الفهرس 
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Abstract
This in vitro study was designed to evaluate the accuracy of different digital /conventional acquisition techniques in recording an edentulous full arch for designing of implant supported all on four prosthesis and their effect on the passivity of fit of the implant supported frameworks.
A master model adopting all on four concept was designed and fabricated utilizing CAI/CAD/CAM technology, first it was designed on CAD software by importing patient’s DICOM files from CBCT images then an STL file was exported to a stereolithography technology based 3d printer. This edentulous master model was to be recorded by different means. In the current study samples were divided into three groups according to method of recording data as follows:
group 1 = Direct digital impression (n=10)
group 2 = Digital impression with auxiliary device (n=10)
group 3 = Conventional impression (n=10)
The scans of each group were tested for their accuracy. Trueness was tested manifesting the deviation of the measurements in each group set compared to the actual dimensions of the scanned object by using a reference scan of the master model utilizing a high-resolution laboratory desktop scanner (inEosx5). Precision was tested manifesting the degree of reproducibility between repeated measurements within the same group. All 3d deviations were measured by superimpositioning of STL files on reverse engineering software (Geomagic Studio 12). The superimpositions results were illustrated as a color difference map. 3D deviation between every 2 scans was measured as arithmetic mean value that was converted to (RMS) root mean square values resulting from the superimpositions.
Within each group the best 6 scans regarding trueness and precision in which they recorded the lowest deviations were selected to design implant supported PMMA bar frameworks, design was carried out on CAD software (Exocad).
A total of 18 frameworks were milled by a 5 axis milling machine, six frameworks from each group, after their production they were all seated on the master model and tested for their passivity of fit by using the one screw test in which only one screw was tightened and marginal discrepancies at the framework/multiunit abutment interface were recorded by imaging with a digital microscope under 40x magnification then importing the scans to a calibrated image software to calculate the marginal discrepancies in microns at the non-screwed implant sites.
All the data was collected, tabulated and statistically analyzed.
Numerical data were explored for normality by checking the distribution of data and using tests of normality (Kolmogorov-Smirnov and Shapiro-Wilk tests). All data showed non-normal (non-parametric) distribution. Data were presented as median and range values. Mann-Whitney U test was used for comparison between two groups. Kruskal-Wallis test was used for comparisons between more than two groups. Dunn’s test was used for pair-wise comparisons when Kruskal-Wallis test is significant.
The significance level was set at P≤ 0.05. Statistical analysis was performed with IBM® SPSS® Statistics Version 20 for Windows.
There was a statistically significant difference between trueness of the three groups (p-value <0.001, effect size=0.941) Digital impression with auxiliary device group showed the statistically significantly lowest mean deviation (hence the highest trueness), followed by the direct digital impression group and the conventional impression group came last with the highest mean deviation value (hence the lowest trueness).
There was a statistically significant difference between precision of the three groups (p-value < 0.001, effect size = 0.230). Conventional impression with auxiliary device group showed the statistically significantly lowest mean deviation (hence the highest precision), followed by the direct digital impression with auxillary device group and direct digital group came last with the highest mean deviation value (hence the lowest trueness).
There was a statistically significant difference between gap distances in the three groups (p-value < 0.001, effect size = 0.1914). Pair-wise comparisons between techniques revealed that Conventional impression showed the statistically significantly highest mean gap distance. Direct digital impression showed statistically significantly lower mean value. Digital impression with auxiliary device showed the statistically significantly lowest mean gap distance.
7. CONCLUSIONS
Within the limitations of this study, the following conclusions could be drawn:
1. Both digital and conventional impressions were found to be clinically valid workflows to record a full arch implant supported restorations and produce frameworks with clinically acceptable passivity.
2. Accuracy and predictability are advocated by the IOS to be a reliable alternative to the conventional workflow for implant full arch rehabilitation.
3. Digital impression with the aid of an auxiliary device delivered the most accurate scans as both trueness and precision values were improved; redeeming it as an accurate and efficient method for full arch registration.
4. The digital impression with the aid of auxiliary device exhibited the most superior fit, on equal terms the two digital approaches generally resulted in overall more accurate fit with less marginal gap when compared to conventional impression.