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The Esthetic Effect of Veneered Zirconia Abutments for Single-Tooth
Implant Reconstructions: A Randomized Controlled Clinical Trial
THOMA, Daniel S, et al.
Abstract
The purposes of this study were to test whether or not veneering of the submucosal part of
zirconia abutments can positively influence the esthetic outcome compared with nonveneered
zirconia abutments; to evaluate the influence of the mucosal thickness on the esthetic
outcomes of the veneered and nonveneered abutments; and to evaluate the thickness of the
peri-implant mucosa compared with the thickness of the gingiva of contralateral tooth sites
Reference
THOMA, Daniel S, et al. The Esthetic Effect of Veneered Zirconia Abutments for Single-Tooth
Implant Reconstructions: A Randomized Controlled Clinical Trial. [Submitted to:] Clinical
Implant Dentistry and Related Research2016, 8
DOI : 10.1111/cid.12388
PMID : 26676273
Available at:
http://archive-ouverte.unige.ch/unige:89032
Disclaimer: layout of this document may differ from the published version.
The Esthetic Effect of Veneered Zirconia Abutments
for Single-Tooth Implant Reconstructions:
A Randomized Controlled Clinical Trial
Daniel S Thoma, PD Dr. med. dent.;* Francine Brandenberg, Dr. med. dent.;† Vincent Fehmer;‡
Nathalie Knechtle;§ Christoph HF Hämmerle, Prof. Dr. med. dent.;¶ Irena Sailer, Prof. Dr. med. dent.**
ABSTRACT
Purpose: The purposes of this study were to test whether or not veneering of the submucosal part of zirconia abutments can
positively influence the esthetic outcome compared with nonveneered zirconia abutments; to evaluate the influence of the
mucosal thickness on the esthetic outcomes of the veneered and nonveneered abutments; and to evaluate the thickness of
the peri-implant mucosa compared with the thickness of the gingiva of contralateral tooth sites.
Materials and Methods: Forty-four single-tooth implants in 44 patients were randomly restored with either cemented (CR)
or screw-retained (SR) reconstructions based on white zirconia abutments (CR-W, SR-W) or pink-veneered zirconia
abutments (CR-P, SR-P). Esthetic outcome measurements were performed based on a spectrophotometric evaluation of
the peri-implant mucosal color. In addition, the thickness of the mucosa was measured. A two-way analysis of variance was
conducted to test the effect of veneering (pink vs white) and mucosa thickness (<2 mm vs 32 mm) on the calculated color
difference ΔE for pooled data of CR and SR reconstructions (p < .05).
Results: Analyses grouping the sites according to veneering of the abutments and mucosal thickness demonstrated less
discoloration for sites with a veneered abutment irrespective of the mucosal thickness: ΔE 4.50 1 1.93 (<2 mm) and ΔE
6.88 1 2.45 (32 mm); CR-P, SR-P) compared with sites without veneering ΔE 9.72 1 3.82 (<2 mm; CR-W, SR-W) and ΔE
8.31 1 2.98 (32 mm). The differences between veneered and nonveneered abutments were significant (p = .032).
Conclusions: Veneering of zirconia abutments with pink veneering ceramic positively influenced the peri-implant mucosal
color.
KEY WORDS: ceramic abutments, crowns, dental abutments, dental implants, zirconia
INTRODUCTION
*Head of academic unit, Clinic of Fixed and Removable Prosthodontics and Dental Material Science, Center of Dental Medicine, University of Zürich, Zürich, Switzerland; †senior teaching and research
assistant, Clinic of Fixed and Removable Prosthodontics and Dental
Material Science, Center of Dental Medicine, University of Zürich,
Zürich, Switzerland; ‡master dental technician, Division of Fixed
Prosthodontics and Biomaterials, Clinic of Dental Medicine, University of Geneva, Zürich, Switzerland; §pre-doc student, Center for
Dental Medicine, University of Zürich, Zürich, Switzerland; ¶professor and head, Clinic of Fixed and Removable Prosthodontics and
Dental Material Science, Center of Dental Medicine, University of
Zürich, Zürich, Switzerland; **professor and head, Division of Fixed
Prosthodontics and Biomaterials, Clinic of Dental Medicine, University of Geneva, Zürich, Switzerland
Dental implants are well established for a variety of indications to support fixed and removable prostheses.
