Superimposition Method Research Articles

Novel application and validation of in vivo micro-CT to study bone modelling in 3D.

The aim is to highlight a novel three-dimensional (3D) imaging methodology using micro-CT scans to visualize and measure bone modelling in an animal model. In order to validate the new methodology, we compared the 3D imaging method to traditional two-dimensional (2D) histomorphometry to assess growth changes in the jaws of a rodent. Rodent animal models. Eleven rats were obtained from a larger previously published study. Sixty undecalcified histological sections from the maxilla and corresponding high-resolution in vivo micro-CT reconstructions were obtained. Bone modelling changes on specific alveolar surfaces were measured using traditional histomorphometry. Measurements of bone growth were also obtained via 3D Slicer software from 3D micro-CT generated models from the same plane containing the histological images. Both qualitative and quantitative 3D methods were compared to traditional histological measurements. Quantitative agreement between methods was categorized as follows: poor (>150μm), good (150-100μm) and excellent (<100μm). Both qualitative (88.3%) and quantitative (86.7%) 3D measurements showed excellent agreement, when compared to histomorphometric measurements. Only 1.7% and 5% of the comparisons exhibited poor agreement (>150μm) for qualitative and quantitative methods, respectively. The new 3D superimposition method compares very favourably with traditional histology. It is likely that in the future, such methods will be used in studies of bone adaptation. The 3D micro-CT qualitative and quantitative methods are reliable for measuring bone modelling changes and compare favourably to histology for the specific application described.

Deviations in palatal region between indirect and direct digital models: an in vivo study

BackgroundStudies focusing on accuracy of intraoral digital models in the palatal region are scarce. The present study aimed to investigate the influence of different scanning sequences on palatal trueness and to assess deviation and distribution character of trueness in palate.MethodsOverall, 35 participants accepted three types of procedures to acquire upper digital models. Indirect models digitalised from plaster models were considered as the reference. Two direct digital models were acquired using TRIOS 3 POD intraoral scanners, namely Groups Tr1 and Tr2, wherein intraoral scanning differed in terms of palatal scanning sequences. Based on a modified dental-level superimposition method, 3D measurements of trueness in palate and palatal vault region (PVR) for palatal stable regional superimposition in Groups Tr1 and Tr2, respectively, were performed. Absolute deviations were measured for trueness, while signed deviations were analysed for shape distortion. Colour-coded maps were used for quantitative analysis of deviation distribution pattern. Paired t test was used to analyse differences in palatal trueness between different scanning sequences. One-way repeated-measures analysis of variance and Bonferroni test were used to compare trueness measurements among different superimposition methods. Intraclass correlation coefficient (ICC) was used to verify reproducibility of the proposed method.ResultsPalatal trueness in Group Tr1 (118.59 ± 37.67 μm) was slightly less accurate than that (108.25 ± 33.83 μm) in Group Tr2 (p = 0.012 < 0.05). Trueness of PVR in Groups Tr1 (127.35 ± 54.11 μm) and Tr2 (118.17 ± 49.52 μm) did not differ significantly (p = 0.149). Moreover, no significant difference was noted in distortion of the palatal region and PVR in Groups Tr1 and Tr2 (p = 0.582 and 0.615, respectively). A similar pattern of palatal trueness was noted in a majority of participants (22/35). For 3D palatal trueness measurement, there were different applications for different superimposition methods. ICC for the proposed method was > 0.90.ConclusionsScanning sequences can affect palatal trueness. Palatal scanning should be initiated at the palatal side of the posterior teeth where the initial scan begins. For 3D PVR superimposition, distal boundary of the selected region should be adjusted mesially whilst referring to intraoral digital models.Trial registrationThe trial has been registered (registration No: R000039467, Trial ID: UMIN000034617, date of registration: 2018/10/24‘retrospectively registered’).

