Quantitative discoloration assessment of peri-implant soft tissue around zirconia and other abutments with different colours: A systematic review and meta-analysis

Abstract

Objectives

The implant abutments, which had their own colour, might cause the discoloration of peri-implant mucosa. We aimed to appraise trails comparing the discoloration of peri-implant soft tissue around zirconia and titanium or golden abutments, the tints of which were vastly different.

Data

We included randomized controlled trials (RCTs), controlled clinical trials (CCTs), cohort studies with patients rehabilitated with zirconia, titanium or golden implant abutments, quantitatively comparing the discoloration of peri-implant soft tissue according to CIE-Lab colour scale.

Sources

A systematic search was conducted in PubMed, EMBASE, CDSR, and CENTRAL databases without any restriction on September 23, 2017. “Grey” literatures were also searched. A manual search was carried out as well.

Study selection

Of 584 articles initially retrieved, eight were eligible for inclusion. After data extraction, meta-analyses with mean differences (MDs) and their 95% confidence intervals (CIs) were employed. Moreover, the risk of bias within or across studies was assessed by Cochrane Collaboration’s tool for assessing risk, the Newcastle-Ottawa scale, funnel plots, or Egger’s test.

Results

Four RCTs and four cohort studies were included. Soft-tissue discoloration around zirconia abutments was significantly less likely compared to that around titanium abutments (MD = −1.84; 95% CI = −3.62 to −0.07; P = 0.04 < 0.05) or golden abutments (MD = −0.90; 95% CI = −1.60 to −0.20; P = 0.01 < 0.05).

Conclusions

Zirconia abutments with white tint compared to grey titanium or golden abutments seem to restore a more appropriate colour match between peri-implant mucosa and natural teeth.

Clinical significance

Based on the present evidence, the “nature-like” zirconia abutments should be applied more often in the clinic.

PROSPERO registration number

CRD42017075930.

Introduction

It has been consistently reported that implant therapy has high survival rates and thus is widely used in tooth replacement treatment [ ]. However, the criteria of successful implant therapy have broadened beyond functional parameters, such as bone integration, survival, and complications [ ], to include the aesthetic attributes of coronal restorations and especially the peri-implant soft tissue [ ]. In 1999, Moon et al. proved that the morphogenesis of supporting structures results in a longer “biologic width” around the artificial implant compared to a natural tooth [ ], which implies that maybe only the soft tissue covers the underling abutment. Moreover, the peri-implant soft tissue has been reported to be particularly more translucent than other gingival tissues due to its reduced vascularization [ ]. The colour of the underlying abutments may shine through the translucent mucosa, impairing the optical aesthetic outcome [ ]. Thus, the colour of abutments may cause discoloration of the peri-implant soft tissue, which may satisfy or dissatisfy the patients as well as the clinicians [ ].

Titanium abutments are consistently considered the “gold-standard” for implant-borne reconstructions [ ]. However, the titanium abutments can lead to a dull greyish discoloration of the peri-implant soft tissue due to its grey colour [ ]. There are several other available metal materials, such as titanium nitride, gold, gold-hued titanium, pink-hued titanium, and so on, most of which provide a “golden” appearance for the abutment to differ from the grey tint of titanium so as to mitigate the “greying effect” [ ].

To seek a tooth-coloured abutment, all-ceramic abutments made of zirconia as well as alumina have been introduced to fabricate the implant abutment due to their semi-translucency [ ], which provide a significant aesthetic improvement [ ]. Moreover, both the flexural strength and the fracture toughness of zirconia have been reported to be almost twice as high as those of alumina [ ]. Thus, zirconia is commonly used for implant abutments, especially in aesthetically demanding regions.

Several objective spectrophotometric analyses for the colour of the peri-implant soft tissue around abutments with different tints (zirconia, titanium, gold, and so on) have been completed [ ]. Quantitative evaluation of discoloration was facilitated by the Commission Internationale de l’Eclairage L*, a*, and b* (CIE-Lab) colour scale system, and the ΔE represented the value of discoloration of peri-implant soft tissue [ ]. However, the results were conflicting. Sailer et al. [ ], as well as Zembic et al. [ ] found that the amount of soft tissue discoloration, interestingly, had no significant difference between zirconia and titanium abutments. Contrarily, Bressan et al. [ ] found titanium abutments indicated significantly greater discoloration compared to zirconia or gold abutments.

To further validate the soft tissue colour change around zirconia and other abutments with different tints, a systematic review and meta-analysis are needed. Hence, the purpose of this paper is to quantitatively investigate the difference between “tooth-like” zirconia abutments and “greyish” titanium abutments or abutments with “golden appearance” (gold, gold-hued titanium, or titanium nitride) on peri-implant soft tissue discoloration.