Metal abutments combined with cemented porcelain
fused-to-metal crowns are considered to be the gold
standard for fixed reconstructions.1–3, rendering high
survival rates even long term.4,5 Even though outstanding functional and mechanical properties have been
Sources of funding
This study was supported and funded by the Clinic of Fixed and
Removable Prosthodontics and Dental Material Science, Center of
Dental Medicine, University of Zurich, Switzerland and the Swiss
Society of Reconstructive Dentistry (SSRD). The implant abutments
were kindly provided by the manufacturer, DENTSPLY Implants,
Mölndal, Sweden.
Corresponding Author: PD Dr. Daniel S. Thoma, Clinic of Fixed and
Removable Prosthodontics and Dental Material Science, Center of
Dental Medicine, Plattenstrasse 11, 8032 Zürich, Switzerland; e-mail:
[email protected]
© 2015 Wiley Periodicals, Inc.
Conflict of interest
The authors declare no conflict of interest.
DOI 10.1111/cid.12388
1
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Clinical Implant Dentistry and Related Research, Volume *, Number *, 2015
reported, the use of metal abutments may be associated with esthetic disadvantages, mainly because of
gray-bluish shimmering through thin peri-implant
mucosa.6–8 This clinically visible discoloration of the
peri-implant tissue may hamper the esthetic appearance
and diminish patient satisfaction.9,10
In order to overcome issues with metal abutments
and based on the desire to improve the esthetic outcome
of implants in anterior jaw regions, zirconia was introduced as abutment material.11 Comparative clinical
studies demonstrated that this material could be successfully used with similar clinical outcomes as metal
abutments.8 In addition, because of its white color, zirconia modifies the appearance of the peri-implant
mucosa positively compared with metal abutments7,12,13
However, the degree of discoloration of the peri-implant
mucosa was still above the desired level of a ΔE = 3.1.14
The main reason for this phenomenon was that zirconia
induced a change in lightness of the peri-implant
mucosa. Interestingly, zirconia abutments led to an
overly pale appearance of the soft tissues while metal
abutments led to darkening.15,16 In addition, it is known
that the esthetic appearance of implant-borne reconstructions depends on the mucosal thickness with a
reported threshold value being 2 mm.6,7 In order to
further optimize the optical outcome especially in cases
with a thin peri-implant mucosa modifications of zirconia abutments were evaluated.17,18 Previous reports have
shown a positive effect on the soft tissue color by pink or
light orange color modifications of the abutments.19
Other studies investigated fluorescence as influencing
factor with inconclusive results.20
The results from the studies mentioned earlier were
inconclusive, and beneficial esthetic outcomes were only
reported for a relatively small number of patients. One
study tested the influence of zirconia abutments modified with a translucent pink veneering ceramic on the
color of the peri-implant mucosa.18 The authors
reported that this modification even led to more discoloration than the nonveneered white zirconia abutments
had caused. A detailed analysis of the results, however,
revealed that this specific pink-veneering ceramic exhibited too high translucency leading to a darkening of the
soft tissues. It was concluded that the lightness of the
pink veneering ceramic was a crucial factor for optimizing the esthetic appearance.18
Hence, changing the pink veneering ceramic to a
less translucent one might offer further esthetic benefits
and should be tested in a larger scale randomized controlled clinical trial.
The aim of the present study was, therefore, to 1)
test whether or not veneering of the submucosal part
of zirconia abutments can positively influence the
esthetic outcome compared with nonveneered zirconia
abutments; 2) to evaluate the influence of the mucosal
thickness on the esthetic outcomes of the veneered
and nonveneered abutments; and 3) to evaluate the
thickness of the peri-implant mucosa compared with
the thickness of the gingiva of contralateral tooth
sites.
The hypotheses of the present study were that 1)
veneering of the submucosal part of zironica abutments
reduces the discoloration of the peri-implant mucosa
compared with nonveneered abutments; 2) the thickness of the mucosa influences the discoloration of the
mucosa with a thin mucosa resulting in a greater discoloration; and 3) the thickness of the peri-implant mucosa
differs from the thickness of the gingiva of the contralateral tooth site.
