Crown Extension Research Articles

Comparison of Root Coverage Procedure done with and without Loupes along with CGF—A Clinical Study

ABSTRACT Background: The coronally advanced flap (CAF) is a regularly used treatment for gingival recession, which is defined by the apical movement of the marginal gingiva, resulting in root exposure and unsightly crown extension. Treatment approaches have evolved, moving toward less invasive procedures like microsurgery. Materials and Methods: Twenty patients with bilateral Miller’s class I and class II gingival recessions, aged between 18 and 40, were chosen at random from the Adhiparasakthi Dental College and Hospital’s outpatient department in Melmaruvathur. A coin toss was used to split the patient population into test and control groups and groups. The test group received CAF with CGF under 3.5 × magnification using dental loupes, whereas the control group had CAF with CGF membrane using standard surgical techniques. Preoperative and three-month postoperative records were made of clinical measures, such as probing depth (PD), clinical attachment level (CAL), recession height (RH), recession width (RW), and width of keratinized tissue (WKT). Results: Both groups’ mean postoperative values showed a significant improvement. Significant decreases in RH (3.0 mm to 0.4 mm, P < 0.0001), RW (2.6 mm to 0.3 mm, P < 0.0001), and WKT (4.2 mm to 6.8 mm, P = 0.0002) were seen in the control group. Significant decreases in RH (2.9 mm to 0.2 mm, P < 0.0001), RW (2.9 mm to 0.2 mm, P < 0.0001), and an increase in WKT (4.1 mm to 6.8 mm, P < 0.0001) were also seen in the test group. After three months, the test group had a mean percentage of 93% while the control group had a mean percentage of 87% root coverage. Conclusion: Adequate root coverage was achieved using both traditional and microsurgical methods. Nonetheless, 3.5 × magnification of CAF with CGF membrane resulted in reduced postoperative discomfort, better healing, more surgical accuracy, and improved ergonomics.

A comparative study of the use of digital technology in the anterior smile experience

Objectivesthis study aims to compare the clinical outcomes of traditional and digital crown extension guides in the aesthetic restoration of anterior teeth. Additionally, the study will analyze the differences in the results of various digital crown extension guides in anterior aesthetic restorations.MethodsSixty-two patients who required aesthetic restoration of their anterior teeth were selected for this study. The patients had a total of 230 anterior teeth and were randomly divided into three groups: a control group of 22 cases who received diagnostic wax-up with pressure film, an experimental group 1 of 20 cases who received 3D printed digital models with pressure film, and an experimental group 2 of 20 patients who received digital dual-positioning guides. The control group had a total of 84 anterior teeth, experimental group 1 had 72 anterior teeth, and experimental group 2 had 74 anterior teeth. The study compared three methods for fabricating crown extension guides: the control group used the diagnostic wax-up plus compression film method, while experimental group 1 used compression film on 3D printed models and experimental group 2 used 3D printed digital dual-positioning crown extension guides. After the crown lengthening surgery, the control group patients wore DMG resin temporary crown material for gingival contouring, while the experimental group patients wore 3D printed resin temporary crowns for the same purpose. The patients were followed up in the outpatient clinic after wearing temporary crowns for 1 month, 3 months, and 6 months, respectively. The clinical results were evaluated in terms of marginal fit, red aesthetic index, and white aesthetic index.ResultsBased on the statistical analysis, the experimental group required significantly fewer follow-up visits and less time for guide design and fabrication compared to the control group. Additionally, the surgical time for the experimental group was significantly shorter than that of the control group. During the postoperative period between the 1st and 3rd month, the PES index scores for the marginal gingival level, proximal, and distal mesiodistal gingival papillae of the experimental group showed a trend of superiority over those of the control group. By the 6th month, the marginal gingival level exhibited a significant difference between the experimental and control groups. The experimental group demonstrated superior results to the control group in terms of shape, contour, and volume of the teeth, color, surface texture, and transparency of the restorations, and features during the 1st and 3rd postoperative months. In the 6th month, the comparative results indicated that the experimental group continued to exhibit superior outcomes to the control group in terms of the shape, color, surface texture, and transparency of the restorations, as well as the characteristics of the teeth. Additionally, the experimental group demonstrated significantly fewer gingival alterations than the control group at 1 month, 3 months, and 6 months post-procedure, with this difference being statistically significant. Furthermore, the combination of 3D printing technology and restorative techniques was utilized, resulting in consistent patient satisfaction.ConclusionDigitalisation plays an important role in anterior aesthetic restorations. The use of digital technology to manage the entire process of anterior cosmetic restorations can improve restorative results, reduce the number of follow-up appointments, shorten consultation time, and achieve better patient satisfaction.