3D superimposition of dental casts based on coloured landmark detection using combined computer vision and 3D computer graphics techniques

ABSTRACTThe aim of this study was to evaluate the validity and reliability of three-dimensional (3D) landmark-based palatal superimposition of digital dental models using the customized software Ortho Mechanics Sequential Analyzer (OMSA) revised by the addition of a computer vision algorithm. The sample consisted of pre- and post-treatment digital maxillary dental models of 20 orthodontic cases. For each case, the pre- and post-treatment digital models were superimposed using colour detection capabilities of a computer vision algorithm added to OMSA. The same set of parameters was measured on the superimposed 3D data by the two software versions for comparison. Agreement in the superimposition outcomes among the two superimposition methods was evaluated with Dahlberg error (DE), intraclass correlation coefficients (ICCs) using two-way ANOVA mixed model for absolute agreement and Bland–Altman agreement limits (LOA). Repeatability was excellent for all variables (all ICCs over 0.99 with the lower 95% confidence limit ≥0.95). The Dahlberg error (DE) ranged from 0.14 mm to 0.36 mm. The absolute error did not exceed 0.5 mm for any variable. The results indicate that OMSA with computer vision algorithms offers a valid and reliable tool for 3D landmark-based digital dental model superimposition using colour detection of three reference points marked along the mid-palatal raphe.

Three-dimensional geometric morphometric measurement and classification of maxillary central incisors

Objectives: Classify and obtain the representative shape of the maxillary central incisor by three -dimensional geometric morphological method.Materials and methods: One hundred three dental plaster models of Chinese juvenile were scanned by a 3D laser scanner, including 51 males and 52 females. The mean value model of all samples was obtained by using Procrustes superimposition method. All samples were classified by k-means cluster analysis. Principal component analysis was performed to assess shape parameters. With the help of thin plate spline (TPS), we explored the anatomical significance of each principal component.Results: All samples were classified into four groups, the number of each group was 14、19、38、32. And obtained the mean value model of all samples and each group. The first ten principal components comprised 86.27% shape variation of maxillary central incisor.Conclusions: It is feasible to classify the maxillary central incisor and calculate the representative mean value model by using Three-dimensional geometric morphometric, which provides the theoretical basis for developing the standard crown data of the maxillary central incisor in CAD/CAM.

Superimposition of maxillary digital models using the palatal rugae: Does ageing affect the reliability?

The aim of this study was to evaluate the reliability of 3-dimensional maxillary dental changes using two methods of digital model superimposition. The Department of Orthodontics of Bauru Dental School, University of São Paulo and University of Michigan Craniofacial Growth Center. Fifteen subjects with normal occlusion. The sample was composed of digital study models of 15 normal occlusion subjects taken at 13 (T1), 18 (T2) and 60years of age (T3). Using the software SlicerCMF 3.1, superimposition (registration) was conducted using 9 landmarks placed on the incisive papilla, second and third palatal rugae and 10mm distal to the third palatal rugae. Two registration methods were compared: landmarks (LA) and regions of interest (ROI). Three-dimensional changes of landmarks on the buccal cusp tip of posterior teeth bilaterally and the incisal edge of the right central incisor were measured by three examiners. Intraclass correlation coefficients and Bland-Altman method evaluated intra- and inter-examiner agreements. Good or excellent intra-examiner agreement was found for T1-T2 and T2-T3 measurements using both registration methods. Inter-examiner agreements were good to excellent for T1-T2 measurements and poor to fair for most T2-T3 measurements. Mean T1-T2 differences were less than 0.5mm for most measurements. Maxillary digital dental models of patients with normal occlusion superimposed on palatal rugae showed an adequate reliability for a 5-year interval comparison using landmarks or regions of interest. Lower than acceptable reproducibility using both superimposition methods was found for a 40-year interval comparison.

Comparison of Ricketts, Pancherz and Centrographic Superimposition Methods in Post-Treatment Assessment of the Effects of Twin Block-Appliance Therapy

