Research Spotlight

Wu, J., Y. Tian, L. Han, C. Liu, T. Sun, L. Li, Y. Yu, B. Lamichhane, R. N. D’Souza, S. E. Millar, R. Krumlauf, D. M. Ornitz, J. Q. Feng, O. Klein, H. Zhao, F. Zhang, R. J. Linhardt and X. Wang (2020). “FAM20B-catalyzed glycosaminoglycans control murine tooth number by restricting FGFR2b signaling.” BMC Biol 18(1): 87.

Full text of this article.

BACKGROUND: The formation of supernumerary teeth is an excellent model for studying the molecular mechanisms that control stem/progenitor cell homeostasis needed to generate a renewable source of replacement cells and tissues. Although multiple growth factors and transcriptional factors have been associated with supernumerary tooth formation, the regulatory inputs of extracellular matrix in this regenerative process remains poorly understood. RESULTS: In this study, we present evidence that disrupting glycosaminoglycans (GAGs) in the dental epithelium of mice by inactivating FAM20B, a xylose kinase essential for GAG assembly, leads to supernumerary tooth formation in a pattern reminiscent of replacement teeth. The dental epithelial GAGs confine murine tooth number by restricting the homeostasis of Sox2(+) dental epithelial stem/progenitor cells in a non-autonomous manner. FAM20B-catalyzed GAGs regulate the cell fate of dental lamina by restricting FGFR2b signaling at the initial stage of tooth development to maintain a subtle balance between the renewal and differentiation of Sox2(+) cells. At the later cap stage, WNT signaling functions as a relay cue to facilitate the supernumerary tooth formation. CONCLUSIONS: The novel mechanism we have characterized through which GAGs control the tooth number in mice may also be more broadly relevant for potentiating signaling interactions in other tissues during development and tissue homeostasis.

Reynolds, J. Z., R. A. Augsburger, K. K. H. Svoboda and P. Jalali (2020). “Comparing dentinal tubule penetration of conventional and ‘HiFlow’ bioceramic sealers with resin-based sealer: An in vitro study.” Aust Endod J.

Full text of this article.

This study compared the depth and percentage of dentinal tubule penetration for single-cone (SC) and warm vertical (WV) obturation techniques with two different bioceramic sealers (BC Sealer [BCS], BC Sealer HiFlow [BCSHF]) and an epoxy resin-based sealer (2Seal easymiX). Fifty canals were filled with BCS, BCSHF or resin-based sealer (RBS). Teeth in BCS and BCSHF groups were filled with SC or WV techniques, and teeth in the control group (RBS) filled with WV technique only. The roots were sectioned at 3 mm and 6 mm levels from the apex and evaluated with a confocal laser microscope. There was significantly greater depth and percentage of sealer penetration at the 6 mm section compared to 3 mm (P < 0.05). No statistically significant difference was found in sealer type or obturation technique at the examined levels (P > 0.05). In conclusion, dentinal tubule penetration was similar comparing BC Sealer, BC Sealer HiFlow and RBS using SC and WV techniques.

Revilla-León, M., J. A. Sorensen, L. Y. Nelson, I. Gamborena, Y. M. Yeh and M. Özcan (2020). “Effect of fluorescent and nonfluorescent glaze pastes on lithium disilicate pressed ceramic color at different thicknesses.” J Prosthet Dent.

Full text of this article.

STATEMENT OF PROBLEM: Materials possessing fluorescent properties are assumed to emit sufficient visible light to change tooth color under daylight illumination. Fluorescent and nonfluorescent glaze pastes are available to finish the surface of a pressed lithium disilicate restoration. However, the effect of a fluorescent-glaze layer on the final color of the restoration remains unclear. PURPOSE: The purpose of this in vitro study was to measure the color dimensions of lithium disilicate glass ceramic with different thicknesses and different surface treatments under daylight (D65) illumination conditions. MATERIAL AND METHODS: A total of 120 pressed lithium disilicate glass ceramic disks were fabricated with 4 different thicknesses: 0.7, 1.2, 1.7, and 2.2 mm. In each thickness, 3 different subgroups were created based on the surface treatment performed (n=10): polished (NG), clear glaze (CG), and fluorescent glaze (FG). For the NG group, disks were polished with 180-, 320-, 600-, 800-, and 1400-grit SiC papers and a polishing machine. For the glazed groups, the CG and FG groups, the specimens were polished with 180-grit SiC papers and the same polishing machine. After the polishing sequence, the final thickness was verified in all groups by using digital calipers (0.5, 1.0, 1.5, and 2.0 mm). Additionally, 20 μL of clear glaze or fluorescent glaze was applied on the CG and FL groups by using an electronic positive displacement repeating pipette. The glaze layer was crystallized in a furnace according to the manufacturer recommendations. Color measurements in the CIELab coordinates were made with a spectrometer coupled to an integrating sphere and a standardized photography gray card as a background. Color difference (ΔE) values were calculated by using the CIE76 and CIEDE2000 formulas. The Shapiro-Wilk test revealed that the data were normally distributed. Two-way ANOVA and the Bonferroni test for multiple comparisons were used to analyze the data (α=.05). RESULTS: Statistically significant differences were found among the groups for the L∗, a∗, and b∗ values for the different ceramic thicknesses and surface finishing treatments evaluated (P<.001), except for the b∗ value between the FG and CG groups (P=.988). The L∗ value on the polished group was significantly higher than that on the glazed specimens, followed by the fluorescent-glazed and then by the clear-glazed specimens (P<.001). The ΔE values using the CIE76 formula varied from 0.87 to 2.76 among specimen groups and from 0.32 to 2.34 using the CIEDE2000 among the tested groups. CONCLUSIONS: Ceramic thickness and surface finishing treatment affected all color dimensions (L∗, a∗, and b∗ values) of lithium disilicate ceramic under daylight conditions. These differences resulted in a perceptible but acceptable color mismatch. The value (L∗ color dimension) of the lithium disilicate ceramic was higher on fluorescent-glazed than on not-fluorescent-glazed specimens.

