International Journal of Computerized Dentistry, 04/2017

Statement of problem: Three-dimensional (3D) intraoral scanning systems allow for the simultaneous acquisition of 3D information about tooth surfaces and a photorealistic view of the patient's tooth colors. Aim: The goal of this study was the in vivo comparison of a new 3D scanner with a color acquisition mode and conventional visual and digital color measurements. Materials and methods: The colors of 40 teeth of 20 patients were evaluated in seven ways: 1) By dentists using the Vita 3D-Master; 2) By dental technicians using the Vita 3D-Master; 3) With the 3Shape Trios device; 4) With the Vita Easyshade device; 5) With the Vita Easyshade Advance device; 6) With the SpectroShade device; and 7) With the SpectroShade Micro device. Digital measurements of Groups 3 to 7 were repeated three times for each tooth. For all groups, both the CIE Lab values and the Vita 3D-Master values were recorded. The repeatability and relative accuracy of the Vita 3D-Master values were analyzed statistically using Pearson's chi-squared test (α 0.05). ΔE values were calculated from the CIE Lab values, which served as a basis for performing multidimensional scaling (MDS) and evaluating differences between the groups using the one-way ANOVA with post hoc Tamhane's test (α 0.05). Results: The results of the ΔE values showed that clinically relevant differences between the evaluation by dentists, dental technicians, and the intraoral scanning device (3Shape) are negligible. The intraoral 3D scanning device (Group 3) and the digital systems (Groups 4 to 7) did not differ significantly in the repeatability of color shade management. The SpectroShade Micro (Group 7) had significantly better relative accuracy than the other devices. Conclusions: The results demonstrate that intraoral scanning systems can be used to measure both tooth color and tooth surface in 3D. Clinical implications: Intraoral optical scanning devices allow for the acquisition of accurate 3D surface data. Tooth color can be evaluated simultaneously and can be used to determine the color of restorations without requiring additional conventional color-measurement methods. Keywords: intraoral scanning, tooth color measurement, spectrophotometer, shade guide, CAD/CAM

Plaster casts can be digitized with desktop scanners, intraoral scanners, and recently also with cone beam computed tomography (CBCT). The aim of this study was to investigate the accuracy of five different CBCT devices digitizing a plaster cast. A study cast serving as a patient was made using the double mix impression technique, and the impression was poured out with plaster. On the resulting plaster cast, arch length (AL), intermolar width (IMW), and intercanine width (ICW) were measured by a coordinate measuring machine (CMM) (Zeiss O-Inspect 422). The patient cast was then scanned by five CBCT devices - CS 9300, CS 9300 Select, CS 8100 3D (all Carestream), Promax 3D Mid (Planmeca), and Whitefox (Acteon) - in eight scan modes. For each CBCT device, 37 scans were performed. The resulting DICOM data were exported as stereolithographic (STL) data and linearly measured using Convince Premium 2012 (3Shape) software. All measurements were compared to the reference master values of the patient cast. The accuracy measurements showed significant differences among the CBCT devices. The highest accuracy was achieved by Whitefox (IMW: mean ± standard deviation (SD): 5.5 ± 5.7 µm) and CS 9300 (IMW: -15 ± 7.4 µm). Comparable results with less accuracy were shown by CS 8100 3D (IMW: -81.2 ± 7.4 µm) and CS 300 Select (IMW: -82.2 ± 6.6 µm). Significantly lower accuracy was shown by Promax 3D Mid (IMW: -126.1 ± 4.8 µm). Some CBCT devices are suitable for the digitization of plaster casts and show very good clinical accuracy. Dental offices equipped with CBCT devices could digitize plaster casts without the need for additional devices. Keywords: CBCT devices, accuracy, indirect digitization, plaster cast, CAD/CAM, stereolithography