Objectives: Aim of this study was to do a comparative post-treatment assessment, using three superimposition methods (Ricketts, Pancherz and Centrographic), in patients with Angle’s Class II Division 1 malocclusion and functional retrusion of mandible following twin block appliance therapy. Methods: In this retrospective cross sectional study, pre and post-treatment lateral cephalometric radiographs of 33 cases were analyzed and compared using Ricketts, Pancherz and Centrographic superimposition methods. Changes were evaluated quantitatively for all three methods using a reference grid. The anteroposterior position of upper and lower centroids with respect to the centroid plane was evaluated. Results: Paired samples t-tests and intraclass correlation coefficient revealed excellent reliability of Ricketts, Pancherz and Centrographic superimposition techniques for all parameters. An advancement of 4.14 + 2.24 and 4.18 + 2.26 in Pancherz, 4.30 + 2.14 and 4.38 + 2.18 in Ricketts and 4.36 + 2.19 and 4.50 + 2.19 in Centrographic superimposition methods was shown by point B and pogonion respectively. The observed advancement of Point B and restriction of mesial movement of upper first molar (U6) was statistically significant for Centrographic method as compared to Pancherz. Advancement of lower centroid was seen in all cases with 72.7% in level with centroid plane and 24.2% within 1mm of it. Conclusions: All three superimposition methods (Ricketts, Pancherz and Centrographic) proved equally reliable in assessing treatment changes following twin block therapy. Forward movement of lower centroid was observed in 100% of the cases indicating true mandibular advancement following twin block appliance therapy in Skeletal Class II Division 1 malocclusions.

Accuracy of complete- and partial-arch impressions of actual intraoral scanning systems in vitro.

Intraoral scanners (IOSs) are widely used for obtaining digital dental models directly from the patient. Additionally, improvements in IOSs are made from generation to generation. The aim of this study was to evaluate the accuracy of new and actual IOS devices for complete- and partial-arch dental impressions in an in vitro setup. A custom maxillary complete-arch cast with teeth made from feldspar ceramic material was used as the reference cast and digitized with a reference scanner (ATOS III Triple Scan MV60). One conventional impression technique using polyvinylsiloxane (PVS) material (President) served as the control (CO), and eight different IOS devices comprising different hardware and software configurations (TRn: Trios 3; TRi: Trios 3 insane; CS: Carestream Dental CS 3600; MD: Medit i500; iT: iTero Element 2; OC4: Cerec Omnicam 4.6.1; OC5: Cerec Omnicam 5.0.0; PS: Primescan) were used to take complete-arch impressions from the reference cast. The impressions were repeated 10 times (n = 10) for each group. Conventional impressions were poured with type IV gypsum and digitized with a laboratory scanner (inEos X5). All datasets were obtained in standard tessellation language (STL) file format and cut to either complete-arch, anterior segment, or posterior segment areas for respective analysis. Values for trueness and precision for the respective areas were evaluated using a three-dimensional (3D) superimposition method with special 3D difference analysis software (GOM Inspect) using (90-10)/2 percentile values. Statistical analysis was performed using either one-way analysis of variance (ANOVA) or Kruskal-Wallis test (α = 0.05). Results are given as median and interquartile range [IQR] values in µm. Statistically significant differences were found between test groups for complete- and partial-arch impression methods in vitro (p < 0.05). Values ranged from 16.3 [2.8] µm (CO) up to 89.8 [26.1] µm (OC4) for in vitro trueness, and from 10.6 [3.8] µm (CO) up to 58.6 [38.4] µm (iT) for in vitro precision for the complete-arch methods. The best values for trueness of partial-arch impressions were found for the posterior segment, with 9.7 [1.2] µm for the conventional impression method (CO), and 21.9 [1.5] µm (PS) for the digital impression method. Within the limitations of this study, digital impressions obtained from specific IOSs are a valid alternative to conventional impressions for partial-arch segments. Complete-arch impressions are still challenging for IOS devices; however, certain devices were shown to be well within the required range for clinical quality. Further in vivo studies are needed to support these results.

In-vitro assessment of the accuracy and reliability of mandibular dental model superimposition based on voxel-based cone-beam computed tomography registration.