MATERIALS AND METHODS
Study Design and Subjects
This study was designed as a randomized controlled
clinical trial. Upon approval by the local ethics committee (KEK-ZH-Nr.2010-0041), 44 patients were consecutively recruited at the Clinic of Fixed and Removable
Prosthodontics and Dental Material Science, University
of Zurich, Switzerland. A sample size calculation was
performed based on a previously published study.18
The recruited patients received 44 dental implants
(OsseoSpeed, DENTSPLY Implants, Mölndal, Sweden)
in the maxilla or mandible replacing incisors, canines, or
premolars (Table 1). The following inclusion criteria
were applied: successfully osseointegrated implants,
good oral hygiene, no signs of bruxism, no systemic
disease, smokers, and nonsmokers. All implants were
planned to be restored with implant-borne single-tooth
reconstructions using customized zirconia abutments
(Atlantis shade 00, DENTSPLY Implants, Mölndal,
Sweden) and all-ceramic crowns. Prior to taking the
final impressions, the patients were randomly (using a
sealed envelope) allocated to receive one of the four
treatment modalities:
1) screw-retained reconstruction (zirconia abutment,
directly veneered) (SR-W);
Esthetics of Veneered Zirconia Abutments
TABLE 1 Implant Distribution with Implant
Location, Length, and Diameter, Treatment Groups
in All 44 Patients
Subject
Number Group
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
43
44
CR-P
CR-W
SR-W
SR-W
SR-W
CR-P
SR-P
SR-W
SR-P
CR-P
SR-W
SR-P
CR-W
CR-P
SR-P
SR-W
CR-P
CR-W
SR-W
CR-W
SR-P
SR-W
CR-P
CR-W
SR-W
CR-W
SR-P
CR-P
SR-W
SR-P
CR-W
CR-P
SR-P
CR-W
SR-W
CR-P
CR-P
CR-W
SR-P
CR-W
SR-W
SR-W
SR-W
Implant Implant
Length Diameter
[mm]
[mm]
11
11
9
11
6
11
11
11
6
15
13
6
13
15
9
9
9
8
8
8
9
11
9
8
13
11
13
11
9
8
8
13
8
9
9
13
8
6
9
8
13
11
8
4
4,5
3,5
3,5
4
4
4
3,5
4
4
3,5
4
4
4
4
4
3,5
4
4
3,5
4
4
4
4
3,5
4
3,5
3,5
3,5
4
4
4
3,5
4
4
4,5
4
4
4
4
4
4
3,5
Jaw
Location
Maxilla
Maxilla
Mandible
Maxilla
Maxilla
Maxilla
Maxilla
Maxilla
Mandible
Maxilla
Maxilla
Mandible
Maxilla
Maxilla
Maxilla
Maxilla
Maxilla
Mandible
Maxilla
Maxilla
Mandible
Maxilla
Mandible
Maxilla
Maxilla
Maxilla
Maxilla
Maxilla
Mandible
Maxilla
Maxilla
Maxilla
Maxilla
Mandible
Maxilla
Maxilla
Maxilla
Maxilla
Maxilla
Mandible
Maxilla
Maxilla
Mandible
25
25
44
12
15
24
24
22
35
21
12
35
14
14
15
14
15
35
15
24
45
14
45
15
22
24
14
22
33
14
24
21
25
35
15
11
25
24
24
45
11
21
45
CR-P = cemented pink; CR-W = cemented white; SR-P = screw-retained
pink; SR-W = screw-retained white.
