved in the examination and were responsible for the following steps: clinical examinations (F.A.F.), interviews (N.S.), photographs (S.P.H.), and radiographs (U.B.). During the appointments, the patients were interviewed and asked to mark their perceived degree of satisfaction with esthetics and comfort according to an 11-point numeric scale. Periodontal parameters were collected by using a periodontal probe (PP12; Deppeler SA) at 6 sites per abutment tooth: presence or absence of plaque (PI),14 presence or absence of bleeding on probing (BOP), location of the free gingival margin (FGM) in relation to the crown margin, and PPDs. The clinical attachment loss was calculated as PPD minus FGM. The endodontic evaluation included vitality testing (CO2 test) and presence or absence of fistulae. Abutment teeth and their corresponding crowns and FPDs were examined for the presence of secondary carious lesions, chipping, loss of retention, fracture of the framework material, and the quality of the marginal adaptation with the modified Forrer et al
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Table 1. Number of participants, restorations, and abutment teeth in 5 groups CP
CV
CC
All Crowns
FPDM
FPDC
All FPDs
Variable
B
F
B
F
B
F
B
F
B
F
B
F
B
No. of participants
5
5
7
6
11
8
21
17
27
24
39
32
67
F 56
No. of restorations
39
39
16
15
20
16
75
70
31
28
52
43
83
71
No. of abutment teeth
39
39
16
15
20
16
75
70
68
62
106
88
174
150
B, baseline; CC, e.max CAD; CP, e.max press; CV, veneered e.max press; F, follow-up; FPDC, zirconia-based; FPDM, metal-ceramic.
Table 2. Periodontal findings per abutment teeth/sites CP Variable N of sites (6 for each tooth) Mean sites with plaque
CV
CC
All Crowns
B (N=39)
F (N=38)
B (N=16)
F (N=15)
B (N=20)
F (N=15)
B (N=75)
234
228
96
90
120
90
450
F (N=68) 408
0.17 ±0.14
0.03 ±0.07
0.12 ±0.14
0.08 ±0.11
0.23 ±0.24
0.01 ±0.04
0.18 ±0.18
0.03 ±0.08
Mean sites with BOP
0.24 ±0.30
0.25 ±0.28
0.44 ±0.33
0.18 ±0.19
0.25 ±0.28
0.12 ±0.13
0.28 ±0.31
0.21 ±0.24
Mean PPD in mm
2.62 ±0.40
2.61 ±0.65
2.38 ±0.57
2.40 ±0.80
3.01 ±0.46
2.60 ±0.90
2.67 ±0.50
2.56 ±0.75
Mean CAL in mm
3.76 ±0.74
2.77 ±0.70
3.44 ±0.94
2.52 ±0.82
4.40 ±1.08*
3.19 ±1.10*
3.66 ±0.81
2.81 ±0.86
Mean recession in mm
0.09 ±0.14
0.16 ±0.27
0.06 ±0.08
0.12 ±0.13
0.36 ±0.36*
0.59 ±0.47*
0.16 ±0.24
0.25 ±0.35
B, baseline; CC, e.max CAD; CP, e.max press; CV, veneered e.max press; F, follow-up. *Statistically significant difference (P<.05) compared with other groups.
United States Public Health Service (USPHS) criteria.15 These criteria were met with an explorer (EXD3; HuFriedy Mfg Co, LLC) and defined as follows: Alfa (A) =no explorer catch; Bravo (B)=slight explorer catch, but no gap; Charlie (C)=gap with some dentin or cement exposure; Delta (D)=new restoration is needed. Radiographs were obtained with an individualized film holder by using acrylic resin (Pattern Resin; GC Germany GmbH) for future evaluations. In the periapical radiographs, the quality of existing endodontic treatment and the presence of periapical lesions, resorption, or caries were assessed. A failure of a crown or an FPD was defined as the loss of the restoration or a situation that resulted in the loss of the abutment teeth. Biological complications were related to the abutment teeth and defined as secondary caries, loss of vitality, periapical radiolucency, and/or presence of 1 or several PPDs 5 mm. Technical complications were related to the restorations and included chipping of veneered ceramic (adhesive, cohesive, or combined), fracture of the framework, loss of retention, or a marginal discrepancy with a value of Delta (D). Descriptive statistics were used for data presentation. Data were listed for crowns and FPDs. The Kruskal-Wallis tests were applied to perform comparisons among more than 2 groups. The Wilcoxon-Mann-Whitney tests and Wilcoxon signed-rank tests were used to compare median values between 2 groups for unpaired and paired data, respectively. No correction for multiple testing was done because of the explorative nature of this study (a=.05). RESULTS Of 136 patients identified, 17 could not be reached, and 25 were not interested in participating for various reasons. Therefore, 82 participants (52 women, 30 men),
Forrer et al
who received 158 crowns and FPDs, participated in the baseline clinical examination. At the follow-up, 70 participants were examined. Twelve participants could not be reexamined; one suffered from dementia, 7 could not be reached, and 4 were no longer interested in participating for various reasons. The number of evaluated participants, restorations, and abutment teeth in the different groups are presented in Table 1. At the baseline examination and at the follow-up examination, 91.5% (75/82) and 93% (66/71), respectively, of the patients were integrated into a regular maintenance system with at least 1 recall per year. Twenty-six (35%) crowns and 63 (76%) FPDs were placed in the predoctoral clinic. Postgraduate dentists placed 49 (65%) crowns and 20 (24%) FPDs. The periodontal parameters of the teeth with crowns at the baseline and the follow-up examinations are presented in Table 2. The clinical attachment level (CAL) was not statistically significantly different. The comparison among the crown groups at the follow-up examination showed significant differences in CAL (P=.004). Post hoc analyses revealed significant differences in CAL between CC and CV and between CV and CP (P=.002 and P=.008, respectively). In Table 3, the changes in the periodontal conditions are listed for those crowns that could be examined at the baseline and the follow-up examinations. The periodontal conditions (mean sites with plaque, mean sites with BOP) of all crowned teeth at the follow-up examination were statistically significantly improved compared with those at the first examination (mean sites with plaque P<.001, mean sites with BOP P=.017). Furthermore, a statistically significant reduction in PPD (P=.031) and an increase in the number of areas with recessions (P=.018) were observed in the CC group.
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Table 3. Changes over time of periodontal conditions Variable
CP (N=38)
CV (N=15)
CC (N=15)
All Crowns (N=68)
Mean change of mean sites with plaque
0.14 ±0.16*
0.06 ±0.15
0.23 ±0.19*
0.14 ±0.17*
Mean change of mean sites with BOP
0.00 ±0.24
0.28 ±0.38*
0.06 ±0.26
0.07 ±0.30*
Mean change of mean PPD 5mm
0.01 ±0.05
0.02 ±0.09
0.02 ±0.06
0.01 ±0.06
Mean change of PPD in mm
-0.01 ±0.49
0.00 ±0.59
-0.32 ±0.49*
-0.08 ±0.49
Mean change of CAL in mm
-0.05 ±0.56
-0.06 ±0.65
-0.13 ±0.55
-0.00 ±0.58
0.07 ±0.23
0.06 ±0.10
Mean change of recession in mm
0.19 ±0.25*
0.09 ±0.22*
CC, e.max CAD; CP, e.max press; CV, veneered e.max press. *Statistically significant difference (P<.05) comparing baseline with follow-up examination.
Table 4. Periodontal findings per abutment teeth/sites FPDM Variable
All FPDs
F (N=61)
B (N=106)
F (N=88)
B (N=174)
408
366
636
528
1044
894
0.20 ±0.23
0.06 ±0.10
0.13 ±0.14
0.05 ±0.08
0.15 ±0.18
0.05 ±0.09
No. of sites (6 for each tooth) Mean sites with plaque
FPDC
B (N=68)
F (N=149)
Mean sites with BOP
0.37 ±0.28
0.17 ±0.18
0.32 ±0.22
0.23 ±0.17
0.34 ±0.24
0.20 ±0.17
Mean PPD in mm
2.88 ±0.56
2.61 ±0.79
2.72 ±0.40
2.53 ±0.76
2.78 ±0.45
2.57 ±0.77
Mean clinical attachment loss in mm
4.36 ±1.23
3.19 ±1.00
3.94 ±0.91*
2.93 ±0.91*
4.10 ±1.07
3.03 ±0.96
Mean recession in mm
0.45 ±0.51
0.54 ±0.48
0.22 ±0.28
0.40 ±0.45
0.31 ±0.39
0.45 ±0.46
B, baseline; F, follow-up; FPDC, zirconia-based; FPDM, metal-ceramic. *Statistically significant difference (P<.05) compared with other groups.
