الفهرس 
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Abstract
This in-vitro study was designed to evaluate the effect of depth and design of an endocrown preparation on the accuracy of 4 intraoral scanners.
Hence the accuracy of intraoral scanners is 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 depths and design for an endocrown on the accuracy of four intraoral scanners.
The preparation was done on freshly extracted human teeth; 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 4.6.1 **Trios 3 and ***Medit I500.
For the trueness measurement all the prepared teeth were scanned with a desktop scanner inEos 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:
(Lower RMS values are better)
1- Significant difference in the trueness of different types of scanners (p<0.001). The highest RMS value was found with Omnicam 4.4 (56.53±6.08), followed by Medit I500 (52.07±8.92), then Omnicam 4.6 (47.68±12.11), while the lowest value was found in Trios (38.81±8.72).
2- Significant difference in trueness of the four intraoral scanners between samples with class (I) design (52.30±10.04) that had significantly higher value than samples with class (II) preparation (45.25±11.33) (p<0.001).
3- Significant difference in trueness of the four intra-oral scanners as a result of the change of the preparation depth, samples with 6 mm depth (55.70±8.22) had significantly higher value than samples with 4 mm depth (41.84±9.46) (p<0.001).
4- There was a significant difference in the precision of different types of scanners (p<0.001). The highest RMS value was found with Omnicam 4.4 (50.79±10.06), followed by Medit I500 (48.94±10.39), then Omnicam 4.6 (42.95±5.04), while the lowest value was found in Trios (37.37±7.05).
5- Significant difference in precision of the four intraoral scanners between samples with class (I) design (47.16±10.03) that had significantly higher value than samples with class (II) preparation (42.86±9.31) (p<0.001).
6- Significant difference in trueness of the four intra-oral scanners as a result of the change of the preparation depth, samples with 6 mm depth (49.17±9.87) had significantly higher value than samples with 4 mm depth (40.85±8.02) (p<0.001).
7- There was a moderate positive correlation between trueness and precision that was statistically significant (rs=0.560, p<0.001).