3
2) screw-retained reconstruction (zirconia abutment,
submucosal part veneered with pink ceramic;
directly veneered) (SR-P) (Figure 1, A–C);
3) cemented reconstruction (zirconia abutment; allceramic crown) (CR-W) (Figure 2, A–C); and
4) cemented reconstruction (zirconia abutment, submucosal part veneered with pink ceramic; allceramic crown) (CR-P)
Prosthetic Protocol and Treatment Modalities. A
computer-assisted design/computer-assisted manufacturing (CAD/CAM) (Atlantis, DENTSPLY Implants)
was used in the fabrication process of all zirconia abutments. In groups SR-P and CR-P, a pink-shaded glass
ceramic was used to veneer the submucosal part of the
abutments (Creation ZI-F, Creation Willi Geller International GmbH; Meiningen, Austria). The thickness of
the ceramic layer was standardized to 0.5 mm at the level
of the abutment/crown junction and decreased continuously toward the implant shoulder. The zirconia abutments were not undergoing any modifications in groups
SR-W and CR-W. In a preliminary clinical try-in session,
the dimension and position of the abutment shoulder
was checked. If necessary, the abutment shoulder height
was modified to position it circumferentially 1 mm
below the mucosal margin. Subsequently, all-ceramic
crowns (emax, Ivoclar Vivadent, Schaan, Liechtenstein)
were manufactured for groups CR-W and CR-P. In
groups SR-W, SR-P the abutments were directly covered
with veneering ceramics (Creation ZI-F, Creation Willi
Geller International GmbH) to fabricate one-piece
single-crown reconstructions. In groups SR-W and
SR-P, the crowns were fixed with a torque of 20 Ncm
onto the implants; the screw access hole was then closed
using a composite material. In groups CR-W and CR-P,
the abutments were screwed with a torque of 20 Ncm.
Subsequently, a retraction cord (Ultrapak, Ultradent
Products GmbH Am Westhover Berg 30 51149 Köln)
was placed around the abutments and all-ceramic
crowns were cemented using a resin cement (Panavia 21,
Kuraray Medical, Kuraray Europe GmbH BU Medical
Products Philipp-Reis-Str. 4 65795 Hattersheim am
Main Deutschland).
Esthetic Assessment
In order to evaluate the influence of the different types
of abutments on the color of the peri-implant tissues a
spectrophotometer (Spectroshade, MHT, MHT Optic
4
Clinical Implant Dentistry and Related Research, Volume *, Number *, 2015
A
B
C
Figure 1 A, Try-in of zirconia abutment (SR-P group). B, Pink-veneered abutment (SR-P group). C, Final all-ceramic screw-retained
reconstruction in situ (SR-P group).
Research AG Mandachstrasse 50 CH-8155 Niederhasli
Switzerland) was used. A detailed description on these
procedures can be found in an earlier publication.18 In
brief, the spectrophotometric measurements were conducted 1 mm below the gingival/mucosal margin at the
implant and the contralateral natural tooth sites. The
implant site was evaluated at three consecutive time
points: preceding the insertion of the abutment, 5–10
minutes after placing the abutment – as soon as the
blanching of the soft tissue disappeared – and 7–10 days
after the crown was placed. The abutment try-in was
performed prior to the veneering stage for SR reconstructions (Figure 1, A) and prior to the fabrication of
the crown for CR reconstructions (Figure 2, A). The data
of each color measurement was expressed using the
CIE-LAB parameters (Commission Internationale de
l’Eclaire; L = lightness, a = chroma along red-green axis,
b = chroma along yellow-blue axis). All measurements
were repeated three times and the mean values thereof
were calculated. The differences (ΔL, Δa, Δb) were converted into the overall color difference ΔE using the
following equation:
ΔE =
(ΔL
2
+ Δa + Δb ).
2
2
The color differences (ΔE) were calculated by comparing the values of the implant site without abutment
versus the contralateral natural tooth, the implant site
with abutment versus the contralateral tooth and the
implant site with CR/SR crown versus the contralateral
tooth.
A
B
In addition, the thickness of the mucosa at the
implant site and the control site (contra-lateral tooth)
was assessed to the nearest 0.5 mm. For that purpose, an
endodontic file was used at a level 1 mm below the
gingival/mucosal margin on the buccal side.7,16,18
Statistical Analysis
The data were analyzed descriptively calculating mean
values and standard deviations. CR and SR modalities
were pooled. The thickness of the peri-implant mucosa
was compared between implant and control tooth using
the paired t-test and the McNemar test. A two-way
analysis of variance (anova) was conducted to test the
effect of the additional veneering and the mucosal thickness (<2 mm vs 3 2 mm) on the calculated color difference ΔE. All statistical tests were performed using the
Statistical Package for the Social Sciences (spss; IBM
SPSS Statistics 22.0 [IBM Schweiz Vulkanstrasse 106
Postfach 8010 Zürich] and a p value <0.05 was considered significant).
