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

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.