Comparison of Extra-short (4 mm) Implants Used as Distal Support of a Maxillary Full-arch Fixed Dental Prosthesis vs. 10 mm Implants Installed After Sinus Floor Elevation.

Recently, 4 mm long implants with a standard diameter have been used for the restoration of the posterior edentulous mandible with favorable results. However, randomized clinical trials reporting the results from full-arch fixed dental prosthesis that included 4 mm long implants placed in the posterior regions of the maxilla have not been published yet. The aim of the present study will be to compare the survival and success rates of 4 mm implants used as distal support of a maxillary full-arch fixed dental prosthesis with standard (10 mm) implants placed in association with a bilateral sinus floor augmentation procedure

Two groups will be randomly prepared, the Short group and the Standard group. In the Short group, one 4 mm long and 4.1 mm in diameter implant (extra-short implant) will be installed in each side of the posterior region of the maxilla. In the Standard group, bilateral sinus floor elevations will be performed. After 4 months of healing, one 10 mm long and 4.1 mm in diameter implant (standard implant) will be installed into each augmented sinus. In the frontal region, four 10 mm long implants will be installed in both groups. Clinical assessments and x-rays will be taken at prosthesis delivering (6-8 weeks after implant installation), and after 6, 12, 18 and 24 months.

Eligibility Criteria:
Inclusion Criteria:

* Edentulous maxilla
* Willing to receive a full arch fixed restoration in the maxilla.
* Latest extraction at least 8 weeks before implant insertion
* Sinus floor height included between 4 to 6 mm
* Bone width in the distal segments sufficient to allow the insertion of a 4 mm long implant of standard diameter.
* In the anterior maxilla (from first premolar to first premolar) bone width sufficient to allow the insertion of 10 mm long implants of standard diameter. Minor horizontal augmentations with guided bone regeneration procedures was allowed in the anterior maxilla.

the opposing arch have to present one of the following conditions:

* natural dentition (at least 10 elements from 3.5 to 4.5)
* Fixed dental prosthesis of at least 10 elements (from 3.5 to 4.5) supported by teeth or implants
* Implant supported or teeth supported overdentures
* Adequate partial removable prostheses.

Exclusion Criteria:

* Presence of conditions requiring prophylactic use of antibiotics (e.g., history of rheumatic heart disease, bacterial endocarditis, cardiac valvular anomalies, prosthetic joint replacements).
* Major systemic diseases, or medical conditions requiring prolonged use of steroids, or alcoholism or chronically drug abuse.
* Current pregnancy or breastfeeding women
* Smokers \> 10 cigarettes per day
* Physical handicaps that would interfere with the ability to perform adequate oral hygiene
* Immunocompromised patients including patients infected with HIV
* Conditions or circumstances, in the opinion of the investigator, which would prevent completion of study participation or interfere with analysis of study results, such as history of non-compliance, or unreliability.
* Patients with an ongoing or previous treatment with bisphosphonates (for at least 2 months for oral therapy or 6 months for IV injection)

Local exclusion criteria

* Local inflammation, including untreated periodontitis
* Pre-cancerous oral lesions
* History of local irradiation therapy
* Severe bruxism or clenching habits
* Patients with inadequate oral hygiene or unmotivated for adequate oral home care
* Previous Guided bone regeneration or Guided tissue regeneration treatment at the implant site
* Total removable prosthesis in the lower arch