Metrotomography is used at the RWTH Aachen to inspect the accuracy of innovative implantology procedures for the fast application of dental prostheses.
A cooperation between the chair for production metrology and quality management at the machine tool lab (WZL) of the RWTH Aachen and the Clinic for Dental Prosthetics at the University Hospital was set up for this interdisciplinary project.
The new implantology procedure will enable fast insertion and precise positioning of the implant in the jawbone of the patient needed for the anchorage for the dental prosthetic. Planning the insertion of the implant is computer-assisted, 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.
Fifteen patients treated with the new procedure were examined during the study, during which the deviation between a model manufactured using the bore template and the corresponding real moulds of the implant situation in the patient’s mouth will be measured to determine the accuracy of the procedure.
The Metrotom 1500 from Carl Zeiss at the WZL will be used for the measurement. This machine 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 also a hazard of shaft probing. Thus, non-contact measurement using x-rays offers clear benefits.
A complete tomograph is made of the single models and moulds using METROTOM without major effort. They are then available as a virtual 3D model. In addition to visualisation and segmenting possibilities, the volume model can also be used to measure the required geometric features.
The evaluation is performed using Calypso measuring software version 4.6 from Carl Zeiss. 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 performed 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 mould model of the inserted implants.