The effect of scanning distance on the accuracy of intra-oral scanners used in dentistry.

The aim of this study was to evaluate the factors affecting intra-oral scanner accuracy by analyzing variation in measurements of a dental model according to scanning distance. A dental cast, including a prepared left mandibular first molar, was used. Rectangular frames measuring 20 × 30 mm with heights of 2.5, 5.0, and 7.5 mm were made. The model was scanned 10 times with a reference scanner to obtain the true value. Scanning was performed 10 times at four distances of 0, 2.5, 5.0, and 7.5 mm with the frame of each height using the following intra-oral scanners: TRIOS; CS 3500; and PlanScan. In the linear distance measurement method (2D), measurements were taken at five parameters using the Rapidform software. In the best-fit alignment method (3D), using the Geomagic Control X, the root mean square values of the two scan images were calculated. In the 2D comparison, the different from the reference value was the smallest at 2.5 and 5.0 mm. In the 3D comparison, 2.5 and 5.0 mm were the most accurate, and 0 mm was the least accurate among the four distances. To the best of our knowledge, this study was the first to evaluate the accuracy of scanning distances, and found a difference between the accuracy of the scanning distance and the accuracy of the scanner. Moreover, the results of this study indicated that the scanning distance was a variable affecting accuracy. Clin. Anat. 32:430-438, 2019. © 2019 Wiley Periodicals, Inc.

Applicability of 3D-dental reconstruction in cervical odontometrics.

OBJECTIVES: The objective of this study was to assess the accuracy, reliability, and reproducibility of computed tomography (CT) images in measuring cervical mesiodistal and buccolingual tooth sizes, by comparing the values obtained by 3D virtual models from CT images with those obtained using digital calipers. MATERIALS AND METHODS: In total, 530 maxillary and mandibular teeth of 51 individuals from two Iron Age sites were scanned using a Siemens Somatom sensation 64-slice computed tomography machine, and the images were reconstructed and measured. Values obtained by direct measurement served as the primary reference for cervical measurements. Intra- and inter-observer reliability was assessed by calculating technical error of measurements (TEM), relative technical error of measurements (rTEM), and the coefficient of reliability (R). RESULTS: Results showed that virtual cervical measurements were not significantly different from the actual measurements, and the correlation of the two measurement methods shows that the methods are comparable. Inter- and intra-observer error analysis also indicated high replicability of measurements with both measuring methods (R > 0.99). The rTEM values for all the measurements were below the 5% standards for anthropometric studies. DISCUSSION: CT is a non-invasive technique that allows for an accurate and detailed visualization of morphological features without causing any damage to teeth. Our findings indicate that virtual odontometric analysis is a reliable method, similar to traditional physical odontometric analysis. Currently, the virtual system is likely to be more suitable for fragile specimens, such as archaeological samples.

Comparison of user satisfaction and image quality of fixed and mobile camera systems for 3-dimensional image capture of edentulous patients: A pilot clinical study.

STATEMENT OF PROBLEM: An evaluation of user satisfaction and image quality of a novel handheld purpose-built mobile camera system for 3-dimensional (3D) facial acquisition is lacking. PURPOSE: The purpose of this pilot clinical study was to assess and compare the effectiveness between a handheld mobile camera system designed for facial acquisition and a fixed static camera arrangement by comparing the time effectiveness and the operator and participant preference for the 2 techniques of image capture. MATERIAL AND METHODS: Completely edentulous participants (n=12: women=7, men=5; mean age: 74.6 years) were included in this pilot study. Images were captured with and without the prostheses in situ while maintaining "serious" and "full-smile" facial expressions. Images were captured using a mobile and a static system. The working times for the participant installation and image captures were recorded. Operator and participant perceptions of the entire experience were recorded by using visual analog scale questionnaires. Nonparametric tests were used for statistical analyses (α=.05). RESULTS: The installation time was significantly shorter for the mobile system (static=24 ±13 seconds; mobile=10 ±10 seconds), but the differences in the image capture times were not statistically significant (static: 29 ±5 seconds; mobile: 40 ±18 seconds). Operator preference was in favor of the mobile system with regard to working time (P=.002), difficulty in using (installation: P=.002; handling: P=.045), and camera weight (P=.002); however, they preferred the static arrangement for image quality (P=.003) and comfort (P=.013). The participants rated the entire photographic experience favorably, and 10 of 12 participants preferred the static camera over the mobile one. CONCLUSIONS: Despite the complexity of the installation, the static system was evaluated better for image quality; the mobile system was easier in installation and handling. The operators preferred the mobile system, and the participants preferred the static system.

