Effectiveness of Removable Prosthesis Retained by 4 Implant-supported Locator-Attachments

1.1 Background and significance

The effectiveness of mandibular overdentures retained by 2 dental implants and its impact on Oral Health-Related Quality of Life (OHRQoL) and patient satisfaction has been extensively documented over the last decades(1-6). According to recent systematic reviews, the implant survival rate of this oral rehabilitation concept reaches more than 95% (7-10). The scientific validation of the efficacy of such a rehabilitation concept has influenced the social security system of several countries like Belgium. Therefore, this treatment approach is nowadays considered as an evidence-based and cost-effective treatment option improving the function and quality of life of mandibular edentulous patients. Unfortunately, cost-effective treatment concept to restore the edentulous maxilla not has been widely documented (11). Many studies display high success rates of fixed implant-supported rehabilitations of the edentulous maxilla (12) but these treatment options remain costly and are therefore reserved to a limited social category of patients.

This work is important because there is a need to provide affordable and efficient implant treatment approaches to restore function and improve satisfaction and OHRQoL of patients with edentulous maxillae.

1.2 Preliminary studies in connection with new projects/continuing projects

Even though some authors have described implant survival rates of implant-retained overdentures in the upper maxilla (8, 13-16), most of the treatment approaches involves bars. The placement of 4 implants and individual attachments is a more cost-effective treatment modality that is poorly documented in the literature in terms of implants and prosthodontics outcomes but also on aspects assessing implant distribution, attachment types and improvement of patient centered outcomes. Therefore, further studies are needed to validate the placement of 4 implants and individual attachment as a reliable treatment modality.

1.3 Research design and methods

The study is designed as a single center prospective cohort study. The study protocol will be submitted to the Ethics Committee of the University Hospital of the University of Liège, Belgium.

A total of 30 patients with edentulous maxillae and at least one short span dentition (fixed) in the lower jaw will be included in the study.

The inclusion and exclusion criteria are listed below:

Inclusion criteria

• Physical status according to the American Society of Anesthesiologists (ASA) = 1, 2
• Wearing a complete upper denture that is adequate and in good conditions
• Signed informed consent form describing the purpose and process of the study

Exclusion criteria

• Uncontrolled periodontitis/peri-implantitis (lower jaw)
• Lack of bone for the placement of 4 implants of 3.3 diameter and 8 mm with bone regeneration.
• Tobacco use > 10cigarettes/day

Pre-treatment examination Clinical evaluation of the upper removable denture and the lower dentition will be done. Oral hygiene instructions will be given.

The patient fulfilling the inclusion criteria will be asked to complete 3 questionnaires for patient satisfaction and OHRQoL and socio-demographic conditions before explaining them the possibilities to be enrolled in a study in order to minimize the risk of bias.

The McGill Denture Satisfaction Instrument (17) will be used to evaluate patients' satisfaction relating to their prostheses. This questionnaire is a treatment-specific patient-based outcome assessing satisfaction relating to 6 aspects of the mandibular prosthesis: general satisfaction, comfort, stability, aesthetics, chewing ability (ease of chewing), chewing efficiency (ability to crush food in small particles), ease of cleaning, ability to speak and oral condition (condition of their mouth, which can refer to oral health status and was measured by "In general, are you satisfied with your oral condition?". The subjects will answer on 100 mm visual analogue scales (VAS) anchored by the words "not at all satisfied" and "extremely satisfied".

The Oral Health Impact Profile (OHIP-20) questionnaire will be used to assess oral health-related quality of life. This 20-item questionnaire measures self-reported impairment in edentulous populations within seven domains: functional limitation, physical pain, psychological discomfort, physical disability, psychological disability, social disability and handicap. The items will be rated on six-point Likert scales ("never" = 1, "rarely" = 2, "occasionally" = 3, "often" = 4, "very often" = 5 or "all of the time" = 6). OHIP-20s total range is therefore 20-120 points, lower scores indicating better oral health-related quality of life (4, 18, 19).

Data on gender, age, level of education, annual household revenue, marital status and lifestyle (living alone or with others) will be obtained from a standard socio-demographic questionnaire.

Cone beam CT s assessment After the informed consent is signed, a CT scan will be done and evaluated by 2 independent surgeons to potentially exclude some patients because of lack of bone availability. In case of disagreement, the case will be discussed.

Surgical procedures Once all patients have been enrolled in the study, the surgeries will be scheduled within the same week. Antibiotics will be prescribed 1 day before surgery and continued for 5 days. Three calibrated and confirmed surgeons will place 4 Narrow Neck (NN) or Regular Neck (RN) Roxolid tissue level implants (Institut Straumann, Basel Switzerland) according to the surgical protocol recommended by the manufacturer. The implant positions have to be determined previously at the time of CT scan evaluation by an agreement between the 2 operators and according to the bone availability. Two implants have to be placed in the lateral or canine region and 2 implants as distal as possible. The implants have to be placed with as parallels as possible. A maximum divergence of 10 will be tolerated. The flap design will be determined according to the available bone quantity and in order to emphasize an adequate quantity of keratinized tissue around the implants. A Cone Beam Computed Tomography (CBCT) scan will be done directly after surgery. Sutures will be performed with silk sutures and removed after 1 week. The removable (conventional) prostheses will be adapted to avoid any contact with the implants. Patients will be followed up at 4 and 8 weeks post-surgery, respectively. At 8 weeks, a panoramic x-ray will be done. If osseointegration is successful, the removable prostheses will be connected to the implants.

Prosthodontics procedures At 8 weeks, prosthesis will be connected to the implant with Locator . The type of Locator attachments will be chosen according to the implant angulation and soft tissue thickness. They will be torqued at 35 N/cm on the osseointegrated implants. Afterwards, the female connection will be fixed into the removable prosthesis with acrylic resin. The effectiveness of retention will be checked and the patient will be taught to put the denture in and out by himself. The occlusion will be controlled and adjusted after these manipulations if necessary.

Follow-up visits Patient will be followed at 1 week after Locator connections and then at 3, 6 and 12 months, respectively. Thereafter, patients were recalled annually. In case of any complications, the patient will be asked to directly contact one of the dentists responsible for the study.

Data collection Data will be collected into a remote and secured database. Automatic data check procedures will be implemented at data entry to warrant quality of the information stored. Access to the database will be limited to the study investigators and data will be kept confidential.

Statistical analyses Results will be summarized as mean and standard deviation (SD) for quantitative variables and as frequency tables for categorical findings at each time point. Longitudinal data will be displayed graphically and analyzed by the general linear mixed model which accounts for repeated values within patients. Success rates will be estimated and associated with 95% confidence intervals (95%CI). The significance level will be set at 5% (P<0.05). Data will be analyzed with Statistical Analyses Software (SAS and S-PLUS softwares).