Table 5. Changes over time of periodontal conditions Variable Mean change of mean sites with plaque
FPDM (N=61)
FPDC (N=88)
Table 6. Number of loss of abutment teeth and survival rate All FPDs (N=149)
0.09 ±0.15* 0.08 ±0.13*
0.09 ±0.14*
Mean change of mean sites with BOP 0.15 ±0.21* 0.09 ±0.18*
0.12 ±0.20*
Mean change of mean PPD 5 mm
0.01 ±0.08
0.02 ±0.06
0.01 ±0.07*
Mean change of PPD in mm
-0.19 ±0.46* -0.15 ±0.36* -0.12 ±0.47*
Mean change of clinical attachment loss in mm
-0.06 ±0.50 -0.01 ±0.38
Mean change of recession in mm
0.12 ±0.18* 0.12 ±0.20*
-0.02 ±0.43
CP
CV
CC
No. of restorations
39
15
16
70
28
43
71
No. of abutment teeth
39
15
16
70
62
88
150
1
0
1
1
0
Failures Survival rate
97.4% 100% 93.8%
All Crowns FPDM FPDC All FPDs
2 97.1%
96.4% 100%
1 98.6%
CC, e.max CAD; CP, e.max press; CV, veneered e.max press; FPDC, zirconia-based; FPDM, metal-ceramic.
0.15 ±0.19*
FPDC, zirconia-based; FPDM, metal-ceramic. *Statistically significant difference (P<.05) comparing baseline with follow-up examination.
The periodontal parameters of the abutment teeth of the FPDs at the baseline and the follow-up examinations are presented in Table 4. In Table 5, the changes in the periodontal conditions are listed for those FPDs that could be examined at the baseline and the follow-up examinations. Between the baseline and follow-up examinations, the mean clinical attachment loss showed no significant difference (P=.903). Significant values for clinical attachment loss were found at the abutment teeth of FPDC (baseline examination P=.037; follow-up examination P=.015). With respect to all FPD abutments, periodontal conditions at the follow-up examination improved significantly compared with the baseline examination (P<.001). A statistically significant reduction in PPD was noted for FPDC (P=.012), and an increase in recession (FPDM P=.002; FPDC P<.001) was noted in both FPD groups. The numbers for loss of abutment teeth and survival rate are presented in Table 6. Both teeth lost with crowns required endodontic treatment, and a post and core was THE JOURNAL OF PROSTHETIC DENTISTRY
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placed. The reason for these 2 failures was a crown fracture at the gingival level. The 3 abutment teeth of an FPDM had a periodontal abscess and required extraction. Therefore, the failures had no prosthetic cause. A total of 19 abutment teeth (8.8%) were affected by biological complications after 6.44 ±1.14 years (Tables 7 and 8). The most prevalent complication at the first examination was a PPD 5 mm at 1 or more abutment tooth (40 sites). Twenty-two restorations had an isolated PPD 5 mm at 1 abutment tooth, 1 FPDM had an increased PPD on both abutment teeth, and 3 FPDM restorations had other complications at the same restoration. At the follow-up, only 6 sites had a PPD 5 mm. Twelve of 139 (8.6%) crowns and FPDs showed technical complications after a mean observation time of 6.44 ±1.14 years (Tables 9 and 10). One FPDC chipped twice. All cohesive chips were located on the cusp tips. Both mixed chips were found on the buccal surface with extension toward the proximal area. Two metal-ceramic FPDs lost retention at approximately 7 and 11 months after cementation. Both FPDs were cemented in the predoctoral clinic. One of the FPDs was cemented with a glass-ionomer cement (Ketac Forrer et al
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Table 7. Number and percentage of biological complications CP Variable
CV
CC
All Crowns
B (N=39)
O (N=38)
B (N=16)
O (N=15)
B (N=20)
O (N=15)
B (N=75)
No. of vital abutment teeth
36
34
13
12
12
9
61
O (N=68) 55
No. of sites (6 for each tooth)
234
228
96
90
120
90
450
408
Caries
0
0
0
0
0
0
0
0
Loss of vitality *
0
1 (2.9%)
0
0
1 (8.3%)
1 (11.1%)
1 (1.6%)
2 (3.6%) 1 (1.5%)
Periapical lesion
0
0
0
0
1 (5.0%)
1 (6.7%)
1 (1.3%)
PPD 5 mm
1 (2.6%)
0
2 (12.5%)
0
1 (5.0%)
0
4 (5.3%)
0
PPD 6 mm
1 (2.6%)
0
0
0
5 (25.0%)
1 (6.7%)
6 (8%)
1 (1.5%)
PPD 7 mm
0
0
0
0
0
0
0
0
Total complications
2
1
2
0
8
3
12
4
5.1%
2.6%
12.5%
0%
40.0%
20.0%
16.0%
5.8%
Complication rate
B, baseline; CC, e.max CAD; CP, e.max press; CV, veneered e.max press; O, overall. *Loss of vitality (%) of abutment tooth.
Table 8. Number and percentage of biological complications FPDM Variable
FPDC
All FPDs
B (N=68)
O (N=61)
B (N=106)
O (N=88)
B (N=174)
No. of vital abutment teeth
48
44
84
72
132
116
No. of sites (6 for each tooth)
408
366
636
528
1044
894
Caries
1 (1.5%)
1 (1.6%)
0
0
1 (0.6%)
1 (0.7%)
Loss of vitality *
1 (2.1%)
1 (2.3%)
3 (3.6%)
3 (4.2%)
4 (3.0%)
4 (3.4%)
Periapical lesion
1 (1.5%)
1 (1.6%)
4 (3.8%)
4 (4.5%)
5 (2.9%)
5 (3.4%)
PPD 5 mm
9 (13.2%)
2 (3.3%)
8 (7.5%)
0
17 (9.8%)
2 (1.3%)
PPD 6 mm
5 (7.4%)
1 (1.6%)
4 (3.8%)
2 (2.3%)
9 (5.2%)
3 (2.0%)
PPD 7 mm
2 (2.9%)
0
2 (1.9%)
0
4 (2.3%)
0
19
6
21
9
40
15
28.0%
9.8%
19.8%
10.3%
23.0%
10.1%
Total complications Complication rate
O (N=149)
B, baseline; FPDC, zirconia-based; FPDM, metal-ceramic; O, overall. *Loss of vitality (%) of vital abutment tooth.
Table 9. Number and percentage of technical complications CP Variable
CV
CC
All Crowns
B (N=39)
O (N=38)
B (N=16)
O (N=15)
B (N=20)
O (N=15)
B (N=75)
O (N=68)
Chipping cohesive
0
0
0
0
1 (5.0%)
1 (6.6%)
1 (1.3%)
1 (1.5%)
Chipping adhesive
0
0
0
0
0
0
0
0
Chipping combined
0
0
0
0
0
0
0
0
Framework fracture
0
0
0
0
0
0
0
0
Loss of retention
0
0
0
0
0
0
0
0
Total complications Complication rate
0
0
0
0
1
1
1
1
0%
0%
0%
0%
5%
6.6%
1.3%
1.5%
B, baseline; CC, e.max CAD; CP, e.max press; CV, veneered e.max press; O, overall.
Cem); however, no information about the cement used for the other FPD was found in the patient file (missing data). Both FPDs were then recemented. At the baseline examination, 5 crowns (7%) and 11 FPDs (6%) had a marginal discrepancy of Charlie (C). One 3-unit FPDM had a marginal discrepancy on both teeth, and the remaining 10 FPDs, only on 1 of the abutment teeth. USPHS scores of Delta (D) were not found. None of the marginal discrepancies of Charlie had worsened between the baseline examination and follow-up. The interview with patients revealed a high level of satisfaction with the esthetics and function of the crowns Forrer et al
and FPDs. The mean and standard deviation of patient satisfaction and change in patient satisfaction are listed in Tables 11 and 12. The patient-reported outcome measures (PROMs) at the follow-up examination showed statistically significant improvements in esthetics (P=.014) and function (P.001) compared with the PROM of the baseline examination. DISCUSSION The null hypothesis that ceramic crowns and FPDs would have similar survival rates and number of complications THE JOURNAL OF PROSTHETIC DENTISTRY
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Table 10. Number and percentage of technical complications FPDM
FPDC
All FPDs
Variable
B (N=31)
O (N=28)
B (N=52)
O (N=43)
B (N=83)
Chipping cohesive
2 (6.5%)
4 (14.3%)
2 (3.8%)
2 (4.7%)
4 (4.8%)
6 (8.5%)
Chipping adhesive
0
0
0
1 (2.3%)
0
1 (1.4%)
Chipping combined
1 (3.2%)
1 (3.6%)
1 (1.9%)
1 (2.3%)
2 (2.4%)
2 (2.8%)
Framework fracture
0
0
0
0
0
0
2 (6.5%)
2 (7.1%)
0
0
2 (2.4%)
2 (2.8%)
Loss of retention Total complications Complication rate in %
O (N=71)
5
7
3
4
8
11
16.1%
25%
5.8%
9.3%
9.6%
15.5%
B, baseline; FPDC, zirconia-based; FPDM, metal-ceramic; O, overall.