A novel in vivo method to evaluate trueness of digital impressions.

BACKGROUND: Intraoral scanners are devices for capturing digital impressions in dentistry. Until now, several in vitro studies have assessed the trueness of digital impressions, but in vivo studies are missing. Therefore, the purpose of this study was to introduce a new method to assess trueness of intraoral scanners and digital impressions in an in vivo clinical set-up. METHODS: A digital impression using an intraoral scanner (Trios® 3 Cart wired, 3Shape, Copenhagen, Denmark) and a conventional alginate impression (Cavex Impressional®, Cavex, Haarlem, the Netherlands) as clinical reference were made for two patients assigned for full mouth extraction. A total of 30 teeth were collected upon surgery after impressions making. The gypsum model created from conventional impression and extracted teeth were then scanned in a lab scanner (Activity 885®, SmartOptics, Bochum, Germany). Digital model of the intraoral scanner (DM), digital model of the conventional gypsum cast (CM) and those of the extracted natural teeth (NT) were imported to a reverse engineering software (3-matic®, Materialise, Leuven, Belgium) in which the three models were registered then DM and CM were compared to their corresponding teeth in NT by distance map calculations. RESULTS: DM had statistically insignificant better trueness when compared to CM for total dataset (p = 0.15), statistically insignificant better trueness for CM when mandibular arches analyzed alone (p = 0.56), while a significantly better DM trueness (p = 0.013) was found when only maxillary arches were compared. CONCLUSIONS: Our results show that digital impression technique is clinically as good as or better than the current reference standard for study models of orthognathic surgery patients.

Accuracy of 3-dimensional curvilinear measurements on digital models with intraoral scanners.

INTRODUCTION: Our objectives were to evaluate and compare the digital dental models generated from 2 commercial intraoral scanners with manual measurements when performing 3-dimensional surface measurements along a curved line (curvilinear). METHODS: Dry mandibles (n = 61) with intact dentition were used. The mandibles were digitized using 2 chair-side intraoral scanners: Cadent iTero (Align Technology, San Jose, Calif) and Lythos Digital Impression system (Ormco, Orange, Calif). Digitized 3-dimensional models were converted to individual stereolithography files and used with commercial software to obtain the curvilinear measurements. Manual measurements were carried out directly on the mandibular teeth. Measurements were made on different locations on the dental arch in various directions. One-sample t tests and linear regression analyses were performed. To further graphically examine the accuracy between the different methods, Bland-Altman plots were computed. The level of significance was set at P <0.05. RESULTS: There were no significant differences between any of the paired methods; this indicated a certain level of agreement between the methods tested (P >0.05). Bland-Altman analysis showed no fixed bias of 1 approach vs the other, and random errors were detected in all comparisons. Although the mean biases of the digital models obtained by the iTero and Lythos scanners, when compared with direct caliper measurements, were low, the comparison of the 2 intraoral scanners yielded the lowest mean bias. No comparison displayed statistical significance for the t scores; this indicated the absence of proportional bias in these comparisons. CONCLUSIONS: The intraoral scanners tested in this study produced digital dental models that were comparatively accurate when performing direct surface measurements along a curved line in 3 dimensions.

Seismic response of 3D steel buildings considering the effect of PR connections and gravity frames.

The nonlinear seismic responses of 3D steel buildings with perimeter moment resisting frames (PMRF) and interior gravity frames (IGF) are studied explicitly considering the contribution of the IGF. The effect on the structural response of the stiffness of the beam-to-column connections of the IGF, which is usually neglected, is also studied. It is commonly believed that the flexibility of shear connections is negligible and that 2D models can be used to properly represent 3D real structures. The results of the study indicate, however, that the moments developed on columns of IGF can be considerable and that modeling buildings as plane frames may result in very conservative designs. The contribution of IGF to the lateral structural resistance may be significant. The contribution increases when their connections are assumed to be partially restrained (PR). The incremented participation of IGF when the stiffness of their connections is considered helps to counteract the no conservative effect that results in practice when lateral seismic loads are not considered in IGF while designing steel buildings with PMRF. Thus, if the structural system under consideration is used, the three-dimensional model should be used in seismic analysis and the IGF and the stiffness of their connections should be considered as part of the lateral resistance system.

