Crown Structures Research Articles

Light absorption and light-use efficiency of juvenile white spruce trees in natural stands and plantations

Aboveground tree growth is influenced by light availability, light capture, and the efficiency captured light is converted into growth. All three factors are influenced by neighborhood species composition and stand structure and can be modified with silvicultural treatments. The objective was to examine the absorption of photosynthetically active radiation (APAR), light-use efficiency (LUE), and aboveground biomass growth of juvenile white spruce (Picea glauca (Moench) Voss) trees in plantations and planted in naturally regenerated stands with diverse species composition. Trees were sampled across a range of sizes, and measurements of white spruce and neighborhood trees were collected at ages seven and eight. Light absorption of individual trees was modeled with MAESTRA accounting for species-specific crown structures of neighboring trees. APAR increased linearly with leaf area in both treatments. The correlation was more influenced by neighborhood competition than self-shading, since self-shading was minimized by crown spread and height growth. Biomass growth increased with increasing APAR in both treatments, but growth for a given unit of APAR was greater in the natural stands, possibly due to greater belowground biomass allocation in plantations due to lower stand densities. LUE declined slightly across the range of tree size, which contrasts most other studies. The decline could be due to juvenile age of the trees and inherent slow growth of spruce species.

STUDY ON THE EXPLAINABLE ABILITY BY USING AIRBORNE LIDAR IN STAND VALUE AND STAND COMPETITION

Abstract. Forest canopy structure is composed by the various species. Sun light is a main factor to affect the crown structures after tree competition. However, thinning operation is an appropriate way to control canopy density, which can adjust the competition conditions in the different crown structures. Recently, Airborne Light Detection and Ranging (LiDAR), has been established as a standard technology for high precision three dimensional forest data acquisition; it could get stand characteristics with three-dimensional information that had develop potential for the structure characteristics of forest canopy. The 65 years old, different planting density of Cryptomeria japonica experiment area was selected for this study in Nanytou, Taiwan. Use the LiDAR image to estimate LiDAR characteristic values by constructed CHM, voxel-based LiDAR, mu0ltiple echoes, and assess the accuracy of stand characteristics with intensity values and field data. The competition index was calculated with field data, and estimate competition index of LiDAR via multiple linear regression. The results showed that the highest accuracy with stand characteristics was stand high which estimate by LiDAR, its average accuracy of 91.03%. LiDAR raster grid size was 20 m × 20 m for the correlation was the best, however, the higher canopy density will reduce the accuracy of the LiDAR characteristic values to estimate the stand characteristics. The significantly affect canopy thickness and the degree of competition in different planting distances.

STUDY ON THE EXPLAINABLE ABILITY BY USING AIRBORNE LIDAR IN STAND VALUE AND STAND COMPETITION

Forest canopy structure is composed by the various species. Sun light is a main factor to affect the crown structures after tree competition. However, thinning operation is an appropriate way to control canopy density, which can adjust the competition conditions in the different crown structures. Recently, Airborne Light Detection and Ranging (LiDAR), has been established as a standard technology for high precision three dimensional forest data acquisition; it could get stand characteristics with three-dimensional information that had develop potential for the structure characteristics of forest canopy. The 65 years old, different planting density of <i>Cryptomeria japonica</i> experiment area was selected for this study in Nanytou, Taiwan. Use the LiDAR image to estimate LiDAR characteristic values by constructed CHM, voxel-based LiDAR, mu0ltiple echoes, and assess the accuracy of stand characteristics with intensity values and field data. The competition index was calculated with field data, and estimate competition index of LiDAR via multiple linear regression. The results showed that the highest accuracy with stand characteristics was stand high which estimate by LiDAR, its average accuracy of 91.03%. LiDAR raster grid size was 20 m × 20 m for the correlation was the best, however, the higher canopy density will reduce the accuracy of the LiDAR characteristic values to estimate the stand characteristics. The significantly affect canopy thickness and the degree of competition in different planting distances.

