Maxillary 3-implant Removable Prostheses Without Palatal Coverage on Locator Abutments

Materials and Methods The protocol is submitted to the Research Ethics Board of the Northern Norway in order to obtain ethics approval prior to commencing the study. All patients will obtain an invitation letter detailing the objectives of the study and requested to sign a consent letter prior to clinical examinations according to principles for good research practice. All patients will be offered a free implant hygiene session and prosthesis cleaning.

Study population All patients treated in a private dental clinic in Drammen, Norway having received a maxillary removable full prosthesis supported on 3 dental implants will be invited to attend evaluations of their intra-oral status annually after implant installation and solicited about treatment satisfaction and daily oral functions. These patients were initially not offered maintenance care at the completion of their treatment.

The implants that have been used are made from titanium with a microrough surface (Astra Tech Implant System, Dentsply Implants, Mølndal, Sweden). All implants have been placed according to the manufacturer's instructions (http://www.dentsplyimplants.no/nb-NO/Implantatsystem/Prosedyrer/Treatment-planning) and fitted with precision attachments (Locator, ZEST Anchors, Escondido, CA, USA. The removable prostheses were made from heat cured poly-methyl-metacrylate (PMMA) incorporating three active matrices).

Recall Procedure Each patient will be invited by letter followed up by a phone call to attend an examination visit. The patients will complete a questionnaire related to changes in general health aspects, their experiences and satisfaction with the reconstructions and eventual need for repair sessions during the last year. Specifically, the medical history and the smoking history (e.g. pack/years) will be assessed. Recordings will be made of general and local factors which may affect the prognosis of the implants and prosthesis. This includes the occurrence of systemic disease since implant placement, regular medication used by patients, smoking status, dental treatment received since implant placement, recall frequency at the dental hygienist and the last dental examination appointment.

Collection of Data from Patients' Charts

General information will be gathered from the patients' charts. Patients' age, self-reported smoking habits and the number of cigarettes per day, medical history, medication intake, reason for tooth loss and the date of prosthesis insertion will be recorded in "patient's summary forms". Type and distribution of implants will be retrieved from patients' charts. Cases with a chart documentation of an incidence of biological or mechanical complications during the follow-up period will be closely reviewed and recorded as following:

1. History of implant loss (Biological complication): Period of service before failure is traced in months for each lost implant. Lost implants will be categorized in three groups: 1) "Early Failure" which refers to implants lost before the insertion of the definite prosthesis. 2) "One-year Failure" addressing implants failed within the first year of loading. 3) "Late Failure" including implants lost more than one year following the insertion of the final prosthesis (Roos-Jansåker et al 2006).
2. History of peri-implant mucositis or peri-implantitis (biological complication): Any recorded incidence of inflammation and suppuration related to the gingival tissue surrounding implants in patients' charts will be gathered and transferred to "patients' summary forms".
3. History of various technical problems encountered following the insertion of the removable prosthesis (mechanical complications):

Any history of mechanical complications such as attachment loosening/fracture and incidences of cracks, chippings and fractures in resin teeth, acrylic body and prosthesis will be recorded in "patients' summary forms".

Post-operation peri-apical radiographs, taken at the day of "stage-one" surgery, will be retrieved from patient's charts and used as the reference point of supporting bone level for each implant. Reference bone levels on mesial and distal sides are determined by measuring the distance between implant platform and the most apical point of the alveolar crestal bone surrounding implant. A mean value between the mesial and distal sides is used for each implant as the reference marginal bone level.