الفهرس 
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Abstract
T
his in-vitro study was designed to evaluate the effect of depth of preparation of an inlay-retained bridge on the accuracy of 3 intraoral scanners.
Hence the accuracy of intraoral scanners are described according to ISO 12836 as trueness and precision. the deviation of measurements between the reference model and the intraoral scan model is termed the ‘trueness’ of impression technique, and the deviation of measurements between digital models of the same intraoral scanner is ‘precision’ of impression technique.
The aim of the study was to evaluate the effect of different preparation depth for an inlay-retained bridge on the accuracy of three intraoral scanners.
The preparation were done on a typodont acrylic model (Nissen, Kyoto, Japan), preparations were done using special abrasive stones by the same operator.
Four intra oral scanners took part in our study the CEREC AC Omnicam 4.4.4, Omnicam 4.6.2. Trios 3 and Medit I500.
For the trueness measurement all the prepared casts are scanned with a desktop scanner in Eos X5* to get a reference model.
All the preparations were scanned with the intraoral scanners 10 times (n=10) with each scanner and then with the help of a reverse engineering 3D analysis software used to superimpose the scans and calculate the amount of deviation between them.
For the precision measurement the calculations are performed intra division which means every scan was considered the reference model once and all the remaining scans were superimposed on it.
A color-difference map (qualitative data) and a report (quantitative data) of the projections were obtained for every single superimposition process.
Data was recorded, tabulated and analyzed. Statistical work was done using t test.
Our results showed that:
1- Significant difference in the trueness of different types of scanners (p<0.001). The highest (RMS) value was found with Medit (58.45±2.63), followed by Omnicam (52.73±3.31) while the least value was found with 3Shape.
2- No statistically significant difference in trueness of the three intra-oral scanners as a result of the change of the preparation depth.
3- There was a significant difference in the precision of different types of scanners (p<0.001). The highest (RMS) value was found with Medit (47.76±8.05), followed by Omnicam (45.39±4.72) while the least value was found with 3Shape (35.28±6.32).
4- No statistically significant difference in the precision of the three intra-oral scanners as a result of the change of the preparation depth.
5- Significant difference in the accuracy of the Omnicam using 4.6.1 software version and Omnicam using 4.4.4 version.
CONCLUSION
Within the limitation of our study, the following conclusions may be drawn:
1) Trios is superior in accuracy than the Omnicam and medit in both 2mm and 3mm sample groups.
2) The trueness of the 3 IOS is not affected by changing the depth of the preparation
3) The precision of Trios and omnicam is not affected by changing the depth of the preparation
4) The precision of the medit I500 scanner was affected by changing the depth of the preparation
5) The accuracy of the omnicam using the cerec 4.6.1 software is higher than the one using cerec 4.4.4.