The purpose of this study is to investigate whether the immediate definitive abutment connection to dental implant is effective in preventing marginal bone loss when compared to the conventional treatment with late abutment/implant connection, which include three disconnections and reconnections.

The proposed study is a randomized clinical trial in which the participants will be allocated into one of the two arms according to the proposed intervention: experimental group, in which the abutments will be permanently connected immediately at the implant placement procedure; and control group (active comparator) with conventional treatment, where the abutments will be disconnected and reconnected three times.

Considering the inclusion and exclusion criteria related to oral and systemic health, a sample of participants will be selected among those partially edentulous patients who seek for dental implants treatment at the Fortaleza University School of Dentistry.

The sample size has been calculated based on the standard deviation of 0.17 mm, significance level of 5% and 80% statistical test power. To detect a clinically significant difference of 0.2 mm, each group should be composed of 11 participants. Therefore, considering a 10% margin for possible dropouts or missing data, the study will include 24 participants divided into two groups. Each participant will receive one or two implants according to his/her needs, so the study may include more than 24 implants.

A single surgeon will perform the implant surgical procedure in order to reduce variations inherent to clinical experience. After local anesthesia and incision on the top of the alveolar ridge, the bone will be exposed by the mucoperiosteal flap elevation. The mucosal thickness will be measured at implant sites, before the lingual/palatal flap elevation, with a periodontal probe.

The drilling sequence will be done according to manufacturer's recommendations, under saline solution irrigation, intermittent movements and speed up to 1200rpm.

The implants should develop a final insertion torque of 32Ncm or above to enable abutment connection torque, indicated at the experimental arm. The implant primary stability will be also measured by resonance frequency analysis (Osstell; Osstell AB, Gothenburg, Sweden). A minimum 65 ISQ will be required to a single-stage surgery. Thus, those implants that do not contemplate these requirements will be excluded from the study and will receive a conventional treatment with two-stage surgery if necessary.

Before finishing the surgical procedure, the volunteers will be randomly assigned to one of the two arms by opening sealed envelopes with a random sequence generated by Excel (Microsoft, Redmond, Washington, USA). Therefore, the surgeon will identify each volunteer's arm only after the end of drilling, insertion and stabilization of the implants.

Each implant allocated at the control arm (active comparator) will receive conventional treatment with three abutment disconnections and reconnections. At the experimental arm, each implant will receive the prosthetic abutment in a definitive way immediately at the surgical procedure, avoiding any abutment disconnection.

The surgeries of both arms will be finished with suture, drug prescription and postoperative recommendations. All implants will receive temporary crowns at three months and definitive prosthesis until six months after surgery.

Intraoral radiographs will be done with paralleling technique immediately after surgery (baseline) and at 3, 6, 12 and 24 months later. The radiographs will have its dimensions corrected at the ImageJ software (National Institutes of Health, Bethesda, Maryland, USA) having implant known dimensions as reference.

Each implant will have its radiographs evaluated by a previously calibrated examiner with a minimum of 0.8 intra-rater reliability for the intraclass correlation coefficient. The examiner will not know to which arm the X-rays belong.

Primary and secondary outcomes data will be submitted to normality test and compared using statistical tests for paired and unpaired samples.

Inclusion Criteria:

• Partially edentulous patients requiring dental implant treatment for one or two dental units;
• Occlusal stability and regular occlusal plane;
• Enough space for implant and prosthesis;
• Good periodontal health
• Keratinized mucosa width > 4mm;
• Implant primary stability > 65 ISQ and insertion torque > 20Ncm;

Exclusion Criteria:

• Diabetes mellitus;
• Treatment with bisphosphonates;
• Head and neck irradiation;
• General contraindications to oral surgery;
• Pregnancy;
• Bone graft;
• Bruxism;
• Smoking habits.