Revilla-León, M., R. Fogarty, J. J. Barrington, A. Zandinejad and M. Özcan (2020). “Influence of scan body design and digital implant analogs on implant replica position in additively manufactured casts.” J Prosthet Dent 124(2): 202-210.

Full text of this article.

STATEMENT OF PROBLEM: Additive manufacturing (AM) technologies can be used to fabricate definitive casts for implant-supported restorations. However, information regarding the accuracy of the implant replica position on the polymeric AM cast generated with different scan bodies and digital implant replica systems is lacking. PURPOSE: The purpose of this in vitro study was to compare with a conventional stone cast the linear and angular discrepancies of the implant analog positions in a polymeric AM cast obtained from 3 different scan body and digital implant replica systems. MATERIAL AND METHODS: A partially edentulous maxillary typodont with 3 implant replicas (Implant replica RP Branemark system; Nobel Biocare) was prepared. Two duplicating methods were evaluated: conventional (CNV group) and AM (AM group) procedures. For the CNV group, polyvinyl siloxane open-tray implant impressions (CNV) were made at room temperature (23 °C). The AM group was further divided into the subgroups Elos Medtech, Nt-Trading, and Dynamic Abutment. For the Elos Medtech subgroup, the corresponding scan bodies were placed on each implant, and the typodont was digitized by using a laboratory scanner (E3 scanner; 3Shape A/S). The same procedure was repeated with the remaining subgroups. All the AM polymer casts were fabricated at once by using the same 3D printer (Eden 500V; Stratasys). Ten specimens of each group were obtained (n=10). A coordinate-measuring machine (CMM) was used to measure the position of each implant replica, and distortion was calculated for each system at the x-, y-, and z-axes and 3D distortion measurement (3D=x(2)+y(2)+z(2)). The Shapiro-Wilk test revealed that the data were not normally distributed. The Kruskal-Wallis and pairwise Mann-Whitney U tests (α=.05) were used for the analysis. RESULTS: The CNV group presented significantly higher linear discrepancy than the Dynamic Abutment group on the x- and y-axes. On the z-axis, however, the CNV group showed significantly lower linear discrepancy than the Nt-Trading and Dynamic Abutment groups. The 3D linear discrepancy was 12 ±12 μm for the CNV group, 4 ±100 μm for the Elos Medtech group, 8 ±52 μm for the Nt-Trading group, and 5 ±19 μm for the Dynamic Abutment. The CNV group demonstrated a significantly higher angle than the Nt-Trading group but a significantly smaller angle than the Elos Medtech and Dynamic Abutment groups. CONCLUSIONS: The AM groups had lower 3D discrepancies than the CNV group. The Dynamic Abutment group had significantly better accuracy for the mesiodistal and buccolingual implant replica positions than the CNV group, but the conventional procedures had significantly better results for the apicocoronal implant replica position. Scan body and digital implant replica design systems only influenced the accuracy of the angular implant replica position on the AM casts.

Piedra-Cascón, W., M. M. Methani, N. Quesada-Olmo, M. J. Jiménez-Martínez and M. Revilla-León (2020). “Scanning accuracy of nondental structured light extraoral scanners compared with that of a dental-specific scanner.” J Prosthet Dent.

Full text of this article.

STATEMENT OF PROBLEM: Diagnostic stone casts can be digitized by using dental optical scanners based on structured light scanning technology. Nondental structured light scanning scanners could also be used; however, the accuracy of these nondental scanners remains unclear. PURPOSE: The purpose of this in vitro study was to measure the scanning accuracy (trueness and precision) of 3 nondental extraoral structured light scanners. MATERIAL AND METHODS: A representative maxillary diagnostic cast was obtained and digitized by using an extraoral dental scanner (Advaa Lab Scan; GC Europe), and a reference or control standard tessellation language file was obtained. Three nondental extraoral scanners were evaluated: groups ND-1 (Space Spider; Artec), ND-2 (Capture Mini; Geomagic), and ND-3 (DAVID SLS3; David). Ten digital scans per group were recorded at a constant room temperature (23 °C) by an experienced geodetic engineer following the manufacturer’s recommendations. The control or reference file was used as a reference to measure the discrepancy between the digitized diagnostic cast and 3 different nondental scans by using an open-source software (CloudCompare v.2.6.1; CloudCompare) and the iterative closest point technique. The Shapiro-Wilk test revealed that the data were normally distributed. The data were analyzed by using 1-way ANOVA, followed by post hoc Bonferroni tests (α=.05). RESULTS: Significant differences between the 3 experimental nondental scanners and the control or reference scan (P<.001) were found. The ND-2 group had the lowest absolute mean error (trueness) and standard deviation (precision) (39 ±139 μm), followed by the ND-3 group (125 ±113 μm) and the ND1 group (-397 ±25 μm). No statistically significant differences were found in the mean error between the ND-2 and ND-3 groups (P=.228). CONCLUSIONS: Only 1 nondental extraoral scanner tested obtained trueness mean values similar to those of the reference dental scanner. In all groups, the precision mean values were higher than their trueness values, indicating low relative precision.