ObjectiveThis study was performed to evaluate the accuracy and reliability of a newly designed method to achieve mandibular dental model superimposition, using voxel-based cone-beam computed tomography (CBCT) registration.MethodsFourteen dry cadaveric mandibles and six teeth extracted from patients with severe periodontitis were used to establish 14 orthodontic tooth-movement models. The protocol consisted of two steps: in the first step, voxel-based CBCT mandible superimposition was performed; the reference comprised the external portion of the symphysis, extending to the first molar. The laser-scanned dental model image was then integrated with the CBCT image to achieve mandibular dental model superimposition. The entire process required approximately 10 minutes. Six landmarks were assigned to the teeth to measure tooth displacement, using tooth displacement on the superimposed laser-scanned mandibles as the reference standard. Accuracy was evaluated by comparing differences in tooth displacement based on the method and the reference standard. Two observers performed superimposition to evaluate reliability.ResultsFor three-dimensional tooth displacements, the differences between the method and the reference standard were not significant in the molar, premolar, or incisor groups (p > 0.05). The intraclass correlation coefficients for the inter- and intra-observer reliabilities of all measurements were > 0.92.ConclusionsOur method of mandibular dental model superimposition based on voxel registration is accurate, reliable, and can be performed within a reasonable period of time in vitro, demonstrating a potential for use in orthodontic patients.

Evaluation of two-dimensional lateral cephalogram and three-dimensional cone beam computed tomography superimpositions: a comparative study

Superimposition of radiographic imaging is used to evaluate patient growth and the effects of surgical and/or orthodontic treatment. The purpose of this study was to compare the outcomes of superimposition between two-dimensional (2D) and three-dimensional (3D) superimpositions. 2D lateral cephalograms were generated from the initial and final cone beam computed tomography scans (CBCT) of 18 patients and superimposed. Both 3D CBCT and 2D CBCT generated lateral cephalograms were oriented to the Frankfort horizontal plane and superimposed according to the American Board of Orthodontics recommendations. Changes in landmark position were quantified from the resulting superimposition outcomes via linear measurements made with Dolphin software. Differences between the two methods were analyzed using paired t-tests. Measurements were repeated twice for 10 randomly selected scans to assess reliability by intra-class correlation coefficient (ICC) analysis. Intra-examiner reliability was high for all measurements (ICC>0.84). Agreement between 2D and 3D superimposition outcomes, as measured by P-values, was low for ANS (P=0.026), B-point (P<0.001), ST Upper lip (P=0.019), U1 tip (P=0.010), and U1 apex (P=0.026). 2D measurements were significantly higher than 3D measurements for ANS, B-point, ST Upper lip, U1 tip, and U1 apex. Findings indicated that both methods of superimposition (2D and 3D) are highly reliable. Statistical differences between 2D and 3D superimposition outcomes were below the threshold of clinical significance.

Evaluation of three-dimensional superimposition technique on parietal bone of the puberty beagle dogs.

This study aimed to (a) evaluate the stability of the parietal bone of 6-9months old beagles and (b) examine whether parietal regional superimposition can provide an atraumatic and effective solution for further maxillary expansion study. Six prepubertal 6-month-old male beagles were included. Six miniscrew markers were inserted into the left and right sides of the parietal bone, and two of them were placed bilaterally near the palatal suture. The subjects were scanned with cone beam computed tomography (CBCT) at three time points of T0 (6months old), T1 (7.5months old) and T2 (9months old), respectively. All skull models were analyzed by both the miniscrew superimposition and the parietal regional superimposition. The two superimposition methods had no significant difference (p>0.05) in displacements of miniscrew markers between left and right first premolars (PM1). The maxillary superimposition between T0 and T2 indicated that the length and width of the maxillary as well as the width of the zygoma root increased significantly (p<0.05), while the height of maxillary had no significant difference (p>0.05) over the 3months. The parietal bone is relatively stable for beagles from 6months old to 9months old and thus can be used as a reference region for 3D skull model superimposition of the beagle dog.

Protein local conformations at the light of a structural alphabet

Protein structures are classically described in terms of secondary structures. Even if the regular secondary structures have relevant physical meaning, their recognition from atomic coordinates has some important limitations such as uncertainties in the assignment of boundaries of helical and β-strand regions. Further, on an average about 50% of all residues are assigned to an irregular state, i.e., the coil. Thus different research teams have focused on abstracting conformation of protein backbone in the localized short stretches. Using different geometric measures, local stretches in protein structures are clustered in a chosen number of states. A prototype representative of the local structures in each cluster is generally defined. These libraries of local structures prototypes are named as alphabets. We have developed a structural alphabet, named Protein Blocks, not only to approximate the protein structure, but also to predict them from sequence [1,2]. Since its development, we and other teams have explored numerous new research fields using this structural alphabet. I will review here some of the most interesting applications: (i) the most efficient protein superimposition methods [3,4], (ii) new ways to analyze protein structures [2], and (iii) new tool for analysis of protein dynamics and allostery [5,6].