Three-dimensional repositioning accuracy of semiadjustable articulator cast mounting systems.

STATEMENT OF PROBLEM: In spite of its importance in prosthesis precision and quality, the 3-dimensional repositioning accuracy of cast mounting systems has not been reported in detail. PURPOSE: The purpose of this study was to quantify the 3-dimensional repositioning accuracy of 6 selected cast mounting systems. Five magnetic mounting systems were compared with a conventional screw-on system. MATERIAL AND METHODS: Six systems on 3 semiadjustable articulators were evaluated: Denar Mark II with conventional screw-on mounting plates (DENSCR) and magnetic mounting system with converter plates (DENCON); Denar Mark 330 with in-built magnetic mounting system (DENMAG) and disposable mounting plates; and Artex CP with blue (ARTBLU), white (ARTWHI), and black (ARTBLA) magnetic mounting plates. Test casts with 3 high-precision ceramic ball bearings at the mandibular central incisor (Point I) and the right and left second molar (Point R; Point L) positions were mounted on 5 mounting plates (n=5) for all 6 systems. Each cast was repositioned 10 times by 4 operators in random order. Nine linear (Ix, Iy, Iz; Rx, Ry, Rz; Lx, Ly, Lz) and 3 angular (anteroposterior, mediolateral, twisting) displacements were measured with a coordinate measuring machine. The mean standard deviations of the linear and angular displacements defined repositioning accuracy. RESULTS: Anteroposterior linear repositioning accuracy ranged from 23.8 ±3.7 µm (DENCON) to 4.9 ±3.2 µm (DENSCR). Mediolateral linear repositioning accuracy ranged from 46.0 ±8.0 µm (DENCON) to 3.7 ±1.5 µm (ARTBLU), and vertical linear repositioning accuracy ranged from 7.2 ±9.6 µm (DENMAG) to 1.5 ±0.9 µm (ARTBLU). Anteroposterior angular repositioning accuracy ranged from 0.0084 ±0.0080 degrees (DENCON) to 0.0020 ±0.0006 degrees (ARTBLU), and mediolateral angular repositioning accuracy ranged from 0.0120 ±0.0111 degrees (ARTWHI) to 0.0027 ±0.0008 degrees (ARTBLU). Twisting angular repositioning accuracy ranged from 0.0419 ±0.0176 degrees (DENCON) to 0.0042 ±0.0038 degrees (ARTBLA). One-way ANOVA found significant differences (P<.05) among all systems for Iy, Ry, Lx, Ly, and twisting. CONCLUSIONS: Generally, vertical linear displacements were less likely to reach the threshold of clinical detectability compared with anteroposterior or mediolateral linear displacements. The overall repositioning accuracy of DENSCR was comparable with 4 magnetic mounting systems (DENMAG, ARTBLU, ARTWHI, ARTBLA). DENCON exhibited the worst repositioning accuracy for Iy, Ry, Lx, Ly, and twisting.

Clinical use of a direct chairside oral scanner: an assessment of accuracy, time, and patient acceptance.

INTRODUCTION: Chairside oral scanners allow direct digital acquisition of the intraoral situation and can eliminate the need for conventional impressions. In this study, we aimed to assess accuracy, scan time, and patient acceptance of a chairside oral scanner when used for full-arch scans; these are critical factors for acceptance of this technology in the orthodontic setting. METHODS: Fifteen patients had digital models made from both intraoral scans (Lava COS; 3M ESPE, St Paul, Minn) and alginate impressions. Each procedure was timed, and patient preference was assessed with a survey. In addition, digital models were made from 5 plaster model pairs using the intraoral scanner and an orthodontic model scanner. Model pairs were digitally superimposed, and differences between models were quantified. Accuracy was assessed using the Bland-Altman method. Time differences were tested for statistical significance with the Student t test. RESULTS: Digital models made using the chairside oral scanner and either impressions or the orthodontic model scanner did not differ significantly. The chair time required to take impressions was significantly shorter than the time required for the intraoral scans. When processing time was included, the time requirement did not differ significantly between methods. Although 73.3% of the patients preferred impressions because they were "easier" or "faster," 26.7% preferred the scan because it was "more comfortable." CONCLUSIONS: Despite the high accuracy of chairside oral scanners, alginate impressions are still the preferred model acquisition method with respect to chair time and patient acceptance. As digital technology continues to progress, intraoral scanning may become more accepted for use in orthodontics.

