The goal of this clinical trail is to evaluate the clinical, radiological and immunological outcomes of the one-piece zirconia abutments (OPZAs) and two-piece zirconia abutments (TPZAs) with friction-fitted titanium bases in single implant crowns in aesthetic region. The main question it aims to answer is:

whether the mechanical properties of one-piece zirconia abutments are the same as those of two-piece zirconia abutments.

Participants who have two missing teeth in aesthetic region will receive the OPZAs for one restoration and the TPZAs for the other.

Researchers will compare OPZAs group (OG) and TPZAs group (TG) to see the clinical, radiological and immunological outcomes of the two.

Objective: To evaluate the clinical, radiological and immunological outcomes of the one-piece zirconia abutments (OPZAs) and two-piece zirconia abutments (TPZAs) with friction-fitted titanium bases in single implant crowns in aesthetic region.

Materials and methods: The study is a single center, split-mouth and randomized controlled clinical trial. Eligible sites of patients will be randomly assigned into two groups: OPZAs group (OG) and TPZAs group (TG). Survival rates, mechanical complication rates, bleeding on probing (BOP%), probing depth (PD), modified plaque index (mPI), marginal bone loss (MBL), concentrations of pro-inflammatory cytokines (TNF-α, IL-6) in peri-implant crevicular fluid (PICF), and pink esthetics score/white esthetics score (PES/ WES) will be evaluated.

Discussion: Results of the present study will help to evaluate the clinical, radiological and immunological outcomes of OPZAs and TPZAs with friction-fitted titanium bases in single implant crowns in aesthetic region and provide evidence for the effects of two types abutments on the health of peri-implant soft and hard tissue.

Inclusion Criteria:

1. age≥18;
2. patients with two missing teeth in esthetic region and plan to be restored with two single implant crowns;
3. adjacent to natural teeth;
4. absence of oral mucosal disease and oral infection;
5. implants with conical connection (Nobel Active, Nobel Biocare® or NobelReplace Conical Connection, Nobel Biocare®);
6. patients with the willingness to participate in the present study.

Exclusion Criteria:

1. heavy smokers (>10 cigarettes/day);
2. uncontrolled periodontitis (Full mouth plaque score>20%, full mouth bleeding score>25%, residual pocket depth>5mm);
3. with systematic diseases that may affect implant therapy, such as uncontrolled diabetes mellitus (Fasting blood-glucose>7.2mmol/L, Glycosylated hemoglobin >7%), current intake of bisphosphonates (treatment for malignancy), pregnant(or plan to get pregnant), with history of radiation therapy in head and neck region.