Table 11. Mean and standard deviation of patient satisfaction and change of patient satisfaction (mean ±SD) CP
CV
CC
All Crowns
Variable
B (N=39)
F (N=39)
C (N=39)
B (N=16)
F (N=15)
C (N=15)
B (N=20)
F (N=16)
C (N=16)
B (N=75)
F (N=70)
C (N=70)
Esthetic
8.9 ±0.5
9.8 ±0.4
0.1 ±0.6
9.7 ±0.6
9.7 ±0.5
0.0 ±0.9
9.4 ±1.2
9.1 ±0.7
-0.2 ±1.1
9.2 ±0.8
9.7 ±0.6
0.5 ±0.9
Function
9.7 ±0.5
9.8 ±0.4
0.2 ±0.6
9.0 ±0.9
9.1 ±1.0
0.1 ±1.1
9.1 ±1.2
9.6 ±0.8
0.7 ±1.1
9.4 ±0.9
9.6 ±0.7
0.3 ±0.8
B, baseline; C, change of patient satisfaction; CC, e.max CAD; CP, e.max press; CV, veneered e.max press; F, follow-up.
Table 12. Mean and standard deviation of patient satisfaction and change of patient satisfaction (mean ±SD) FPDM
FPDC
All FPDs
Variable
B (N=31)
F (N=28)
C (N=28)
B (N=52)
F (N=43)
C (N=43)
B (N=83)
F (N=71)
C (N=71)
Esthetic
9.3 ±1.3
8.9 ±2.0
-0.3 ±2.3
9.4 ±0.8
9.5 ±0.9
0.0 ±0.9
9.3 ±1.0
9.2 ±1.5
-0.1 ±1.6
Function
9.3 ±1.8
9.1 ±2.0
-0.0 ±2.1
8.8 ±1.3
9.5 ±0.9
0.7 ±1.4
8.9 ±1.5
9.4 ±1.4
0.4 ±1.7
B, baseline; C, change of patient satisfaction; F, follow-up; FPDC, zirconia-based; FPDM, metal-ceramic.
as those of metal-ceramic FPDs was accepted. The periodontal condition observed at the baseline examination around the abutment teeth was unexpectedly poor. As far as BOP is concerned, a complete-mouth percentage below 20% would have been desirable to reduce the risk of future attachment loss.16 Even more concerning were the sites with PPDs 5 mm, which, in combination with BOP, put the dentition, and specifically the abutment teeth, at a higher risk for additional attachment loss or, in the long-run, even tooth loss.17 A few months after the delivery of crowns and FPDs, some patients relapsed in their efforts at optimal plaque control,18 resulting in a deterioration of the periodontal parameters obtained at the end of the active periodontal and restorative treatment.19 Similarly, at the baseline examination of the present study, a PPD 5 mm was observed on 13.3% of crowns and 17.2% of the FPD abutment teeth. In a recent report on 104 pressed lithium disilicate (IPS e.max) crowns, none of the abutment teeth showed PPD 4 mm after up to 9 years.7 At the follow-up examination, periodontal parameters had improved considerably. Participating in the study seemed to improve these parameters. The patients were informed about their conditions and motivated to improve their oral hygiene and adhere to a strict recall interval. At 6 years of function, 2 of 70 lithium disilicate crowns failed (97.1% survival). One technical (1.5%) and 4 THE JOURNAL OF PROSTHETIC DENTISTRY
biological (5.8%) complications were detected. In a prospective split-mouth study, a 7-year survival rate of 100% for pressed lithium disilicate (IPS e.max press) and 97% for ProCAD (Ivoclar Vivadent AG) partial crowns was reported. No secondary caries, no endodontic complications, and no postoperative complaints were reported. Small cohesive ceramic fractures were noted in 5 patients.20 In a systematic review6 with short- (1 to 5 years) and medium-term (5 to 10 years) survival rates of 849 different lithium disilicate crowns (Empress II, IPS e.max press, IPS e.max CAD, and 2 studies with unspecified lithium disilicate crowns), the most common technical complication reported was fracture of the core framework, followed by chipping of the veneering ceramic and debonding of the restoration. The most commonly reported biological complications included the need for endodontic treatment and the presence of secondary caries. Favorable short-term survival rates were reported, but the estimated promising cumulative survival rate at 5 years was based on limited data.6 The results of the present report are similar to those of these clinical studies, where varying restoration designs and materials were involved. In the present study, complete-coverage crowns out of 1 material (e.max lithium disilicate) were examined. The sample sizes in the 3 subgroups were low, unevenly distributed, and not randomly assigned. Forrer et al
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At 6 years, the survival rate for all FPDs was 98.6% (1/ 71 failure). According to a systematic review,10 less favorable clinical outcomes for ceramic FPDs can be expected compared with metal-ceramics. The estimated survival rates after 5 years for ceramic FPDs were lower than those of metal-ceramic FPDs (summary estimate of 89.1% for reinforced glass-ceramic, 86.2% for glass infiltrated alumina, 90.4% for zirconia, and 94.4% for metal-ceramic).10 The number of chippings was found to be similar In FPDM (5/28) and FPDC (4/43). This contradicts the findings of a systematic review,21 in which the frequency of veneer chipping was significantly higher in zirconia FPDs than in the metal-ceramic FPDs (54% versus 34%). The positive trend to obtaining a more stable veneer ceramic on zirconia frameworks can be explained with improvements in the characteristics of materials and fabrication.22-24 Loss of retention occurred in 2 FPDMs after less than a year, whereas, based on analyses of data from a systematic review, the incidences of loss of retention were significantly higher for zirconia FPDs than those for metal-ceramic FPDs.10 However, no statistical differences were found with respect to technical and biological problems according to 2 recent RCTs.11,12 The PROMs related to esthetic and functional satisfaction identified on an 11-point numeric scale reached high scores with all 5 groups of crowns and FPDs. This was consistent with a recent study that assessed functional and esthetic satisfaction and evaluated changes in oral health-related quality of life (OHRQoL) after insertion of a metal-ceramic or a ceramic veneered zirconia posterior 3-unit FPD. Patients experienced improved OHRQoL and increased satisfaction with function and esthetics. No essential differences were observed between metal-ceramic and ceramic FPDs when evaluated by the patient or the clinicians.25 Limitations of the present study included that it was a retrospective clinical study without randomization. Many students/dentists and dental technicians were involved in the treatment and production of the crowns and FPDs. These unregulated parts of the study should be controlled in future studies to minimize variables to observe the materials’ performance. In addition, randomization can be used to minimize bias. The observation time was of medium term, and the sample size for patients and restorations was small. Future studies with a higher number of participants and restorations should be carried out to investigate the long-term outcomes. The present data, nevertheless, indicate that lithium disilicate is a suitable material for restoring teeth with crowns and that veneered zirconia FPDs serve as an alternative to metal-ceramic FPDs for the assessment time used in this study.
