This study designed as a randomized controlled split-mouth trial will be conducted at the Dental Clinic of the University of Valencia. The aim will be to assess differences in clinical, radiological and microbiological outcomes between implants with 2 different connections: internal hexagon and conical connection. Following the premises, to minimize the bias related to prosthetic phase and maximize the effect of connections on MBL changes, a 1abutment-1time protocol will be used.

The study hypothesis is that there will be no statistically significant differences between both implant connections.

Inclusion Criteria:

• able to sign an informed consent form
• aged 25 years or more
• Any patient requiring two implant-supported crowns in the lower or upper jaw
• Kennedy class I, II, and III;
• teeth extracted at least 6 months before implant placement;
• sufficient bone volumes to accommodate dental implants without augmentation procedure

Exclusion Criteria:

• General medical and/or psychiatric contraindications to implant surgery,
• Pregnancy or nursing,
• Heavy smoking (more than 10 cigarettes/day),
• Treatment with anticoagulant drugs (International Normalized Ratio under 1.8), bisphosphonates, steroid therapy or anticonvulsants drugs.
• No regenerated bone
• Untreated Periodontal disease and inability of the patient to maintain reasonable oral hygiene according to study requirements.
• Patients with history of alcohol, narcotics or drug abuse. (Alcoholism: more than two bottles of beer per day)
• Patients receiving radiotherapy, chemotherapy or any other immunosuppressive treatment, or who have been administered radiotherapy in the last 5 years. (Patients through at any time received radiotherapy to the head and neck region should be excluded anyway.)
• Metabolic bone disorders
• Uncontrolled bleeding disorders such as: hemophilia, thrombocytopenia, granulocytopenia.
• Degenerative diseases.
• Osteoradionecrosis.
• Renal failure.
• Organ transplant recipients.
• HIV positive.
• Malignant diseases.
• Diseases that compromise the immune system.
• Unbalanced diabetes mellitus. (HbA1c above 6.5), Uncontrolled endocrine diseases
• Psychotic diseases.
• Hypersensitivity to one of the components of the implant in general and titanium in particular.
• Women who are pregnant or lactating.
• Lack of patient cooperation.
• Parafunctional habits, such as Bruxism or Temporomandibular joint disease.
• Various pathologies of the oral mucosa for example: Benign mucous pemphigoid, desquamative ginigivitis, erosive lichen planus, malignancy of oral cavity, bolus erosive diseases of the oral mucosa.