CROWN LENGTHENING: DECISIVE FOR SUSTENANCE OF BIOLOGICAL WIDTH

A majority of periodontal procedures performed today are related with clinical crown extension for esthetic or functional needs related to varied etiologies. Difculty in maintaining appropriate gingival biological width is a frequent problem which is encountered in such type of reconstruction. Various techniques are used for crown lengthening. Techniques such as gingivectomy, ap with osseous resection, apically positioned ap with or without the osseous resection have been used for crown lengthening procedure. Methodology: Article consists of a case report of a female patient with the requirement of crown lengthening. Bone mapping under LA was done using the Goldman fox probe. Inverse- beveled incision was given followed by sulcular incision and the gingival collar was removed. In this case to perform osseous resection, ap was elevated and bone cutting was done. Result: In this case the desired lengthening of crown was achieved with the good healed surrounding. Conclusion: Crown Lengthening is a surgical procedure that requires exposure of adequate tooth structure for restorative procedures. The scope of crown lengthening procedure is really wide and renement in the treatment modalities are needed.

Including tree spatial extension in the evaluation of neighborhood competition effects in Bornean rain forest.

Classical tree neighborhood models use size variables acting at point distances. In a new approach here, trees were spatially extended as a function of their crown sizes, represented impressionistically as points within crown areas. Extension was accompanied by plasticity in the form of crown removal or relocation under the overlap of taller trees. Root systems were supposedly extended in a similar manner. For the 38 most abundant species in the focal size class (10–<100 cm stem girth) in two 4‐ha plots at Danum (Sabah), for periods P1 (1986–1996) and P2 (1996–2007), stem growth rate and tree survival were individually regressed against stem size, and neighborhood conspecific (CON) and heterospecific (HET) basal areas within incremented steps in radius. Model parameters were critically assessed, and statistical robustness in the modeling was set by randomization testing. Classical and extended models differed importantly in their outcomes. Crown extension weakened the relationship of CON effect on growth versus plot species’ abundance, showing that models without plasticity overestimated negative density dependence. A significant negative trend of difference in CON effects on growth (P2−P1) versus CON or HET effect on survival in P1 was strongest with crown extension. Model outcomes did not then support an explanation of CON and HET effects being due to (asymmetric) competition for light alone. An alternative hypothesis is that changes in CON effects on small trees, largely incurred by a drought phase (relaxing light limitation) in P2, and following the more shaded (suppressing) conditions in P1, were likely due to species‐specific (symmetric) root competition and mycorrhizal processes. The very high variation in neighborhood composition and abundances led to a strong “neighborhood stochasticity” and hence to largely idiosyncratic species’ responses. A need to much better understand the roles of rooting structure and processes at the individual tree level was highlighted.

A Comprehensive Update on Crown-Lengthening Procedures with New Concepts and Inputs

A majority of periodontal procedures performed today are related with clinical crown extension for esthetic or functional needs related to varied etiologies. The concepts and understanding about any particular treatment keep evolving and further refinements happen with each passing year. The objective of the review is to put forth the various new innovative inputs and concepts regarding crown-lengthening procedures (CLPs) as envisioned by the author and provide a relevant review on various surgical procedures. To the extent possible, a retrospective evaluation of the available literature on CLPs and associated treatment modalities were undertaken. Personal evaluations based on a cumulative understanding of various clinical situations being presented for CLPs across many years were instrumental in writing this review. A new perspective on need-based area-specific CLPs is presented in the review which can be appropriated with any presenting clinical scenario. The review also proposes a new categorization of apically repositioned flaps in multiple types, which may expand our surgical options. A new treatment algorithm based on proposed residual attached gingiva is introduced. The review also deals with a modified proposal for the restorative considerations and a CLP format for record keeping. The scope of CLPs is really wide and refinements in the treatment modalities are need of the hour. The expansion of CLP concept and innovative inputs will definitely appeal to an astute clinician.

Miscibility and wettability: how interfacial tension influences droplet impact onto thin wall films

Abstract

Odontochronologies in male and female mandrills (Mandrillus sphinx) and the development of dental sexual dimorphism.

