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1
Tahar, K. N., M. A. Asmadin, S. A. H. Sulaiman, N. Khalid, A. N. Idris, and M. H. Razali. "Individual Tree Crown Detection Using UAV Orthomosaic." Engineering, Technology & Applied Science Research 11, no. 2 (April 11, 2021): 7047–53. http://dx.doi.org/10.48084/etasr.4093.
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Unmanned Aerial Vehicles (UAVs) are increasingly used in forestry as they are economical and flexible. This study aims to present the advantages of the drone photogrammetry method in collecting individual tree crowns, as individual tree crown detection could deliver essential ecological and economic information. The referred accuracy for individual tree crown extraction is 79.2%. Only crowns that were clearly visible were selected and manually delineated on the image because the distribution of the true crown size is significantly different from the segmented crowns. The aim of this study is to investigate UAVs orthomosaics in individual tree crown detection. The objectives of this study are to produce the orthomosaic of tree crown extraction mapping using the Pix4D software and analyze the tree crowns using tree crown delineation and the OBIA algorithm. Data processing involves the processing of aerial images using Pix4Dmapper. Automatic tree crown detection involves a tree crown delineation algorithm and OBIA operations to process the tree crown extraction. The crown delineation algorithm and OBIA algorithm operation will be compared to the actual tree crown measurement in terms of diameter and area. The tree crown delineation method obtained a 0.347m mean diameter difference from the actual tree crown diameter, while the OBIA approach obtained 4.98m. The tree crown delineation method obtained 97.26% of the actual tree crown area, while OBIA obtained 91.74%.
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Yoshimura, Kenichi. "Spatial distribution and morphology of shoots in the variant crown form of Rhododendron reticulatum." Botany 88, no. 11 (November 2010): 995–1005. http://dx.doi.org/10.1139/b10-071.
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Rhododendron reticulatum D. Don ex G.Don is a common understory shrub in western Japan that exhibits highly plastic crown architecture and occurs in various light environments. I investigated how functional differentiation and spatial distribution of long and short shoots contribute to the plasticity of crown architecture of R. reticulatum. Crown form was derived from the crown depth/width ratio. Crown depth/width ratio was higher in sun-lit crowns. In crowns with higher depth/width ratio, long shoots were distributed in upper positions of the crown. Long shoots grew vertically and horizontally. In crowns with lower depth/width ratio, long shoots were arranged in the outer position of the crown and grew outward. Within neighboring shoots, long shoots had less mass than their paired short shoots. Results suggest that long shoots of R. reticulatum function to expand the crown and to reduce leaf overlap in multilayer crowns, which are found in high-light environments, while both long and short shoots function to minimize leaf overlap in monolayer crowns, which are found in shaded environments. Plasticity of crown architecture by altering shoot position and shoot morphology allows growth under various light environments in the forest understory.
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Mao, Hua, John B. Thorne, Jennifer S. Pharr, and Robert E. Gawley. "Effect of crown ether ring size on binding and fluorescence response to saxitoxin in anthracylmethyl monoazacrown ether chemosensors." Canadian Journal of Chemistry 84, no. 10 (October 1, 2006): 1273–79. http://dx.doi.org/10.1139/v06-093.
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Convenient macrocyclization synthetic routes for the preparation of different-sized monoaza anthracylmethyl crown ether chemosensors (15-crown-5, 18-crown-6, 21-crown-7, 24-crown-8, and 27-crown-9) are described. Evaluation of these crowns as chemosensors for saxitoxin revealed that the larger crowns have moderately higher binding constants, with the 27-crown-9 chemosensor having the largest binding constant (2.29 × 105 (mol/L)–1). Fluorescence enhancements of 100% were observed at saxitoxin concentrations of 5 µmol/L, which is close to the detection limit in mouse bioassay.Key words: anthracene, crown ethers, saxitoxin, paralytic shellfish poison (PSP), binding constants; chemosensors.
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Bamdadian, Zhaleh, Nilgoon Pasdar, Abdolhamid Alhavaz, Shahram Ghasemi, and Ali Bijani. "Comparative Evaluation of Physical and Mechanical Properties of Different Brands of Primary Molar Stainless-Steel Crowns: An In Vitro Study." Open Access Macedonian Journal of Medical Sciences 7, no. 23 (December 10, 2019): 4120–26. http://dx.doi.org/10.3889/oamjms.2019.861.
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BACKGROUND: There is some cases of perforation and undesirable properties of some primary molars stainless steel crowns.
AIM: The aim of this study was to compare the physical and mechanical properties of different commercial brands of these crowns.
METHODS: In an in vitro study, a total of 10 stainless steel tooth crowns of the second primary mandibular molars size 6 of 4 different commercial brands (a total of 280 crowns) were evaluated. These crowns were included KTR Pre-trimmed and Crimped Nichro Stainless Steel Primary Molar Crowns (KTR, China); 3M Stainless Steel Primary Molar Crowns (ESPE, St paul; USA); NuSmile SSC Pre-contoured (Inc, Houstone, TX; USA) and Kids crown (Shinghung, Seoul; Korea). Corrosion and galvanic corrosion, wear, microhardness, compressive strength, fatigue strength of crowns and weight percent of elements were investigated.
RESULTS: The highest rate of microhardness, compressive and Fatigue strength of the crowns were made by Nu Smile > 3M > Kids Crown > KTR respectively. The highest rate of corrosion potential in corrosion and Galvanic corrosion tests was in KTR > Kids crowns > 3M > Nu smile respectively. The order of crown wear was KTR > Kids Crown > 3M > Nu Smile respectively. The highest amount of nickel element was found in the Nu Smile crown and the highest amount of chrome in the 3M crown with a significant difference with others (p < 0.001). The KTR and Kids crowns lacked molybdenum.
CONCLUSION: The results showed that Nu Smile crown has better physical and mechanical properties than other evaluated crowns in this study.
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Fish, Heather, Victor J. Lieffers, Uldis Silins, and Ronald J. Hall. "Crown shyness in lodgepole pine stands of varying stand height, density, and site index in the upper foothills of Alberta." Canadian Journal of Forest Research 36, no. 9 (September 1, 2006): 2104–11. http://dx.doi.org/10.1139/x06-107.
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Crown shyness is the empty space between crowns in fully stocked stands that is not related to tree-fall gaps. The objectives of this study were to determine the stand and site factors that control crown shyness in lodgepole pine (Pinus contorta Dougl. ex Loud.) stands and to evaluate whether stands experiencing crown shyness compensate for leaf area losses by maintaining longer crowns. We measured canopy closure (i.e., the inverse of crown shyness), crown radius and length, and green litterfall in stands of various height, relative density, and site index. Canopy closure decreased with stand height and increased with site index and relative density. Green litterfall increased with height and relative density. Crown radius and crown length reached a plateau by 8-10 m height, despite increased spacing between tree boles with increasing stand height. Crown radius increased with height and site index but declined with relative density and slenderness coefficient. Crown length also increased with height and site index but declined with slenderness coefficient. Despite the fact that, in tall stands, where >50% of the sky was not covered by crowns, there was not an accompanying increase in crown length to take advantage of the apparent increase in light transmission to the lower crown.
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Zhang, Li Xian, and Yu Xiao Liu. "Fracture Resistance and Failure Mode of Different Type of Ceramic Crowns." Solid State Phenomena 330 (April 12, 2022): 119–24. http://dx.doi.org/10.4028/p-44ir6o.
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Objective: To study the fracture resistance and failure modes of different type of ceramic crowns. Methods: Four groups of crown including zirconia-veneering porcelain crown (Group 1), whole zirconia crown (CAD/CAM, Group 2), cast ceramic crown (Group 3) and glass ceramic crown (CAD/CAM, chairside, Group 4) with the same thickness were manufactured, each group own 12 crowns. The fracture resistance test and failure modes analysis of the specimens were conducted, SPSS22.0 was used to analyze the difference among the groups. Results: The fracture strength of Group 2 is significantly higher than other three group (P<0.05), Statistical significance was found between group 3 and group 1, group 4. No Statistical significance was found between group 1 and group 4. The failure modes of the whole zirconia crown, the cast ceramic crown and the glass ceramic crown are complete crown fracture; 33% of the zirconia-veneering porcelain crown showed veneering layer fracture, the other 67% showed complete crown fracture. Conclusion: The fracture resistance of the whole zirconia crown are higher than the cast ceramic crown, the zirconia-veneering crown and the glass ceramic crown and the glass ceramic crown (CAD/CAM) is a very convenient prostheses. The failure modes are significantly influenced by the type of the crown.
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Rahate, Ishani, Punit Fulzele, and Nilima Thosar. "Comparative evaluation of clinical performance, child and parental satisfaction of Bioflx, zirconia and stainless steel crowns in pediatric patients." F1000Research 12 (December 21, 2023): 756. http://dx.doi.org/10.12688/f1000research.133464.2.
