Trueness of extra-oral scanner in relation to two span lengths. An in-vitro study

Statement of the problem:
Extraoral scanners have been used widely nowadays however there are certain conditions that could affect their accuracy which will subsequently affect the success of the final restoration.
Objective:
The aim of this study was to determine the accuracy of extraoral scanner in relation to two span lengths.
Materials and methods:
A typodont (Nissin Dental, Kyoto Japan) was used and two bridges with different span lengths were prepared, the first one with missing upper left second premolar (short straight span (GS)) and the other with missing upper left first and second premolars (long curved span (GL)). Indentations were made on each abutment to be taken as a reference for measurements. For both groups reference scan was taken by inEos X5 extra-oral scanner. Then five physical impression was taken for each group using vinylpolysiloxane impression material (Honigum, Germany) and then poured into type IV dental stone. Casts of each group were scanned using DOF extraoral scanner (DOF Company, Korea). Measurements were made from the indentations on the reference scan and the sample scans, compared with each-other and root mean square value (RMS) was obtained to evaluate the trueness.
Results:
Comparison between short and long span bridges revealed that there was no statistically significant difference between trueness values of short and long span bridges. Where RMS mean for the short span was 0.0727 mm and that for the long span was 0.1069 mm.
Conclusions:
Different span lengths do not seem to affect the trueness of the extra-oral scanner tested.