Objectives: To evaluate the in vitro accuracy of digital impressions for three-dimensional (3D) volumetric measurement of residual coronal tooth structure postendodontic cavity preparation, with reference to micro-computed tomography (μCT). Methods: Quantification of the accuracy and precision of the intraoral digital scanner (3M True Definition Scanner - IOS) was performed using a metrology gauge block and a profilometric calibration model. Thirty-four human extracted molars with endodontic access cavities were scanned using both intraoral scanning (test scanner) in high-resolution mode, and µCT (reference scanner: GE Locus SP μCT scanner) in high- (HiResCT) and low- (LoResCT) resolution modes. Comparisons of volumetric accuracy and 3D profilometric deviations were performed using surface metrology software. One-way repeated measures analysis of variance (ANOVA), in combination with the Bonferroni post hoc test, was implemented to compare the differences in volume measurements between scanning methods. Results: Digital scanning revealed smaller volume measurements by 1.36% and 0.68% compared to HiResCT and LoResCT, respectively. There was a statistically significant difference in the volumetric measurements obtained from the IOS scanner and both HiResCT and LoResCT scans (P 0.001). Analysis of the mean 3D profilometric deviations revealed that the IOS displayed greater surface deviation (± 27/33 μm) vs HiResCT and LoResCT (± 16/32 μm). Conclusions: Although volumetric measurements of endodontically accessed teeth were up to 1.36% smaller in comparison to µCT, the digital scanner was able to reliably measure the extra- and intracoronal aspect of the endodontically accessed tooth. Keywords: intraoral scanner, micro-computed tomography, endodontic cavity preparation, residual coronal tooth structure, volumetric, metrology

Objective: The aim of this study was to assess how faces with different lower facial height (LFH) were visually perceived by laypersons using eye-tracking technology. Materials and method: A total of 48 facial images of volunteers with different LFH (normodivergent, hypodivergent, hyperdivergent) were randomly viewed by 50 participants (25 male, 25 female) using Tobii Eye Tracker (Tobii T60, Tobii Technology AB, Sweden). Facial images with normal lower anterior facial height (LAFH) were used as the control group. All images were divided into three areas of interest (AOI): eyes, nose, and lower face. Eye movements of participants were analyzed with Tobii Studio software (version 3.3.1, Tobii Technology). Time to first fixation (TFF), fixation before (FB) (initial attentional capture), fixation duration (FD), and fixation count (FC) (sustained attention) parameters were measured and compared between image groups. Repeated measures ANOVA, independent samples t test, and intraclass correlation coefficient (ICC) were used for statistical analysis. Results: In all image groups, the eyes were the most remarkable area that was looked at most and longest. A significant main effect was revealed for TFF on the lower face area between image groups: F (2.98) = 9.61, P = 0.00, η2 = 0.164. The lower face area of the hyperdivergent images was found to capture initial attention faster than that of the other images. A significant main effect was revealed for FD on the lower face area between image groups: F (2.98) = 22.98, P = 0.00, η2 = 0.319. Conclusions: Increased and decreased LFH affected visual perception. The difference in LFH did not alter the hierarchy of visual perception. Keywords: lower facial height (LFH), visual perception, eye tracking

Objectives: Double-crown attachments, such as conical crowns (CCs), can retain removable partial prostheses. Digital manufacturing enables the use of innovative materials such as zirconia, and new workflows. The aim of this study was to investigate options for the adjustment of retention forces of all-zirconia CCs. Materials and methods: Single zirconia primary crowns were produced with convergence angles (α) of 3 and 4 degrees, together with monolithic zirconia secondary crowns (n = 8 for α = 3 degrees; n = 8 for α = 4 degrees). Retention was measured by fitting the crowns with forces F = 12.5 to 100 N, and evaluating the magnitudes of the forces required for loosening (L). L/F ratios were recorded, and the coefficient of friction (µ0) was calculated. To limit the maximum force required for loosening, and to prevent high tensile stresses within the crowns, the width of the occlusal gap between the primary and secondary crowns was limited by the implementation of occlusal stops. Results: True convergence angles were more conical than expected, by approximately 0.3 degrees. For α = 3 degrees and α = 4 degrees, L/F ratios were 0.308 (SD 0.04) and 0.208 (SD 0.068), respectively. The overall coefficient of static friction was µ0 = 0.113. Maximum retention forces were successfully controlled; the average values were 12.1 N (SD 4.5 N) for zirconia occlusal stops, and 12.8 N (SD 3.3 N) for composite occlusal stops. Conclusion: The clinically desired L/F ratio of 1/3 was achieved by selecting 3-degree burs for fabrication of all-zirconia CCs. It is possible to limit retention, thereby reducing tensile stress in the circumferential direction in secondary crowns. Keywords: CAD/CAM, prosthetic dentistry, bioengineering, biomechanics, ceramics, removable dental prosthesis

The last few decades have seen an upward trend of the pathologies of abrasion, erosion, and abfraction. These pathologies, especially in combination, can provoke a significant loss of tooth substance. Nowadays, modern digital chairside technologies and new restorative materials allow clinicians to restore the lost tooth structure with a minimally invasive and fully digital approach. This article describes a step-by-step procedure of a full-mouth rehabilitation performed with a total digital chairside approach in several appointments. Keywords: Digital workflow, CAD/CAM, full-mouth rehabilitation, DVO augmentation