Analysis of the impact of the facial scanning method on the precision of a virtual facebow record technique: An in vivo study.

STATEMENT OF PROBLEM: Virtual facebow record techniques typically record the relationship of a maxillary digital scan to facial landmarks by aligning it to a 3-dimensional face scan. Three-dimensional face scans can be acquired with different facial scanning methods, but the impact of the facial scanning method on the accuracy (trueness and precision) of a virtual facebow record technique remains unclear. PURPOSE: The purpose of this in vivo study was to assess the impact of the facial scanning method on the precision under the repeatability conditions (repeatability) of a virtual facebow record technique. MATERIAL AND METHODS: Repeatability of the virtual facebow record technique with the following 3 clinical-grade facial scanning methods was determined and compared: a professional handheld scanner based on structured blue light scanning technology (PHS method); an attachment-type 3-dimensional sensor camera connected to a tablet and controlled with a mobile application (3DSC-T method); and a smartphone with an integrated 3-dimensional sensor camera controlled with a mobile application (3DSC-S method). To determine the repeatability of the virtual facebow record technique with each facial scanning method, 8 virtual facebow records of a completely dentate adult with class I occlusion and mesoprosopic facial form were obtained (8×3=24 in total); with these, 8 locations of a maxillary digital scan with respect to a common 3-dimensional face scan were obtained. Repeatability was determined in terms of deviations between located maxillary digital scans, determined, in turn, by calculating the distances between corresponding vertices for each of the possible nonrepeating combinations of pairs of located maxillary digital scans (8C2=28). Finally, the repeatability of the virtual facebow record technique with the different facial scanning methods was compared by using the Welch ANOVA test and the post hoc Games-Howell test (both α=.05). RESULTS: The repeatability of the virtual facebow record technique with PHS, 3DSC-T, and 3DSC-S facial scanning methods resulted in 0.243 ±0.094 mm, 0.437 ±0.171 mm, and 1.023 ±0.399 mm, respectively. Comparison of these results revealed that the facial scanning method had a statistically significant effect on the repeatability of the virtual facebow record technique (P<.001) and that its repeatability was statistically significantly greater with the PHS facial scanning method than with the 3DSC-T and 3DSC-S facial scanning methods and greater with the 3DSC-T facial scanning method than with the 3DSC-S facial scanning method (P<.001 for all pairwise comparisons). CONCLUSIONS: This study found that the facial scanning method had a great impact on the repeatability of the virtual facebow record technique and that the virtual facebow record technique was more repeatable with more accurate facial scanning methods.

Evaluation of repeatability of different alignment methods to obtain digital interocclusal records: An in vitro study.

STATEMENT OF PROBLEM: The alignment of the maxillary and mandibular digital scans obtained with an intraoral scanner (IOS) generates digital interocclusal records. Although the accuracy of maxillary and mandibular digital scans obtained from an IOS is widely studied, the accuracy of digital interocclusal records obtained with them is not; even less studied is the accuracy (trueness and precision) of the alignment methods that are available to obtain them. PURPOSE: The purpose of this in vitro study was to assess the precision under repeatability conditions (repeatability) of the different alignment methods used to obtain digital interocclusal records. MATERIAL AND METHODS: Digital scans of maxillary and mandibular casts of a dentate healthy adult were acquired with an IOS. Casts were then mounted in maximum intercuspal position in a semi-adjustable mechanical articulator (1801 AR Model PSH Articulator), and left and right occlusal digital scans were acquired with the IOS. Occlusal digital scans were repeated 7 times under repeatability conditions. After obtaining each pair of occlusal digital scans, the software program of the IOS automatically aligned the maxillary and mandibular digital scans with occlusal digital scans (TRI method), resulting in 7 digital interocclusal records composed of aligned maxillary and mandibular digital scans and occlusal digital scans. All 7 sets of aligned digital scans were exported and realigned in a dental computer-aided design software program by means of global and reference alignment methods (EXO-B and EXO-R methods, respectively). To assess the repeatability, the 7 aligned digital scan sets of each group were repositioned in the common coordinate system by aligning maxillary digital scans, and repeatability was calculated in terms of the distance between the vertices of the mandibular digital scans for each of the possible nonrepeating combinations of pairs (7C2=21). The repeatability was tested by using the Kruskal-Wallis test for nonparametric distribution followed by the Mann-Whitney U test and Bonferroni correction for pairwise comparisons (α=.05). RESULTS: The median with interquartile range for the TRI alignment method was 47 (27) µm for the EXO-B method 41 (25) µm and 16 (5) µm for EXO-R. The Kruskal-Wallis test showed statistical difference between test groups (P<.05). The post hoc Dunn test with Bonferroni adjustment detected significant statistical differences between the EXO-R-TRI (P<.001) and EXO-R-EXO-B (P<.001) alignment methods. CONCLUSIONS: This study found that the alignment method could influence the repeatability of digital interocclusal records. The reference best-fit alignment method (EXO-R) provided better repeatability.