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CONCLUSIONS Based on the findings of this clinical study, the following conclusions were drawn: 1. Survival rate for ceramic crowns and FPDs was 97.9% after a mean observation time of 6.44 ±1.14 years. 2. Biological complications were more common than technical complications, and complications were more frequent in FPDs than in crowns. 3. The level of oral hygiene deteriorated after the active treatment phase but had improved for some patients after entering the study. 4. The complications were comparable for zirconia FPDs and metal-ceramic FPDs. 5. Participants indicated a high degree of satisfaction with function and esthetics. 6. In the medium term, ceramic restorations made of the tested materials and with the tested processing steps are promising alternatives to MCCs and metal-ceramic FPDs. REFERENCES 1. McLaren EA. All-ceramic alternatives to conventional metal-ceramic restorations. Compend Contin Educ Dent 1998;19:307-8. 10, 12 passim; quiz 26. 2. Touati B. Innovative dental ceramics: expanding the material alternatives. Pract Proced Aesthet Dent 2005;17:357-8. 3. Christensen GJ. The all-ceramic restoration dilemma: where are we? J Am Dent Assoc 2011;142:668-71. 4. Chu SJ. Current clinical strategies with lithium-disilicate restorations. Compend Contin Educ Dent 2012;33. 64, 6-7. 5. Gehrt M, Wolfart S, Rafai N, Reich S, Edelhoff D. Clinical results of lithiumdisilicate crowns after up to 9 years of service. Clin Oral Investig 2013;17: 275-84. 6. Pieger S, Salman A, Bidra AS. Clinical outcomes of lithium disilicate single crowns and partial fixed dental prostheses: a systematic review. J Prosthet Dent 2014;112:22-30. 7. Afrashtehfar KI, Brägger U, Treviño-Santos A, Freitas de Souza R. Letters to the editor. Evid Based Dent 2017;18:2. 8. Sax C, Hammerle CH, Sailer I. 10-year clinical outcomes of fixed dental prostheses with zirconia frameworks. Int J Comput Dent 2011;14:183-202. 9. Sailer I, Feher A, Filser F, Luthy H, Gauckler LJ, Scharer P, et al. Prospective clinical study of zirconia posterior fixed partial dentures: 3-year follow-up. Quintessence Int 2006;37:685-93. 10. Pjetursson BE, Sailer I, Makarov NA, Zwahlen M, Thoma DS. All-ceramic or metal-ceramic tooth-supported fixed dental prostheses (FDPs)? A systematic review of the survival and complication rates. Part II: Multiple-unit FDPs. Dent Mater 2015;31:624-39. 11. Sailer I, Gottnerb J, Kanelb S, Hammerle CH. Randomized controlled clinical trial of zirconia-ceramic and metal-ceramic posterior fixed dental prostheses: a 3-year follow-up. Int J Prosthodont 2009;22:553-60. 12. Sailer I, Strasding M, Valente NA, Zwahlen M, Liu S, Pjetursson BE. A systematic review of the survival and complication rates of zirconia-ceramic and metal-ceramic multiple-unit fixed dental prostheses. Clin Oral Implants Res 2018;29 Suppl 16:184-98. 13. Poggio CE, Ercoli C, Rispoli L, Maiorana C, Esposito M. Metal-free materials for fixed prosthodontic restorations. Cochrane Database Syst Rev 2017;12: CD009606. 14. O’Leary TJ, Drake RB, Naylor JE. The plaque control record. J Periodontol 1972;43:38. 15. Ryge G, Snyder M. Evaluating the clinical quality of restorations. J Am Dent Assoc 1973;87:369-77. 16. Joss A, Adler R, Lang NP. Bleeding on probing. A parameter for monitoring periodontal conditions in clinical practice. J Clin Periodontol 1994;21:402-8. 17. Matuliene G, Pjetursson BE, Salvi GE, Schmidlin K, Bragger U, Zwahlen M, et al. Influence of residual pockets on progression of periodontitis and tooth loss: results after 11 years of maintenance. J Clin Periodontol 2008;35:685-95.
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18. Heschl A, Haas M, Haas J, Payer M, Wegscheider W, Polansky R. Maxillary rehabilitation of periodontally compromised patients with extensive onepiece fixed prostheses supported by natural teeth: a retrospective longitudinal study. Clin Oral Investig 2013;17:45-53. 19. Bragger U, Hakanson D, Lang NP. Progression of periodontal disease in patients with mild to moderate adult periodontitis. J Clin Periodontol 1992;19:659-66. 20. Guess PC, Selz CF, Steinhart YN, Stampf S, Strub JR. Prospective clinical split-mouth study of pressed and CAD/CAM all-ceramic partial-coverage restorations: 7-year results. Int J Prosthodont 2013;26:21-5. 21. Heintze SD, Rousson V. Survival of zirconia- and metal-supported fixed dental prostheses: a systematic review. Int J Prosthodont 2010;23:493-502. 22. Yamamoto LT, Rodrigues VA, Dornelles LS, Bottino MA, Valandro LF, Melo RM. Low-fusing porcelain glaze application on 3Y-TZP surfaces can enhance zirconia-porcelain adhesion. Braz Dent J 2016;27:543-7. 23. Madani A, Nakhaei M, Karami P, Rajabzadeh G, Salehi S, Bagheri H. Sol-gel dip coating of yttria-stabilized tetragonal zirconia dental ceramic by aluminosilicate nanocomposite as a novel technique to improve the bonding of veneering porcelain. Int J Nanomedicine 2016;11:3215-23. 24. Passos SP, Linke B, Major PW, Nychka JA. Improving the compatibility of a Y-TZP/porcelain system using a new composite interlayer composition. J Mech Behav Biomed Mater 2017;65:11-9.
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25. Nicolaisen MH, Bahrami G, Schropp L, Isidor F. Functional and esthetic comparison of metal-ceramic and all-ceramic posterior three-unit fixed dental prostheses. Int J Prosthodont 2016;29:473-81. Corresponding author: Dr Fiona Alena Forrer Department of Reconstructive Dentistry and Gerodontology School of Dental Medicine University of Bern Freiburgstrasse 7, 3010 Bern SWITZERLAND Email: fi[email protected] Acknowledgments The authors express their gratitude to the biomedical engineer Walter B. Buergin for his support in statistical questions and to the statisticians Anja Mühlemann, Gabriel Fischer, and Lukas Martig for performing the statistical analysis. Copyright © 2019 by the Editorial Council for The Journal of Prosthetic Dentistry. https://doi.org/10.1016/j.prosdent.2019.08.012
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Clinical performance and patient satisfaction obtained with tooth-supported ceramic crowns and fixed partial dentures Fiona Alena Forrer, Dr med dent,a Nicole Schnider, Dr med dent,b Urs Brägger, Prof Dr,c Burak Yilmaz, DDS, PhD, PD, Dr,d and Stefan Paul Hicklin, Dr med dente
ABSTRACT Statement of problem. Studies reporting survival rates along with patient-centered outcomes are necessary to select the appropriate restorative material for crowns and fixed partial dentures (FPDs). However, studies that report the survival and complication rates of lithium disilicate crowns and the performance of zirconia FPDs compared with metal-ceramic FPDs are lacking. Purpose. The purpose of this clinical study was to assess the failure and complication incidence of tooth-supported ceramic crowns and FPDs in function for at least 5 years. Groups included were pressed lithium disilicate crowns (CP), veneered pressed lithium disilicate crowns (CV), and computer-aided design and computer-aided manufacturing (CAD-CAM) lithium disilicate crowns (CC). Veneered zirconia-based FPDs (FPDC) were compared with metal-ceramic FPDs (FPDM). Outcomes were survival and failure, success and complications, periodontal conditions, and patient satisfaction assessed at 2 examinations (at baseline 1 year after delivery and at the follow-up examination 5 years of function). Material and methods. Eighty-two participants with 158 restorations (CP=39, CV=16, CC=20, FPDM=30, FPDC=53) were examined (2.38 ±0.96 years after delivery) to form the baseline data. For the prospective follow-up examination, 70 participants with 141 restorations (CP=39, CV=15, CC=16, FPDM=28, FPDC=43) were examined 4.08 ±0.36 years later. Results. At the follow-up, restorations were in function for a mean of 6.44 ±1.14 years. Survival rates for crowns were 97.1% (CP=97.4%, CV=100%, and CC=93.8%) and 98.6% for FPDs (FPDM=96.4%, FPDC=100%). Among the 68 crowns, 1 technical and 4 biological complications were recorded. FPDs had more biological and technical complications than crowns (15/149 abutment teeth and 11/71 restorations). Technical complications were seen in 9.3% of zirconia FPDs compared with 25% for metal-ceramic FPDs. Complications were commonly observed at the baseline examination (crowns: 12/75 biological and 1/75 technical; FPDs: 40/174 abutment teeth with biological and 8/83 FPDs with technical complications). The periodontal conditions improved significantly after baseline. The patients reported a high level of satisfaction with the esthetics and function of the crowns and FPDs. Conclusions. Survival rate for ceramic crowns and FPDs was 97.9% after a mean observation time of 6.44 ±1.14 years. Biological complications were more commonly observed than technical complications, and complications were more common in FPDs than in crowns. The complication rate was similar for zirconia FPDs and metal-ceramic FPDs. Adherence to strict maintenance measures may have reduced the risk of biological complications. (J Prosthet Dent 2019;-:---)
Newly developed dental materials and innovative production processes have been used to provide patients with esthetic fixed restorations.1,2 Currently, lithium disilicate and zirconium dioxide represent the most commonly used ceramics in fixed prosthodontics.3,4
Glass ceramics with a high lithium disilicate content demonstrated adequate stability to serve as a reliable material for crowns.5 The analysis of data obtained from 12 clinical studies for lithium disilicate crowns and FPDs revealed
This investigation was financed by the Department of Reconstructive Dentistry and Gerodontology, University of Bern. There are no other sources of funding. a Senior Lecturer, Department of Reconstructive Dentistry and Gerodontology, School of Dental Medicine, University of Bern, Bern, Switzerland. b Postgraduate student, Department of Reconstructive Dentistry and Gerodontology, School of Dental Medicine, University of Bern, Bern, Switzerland. c Professor and Chair, Department of Reconstructive Dentistry and Gerodontology, School of Dental Medicine, University of Bern, Bern, Switzerland. d Associate Professor, Division of Restorative and Prosthetic Dentistry, The Ohio State University College of Dentistry, Columbus, Ohio. e Senior Lecturer, Division of Fixed Prosthodontics and Biomaterials, University Clinics of Dental Medicine, University of Geneva, Geneva, Switzerland.
