Soft Tissue Width and Abutment Height Influence Peri-implant Bone Resorption

The purpose of this clinical and radiographic study will be to determine what influence on marginal bone loss has the thickness of soft tissues and the height of the prosthetic abutment and eventually determine which of the two factors is the most important.This research was designed as a multicentre cohort observational study. Two clinical centers will treat patients through the placement of a single dental implant. The implants will be prosthetically loaded about 4 months after placement and periapical radiographs will be acquired at each time-point.

All patients will receive antibiotic prophylaxis with 2 g of amoxicillin one hour before surgery. With the help of a dissector, a full thickness vestibular flap will be carefully arranged and the vertical thickness of soft tissues will be measured with a probe marked every 1.0 mm. If the vertical thickness of the soft tissue is 2 mm or less, the tissue will be considered thin. If the thickness of the mucosa is greater than 2 mm, it will be considered thick. After the measurement, the lingual flap will be elevated at full thickness, and the site for site placement will be prepared. The implant bed will be at least 1.5 mm from the adjacent tooth or teeth, and must be surrounded by at least 1 mm bone in both buccal and lingual directions. A 3,75 mm diameter and internal hexagonal connection implant will be placed at the level of the bone crest according to the manufacturer's recommendations. Operators will be free to choose the most suitable system length (8, 10, 11.5 mm). All implants will be submerged according to a traditional two-stage protocol. After insertion, the flaps will be sutured without tension with interrupted sutures. Patients of both groups will be instructed to disinfect the site by rinsing twice daily for one week for 1 minute with 0.12% chlorhexidine. After 4 months of healing, the treated area will be reopened for connecting the healing abutments with a crestal incision that will retain the keratinized tissue; The same soft tissue measurements will be repeated as confirmation of what was done during the first surgical implant insertion phase. The implants will be considered osteointegrated successfully if they are clinically intact unless they show obvious radiotransparency and patients will not report any pain. After this step, it will be possible to divide the patients into 2 groups according to the thickness of the soft tissue: a group with thick tissue (more than 2.0 mm); Slim tissue group (less than 2.0 mm). The prosthetic framework will be bonded directly to prefabricated titanium abutment (1 or 3 mm). This will result in the formation of 4 different subgroups: a group with thick tissue and high prosthetic abutment; A group with thick tissue and low prosthetic stump; a group with thin tissue and high prosthetic abutment; a group with thin tissue and low prosthetic abutment.

All the implants will be rehabilitated by the dentist with screwed restorations. After prosthetic treatment, patients will receive oral hygiene instructions and will be monitored through calls to ensure periodontal health throughout the study period.

General inclusion criteria were:

• age>18 years;
• good general health;
• non smokers;
• absence of systemic diseases affecting bone metabolism and wound healing; - no regular medication consumption for at least 3 months prior to treatment; - patient willing and fully capable to comply with the study protocol;
• written informed consent given.

Local inclusion criteria were:

• presence of keratinized mucosa with a minimum bucco-lingual width of 3 mm; - bone crest with at least 6 mm of width and 9 mm of height above the mandibular canal, without concomitant or previous bone augmentation procedures;
• presence of the opposing dentition.

Exclusion criteria

were:

• history of head or neck radiation therapy;
• uncontrolled diabetes (HBA1c >7.5%);
• active infections;
• immunocompromised patients (HIV infection or chemotherapy within the past 5 years);
• present or past treatment with intravenous bisphosphonates;
• patient pregnancy or lactating at any time during the study;
• poor oral hygiene and motivation;
• untreated periodontal disease;
• psychological or psychiatric problems;
• alcohol or drugs abuse;
• participating in other studies, if the present protocol could not be properly followed;
• lack of implant primary stability.