Accuracy Of Full Arch Scans With Intraoral Scanner And Accuracy Of Scan Results Between Examiners

Objectives:Intraoral scanners are used alternatively to conventional impression techniques and materials.The aims of this study were to evaluate the accuracy of full arch scans with iTero scanner(Align Technology,San Jose,Calif,USA)under in-vivo condition and in-vitro condition.In addition,we bring out an in-vitro study to evaluate the accuracy of scan results between examiners using standard stone models.Materials and Methods:1.Evaluation of the accuracy of full arch scans15 subjects were included in this study and three types of digital models of their arches were taken.They received full-arch intraoral scans with iTero and the scans were converted into digital models(Group T).Then the subjects had conventional impressions with polyvinyl siloxane material,stone cast models manufactured from the impressions were digitized with iTero(Group D)and an extraoral scanner(Activity888,Smart optics,Germany),the latter scans were used as reference models(Group P)to evaluate the trueness.1 subject received full-arch intraoral scans with iTero 10 times and his stone models were taken full-arch extraoral scans with iTero 10 times to evaluate the precision.2.Evaluation of the accuracy of scan results between examinersStandard stone models which can fit with the head-simulator are objects in this study and scans using extraoral scanner are named as RU?RL.Each examiner scan the model which are fixed in head-simulator and out of the head-simulator under direct vision and named the scans as A1TU-A10TU,A1TL-A10TL B1TU-B10TU,B1TL-B10TL respectively.3.Image processing and statisticsAll the.stl files were aligned and trimmed in 3D reverse engineering software,test models were registered with corresponding reference models under best-fit-alignment and then record results of 3D analysis.Kolmogorov-Smirnoff was used to test the normal distribution of each group,and the homogeneity of variance was tested by Levene's test.If the data has normal distribution and homogeneity of variance,the t test was used to compare the differences between the two groups,if not,the Kruskal-Wallis test was used.P<0.05 means significant difference.Results:1.Evaluation of the accuracy of full arch scans with iTeroThe trueness of intraoral scans is 100.0±26.9?m,of extraoral scans of stone models is 80.74±20.33?m,the trueness between two conditions had significant differences,P<0.01.The precision of intraoral scans is 77.05±12.73pm,of extraoral scans of stone models is 46.72±16.35?m,the precision between two conditions had significant differences,P<0.01.2.Evaluation of the accuracy of scan results between examinersWhile using head-simulator,the trueness of iTero was 104.80±13.41?m,the trueness between upper and lower arch had significant differences.Under direct vision,the trueness of iTero was 106.36±12.37?m,the trueness between upper and lower arch had significant differences.The trueness between two conditions had no significant difference,P>0.05.While using head-simulator,the precision of iTero was 49.40±19.10?m.Under direct vision,the precision of iTero was 59.54±19.43?m,the precision between upper and lower arch had significant differences.The trueness between two conditions had significant differences,P<0.01.Conclusions:1.The accuracy of iTero in full arch scans is clinically acceptable while using model scans from Activity 888 as reference,but accuracy of iTero in extraoral scans is better than it in intraoral scans.2.Scan results between examiners in-vitro study have acceptable trueness and precision,but all the examiners should receive correct training.