Background: Lateral maxillary sinus augmentation (MSA) is a predictable bone regeneration technique in case of atrophy of the posterior-upper maxilla. Aimed at obtaining quantity and quality of bone suitable for receiving osseointegrated implants, its success is largely due to the skill of the surgeon, but also to the characteristics of the biomaterial used.

Methods: Twenty-four patients needing MSA were included in the study. The patients were randomly allocated to 3 different groups: Anorganic Bovine Bone Mineral (ABBM) as control, Tricalcium Phosphate (TCP) with or without hyaluronic acid (HA) as test groups. Nine months after MSA bone biopsies were harvested for the histomorphometric analysis. Secondary outcomes were mean bone gain, intraoperative and post-operative complications, implant insertion torque, implant failure and patient related outcome measures (PROMs).

The implant-prosthetic rehabilitation of the atrophic maxilla requires the creation of sufficient volumetric quantity of bone, through regeneration techniques, necessary to position the implants.

Maxillary sinus augmentation (MSA) is probably the most predictable and best performing technique.

The present randomized controlled study aims to evaluate and compare, histomorphometrically and clinically three different bone substitutes such as: ABBM, Tricalcium Phosphate (TCP) with or without the addition of hyaluronic acid (HA) that were used for lateral MSA. This study population will be followed until the 3rd year. This study describes histological differences between the three groups at 9 months.

All the patients enrolled in the study received a session of oral hygiene and a periodontal examination before the surgical procedure to obtain a more favorable oral environment for wound healing. A CBCT was mandatory for all included cases to verify that the maxillary sinus was clear and that the residual bone height was 3 mm or less. All the enrolled patients received 2 gr. of amoxicillin and clavulanic acid (or 600 mg. of clindamycin for those who were allergic to penicillins) as a pre-medication one-hour before surgery. All patients rinsed for 1 minute with 0.2% chlorhexidine mouthwash (and twice a day for the following 3 weeks). Local anesthesia was administered, a mid-crestal incision with mesial and distal release were performed to access the lateral bone wall of the maxillary sinus, subsequently, ultrasound bone surgery (Piezosurgery ®, Carasco, Italy) with specific tips was used for the bone window osteotomy (Figure 1-A). The Schneiderian membrane was reflected and lifted up medially with flat sinus curettes. Once the sinus membrane was completely lifted a bioabsorbable pericardium membrane (Smartbrane, Regedent AG, Zurich, Switzerland) was applied to protect it (Figure 1-B). The randomization sealed envelopes were opened and the clinician allocated the patients to one of the three experimental groups:

1. Control group that received Demineralized Bovine Bone Mineral (Bio-Oss Cancellous, Geistlich, Wolhunsen, Switzerland);
2. Test group 1 that received TCP with particle size ranging from 250 to 1000 µm (Osopia, Regedent, Zurich, Switzerland);
3. Test group 2 that received TCP as in test group1 plus crosslinked Hyaluronic Acid (Hyadent BG, Regedent, Zurich, Switzerland) with a ratio 2 to 1.

the bony window was repositioned, stabilized and covered with a resorbable pericardium membrane. Nine months after the MSA a CBCT analysis was required to evaluate the total bone height gain.

Depending on the treatment plan, between one and three implants, bone level (BL) or tissue level (TL), of two different manufacturers (Institut Straumann AG, Basel, Switzerland and Sweden & Martina, Due Carrare, Italy) were positioned. While preparing the osteotomy implant site a bone biopsy was harvested using a trephine. The implant insertion torque was measured in Ncm for each implant.

All patients were prescribed 1gr amoxicillin + clavulanic acid twice daily for 7 days (for those who were allergic to penicillin 300mg clindamycin 3 times daily for 7 days) as post-operative prophylaxis. All patients received 8mg of dexamethasone immediately after surgery and 4 mg of dexamethasone per day were prescribed for the following 5 days. Analgesics were prescribed (1gr paracetamol 3 times daily) according to patients' need. The use of removable temporary restorations was not recommended during the healing period.

After an osseointegration period of 3 months, the implants were restored. The prosthetic procedures were similar for all groups, impressions were taken with a polyether rubber material (Impregum, Espe Dental AG, Seefeld, Germany) and a customized impression tray. Final Zirconia screw-retained restorations were delivered after a period of 2/3 weeks, peri-apical radiographs were taken and oral hygiene instructions were given to all participants in the study.

Inclusion Criteria:

• need for maxillary sinus augmentation
• 18 years or older
• residual ridge height less than 3mm

Exclusion Criteria:

• full contraindication to implant surgery,
• systemic diseases that could negatively influence wound healing;
• heavy smokers (more than 10 cigarettes/day);
• head and neck irradiation treatment;
• uncontrolled diabetes;
• chronic or acute sinus pathology;
• uncontrolled periodontal disease;
• full mouth plaque and bleeding score higher than 25%,
• tooth extractions in the previous 2 months

The envelope with the group assignment will be opened by the surgeon at the time of surgery and the patient won't be informed.

The clinician who registers clinical parameters won't be informed of the group allocation. The histologist will receive biopsies with a numeric code but without informations of the graft material used.