Fracture-resistant monolithic dental crowns

ObjectiveTo quantify the splitting resistance of monolithic zirconia, lithium disilicate and nanoparticle-composite dental crowns. MethodsFracture experiments were conducted on anatomically-correct monolithic crown structures cemented to standard dental composite dies, by axial loading of a hard sphere placed between the cusps. The structures were observed in situ during fracture testing, and critical loads to split the structures were measured. Extended finite element modeling (XFEM), with provision for step-by-step extension of embedded cracks, was employed to simulate full failure evolution. ResultsExperimental measurements and XFEM predictions were self-consistent within data scatter. In conjunction with a fracture mechanics equation for critical splitting load, the data were used to predict load-sustaining capacity for crowns on actual dentin substrates and for loading with a sphere of different size. Stages of crack propagation within the crown and support substrate were quantified. Zirconia crowns showed the highest fracture loads, lithium disilicate intermediate, and dental nanocomposite lowest. Dental nanocomposite crowns have comparable fracture resistance to natural enamel. SignificanceThe results confirm that monolithic crowns are able to sustain high bite forces. The analysis indicates what material and geometrical properties are important in optimizing crown performance and longevity.

Variation in Cuspal Morphology in Maxillary First Permanent Molar with Report of 3 Cusp Molar- A Prevalence Study.

Human teeth has always been known for morphological variations in both the crown and root structures. The corono-morphological variations can be in the form of extra cusp or missing cusp. Permanent maxillary first molars are the biggest teeth in maxillary arch and have a high anchorage value and are known for their four cusp and five cusp patterns, if present with cusp of Carebelli. The aim of this study was to determine the prevalence of cuspal variations and quantification of cusps of permanent maxillary first molar in Malwa population. A total of 1249 individuals were studied at Government College of Dentistry, Indore, Madhya Pradesh, India, to evaluate the number of cusps in permanent maxillary first molars. Of the studied 1249 individuals, permanent maxillary first molars had five cusps in 407 (32.6%) cases while 838 (67.08%) cases had four cusp and four (0.32%) cases had three cusps. The four cases having three cusp permanent maxillary first molars were present unilaterally and only in females. This article emphasizes the presence of permanent maxillary first molar with only three cusps in the Malwa population of India. It also reviews the literature in respect to this rare anomaly and calls for continuous and close monitoring to report such cases in the future.

Tooth Germ-Like Construct Transplantation for Whole-Tooth Regeneration: An In Vivo Study in the Miniature Pig.

The purpose of this study was to demonstrate the feasibility of whole-tooth regeneration using a tooth germ-like construct. Dental pulp from upper incisors, canines, premolars, and molars were extracted from sexually mature miniature pigs. Pulp tissues were cultured and expanded in vitro to obtain dental pulp stem cells (DPSCs), and cells were differentiated into odontoblasts and osteoblasts. Epithelial cells were isolated from gingival epithelium. The epithelial cells, odontoblasts, and osteoblasts were seeded onto the surface, upper, and lower layers, respectively, of a bioactive scaffold. The lower first and second molar tooth germs were removed bilaterally and the layered cell/scaffold constructs were transplanted to the mandibular alveolar socket of a pig. At 13.5 months postimplantation, seven of eight pigs developed two teeth with crown, root, and pulp structures. Enamel-like tissues, dentin, cementum, odontoblasts, and periodontal tissues were found upon histological inspection. The regenerated tooth expressed dentin matrix protein-1 and osteopontin. All pigs had regenerated molar teeth regardless of the original tooth used to procure the DPSCs. Pigs that had tooth germs removed or who received empty scaffolds did not develop teeth. Although periodontal ligaments were generated, ankylosis was found in some animals. This study revealed that implantation of a tooth germ-like structure generated a complete tooth with a high success rate. The implant location may influence the morphology of the regenerated tooth.

Creep-assisted slow crack growth in bio-inspired dental multilayers

Ceramic crown structures under occlusal contact are often idealized as flat multilayered structures that are deformed under Hertzian contact loading. Previous models treated each layer as linear elastic materials and resulted in differences between the measured and predicted critical loads. This paper examines the combined effects of creep (in the adhesive and substrate layers) and creep-assisted slow crack growth (in the ceramic layer) on the contact-induced deformation of bio-inspired, functionally graded multilayer (FGM) structures and the conventional tri-layers. The time-dependent moduli of each of the layers were determined from constant load creep tests. The resulting modulus–time characteristics were modeled using Prony series. These were then incorporated into a finite element model for the computation of stress distributions in the sub-surface regions of the top ceramic layer, in which sub-surface radial cracks, are observed as the clinical failure mode. The time-dependent stresses are incorporated into a slow crack growth (SCG) model that is used to predict the critical loads of the dental multilayers under Hertzian contact loading. The predicted loading rate dependence of the critical loads is shown to be consistent with experimental results. The implications of the results are then discussed for the design of robust dental multilayers.