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Background Pediatric dental treatment is challenging in patients with early childhood caries. For clinician its difficult to manage child and provide good work at the same time. Its necessity to have the best equipments as well as materials. Nowadays, aesthetics play an important role in managing decayed teeth. Zirconia crown is better option but requires excessive preparation. As Bioflx is newly developed crown and has combined stainless steel and zirconia properties. Aim To assess the clinical performance and child and parental satisfaction of Bioflex crowns compared to zirconia and stainless steel crowns. Methods In this comparative study of Bioflx crowns with zirconia and stainless steel crowns, children aged three to seven years old will be selected, and 72 primary teeth requiring crowns will be randomly distributed into three groups, n = 24: Group I: Preformed stainless steel crown, control; Group II: Preformed Bioflex crown; Group III: Preformed zirconia crown. Crowns will be evaluated for recurrent caries, plaque accumulation, restoration failure, gingival status opposing tooth wear, and clinicians and parental satisfaction at zero, three, six, and 12 months. Results Bioflx crown will have better clinical as well as parental satisfaction among zirconia and stainless steel crowns. Conclusions The Bioflx crown can be used as an alternative economical esthetic full-coronal restoration for primary teeth. Trial registration CTRI registration number: CTRI/2023/05/052256; Date of registration: May 03, 2023. Protocol version Two; Date: April 22, 2023
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Rocha, Adna Alves, Marco Aurélio de Carvalho, Dimorvan Bordin, Altair Antoninha Del Bel Cury, and Priscilla Cardoso Lazari-Carvalho. "Biomechanical behavior of different designs of hybrid abutment-restoration on the posterior crown: a finite element analysis." Brazilian Dental Journal 34, no. 6 (2023): 140–49. http://dx.doi.org/10.1590/0103-6440202305539.
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Abstract This study aimed to evaluate the influence of material and crown design on the biomechanical behavior of implant-supported crowns with hybrid abutment (HA) through three-dimensional (3D) finite element analysis. The study factors were the type of material used as the mesostructure or crown (zirconia, lithium disilicate, and hybrid ceramic) and the crown design cemented to the titanium base (mesostructure cemented to the titanium base and a crown cemented on it (HaC); hybrid crown-abutment, the abutment and crown are manufactured as a single piece and cemented to the titanium base (HC); monolithic crown cemented on the titanium base and screwed to the implant (CS); and monolithic crown cemented on the titanium base (CC). Four 3D models were constructed using an implant with an internal connection, and an oblique load of 130 N was applied at 45° to the long axis of the implant. The models were evaluated using the von Mises stress for crown, abutment, screw, and implant and maximum principal stress for bone tissues. The lowest stresses occurred in the groups with a lower elastic modulus material, mainly hybrid ceramics, considered a material with greater resilience. The cemented crown group presented the lowest stress values. The stresses were concentrated in the cervical region of the crown at the titanium crown/base interface. Mesostructures made of materials with a higher elastic modulus exhibited a higher concentration of stress. The presence of a screw hole increased the stress concentration in the ceramic crown. Cemented ceramic crowns exhibited better biomechanical behavior than screw-retained crowns.
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Zhou, Jun Wei, and Da Zheng Wang. "Parametric Study of Crowned Blade in Horizontal Axial Turbine." Advanced Materials Research 732-733 (August 2013): 443–50. http://dx.doi.org/10.4028/www.scientific.net/amr.732-733.443.
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The horizontal axial turbine could extract kinetic energy from both wind and tidal stream. In this paper, a type of horizontal axial turbine was designed with a crown stalled on the blade tip and the turbine was analyzed in a tidal stream. Several turbines with different geometries of the crowns were compared, whose power coefficients were numerically simulated by the CFD method. Effects of the crown design parameters, such as crown setting directions and different widths on turbine efficiency were discussed. Furthermore, when the turbine worked at different tip speed ratio, the results were discussed, either. By analysis of the results, it is could be concluded that a circular crown was sufficient to eliminate blade tip loss caused by tip leakage flow. The upstream semicircle crown modified the corresponding side foil pressure distribution to the design value, and so did the downstream semicircle crown. In the ellipse crowns testing, turbine efficiency was approximately in line with the value of crowns width. When the turbine with the circular crown worked at a little higher tip speed ratio than the design value, the crown was effective as before.
10
Zeide, Boris, and Peter Pfeifer. "A Method for Estimation of Fractal Dimension of Tree Crowns." Forest Science 37, no. 5 (November 1, 1991): 1253–65. http://dx.doi.org/10.1093/forestscience/37.5.1253.
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Abstract A method is proposed for estimating fractal dimension of tree crowns from measurements of foliage mass and crown volume. Because fractal dimensions for each of the ten investigated species were greater than two, crown surface and volume depend on the unit of measurement. The power relationship between foliage mass and crown volume reflects self-similarity of tree crowns. In all studied cases, fractal dimensions of dominant trees were greater than those of intermediate trees of the same species. Fractal dimension can be used as an indicator of tolerance, crown class, and foliage distribution within a crown. For. Sci. 37(5):1253-1265.
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Rahate, Ishani, Punit Fulzele, and Nilima Thosar. "Comparative evaluation of clinical performance, child and parental satisfaction of Bioflex, zirconia and stainless steel crowns in pediatric patients." F1000Research 12 (June 27, 2023): 756. http://dx.doi.org/10.12688/f1000research.133464.1.
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Background: Pediatric treatment is challenging in patients with early childhood caries. It is difficult due to the adjacency of pulp, miniature tooth size, and thin enamel compared to permanent dentition. Nowadays, aesthetics play an important role in managing decayed teeth, and children need treatment that includes full coverage crowns in either stainless steel or anesthetic crown in zirconia or the recently developed Bioflex crown. The Bioflex crowns are highly flexible and aesthetically preformed pediatric crowns with combined stainless steel and zirconia properties. This study aims to assess the clinical performance and child and parental satisfaction of Bioflex crowns compared to zirconia and stainless steel crowns. Methods: In the current in-vivo comparison of Bioflex crowns with zirconia and stainless steel crowns, children aged three to seven years old will be selected, and 72 primary teeth requiring crowns will be randomly distributed into three groups, n = 24: Group I: Preformed stainless steel crown, control; Group II: Preformed Bioflex crown; Group III: Preformed zirconia crown. Crowns will be evaluated for recurrent caries, plaque accumulation, restoration failure, gingival status opposing tooth wear, and clinicians and parental satisfaction at zero, three, six, and 12 months. Newly introduced aesthetic crowns will serve as a versatile alternative for restoring primary decayed teeth that over-performed aesthetic and conventional crowns. Conclusions: The Bioflex crown will be assessed as a better aesthetic substitute for the future, and the satisfaction level of parents will be evaluated. Trial registration: CTRI registration number: CTRI/2023/05/052256; Date of registration: May 03, 2023. Protocol version: Two; Date: April 22, 2023
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Umeki, Kiyoshi. "A comparison of crown asymmetry between Piceaabies and Betulamaximowicziana." Canadian Journal of Forest Research 25, no. 11 (November 1, 1995): 1876–80. http://dx.doi.org/10.1139/x95-202.
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Morphological plasticity in terms of asymmetric display of crowns was compared between Piceaabies (L.) Karst. and Betulamaximowicziana Regel. To evaluate crown asymmetry in relation to local environment, a model that predicts crown asymmetry from topography and configuration of neighbors was applied to data derived from a mixed forest in Hokkaido, northern Japan. Betulamaximowicziana had greater crown asymmetry than P. abies in absolute value. However, observed crown asymmetry of both species was determined by local environment to similar degrees. Some other differences were found between the two species. Crowns of P. abies were more influenced by neighbors than topography, while crowns of B. maximowicziana were more influenced by topography than neighbors. Crowns of P. abies were influenced mainly by larger neighbors, while crowns of B. maximowicziana were influenced by large and by relatively small neighbors.
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Ex, Seth, Frederick W. Smith, and Tara L. Keyser. "Characterizing crown fuel distribution for conifers in the interior western United States." Canadian Journal of Forest Research 45, no. 7 (July 2015): 950–57. http://dx.doi.org/10.1139/cjfr-2014-0503.
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Canopy fire hazard evaluation is essential for prioritizing fuel treatments and for assessing potential risk to firefighters during suppression activities. Fire hazard is usually expressed as predicted potential fire behavior, which is sensitive to the methodology used to quantitatively describe fuel profiles: methodologies that assume that fuel is distributed uniformly throughout crowns have been shown to predict less severe fire behavior than those that assume more realistic nonuniform fuel distributions. We used crown fuel data from seven interior western United States conifer species to characterize within-crown fuel distributions. Fuel was shifted upward and concentrated in crowns in crowded stands compared with crowns in open stands, which suggests that the vertical distribution of fuel is shaped by foliage concentration in favorable light environments near the top of crowns and echoes the predictable relationship between crown ratio and stand density. However, unlike crown ratio, the relationship between within-crown foliage distribution and stand density was independent of the shade tolerance of a species. This implies that there is a general relationship between stand density and within-crown fuel distribution for conifers and that species differences in fuel profiles related to shade tolerance are expressed primarily in the relationship between stand density and crown ratio.
