Precision of fit of one-piece zirconia and cast frameworks

Objectives: Poorly fitting frameworks are the most common reason for complications in the life-time survival of dental implants. This study evaluated and compared the precision of fit of CAD/CAM one-piece zirconia fixed complete denture frameworks and cast frameworks.

Methods: Ten Procera zirconia substructures were fabricated using a CAD/CAM technique. Five cast implant frameworks of high noble metal (Palladium-Gold) were fabricated by 5 different dental laboratories. Laboratories were instructed to use their preferred technique to obtain the optimum fit. Using a Zeiss Coordinate Measuring Machine and CALYPSO measuring software positions of implant replicas in the gypsum model were determined. Positions were then matched to the measured positions of the framework cylinders.

All samples were analyzed measuring the position of the replicas in the A translation matrix calculated by the rigid body transformation method. This method translates the cylinder positions and minimizes the point-to-point distance between the two data sets. The best fit between the replica and the framework was completed by making each corresponding cylinder the origin (0,0,0). This was done systematically until there were six best fit data sets from which the minimum gap data set was chosen. All the data were transformed into the coordinate system: Cylinder#1(0,0,0), #6(x,0,0), #3(x,y,0) prior to making comparisons.

Results: The following are the Centroid, MaxGap, MiniGap and the maximum minus minimum angular gap measurements between the implant replicas and the corresponding zirconia and cast framework cylinders.

Method          Centroid        MaxGap         MiniGap         Maximum-Minimum

Cast                21.3                25.6                17.1                            8.5

Zirconia           8.9                10.6                  7.2                            3.4

Conclusions: CAD/CAM one-piece zirconia fixed complete denture frameworks provide an improved precision of fit over that of cast frameworks

<>Supported by NobelBiocare/ University of Michigan Center for Excellence