New applications for three-dimensional follow-up and quality control using optical impression systems and OraCheck.

Intraoral and extraoral scanning systems are continuously improving in terms of operational reliability and image quality. This creates new application options for the standard use of these systems in dental practice. Three-dimensional scans for volumetric and differential analysis of jaw position over time can be generated by superimposing partial or full-arch scans recorded at different time points. These analyses can be performed in a wide range of dental applications to compare and follow treatments or diagnoses over time. In this article, we will describe the indications and applications for OraCheck, a new software application that will be available to Cerec users in Spring 2014.

An in vitro comparison of subjective image quality of panoramic views acquired via 2D or 3D imaging.

OBJECTIVES: The objective of this study is to compare subjective image quality and diagnostic validity of cone-beam CT (CBCT) panoramic reformatting with digital panoramic radiographs. MATERIALS AND METHODS: Four dry human skulls and two formalin-fixed human heads were scanned using nine different CBCTs, one multi-slice CT (MSCT) and one standard digital panoramic device. Panoramic views were generated from CBCTs in four slice thicknesses. Seven observers scored image quality and visibility of 14 anatomical structures. Four observers repeated the observation after 4 weeks. RESULTS: Digital panoramic radiographs showed significantly better visualization of anatomical structures except for the condyle. Statistical analysis of image quality showed that the 3D imaging modalities (CBCTs and MSCT) were 7.3 times more likely to receive poor scores than the 2D modality. Yet, image quality from NewTom VGi® and 3D Accuitomo 170® was almost equivalent to that of digital panoramic radiographs with respective odds ratio estimates of 1.2 and 1.6 at 95% Wald confidence limits. A substantial overall agreement amongst observers was found. Intra-observer agreement was moderate to substantial. CONCLUSIONS: While 2D-panoramic images are significantly better for subjective diagnosis, 2/3 of the 3D-reformatted panoramic images are moderate or good for diagnostic purposes. CLINICAL RELEVANCE: Panoramic reformattings from particular CBCTs are comparable to digital panoramic images concerning the overall image quality and visualization of anatomical structures. This clinically implies that a 3D-derived panoramic view can be generated for diagnosis with a recommended 20-mm slice thickness, if CBCT data is a priori available for other purposes.

Three-dimensional volume tomographic study of the imaging accuracy of impacted teeth: MSCT and CBCT comparison--an in vitro study.

The aim of this study was to analyze the imaging accuracy of cone beam computed tomography (CBCT) data sets compared with multislice spiral computed tomography (MSCT) data sets in determining the exact mesiodistal width of unerupted porcine tooth germs and to compare the radiologically obtained results of width measurements with the actual mesiodistal dimension of the tooth germs. In MSCT and CBCT data sets, the largest diameter of 24 tooth germs was determined with the aid of the mesial and distal contact points. The reference method used was mesiodistal width measurement using sliding callipers after the tooth germs had been osteotomized. Accuracy and precision were ascertained with difference plots and a one-way model II analysis of variance with random effects. Analysis of accuracy revealed marked differences between the measuring methods in the difference plot: slightly higher mean values were measured by MSCT and markedly lower values by CBCT than by the reference method (calliper); the mean deviation was significantly greater for CBCT. The width of the confidence interval in the comparison of CBCT versus clinical measurements is more than 4 times higher than in the comparison of MSCT versus clinical values. Precision analysis found that repeatability was twice as high with CBCT as with clinical measurement, whereas MSCT and clinical measurement differed only slightly. The mesiodistal width of displaced teeth can be determined by MSCT but also by CBCT. MSCT is superior to CBCT in determining tooth width; the difference was statistically significant (P = 0.05).

New method for detection of complex 3D fracture motion--verification of an optical motion analysis system for biomechanical studies.