Analysis of the influence of the facial scanning method on the transfer accuracy of a maxillary digital scan to a 3D face scan for a virtual facebow technique: An in vitro study.

STATEMENT OF PROBLEM: With the emergence of virtual articulators, virtual facebow techniques have been developed for mounting maxillary digital scans to virtual articulators. Different scanning methods can be used to obtain 3D face scans, but the influence that these methods have on the accuracy with which a maxillary digital scan is transferred to a 3D face scan is unknown. PURPOSE: The purpose of this in vitro study was to analyze the influence of the facial scanning method on the accuracy with which a maxillary digital scan is transferred to a 3D face scan in a virtual facebow technique. MATERIAL AND METHODS: According to a virtual facebow technique, a maxillary digital scan was transferred to a standard virtual patient-who had the maxillary digital scan in its real location-guided by an intraoral transfer element by using different 3D face scans with the intraoral transfer element in place (reference 3D face scans) obtained with 2 different scanning methods: 10 obtained with an accurate scanning method based on structured white light technology and 10 obtained with a less accurate scanning method based on structure-from-motion technology. For each situation, deviation between the maxillary digital scan at the location obtained via the virtual facebow technique and at its real location was obtained in terms of distance by using a novel methodology. From these distances, the accuracy was assessed in terms of trueness and precision, according to the International Organization for Standardization (ISO) 5725-1. The Student t test with Welch correction was used to determine if the accuracy with which the maxillary digital scan was transferred to the standard virtual patient was influenced by the facial scanning method used to obtain the reference 3D face scans (α=.05). RESULTS: Significant differences (P<.05) were found among the trueness values obtained when using the different facial scanning methods, with a very large effect size. A trueness of 0.138 mm and a precision of 0.022 mm were obtained by using the structured white light scanning method, and a trueness of 0.416 mm and a precision of 0.095 mm were acquired when using the structure-from-motion scanning method. CONCLUSIONS: The accuracy with which a maxillary digital scan is located with respect to a 3D face scan in a virtual facebow technique is strongly influenced by the facial scanning method used.

Use of measuring gauges for in vivo accuracy analysis of intraoral scanners: a pilot study.

PURPOSE: The purpose of this study is to present a methodology to evaluate the accuracy of intraoral scanners (IOS) used in vivo. MATERIALS AND METHODS: A specific feature-based gauge was designed, manufactured, and measured in a coordinate measuring machine (CMM), obtaining reference distances and angles. Then, 10 scans were taken by an IOS with the gauge in the patient's mouth and from the obtained stereolithography (STL) files, a total of 40 distances and 150 angles were measured and compared with the gauge's reference values. In order to provide a comparison, there were defined distance and angle groups in accordance with the increasing scanning area: from a short span area to a complete-arch scanning extension. Data was analyzed using software for statistical analysis. RESULTS: Deviations in measured distances showed that accuracy worsened as the scanning area increased: trueness varied from 0.018 ± 0.021 mm in a distance equivalent to the space spanning a four-unit bridge to 0.106 ± 0.08 mm in a space equivalent to a complete arch. Precision ranged from 0.015 ± 0.03 mm to 0.077 ± 0.073 mm in the same two areas. When analyzing angles, deviations did not show such a worsening pattern. In addition, deviations in angle measurement values were low and there were no calculated significant differences among angle groups. CONCLUSION: Currently, there is no standardized procedure to assess the accuracy of IOS in vivo, and the results show that the proposed methodology can contribute to this purpose. The deviations measured in the study show a worsening accuracy when increasing the length of the scanning area.

Determining the requirements, section quantity, and dimension of the virtual occlusal record.

STATEMENT OF PROBLEM: Conventional methods associated with many processes in dentistry are being replaced by methods that use digital technology. One of these processes is the making of occlusal records for the positioning of casts in a virtual articulator. Conventional interocclusal records and the articulator are currently being replaced by the intraoral virtual occlusal record and the virtual articulator. PURPOSE: The purpose of this study was to determine the requirements, quantity, and dimensions of the virtual occlusal record procedure in order to locate the mandibular cast's 3-dimensional (3D) spatial position in reference to its corresponding maxillary cast on a virtual articulator. MATERIAL AND METHODS: For the conventional procedure, 6 sets of casts were located in maximal intercuspal position without any interocclusal record. Then, using articulating paper, the occlusal contacts were determined. Afterward, the occlusal relationships and stone cast were digitized with a 3D scanner. To locate the maxillary cast, the occlusal contacts were compared by taking different sections as the virtual occlusal record. Finally, the optimum dimension of the virtual occlusal record was determined. RESULTS: This study determines the requirements, quantity, and dimensions of the virtual occlusal record using current reverse engineering tools. The combinations of the sections were first determined as follows: 3 sections (2 lateral and 1 frontal) and 2 lateral sections proved to be the most accurate. Then, the predictive values (PV) for dimension determination for the left-right lateral combination were calculated. CONCLUSIONS: The main conclusion of this study was that the combination of left and right lateral occlusal records was the most convenient. Additionally, the minimum optimum dimension for a virtual occlusal record was 12×15 mm.