Background The success rate of implant-supported prostheses for edentulous patients is relatively high. However, the incidence of biological complications, especially peri-implant mucositis and peri-implantitis, increases yearly after the placement of prostheses. The accumulation of pathogenic bacteria adjacent to a prosthesis is the main cause of biological complications. Titanium, one of the classical materials for implant-supported prostheses, performs well in terms of biocompatibility and ease of maintenance, but is still susceptible to biofilm formation. Zirconia, which has emerged as an appealing substitute, not only has comparable properties, but presents different surface properties that influence the adherence of oral bacteria. However, evidence of a direct effect on oral flora is limited. Therefore, the aim of the present study was to assess the effects of material properties on biofilm formation and composition. Methods The proposed study is designed as a 5-year randomized controlled trial. We plan to enroll 44 edentulous (mandible) patients seeking full-arch, fixed, implant-supported prostheses. The participants will be randomly allocated to one of two groups: group 1, in which the participants will receive zirconia frameworks with ceramic veneering, or group 2, in which the participants will receive titanium frameworks with acrylic resin veneering. Ten follow-up examinations will be completed by the end of this 5-year trial. Mucosal conditions around the implants will be recorded every 6 months after restoration. Peri-implant submucosal plaque will be collected at each reexamination, and bacteria flora analysis will be performed with 16S rRNA gene sequencing technology in order to compare differences in microbial diversity between groups. One week before each visit, periodontal maintenance will be arranged. Each participant will receive an X-ray examination every 12 months as a key index to evaluate the marginal bone level around the implants. Discussion The current study aims to explore the oral microbiology of patients following dental restoration with zirconia ceramic frameworks or titanium frameworks. The features of the microbiota and the mucosal condition around the two different materials will be evaluated and compared to determine whether zirconia is an appropriate material for fixed implant-supported prostheses for edentulous patients. Trial registration International Clinical Trials Registry Platform (ICTRP) ChiCTR2000029470. Registered on 2 February 2020. http://www.chictr.org.cn/searchproj.aspx?

IntroductionImplant-supported prostheses are often successfully used in edentulous patients. However, the incidences of peri-implant mucositis and peri-implantitis increase over time. The accumulation of pathogenic bacteria adjacent to prostheses can induce peri-implant disease. Plaque removal is recommended to prevent and manage peri-implant diseases. The purpose of this study is to compare the plaque removal efficacy of ultrasonic debridement with/without erythritol air-polishing powder around implants and bridges in patients with full-arch fixed implant-supported prostheses as well as the effects of these two methods on the rates of peri-implant mucositis and peri-implantitis, and the submucosal microbiota composition over 5 years in patients undergoing supportive periodontal therapy.Methods and analysisWe plan to enrol 10 edentulous (maxilla and/or mandible) patients seeking full-arch fixed implant-supported prostheses. The study will use a split-mouth model in which contralateral quadrants are randomly assigned to two groups. Group 1: one contralateral quadrant of full-arch fixed implant-supported prostheses will undergo ultrasonic debridement combined with erythritol air-polishing powder. Group 2: a separate contralateral quadrant of full-arch fixed implant-supported prostheses will undergo ultrasonic debridement. The 5-year trial will involve a total of 10 re-examinations per participant. The mucosal conditions around the implants will be recorded at 6-month intervals after restoration. Peri-implant submucosal plaque will be collected at each re-examination, and the bacterial flora will be analysed by 16s ribosomal RNA gene sequencing. X-ray examinations will be conducted at 12-month intervals to evaluate the marginal bone level around implants.Ethics and disseminationThis prospective single-centre, randomised controlled trial (PKUSSIRB-202054045) has been approved by the Ethics Committee of Stomatology School and Hospital of Peking University. Data will be registered with the International Clinical Trials Registry Platform. Additionally, we will disseminate the results via publication in scientific journals.Trial registration numberChiCTR-2000032431.

• Background: Implant-supported prostheses are applied in edentulous patients with high success rate. However, the incidence rate of biological complications namely peri-implant mucositis and peri-implantitis increases year by year after the placement of prostheses. Pathogenic bacteria accumulated adjacent to prostheses is proved to be the main reason of biological complication. Titanium, one of the classical materials for implant-supported prostheses, performs well in the aspect of biocompatibility and ease maintenance, but is still susceptible for biofilm formation. Zirconia, emerging as an appealing substitute, not only has comparable properties, but presents different surface properties influencing oral bacteria adhesion. However, scarce scientific research proves its direct effect on oral bacteria flora. Study exploring the different effects of material properties on biofilm formation and composition might provide a clue on this topic.• Methods: The proposed study is designed as a 5-year randomized controlled trial. We plan to enroll 36 edentulous (maxilla and/or mandible) patients seeking of full-arch fixed implant-supported prostheses. The participants will be randomly divided into two groups. Group 1: participants will be restored with zirconia frameworks with ceramic veneering; Group 2: participants will be restored with titanium frameworks with acrylic resin veneering. Ten reexaminations will be completed at the end of this 5-year trial. Mucosal conditions around the implants will be recorded every six months after restoration. Peri-implant submucosal plaque will be collected at each reexamination, and bacteria flora analysis will be performed with 16S rRNA gene sequencing technology, to compare the differences in microbial diversity between two groups. X-ray examination will be applied every 12 months as a key index to evaluate the marginal bone level around implants.• Discussion: The current study aims to explore the oral microbiology of patients restored with zirconia ceramic frameworks and those restored with titanium frameworks. By evaluating and comparing the features of the microbiota and the mucosal condition around two different materials, whether zirconia to be a recommendable material for fixed implant-supported prostheses could be figured out. This study aims to provide a tangible decision-making suggestion for full arch implant-supported prosthesis in edentulous patients. • Trial registration: International Clinical Trials Registry Platform (ICTRP), ID: ChiCTR2000029470. Registered on 2 February 2020.