BACKGROUND: Fracture-healing depends on interfragmentary motion. For improved osteosynthesis and fracture-healing, the micromotion between fracture fragments is undergoing intensive research. The detection of 3D micromotions at the fracture gap still presents a challenge for conventional tactile measurement systems. Optical measurement systems may be easier to use than conventional systems, but, as yet, cannot guarantee accuracy. The purpose of this study was to validate the optical measurement system PONTOS 5M for use in biomechanical research, including measurement of micromotion. METHODS: A standardized transverse fracture model was created to detect interfragmentary motions under axial loadings of up to 200 N. Measurements were performed using the optical measurement system and compared with a conventional high-accuracy tactile system consisting of 3 standard digital dial indicators (1 µm resolution; 5 µm error limit). RESULTS: We found that the deviation in the mean average motion detection between the systems was at most 5.3 µm, indicating that detection of micromotion was possible with the optical measurement system. Furthermore, we could show two considerable advantages while using the optical measurement system. Only with the optical system interfragmentary motion could be analyzed directly at the fracture gap. Furthermore, the calibration of the optical system could be performed faster, safer and easier than that of the tactile system. CONCLUSION: The PONTOS 5 M optical measurement system appears to be a favorable alternative to previously used tactile measurement systems for biomechanical applications. Easy handling, combined with a high accuracy for 3D detection of micromotions (≤ 5 µm), suggests the likelihood of high user acceptance. This study was performed in the context of the deployment of a new implant (dynamic locking screw; Synthes, Oberdorf, Switzerland).

A new method to measure mesiodistal angulation and faciolingual inclination of each whole tooth with volumetric cone-beam computed tomography images.

INTRODUCTION: The purpose of this study was to develop a methodology to measure the mesiodistal angulation and the faciolingual inclination of each whole tooth (including the root) by using 3-dimensional volumetric images generated from cone-beam computed tomography scans. METHODS: A plastic typodont with 28 teeth in ideal occlusion was fixed in position in a dry human skull. Stainless steel balls were fixed to the occlusal centers of the crowns and to the apices or bifurcation or trifurcation centers of the roots. Cone-beam computed tomography images were taken and rendered in Dolphin 3D (Dolphin, Chatsworth, Calif). The University of Southern California root vector analysis program was developed and customized to digitize the crown and root centers that define the long axis of each whole tooth. Special algorithms were used to automatically calculate the mesiodistal angulation and the faciolingual inclination of each whole tooth. Angulation measurements repeated 5 times by using this new method were compared with the true values from the coordinate measuring machine measurements. Next, the root points of 8 selected typodont teeth were modified to generate known angulation and inclination values, and 5-time repeated measurements of these teeth were compared with the known values. RESULTS: Intraclass correlation coefficients for the repeated mesiodistal angulation and faciolingual inclination measurements were close to 1. Comparisons between our 5-time repeated angulation measurements and the coordinate measuring machine's true angulation values showed 5 teeth with statistically significant differences. However, only the maxillary right lateral incisor showed a mean difference that might exceed 2.5° for clinical significance. Comparisons between the 5-repeated measurements of 8 teeth with known mesiodistal angulation and faciolingual inclination values showed no statistically significant differences between the measured and the known values, and no measurement had a 95% confidence interval beyond 1°. CONCLUSIONS: We have developed the novel University of Southern California root vector analysis program to accurately measure each whole tooth mesiodistal angulation and faciolingual inclination, in a clinically significant level, directly from the cone-beam computed tomography volumetric images.

Testing the accuracy of 3D automatic landmarking via genome-wide association studies.

Various advances in 3D automatic phenotyping and landmark-based geometric morphometric methods have been made. While it is generally accepted that automatic landmarking compromises the capture of the biological variation, no studies have directly tested the actual impact of such landmarking approaches in analyses requiring a large number of specimens and for which the precision of phenotyping is crucial to extract an actual biological signal adequately. Here, we use a recently developed 3D atlas-based automatic landmarking method to test its accuracy in detecting QTLs associated with craniofacial development of the house mouse skull and lower jaws for a large number of specimens (circa 700) that were previously phenotyped via a semiautomatic landmarking method complemented with manual adjustment. We compare both landmarking methods with univariate and multivariate mapping of the skull and the lower jaws. We find that most significant SNPs and QTLs are not recovered based on the data derived from the automatic landmarking method. Our results thus confirm the notion that information is lost in the automated landmarking procedure although somewhat dependent on the analyzed structure. The automatic method seems to capture certain types of structures slightly better, such as lower jaws whose shape is almost entirely summarized by its outline and could be assimilated as a 2D flat object. By contrast, the more apparent 3D features exhibited by a structure such as the skull are not adequately captured by the automatic method. We conclude that using 3D atlas-based automatic landmarking methods requires careful consideration of the experimental question.

