Digital Laser Scanner Research Articles

Digitizing an Excavation: A Laser Scanning Database of Maya Architectural Remains

Excavating an ancient Maya city requires a long-term archaeological project that entails adequate documentation procedures for the unearthed remains, frequently of monumental scale and with difficult preservation conditions. A digital laser scanner survey methodology was designed and implemented to document the exposed architecture and to follow-up the archaeological excavation of the Maya site of La Blanca (Peten, Guatemala). All scans collected during the different field seasons were stored and aligned in a common reference system. Thus, an accurate digital three-dimensional database was obtained, including all the architectural remains found, some of which had to be reburied to ensure their preservation. The resulting database is a helpful repository that facilitates to extract all the graphic outputs required for: planning the next excavation campaigns, monitoring the preservation of the buildings, studying the architecture and construction technology in detail, and disseminating the excavation results. This paper describes the methodology and procedures used to build-up this database.

Effect of luting space and cements on retention of implant supported crowns fabricated by laser sintering

Background: The aim of this study was to evaluate the retention strength of five different cements used for implant supported crowns with two cement gap values. Methods: Standard titanium abutments were scanned by means of a 3D digital laser scanner. 100 standard metal copings were designed by a CAD/CAM system with two cement gap values (20 and 40μm). The copings were cemented to the abutments using the following five cements (n=10). Poly F (PF), GC FujiCEM (GCF), Rely X (RX), MIS Crown Set(MCS) and Multilink N (MN). The specimens were placed in 100% humudity for 24 hours then specimens were thermal cycled 1000 times. After thermal cycling specimens were subjected to a pull-out test using a universal testing machine at a 0.5 mm/min crosshead speed. The test results were analyzed with two-way ANOVA, followed by multiple comparisons using Tamhane tests (α=0.05). Results: Statistical analysis revealed that significant differences were observed among cement groups (p<0.05). PF and MN had the highest and the least mean retentive strength, respectively. No significant difference was found between RX and MCS. Increasing the cement gap from 20 to 40 μm improved retention significantly for each cement group (p<0.05). Conclusion: The ranking of cements presented in the study is meant to be an arbitrary guide for the clinician in deciding the appropriate cement selection for CAD/CAM fabricated metal copings onto implant abutments.

Morphometric analysis and classification of the three‐dimensional geometry of shatter cones

AbstractShatter cones are curved fractures decorated with divergent striations that are exclusively associated with impact metamorphism. The terminology “cone” was chosen from the observation of complete or near‐complete, roundish, axisymmetric objects with a well‐defined apex/apical area. It also imprecisely extends to the curved or subplanar fractures decorated with striations commonly observed at impact sites. The geometry of these objects is therefore highly variable but its significance was never addressed due to the lack of appropriate data. Here, we apply two methods to derive shape models of shatter cones. The first one is based on images acquired using a commercial camera and may be applied on large samples in the field. The second one uses an articulated arm equipped with a digital laser scanner and produces high‐resolution and precision shape models of hand‐sized samples. The analysis of 20 shape models of shatter cones from nine different impact sites indicates that the surface of shatter cones may be described by quadric surfaces and are generally consistent with hyperboloids, whereas occurrence of paraboloid objects cannot be ruled out. The surface characteristics are generally not consistent with the mathematical definition of a cone. The value of these shape models to discriminate between the different hypotheses of formation of shatter is still limited, as it remains to be resolved which type of surface pertains to which hypothesis. This requires theoretical developments, and experimental or numerical simulations of the propagation of tensile fractures associated with shock waves.

Line fitting in Euclidean 3D space

Over a century ago Pearson solved the problem of fitting lines in 2D space to points with noisy coordinates in both dimensions. Surprisingly, however, the case of fitting lines in 3D space has seen little attention, though Adcock long ago published a brief (one page) article claiming that the solution that minimized orthogonal distances is the most probable. We solve this problem using a new algorithm for the Total Least-Squares (TLS) solution within an Errors-In-Variables Model, respectively an equivalent nonlinear Gauss-Helmert Model. Following Roberts, only four parameters are estimated, thereby avoiding over-parametrization that may lead to unnecessary singularities and, hence, require the introduction of constraints to the model. The current pervasiveness of Global Navigation Satellite Systems, robotic total stations, and digital laser scanners as sources of geodetic observations means that geodetic engineers and scientists now commonly work with observational models in 3D space as opposed to classical geodetic methods that often separated horizontal and vertical observational models. And while several papers have been written describing a TLS solution for line fitting problems in 2D space, the extension to 3D space is not readily apparent from these works. This further motivates the treatment of the 3D problem in some detail in this contribution.

Cement Selection for Implant‐Supported Crowns Fabricated with Different Luting Space Settings

To measure and compare the retentive strength of cements specifically formulated for luting restorations onto implant abutments and to investigate the effect of varying cement gap on retention strength of implant-supported crowns. Standard titanium abutments were scanned by means of a 3D digital laser scanner. One hundred and sixty standard metal copings were designed by a Computer Aided Design/Computer Aided Manufacturing (CAD/CAM) system with two cement gap values (20 and 40 μm). The copings were cemented to the abutments using the following eight cements with one being the control, zinc oxide temporary cement, while the other seven were specifically formulated implant cements (n = 10): Premier Implant Cement, ImProv, Multilink Implant, EsTemp Implant, Cem-Implant, ImplaTemp, MIS Crown Set, and TempBond NE. The specimens were placed in 100% humidity for 24 hours, and subjected to a pull-out test using a universal testing machine at a 0.5 mm/min crosshead speed. The test results were analyzed with two-way ANOVA, one-way ANOVA, post hoc Tamhane' s T2, and student's t-tests at a significance level of 0.05. Statistical analysis revealed significant differences in retention strength across the cement groups (p < 0.01). Resin-based cements showed significantly higher decementation loads than a noneugenol zinc oxide provisional cement (TempBond NE) (p < 0.01), with the highest tensile resistance seen with Multilink Implant, followed by Cem-Implant, MIS Crown Set, ImProv, Premier Implant Cement, EsTemp Implant, and ImplaTemp. Increasing the cement gap from 20 to 40 μm improved retention significantly for the higher strength cements: Multilink Implant, Premier Implant Cement, ImProv, Cem-Implant, and MIS Crown Set (p < 0.01), while it had no significant effect on retention for the lower strength cements: EsTemp Implant, ImplaTemp, and TempBond NE (p > 0.05). Resin cements specifically formulated for implant-supported restorations demonstrated significant differences in retention strength. The ranking of cements presented in the study is meant to be an arbitrary guide for the clinician in deciding the appropriate cement selection for CAD/CAM-fabricated metal copings onto implant abutments with different luting space settings.

Experimental methodology for digital breast shape analysis and objective surgical outcome evaluation

Outcome evaluation in cosmetic and reconstructive surgery of the breast is commonly performed visually or employing bi-dimensional photography. The reconstructive process in the era of anatomical implants requires excellent survey capabilities that mainly rely on surgeon experience. In this paper we present a set of parameters to unambiguously estimate the shape of natural and reconstructed breast. A digital laser scanner was employed on seven female volunteers. A graphic depiction of curvature of the thoracic surface has been the most interesting result. Further work is required to provide clinical and instrumental validation to our technique.