الفهرس 
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Abstract
SUMMARY
T
his in-vitro study was designed to evaluate the accuracy of 2 intraoral scanners regarding different designs of preparation.
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 convergence angle of axial walls in single crown preparation and the different divergence angle in inlay preparation on the accuracy of both scanners, also the effect of arch contour on the accuracy of the scanners by comparing the results of anterior and posterior bridge and the effect of the complexity of the scan on the accuracy by comparing the results of single cown preparation with the posterior bridge.
The preparation were done on a typodont acrylic model (Nissen, Kyoto, Japan), with the aid of computer numerical control machine (CNC machine).
Two intra oral scanners took part in our study the CEREC AC Omnicam * and the Trios•.
We divided our groups into four subgroups. Extraoral subgroup which in turn divided into two divisions the 60 convergence and the 120 convergence, the intraoral subgroup which is divided also into 60 divergence division and 120 divergence division, the anterior bridge subgroup and the posterior bridge subgroup.
For the trueness measurement all the prepared casts are scanned with a desktop scanner inEos X5 (Dentsply, Sirona) 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 models 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:
Omnicam and Trios in scanning crown preparation with 60 convergence but a significant difference in 120 convergence
2) No statistically significant difference in accuracy comparing between the 2 IOS in scanning inlay with 60 or 120 divergence
3) A statistically significant difference in trueness between the 2 IOS in scanning anterior or posterior bridge.
4) A significant difference in the trueness of Omnicam comparing between the convergent angle of the crown with higher deviation of the 6° crown.
5) No statistically significant difference in accuracy of the Omnicam and Trios comparing between inlay with 60 and 120 divergence except in trueness of Omnicam with higher deviation of 60 divergence.
6) Statistically significant difference in the 2 IOS comparing between single preparation and posterior 3 units bridge preparation with high deviation of the bridge except for the precision of the Omnicam showing no significant difference.
7) No statistically significant difference in accuracy of the 2 IOS comparing between scanning of anterior and posterior bridge. Except for the precision of Trios having significant difference with high deviation of posterior bridge