VISUALISATION WITH G.I.S OF AGIA EIRINI GORGE AT THE SOUTHERN MARGINS OF THE WHITE MOUNTAINS, SW CRETE

Sustainable management of protected areas requires good knowledge of the entire system. Complicated natural systems require for their management the use of digital information systems, that would allow the integration of all the available information on the studied natural system as well as the elements of new researches. Among the natural systems the gorges constitute mainly geological structrures. The aim of the present study is the development of a 3D digital morphotectonic model for the Agia Eirini Gorge, crossing the southern limbs of mountain Lefka Ori in South-Western Crete. The work is divided in two parts, on one side in the creation of suitable backgrounds that is reqi ired for the creation of a 3D model and on the other hand the placement of the spatial data into the model. For the creation of the digital terrain model (DTM) of the gorge area, maps at a 1:5.000 scale, obtained from the Army Geographic Service were digitised using CAD Overlay 2000i software. The data obtained were transferred into SURPAC 2000 supplemented with orthophotomaps of the region with the method of superimposition. The initial data drawn from the existing geological map of the region were evaluated by data obtained from field work. This methodology allows integration of all available information for the system under study, including newly acquired data

Accuracy of 9 intraoral scanners for complete-arch image acquisition: A qualitative and quantitative evaluation

Statement of problemDifferent intraoral scanners (IOSs) are available for digital dentistry. However, information on the accuracy of various IOSs for complete-arch digital scans is limited. PurposeThe purpose of this in vitro study was to evaluate the trueness and precision of complete-arch digital scans produced by 9 IOSs, using the superimposition method, and to compare them based on characteristics including the data capture principle and mode and the need for powder coating. Material and methodsNine IOSs were used to obtain standard tessellation language (STL) data for a bimaxillary complete-arch model with various cavity preparations (N=10). The scanning performance was evaluated quantitatively and qualitatively. For quantitative evaluation, the images were processed and analyzed using 3-dimensional (3D) analysis software. After we superimposed the datasets, trueness was obtained by comparing it with the reference scan, and precision was obtained from intragroup comparisons. The IOSs were compared based on the data capture principle and mode and the need for powder coating. Statistical analyses were conducted using a Kruskal-Wallis test, followed by multiple Mann-Whitney U tests for pairwise comparisons among groups (α=.05). For qualitative evaluation, surface smoothness and sharp edge reproducibility of the digital images were compared. ResultsThe median precision values were lowest in the TRIOS model (average, 34.70 μm; maximum, 263.55 μm) and highest in the E4D model (average, 357.05 μm; maximum 2309.45 μm). Median average trueness values were lowest in the TRIOS model (42.30 μm) and highest in the Zfx IntraScan model (153.80 μm). The CS 3500 model had the lowest median maximum trueness values (450.75 μm); the E4D model had the highest values (2680.55 μm). Individual image and video sequence data captures showed similar median average trueness values (P>.05); the median maximum values of individual images were higher than those of the video sequence (P<.05). Swept source optical coherence tomography (SS-OCT) exhibited higher trueness values than those of other scanning principles (P<.05). The FastScan and True Definition, which require powder coating, showed significantly better trueness than other IOSs that did not require powdering (P<.05). The E4D, PlanScan, and Zfx IntraScan models had an increased tendency to produce images with imperfect surface features and to round off sharp edges. ConclusionsThe E4D and Zfx IntraScan models did not perform as accurately as the other IOSs. The data capture principle of SS-OCT and the mode of individual image acquisition exhibited inferior trueness. The FastScan and True Definition, which require powder coating, exhibited better trueness. The qualitative aspects of the IOSs varied in terms of polygon shapes, sharp edge reproducibility, and surface smoothness.

