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Preprint 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 2 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. 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