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Goelz, J. C. G. "Open-Grown Crown Radius of Eleven Bottomland Hardwood Species: Prediction and Use in Assessing Stocking." Southern Journal of Applied Forestry 20, no. 3 (August 1, 1996): 156–61. http://dx.doi.org/10.1093/sjaf/20.3.156.
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Abstract Equations were prepared to predict crown radius for eleven species of open-grown bottomland hardwood trees. Crown radius was predicted as a function of diameter at breast height (dbh) and as a function of dbh, total height, and crown ratio. Equations were prepared for individual species and species groups. Pecan (Carya illinoensis (Wangenh.) K. Koch) has the largest crowns over a broad range of dbh. Eastern cottonwood (Populus deltoides Bartr. ex Marsh.) has the smallest crowns for most levels of dbh. Sweetgum (Liquidambar styraciflua L.) has relatively small crowns for trees of small dbh, but crown radius is comparable to most species at the largest dbh. The crown radius predictions may be used to calculate crown competition factor. B-lines of stocking may be calculated that represent a stand of one species as well as a mixed-species stand of any particular species proportion. South. J. Appl. For. 20(3):156-161.
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Boivin, Frédéric, Alain Paquette, Pierre Racine, and Christian Messier. "A fast and reliable method for the delineation of tree crown outlines for the computation of crown openness values and other crown parameters." Canadian Journal of Forest Research 41, no. 9 (September 2011): 1827–35. http://dx.doi.org/10.1139/x11-107.
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Numerous crown parameters (e.g., leaf area index, diameter, height, volume) can be obtained via the analysis of tree crown photographs. In all cases, parameter values are functions of the position of the crown outline. However, no standardized method to delineate crowns exists. To explore the effect of different outlines on tree crown descriptors, in this case crown openness (CO), and facilitate the adoption of a standard method free of user bias, we developed the program Crown Delineator that automatically delineates any outline around tree crowns following predetermined sensibility settings. We used different outlines to analyze tree CO in contrasting settings: using saplings from four species in young boreal mixedwood forests and medium-sized hybrid poplar trees from a low-density plantation. In both cases, the estimated CO increases when calculated from a looser outline, which had a strong influence on understory available light simulations using a forest simulator. These results demonstrate that the method used to trace crown outlines is an important step in the determination of CO values. We provide a much-needed computer-assisted solution to help standardize this procedure, which can also be used in many other situations in which the delineation of tree crowns is needed (e.g., competition and crown shyness).
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Seethepalli, Anand, Haichao Guo, Xiuwei Liu, Marcus Griffiths, Hussien Almtarfi, Zenglu Li, Shuyu Liu, et al. "RhizoVision Crown: An Integrated Hardware and Software Platform for Root Crown Phenotyping." Plant Phenomics 2020 (February 15, 2020): 1–15. http://dx.doi.org/10.34133/2020/3074916.
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Root crown phenotyping measures the top portion of crop root systems and can be used for marker-assisted breeding, genetic mapping, and understanding how roots influence soil resource acquisition. Several imaging protocols and image analysis programs exist, but they are not optimized for high-throughput, repeatable, and robust root crown phenotyping. The RhizoVision Crown platform integrates an imaging unit, image capture software, and image analysis software that are optimized for reliable extraction of measurements from large numbers of root crowns. The hardware platform utilizes a backlight and a monochrome machine vision camera to capture root crown silhouettes. The RhizoVision Imager and RhizoVision Analyzer are free, open-source software that streamline image capture and image analysis with intuitive graphical user interfaces. The RhizoVision Analyzer was physically validated using copper wire, and features were extensively validated using 10,464 ground-truth simulated images of dicot and monocot root systems. This platform was then used to phenotype soybean and wheat root crowns. A total of 2,799 soybean (Glycine max) root crowns of 187 lines and 1,753 wheat (Triticum aestivum) root crowns of 186 lines were phenotyped. Principal component analysis indicated similar correlations among features in both species. The maximum heritability was 0.74 in soybean and 0.22 in wheat, indicating that differences in species and populations need to be considered. The integrated RhizoVision Crown platform facilitates high-throughput phenotyping of crop root crowns and sets a standard by which open plant phenotyping platforms can be benchmarked.
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Gan, Yi, Quan Wang, and Atsuhiro Iio. "Tree Crown Detection and Delineation in a Temperate Deciduous Forest from UAV RGB Imagery Using Deep Learning Approaches: Effects of Spatial Resolution and Species Characteristics." Remote Sensing 15, no. 3 (January 29, 2023): 778. http://dx.doi.org/10.3390/rs15030778.
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The automatic detection of tree crowns and estimation of crown areas from remotely sensed information offer a quick approach for grasping the dynamics of forest ecosystems and are of great significance for both biodiversity and ecosystem conservation. Among various types of remote sensing data, unmanned aerial vehicle (UAV)-acquired RGB imagery has been increasingly used for tree crown detection and crown area estimation; the method has efficient advantages and relies heavily on deep learning models. However, the approach has not been thoroughly investigated in deciduous forests with complex crown structures. In this study, we evaluated two widely used, deep-learning-based tree crown detection and delineation approaches (DeepForest and Detectree2) to assess their potential for detecting tree crowns from UAV-acquired RGB imagery in an alpine, temperate deciduous forest with a complicated species composition. A total of 499 digitized crowns, including four dominant species, with corresponding, accurate inventory data in a 1.5 ha study plot were treated as training and validation datasets. We attempted to identify an effective model to delineate tree crowns and to explore the effects of the spatial resolution on the detection performance, as well as the extracted tree crown areas, with a detailed field inventory. The results show that the two deep-learning-based models, of which Detectree2 (F1 score: 0.57) outperformed DeepForest (F1 score: 0.52), could both be transferred to predict tree crowns successfully. However, the spatial resolution had an obvious effect on the estimation accuracy of tree crown detection, especially when the resolution was greater than 0.1 m. Furthermore, Dectree2 could estimate tree crown areas accurately, highlighting its potential and robustness for tree detection and delineation. In addition, the performance of tree crown detection varied among different species. These results indicate that the evaluated approaches could efficiently delineate individual tree crowns in high-resolution optical images, while demonstrating the applicability of Detectree2, and, thus, have the potential to offer transferable strategies that can be applied to other forest ecosystems.
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Miller, Nathan L., and Cynthia M. Ocamb. "Relationships Between Yield and Crown Disease of Sweet Corn Grown in the Willamette Valley of Oregon." Plant Health Progress 10, no. 1 (January 2009): 9. http://dx.doi.org/10.1094/php-2009-0831-01-rs.
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Sweet corn (Zea mays L.) yields in the Willamette Valley of Oregon declined during the 1990s. Severe root rot affected some plants shortly before harvest, but was absent in other plants that showed secondary symptoms of reduced ear yield and leaf death; necrosis of stalk nodes and crown tissues was found instead. Studies were done to determine if there is a relationship among yield and necrosis of crowns, stalk nodes, nodal roots, radicles, or sub-crown internodes. An image analysis program was used to quantify the grayscale value of crown and node tissues. Regression analysis indicates that plants with darker crown tissues have lower ear weights. Rots of the nodal roots, radicle, or sub-crown internode were poor predictors of ear weight at harvest. When either Fusarium oxysporum or F. verticillioides were isolated from crowns of commercial sweet corn plants, these crowns had significantly darker grayscale values than those from which neither species was isolated; ear weights were also lower when F. oxysporum was isolated from the crown or a stalk node. Accepted for publication 13 July 2009. Published 31 August 2009.
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Soleimani, Fatemeh, Hamid Jalali, Azam Sadat Mostafavi, Somayeh Zeighami, and Maryam Memarian. "Retention and Clinical Performance of Zirconia Crowns: A Comprehensive Review." International Journal of Dentistry 2020 (October 15, 2020): 1–6. http://dx.doi.org/10.1155/2020/8846534.
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Zirconia has been used for rehabilitation of edentulous spaces approximately for a decade, and there have been several reports regarding the clinical performance and retention of zirconia crowns. Outstanding mechanical properties, biocompatibility, and excellent aesthetics make zirconia-based crowns as a popular crown among the current all-ceramic crowns in restorative dentistry. However, restoration with a zirconia crown is a challenging treatment. The goal of this study was to assess the current literature to summarize the studies reporting the effective risk factors on retention of zirconia crowns to provide clinicians with a useful point of view in the decision-making process for use of these restorations. Literature based-search was performed to find related articles until August 2020 using EMBASE, Google Scholar, and MEDLINE. Search terms used were “zirconia restorations properties,” “zirconia crowns clinical performance,” “zirconia crown survival,” “biological complications,” and “zirconia crown retention.” Results were limited to papers available in English. The references of all related literature were also searched for further citations. Overall, although clinical long-term and follow-up studies are a vital requirement to conclude that zirconia has great reliability, it seems that zirconia crown restorations are both well tolerated and sufficiently resistant.