RESULTS
All 44 included patients were treated according to the
randomized treatment protocol and finished the study.
Neither biological nor technical complications occurred
during the present study period.
The thickness of the peri-implant mucosa in the
four treatment groups amounted to 1.9 mm 1 1.1 mm
(CR-W), 2.0 mm 1 0.4 mm (SR-W), 2.4 1 0.5 mm
(CR-P) and to 1.2 mm 1 0.6 mm (SR-P). The respective
gingival thickness at the contralateral tooth sites was
C
Figure 2 A, Try-in of zirconia abutment (CR-W group). B, Final abutment and final all-ceramic crown (CR-W group); extra-oral
view. C, Final all-ceramic cemented reconstruction in situ (CR-W group); intraoral view.
Esthetics of Veneered Zirconia Abutments
1.0 mm 1 0.4 mm (CR-W), 1.2 mm 1 0.4 mm (SR-W),
1.5 mm 1 0.3 mm (CR-P) and 0.7 mm 1 0.3 mm (SRP). In general (pooled for all groups and implant sites),
the mucosa thickness for the implant site
(1.9 1 0.7 mm) was significantly higher than for the
control tooth (1.1 1 0.4 mm; paired t-test, p < .001).
This was further reflected in a higher number of implant
sites exhibiting a peri-implant mucosal thickness
of 3 2 mm (61%) as compared with contralateral tooth
sites with a gingival thickness 3 2 mm (9%; McNemar
test p < .001).
The detailed spectrophotometric data are presented
in Tables 2–4. Implant sites without abutments induced
a visible discoloration of the peri-implant mucosa in all
groups, independent of the mucosal thickness compared
with contralateral tooth sites and independent of the
group ranging between a ΔE of 11.29 and a ΔE of 13.04
(Tables 2–4). With every subsequent step, that is insertion of an abutment and insertion of the final reconstruction, ΔE values (difference between the implant site
and the control tooth) decreased. The insertion of an
abutment revealed a ΔE of 7.55 1 3.02 (groups SR-P/
CR-P) and of ΔE 7.52 1 2.29 (groups SR-W/CR-W)
(Table 2). Measurements taken after the insertion of the
final reconstructions demonstrated a mean discoloration of ΔE 6.16 1 2.48 for groups SR-P/CR-P and of ΔE
8.31 1 3.33 for groups SR-W/ CR-W. When sites were
analyzed depending on the mucosal thickness (<2 mm
vs 32 mm), mean ΔE values were similar, but revealed a
large standard deviation resulting in a ΔE of 7.11 1 3.94
(thickness of <2 mm) and of 7.47 1 2.65 (32 mm)
(Table 3). Analyses grouping the sites according to
veneering of the abutments and mucosal thickness demonstrated less discoloration for sites with a veneered
abutment irrespective of the mucosal thickness: ΔE
4.50 1 1.93 (<2 mm) and ΔE 6.88 1 2.45 (32 mm)
(CR-P, SR-P) compared with sites without veneering ΔE
9.72 1 3.82 (<2 mm) and ΔE 8.31 1 2.98 (32 mm)
(CR-W, SR-W) (Table 4). The differences between
veneered and nonveneered abutments were significantly
different (two-way anova, F1,14 = 5.7, p = .032,
eta2 = 0.29). None of the other comparisons were statistically significant (p > .1).
DISCUSSION
The results of the present study demonstrated that
veneering of the submucosal part of zirconia abutments
with pink veneering ceramic led to esthetic benefits. This
5
TABLE 2 Color Assessment: Differences between
Pink (CR-P/SR-P) and White Abutments
(CR-W/SR-W)
Group
ΔE no abutment versus abutment
Mean
Standard deviation
Median
Percentile 25
Percentile 75
ΔE no abutment versus crown
Mean
Standard deviation
Median
Percentile 25
Percentile 75
ΔE crown versus control tooth
Mean
Standard deviation
Median
Percentile 25
Percentile 75
ΔE crown versus abutment
Mean
Standard deviation
Median
Percentile 25
Percentile 75
ΔE no abutment versus control tooth
Mean
Standard deviation
Median
Percentile 25
Percentile 75
ΔE abutment versus control tooth
Mean
Standard deviation
Median
Percentile 25
Percentile 75
Pink
White
9.51
3.92
9.37
6.12
11.61
7.50
2.24
7.12
6.28
8.15
9.73
5.04
8.97
5.58
13.01
9.16
4.30
12.04
5.40
12.43
6.16
2.48
6.22
5.07
8.24
8.31
3.33
6.97
6.29
10.52
5.52
2.62
5.38
3.38
6.22
5.11
1.72
5.97
3.73
6.01
12.54
5.17
9.72
8.56
16.77
11.30
2.56
10.91
9.48
12.36
7.55
3.02
7.81
5.44
9.94
7.52
2.29
8.32
4.96
8.63
ΔE = color difference.
