Background: 
Implant-overdentures (IODs) supported by titanium bars improve stability and comfort in edentulous patients being unsatisfied with their complete dentures. Today’s computer-assisted design/computer-assisted manufacture (CAD/CAM) technology allows for fabrication of bars made from titanium but also from zirconium dioxide (ZrO). However, ZrO bars have not been in clinical use on a standard basis. Thus, scientific data with focus on ZrO bar reliability and peri-implant bone resorption are missing.

Aim/Hypothesis: 
To report on the clinical short-term outcomes of CAD/CAM ZrO bars and respective mandibular IODs, and on the radiographical crestal bone level changes after 12-months. The null-hypothesis was that the bar fracture rate would be < 5% and no significant crestal bone resorption would occur.

Materials and Methods: 
Fifteen edentulous patients (53% men) with a mean age of 62 years were treated with a total of 30 implants, i.e. two interforaminal standard diameter implants (NobelReplace Select RP) per patient. After a healing time of six weeks, all patients received a mandibular IOD supported by a CAD/CAM ZrO bar milled from one homogenous block. All bars had a rigid design (Dolder) with bilateral 7mm extensions and were retained with 35Ncm directly on the implant, using a specific screw, and without titanium base at the interface. Female parts in the IOD were prefabricated gold attachments. The maxilla was rehabilitated with a complete denture and a lingualised occlusion concept was applied. Panoramic radiographs were taken at delivery and at the one year appointment. Prosthetic complications such as bar fractures and the need for maintenance service of the anchorage system, as well as biological outcomes including implant survival and crestal peri-implant bone level changes were recorded.

Resultats: 
All the 30 implants osseointegrated without complications and were successfully in use at the 12-months recalls. One patient showed generalised hyperplasia of the mucosa around the bar. Radiographic measurements of the crestal bone resorption at mesial and distal implant sites revealed bone level changes of -2.9mm to +1.4mm (mean +0.2mm) after 12 months. While 10% percent of the sites showed bone levels with an increase of >1mm and 62% between 0 and 1mm, 27% had a loss of maximally 1mm and one site was measured -2.9mm without clinical signs of inflammation. All the 15 ZrO bars and corresponding IODs were successfully in use without fracture or any technical complications. No special maintaining service was recorded other than removal of superficial bar discoloration at lingual sites.

Conclusions and Clinical Implications: 
None of the 15 ZrO bars and IODs showed a fracture or a prosthetic complication after 12 months. Survival and success rate of the 30 implants were 100% with stable crestal bone levels. These short-term results of this prospective study showed that the use of ZrO bar with its unique biocompatibility and, due to its white colour, easiness to perform and control good cleansability for elder patients is possible with a high predictability and without technical or biological complications.

Zirconia bars supporting mandibular implant-overdentures. Short-term outcome of a prospective study.