Master preparation artefact
The master artefact is a standard training model with four preparations. The form of the artefact was scanned using the Renishaw inciseTM scanner, whose accuracy is calibrated to the ISO 10360-4 standard.
Impressions of the master are taken with the material of interest. Models are made from each impression with the same model stone material. The stone material used was the best performing stone in the long-scale accuracy tests.
Since the majority of errors come from the impression, keeping the stone consistent means that we can eliminate stone errors, resulting in an impression comparison.
Example of a poor impression
Once the impression has been taken, it too is scanned on the inciseTM scanner, and its shape is compared with the artefact.
This example is a silicone material. Even with the most popular silicone materials, there could be an error which leads to an unacceptable clinical result.
The largest model errors here are almost double the 100 µm limit for ideal marginal adaptation.
Example of a good impression
Errors in the best performing impression material are all within 50 µm.
Conclusions
- The choice of impression material alone could mean the difference between a crown being clinically acceptable and unacceptable
This is a measure of how well the model reproduces the shape and fine detail of the preparation - important for marginal adaptation on crowns.