finding was independent of the mucosal thickness. Furthermore, this modification was effective at SR and CR
implant-borne reconstructions.
In order to achieve an optimal esthetic outcome, the
choice of the reconstructive material for implant-borne
restorations is considered a critical element.21 This is
6
Clinical Implant Dentistry and Related Research, Volume *, Number *, 2015
TABLE 3 Color Assessment: Differences between
Different Mucosal Thicknesses (<2 mm vs 32 mm)
Mucosa Thickness
<2 mm
ΔE no abutment versus abutment
Mean
Standard deviation
Median
Percentile 25
Percentile 75
ΔE no abutment versus crown
Mean
Standard deviation
Median
Percentile 25
Percentile 75
ΔE crown versus control tooth
Mean
Standard deviation
Median
Percentile 25
Percentile 75
ΔE crown versus abutment
Mean
Standard deviation
Median
Percentile 25
Percentile 75
ΔE no abutment versus control tooth
Mean
Standard deviation
Median
Percentile 25
Percentile 75
ΔE abutment versus control tooth
Mean
Standard deviation
Median
Percentile 25
Percentile 75
TABLE 4 Color Assessment: Differences between
Pink (CR-P/SR-P) and White (CR-W/SR-W)
Abutments Grouped for Mucosa Thickness
Pink
32 mm
White
Mucosa Thickness Mucosa Thickness
8.50
2.40
8.89
6.12
10.55
8.59
3.85
6.77
6.15
10.91
8.89
4.26
8.97
5.40
12.74
9.76
4.90
12.04
5.58
13.01
7.11
3.94
6.23
5.26
8.67
7.47
2.65
6.89
5.85
9.37
6.29
2.35
6.01
5.38
6.22
4.91
2.11
4.10
3.18
6.01
11.62
2.92
11.41
9.27
13.97
12.23
4.81
10.59
9.47
16.23
9.45
2.61
9.94
8.63
10.96
6.75
2.35
7.21
4.66
8.36
ΔE = color difference.
based on the fact that the gingiva/mucosa is more
susceptible to discoloration observed by the human eye
than the tooth itself with reported threshold values of
ΔE 3.1 (gingiva14) and of ΔE 3.7 (tooth22). Various materials were evaluated in the past to optimize the appearance of the color of the peri-implant mucosa with
implant-borne reconstructions. These encompassed
ΔE no abutment
versus abutment
Mean
Standard deviation
Median
Percentile 25
Percentile 75
ΔE no abutment
versus crown
Mean
Standard deviation
Median
Percentile 25
Percentile 75
ΔE crown versus
control tooth
Mean
Standard deviation
Median
Percentile 25
Percentile 75
ΔE crown versus
abutment
Mean
Standard deviation
Median
Percentile 25
Percentile 75
ΔE no abutment
versus control
tooth
Mean
Standard deviation
Median
Percentile 25
Percentile 75
ΔE abutment versus
control tooth
Mean
Standard deviation
Median
Percentile 25
Percentile 75
ΔE = color difference.
<2 mm
32 mm
<2 mm
32 mm
9.29
2.39
9.72
7.51
11.08
9.65
4.92
8.11
6.02
15.06
7.45
2.42
7.12
5.21
10.01
7.53
2.38
6.77
6.28
8.15
8.53
4.44
8.97
3.89
12.74
10.33
5.61
9.44
5.58
15.66
9.42
5.68
9.42
5.40
13.44
9.06
4.43
12.04
5.91
12.11
4.50
1.93
5.26
2.30
5.93
6.88
2.45
6.80
5.07
8.45
9.72
3.82
8.67
6.54
13.96
8.31
2.98
6.97
6.29
10.52
7.24
2.53
6.22
5.38
10.13
4.66
2.40
3.49
3.18
5.59
4.87
1.61
4.87
3.73
6.01
5.20
1.94
5.97
4.10
6.01
11.67
3.37
11.62
8.80
14.55
13.04
6.18
9.72
8.56
17.24
11.41
.
