QMT Features: April 2009
Metrotomography measuring technology enables perfect fit of dental prosthetics
Just how accurately can dental prosthetic implants be inserted? Computer-enhanced planning of the insertion helped to create a perfectly aligned template that will ensure the precision of the boreholes in the jaw bones

New implantology procedures for dental prosthetics should be applied as quickly as possible and with maximum precision. But just how accurately can implants be inserted?

This was examined by the chair for production metrology and quality management at the machine tool lab (WZL) of the RWTH Aachen, Germany, and the Clinic for Dental Prosthetics at the University Hospital as part of an interdisciplinary project. They used a METROTOM computer tomograph from Carl Zeiss for the project.

It is important to quickly insert and precisely position the implants  in the jaw bone so as to anchor the dental prosthetics. The computer-enhanced planning of the insertion incorporates the current bone situation and the fictional position of the implant. A stereo lithography process is then used to create a perfectly aligned template that will ensure the precision of the boreholes in the jaw bones. During the study, the deviations between a model manufactured using the borehole template and the real molds of the implant situation in the patient’s mouth will be measured to verify the accuracy of the procedure.

A METROTOM 1500 computer tomography from Carl Zeiss was used at the WZL for the measurements. It enables determination of all important geometric features of the implants within a short time. In particular, the relative positions 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. Cylindrical metal spacing sleeves are screwed into the model at the corresponding positions in order to capture the orientation of the implants.

This provides a sufficient number of probing points. Because each implant is unique, the single measurement plans must be manually generated. Due to the different orientation of the spacing sleeves, capturing the positions of the implants using contact measurements is very time consuming. Furthermore, there is a risk of shaft probing and thus damage to the stylus.

Measurements with the computer tomography – with x-rays – provide clear benefits: the model and molds can be easily and completely examined. They are then available as virtual 3D models. In addition to visualization and segmenting possibilities, a volume model can also be used to measure the required geometric features. CALYPSO measuring software from Carl Zeiss is used for the evaluation. CALYPSO takes the point cloud generated by METROTOM and creates a surface model.

Although each dataset is unique, a measurement ­– including the generation of the required basic coordinate system – can be completed in 15 minutes. The results are documented as a clearly arranged measurement log, which is then used as a reference for the subsequent comparison with the mold models of the inserted implants.

email: marc.wagener@zeiss.de


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