Trueness and precision of scanning abutment impressions and stone models according to dental CAD/CAM evaluation standards

PURPOSE: The purpose of the present study was to compare scanning trueness and precision between an abutment impression and a stone model according to dental computer-aided design/computer-aided manufacturing (CAD/CAM) evaluation standards. MATERIALS AND METHODS: To evaluate trueness, the abutment impression and stone model were scanned to obtain the first 3-dimensional (3-D) stereolithography (STL) file. Next, the abutment impression or stone model was removed from the scanner and re-fixed on the table; scanning was then repeated so that 11 files were obtained for each scan type. To evaluate precision, the abutment impression or stone model was scanned to obtain the first 3-D STL file. Without moving it, scanning was performed 10 more times, so that 11 files were obtained for each scan type. By superimposing the first scanned STL file onto the other STL files one by one, 10 color-difference maps and reports were obtained; i.e., 10 experimental scans per type. The independent t-test was used to compare root mean square (RMS) data between the groups (α=.05). RESULTS: The RMS±SD values of scanning trueness of the abutment impression and stone model were 22.4±4.4 and 17.4±3.5 µm, respectively (P < .012). The RMS±SD values of scanning precision of the abutment impression and stone model were 16.4±2.9 and 14.6±1.6 µm, respectively (P=.108). CONCLUSION: There was a significant difference in scanning trueness between the abutment impression and stone model, as evaluated according to dental CAD/CAM standards. However, all scans showed high trueness and precision.

Evaluation of the reproducibility of various abutments using a blue light model scanner

PURPOSE: To evaluate the reproducibility of scan-based abutments using a blue light model scanner. MATERIALS AND METHODS: A wax cast abutment die was fabricated, and a silicone impression was prepared using a silicone material. Nine study dies were constructed using the prepared duplicable silicone, and the first was used as a reference. These dies were classified into three groups and scanned using a blue light model scanner. The first three-dimensional (3D) data set was obtained by scanning eight dies separately in the first group. The second 3D data set was acquired when four dies were placed together in the scanner and scanned twice in the second group. Finally, the third 3D data set was obtained when eight dies were placed together in the scanner and scanned once. These data were then used to define the data value using third-dimension software. All the data were then analyzed using the non-parametric Kruskal–Wallis H test (α=.05) and the post-hoc Mann-Whitney U-test with Bonferroni's correction (α=.017). RESULTS: The means and standard deviations of the eight dies together were larger than those of the four dies together and of the individual die. Moreover, significant differences were observed among the three groups (P < .05). CONCLUSION: With larger numbers of abutments scanned together, the scan becomes more inaccurate and loses reproducibility. Therefore, scans of smaller numbers of abutments are recommended to ensure better results.

Repeatability and reproducibility of individual abutment impression, assessed with a blue light scanner

PURPOSE: We assessed the repeatability and reproducibility of abutment teeth dental impressions, digitized with a blue light scanner, by comparing the discrepancies in repeatability and reproducibility values for different types of abutment teeth. MATERIALS AND METHODS: To evaluate repeatability, impressions of the canine, first premolar, and first molar, prepared for ceramic crowns, were repeatedly scanned to acquire 5 sets of 3-dimensional data via stereolithography (STL) files. Point clouds were compared and the error sizes were measured (n=10, per type). To evaluate reproducibility, the impressions were rotated by 10-20° on the table and scanned. These data were compared to the first STL data and the error sizes were measured (n=5, per type). One-way analysis of variance was used to assess the repeatability and reproducibility of the 3 types of teeth, and Tukey honest significant differences (HSD) multiple comparison test was used for post hoc comparisons (α=.05). RESULTS: The differences with regard to repeatability were 4.5, 2.7, and 3.1 µm for the canine, premolar, and molar, indicating the poorest repeatability for the canine (P<.001). For reproducibility, the differences were 6.6, 5.8, and 11.0 µm indicating the poorest reproducibility for the molar (P=.007). CONCLUSION: Our results indicated that impressions of individual abutment teeth, digitized with a blue light scanner, had good repeatability and reproducibility.

