Study Title: Changes on the Interproximal marginal bone level after CAD-CAM designed bridges directly placed on bone-level implants, or with intermediate abutments. A Randomized Clinical Trial.

• Objectives: To evaluate differences on changes on the interproximal marginal bone level 12 months after the connection of CAD/CAM designed prosthesis with an intermediate abutment (3mm long) or directly placed to bonelevel implants. Secondary objectives will be evaluate changes on the soft tissues and implant survival, as well as patients' satisfaction 3, 6 and 12 months after the connection of the definitive prosthesis.
• Design and Outcomes: Randomized double-blinded clinical trial with parallel design to asses the effect of CADCAM designed bridges directly placed
• Interventions and Duration: Patients will be selected according to the inclusion/exclusion criteria among those who attend the Unit of Periodontology of the University of Santiago de Compostela. After clinical and radiological implant planning, implant surgical placement will be scheduled. 2 MOZO GRAU® INHEX ST implants, with 3.75 mm or 4.25 mm of diameter and 8mm, 10mm or 11.5mm length will be placed on each patient, according to the bone availability. After 8 weeks of submerged healing, second stage surgery will be performed and definitive impression will be taken. All groups patients will keep a heeling abutment until the definitive prosthesis is placed, 3 weeks later (test group: direct to implant / control group: abutment 3 mm long). Clinical and radiological assessment after 1, 3, 6 and 12 months will be performed. Each participant will be on study about 15 months since the recruitment visit until the end of the study.
• Sample Size and Population: Based on previous studies, a sample size calculation determined that a group of 32 subjects, considering possible dropouts, will provide 80% power to detect a true radiographic difference of 0.80mm between groups after 12 months of observation since the definitive prosthesis connection. (Blanco et al 2017, Nóvoa et al 2017). A common standard deviation between groups was calculated (SD=0.715268015). A p ≤ 0.05 value will be considered significant (JM. Domenech & R. Granero 2010). A balanced random permuted block will be applied to prepare the randomization tables, stratifying for smoking habits (yes/no) with a 1:1 ratio between test and control groups.

Changes on the interproximal periimplant marginal bone level measured as the distance between the bone crest to the first implant to bone contact, using periapical radiographs, will be evaluated.

Each patient will receive to implants that will be rehabilitated with an implant supported prosthesis, being the test group a prosthesis connected directly to the implants, while the control group will be a prosthesis connected to the implants through intermediate abutments.

Inclusion Criteria:

• Patients with systemic and periodontal health, over 18 years old, with a Plaque Index lower than 25%.

  • Patients with an absence of at least two contiguous teeth, with natural proximal teeth, excluding the anterior upper zone, allowing the rehabilitation with bridges with two implants and two to four prostheses units
  • Adequate bone quality available that allows the placement of MOZO GRAU® INHEX ST implants with diameters of 3.75 mm or 4.25 mm and lengths of 8, 10 and 11.5 mm.
  • At least 2mm of keratinized gingiva.
  • Natural antagonic teeth or implants with fixed restorations.

Exclusion Criteria:

• • Systemic Factors:

  • Long term use of systemic medication that may interfere with bone metabolism or medical conditions that require prolonged use of steroids and / or medication that may interfere with bone metabolism
  • History of leukocyte dysfunction and deficiency, immunodeficiency syndromes, renal failure or bonemetabolic disorders such as osteoporosis
  • Physical disabilities that may interfere with proper oral hygiene
  • Use of any medication or device in research for a period of 30 days prior to the implant surgery in the study
  • Alcoholism or drug abuse
  • Smoker of more than 10 cigarettes per day
  • Conditions or circumstances which could prevent compliance with the participation in the study or interfere with the analysis of the results, such as a history of non-compliance or lack of reliability.
  • Local Factors:
  • History of local radiotherapy
  • Bruxism
  • Mucosal diseases, such as Oral Lichen Planus
  • Not treated periodontitis
  • Persistent intraoral infection
  • Crestal bone regeneration less than 3 months before the implant placement
  • Not healed extraction sockets (less than 6 weeks post-extraction
  • Anterior aesthetic sextant of the maxilla

Participant and care provider are blinded, the outcomes assessor is also masked but the investigator knows if the participant belongs to group A or B when the data is recorded