Background: The control and maintenance of implants, bone tissue and soft tissue are fundamental for the clinical success of implant prostheses (PSIs). The type of ceramic surface finish can modify the biological response of peri-implant tissues adjacent to PSIs over time.

Objective: To prospectively assess whether the peri-implant health of soft and hard tissues adjacent to monolithic zirconia PSIs varies with the type of surface finish (glazed or polished). It will also be evaluated if the patient perceives any clinical, comfort or satisfaction difference.

Methodology: The study design is a randomized, prospective, paired clinical trial, with intra-subject comparison. The sample will consist of consecutive patients in need and indication for treatment with monolithic zirconia PSIs, attended at the Military Policlinic of Porto Alegre and in a private practice by a single specialist researcher. For each PSI, the allocation of a glazed or polished surface in contact with the soft gingival tissue will be randomized on the mesial and distal sides of the crown. Data will be collected by routine clinical and radiographic examination with a focus on peri-implant health (hygiene index, gingival bleeding index, crestal bone level), satisfaction questionnaire and intraoral images (thermography and photographs), after one week of installation of the PSI and in six months, one year and two years. The data will be analyzed by descriptive and inferential statistics, at the significance level of 0.05.

The control and maintenance of implant, bone and soft tissue are fundamental for the clinical success of prostheses over implants (PSIs). The type of ceramic surface finish can modify the biological response of peri-implant tissues adjacent to PSIs over time.

AIM To prospectively assess whether the peri-implant health of soft and hard tissue adjacent to monolithic PSIs varies with the type of surface finish (glazed or polished).

METHODS The study design is a randomized, prospective, paired, clinical trial with intra-subject comparison, and the research protocol will follow the Resolution 466/12 of the Brazilian National Health Council and the Declaration of Helsinki.

Sample A non-probabilistic sample will consist of consecutive patients in need of treatment with unitary PSIs made of monolithic zirconia, being attended at the Military Polyclinic of Porto Alegre and in a private practice by the same specialist researcher (DBS). Patients will be selected according to the eligibility criteria.

Sample size calculation: In the systematic review of Linkevicius and Vaitelis (2015) on the effect of zirconia or titanium abutments on peri-implant tissues, the 11 clinical studies included for biological outcomes had samples from 11 to 81 patients, with 11 to 45 abutments. In a total of 145 zirconia abutments, 12 (8.2%) had biological complications. There is no current clinical studies on glaze and PSI polishing in monolithic zirconia and outcomes of peri-implant health. So, a priori, the initial sample will consist of 30 PSIs (30 pairs to be compared: Glaze vs. Polishing). The definitive sample size will be calculated after preliminary data analysis from the initial six months of data collection.

PSIs crowns will be made on metallic abutments (Variobase or Anatomic Abutment, Straumann) and milled in monolithic zirconia (Amann Girrbach, Austria), using a CAD/CAM technique with molding or intra-oral scanning and in-lab milling. For each PSI, the mesial and distal faces will receive one experimental treatment (surface finishing) at random, to be defined by drawing lots: glazed surface treatment (Ceramill Stain & Glaze Kit), or polished surface treatment (polishing rubbers kit in the sequence indicated by the manufacturer - EVE DIACERA Finishing and Polishing Kit, EVE Ernst Vetter GmbH - Germany).

All PSIs will be installed according to standardized clinical protocol in the routine of dental clinics where the patients will be seen. After installing the PSI, the clinical data will be collected by clinical-radiographic exam and photographs at the following times: after one week of installation of the PSI (T0 - baseline) and in six months (T1), one year (T2) and two years (T3) of follow-up.

Clinical-radiographic Examination A single trained examiner (D.B.S.) will carry out the collection of clinical and radiographic data for each PSI installed through non-invasive procedures already used in dentistry.

In the clinical exam the following aspects will be evaluated on each face (glazed or polished) of the PSI:

• Hygiene Index: will be visually evaluated the presence of bacterial plaque (biofilm) and the presence of visible inflammation.
• Index of Gingival Bleeding: Gingival probe around the zirconia crown, as per the last consensus of Periodontics (Peri-implant diseases and conditions: Consensus report of workgroup 4 of the 2017 World Workshop on the Classification of Periodontal and Peri-Implant Diseases and Conditions).
• Patient Satisfaction: a 100-mm visual analogue scale will be used
• Infrared thermography
• Radiographic evaluation for peri-implant levels analysis (potential bone loss)

Statistical analysis The data will be analyzed by descriptive and inferential statistics (alpha = 0.05).

Inclusion Criteria:

• Healing time of at least two months for patients who underwent extraction in areas to be rehabilitated with implants
• Adequate bone volume at the implant site (ie, sufficient for placement of an implant of at least 3.3 mm in diameter and 6 mm in length) assessed by preoperative CT and clinical evaluation.
• Use of Straumann bone level or conical bone level implants, with NC or RC platforms.

Exclusion Criteria:

• Patients with systemic diseases (e.g., heart disease, leukocyte and coagulation disorders, metabolic disorders, immunosuppression)
• History of radiotherapy in the head and neck region
• Current treatment with steroids and/or bisphosphonates
• Neurological or psychiatric impairment that can interfere with good oral hygiene
• Smoking (more than 10 cigarettes a day)
• History of illicit drug or alcohol abuse

IPD may be shared with other researchers upon justified request.

The randomisation of surface finishing treatment per side (mesial or distal) of each zirconia crown will be made at the laboratory fabrication step, and the treatment codes will be known only by the certified technician and Projec PI. The clinician, who is also the investigator and outcomes assessor, will not assess the codes until the final data analysis.