Table 5 Summary of international studies with evidence level 2

Medeiros et al. [17]

16

1. The zirconium abutments showed excellent soft-tissue reactions (3 studies).

2. The gingival recession increased in the zirconium abutments (1 study).

3. No biological difference was observed between the titanium and zirconium abutments (9 studies).

4. The zirconium abutments provided the gingival contour and anatomical shape of the natural teeth as well as have excellent esthetic features (3 studies).

1. Zirconium abutments are recommended for the anterior teeth.

2. Long-term studies are required to evaluate biological reactions.

Guess et al. [18]

18 (4)

The survival rate of the zirconium abutments was 100% (F/U period: 6 months-4 years).

As there are limited clinical data on zirconium abutments, their routine use in dental clinics is not recommended.

Gomes et al. [19]

20 (5)

1. The survival rate of the zirconium abutments was good.

2. The titanium abutments had more bone resorption than the zirconium abutments.

3. The zirconium abutments were esthetically and functionally stable.

4. No zirconium abutment fracture was observed for four years.

5. The zirconium abutments had less bacteria accumulation than the titanium abutments.

More studies on the long-term clinical success of zirconium abutments are required.

Nakamura et al. [20]

25 (8)

1. The zirconium abutments were acceptable for anterior teeth in the biological and mechanical aspects.

2. Zirconium had less early plaque accumulation than titanium.

The zirconium abutment has the potential to be used as a dental implant abutment material.

Linkevicius et al. [21]

9 (1)

Titanium abutments do not maintain a higher bone level than gold, aluminum oxide, and zirconium abutments.

Due to the lack of clinical studies, the stability of zirconium abutments cannot be determined.