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Power, Hugues, Valerie LeMay, Frank Berninger, Derek Sattler, and Daniel Kneeshaw. "Differences in crown characteristics between black (Picea mariana) and white spruce (Picea glauca)." Canadian Journal of Forest Research 42, no. 9 (September 2012): 1733–43. http://dx.doi.org/10.1139/x2012-106.
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Black spruce ( Picea mariana (Mill.) Britton, Sterns & Poggenb.) and white spruce ( Picea glauca (Moench) Voss) are phylogenetically proximal species that differ in productivity. Crown characteristics of these two species have not been extensively studied, in spite of the importance of these two species to the Canadian boreal forest and the importance of tree crowns for understanding and modelling tree growth. In this paper, we characterize and compare the crown lengths, crown profiles (i.e., radii), shapes, and surface areas of these two species using 65 white spruce and 57 black spruce trees destructively sampled in the provinces of Alberta, Ontario, and Quebec, Canada. Crown length was measured on every sample tree, while crown profile was obtained by reconstructing crowns from branch measurements. Our results showed that crown lengths did not differ between these two species given the same tree size and growth conditions. However, these two species establish under different growth conditions resulting in crown length differences. Further, differences in crown radii and profiles were found even under the same growth conditions. White spruce trees had wider crown radii and profiles changed from a parabola to a cone shape under increased density. As a result, differences in crown surface areas were found.
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Clatterbuck, Wayne K., Tyler M. L. Brannon, and Edward C. Yost. "Branch Elongation, Bud Durability, and Wind-Generated Crown Movement Associated with Crown Abrasion in Deciduous Trees." Forests 15, no. 2 (January 28, 2024): 247. http://dx.doi.org/10.3390/f15020247.
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Trees that grow in close proximity to other trees are subject to crown and branch abrasion, causing mechanical injury. The loss of branch tips and buds through abrasion can affect the architecture and growth of tree crowns. This research quantifies the impacts of crown abrasion between neighboring trees of several deciduous species and how crown abrasion may influence stand dynamics. Tree interactions were evaluated during the dormant and growing seasons to determine how wind-generated movement affects crowns under foliated and un-foliated conditions. Branch elongation was measured in tree crowns where growth was both inhibited and uninhibited by adjacent trees. Bud durability was evaluated by growing season for species with determinate and indeterminate shoot growth forms using a pendulum impact tester. Crown movement during wind events was assessed by using three-axial accelerometers in the outermost points of tree crowns. Accelerometers logged the movement of branches in the tree crown. By using both the crown sway acceleration and associated bud durability and mass data, the possible force necessary to break or abrade buds and branches was calculated at different wind speeds. Branch elongation was greater for most species on the exposed side of the crown that was not affected by adjacent trees. Preformed buds from the determinate growth form were determined to have greater durability than sustained growth or indeterminant buds. Acceleration from wind gusts increased more rapidly as wind speed intensified in the growing season when leaves were on the tree than in the dormant season. This research suggests that crown abrasion contributes to the development of mixed species stands by reducing crown size and growth therefore allowing slower-growing species with determinant growth to stratify above faster growing trees with indeterminant growth.
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Tribst, João Paulo Mendes, Amanda Maria de Oliveira Dal Piva, Azeem Ul Yaqin Syed, Mohammed Alrabiah, Khulud A. Al-Aali, Fahim Vohra, and Tariq Abduljabbar. "Comparative Stress Analysis of Polyetherketoneketone (PEKK) Telescopic Crowns Supported by Different Primary Crown Materials." Applied Sciences 12, no. 7 (March 28, 2022): 3446. http://dx.doi.org/10.3390/app12073446.
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The present study aimed to investigate the stress distribution of secondary telescopic crowns made of polyetherketoneketone (PEKK) combined with different primary crown (PC) materials (Zirconia, CoCr, Titanium, and PEKK) using finite element analysis. The geometric model was composed of bone tissue, periodontal ligament, root dentin, cement layer, primary crown, and secondary telescopic crown (SC). A total of four models were evaluated in which the secondary crowns were simulated in PEKK. The models were designed in CAD software and exported to the computer aided engineering software for the statistic structural analysis simulation. The materials were considered isotropic, with linear behavior and elastic properties. The model was fixed in the bone base and the load was applied at the occlusal surface of the crowns with 600 N. The results were required in von-Mises stress for the primary crown, secondary crown, cement layer, and Equivalent Strain to the periodontal ligament and bone tissue. Results show that the material influenced the stress distribution. The higher the PC elastic modulus, the higher the stress magnitude on the SC and cement layer. In the present study, the use of milled high-density polymer for primary crown presented a promising biomechanical behavior as an alternative material for double-crown design.
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Tribst, João P. M., Amanda M. O. Dal Piva, Alexandre L. S. Borges, Lilian C. Anami, Cornelis J. Kleverlaan, and Marco A. Bottino. "Survival Probability, Weibull Characteristics, Stress Distribution, and Fractographic Analysis of Polymer-Infiltrated Ceramic Network Restorations Cemented on a Chairside Titanium Base: An In Vitro and In Silico Study." Materials 13, no. 8 (April 16, 2020): 1879. http://dx.doi.org/10.3390/ma13081879.
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Different techniques are available to manufacture polymer-infiltrated ceramic restorations cemented on a chairside titanium base. To compare the influence of these techniques in the mechanical response, 75 implant-supported crowns were divided in three groups: CME (crown cemented on a mesostructure), a two-piece prosthetic solution consisting of a crown and hybrid abutment; MC (monolithic crown), a one-piece prosthetic solution consisting of a crown; and MP (monolithic crown with perforation), a one-piece prosthetic solution consisting of a crown with a screw access hole. All specimens were stepwise fatigued (50 N in each 20,000 cycles until 1200 N and 350,000 cycles). The failed crowns were inspected under scanning electron microscopy. The finite element method was applied to analyze mechanical behavior under 300 N axial load. Log-Rank (p = 0.17) and Wilcoxon (p = 0.11) tests revealed similar survival probability at 300 and 900 N. Higher stress concentration was observed in the crowns’ emergence profiles. The MP and CME techniques showed similar survival and can be applied to manufacture an implant-supported crown. In all groups, the stress concentration associated with fractographic analysis suggests that the region of the emergence profile should always be evaluated due to the high prevalence of failures in this area.
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Mattoo, Khurshid A., Faisal M. Alkhayrat, Hussam A. Madkhali, Ibrahim H. Geathy, Mohammed AW Qahhar, and Ahmed Yaqoub. "Subjective Differences between Dentists and Patients about Relative Quality of Metal Ceramic Restorations placed in the Esthetic Zone." Journal of Contemporary Dental Practice 18, no. 2 (2017): 112–16. http://dx.doi.org/10.5005/jp-journals-10024-2000.
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ABSTRACT Introduction Esthetic perceptions could differ between the dentist and his patients among various regions and cultures. Aim The aims of this study were to evaluate the subjective differences between the dentist and the patient in terms of esthetics of metal-ceramic crowns (MCcs). The study also aims to compare the mesiodistal (MD) and buccolingual (BL) dimensions of the cemented crown with its respective natural antimeric tooth. Materials and methods A total of 85 patients seeking treatment for a single crown (MC) were treated by the undergraduate students under supervision of respective academic staff. After cementation of the crowns, a 9-point questionnaire was given to patient and different dentists. A treatment cast for every single crown was poured. Then, the MD and BL dimensions of the crowns were compared against their respective antimeric tooth. Results The dentists and the patients agreed in the range of 50.5 to 90.5%. Least subjective differences were found for the length and width of the cemented crowns. The highest differences were noted for symmetry between the cemented crown and its antimeric natural tooth. A total of 31 to 38% of the patients differed from the dentist's evaluation for shade of the crown, color of the crown at the margin, contour of the crown, and the relationship of the crowns with the surrounding gingiva. The highest MD and BL dimensions were in the cemented crown of canines, while the lowest MD and BL diameters were for the cemented crowns of the lateral incisor crowns. Conclusion Dentist and patient mostly agreed in terms of length (90%), width (81%) and relation of crown with free gingiva (74%). However, they differed mostly on the symmetry of the cemented crowns. The highest MD dimensions and BL diameter were in the cemented MCcs of canine, while the lowest were with lateral incisors. Clinical significance While fabricating a dental prosthesis, the dentist must know about patients’ perception of esthetics; otherwise both clinical and laboratory efforts would not be enough to satisfy the esthetic needs of the patient even if the restoration is technically correct. Perceptions related to symmetry differ mostly between dentist and patient. How to cite the article Al Moaleem MM, Alkhayrat FM, Madkhali HA, Geathy IH, Qahhar MAW, Yaqoub A, Mattoo KA. Subjective Differences between Dentists and Patients about Relative Quality of Metal Ceramic Restorations placed in the Esthetic Zone. J Contemp Dent Pract 2017;18(2):112-116.
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L Z G, Touyz. "A successful, temporary, pragmatic, emergency management of dislodged crowns." Journal of Management and Science 12, no. 3 (September 30, 2022): 142–43. http://dx.doi.org/10.26524/jms.12.55.