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Clinical Implications Clinicians may confidently consider the use of pressed or CAD-CAM lithium disilicate crowns and veneered zirconia-based FPDs given the promising 6-year outcomes found in this study, as well as the reported high patient satisfaction with respect to function and esthetics.
promising survival rates with 100% at 1 year, 97.8% at 5 years, and 96.7% at 10 years for the crowns.6 Approximately, 50% of the 849 included crowns were fabricated out of a recently introduced material (IPS e.max; Ivoclar Vivadent AG), and, of those, approximately 50% were in use for a follow-up time of 18 months.6 Studies comparing the survival of lithium disilicate crowns processed with different techniques (CAD, press technique, monolithic, or veneered) and reporting detailed complication rates and patient-centered outcomes such as patient satisfaction are lacking, and the need for clinical studies for these comparisons has been noted.7 The clinical outcomes of the initial zirconia restorations did not match the results obtained with conventional metal-ceramic FPDs.8-10 However, a randomized clinical trial (RCT)11 with newer zirconia materials and improved fabrication methods revealed improved outcomes comparable with those of metal-ceramic FPDs. At 5 years, the survival rates were 100% in both groups.11 At the 10-year examination, a survival estimate of 91.3% was reported for the zirconia FPDs compared with 100% for the metal-ceramic FPDs. A higher rate of framework fracture, debonding, major fracture of the veneering material, and poor marginal adaptation were also noted for the ceramic FPDs.12 A recent systematic review13 concluded that more studies are needed to compare the clinical performance of newly introduced materials with that of metal-ceramic FPDs. The purpose of this clinical study was to assess the incidence of failure and complications with toothsupported ceramic crowns and FPDs in function for at least 5 years. The included groups were pressed lithium disilicate crowns (CP), pressed lithium disilicate crowns with a veneer (CV), and CAD-CAM lithium disilicate crowns (CC). Veneered zirconia-based FPDs (FPDC) were compared with conventional metal-ceramic FPDs (FPDM). Outcomes were survival and failure, success and complications, periodontal conditions, and patient satisfaction assessed at 2 examinations, the first being the baseline 1 year after delivery and the follow-up examination 5 years of function. The null hypothesis was that ceramic crowns and FPDs would show similar THE JOURNAL OF PROSTHETIC DENTISTRY
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survival and complication rates to those of metal-ceramic FPDs. MATERIAL AND METHODS The participants included in this study were retrospectively recruited from a pool of patients in the former Division of Fixed Prosthodontics at the University of Bern, Switzerland. The study protocol was accepted by the Ethics Committee Bern (KEK-Nr. 020/13). Inclusion criteria were defined as insertion of at least 1 of the following: a lithium disilicate crown, a zirconiabased FPD, and/or a metal-ceramic FPD in the predoctoral clinic or the postgraduate program between January 2009 and November 2013. All patients received an initial dental prophylaxis treatment before the restorative phase. The abutment teeth were not prepared if the patients’ oral hygiene level indicated a complete-mouth plaque index,14 if a BOP of >20% was observed, or if probing pocket depths (PPDs) of 5 mm were found on abutment teeth. The restorations were cemented with a glass-ionomer (Ketac Cem; 3M ESPE AG) or composite resin (RelyX Unicem [3M ESPE AG], Variolink II [Ivoclar Vivadent AG], or Panavia 21 [Kuraray Dental GmbH]). The baseline clinical examination took place between June 2013 and May 2014, and the follow-up examinations were performed between September 2017 and May 2018. Data on the type of material; date of insertion; location; number of replaced teeth; number of abutment teeth, pontics, and cantilever; cement applied; vitality at the date of cementation; and provider were retrieved from the patients’ charts. According to a standardized procedure, one examiner scored the parameters for all patients. Four of the authors were involved in the examination and were responsible for the following steps: clinical examinations (F.A.F.), interviews (N.S.), photographs (S.P.H.), and radiographs (U.B.). During the appointments, the patients were interviewed and asked to mark their perceived degree of satisfaction with esthetics and comfort according to an 11-point numeric scale. Periodontal parameters were collected by using a periodontal probe (PP12; Deppeler SA) at 6 sites per abutment tooth: presence or absence of plaque (PI),14 presence or absence of bleeding on probing (BOP), location of the free gingival margin (FGM) in relation to the crown margin, and PPDs. The clinical attachment loss was calculated as PPD minus FGM. The endodontic evaluation included vitality testing (CO2 test) and presence or absence of fistulae. Abutment teeth and their corresponding crowns and FPDs were examined for the presence of secondary carious lesions, chipping, loss of retention, fracture of the framework material, and the quality of the marginal adaptation with the modified Forrer et al
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Table 1. Number of participants, restorations, and abutment teeth in 5 groups CP
CV
CC
All Crowns
FPDM
FPDC
All FPDs
Variable
B
F
B
F
B
F
B
F
B
F
B
F
B
No. of participants
5
5
7
6
11
8
21
17
27
24
39
32
67
F 56
No. of restorations
39
39
16
15
20
16
75
70
31
28
52
43
83
71
No. of abutment teeth
39
39
16
15
20
16
75
70
68
62
106
88
174
150
B, baseline; CC, e.max CAD; CP, e.max press; CV, veneered e.max press; F, follow-up; FPDC, zirconia-based; FPDM, metal-ceramic.
Table 2. Periodontal findings per abutment teeth/sites CP Variable N of sites (6 for each tooth) Mean sites with plaque
CV
CC
All Crowns
B (N=39)
F (N=38)
B (N=16)
F (N=15)
B (N=20)
F (N=15)
B (N=75)
234
228
96
90
120
90
450
F (N=68) 408
0.17 ±0.14
0.03 ±0.07
0.12 ±0.14
0.08 ±0.11
0.23 ±0.24
0.01 ±0.04
0.18 ±0.18
0.03 ±0.08
Mean sites with BOP
0.24 ±0.30
0.25 ±0.28
0.44 ±0.33
0.18 ±0.19
0.25 ±0.28
0.12 ±0.13
0.28 ±0.31
0.21 ±0.24
Mean PPD in mm
2.62 ±0.40
2.61 ±0.65
2.38 ±0.57
2.40 ±0.80
3.01 ±0.46
2.60 ±0.90
2.67 ±0.50
2.56 ±0.75
Mean CAL in mm
3.76 ±0.74
2.77 ±0.70
3.44 ±0.94
2.52 ±0.82
4.40 ±1.08*
3.19 ±1.10*
3.66 ±0.81
2.81 ±0.86
Mean recession in mm
0.09 ±0.14
0.16 ±0.27
0.06 ±0.08
0.12 ±0.13
0.36 ±0.36*
0.59 ±0.47*
0.16 ±0.24
0.25 ±0.35
B, baseline; CC, e.max CAD; CP, e.max press; CV, veneered e.max press; F, follow-up. *Statistically significant difference (P<.05) compared with other groups.
United States Public Health Service (USPHS) criteria.15 These criteria were met with an explorer (EXD3; HuFriedy Mfg Co, LLC) and defined as follows: Alfa (A) =no explorer catch; Bravo (B)=slight explorer catch, but no gap; Charlie (C)=gap with some dentin or cement exposure; Delta (D)=new restoration is needed. Radiographs were obtained with an individualized film holder by using acrylic resin (Pattern Resin; GC Germany GmbH) for future evaluations. In the periapical radiographs, the quality of existing endodontic treatment and the presence of periapical lesions, resorption, or caries were assessed. A failure of a crown or an FPD was defined as the loss of the restoration or a situation that resulted in the loss of the abutment teeth. Biological complications were related to the abutment teeth and defined as secondary caries, loss of vitality, periapical radiolucency, and/or presence of 1 or several PPDs 5 mm. Technical complications were related to the restorations and included chipping of veneered ceramic (adhesive, cohesive, or combined), fracture of the framework, loss of retention, or a marginal discrepancy with a value of Delta (D). Descriptive statistics were used for data presentation. Data were listed for crowns and FPDs. The Kruskal-Wallis tests were applied to perform comparisons among more than 2 groups. The Wilcoxon-Mann-Whitney tests and Wilcoxon signed-rank tests were used to compare median values between 2 groups for unpaired and paired data, respectively. No correction for multiple testing was done because of the explorative nature of this study (a=.05). RESULTS Of 136 patients identified, 17 could not be reached, and 25 were not interested in participating for various reasons. Therefore, 82 participants (52 women, 30 men),
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who received 158 crowns and FPDs, participated in the baseline clinical examination. At the follow-up, 70 participants were examined. Twelve participants could not be reexamined; one suffered from dementia, 7 could not be reached, and 4 were no longer interested in participating for various reasons. The number of evaluated participants, restorations, and abutment teeth in the different groups are presented in Table 1. At the baseline examination and at the follow-up examination, 91.5% (75/82) and 93% (66/71), respectively, of the patients were integrated into a regular maintenance system with at least 1 recall per year. Twenty-six (35%) crowns and 63 (76%) FPDs were placed in the predoctoral clinic. Postgraduate dentists placed 49 (65%) crowns and 20 (24%) FPDs. The periodontal parameters of the teeth with crowns at the baseline and the follow-up examinations are presented in Table 2. The clinical attachment level (CAL) was not statistically significantly different. The comparison among the crown groups at the follow-up examination showed significant differences in CAL (P=.004). Post hoc analyses revealed significant differences in CAL between CC and CV and between CV and CP (P=.002 and P=.008, respectively). In Table 3, the changes in the periodontal conditions are listed for those crowns that could be examined at the baseline and the follow-up examinations. The periodontal conditions (mean sites with plaque, mean sites with BOP) of all crowned teeth at the follow-up examination were statistically significantly improved compared with those at the first examination (mean sites with plaque P<.001, mean sites with BOP P=.017). Furthermore, a statistically significant reduction in PPD (P=.031) and an increase in the number of areas with recessions (P=.018) were observed in the CC group.