11.41
11.41
11.41
11.29
2.81
10.75
9.48
12.36
9.65
2.96
10.45
7.69
11.61
6.15
2.30
6.66
4.15
8.17
8.63
–
8.63
8.63
8.63
7.34
2.46
7.64
4.96
8.40
Esthetics of Veneered Zirconia Abutments
titanium, glass-reinforced alumina, zirconia and anodized titanium.8,15,19,20,23,24 The data of most of these
studies were inconclusive, but suggested that neither
metals nor zirconia materials was an optimal choice as
both reconstructive materials led to discoloration of the
peri-implant mucosa.6–8,17 More recently, zirconia abutments were veneered with pink ceramics in order to
reduce discoloration of the covering mucosa.18 The outcomes of that clinical pilot study indicated that the
chosen pink veneering ceramic was not beneficial compared with native zirconia mainly due to the high translucency, which led to a decrease in brightness and
eventually to a grayish discoloration of the mucosa.
Therefore, in the present study, the previously used pink
veneering ceramic was modified adding more opacity
(G – 6 dark pink opaque) (Creation ZI-F, Creation Willi
Geller International GmbH). The results indicated that
this modification of the pink veneering ceramic was
more favorable than the one in the previous clinical
study. This observation corroborates previous clinical
data on the optic effect of fluorescent abutments demonstrating a beneficial effect on the appearance of the
mucosal color.17
It has previously been reported that the mucosal
thickness has a significant influence on the esthetic
outcome of implant-supported reconstructions.7 It was
observed that the threshold value of the mucosal thickness to mask color differences by the human eye was
2 mm.12 This is underlined by the findings of the present
study that indicated lower ΔE values for sites with a
mucosal thickness of 32 mm compared with sites
with a thickness of <2 mm for nonveneered zirconia
abutments.
Sites with a pink veneered abutment and a thin
mucosa resulted in the most favorable esthetic outcomes. For thick soft tissues ΔE values were still lower
for pink veneered abutment compared with original
white zirconia abutments, but slightly higher compared
with sites with a thickness of less than 2 mm. This observation supports the clinical findings that at sites with a
thick mucosa, the abutment color does not play a crucial
role, whereas with a thin mucosa it does. The pink
veneering tested in the present study appears a clinically
suitable method for minimizing discoloration at both
SR and CR reconstructions. Nevertheless, none of the
materials and modifications led to discoloration of the
mucosa that was below the clinically visible threshold
value of ΔE 3.1. Further in vitro studies and subsequent
7
clinical studies are needed to elucidate the benefits and
limitations of zirconia abutment modifications.
CONCLUSIONS
Veneering of zirconia abutments with pink veneering
ceramic positively influenced the peri-implant mucosal
color and led to a more favorable esthetic outcome compared with reconstructions with nonveneered zirconia
abutments. Yet, the placement of zirconia abutments
and all-ceramic reconstructions generally led to a visible
discoloration (ΔE > 3.1) of the peri-implant mucosal
color compared with contralateral tooth sites irrespective of the treatment modality. This discoloration was
more pronounced in sites with a thin (<2 mm) mucosa
with nonveneered abutments, whereas veneering
reduced the discoloration with <2 mm mucosa thickness compared with sites with >2 mm mucosa thickness.
Moreover, the majority of implant sites had a periimplant mucosal thickness of 32 mm.
ACKNOWLEDGEMENTS
The authors thank Dr. Caroline Lustenberger, Clinic of
Fixed and Removable Prosthodontics and Dental Material Science, University of Zurich, for performing the
statistical analysis. The support of Gisela Müller, study
monitor at the Clinic of Fixed and Removable Prosthodontics and Dental Material Science, Center for Dental
Medicine, University of Zurich, is highly acknowledged.
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