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Full crowns are often used as treatment in dentistry. Dislodgement of a crown may occur at any time if a negative tensile force on the crown allows displacement. Keeping the displaced crown in situ is problematic, as the crown tends to come off the stump,may be lost and or swallowed. Emergency refixing is often not feasible or available. This note suggests an easy, successful,emergency management of temporarily refixing the crown with sugarless chewing gum until the crown can be recemented by a dentist.
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Allen, Douglas C., Charles J. Barnett, Imants Millers, and Denis Lachance. "Temporal change (1988–1990) in sugar maple health, and factors associated with crown condition." Canadian Journal of Forest Research 22, no. 11 (November 1, 1992): 1776–84. http://dx.doi.org/10.1139/x92-232.
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Change in the health of sugar maple (Acersaccharum Marsh.) and associated northern hardwoods was evaluated for 3 years (1988–1990) in seven states and four provinces. Generally, levels of crown dieback and crown transparency (a measure of foliage density) in 165 stands decreased during this period. In 1990, less than 7% of all dominant–codominant sugar maples (n = 7317) exhibited crown dieback ≥ 20%. Significantly (p = 0.05) fewer of these maples were classified as having high crown transparency (≥ 30%) in 1990 compared with 1988. Crowns of maples that received moderate (31–60%) or heavy (> 60%) pear thrips (Taeniothripsinconsequens (Uzel)) damage for 1 year recovered the following year. Crowns of maples exposed to severe drought in 1988 (Wisconsin) continued to show the effects (high transparency) of this stress in 1990. A majority (69–71%) of the dominant–codominant sugar maples with high (≥ 20%) crown dieback had bole and (or) root damage. Of those maples with crown dieback ≥ 50%, 86% had bole and (or) root damage. The condition of sugar maple in operating sugar bushes and undisturbed stands was similar. The condition of sugar maple crowns was similar in locations presumably exposed to low, medium, and high levels of sulfate deposition.
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Harshitha, A. K., H. T. Ajay Rao, K. Sundeep Hegde, Sharan S. Sargod, Shrivya Saloni Mahaveeran, and Arya Devan. "Comparative evaluation on clinical success rate of prefabricated zirconia crowns and stainless steel crowns in primary molars." International Journal of Oral Health Dentistry 7, no. 3 (September 15, 2021): 180–86. http://dx.doi.org/10.18231/j.ijohd.2021.036.
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To compare the clinical success rate of Prefabricated Zirconia crowns and stainless steel crowns on primary molars: It is an in-vivo study which was performed on 52 pulpally treated primary molars of children aged 4–9 years were randomly divided into two equal groups of stainless steel crown and Prefabricated Zirconia crowns. Tooth preparation was done according to the manufacturer’s recommendations and crowns were cemented. All crowns were cemented with Type I Glass ionomer cement (GIC) luting cement. Crowns were evaluated clinically for its crown retention, marginal integrity and gingival health at 3 months and 6 months.: Clinical success for stainless steel crowns and Prefabricated Zirconia crowns towards crown retention and marginal integrity were similar with no statistical difference between them. All Prefabricated Zirconia crowns showed healthy gingiva whereas 53.8% (14 out of 26) Stainless Steel crowns showed mild gingival inflammation at 3 and 6 months which was statistically significant (P ≤0.01). Both prefabricated zirconia and stainless steel crowns showed no statistical difference for crown retention and marginal integrity throughout the study. Gingival health was significantly higher for Prefabricated Zirconia crowns compared with stainless steel crowns. Therefore clinical success rate for Prefabricated Zirconia crowns were better when compared to stainless steel crowns. So Prefabricated Zirconia crowns can be considered as an esthetic alternative in future.
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Biging, Greg S., and Lee C. Wensel. "Estimation of crown form for six conifer species of northern California." Canadian Journal of Forest Research 20, no. 8 (August 1, 1990): 1137–42. http://dx.doi.org/10.1139/x90-151.
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Geometric models are presented for the prediction of crown volume and width at any height in the crown of six conifer species in the Sierra Nevada. Crown volume is defined as the geometric space occupied by the crown and is allometrically related to the diameter, height, and crown ratio of individual trees. Crown diameter is derived from crown volume, tree height, and crown ratio. The crown volumes and associated measures can be used to compute indices of individual tree competition such as those used in the CACTOS (California Conifer Timber Output Simulator) system or to compute other measures such as wildlife habitat suitability or insect damage potential. Estimation equations are developed by regression using data collected on crowns of 593 felled trees. The equations use dbh, total height, and crown ratio to estimate total crown volume, crown volume above a specified height, and cumulative crown cross sectional area at a specified height.
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Aristiyanto, Regia, and Diatri Nari Ratih. "Functional Crown Lengthening: Biological Width Correction." Journal of Indonesian Dental Association 3, no. 1 (February 20, 2020): 43. http://dx.doi.org/10.32793/jida.v3i1.427.
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Introduction: Functional crown lengthening is one of the most common surgical procedures that facilitating restorative treatment. It was done on teeth with inadequate clinical crowns in the presence of deep and subgingival pathologies. Inadequate clinical crowns defined as tooth with less than 2 mm cervico-incisal of sound. Case Report: The 32 years old female patient complained on broken restoration on upper left anterior tooth since one week ago. He also complained about upper right anterior tooth that turned brown. The tooth had received root canal treatment with direct composite restoration since 3 years ago, but the restoration on tooth 11 and 21 was broken. The remaining crown on tooth 11 and 21 was less than 2 mm. The periapical radiograph examination showed tooth 11 and 21 was non-hermetic obturation. Functional crown lengthening and root canal treatment was performed on teeth 11 and 21, with porcelain crown restoration and fiber post. Conclusion: Functional crown lengthening result affects the quality of post retreatment restoration. The success of functional crown lengthening is marked by no recurrent gingival hyperplasia after functional crown lengthening.
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Zeide, Boris, and Charles A. Gresham. "Fractal dimensions of tree crowns in three loblolly pine plantations of coastal South Carolina." Canadian Journal of Forest Research 21, no. 8 (August 1, 1991): 1208–12. http://dx.doi.org/10.1139/x91-169.
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Because crown structure is closely associated with many aspects of tree growth, fractal dimension of the crown is likely to be a useful indicator of tree form as well as growth. This paper investigates the relationship between the fractal dimension of crowns and two growth-regulating factors, site quality and thinning intensity. The two-surface method allows one to calculate fractal dimension from the regression of foliage area (or mass) on the area (or volume) of the convex hull that envelopes the crown. The hull's volume can be computed from the length and width of a crown using an equation that accounts for the change in crown shape. Fractal dimensions of tree crowns were calculated for three loblolly pine (Pinustaeda L.) plantations of coastal South Carolina using detailed measurements of 72 dominant and intermediate trees. Analyses of data and the involved processes suggest that the fractal dimension of crown surface may change with site quality and thinning intensity.
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Konôpka, Bohdan, Jozef Pajtík, Vladimír Šebeň, Katarína Merganičová, and Peter Surový. "Silver birch aboveground biomass allocation pattern, stem and foliage traits with regard to intraspecific crown competition." Central European Forestry Journal 66, no. 3 (August 24, 2020): 159–69. http://dx.doi.org/10.2478/forj-2020-0013.
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Abstract In the conditions of Central Europe, silver birch (Betula pendula Roth) has so far not been an important species for commercial purposes but might be relevant from ecological point of view. For instance, prompt succession by birch and other pioneer tree species at large-scale post-disturbance areas is necessary to compensate for previous carbon losses by natural disasters. Therefore, our attention was focused on 14-year-old birch trees growing at the wind-thrown area in the High Tatra Mts. (northern Slovakia). We sampled aboveground biomass of 20 silver birch trees representing four classes of crown competition: 0 – competition free crowns, 1 – crowns under mild competition, 2 – crowns under moderate competition, 3 – crowns under severe competition. We studied biomass allocated to stems, branches and foliage, and basic properties of stems and foliage. The crown-competition free birches were nearly 13 m high, and their aboveground tree biomass was 150 kg. The biomass of birches under severe competition was five times lower. Crown competition modified biomass ratios of foliage to branch as well as of branch to stem. Our results showed that birches under severe competition stress invest more in height than in diameter. At the same time, crown competition modified foliage weight and specific leaf area (SLA), which was clear mostly in the upper part of the crowns. However, foliage area was influenced by crown competition only to a negligible extent. Our main finding is that foliage position (upper, middle or lower third of crown) affected foliage properties more than intraspecific crown competition. Finally, we pointed out that silver birch is a rather productive species that is not ecologically demanding. Therefore, it might be a prospective tree species under the ongoing climate change and the present period of intensification in renewable resources utilisation.
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Cohn, Gregory M., Russell A. Parsons, Emily K. Heyerdahl, Daniel G. Gavin, and Aquila Flower. "Simulated western spruce budworm defoliation reduces torching and crowning potential: a sensitivity analysis using a physics-based fire model." International Journal of Wildland Fire 23, no. 5 (2014): 709. http://dx.doi.org/10.1071/wf13074.