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Table 3. Changes over time of periodontal conditions Variable
CP (N=38)
CV (N=15)
CC (N=15)
All Crowns (N=68)
Mean change of mean sites with plaque
0.14 ±0.16*
0.06 ±0.15
0.23 ±0.19*
0.14 ±0.17*
Mean change of mean sites with BOP
0.00 ±0.24
0.28 ±0.38*
0.06 ±0.26
0.07 ±0.30*
Mean change of mean PPD 5mm
0.01 ±0.05
0.02 ±0.09
0.02 ±0.06
0.01 ±0.06
Mean change of PPD in mm
-0.01 ±0.49
0.00 ±0.59
-0.32 ±0.49*
-0.08 ±0.49
Mean change of CAL in mm
-0.05 ±0.56
-0.06 ±0.65
-0.13 ±0.55
-0.00 ±0.58
0.07 ±0.23
0.06 ±0.10
Mean change of recession in mm
0.19 ±0.25*
0.09 ±0.22*
CC, e.max CAD; CP, e.max press; CV, veneered e.max press. *Statistically significant difference (P<.05) comparing baseline with follow-up examination.
Table 4. Periodontal findings per abutment teeth/sites FPDM Variable
All FPDs
F (N=61)
B (N=106)
F (N=88)
B (N=174)
408
366
636
528
1044
894
0.20 ±0.23
0.06 ±0.10
0.13 ±0.14
0.05 ±0.08
0.15 ±0.18
0.05 ±0.09
No. of sites (6 for each tooth) Mean sites with plaque
FPDC
B (N=68)
F (N=149)
Mean sites with BOP
0.37 ±0.28
0.17 ±0.18
0.32 ±0.22
0.23 ±0.17
0.34 ±0.24
0.20 ±0.17
Mean PPD in mm
2.88 ±0.56
2.61 ±0.79
2.72 ±0.40
2.53 ±0.76
2.78 ±0.45
2.57 ±0.77
Mean clinical attachment loss in mm
4.36 ±1.23
3.19 ±1.00
3.94 ±0.91*
2.93 ±0.91*
4.10 ±1.07
3.03 ±0.96
Mean recession in mm
0.45 ±0.51
0.54 ±0.48
0.22 ±0.28
0.40 ±0.45
0.31 ±0.39
0.45 ±0.46
B, baseline; F, follow-up; FPDC, zirconia-based; FPDM, metal-ceramic. *Statistically significant difference (P<.05) compared with other groups.
Table 5. Changes over time of periodontal conditions Variable Mean change of mean sites with plaque
FPDM (N=61)
FPDC (N=88)
Table 6. Number of loss of abutment teeth and survival rate All FPDs (N=149)
0.09 ±0.15* 0.08 ±0.13*
0.09 ±0.14*
Mean change of mean sites with BOP 0.15 ±0.21* 0.09 ±0.18*
0.12 ±0.20*
Mean change of mean PPD 5 mm
0.01 ±0.08
0.02 ±0.06
0.01 ±0.07*
Mean change of PPD in mm
-0.19 ±0.46* -0.15 ±0.36* -0.12 ±0.47*
Mean change of clinical attachment loss in mm
-0.06 ±0.50 -0.01 ±0.38
Mean change of recession in mm
0.12 ±0.18* 0.12 ±0.20*
-0.02 ±0.43
CP
CV
CC
No. of restorations
39
15
16
70
28
43
71
No. of abutment teeth
39
15
16
70
62
88
150
1
0
1
1
0
Failures Survival rate
97.4% 100% 93.8%
All Crowns FPDM FPDC All FPDs
2 97.1%
96.4% 100%
1 98.6%
CC, e.max CAD; CP, e.max press; CV, veneered e.max press; FPDC, zirconia-based; FPDM, metal-ceramic.
0.15 ±0.19*
FPDC, zirconia-based; FPDM, metal-ceramic. *Statistically significant difference (P<.05) comparing baseline with follow-up examination.
The periodontal parameters of the abutment teeth of the FPDs at the baseline and the follow-up examinations are presented in Table 4. In Table 5, the changes in the periodontal conditions are listed for those FPDs that could be examined at the baseline and the follow-up examinations. Between the baseline and follow-up examinations, the mean clinical attachment loss showed no significant difference (P=.903). Significant values for clinical attachment loss were found at the abutment teeth of FPDC (baseline examination P=.037; follow-up examination P=.015). With respect to all FPD abutments, periodontal conditions at the follow-up examination improved significantly compared with the baseline examination (P<.001). A statistically significant reduction in PPD was noted for FPDC (P=.012), and an increase in recession (FPDM P=.002; FPDC P<.001) was noted in both FPD groups. The numbers for loss of abutment teeth and survival rate are presented in Table 6. Both teeth lost with crowns required endodontic treatment, and a post and core was THE JOURNAL OF PROSTHETIC DENTISTRY
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placed. The reason for these 2 failures was a crown fracture at the gingival level. The 3 abutment teeth of an FPDM had a periodontal abscess and required extraction. Therefore, the failures had no prosthetic cause. A total of 19 abutment teeth (8.8%) were affected by biological complications after 6.44 ±1.14 years (Tables 7 and 8). The most prevalent complication at the first examination was a PPD 5 mm at 1 or more abutment tooth (40 sites). Twenty-two restorations had an isolated PPD 5 mm at 1 abutment tooth, 1 FPDM had an increased PPD on both abutment teeth, and 3 FPDM restorations had other complications at the same restoration. At the follow-up, only 6 sites had a PPD 5 mm. Twelve of 139 (8.6%) crowns and FPDs showed technical complications after a mean observation time of 6.44 ±1.14 years (Tables 9 and 10). One FPDC chipped twice. All cohesive chips were located on the cusp tips. Both mixed chips were found on the buccal surface with extension toward the proximal area. Two metal-ceramic FPDs lost retention at approximately 7 and 11 months after cementation. Both FPDs were cemented in the predoctoral clinic. One of the FPDs was cemented with a glass-ionomer cement (Ketac Forrer et al
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Table 7. Number and percentage of biological complications CP Variable
CV
CC
All Crowns
B (N=39)
O (N=38)
B (N=16)
O (N=15)
B (N=20)
O (N=15)
B (N=75)
No. of vital abutment teeth
36
34
13
12
12
9
61
O (N=68) 55
No. of sites (6 for each tooth)
234
228
96
90
120
90
450
408
Caries
0
0
0
0
0
0
0
0
Loss of vitality *
0
1 (2.9%)
0
0
1 (8.3%)
1 (11.1%)
1 (1.6%)
2 (3.6%) 1 (1.5%)
Periapical lesion
0
0
0
0
1 (5.0%)
1 (6.7%)
1 (1.3%)
PPD 5 mm
1 (2.6%)
0
2 (12.5%)
0
1 (5.0%)
0
4 (5.3%)
0
PPD 6 mm
1 (2.6%)
0
0
0
5 (25.0%)
1 (6.7%)
6 (8%)
1 (1.5%)
PPD 7 mm
0
0
0
0
0
0
0
0
Total complications
2
1
2
0
8
3
12
4
5.1%
2.6%
12.5%
0%
40.0%
20.0%
16.0%
5.8%
Complication rate
B, baseline; CC, e.max CAD; CP, e.max press; CV, veneered e.max press; O, overall. *Loss of vitality (%) of abutment tooth.