Validation of SPAMM tagged MRI based measurement of 3D soft tissue deformation.

PURPOSE: This study presents and validates a novel (non-ECG-triggered) MRI sequence based on spatial modulation of the magnetization (SPAMM) to noninvasively measure 3D (quasistatic) soft tissue deformations using only six acquisitions (three static and three indentations). In the current SPAMM tagged MRI approaches, data are typically constructed from many repeated motion cycles. This has so far restricted its application to the measurement of highly repeatable and periodic movements (e.g., cardiac deformation). In biomechanical applications where soft tissue deformation is artificially induced, often by indentation, significant repeatability constraints exist, and for clinical applications, discomfort and health issues generally preclude a large number of repetitions. METHODS: A novel (non-ECG-triggered) SPAMM tagged MRI sequence is presented, whereby a single 1-1 (first order) SPAMM set is acquired following a 3D transient field echo acquisition. Full 3D deformation measurement is achieved through the combination of only six acquisitions (three static and three motion cycles). The 3D deformation measurements were validated using quasistatic indentation tests and marker tracking in a silicone gel soft tissue phantom. In addition, the technique's ability to measure 3D soft tissue deformation in vivo was evaluated using indentation of the biceps region of the upper arm in a volunteer. RESULTS: Following comparison to marker tracking in the silicone gel phantom, the SPAMM tagged MRI based displacement measurement demonstrated subvoxel accuracy with a mean displacement difference of 72 microm and a standard deviation of 289 microm. In addition, precision of displacement magnitude was evaluated for both the phantom and the volunteer data. The standard deviations of the displacement magnitude with respect to the average displacement magnitude were 75 and 169 microm for the phantom and volunteer data, respectively. CONCLUSIONS: The subvoxel accuracy and precision demonstrated in the phantom in combination with the precision comparison between the phantom and the volunteer data provide confidence in the methods presented for measurement of soft tissue deformation in vivo. To the author's knowledge, since only six acquisitions are required, the presented methodology is the fastest SPAMM tagged MRI method currently available for the noninvasive measurement of quasistatic 3D soft tissue deformation.

Accuracy of templates for navigated implantation made by rapid prototyping with DICOM datasets of cone beam computer tomography (CBCT).

The aim of this study is to evaluate the accuracy of a surgical template-aided implant placement produced by rapid prototyping using a DICOM dataset from cone beam computer tomography (CBCT). On the basis of CBCT scans (Sirona® Galileos), a total of ten models were produced using a rapid-prototyping three-dimensional printer. On the same patients, impressions were performed to compare fitting accuracy of both methods. From the models made by impression, templates were produced and accuracy was compared and analyzed with the rapid-prototyping model. Whereas templates made by conventional procedure had an excellent accuracy, the fitting accuracy of those produced by DICOM datasets was not sufficient. Deviations ranged between 2.0 and 3.5 mm, after modification of models between 1.4 and 3.1 mm. The findings of this study suggest that the accuracy of the low-dose Sirona Galileos® DICOM dataset seems to show a high deviation, which is not useable for accurate surgical transfer for example in implant surgery.

The accuracy of optical scanning: influence of convergence and die preparation.

The purpose of this study was to determine the reliability of the data acquisition and modeling process of laser and white light scanners by evaluating the reproducibility of digitized simulated crowns with different convergences. A secondary purpose was to analyze the influence of die preparation by testing this hypothesis with a set of dies without ditching compared with a set with well-defined margins. Ditching or trimming the die defines the position of the margin and acts as a guide to gingival contour when the restoration is being waxed. Two light scanners (a white light optical scanner [Steinbichler Gmbh, Neubeuern, Germany] and red laser light scanner [TurboDent System, Taichung, Taiwan]) were evaluated. Two sets of simulated crowns were fabricated as cone frustrum models with a total occlusal convergence (TOC) of 0°, 5°, 10°, 15°, 20°, and 25° and a 9-mm base and 3-mm height using a precision milling machine and computer-aided design/computer-aided manufacturing (CAD/CAM) technique. One set of the dies was ditched immediately below the finish line to enhance marginal definition. Each die was optically digitized five times directly with the two different measuring systems. The area of each triangle in the scan that is occlusal to the margin line was calculated and summed to produce the final surface area measurement provided. The digitizing error was compared with the computed surface area of the original master die sets and compared with a paired t-test (df=4; 95% CI). There was no difference in accuracy of the untrimmed dies between the two systems evaluated. We also did not find any difference in the 0° (p=0.12) and 5° degree (p=0.21) groups among the ditched dies. However, when the TOC exceeded 5°, there was a significant difference between the two groups, with the laser groups having a smaller error percentage. Three-dimensional light scanning was not affected by the convergence angle except in the 0°-5° range. Trimming the dies greatly affected the accuracy of scanning.

