Taking a Bite: Dental Implants

When it comes to dental implants, fast and accurate positioning of the implant is vital to keep patient discomfort to a minimum. The team at the RWTH College in Aachen/Germany uses metrotomography to inspect the accuracy of innovative implantology procedures for the fast application of dental pros theses . For thi s interdisciplinary project, the chair for production metrology and quality management at the machine tool lab (WZL) of RWTH Aachen collaborated with the Clinic for Dental Prosthetics at the University Hospital.

The new implantology procedure will enable fast insertion and precise positioning of the implant in the jaw bone of the patient needed for the anchorage for the dental prosthetic. Planning the insertion of the implant is computerassisted, taking into consideration the current bone situation and the fictional position of the subsequent implant. On this basis, a state-of-the-art stereo lithography process is used to create a perfectly-aligned template that will ensure the precision of the bores.

For the study, 15 patients who were treated with the new procedure were examined. To determine the accuracy of the procedure, the deviations between a model manufactured using the bore template and the corresponding real molds of the implant in the patient's mouth were measured.

The Metrotom 1500 from Carl Zeiss is used for the measurement. This enables determination of all important geometric features of the implants within a short time. In particular, the relative positions in relation to a defined intersection plane and the angular orientations of the implants to each other are relevant to ensure the accuracy of the fit of the subsequent prosthetic. Here, the position deviations must not exceed 0.1mm. Cylindrical metal spacer sleeves will be screwed into the models at the corresponding positions, which leads to a sufficient number of probing points, to reliably capture the orientation of the implants. Every implant to be examined is unique, requiring manual creation of the single inspection plans. As a result of the differing orientation of the spacer sleeves, it is not possible to capture the position of the implant by contact without using more involved methods and there is a hazard of shaft probing. Therefore, non-contact measurement using X-rays offers clear benefits.

A complete image is generated of the single models and molds using Metrotom. They are then available as virtual 3D models. In addition to visualization and segmenting possibilities, the volume model can also be used to measure the required geometric features.

The evaluation is performed using Zeiss Calypso measuring software. The point cloud generated by Metrotom is entered into Calypso and transferred to a surface model. Although each dataset is unique, the measurement including the generation of the required basic coordinate system can be completed within 15 minutes. The results are then clearly documented in a measurement log which is then used as a reference for the subsequent comparison with the mold model of the inserted implants. The use of metrotomography and the successful collaborative efforts made it possible to lay the foundation for the qualification of a new and promising medical procedure.

WZL of RWTH Aachen works to integrate concepts that are developed and customized for implementation in companies. Metrology procedures for practical use are being developed, qualified and optimized. The result is manufacturing companies receive support while enhancing their competitiveness.