Early stalked stages in ontogeny of the living isocrinid sea lily Metacrinus rotundus

AbstractThe early stalked stages of an isocrinid sea lily, Metacrinus rotundus, were examined up to the early pentacrinoid stage. Larvae induced to settle on bivalve shells and cultured in the laboratory developed into late cystideans. Three‐dimensional (3D) images reconstructed from very early to middle cystideans indicated that 15 radial podia composed of five triplets form synchronously from the crescent‐shaped hydrocoel. The orientation of the hydrocoel indicated that the settled postlarvae lean posteriorly. In very early cystideans, the orals, radials, basals and infrabasals, with five plates each in the crown, about five columnals in the stalk, and five terminal stem plates in the attachment disc, had already formed. In mid‐cystideans, an anal plate appeared in the crown. Late cystideans cultured in the field developed into pentacrinoids about 5 months after settlement. These pentacrinoids shared many crown structures with adult sea lilies. On the other hand, many features of the stalk differed from those in adult isocrinids, while sharing many characteristics with the stalk of feather star pentacrinoids, including disc‐like proximal columnals, high and slender median columnals, synarthrial articulations developmentally derived from the symplexial articulations, limited formation of cirri only in the proximal columnal(s), and an attachment disc. On the basis of these findings, phylogenetic relationships among extant crinoid orders are discussed.

Bioengineered post-natal recombinant tooth bud models.

The long-term goal of this study is to devise reliable methods to regenerate full-sized and fully functional biological teeth in humans. In this study, three-dimensional (3D) tissue engineering methods were used to characterize intact postnatal dental tissue recombinant constructs, and dental cell suspension recombinant constructs, as models for bioengineered tooth development. In contrast to studies using mouse embryonic dental tissues and cells, here the odontogenic potential of intact dental tissues and dental cell suspensions harvested from post natal porcine teeth and human third molar wisdom tooth dental pulp were examined. The recombinant 3D tooth constructs were cultured in osteogenic media in vitro for 1 week before subcutaneous transplantation in athymic nude rat hosts for 1 month or 3 months. Subsequent analyses using X-ray, histological and immunohistochemical methods showed that the majority of the recombinant tooth structures formed calcified tissues, including osteodentin, dentin cementum, enamel and morphologically typical tooth crowns composed of dentin and enamel. The demonstrated formation of mineralized dental tissues and tooth crown structures from easily obtained post-natal dental tissues is an important step toward reaching the long-term goal of establishing robust and reliable models for human tooth regeneration. Copyright © 2014 John Wiley & Sons, Ltd.

Thermocavitation melt instability and micro-crown formation near the threshold for femtosecond laser spallation of a silicon surface

Thermocavitation instability of a molten layer on a silicon surface was experimentally revealed in the form of a microscale surface crown-like feature produced by multiple infrared or visible femtosecond laser pulses near the spallation threshold fluence. The number of crown spikes varied versus the crown perimeter, monotonically increasing with increasing laser shot number. The instability dynamics was described in terms of the intermediate crown structures (the spike number) using the proposed thermocavitation model based on the Kuramoto-Sivashinsky hydrodynamic equation.

Marcadores candidatos, estrategias de cultivo y perspectivas de las DPSCs como terapia celular en odontología