Preferred image quality metric for shifted superimposition-based resolution-enhanced images

Shifted superimposition is a resolution-enhancement method that has gained popularity in the projector industry the last couple of years. This method consists of shifting every other projected frame spatially with subpixel precision, and by doing so creating a new pixel grid on the projected surface with smaller effective pixel pitch. There is still an open question of how well this technique performs in comparison with the native resolution, and how high the effective resolution gain really is. To help investigate these questions, we have developed a framework for simulating different superimposition methods over different image contents, and evaluate the result using several image quality metrics (IQMs). We have also performed a subjective experiment with observers who rate the simulated image content, and calculated the correlation between the subjective results and the IQMs. We found that the visual information fidelity metric is the most suitable to evaluate natural superimposed images when subjective match is desired. However, this metric does not detect the distortion in synthetic images. The multiscale structural similarity metric which is based on the analysis of image structure is better at detecting this distortion.

Three-dimensional stability analysis of maxillomandibular advancement surgery with and without articular disc repositioning

This retrospective cohort study aimed to assess, three-dimensionally, mandible and maxilla changes following maxillomandibular advancement (MMA), with and without repositioning of TMJ articular discs. The sample comprised cone-beam computed tomography data from 32 subjects: group 1 (n = 12) without disc displacement and group 2 (n = 20) with bilateral disc repositioning. An automatic cranial base superimposition method was used to register the images at three time points: T1 (preoperative), T2 (postoperative), and T3 (at least 11 months follow-up). To assess surgical changes (T2–T1) and adaptive responses (T3–T2), the images were compared quantitatively and qualitatively using the shape correspondence method. The results showed that surgical displacements were similar in both groups for all the regions of interest except the condyles, which moved in opposite directions — group 1 to superior and posterior positions, and group 2 to inferior and anterior positions. For adaptive responses, we observed high individual variability, with lower variability in group 2. Sagittal relapse was similar in both groups. In conclusion, there were no significant differences in skeletal stability between the two groups. The maxillomandibular advancement surgeries, with rotation of the occlusal plane, had stable results for both groups immediately after surgery and at 1-year follow-up.

Three-dimensional surface models of the facial soft tissues acquired with a low-cost scanner

Although there has been an increase in three-dimensional (3D) scanning methods available on the market, they are generally expensive. The DI3D system is considered a good scanner for the acquisition of soft tissue surface images. The Microsoft Kinect scanner is a much more affordable alternative for acquiring 3D models. The aim of this study was to determine whether the precision and accuracy of Kinect are similar to those of DI3D. To verify the accuracy, 10 patients were scanned with both methods The models of each patient acquired from the two scanners were superimposed using a surface-to-surface registration technique, and the distances between the models were recorded for 10 different anatomical regions of interest. For the evaluation of precision, one patient was scanned 11 different times with the Kinect scanner, and these models were compared using the same superimposition method. It was found that the average difference between the two methods was 0.3±2.03mm. The assessment of reproducibility showed an average difference between the images taken with Kinect of 0.1±0.6mm (P<0.05, one-sample t-test). Thus, Kinect showed good precision and reasonable accuracy, and appears to be an interesting and promising resource for facial analysis.

Superimposition of 3D digital models: A case report

Superimposition of digital models may be performed to assess tooth movement in three dimensions. Detailed analysis of changes in tooth position after treatment may be achieved by this method. This article describes the method of superimposing digital models with a clinical case. It emphasizes the difficult procedure of superimposing 3D models in the lower arch. A methodology for superimposing mandibular models acquired with a structured light 3D scanner is discussed. Superimposition of digital models is useful to analyse tooth movement in the three planes of space, presenting advantages over the method of cephalogram superimposition. It seems feasible to superimpose digital models in the lower arch in patients without growth by using a coordinate system based on the palatal rugae and occlusion. The described method aims to advance the difficult procedure of superimposing digital models in the mandibular arch, but further research is nonetheless required in this field.

Precision and reliability of Dolphin 3-dimensional voxel-based superimposition.