Cranial base foramen location accuracy and reliability in cone-beam computerized tomography.

INTRODUCTION: The purpose of this study was to evaluate the reliability and accuracy in locating several different foramina in the cranial base by using cone-beam computerized tomography (CBCT) images for future use in establishing reference coordinate systems. METHODS: CBCT images from 10 dry skulls were taken with and without the foramina ovale, spinosum, and rotundum, and the hypoglossal canals filled with radiopaque gutta-percha (gold standard). Three evaluators identified the foramen landmarks in the CBCT images without gutta-percha. Mean differences and main researcher intraexaminer and interexaminer reliability were measured by using intraclass correlation coefficients for all landmark coordinates. Descriptive statistics were calculated with respect to the landmark coordinates and distances to the reference points. RESULTS: Intraexaminer and interexaminer reliability values for the x-, y-, and z-coordinates for all landmarks were greater than 0.9 with the exception of 4 (of 72) points that still had acceptable interexaminer reliability (>0.75). Mean measurement error differences obtained in the principal investigator's trials were primarily less than 0.5 mm. When comparing the mean distance differences of the same examiner and between the 3 examiners with the gold standard, the highest difference obtained was 1.3 mm. CONCLUSIONS: Foramina spinosum, ovale, and rotundum, and the hypoglossal canal all provided high intraexaminer reliability and accuracy, and can be considered acceptable landmarks to use in establishing reference coordinate systems for future 3-dimensional superimposition analysis.

Evaluating craniofacial asymmetry with digital cephalometric images and cone-beam computed tomography.

INTRODUCTION: The aim of this study was to evaluate craniofacial asymmetry by using 2-dimensional (2D) posteroanterior cephalometric images, 3-dimensional cone-beam computed tomography (CBCT), and physical measurements (gold standard). METHODS: Ten dry human skulls were assessed, and radiopaque markers were placed on 17 skeletal landmarks. Twenty linear measurements were taken on each side to compare the right and left sides and to compare these measurements with the physical measurements made with a digital caliper. To acquire the 2D posteroanterior radiographs, an Extraoral Phosphor Storage Plate (Air Techniques, Chicago, Ill) was used as the image receptor with a Eureka x-ray-Duocon Machlett unit (Machlett Laboratores, Chicago, Ill). Three-dimensional imaging data were acquired from a CB MercuRay (Hitachi Medical, Tokyo, Japan). RESULTS: On average, the right side was larger than the left for most of the 20 distances evaluated in the digital 2D and the CBCT images, and there was poor agreement between the digital 2D images and the physical measurements (kappa = 0.0609) and almost perfect agreement (kappa = 0.92) between the CBCT and physical measurements when individual measurements were considered. CONCLUSIONS: Human skulls, with no apparent asymmetry, had some differences between the right and left sides, with dominance for the right side but with no clinical significance. CBCT can better evaluate craniofacial morphology when compared with digital 2D images.

Rapid particle size measurement using 3D surface imaging.

The present study introduces a new three-dimensional (3D) surface image analysis technique in which white light illumination from different incident angles is used to create 3D surfaces with a photometric approach. The three-dimensional features of the surface images created are then used in the characterization of particle size distributions of granules. This surface image analysis method is compared to sieve analysis and a particle sizing method based on spatial filtering technique with nearly 30 granule batches. The aim is also to evaluate the technique in flowability screening of granular materials. Overall, the new 3D imaging approach allows a rapid analysis of large amounts of sample and gives valuable visual information on the granule surfaces in terms of surface roughness and particle shape.