Materials and methods

The present meta-analysis was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [ ]. The protocol for this meta-analysis was registered in the International Prospective Register of Systematic Reviews (PROSPERO) ( www.crd.york.ac.uk/PROSPERO/ ) (registration number: CRD42017075930).

PICOS question

As recommended by the Centre for Evidence-Based Medicine (University of Oxford, Oxford, UK), the focused participants, interventions, comparisons, and outcomes (PICO) question was as follows: How do zirconia and other abutments with different tints affect the colour of peri-implant soft tissue?

Participants: edentulous patients restored with implant abutments

Interventions: insertion of zirconia abutments, which connected the implants and the upper crowns and were surrounded by the peri-implant soft tissue

Comparisons: titanium abutments and golden (containing gold, gold-hued titanium, and titanium nitride) abutments, which connected the implants and the upper crowns and were surrounded by the peri-implant soft tissue

Outcomes: quantitative discoloration assessment of peri-implant soft tissue around the abutments using the CIE Lab colour space coordinates, in which the ΔE is the most important parameter for evaluating the discoloration [ ]

Study design: randomized-controlled clinical trials (RCTs), controlled clinical trials (CCTs), and prospective or retrospective cohort studies

Inclusion criteria

The following inclusion criteria were employed:

Clinical studies based on human subjects only

Studies that included patients rehabilitated with zirconia, titanium or golden implant abutments

RCTs, CCTs, prospective, or retrospective cohort studies

The discoloration of peri-implant soft tissue had to be quantitatively assessed according to CIE-Lab colour scale

Studies that compared zirconia implant abutments with titanium abutments or golden abutments

Studies with details of the measuring techniques

Exclusion criteria

Furthermore, the following exclusion criteria were determined:

In vitro or animal studies and case studies

Studies based only on subjective measurements, questionnaires, or interviews

Multiple studies on the same patient cohorts

Information sources and literature search

The literature search was conducted in duplicate by two independently working reviewers (H.C. and J.C.). Any disagreement was resolved by consensus between the two authors. An electronic systematic search of four databases, including PubMed, EMBASE, Cochrane Database of Systematic Reviews (CDSR), and Cochrane Central Register of Controlled Trials (CENTRAL) database was performed for relevant articles in the English language on September 23, 2017. No time filter was used. The search consisted of the terms (‘color’ OR ‘colors’ OR ‘colour’ OR ‘colours’ OR ‘esthetic’ OR ‘esthetics’ OR ‘aesthetic’ OR ‘aesthetics’) AND (‘implant’ OR ‘abutment’ OR ‘abutments’) AND ‘zirconia’. For the “grey” literatures (such as ongoing clinical studies or registries), ClinicalTrials.gov and the International Clinical Trials Registry Platform (ICTRP, WHO) were searched; the ProQuest Dissertation Abstracts and Thesis database were also searched for related dissertations and Conference Proceedings. Citation Index-Science (CPCI-S) was searched for conference proceedings; additionally, some other online resources such as the System for Information on Gray Literature in Europe database (SIGLE), National Technical Information Service (NTIS), and science.gov were also searched. Subsequently, as a complement to the electronic search, a manual search was carried out on the bibliographies from selected full-text articles and related reviews.

Study selection

Study selection was performed by one reviewer (H.C.) and was subsequently carried out by a second one (J.C.). After the initial scanning of the titles and abstracts, studies were selected if they fulfilled the inclusion criteria. Then, the reviewers independently judged the full-text articles. The eligibility of potential articles for this meta-analysis was confirmed through discussion or by a third reviewer (X.L.). The agreement between the reviewers in study inclusions was assessed by the kappa statistic.

Data collection and data items

The data were extracted on standardized piloted forms by the same two independent reviewers (H.C. and J.C.) according to the purpose of the present systematic review and meta-analysis. If any disagreement was found, a third reviewer was consulted (X.L.). Of the included studies, basic information was extracted onto a purpose-designed data collection form and included the following parameters: author, year, study design, comparison of implant abutments, total number of patients, sample size of abutments, age range, test site, drop out, and value of the discoloration of peri-implant soft tissue (δE).

Risk of bias in individual trials

The bias of the included RCTs was evaluated by Cochrane Collaboration’s tool for assessing risk [ ] with the software RevMan version 5.3 (The Cochrane Collaboration, Copenhagen, Denmark). The bias and quality of the selected non-randomized studies were assessed using the Newcastle-Ottawa scale, including three different parts of selection, comparability, and outcome. The bias in the studies was assessed with a star scoring scale, where higher scores meant higher quality studies [ ]. The same two reviewers (H.C. and J.C.) assessed all the selected articles independently.