Accuracy of 3D white light scanning of abutment teeth impressions: evaluation of trueness and precision

PURPOSE: This study aimed to evaluate the accuracy of digitizing dental impressions of abutment teeth using a white light scanner and to compare the findings among teeth types. MATERIALS AND METHODS: To assess precision, impressions of the canine, premolar, and molar prepared to receive all-ceramic crowns were repeatedly scanned to obtain five sets of 3-D data (STL files). Point clouds were compared and error sizes were measured (n=10 per type). Next, to evaluate trueness, impressions of teeth were rotated by 10degrees-20degrees and scanned. The obtained data were compared with the first set of data for precision assessment, and the error sizes were measured (n=5 per type). The Kruskal-Wallis test was performed to evaluate precision and trueness among three teeth types, and post-hoc comparisons were performed using the Mann-Whitney U test with Bonferroni correction (alpha=.05). RESULTS: Precision discrepancies for the canine, premolar, and molar were 3.7 microm, 3.2 microm, and 7.3 microm, respectively, indicating the poorest precision for the molar (P<.001). Trueness discrepancies for teeth types were 6.2 microm, 11.2 microm, and 21.8 microm, respectively, indicating the poorest trueness for the molar (P=.007). CONCLUSION: In respect to accuracy the molar showed the largest discrepancies compared with the canine and premolar. Digitizing of dental impressions of abutment teeth using a white light scanner was assessed to be a highly accurate method and provided discrepancy values in a clinically acceptable range. Further study is needed to improve digitizing performance of white light scanning in axial wall.

White light scanner-based repeatability of 3-dimensional digitizing of silicon rubber abutment teeth impressions

PURPOSE: The aim of this study was to evaluate the repeatability of the digitizing of silicon rubber impressions of abutment teeth by using a white light scanner and compare differences in repeatability between different abutment teeth types. MATERIALS AND METHODS: Silicon rubber impressions of a canine, premolar, and molar tooth were each digitized 8 times using a white light scanner, and 3D surface models were created using the point clouds. The size of any discrepancy between each model and the corresponding reference tooth were measured, and the distribution of these values was analyzed by an inspection software (PowerInspect 2012, Delcamplc., Birmingham, UK). Absolute values of discrepancies were analyzed by the Kruskal-Wallis test and multiple comparisons (alpha=.05). RESULTS: The discrepancy between the impressions for the canine, premolar, and molar teeth were 6.3 microm (95% confidence interval [CI], 5.4-7.2), 6.4 microm (95% CI, 5.3-7.6), and 8.9 microm (95% CI, 8.2-9.5), respectively. The discrepancy of the molar tooth impression was significantly higher than that of other tooth types. The largest variation (as mean [SD]) in discrepancies was seen in the premolar tooth impression scans: 26.7 microm (95% CI, 19.7-33.8); followed by canine and molar teeth impressions, 16.3 microm (95% CI, 15.3-17.3), and 14.0 microm (95% CI, 12.3-15.7), respectively. CONCLUSION: The repeatability of the digitizing abutment teeth's silicon rubber impressions by using a white light scanner was improved compared to that with a laser scanner, showing only a low mean discrepancy between 6.3 microm and 8.9 microm, which was in an clinically acceptable range. Premolar impression with a long and narrow shape showed a significantly larger discrepancy than canine and molar impressions. Further work is needed to increase the digitizing performance of the white light scanner for deep and slender impressions.

The Clinical Study on the Epileptiform Discharges and Imaging Study in Newborn with Seizures

PURPOSE: Neonatal seizures are mostly symptomatic and have variable atypical clinical features with very different EEG findings from those of post-neonatal period. This study was performed to determine the common types of epileptiform discharges and their relationship with abnormalities in imaging study in neonates with seizures. METHODS: Fourty one neonates under 7 days of age who had been hospitalized at the Hanyang university hospital from June 1993 to May 1997 were studied retrospectively. Their medical records, results of EEG and brain imaging study were reviewed. RESULTS: 1) The types of neonatal seizures were subtle, generalized tonic, multifocal clonic, focal clonic, myoclonic in order of frequency. 2) The most common epileptiform discharge was excessive sharp transients recorded in 28 cases and the rest showed multifocal spikes, sharp waves, repetitive alpha, repetitive theta in order. Epileptiform discharges appeared on the both hemisphere in 24 cases, right hemisphere in 9 cases and left hemisphere in 8 cases. 3) Imaging study showed no abnormal findings in 27 cases and abnormal findings in 14 cases such as brain edema, intracranial hemorrhage, leukomalacia, subarachnoid hemorrhage, cephalhematoma, craniosynostosis. 4) Among 14 cases with radiological abnormalities, 5 cases had localized abnormalities and 3 of them had the abnormal EEG discharges on the same area concomittantly. But in total only 3 cases of 17 cases with localized epileptiform discharges had abnormalities in imaging study on the same site and so significant relationship between two studies was not observed. 5) As for the prognosis of seizures, subsided in 23 cases without any antiepileptic drugs, 13 cases had no seizure after taking medicine for few days and 5 cases needed continuous antiepileptic drug. CONCLUSION: This study showed no meaningful relationship between abnormal EEG findings and localization by imaging study in neonatal seizure but we concluded that brain imaging study was needed to determine degree of encephalopathy in neonatal seizures.