الفهرس 
REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
This invitro study was designed to evaluate the accuracy of two digital workflows: Direct workflow and indirect workflow on fully edentulous arch restored by 4 implants with two distal implants angulations 30ᵒ angle of divergence and 45ᵒ angle of divergence.
The measurement of accuracy was done by best fit algorithm and RMS calculation and the absolute linear deviation.
Digital optical scanning was advocated as an alternative of the conventional impression to record intraoral anatomy and implant coordinates, improving patient comfort and acceptance but the accuracy of digital impressions is still controversial for complete arch implant cases, and specifically all-on-four cases. Intraoral scanning has benefits over conventional impression making, the aim of the study was to know whether scanning is sufficiently accurate for multiple implants.
2 models with a shape of arch mimicking the maxillary arch, 16 mm in width and 14 mm in height were fabricated having 4 implant analogues. The models were designed with two anterior implants in the position of the canines and two posterior implants in the position of first molar. The 2 anterior scan bodies at canines positions with 0◦ horizonal angulation parallel to each other, and 2 posterior with 30◦ distal angulation in the first model and 45◦ in the second one.
The direct workflow uses three different types of intraoral scanners: Cerec Prime scan (Sirona Dental System GmBH, Germany), Trios 4 (3 Shape,Copenhagen, Denmark) and Medit i600(Medit, Seoul, Korea) With two scanning protocols, the unmodified non splinted and splinted. The indirect workflow uses three different types of extraoral scanners: IneosX5 (Sirona Dental System GmBH, Germany), E1 (3shape, Copenhagen, Denmark) and Medit 710 (Medit, Seoul, Korea).
The two digital workflows were first divided into 2 groups according to the workflow group D which is the direct digital workflow and group I which is the indirect digital workflow. The resin models which in turn were divided into two subgroups according to the angulation of the posterior implants subgroup 1 the 30 degrees distally tilted posterior implants and subgroup 2, the 45 degrees distally tilted posterior implants. Ater that each subgroup was divided into 2 divisions according to splinting into division A the splinted scan bodies and division B, the non-splinted scan bodies. .Division A was also divided according to the type of intraoral scanner into subdivision T which is Trios 4, subdivision P which is Cerec Primescan.and subdivision M which is Medit i600.In group I each subgroup was divided into 2 divisions according to type of scanner division I representing IneosX5 and division T representing t710 and division E representing E1.
Then design of a 2-element thick model in the form of rectangle with having a knob on one side and a hole on the other side, aimed to form a modular chain around the scan bodies as an auxillary geometic device used in the splinted group. Then scanning was done with the intraoral scanner each scanner scan 7times. And then the fabrication of the model through the indirect workflow with the use of open tray technique and splinting of the impression posts with floss and flowable composite.
Single step impression technique with addition silicone was done and pouring of the caat to get the gypsum models. And the securing the scanbodies to scan with the extra oral scanners.
Each scan body of the test scans was aligned through the CAD software to its corresponding CAD file of the ISB library in order to allow the digital analogue matching.
And then superimposition of the tested datasets with the initial design on the reverse engineering software (Geomagic control X) with the best fit alignment and calculation of the RMS to get the 3D deviation.
A color-difference map (qualitative data) and a report (quantitative Data) of the projections were obtained for every single superimposition process.
Also the calculation of the absolute linear distance between the scan bodies of the tested data sets on the reverse engineering software.
Data was recorded, tabulated and analyzed. Statistical work was done using t test.
Our results showed that:
1) No statistical significance difference between the direct and indirect workflow concerning the 3D deviation and the absolute linear deviation
2) No statistical significance difference between the 30ᵒ the 45ᵒ divergence of the posterior implants concerning the 3D deviation in the 2 different workflows
3) A statistical significance difference between the 30ᵒ the 45ᵒ divergence of the posterior implants concerning the linear deviation in the indirect workflow
4) A statistical significance difference between the different type of IOS in the direct workflow concerning the 3D deviation and linear deviation. The highest value of RMS and linear deviation was found in Medit i600 followed by trios 4 and Cerec primescan.
5) A statistical significance difference between the different type of EOS in the indirect workflow concerning the 3D deviation .The highest value of RMS was found in inEos x5 , followed by Medit 710 , while the lowest value was found in E1 3shape. While there was no significant difference between different groups in the difference of linear deviation.
6) A statistically significance difference between he splinted and the non-splinted group concerning the 3D deviation .Not splinted samples had a significantly higher value of RMS than splinted samples.while in the difference of linear value not splinted samples had a higher value than splinted samples yet the difference was not statistically significant.
7) A statistically significance difference concerning the difference in absolute linear deviation between the distance between 2 parallel implants and the distance between the straight and angled implant.
CONCLUSIONS
Within the limitation of our study, the following conclusions may be
drawn:
1) The accuracy of direct digital workflow is comparable with the indirect workflow
2) The increase in the divergence angle only affect the absolute linear distance in the indirect workflow and doesn’t have an effect on the direct digital workflow.
3) The type of scanner affects the accuracy of the direct and indirect workflow having the Cerec primescan as the most accurate IOS and E1 3shape as the most accurate EOS
4) Splinting of the scan bodies improves the accuracy of the direct workflow.
LIMITATIONS
1) In vitro model cannot accurately simulate hard and soft-tissue interaction, and it excludes adverse factors known to negatively affect the quality of impressions such as saliva, blood, cervicular fluid. Thus, the clinical reality may prove to be more challenging than conditions in this study.
2) The present study was carried out at room temperature (23 ᵒC) and not mouth temperature (37 ᵒC). Therefore, the thermal contraction of the conventional impression material was not modeled, and a more accurate impression was made than in clinical practice.