الفهرس 
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Abstract
The quality of the implant supported prosthesis and its long-term survival depends on the accuracy of the workflow components. CAD/CAM technologies allow the full digitization of the workflow, using IOSs and digital manufacturing techniques.
The main feature to be evaluated in an intraoral scanner is accuracy. According to ISO 12836, the accuracy of an impression technique is defined in terms of trueness and precision. Trueness is defined as the difference in measurement between the reference model and the scan model and precision is the difference in measurement between digital models created using the same impression technique.
This in-vitro study was designed to evaluate the effect of scanners accuracy of two intraoral scanners (Cerec Omnicam and Cerec Primescan) on the fabrication of implant-supported fixed partial dentures.
For the trueness measurement, an additively manufactured model was scanned using a desktop scanner (inEos X5) which was used as the reference scanner to obtain the reference dataset. The two intraoral scanners were used to record 15 different impressions (n=15) and with the help of a reverse engineering 3D analysis software (Geomagic Control X), the digitized measurement models were superimposed on the reference to calculate the amount of deviation or RMS value of error.
For the precision measurement, the calculations were done within each subgroup. Each scan was considered as the reference superimposing the remaining 14 scans to calculate the amount of deviation or RMS value of error.
The technique of fabrication is one of the factors which affects the marginal adaptation and accuracy of provisional dental prosthesis. The CADCAM techniques (subtractive and additive manufacturing techniques) for the construction of interim implant supported fixed partial dentures were recently introduced. However, there is minimal scientific evidence which technique is more effective for producing implant- supported provisional dental prosthesis with predictable accuracy.
The aim of the present study was to compare the accuracy of implant-supported fixed partial dentures fabricated by two different digital methods, subtractive and additive manufacturing techniques, and to evaluate the effect of the two techniques on the marginal fit of implant- supported provisional dental prosthesis.
24 interim fixed partial dentures were constructed, 12 subtractively manufactured FPDs and 12 additively manufactured FPDs (n=12 per each group) and seated over ti-bases, ready for 3D trueness evaluation. Optical impressions (STL file) for each of the 24 manufactured FPDs were done and superimposed on the original CAD file using 3D analysis software (Geomagic Control X). The RMS of error was calculated for each of the test groups. Finally, color difference maps and reports were generated for all the test groups. Data was recorded, tabulated, and analyzed. Statistical work was done using the Mann-Whitney U test.
Lastly, the marginal fit of the manufactured FPDs was assessed by using stereomicroscope. Four equidistant measurement points were taken from each surface (buccal, lingual, mesial/ distal) with a total of 12 points for each retainer of the FDP and with the aid of an image analysis software, the marginal gap was evaluated qualitatively for all these points. Data obtained was collected, tabulated, and subjected to statistical analysis.
Results:
Regarding the accuracy of intraoral scanners, the best trueness values were recorded by Primescan as it showed the least deviations values from the reference scan. Regarding precision of intraoral scanners, no statistical difference was found between the two intraoral scanners.
Regarding the 3D trueness of the manufactured interim FPDs, there was a statistically significant difference between the subtractive and additively manufactured FPDs, where the subtractively manufactured FPSs showed less deviation values than the additively manufactured FPDs.
Regarding the marginal area trueness of manufactured interim FPDs, no statistical differences were found between subtractively manufactured and additively manufactured ones.
Regarding the marginal fit of the manufactured FDPs, the results showed that there was statistically significant difference between the marginal gap values of the two tested groups where the subtractively manufactured FPSs showed less gap values than the additively manufactured FPDs.