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The widespread, native defoliator western spruce budworm (Choristoneura occidentalis Freeman) reduces canopy fuels, which might affect the potential for surface fires to torch (ignite the crowns of individual trees) or crown (spread between tree crowns). However, the effects of defoliation on fire behaviour are poorly understood. We used a physics-based fire model to examine the effects of defoliation and three aspects of how the phenomenon is represented in the model (the spatial distribution of defoliation within tree crowns, potential branchwood drying and model resolution). Our simulations suggest that fire intensity and crowning are reduced with increasing defoliation compared with un-defoliated trees, regardless of within-crown fuel density, but torching is only reduced with decreasing crown fuel density. A greater surface fire intensity was required to ignite the crown of a defoliated compared with an un-defoliated tree of the same crown base height. The effects of defoliation were somewhat mitigated by canopy fuel heterogeneity and potential branchwood drying, but these effects, as well as computational cell size, were less pronounced than the effect of defoliation itself on fire intensity. Our study suggests that areas heavily defoliated by western spruce budworm may inhibit the spread of crown fires and promote non-lethal surface fires.
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Antos, Joseph A., Roberta Parish, and Gordon D. Nigh. "Effects of neighbours on crown length of Abies lasiocarpa and Picea engelmannii in two old-growth stands in British Columbia." Canadian Journal of Forest Research 40, no. 4 (April 2010): 638–47. http://dx.doi.org/10.1139/x10-011.
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Crown length is a key aspect of vertical structure in multi-aged, multistrata, mixed-species forests. Crown length, defined as the distance from the tree top to the lowest live branch whorl, was determined for 3169 mapped trees ≥4.0 cm in diameter, in four 0.25 ha plots in each of two old-growth Abies lasiocarpa (Hook.) Nutt. – Picea engelmannii Parry ex Engelm. stands. We randomly selected half the trees to build models and half for validation. Crown length was modelled as a function of tree height, incorporating modifiers to account for neighbouring trees. The inclusion radius and height threshold for competition were 3 m and 70%, respectively. The addition of two modifiers significantly improved the model for A. lasiocarpa; crown length decreased as the number of neighbours increased and as the height of surrounding trees increased. In contrast, none of the modifiers significantly improved the model for P. engelmannii. Except at high levels of competition, Abies crowns were longer than those of Picea. However, both species in these forests have long crowns, typically three-quarters of the tree height and rarely less than half. The tightly programmed conical crown architecture of these species likely contributes to long crowns and to the limited effects of neighbours on crown length.
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Wilson, Neil A., Shaun A. Whitehead, Ivar A. Mjör, and Nairn HF Wilson. "Reasons for the Placement and Replacement of Crowns in General Dental Practice." Primary Dental Care os10, no. 2 (April 2003): 53–59. http://dx.doi.org/10.1308/135576103322500746.
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Aims The purpose of the study was to apply established methods to survey reasons for the placement and replacement of crowns in general dental practice in the United Kingdom. Materials and Methods One hundred and twenty-eight general dental practitioners were recruited. Participants recorded the principal reason for the provision of each initial and replacement crown they provided over a 12-week period. Results Overall, data were collected from 92 practitioners in respect of 1714 patients and 2164 crowns, of which 1452 (67%) were initial placements and 712 (33%) replacements. The teeth most frequently crowned were maxillary incisors (33%), with 72% of the crowns surveyed being of the porcelain bonded to metal variety. Overall 64% of the initial placement crowns were provided because of restoration failure (26%) or tooth fracture (38%). The most common reason for crown replacement was crown failure (27%). Conclusion It is concluded that surveys of the type reported may provide new insights into the reasons for and pattern of provision of initial placement and replacement crowns in clinical practice. In this study the most common reason for the provision of initial placement crowns was tooth fracture. The most common reason for the replacement of crowns, notably porcelain jacket crowns, was crown fracture.
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Javed, Faizan, Aysha Arif, and Farhan Raza Khan. "Comparison of marginal accuracy in two different materials used in provisional crown & bridge – an in vitro experimental study." Journal of the Pakistan Medical Association 73, no. 3 (February 15, 2023): 567–74. http://dx.doi.org/10.47391/jpma.5008.
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Objective: To determine the difference in the marginal accuracy at buccal, lingual, mesial and distal margins of temporary crowns fabricated with bisacryl-based temporary crown material. Method: The in-vitro, experimental, laboratory-based study was conducted at the Aga Khan University, Karachi, from September to December 2019, and comprised two bisacryl-based temporary crown material, Integrity and Protemp 4, which were used to fabricate a sample of 24 temporary crowns. A pre-operative polyvinyl siloxane impression served as a template for temporary crown fabrication. A right mandibular molar tooth on a typodont was prepared to receive a crown. The provisional crown material was syringed onto the template and was allowed to cure. All four surfaces of the crown were observed under a stereomicroscope equipped with digital single-lens reflex camera at 25.6x magnification. An image of each surface was captured and a photographic record was maintained. An image processing software was used for the measurement of marginal discrepancy. Marginal accuracy among the four surfaces was assessed. Data was analysed using SPSS 23. Results: Mean marginal discrepancy for provisional crowns fabricated with Protemp 4 and Integrity was 410±222um and 319±176um, respectively. The marginal discrepancy between the two groups was statistically significant (p=0.027), with buccal margin exhibiting the most discrepancy (p<0.01). Conclusions: Integrity showed less microleakage than Protemp 4. Among all the walls, the buccal wall showed the most microleakage. Marginal accuracy was found to be dependent upon the type of provisional crown material and the side of the prepared axial wall. Key Words: Crowns, Dental marginal adaptation, Tooth preparation, Dental materials.
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Escoto-Rodríguez, Martín, José M. Facelli, and Jennifer R. Watling. "Do wide crowns in arid woodland trees reflect hydraulic limitation and reduction of self-shading?" Functional Plant Biology 41, no. 12 (2014): 1221. http://dx.doi.org/10.1071/fp14022.
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In arid regions many tree species develop broad crowns. A number of hypotheses involve trade-offs between growth in height and horizontal spreading, but there is no explanation for the switch from vertical to horizontal growth during development. Using Acacia papyrocarpa Benth as a model, we measured tree height and crown shape across different sites and topographic positions. We also measured δ13C of phyllodes from crown tops and lateral spreading branches. Trees were significantly taller at the base of a hill, where water availability is typically greater, than on the adjacent steep hillslope. In contrast, δ13C from the treetops was not significantly different across this topographic gradient, despite variation in tree height. In addition, δ13C was higher at treetops than in lower, lateral branches. These observations are consistent with hydraulic limitation to tree height. The shape of mature and young crowns in open environments was not symmetrical. At all sites, branches were shortest, but tree crowns tallest, on south-facing (i.e. shadiest) aspect of crowns. This suggests that light limitation may also affect crown development. If upper branches become water-limited and lower branches light-limited, then middle lateral branches become the less-stressed part of the crown and may grow more, producing a broad crown.
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He, Jinchao, Hao Yuan, Xiaolong He, Chunhang Xie, Haonan Peng, and Ruichang Hu. "Droplet Impact on a Moving Thin Film with Pseudopotential Lattice Boltzmann Method." Mathematical Problems in Engineering 2020 (July 15, 2020): 1–15. http://dx.doi.org/10.1155/2020/1801639.
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The pseudopotential lattice Boltzmann method (LBM) with a tunable surface tension term is applied to study a droplet impact on a moving thin film. The Re effects of dimensionless parameters on the upstream and downstream crown evolution are studied, including Reynolds number (Re), Weber number (We), liquid film thickness, and horizontal velocity of the liquid film. The movement of the liquid film causes the asymmetry development of the upstream and downstream crown. Both the instability of upstream and downstream crowns increases with the increase of Re and We, and the upstream crown becomes more prone to break up. And a critical value of film thickness exists with the height of the upstream and downstream liquid crowns reaches the maximum value. And the velocity of liquid film restrains the development of the height of the upstream and downstream crowns, but it promotes the growth of the crown radius.
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Sterba, Hubert, and Ralph L. Amateis. "Crown efficiency in a loblolly pine (Pinus taeda) spacing experiment." Canadian Journal of Forest Research 28, no. 9 (September 1, 1998): 1344–51. http://dx.doi.org/10.1139/x98-115.
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Crown efficiency was first defined by Assmann (1961. Waldertragskunde. BLV, München) as individual tree volume increment per unit of crown projection area. He hypothesized that within a given crown class, smaller crowns are more efficient because their ratio between crown surface and horizontal crown projection is higher. Data from a loblolly pine (Pinus taeda L.) spacing experiment were used to test if this hypothesis also holds in young loblolly pine stands and, if so, to determine if it explains the increment differences between spacings in the spacing experiment. Using individual tree height relative to plot dominant height to describe crown class, within-plot regression showed that crown efficiency decreased with crown size for trees below dominant height. This relationship was much less pronounced than indicated from Assmann's examples, although the crown surface to crown projection ratio behaved in the same way as Assmann had hypothesized. Crown efficiency as well as the crown surface to crown projection area ratio decreased with increasing density. Basal area increment per hectare increased until total crown closure approached 130% and then stayed constant. This major impact of total crown coverage brings into question the usefullness of crown efficiency as an indicator for unit area growth.