Summary measures and synthesis of results

Extracted data were analysed using the software RevMan version 5.3 (The Cochrane Collaboration, Copenhagen, Denmark) and Stata MP version 14 (StataCorp LP, College Station, TX). Data from all eligible studies were dichotomous. To compare the difference between the discoloration of peri-implant soft tissue around zirconia and those around other abutments with different colours for each study, the mean difference (MD) with a 95% confidence interval (CI) was calculated. As heterogeneity was observed using the Cochran Q test and I 2 statistics, either a random-effects model or a fixed-effects model was employed.

Risk of bias across studies

The publication bias across studies was assessed by drawing funnel plots and employing Egger’s test in the meta-analysis [ ].

Additional analyses

Whenever heterogeneity was observed, sensitivity analyses were conducted to identify whether any of the included studies should be excluded to reduce the heterogeneity. No subgroup analysis was performed.

Materials and methods

The present meta-analysis was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [ ]. The protocol for this meta-analysis was registered in the International Prospective Register of Systematic Reviews (PROSPERO) ( www.crd.york.ac.uk/PROSPERO/ ) (registration number: CRD42017075930).

PICOS question

As recommended by the Centre for Evidence-Based Medicine (University of Oxford, Oxford, UK), the focused participants, interventions, comparisons, and outcomes (PICO) question was as follows: How do zirconia and other abutments with different tints affect the colour of peri-implant soft tissue?

Participants: edentulous patients restored with implant abutments

Interventions: insertion of zirconia abutments, which connected the implants and the upper crowns and were surrounded by the peri-implant soft tissue

Comparisons: titanium abutments and golden (containing gold, gold-hued titanium, and titanium nitride) abutments, which connected the implants and the upper crowns and were surrounded by the peri-implant soft tissue

Outcomes: quantitative discoloration assessment of peri-implant soft tissue around the abutments using the CIE Lab colour space coordinates, in which the ΔE is the most important parameter for evaluating the discoloration [ ]

Study design: randomized-controlled clinical trials (RCTs), controlled clinical trials (CCTs), and prospective or retrospective cohort studies

Inclusion criteria

The following inclusion criteria were employed:

Clinical studies based on human subjects only

Studies that included patients rehabilitated with zirconia, titanium or golden implant abutments

RCTs, CCTs, prospective, or retrospective cohort studies

The discoloration of peri-implant soft tissue had to be quantitatively assessed according to CIE-Lab colour scale

Studies that compared zirconia implant abutments with titanium abutments or golden abutments

Studies with details of the measuring techniques

Exclusion criteria

Furthermore, the following exclusion criteria were determined:

In vitro or animal studies and case studies

Studies based only on subjective measurements, questionnaires, or interviews

Multiple studies on the same patient cohorts

Information sources and literature search

The literature search was conducted in duplicate by two independently working reviewers (H.C. and J.C.). Any disagreement was resolved by consensus between the two authors. An electronic systematic search of four databases, including PubMed, EMBASE, Cochrane Database of Systematic Reviews (CDSR), and Cochrane Central Register of Controlled Trials (CENTRAL) database was performed for relevant articles in the English language on September 23, 2017. No time filter was used. The search consisted of the terms (‘color’ OR ‘colors’ OR ‘colour’ OR ‘colours’ OR ‘esthetic’ OR ‘esthetics’ OR ‘aesthetic’ OR ‘aesthetics’) AND (‘implant’ OR ‘abutment’ OR ‘abutments’) AND ‘zirconia’. For the “grey” literatures (such as ongoing clinical studies or registries), ClinicalTrials.gov and the International Clinical Trials Registry Platform (ICTRP, WHO) were searched; the ProQuest Dissertation Abstracts and Thesis database were also searched for related dissertations and Conference Proceedings. Citation Index-Science (CPCI-S) was searched for conference proceedings; additionally, some other online resources such as the System for Information on Gray Literature in Europe database (SIGLE), National Technical Information Service (NTIS), and science.gov were also searched. Subsequently, as a complement to the electronic search, a manual search was carried out on the bibliographies from selected full-text articles and related reviews.

Study selection

Study selection was performed by one reviewer (H.C.) and was subsequently carried out by a second one (J.C.). After the initial scanning of the titles and abstracts, studies were selected if they fulfilled the inclusion criteria. Then, the reviewers independently judged the full-text articles. The eligibility of potential articles for this meta-analysis was confirmed through discussion or by a third reviewer (X.L.). The agreement between the reviewers in study inclusions was assessed by the kappa statistic.