Tissue engineering based on dental pulp stem cells is considered as a promising approach for regenerative dentistry. It purports the final target of morphologically and functionally replacing periodontal tissues and/or lost teeth by means of the in vitro synthesis of tissue-analog substitutes, or even a human tooth (called bio-tooth). Dental pulp stem cells represent a colony of adult cells which have the ability to auto-renovate and differentiate in different lineages. Dental pulp stem cells exact origin has yet to be fully determined; these stem cells seem to be the source of odontoblasts, which contribute to the formation of the dentin-pulp complex. Recently, achievements obtained through research conducted on stem cells, have allowed us to contemplate the possible therapeutic applications of dental pulp stem cells. Some studies have shown that dental pulp stem cells are able to produce in vivo dental tissues, including dental pulp and crown structures. Other research has demonstrated that these stem cells differentiate in vivo and in vitro into osteoblasts, neuroblasts, chondrocytes fibroblasts, and endothelium. In theory, a bio-tooth synthesized from autogenic dental pulp stem cells should be the best option to recover the whole structure and function of a human tooth. The aim of the present review article was to undertake a brief description of the location, origin, isolation and candidate markers of dental pulp stem cells in order to thus present application perspectives to be used in the dental clinic.

Forest Canopy Interception Loss Across Temporal Scales: Implications for Urban Greening Initiatives

Increasing urban forest canopy coverage due to greening initiatives requires watershed managers to balance societal water practices with forest hydrological processes. One such process, canopy rainfall interception, can remove substantial portions of precipitation from catchments by simply intercepting, storing, and evaporating meteoric water. We performed a field study examining interception losses across temporal scales comparing two landscaping species of contrasting crown structures (Fagus grandifolia Ehrh., American beech, and Liriodendron tulipifera L., yellow poplar), native to the highly urbanized northeastern United States, to highlight the effect of landscape design on urban water and storm water management. Results show that landscape designs using the rougher bark texture, lower branch inclination, and thinner canopy of L. tulipifera can increase water losses during rainfall and, therefore, can be used to improve storm water management. On the other hand, the smoother bark, higher branch inclination, and deeper canopy of F. grandifolia decreased water losses, allowing greater water transfer to the surface or subsurface. Thus, interception-related water resource losses during urban forestry projects can be manipulated to benefit urban sustainability efforts if designers consider the multifaceted ramifications of planting different tree species with differing canopy structures.

Comparison of conventional measurement and LiDAR-based measurement for crown structures

Tree crown projection area and crown volume are the important parameters for the estimation of biomass and other forestry science applications. However, it is difficult to validate their accuracy. In this research, measurement errors were quantified based on the 3D virtual LiDAR dataset of 22 common tree species in Beijing, China, which were derived from high-resolution terrestrial laser scanner. The hypotheses include that: (1) primary sources of height measurement are the violations of Total station based on the triangulation theory; (2) approximation of tree crown projections with 4-point fixed angles are not precise enough for irregular crown silhouettes; and (3) tree crown volumes obtained by conventional method with a taper’s formula (VC) are not corresponding to the need of accurate measurement. The relative accuracies derived from total station measurements between crown base height (BT) and tree height (HT) were compared. Meanwhile, different methods for tree crown projections and crown volumes were researched. The results show that the measurement errors of HT (RMSE=4.56m) is higher than that of BT (RMSE=3.35m), VC (RMSE=45.0243m3) is 8.03% on average smaller than VVC (RMSE=48.56094m3), A4 is 25.5% on average larger than AV. The deviations between filed investigation method and virtual 3D LiDAR data could be attributed to irregularity of the crowns’ silhouettes. Based on the results, we propose that: (1) the use of 8-point or 16-point projection with fixed angles to estimate crown projections and (2) different regular volume formula to simulate crown volume according to the tree crown shapes.

The extraction of forest CO2 storage capacity using high-resolution airborne lidar data

With the increasing concern about global warming, the estimation of the CO2 sink capacity of the biosphere has become one of the main issues of remote sensing studies. This paper discusses the estimation of CO2 storage capacity in forests using airborne light detection and ranging (lidar) data. To achieve the correct biomass estimation, a processing chain consisting of the bare earth digital terrain model (DTM) extraction and individual tree crown segmentation has been constructed and applied to the dense airborne lidar data. As a result of the sample processing, the reliable bare earth DTM and tree boundaries were extracted in the study area with an overall accuracy of 71%. The total estimated CO2 storage capacity in the study area using the extracted tree crown structures is accurate, with only a 7% error level compared to field measurements.