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Aryal, Bimal, James Steenberg, and Peter Duinker. "The Effects of Residential Street Tree Spacing and Crown Interactions on Crown Dimensions and Canopy Cover." Arboriculture & Urban Forestry 47, no. 5 (September 1, 2021): 183–95. http://dx.doi.org/10.48044/jauf.2021.017.
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Urban trees provide people with a range of ecosystem services. Trees planted along streets have been a large focus of urban forest research and practice, and municipalities invest significant resources in their survival. However, the optimal spacing of street trees is not addressed in the scientific literature, and existing municipal street tree spacing standards are highly variable and poorly enforced. In this study, we examine variability in crown shape and size for street trees to test for possible interaction effects at closer spacings. We measured variability in crown diameters both parallel and perpendicular to street tree rows to test whether changes in crown dimensions can be explained by interaction effects with neighbouring trees, and whether crown interactions lead to a reduction in total crown projection area (i.e., canopy cover). We measured the crown dimensions and diameter at breast height of 1,338 street trees in Halifax, Canada. We used two-way analysis of variance to test whether crown shape and crown projection area were affected by crown interactions and spacing. We found that the effect of narrower spacing and interactions (i.e., crowns touching/overlapping) among trees translated to crowns extending away from the direction of interaction. We also found that these changing crown dimensions were associated with increases in canopy cover. Urban forest ecosystems are a vital resource for the increasingly urban population. There is a need for empirical research on spacing standards and practices that investigate their influence on the supply of ecosystem services, such as stormwater retention, air pollution removal, and cooling.
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Larsson, Adam, Justice Manuh, and Bruno Ramos Chrcanovic. "Risk Factors Associated with Failure and Technical Complications of Implant-Supported Single Crowns: A Retrospective Study." Medicina 59, no. 9 (September 5, 2023): 1603. http://dx.doi.org/10.3390/medicina59091603.
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Background and Objectives: Implant-supported single crowns have become a routine approach for the replacement of missing single teeth, being considered as one of the most common ways of rehabilitation when adjacent teeth are healthy. The present retrospective study aimed to investigate the risk factors possibly associated with failure and technical complications of implant-supported single crowns and their supporting implants. Materials and Methods: Patients treated at one faculty (2009–2019) were considered for inclusion. Complications investigated included ceramic fracture/chipping, crown loss of retention/mobility, crown failure/fracture, loosening/loss/fracture of prosthetic screw, and implant failure/fracture. Any condition/situation that led to the removal/replacement of crowns (implant failure not included) was considered prosthesis failure. Univariate/multivariate Cox regression models were used to evaluate the associations between clinical covariates and failure. Results: 278 patients (358 crowns) were included. Mean ± SD follow-up was 56.5 ± 29.7 months. Seven implants (after a mean of 76.5 ± 43.7 months) and twenty crowns (21.3 ± 23.5 months) failed. The cumulative survival rate (CSR) for crowns was 93.5% after 5, remaining at 92.2% between 6 and 11 years. The most common reasons for crown failure were porcelain large fracture (n = 6), crown repeatedly loose (n = 6), and porcelain chipping (n = 5). Men and probable bruxism were identified in the Cox regression model as being associated with crown failure. The most common observed technical complications were mobility of the crown and chipping of the ceramic material, with the latter being observed even in crowns manufactured of monolithic zirconia. Cases with at least one technical complication (not considering loss of screw hole sealing) were more common among probable bruxers than in non-bruxers (p = 0.002). Cases of ceramic chipping were more common among bruxers than in non-bruxers (p = 0.014, log-rank test). Conclusions: Probable bruxism and patient’s sex (men) were factors associated with a higher risk of failure of implant-supported single crowns.
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van Foreest, Andries, and Joost Roeters. "Evaluation of the Clinical Performance and Effectiveness of Adhesively-Bonded Metal Crowns on Damaged Canine Teeth of Working Dogs over a Two- to 52-Month Period." Journal of Veterinary Dentistry 15, no. 1 (March 1998): 13–20. http://dx.doi.org/10.1177/089875649801500101.
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In this clinical study, 41 metal full crown restorations of canine teeth were placed in 18 working dogs. Twenty-six canine teeth had severe attrition with no involvement of the pulp cavities; 15 fractured canine teeth were endodontically treated. With the exception of one tooth, at least one-third of the coronal part of each canine tooth was available for a supragingivally performed, minimal tooth crown preparation. A dental resin luting cement technique was used to bond the electrolytically etched crown (made from an alloy of cobalt-chrome-molybdenum) to the tooth. The metal crowns were slightly shorter and with a more rounded tip than the original tooth. Posts or post-and-core techniques were not used. Median follow-up period was 30 months (range 2 to 61 months), at which time 36 crowns were found to be intact and functional. Five crowns were lost; three as a result of subsequent injury and fracture of the tooth below the crown; one as a result of use of less than one-third of the coronal portion of the tooth for retention of the crown; and one as a result of an oblique fracture of the root.
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Peterson, J. A., J. R. Seiler, J. Nowak, S. E. Ginn, and R. E. Kreh. "Growth and Physiological Responses of Young Loblolly Pine Stands to Thinning." Forest Science 43, no. 4 (November 1, 1997): 529–34. http://dx.doi.org/10.1093/forestscience/43.4.529.
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Abstract Although yield responses to thinning in loblolly pine have been well documented, short- and long-term morphological and physiological changes are largely unknown. To investigate these responses, three 8-yr-old, 0.2024 ha replicate stands of loblolly pine were thinned by 50% in May 1988, and bole growth and morphological changes in the crown were measured annually for the next 6 yr. In situ gas exchange measurements were monitored in the upper and lower third of the crowns monthly during the third through sixth growing seasons following thinning. First- and second-year physiological responses to thinning have been reported earlier (Ginn et al. 1991). Thinning slowed live crown recession and increased crown diameters resulting in increased photosynthetic surface area per tree. Over the 6 yr study period, the crown diameters of thinned trees increased 82% while the crown diameters of control trees increased only 20%. Larger bole diameters were observed for thinned trees four growing seasons after thinning. Photosynthetic rate and needle conductance did not increase overall, but were increased in the lower crown foliage of thinned trees. Needle dark respiration was higher in thinned stands in both the upper and lower crowns. Increased bole diameter growth is likely the result of the large increases in foliar biomass as well as initially higher physiological activity in the lower crowns of thinned stands. For. Sci. 43(4):529-534.
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Wu, Xuhan, Weiliang Fan, Huaqiang Du, Hongli Ge, Feilong Huang, and Xiaojun Xu. "Estimating Crown Structure Parameters of Moso Bamboo: Leaf Area and Leaf Angle Distribution." Forests 10, no. 8 (August 14, 2019): 686. http://dx.doi.org/10.3390/f10080686.
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Both leaf area (LA) and leaf angle distribution are the most important eco-physiological measures of tree crowns. However, there are limited published investigations on the two parameters of Moso bamboo (Phyllostachys edulis (Carrière) J. Houz., abbreviated as MB). The aim of this study was to develop allometric equations for predicting crown LA of MB by taking the diameter at breast height (DBH) and tree height (H) as predictors and to investigate the leaf angle distribution of a MB crown based on direct leaf angle measurements. Data were destructively sampled from 29 MB crowns including DBH, H, biomass and the area of sampled leaves, biomass of total crown leaves, and leaf angles. The results indicate that (1) the specific leaf area (SLA) of a MB crown decreases from the bottom to the top; (2) the vertical LA distribution of MB crowns follow a “Muffin top” shape; (3) the LA of MB crowns show large variations, from 7.42 to 74.38 m2; (4) both DBH and H are good predictors in allometry-based LA estimations for a MB crown; (5) linear, exponential, and logarithmic regressions show similar capabilities for the LA estimations; (6) leaf angle distributions from the top to the bottom of a MB crown can be considered as invariant; and (7) the leaf angle distribution of a MB crown is close to the planophile case. The results provide an important tool to estimate the LA of MB on the standing scale based on DBH or H measurements, provide useful prior knowledge for extracting leaf area indexes of MB canopies from remote sensing-based observations, and, therefore, will potentially serve as a crucial reference for calculating carbon balances and other ecological studies of MB forests.
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Nikhil, Das K. R., Krishnamoorthy S H, Sathyaprasad Savitha, Antony Allwin, and S. Nandan. "Clinical Evaluation of Zirconia and Stainless-Steel crowns in Primary Molars - A Randomized Control Trial." International Journal of Pedodontic Rehabilitation 7, no. 2 (December 19, 2022): 30–38. http://dx.doi.org/10.56501/intjpedorehab.v7i2.571.
