No researcher available to conduct the study.

In dental implant restoration, available literature demonstrates the advantage of using tall abutments, with a change of diameter with respect to the implant and a conical internal connection in the abutment-implant gap. However, for multiple restorations, the abutment-prosthesis connection has not been studied in detail. The "multi-unit" systems, both standard and brand specific, have either a flat or butt joint or an cone. In any case, both are external connection systems. Recently, an internal-type abutment-prosthesis connection system has been developed. Although it is proving its usefulness in single restorations, its use in multiple restorations compared to traditional systems has not been studied.

Therefore, taking into account all of the above, the present study has the overall objective of analyzing marginal bone loss (MBL) and adaptation of soft tissues by comparing a multiple prosthesis system of the "external, flat" type versus an external system of the "internal, conical" type.

Inclusion criteria:

• Kennedy class I or II (unilateral or bilateral free end) or III (posterior intermediate edentulous section) mandibular requiring 2 implants to restore at least 2 molars, 2 molars and 1 premolar, or 2 premolars and 1 molar.
• Possibility of placing a transgingival abutment at least 2 mm high.

Exclusion criteria:

• Need for simultaneous bone augmentation.
• Heavy smokers (>10 cigarettes/day).
• Uncontrolled type 1 or 2 diabetes (HgA1c>8).
• Known autoimmune or inflammatory disease.
• Serious blood disorders, such as hemophilia or leukemia.
• Local or systemic infection that may compromise normal healing (e.g., extensive periapical pathology).
• Liver or kidney dysfunction/failure.
• Currently receiving cancer treatment or within 18 months from completion of radio- or chemotherapy.
• Long-term history of oral bisphosphonates use (i.e., 10 years or more).
• History of intravenous bisphosphonates.
• Long-term (>3 months) history of antibiotics or drugs known to alter the inflammation and/or immunological system 3 months before inclusion.
• Severe osseous diseases (e.g., Paget disease of bone).
• Pregnant women or nursing mothers.
• Not able or not willing to follow instructions related to the study procedures.