Data collection and data items

The data were extracted on standardized piloted forms by the same two independent reviewers (H.C. and J.C.) according to the purpose of the present systematic review and meta-analysis. If any disagreement was found, a third reviewer was consulted (X.L.). Of the included studies, basic information was extracted onto a purpose-designed data collection form and included the following parameters: author, year, study design, comparison of implant abutments, total number of patients, sample size of abutments, age range, test site, drop out, and value of the discoloration of peri-implant soft tissue (δE).

Risk of bias in individual trials

The bias of the included RCTs was evaluated by Cochrane Collaboration’s tool for assessing risk [ ] with the software RevMan version 5.3 (The Cochrane Collaboration, Copenhagen, Denmark). The bias and quality of the selected non-randomized studies were assessed using the Newcastle-Ottawa scale, including three different parts of selection, comparability, and outcome. The bias in the studies was assessed with a star scoring scale, where higher scores meant higher quality studies [ ]. The same two reviewers (H.C. and J.C.) assessed all the selected articles independently.

Summary measures and synthesis of results

Extracted data were analysed using the software RevMan version 5.3 (The Cochrane Collaboration, Copenhagen, Denmark) and Stata MP version 14 (StataCorp LP, College Station, TX). Data from all eligible studies were dichotomous. To compare the difference between the discoloration of peri-implant soft tissue around zirconia and those around other abutments with different colours for each study, the mean difference (MD) with a 95% confidence interval (CI) was calculated. As heterogeneity was observed using the Cochran Q test and I 2 statistics, either a random-effects model or a fixed-effects model was employed.

Risk of bias across studies

The publication bias across studies was assessed by drawing funnel plots and employing Egger’s test in the meta-analysis [ ].

Additional analyses

Whenever heterogeneity was observed, sensitivity analyses were conducted to identify whether any of the included studies should be excluded to reduce the heterogeneity. No subgroup analysis was performed.

Results

Study selection

570 and 14 records were respectively identified through electronic and manual searches ( Fig. 1 ). After removal of duplicates and initial screening by titles and abstracts, 50 records remained. After careful full-text assessment, a total of eight articles, all pertaining to unique trials, were left as eligible studies for this systematic review and meta-analysis.

Fig. 1
PRISMA flow program for study selection for this systematic review and meta-analysis.

The kappa values for the agreement between the reviewers in study inclusions were 0.94 (initial screening by titles and abstracts) and 0.97 (full-text assessment), denoting an “almost perfect” inter-agreement [ ].

Study characteristics

The characteristics of the included studies are shown in Table 1 . Among these, four (50.0%) were randomized controlled trials and four (50.0%) were prospective cohort studies, including 365 abutments of zirconia and titanium or golden materials. Among these eight studies, five investigated the differences among zirconia, titanium and golden abutments, while three observed the comparison between zirconia and titanium abutments only.

Table 1
Characteristics of the included studies.
Nr Study (Year of publication) Study design Comparison Total number of patients Sample size of ZrO 2 abutments Sample size of Ti abutments Sample size of golden abutments Age range Test site Drop out
1 Martínez-Rus F, et al 2017 Prospective ZrO 2 /Ti/golden abutments 20 20 20 20 24-69 1 mm apical to the free gingival margin 0
2 Ferrari M, et al 2017 RCT ZrO 2 /Ti/golden abutments NA 28 30 31 ≥18 1 mm apical to the free gingival margin 0
3 Kim A, et al 2016 Retrospective ZrO 2 /Ti/golden abutments 30 10 10 10 ≥18 Between 1 and 4 mm apical to the free gingival margin 0
4 Lops D, et al 2016 Prospective ZrO 2 /Ti/golden abutments 15 15 15 15 NA Within 4 mm apical to the free gingival margin 0
5 Cosgarea R, et al 2015 RCT ZrO 2 /Ti abutments 11 11 11 NR NA 1 mm apical to the free gingival margin 0
6 Bressan E, et al 2011 Prospective ZrO 2 /Ti/golden abutments 20 20 20 20 NR Within 4 mm apical to the free gingival margin 0
7 Zembic A, et al 2009 RCT ZrO 2 /Ti abutments 22 18 10 NR NA 1 mm apical to the free gingival margin 4
8 Sailer I, et al 2009 RCT ZrO 2 /Ti abutments 22 19 12 NR NA 1 mm apical to the free gingival margin 0
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Jun 17, 2018 | Posted by in General Dentistry | Comments Off on Quantitative discoloration assessment of peri-implant soft tissue around zirconia and other abutments with different colours: A systematic review and meta-analysis
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