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Background and Aim: Aesthetic alternatives to stainless steel crown for restoring primary molars attain a growing interest. The aim of the study was clinical evaluation and comparison of zirconia and stainless steel crown in primary molars (clinical and radiograph) Methods: A randomized controlled study was conducted on children of age group of 5 to 8 years of age visiting, KVG Dental College and Hospital, Sullia and who were meet the inclusion criteria of the study. The study population was randomly divided into two groups of 24 each. Group I: stainless steel crown, Group II: zirconia crown. Post endodontic tooth preparation was done and selected stainless steel and zirconia crowns followed by cemented using type 1 glass ionomer cement. The subjects was be recalled after 3, 6 and 9 months to check gingival index, oral hygiene index and bone health of the tooth using intraoral periapical radiograph. Results: There was significant increase in score of gingival index and OHI score for both SSC and zirconia crowns after 3 month followed by reduction in score at 6 and 9 months. There was no statistically significant difference in alveolar bone height in both groups (zirconia and SSCs) for 6 months. Conclusion: Zirconia crowns presented to be an excellent choice for primary posterior teeth full coverage restorations. Zirconia crowns performed better than SSCs in the aspect of gingival response and prevention of plaque adhesion. Keywords: zirconia crowns, stainless steel crown, primary molars, esthetics, dental caries.
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Aisyah Bella Azzanjani and Dian Setiawati. "Effect of artificial crowns on periodontal tissues (Literature Review)." Makassar Dental Journal 11, no. 3 (December 19, 2022): 387–90. http://dx.doi.org/10.35856/mdj.v11i3.664.
Full textAbstract:
Dental crowns are artificial teeth that are permanently attached to teeth that have been prepared to repair part or all of the damaged tooth surface and to replace toothloss. Making a crown must consider several factors, including being able to maintain and pro-tect existing teeth and surrounding tissues. This literature review isaimed to describe the effect of crown use on periodontal tis-sue. A total of 20 articles collected from various electronic databases and manual searches wereincluded in this literature. Plaque is a major etiologic factor of gingival inflammation and inadequate crown design can lead to plaque accumulation. Dental crowns can cause inflammation of the periodontal tissues, if cervical endings and preparation margins as well as oral hygiene principles are not observed during the crown fabrication process. It is concluded that crown design plays a very important role in determi-ning the condition of periodontal tissues. Appropriate designand good oral hygiene are important to reduce the occurrence of periodontal disease.
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Vidya, Nursolihati, and Osa Amila Hafiyyah. "FUNCTIONAL CROWN LENGTHENING AS A PRE-RESTORATIVE PROCEDURE IN THE AESTHETIC ZONE." Interdental Jurnal Kedokteran Gigi (IJKG) 20, no. 1 (April 21, 2024): 149–55. http://dx.doi.org/10.46862/interdental.v20i1.7863.
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Introduction: Crown lengthening is a surgical procedure to increase the height of the clinical crown for aesthetic and restorative purposes, or combination. The indications include treatment of subgingival caries and altered passive eruption. Functional crown lengthening for restorative purposes in the esthetic zone should consider the concept of biologic width and the ideal proportion of the dentogingival complex. Case: A 39-year-old male patient was referred from the Department of Conservative Dentistry, RSGM UGM Prof. Soedomo to expose the maxillary anterior teeth crowns for full crown and veneer restorations. Clinical examination showed 11, 12, and 12 post root canal treatment with 3-4 mm remaining crowns. Teeth 13, 21, 22, and 23 appear short, excessive gingival display of 3 mm, with a diagnosis of altered passive eruption type 1B. Treatment: Functional crown lengthening was performed by gingivectomy followed by flap elevation, ostectomy, and osteoplasty. A fenestration was found at the apical of 22 and treated with regenerative procedure. Full crowns and veneers insertion was done 3 months after surgery. Crown lengthening as a pre-restorative procedure is a multidisciplinary treatment that considers the need for restoration by re-establishing the biologic width, to prevent inflammation and bone loss. In addition, adequate post- surgical tissue healing time prior to restoration is necessary to avoid gingival margin rebound and to assure long-term success of the restoration. Conclusionn : Functional crown lengthening as a pre-restorative procedure in the esthetic zone can gives satisfactory and stable results, with careful examination and correct surgical procedure.
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Dai, Mingrui, and Guohua Li. "Soft Segmentation and Reconstruction of Tree Crown from Laser Scanning Data." Electronics 12, no. 10 (May 19, 2023): 2300. http://dx.doi.org/10.3390/electronics12102300.
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Point cloud data obtained by laser scanning can be used for object shape modeling and analysis, including forest inventory. One of the inventory tasks is individual tree extraction and measurement. However, individual tree segmentation, especially tree crown segmentation, is challenging. In this paper, we present a novel soft segmentation algorithm to segment tree crowns in point clouds automatically and reconstruct the tree crown surface from the segmented crown point cloud. The soft segmentation algorithm mainly processes the overlapping region of the tree crown. The experimental results showed that the segmented crown was accurate, and the reconstructed crown looked natural. The reconstruction algorithm was highly efficient in calculating the time and memory cost aspects since the number of the extracted boundary points was small. With the reconstructed crown geometry, the crown attributes, including the width, height, superficial area, projecting ground area, and volume, could be estimated. The algorithm presented here is effective for tree crown segmentation.
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Bonifacius, Setyawan, and Sri Wahyuningsih Rais. "Restorasi mahkota pasak pada gigi dengan jarak serviko-oklusal pendek Dowel crown restoration on tooth with short cervico-occlusal distance." Journal of Dentomaxillofacial Science 11, no. 3 (October 30, 2012): 165. http://dx.doi.org/10.15562/jdmfs.v11i3.332.
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Dowel crown restoration is a restoration which is often performed by dentists in daily practice. Dental crowns requirethe dowel crown restoration due to several factors including the crown damage cause has been very severe. Dowelcrown restoration usually consists of two parts, namely dowel with core and crown restoration on it. The core must behigh enough in cervico-occlusal direction to obtain sufficient retention for the attachment of the crown. In some casesthis condition cannot be fulfilled because the cervico-occlusal distances are too short resulting from extrusion of thetooth. This paper is reporting a case of management tooth maxillary second premolar with limited cervico-occlusaldimension with dowel crown restoration in one unit. The technique was a combination of direct and indirect method.The result was an accurate and retentive dowel crown, and has a good aesthetic.
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Donelan, Matthew, and Kenneth Corey. "100 ROLE OF LIGHT INTENSITY IN THE DEVELOPMENT OF OSTRICH FERN." HortScience 29, no. 5 (May 1994): 442e—442. http://dx.doi.org/10.21273/hortsci.29.5.442e.
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Crowns of ostrich fern (Matteuccia struthiopteris L. Todaro) were field-planted in June 1993 on a Hadley silt loam in South Deerfield, Mass. Shade cloth was used to alter light intensity to determine if light intensity effects growth and development of fronds and crowns. Light levels were 22% (low), 45% (intermediate), 72% (high), and 100% (full) of ambient conditions. Survival of crowns decreased with increasing light intensity with only 22% survival under full light. Low, intermediate, and high light levels resulted in 89%, 75%, and 56%, respectively, of crowns producing shoots. Light intensity did not effect the number or length of fronds produced. Frond length reached a maximum after 2 months growth. Development of secondary crowns was enhanced at intermediate and high light intensities. Final crown weight was significantly correlated with initial crown weight regardless of light intensity. Crowns will be vernalized and forced hydroponically to determine effects of light intensity and crown size on growth of croziers.
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Gao, Huilin, Jian Feng, You Yin, Wanjin Hu, Yang Qu, and Mingguo Liu. "Effect of strip shelterwood-cuts on the crown morphology plasticity of natural regenerated Pinus tabuliformis saplings in northeastern China." PeerJ 8 (August 26, 2020): e9826. http://dx.doi.org/10.7717/peerj.9826.
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The study analysed the effect of shelterwood-cut strips on the outermost crown profiles and crown characteristics of naturally regenerated Pinus tabuliformis saplings in northeastern China. A total of 49 regenerated saplings from shelterwood-cut strips and 30 from uncut strips were collected. Nonlinear quantile regression was used to develop the outermost crown profile model for the saplings from the shelterwood-cut and uncut strips. The quantile value suitable for describing the outermost crown profiles of the two types of strips was selected using nonparametric boundary regression. The difference in crown morphologies between the shelterwood-cut strips and uncut strips was compared. The results showed that with the same diameter at breast height, the crown radii of the uncut strip saplings were larger than those of the shelterwood-cut strip saplings within the range of 0.2–1.0 for the relative depth into the crown. The largest crown radius of the saplings from the uncut strips was larger than that of the saplings from the shelterwood-cut strips. The inflection points of the shelterwood-cut strip sapling crowns were larger than those of the uncut strip sapling crowns. The crown volume of the small uncut strip saplings was larger than that of the shelterwood-cut strip saplings, and the difference in crown volume decreased with increasing sapling size. The saplings in the early stage of the uncut strips showed a greater growth rate than those of the shelterwood-cut strips, but their growth rate slowed over the long term according to branch-length annual growth. The present study provides a reference for forest management strategy decision making in promoting natural regeneration.