Superimposition of 2 cone-beam computed tomography images is possible by using landmarks, surfaces, or density information (voxel-based). Voxel-based superimposition is automated and uses the most image content, providing accurate results. Until recently, this superimposition was extremely laborious, but a user-friendly voxel-based superimposition has recently been introduced. Our aim was to evaluate the precision and reliability of Dolphin 3-dimensional voxel-based superimposition (Dolphin Imaging, Chatsworth, Calif). This was a retrospective study using existing scans of 31 surgical orthodontic patients with a mean age of 21±8years (range, 15-47years). Each patient had a presurgical and a postsurgical scan taken within 12months. Surgical patients were used since the reference area for superimposition was not affected by growth or surgical procedures. The volumes were superimposed using voxel-based methods from Dolphin Imaging and a tested method used previously. This method uses 2 open-source programs and takes about 3hours to complete, whereas the Dolphin method takes under 5minutes. The postsurgical scan was superimposed on the presurgical scan at the cranial base. Postsurgical registrations forboth methods were compared with each other using the absolute closest point color map, with emphasis on 7 regions (nasion, A-point, B-point, bilateral zygomatic arches, and bilateral gonions). Intraclass correlations showed excellent reliability (0.96). The mean differences between the 2 methods were less than 0.21mm (voxel size, 0.38). The smallst difference was in the left zygomatic area at 0.09±0.07mm, and the largest was in the right gonial region at 0.21±0.13mm. Dolphin 3-dimensional voxel-based superimposition, a fast and user-friendly method, is precise and reliable.

Protein Local Conformations at the Light of a Structural Alphabet

Protein structures are classically described in terms of secondary structures. Even if the regular secondary structures have relevant physical meaning, their recognition from atomic coordinates has some important limitations such as uncertainties in the assignment of boundaries of helical and β-strand regions. Further, on an average about 50% of all residues are assigned to an irregular state, i.e., the coil. Thus different research teams have focused on abstracting conformation of protein backbone in the localized short stretches. Using different geometric measures, local stretches in protein structures are clustered in a chosen number of states. A prototype representative of the local structures in each cluster is generally defined. These libraries of local structures prototypes are named as “structural alphabets”. We have developed a structural alphabet, named Protein Blocks, not only to approximate the protein structure, but also to predict them from sequence. Since its development, we and other teams have explored numerous new research fields using this structural alphabet. I will review here some of the most interesting applications: (i) the most efficient protein superimposition methods, (ii) new ways to analyse protein structures, and (iii) new tool for analysis of protein dynamics and allostery.

Evaluation of Peri-Implant Bone Reduction Levels from Superimposition Perspective: Pilot Study among Ukrainian Implantology Practice

Objective: To evaluate the possibility and efficiency of using adapted peri-implant bone evaluation method based on the principle of graphical superimposition and compare it to the possibilities of using sagittal sections of CBCT results to register the dynamics of peri-implant bone changes during the first year of implant functioning. Material and Methods: 108 pairs of DICOM data sets were selected and pre-anonymized and coded in Planmeca Romexis ® Viewer software. Each pair of datasets consisted of a CBCT file, obtained immediately after the installation of a dental implant, and one year after its operation. The first method of peri-implant bone changes evaluation was carried out by analyzing the sagittal sections of the CBCT data from the mesial and distal sides of the implant. The second method was followed by original algorithm, which included specific steps of superimposition of graphical images. Results: Superimposition method helped to establish volumetric parameter of circular bone reduction around dental implants after 1 year of their functioning. Such average values for the maxillary distal implants were 3.547 mm3, maxillary frontal implants – 3.118 mm3, mandibular distal implants – 2.614 mm3, mandibular frontal implants – 2.456 mm 3. Correlation values between averages of vertical bone loss parameters and volumetric bone loss parameters riches r=0.954. Among all patients the highest peri-implant bone reduction rates were observed in the distal and frontal areas of the maxilla, even though statistical difference among such parameters of implants installed at the areas of mandible and maxilla was not significant (p > 0.05). Such observation was established during the analysis of results obtained both by digital sagittal cross section from CBCT results and by superimposition method. Conclusion: Using the superimposition principle allows us to evaluate the individual indicator of volumetric bone loss at the peri-implant region. The possibility of taking into account the parameters of bone tissue volume reduction, instead of just geometrical parameter of bone height, allows to individualize the parameters of bone loss among patients of different prosthetic rehabilitation group.