Table 8. Number and percentage of biological complications FPDM Variable
FPDC
All FPDs
B (N=68)
O (N=61)
B (N=106)
O (N=88)
B (N=174)
No. of vital abutment teeth
48
44
84
72
132
116
No. of sites (6 for each tooth)
408
366
636
528
1044
894
Caries
1 (1.5%)
1 (1.6%)
0
0
1 (0.6%)
1 (0.7%)
Loss of vitality *
1 (2.1%)
1 (2.3%)
3 (3.6%)
3 (4.2%)
4 (3.0%)
4 (3.4%)
Periapical lesion
1 (1.5%)
1 (1.6%)
4 (3.8%)
4 (4.5%)
5 (2.9%)
5 (3.4%)
PPD 5 mm
9 (13.2%)
2 (3.3%)
8 (7.5%)
0
17 (9.8%)
2 (1.3%)
PPD 6 mm
5 (7.4%)
1 (1.6%)
4 (3.8%)
2 (2.3%)
9 (5.2%)
3 (2.0%)
PPD 7 mm
2 (2.9%)
0
2 (1.9%)
0
4 (2.3%)
0
19
6
21
9
40
15
28.0%
9.8%
19.8%
10.3%
23.0%
10.1%
Total complications Complication rate
O (N=149)
B, baseline; FPDC, zirconia-based; FPDM, metal-ceramic; O, overall. *Loss of vitality (%) of vital abutment tooth.
Table 9. Number and percentage of technical complications CP Variable
CV
CC
All Crowns
B (N=39)
O (N=38)
B (N=16)
O (N=15)
B (N=20)
O (N=15)
B (N=75)
O (N=68)
Chipping cohesive
0
0
0
0
1 (5.0%)
1 (6.6%)
1 (1.3%)
1 (1.5%)
Chipping adhesive
0
0
0
0
0
0
0
0
Chipping combined
0
0
0
0
0
0
0
0
Framework fracture
0
0
0
0
0
0
0
0
Loss of retention
0
0
0
0
0
0
0
0
Total complications Complication rate
0
0
0
0
1
1
1
1
0%
0%
0%
0%
5%
6.6%
1.3%
1.5%
B, baseline; CC, e.max CAD; CP, e.max press; CV, veneered e.max press; O, overall.
Cem); however, no information about the cement used for the other FPD was found in the patient file (missing data). Both FPDs were then recemented. At the baseline examination, 5 crowns (7%) and 11 FPDs (6%) had a marginal discrepancy of Charlie (C). One 3-unit FPDM had a marginal discrepancy on both teeth, and the remaining 10 FPDs, only on 1 of the abutment teeth. USPHS scores of Delta (D) were not found. None of the marginal discrepancies of Charlie had worsened between the baseline examination and follow-up. The interview with patients revealed a high level of satisfaction with the esthetics and function of the crowns Forrer et al
and FPDs. The mean and standard deviation of patient satisfaction and change in patient satisfaction are listed in Tables 11 and 12. The patient-reported outcome measures (PROMs) at the follow-up examination showed statistically significant improvements in esthetics (P=.014) and function (P.001) compared with the PROM of the baseline examination. DISCUSSION The null hypothesis that ceramic crowns and FPDs would have similar survival rates and number of complications THE JOURNAL OF PROSTHETIC DENTISTRY
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Table 10. Number and percentage of technical complications FPDM
FPDC
All FPDs
Variable
B (N=31)
O (N=28)
B (N=52)
O (N=43)
B (N=83)
Chipping cohesive
2 (6.5%)
4 (14.3%)
2 (3.8%)
2 (4.7%)
4 (4.8%)
6 (8.5%)
Chipping adhesive
0
0
0
1 (2.3%)
0
1 (1.4%)
Chipping combined
1 (3.2%)
1 (3.6%)
1 (1.9%)
1 (2.3%)
2 (2.4%)
2 (2.8%)
Framework fracture
0
0
0
0
0
0
2 (6.5%)
2 (7.1%)
0
0
2 (2.4%)
2 (2.8%)
Loss of retention Total complications Complication rate in %
O (N=71)
5
7
3
4
8
11
16.1%
25%
5.8%
9.3%
9.6%
15.5%
B, baseline; FPDC, zirconia-based; FPDM, metal-ceramic; O, overall.
Table 11. Mean and standard deviation of patient satisfaction and change of patient satisfaction (mean ±SD) CP
CV
CC
All Crowns
Variable
B (N=39)
F (N=39)
C (N=39)
B (N=16)
F (N=15)
C (N=15)
B (N=20)
F (N=16)
C (N=16)
B (N=75)
F (N=70)
C (N=70)
Esthetic
8.9 ±0.5
9.8 ±0.4
0.1 ±0.6
9.7 ±0.6
9.7 ±0.5
0.0 ±0.9
9.4 ±1.2
9.1 ±0.7
-0.2 ±1.1
9.2 ±0.8
9.7 ±0.6
0.5 ±0.9
Function
9.7 ±0.5
9.8 ±0.4
0.2 ±0.6
9.0 ±0.9
9.1 ±1.0
0.1 ±1.1
9.1 ±1.2
9.6 ±0.8
0.7 ±1.1
9.4 ±0.9
9.6 ±0.7
0.3 ±0.8
B, baseline; C, change of patient satisfaction; CC, e.max CAD; CP, e.max press; CV, veneered e.max press; F, follow-up.
Table 12. Mean and standard deviation of patient satisfaction and change of patient satisfaction (mean ±SD) FPDM
FPDC
All FPDs
Variable
B (N=31)
F (N=28)
C (N=28)
B (N=52)
F (N=43)
C (N=43)
B (N=83)
F (N=71)
C (N=71)
Esthetic
9.3 ±1.3
8.9 ±2.0
-0.3 ±2.3
9.4 ±0.8
9.5 ±0.9
0.0 ±0.9
9.3 ±1.0
9.2 ±1.5
-0.1 ±1.6
Function
9.3 ±1.8
9.1 ±2.0
-0.0 ±2.1
8.8 ±1.3
9.5 ±0.9
0.7 ±1.4
8.9 ±1.5
9.4 ±1.4
0.4 ±1.7
B, baseline; C, change of patient satisfaction; F, follow-up; FPDC, zirconia-based; FPDM, metal-ceramic.
as those of metal-ceramic FPDs was accepted. The periodontal condition observed at the baseline examination around the abutment teeth was unexpectedly poor. As far as BOP is concerned, a complete-mouth percentage below 20% would have been desirable to reduce the risk of future attachment loss.16 Even more concerning were the sites with PPDs 5 mm, which, in combination with BOP, put the dentition, and specifically the abutment teeth, at a higher risk for additional attachment loss or, in the long-run, even tooth loss.17 A few months after the delivery of crowns and FPDs, some patients relapsed in their efforts at optimal plaque control,18 resulting in a deterioration of the periodontal parameters obtained at the end of the active periodontal and restorative treatment.19 Similarly, at the baseline examination of the present study, a PPD 5 mm was observed on 13.3% of crowns and 17.2% of the FPD abutment teeth. In a recent report on 104 pressed lithium disilicate (IPS e.max) crowns, none of the abutment teeth showed PPD 4 mm after up to 9 years.7 At the follow-up examination, periodontal parameters had improved considerably. Participating in the study seemed to improve these parameters. The patients were informed about their conditions and motivated to improve their oral hygiene and adhere to a strict recall interval. At 6 years of function, 2 of 70 lithium disilicate crowns failed (97.1% survival). One technical (1.5%) and 4 THE JOURNAL OF PROSTHETIC DENTISTRY
biological (5.8%) complications were detected. In a prospective split-mouth study, a 7-year survival rate of 100% for pressed lithium disilicate (IPS e.max press) and 97% for ProCAD (Ivoclar Vivadent AG) partial crowns was reported. No secondary caries, no endodontic complications, and no postoperative complaints were reported. Small cohesive ceramic fractures were noted in 5 patients.20 In a systematic review6 with short- (1 to 5 years) and medium-term (5 to 10 years) survival rates of 849 different lithium disilicate crowns (Empress II, IPS e.max press, IPS e.max CAD, and 2 studies with unspecified lithium disilicate crowns), the most common technical complication reported was fracture of the core framework, followed by chipping of the veneering ceramic and debonding of the restoration. The most commonly reported biological complications included the need for endodontic treatment and the presence of secondary caries. Favorable short-term survival rates were reported, but the estimated promising cumulative survival rate at 5 years was based on limited data.6 The results of the present report are similar to those of these clinical studies, where varying restoration designs and materials were involved. In the present study, complete-coverage crowns out of 1 material (e.max lithium disilicate) were examined. The sample sizes in the 3 subgroups were low, unevenly distributed, and not randomly assigned. Forrer et al
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At 6 years, the survival rate for all FPDs was 98.6% (1/ 71 failure). According to a systematic review,10 less favorable clinical outcomes for ceramic FPDs can be expected compared with metal-ceramics. The estimated survival rates after 5 years for ceramic FPDs were lower than those of metal-ceramic FPDs (summary estimate of 89.1% for reinforced glass-ceramic, 86.2% for glass infiltrated alumina, 90.4% for zirconia, and 94.4% for metal-ceramic).10 The number of chippings was found to be similar In FPDM (5/28) and FPDC (4/43). This contradicts the findings of a systematic review,21 in which the frequency of veneer chipping was significantly higher in zirconia FPDs than in the metal-ceramic FPDs (54% versus 34%). The positive trend to obtaining a more stable veneer ceramic on zirconia frameworks can be explained with improvements in the characteristics of materials and fabrication.22-24 Loss of retention occurred in 2 FPDMs after less than a year, whereas, based on analyses of data from a systematic review, the incidences of loss of retention were significantly higher for zirconia FPDs than those for metal-ceramic FPDs.10 However, no statistical differences were found with respect to technical and biological problems according to 2 recent RCTs.11,12 The PROMs related to esthetic and functional satisfaction identified on an 11-point numeric scale reached high scores with all 5 groups of crowns and FPDs. This was consistent with a recent study that assessed functional and esthetic satisfaction and evaluated changes in oral health-related quality of life (OHRQoL) after insertion of a metal-ceramic or a ceramic veneered zirconia posterior 3-unit FPD. Patients experienced improved OHRQoL and increased satisfaction with function and esthetics. No essential differences were observed between metal-ceramic and ceramic FPDs when evaluated by the patient or the clinicians.25 Limitations of the present study included that it was a retrospective clinical study without randomization. Many students/dentists and dental technicians were involved in the treatment and production of the crowns and FPDs. These unregulated parts of the study should be controlled in future studies to minimize variables to observe the materials’ performance. In addition, randomization can be used to minimize bias. The observation time was of medium term, and the sample size for patients and restorations was small. Future studies with a higher number of participants and restorations should be carried out to investigate the long-term outcomes. The present data, nevertheless, indicate that lithium disilicate is a suitable material for restoring teeth with crowns and that veneered zirconia FPDs serve as an alternative to metal-ceramic FPDs for the assessment time used in this study.