Structural crown properties of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica [L.]) in mixed versus pure stands revealed by terrestrial laser scanning

How tree morphology develops in mixed-species stands is essential for understanding and modelling mixed-stand dynamics. However, research so far focused on the morphological variation between tree species and neglected the variation within a species depending on intra- and interspecific competition. Our study, in contrast, addresses crown properties of nine mature Norway spruces (Picea abies [L.] Karst.) of a pure stand and compares them with ten spruces growing in mixture with European beech (Fagus sylvatica [L.]). The same was done with 11 pure stand beeches and 12 beeches growing in mixture with spruce. Through application of a terrestrial laser scanner and a new skeletonization approach, we deal with both species’-specific morphological traits such as branch angle, branch length, branch bending, crown volume and space occupation of branches within the crown, some of which were hardly accessible so far. Special attention is paid to distinct differences between trees growing in mixed and pure stands: for spruce, our study reveals significantly longer branches and greater crown volumes in the mixed stand when compared to the pure stand. In case of European beech, individuals growing in mixture show flatter branch angles, more distinct ramification, greater crown volumes and a lower share of a single branch’s space occupation in the total crown volume. The results show that the presented methods yield detailed information on the morphological traits analyzed in this study and that interspecific competition on its own may have a significant impact on crown structures. Implications for production ecology and stand dynamics of mixed-species forests are discussed.

Misfit and microleakage of implant-supported crown copings obtained by laser sintering and casting techniques, luted with glass-ionomer, resin cements and acrylic/urethane-based agents

ObjectivesThis study evaluated the marginal misfit and microleakage of cement-retained implant-supported crown copings. MethodsSingle crown structures were constructed with: (1) laser-sintered Co–Cr (LS); (2) vacuum-cast Co–Cr (CC) and (3) vacuum-cast Ni–Cr–Ti (CN). Samples of each alloy group were randomly luted in standard fashion onto machined titanium abutments using: (1) GC Fuji PLUS (FP); (2) Clearfil Esthetic Cement (CEC); (3) RelyX Unicem 2 Automix (RXU) and (4) DentoTemp (DT) (n=15 each). After 60 days of water ageing, vertical discrepancy was SEM-measured and cement microleakage was scored using a digital microscope. Misfit data were subjected to two-way ANOVA and Student–Newman–Keuls multiple comparisons tests. Kruskal–Wallis and Dunn's tests were run for microleakage analysis (α=0.05). ResultsRegardless of the cement type, LS samples exhibited the best fit, whilst CC and CN performed equally well. Despite the framework alloy and manufacturing technique, FP and DT provide comparably better fit and greater microleakage scores than did CEC and RXU, which showed no differences. ConclusionsDMLS of Co–Cr may be a reliable alternative to the casting of base metal alloys to obtain well-fitted implant-supported crowns, although all the groups tested were within the clinically acceptable range of vertical discrepancy. No strong correlations were found between misfit and microleakage. Notwithstanding the framework alloy, definitive resin-modified glass-ionomer (FP) and temporary acrylic/urethane-based (DT) cements demonstrated comparably better marginal fit and greater microleakage scores than did 10-methacryloxydecyl-dihydrogen phosphate-based (CEC) and self-adhesive (RXU) dual-cure resin agents.

Bio-inspired dental multilayers: Effects of layer architecture on the contact-induced deformation

The ceramic crown structures under occlusal contact are idealized as flat multilayered structures that are deformed under Hertzian contact loading. Those multilayers consist of a crown-like ceramic top layer, an adhesive layer and the dentin-like substrate. Bio-inspired design of the adhesive layer proposed functionally graded multilayers (FGM) that mimic the dentin–enamel junction in natural teeth. This paper examines the effects of FGM layer architecture on the contact-induced deformation of bio-inspired dental multilayers. Finite element modeling was used to explore the effects of thickness and architecture on the contact-induced stresses that are induced in bio-inspired dental multilayers. A layered nanocomposite structure was then fabricated by the sequential rolling of micro-scale nanocomposite materials with local moduli that increase from the side near the soft dentin-like polymer composite foundation to the side near the top ceramic layer. The loading rate dependence of the critical failure loads is shown to be well predicted by a slow crack growth model, which integrates the actual mechanical properties that are obtained from nanoindentation experiments.

