The aim of this study was to compare the influence of the abutment height and insertion timing on early marginal bone loss (MBL) in posterior mandibular partial implant-supported restorations.

Material and methods: The study was planned as a prospective, randomized, controlled parallel group including subjects in need of two implants for the restoration of an edentulous posterior mandibular area. Data were gathered on age, gender, attached gingiva height, bleeding on probing (BoP), smoking habits and previous periodontitis. The patients were allocated into three groups: Group A implants were immediately connected to 2 mm height abutments; Group B implants were immediately connected to 1 mm height abutments; Group C implants were left to heal in a sub-mucosal position and 2 mm abutments were inserted in a second stage surgery. Peri-apical radiographs were taken at the implant surgery (baseline), 4 weeks after surgery (T1), 16 weeks after implant placement at the final restoration delivery (T2) and 1-year after implant placement (T3).

Inclusion Criteria:

• patients age > 18 years;
• American Society of Anaesthesiologists (ASA) status I;
• no systemic medication or condition known to potentially alter bone metabolism; - absense of acute periodontal condition.

Exclusion Criteria:

• lack of primary stability at implant surgery;
• need for bone regeneration procedures during surgery;
• inability to correct place the implant in accordance with the prosthetic requirements.