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CONCLUSIONS Based on the findings of this clinical study, the following conclusions were drawn: 1. Survival rate for ceramic crowns and FPDs was 97.9% after a mean observation time of 6.44 ±1.14 years. 2. Biological complications were more common than technical complications, and complications were more frequent in FPDs than in crowns. 3. The level of oral hygiene deteriorated after the active treatment phase but had improved for some patients after entering the study. 4. The complications were comparable for zirconia FPDs and metal-ceramic FPDs. 5. Participants indicated a high degree of satisfaction with function and esthetics. 6. In the medium term, ceramic restorations made of the tested materials and with the tested processing steps are promising alternatives to MCCs and metal-ceramic FPDs. REFERENCES 1. McLaren EA. All-ceramic alternatives to conventional metal-ceramic restorations. Compend Contin Educ Dent 1998;19:307-8. 10, 12 passim; quiz 26. 2. Touati B. Innovative dental ceramics: expanding the material alternatives. Pract Proced Aesthet Dent 2005;17:357-8. 3. Christensen GJ. The all-ceramic restoration dilemma: where are we? J Am Dent Assoc 2011;142:668-71. 4. Chu SJ. Current clinical strategies with lithium-disilicate restorations. Compend Contin Educ Dent 2012;33. 64, 6-7. 5. Gehrt M, Wolfart S, Rafai N, Reich S, Edelhoff D. Clinical results of lithiumdisilicate crowns after up to 9 years of service. Clin Oral Investig 2013;17: 275-84. 6. Pieger S, Salman A, Bidra AS. Clinical outcomes of lithium disilicate single crowns and partial fixed dental prostheses: a systematic review. J Prosthet Dent 2014;112:22-30. 7. Afrashtehfar KI, Brägger U, Treviño-Santos A, Freitas de Souza R. Letters to the editor. Evid Based Dent 2017;18:2. 8. Sax C, Hammerle CH, Sailer I. 10-year clinical outcomes of fixed dental prostheses with zirconia frameworks. Int J Comput Dent 2011;14:183-202. 9. Sailer I, Feher A, Filser F, Luthy H, Gauckler LJ, Scharer P, et al. Prospective clinical study of zirconia posterior fixed partial dentures: 3-year follow-up. Quintessence Int 2006;37:685-93. 10. Pjetursson BE, Sailer I, Makarov NA, Zwahlen M, Thoma DS. All-ceramic or metal-ceramic tooth-supported fixed dental prostheses (FDPs)? A systematic review of the survival and complication rates. Part II: Multiple-unit FDPs. Dent Mater 2015;31:624-39. 11. Sailer I, Gottnerb J, Kanelb S, Hammerle CH. Randomized controlled clinical trial of zirconia-ceramic and metal-ceramic posterior fixed dental prostheses: a 3-year follow-up. Int J Prosthodont 2009;22:553-60. 12. Sailer I, Strasding M, Valente NA, Zwahlen M, Liu S, Pjetursson BE. A systematic review of the survival and complication rates of zirconia-ceramic and metal-ceramic multiple-unit fixed dental prostheses. Clin Oral Implants Res 2018;29 Suppl 16:184-98. 13. Poggio CE, Ercoli C, Rispoli L, Maiorana C, Esposito M. Metal-free materials for fixed prosthodontic restorations. Cochrane Database Syst Rev 2017;12: CD009606. 14. O’Leary TJ, Drake RB, Naylor JE. The plaque control record. J Periodontol 1972;43:38. 15. Ryge G, Snyder M. Evaluating the clinical quality of restorations. J Am Dent Assoc 1973;87:369-77. 16. Joss A, Adler R, Lang NP. Bleeding on probing. A parameter for monitoring periodontal conditions in clinical practice. J Clin Periodontol 1994;21:402-8. 17. Matuliene G, Pjetursson BE, Salvi GE, Schmidlin K, Bragger U, Zwahlen M, et al. Influence of residual pockets on progression of periodontitis and tooth loss: results after 11 years of maintenance. J Clin Periodontol 2008;35:685-95.
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18. Heschl A, Haas M, Haas J, Payer M, Wegscheider W, Polansky R. Maxillary rehabilitation of periodontally compromised patients with extensive onepiece fixed prostheses supported by natural teeth: a retrospective longitudinal study. Clin Oral Investig 2013;17:45-53. 19. Bragger U, Hakanson D, Lang NP. Progression of periodontal disease in patients with mild to moderate adult periodontitis. J Clin Periodontol 1992;19:659-66. 20. Guess PC, Selz CF, Steinhart YN, Stampf S, Strub JR. Prospective clinical split-mouth study of pressed and CAD/CAM all-ceramic partial-coverage restorations: 7-year results. Int J Prosthodont 2013;26:21-5. 21. Heintze SD, Rousson V. Survival of zirconia- and metal-supported fixed dental prostheses: a systematic review. Int J Prosthodont 2010;23:493-502. 22. Yamamoto LT, Rodrigues VA, Dornelles LS, Bottino MA, Valandro LF, Melo RM. Low-fusing porcelain glaze application on 3Y-TZP surfaces can enhance zirconia-porcelain adhesion. Braz Dent J 2016;27:543-7. 23. Madani A, Nakhaei M, Karami P, Rajabzadeh G, Salehi S, Bagheri H. Sol-gel dip coating of yttria-stabilized tetragonal zirconia dental ceramic by aluminosilicate nanocomposite as a novel technique to improve the bonding of veneering porcelain. Int J Nanomedicine 2016;11:3215-23. 24. Passos SP, Linke B, Major PW, Nychka JA. Improving the compatibility of a Y-TZP/porcelain system using a new composite interlayer composition. J Mech Behav Biomed Mater 2017;65:11-9.
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25. Nicolaisen MH, Bahrami G, Schropp L, Isidor F. Functional and esthetic comparison of metal-ceramic and all-ceramic posterior three-unit fixed dental prostheses. Int J Prosthodont 2016;29:473-81. Corresponding author: Dr Fiona Alena Forrer Department of Reconstructive Dentistry and Gerodontology School of Dental Medicine University of Bern Freiburgstrasse 7, 3010 Bern SWITZERLAND Email: fi[email protected] Acknowledgments The authors express their gratitude to the biomedical engineer Walter B. Buergin for his support in statistical questions and to the statisticians Anja Mühlemann, Gabriel Fischer, and Lukas Martig for performing the statistical analysis. Copyright © 2019 by the Editorial Council for The Journal of Prosthetic Dentistry. https://doi.org/10.1016/j.prosdent.2019.08.012
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