Tooth morphology of Echimyidae (Rodentia, Caviomorpha): homology assessments, fossils, and evolution

Echimyidae constitute the most important radiation of caviomorph rodents in the Neotropical region, represented by 20 extant genera and several extinct species. Both in extant and fossil forms, this diversity is reflected by a significant morphological variation found in crown structures of the cheek teeth. Different hypotheses of primary homology have been proposed for these structures, which, in turn, support diverse dental evolutionary hypotheses. In this contribution we inspect the main structures (cusps and lophids) of the lower deciduous teeth and molars in extinct and extant Echimyidae, and establish their topological correspondences. Comparisons with cusps and lophids of Erethizontidae are emphasized. We explore the testing of alternative primary hypotheses of lophid correspondences in a cladistic context. Following a ‘dynamic’ approach, we select the hypothesis of primary homology, which produced the more parsimonious results, and evaluate the evolutionary transformations of the dental characters analysed. In this context, the phylogenetic relationships of living Myocastor coypus (Molina, 1782) with the extinct Tramyocastor and Paramyocastor are tested. Our results indicate that pentalophodonty is the derived condition for the lower molars in Echimyidae, that trilophodonty evolved independently at least three times during the evolutionary history of these rodents, and that tetralophodonty represents the plesiomorphic condition. This study shows that dental evolution in echimyids can be better understood when occlusal structures are expressed as reliably comparable characters, and when fossils are taken into account.

Crown structure differences and dynamics in 100-year-old and old-growth Eucalyptus obliqua trees

Summary The crown structures of eight old-growth (∼450 y) and eight 100-y-old intermixed Eucalyptus obliqua trees at Warra LTER, southern Tasmania, were mapped by direct climbing and vector-based surveys. The quantitative maps were statistically compared between age classes. The older trees had a more variable crown structure and size range when compared with the unaltered growth pattern of branches in the generally rounder-crowned younger trees. The older trees were more decayed, with more dead wood in the crown and, in some cases, a snapped trunk. The 100-y trees averaged 44.5 m tall, 1.04 m DBH and 14.1 m3 trunk wood volume. The older trees were larger in many dimensions, averaging 60.8 m tall, 2.79 m DBH and 97.3 m3 trunk wood volume. Principal components analysis delineated the age classes clearly along Axis 1, weighted on measures of tree size and branch size, and slightly less so along Axis 2, weighted on branch numbers and total crown volume. Evidence of higher structural diversity was detected in old trees lacking visible evidence of fire and in 100-y trees that were less dominant in the canopy. Marked differences in crown structure were detected visually, and the inter-branch dynamics at the tree scale responsible for these differences elucidated an analogy to inter-tree dynamics at the forest scale.

Relationships between crown architecture and available irradiance in two cerrado species with different leaf phenologies

Structural differences between cerrado species with different leaf phenologies are linked to crown architecture, leaf production, and biomass allocation to shoots and leaves. The present study characterized crown structures and the patterns of biomass allocation to leaves and shoots in two woody cerrado species with contrasting leaf phenologies and quantified the irradiance reaching their leaves to determine the best period during the day for photosynthetic activity. The shoots and leaves of five individuals of both Annona coriacea (deciduous) and Hymenaea stigonocarpa (evergreen) were collected along a 50 m transect in a cerrado fragment within the urban perimeter of Catalao - GO, to determine their patterns of biomass allocation in their crowns. The evergreen H. stigonocarpa had significantly higher mean values of shoot inclination (SI), petiole length (PL), leaf area (LA), leaf display index (LDI), and individual leaf area per shoot (ILA), while the deciduous species A. coriacea had significantly higher leaf numbers (LN). The more complex crown of H. stigonocarpa had shoots in more erect positions (orthotropic), with intense self-shading within shoots; A. coriacea, on the other hand, had slanting (plagiotropic) shoots in the crown, allowing similar irradiance levels to all leaf surfaces. The production of plagiotropic shoots by the deciduous species (A. coriacea) is a strategy that enables its use of incident sunlight early in the morning and preventing excessive water loss or excessive irradiance. Hymenaea stigonocarpa (an evergreen), by contrast, had orthotropic shoots and uses intense self-shading as a strategy to avoid excessive irradiance, especially at midday. Differences in crown architectures between evergreen and deciduous species of cerrado sensu stricto can therefore be viewed as adaptations to the environmental light regime.