Short Implants Supporting Single Crowns in the Posterior Region

The aim of the present project is to evaluate functional, biological and technical variables, as well as quality of life and satisfaction as indicators of long-term clinical performance of single prostheses on short implants in the posterior region with a 10-year prospective follow-up. This proposal refers to a clinical research project with a 10-year follow-up of single crowns on short implants (6 mm) in the posterior region of the maxilla and mandible. The cohort has started in 2010 through a project funded by the International Team for Implantology. The main clinical results with a 4-year follow-up showed the influence of biomechanical factors (implant/crown ratio) on short-term treatment success and increased risk over time. The sample will consist of participants from the cohort of the research project established in 2010, who received a single crown on a short implant (6-mm Standard Plus Wide Neck SLA) in the posterior region of the maxilla or mandible according to eligibility criteria and standardized clinical procedures. Data will be collected by clinical and image exams, questionnaires (for sleep bruxism, satisfaction and quality of life), recording of maximum occlusal force, measurement of perimplant bone changes, and calculation of the clinical crown-implant ratio. Data will be analyzed by descriptive and inferential statistics with survival analysis and multivariable models, if assumptions are met, at the significance level of 0.05.

AIMS

General Aim:

To evaluate the clinical performance of single crowns on short (6-mm) implants in the posterior region of the maxilla and mandible, according to functional, biological and technical variables, as well as patient satisfaction and quality of life as indicators of clinical success after ten years of use.

Specific Aims: This study will

* Measure the long-term success and survival rates of short implants (6-mm) and single crowns in the posterior region, through a 10-year prospective follow-up.
* Identify risk factors for failure and complication of short implant and single crowns.
* Compare the general satisfaction and quality of life of patients with and without failures/complications.

RESEARCH DESIGN AND METHODS

Study design and sample

The study design is characterized as a cohort, prospective, observational study, as a continuation of the original clinical project established in 2010 (ITI Small Grant 688_2010: 'Risk Factors on the Prognosis of Single Short Implants in the Posterior Region - A Prospective Clinical Study'). The description and results of the 2010-cohort project have been published previously. The present protocol was approved by the University Institutional Review Board and registered in the Brazilian Ministry of Health registry 'Plataforma Brasil' (CAAE: 26192919.5.0000.5336). The study sample will consist of participants from the 2010-cohort, who were selected according to the eligibility criteria.

The 2010-cohort consisted of 20 patients who received 46 Standard Plus Wide Neck SLA (Straumann Dental Implant System, Waldenburg, Switzerland) 6-mm implants and metal-ceramic crowns cemented over SynOcta abutments (Straumann Dental Implant System, Waldenburg, Switzerland) in a private practice setting.

The patients will be recalled for a 10-year follow-up research exam and will sign a new informed consent form. Whenever possible the same instruments adopted in the first 2010-cohort study will be used for comparison purposes.

Clinical examination

Clinical data will be collected on current socio-demographic and anthropometric variables, general health, oral conditions of hard and soft tissues, occlusal status, level of oral hygiene, gingival probing, and presence of any problems with implants and prostheses.

A self-report questionnaire for diagnosis of possible bruxism will be used. The maximum occlusal force will be measured using a cross-arch compressive force transducer (Sensotec 13/2445-02, United States).

The distribution and relative force of occlusal contacts will be assessed using the T-Scan III equipment (Tekscan, United States). Patients will be asked to bite the intraoral device five times for records in centric occlusion, lateral and protrusion movements.

Patient's Perception

The patient's overall satisfaction with the treatment results will be assessed with an instrumental question: 'How satisfied are you with the results of the single crown supported by a short implant? Please rate it from zero (equal to no satisfied at all) to ten (equal to completely satisfied) on this line (10-point VAS)'.

Oral health-related quality of life will be assessed by using the OHIP-14 instrument, composed of 14 questions that cover seven dimensions: functional limitation, physical pain, psychological discomfort, physical disability, disability social, psychological disability and disability. Each question offers five alternatives: never (0), rarely (1), sometimes (2), repeatedly (3) and always (4), and the total score ranges from 0 to 56. The additive method will be used for data analysis.

Assessment of perimplant bone changes and clinical C/I ratio

Perimplant bone changes will be assessed by using periapical radiographs and cone beam computed tomography (CBCT) images for longitudinal 2-D and 3-D analyses, respectively. Periapical digital radiographs of the implants will be performed using the long cone parallelism technique. Using the computer program ImageJ version 1.3v (National Institutes of Health, Bethesda, MD, USA), the marginal bone levels in relation to the implant platform will be measured. CBCT images will be used for 3-D analysis of perimplant bone changes over time. The images will be superimposed using reference points to compute volumetric bone loss and morphological analysis of bone changes of cortical bone.

Two measurements of each outcome measure will be performed by a blind examiner with a 30-day interval for error/agreement evaluation and averaged for statistical analysis. In addition, the radiographic trabecular bone changes in density will be evaluated by means of gray levels and texture analysis variables. Longitudinal radiographic images of each implant were superimposed, and the same regions of interest were selected for measurement of gray levels statistics (mean gray levels, standard deviation and coefficient of variation) and texture parameters (correlation, contrast, entropy and angular second moment). The free software ImageJ will be used for gray levels and texture analysis by means of the GLCM Texture Tool plugin.

Clinical C/I ratio will be calculated on the periapical radiographic image: The mean bone level from the implant platform to the most coronal level of the bone-implant contact, on both mesial and distal surfaces, will be subtracted from the actual implant size to compute the clinical implant length. The clinical crown will be measured from the most coronal bone-to-implant contact point to the highest cusp point. The clinical crown value will be divided by the clinical implant value to compute the clinical C/I ratio.

Statistical analysis

Data will be analyzed by descriptive and inferential statistics at the significance level of 0.05. The success/survival estimates of implants and prostheses will be performed through survival analysis. The general satisfaction and OHIP-14 data will be analyzed to compare groups with and without complications. If preliminary assumptions are met, multiple linear regression of mixed effects models should be used. Multivariate models will be compared over time to assess possible differences in short (1 year), medium (4 years) and long (10 years) clinical follow-up periods.

Measures to Protect or Minimize Eventual Risk and Data Confidentiality

All procedures follow a protocol approved by the university IRB and biosafety standards. Data will be stored in a locked room, and access will be restricted. The PI will be legally responsible for all stages of the research development and its dissemination.

Eligibility Criteria:
The study sample will consist of participants from the 2010-cohort, who were selected according to the following eligibility criteria:

Inclusion Criteria:

* need for single implants in the posterior region of the maxilla and mandible;
* indication of 6-mm implants according to preoperative evaluation

Exclusion Criteria:

* previous problems with osseointegration failure in the region of interest;
* bone graft or use of biomaterials;
* diabetes;
* heavy tobacco use (over 10 cigarettes per day);
* immunosuppression;
* local radiation therapy;
* poor oral hygiene;
* active periodontal disease in the remaining teeth;
* cystic or neoplastic lesions;
* removable dentures in the opposing arch.