We examine how dental sexual dimorphism develops in mandrills, an extremely sexually dimorphic primate. We aimed to (a) establish the chronology of dental development (odontochronology) in male and female mandrills, (b) understand interindividual and intersex variation in odontochronologies, and (c) determine how dental sexual dimorphism is achieved. We prepared histological ground sections from the permanent teeth of four female and four male mandrills from the semi-free ranging colony at the Centre International de Recherches Médicales, Franceville, Gabon. We used the microscopic growth increments in the sections to create odontochronologies. We compared ages at crown initiation, crown formation times (CFT) and crown extension rates (CER) between individuals and sexes to assess interindividual and intersex variation. All mandrill teeth are sexually dimorphic in size. Dental sexual dimorphism in mandrills is achieved via sex differences in the duration of growth (bimaturism) and in growth rates. We also found interindividual and intersex variation in the ages at initiation and completion of crown formation. Our results show that the rate of ameloblast differentiation varies between individuals and that selection for both the age at tooth initiation and CER has occurred independently in males and females to ensure that the teeth develop at appropriate times relative to the growth of the sexually dimorphic jaws. They also show that canine dimorphism is achieved through differences in both CER and CFT, unlike extant great apes or Cantius. Given at least three mechanisms for achieving canine dimorphism, we need more information to trace the evolution of this trait in primates.

Effect of patient- and surgery-related factors on supracrestal tissue reestablishment after crown lengthening procedure.

The standard application of a mean value of 2.04 mm for the biologic width has been demonstrated to result in inconsistent amounts of tooth extension following a crown lengthening procedure. Biologic width has been replaced by the supracrestal gingival tissue dimension, which includes the biologic width and sulcular depth. The question whether supracrestal gingival tissue dimension established at tissue maturation following a crown lengthening procedure is not significantly different from the presurgical dimension has not been fully answered. The primary objectives of the present prospective clinical study were to compare the preoperative and the 24-week dimensions of supracrestal gingival tissue following a crown lengthening procedure and assess the alterations in gingival margin position. A secondary objective was to assess selected patient- and surgery-related factors on supracrestal gingival tissue reestablishment. Twenty adult systemically healthy patients requiring a crown lengthening procedure were recruited for the study. A crown lengthening procedure was performed at 33 teeth and the patients were followed up to 24 weeks. The following parameters were recorded using customized stents for measurement reproducibility: stent-gingival margin (baseline, immediately after surgery, and at 6, 12, and 24 weeks), stent-bottom of sulcus (baseline and at 6, 12, and 24 weeks), stent-bone crest (baseline, at completion of osseous resection, and at 24 weeks), bone thickness (baseline, postsurgery), buccal gingival thickness (baseline, 24 weeks), and radiographic interproximal bone width (baseline, 24 weeks). Supracrestal gingival tissue, crown extension, and distance between the immediate postoperative position of the gingival margin relative to the contoured bone crest (F) were calculated. There were no statistically significant differences between supracrestal gingival tissue measurements at baseline and at 24 weeks for any of the four tooth sides. Crown extension remained significantly increased at 24 weeks compared to baseline for all sides, with the largest amounts of gingival creeping mesially and distally. A highly significant positive correlation (r = 0.97, P < .001) was demonstrated between flap positioning and stability of the gingival margin during the healing period. The closer was the F measurement to baseline supracrestal gingival tissue dimension, the less change in gingival margin was observed. The preliminary results of this investigation suggest the following: The presurgical supracrestal gingival tissue dimension can be used as a guideline measurement in crown lengthening procedures as it is reestablished with a similar apico-coronal dimension 24 weeks postoperatively; and crown extension is stable when the distance between the sutured gingival margin and the contoured osseous crest is similar to the preoperative supracrestal gingival tissue dimension.

Enamel formation and growth in non-mammalian cynodonts.

The early evolution of mammals is associated with the linked evolutionary origin of diphyodont tooth replacement, rapid juvenile growth and determinate adult growth. However, specific relationships among these characters during non-mammalian cynodont evolution require further exploration. Here, polarized light microscopy revealed incremental lines, resembling daily laminations of extant mammals, in histological sections of enamel in eight non-mammalian cynodont species. In the more basal non-probainognathian group, enamel extends extremely rapidly from cusp to cervix. By contrast, the enamel of mammaliamorphs is gradually accreted, with slow rates of crown extension, more typical of the majority of non-hypsodont crown mammals. These results are consistent with the reduction in dental replacement rate across the non-mammalian cynodont lineage, with greater rates of crown extension required in most non-probainognathians, and slower crown extension rates permitted in mammaliamorphs, which have reduced patterns of dental replacement in comparison with many non-probainognathians. The evolution of mammal-like growth patterns, with faster juvenile growth and more abruptly terminating adult growth, is linked with this reduction in dental replacement rates and may provide an additional explanation for the observed pattern in enamel growth rates. It is possible that the reduction in enamel extension rates in mammaliamorphs reflects an underlying reduction in skeletal growth rates at the time of postcanine formation, due to a more abruptly terminating pattern of adult growth in these more mammal-like, crownward species.

How management intensity and neighborhood composition affect the structure of beech (Fagus sylvatica L.) trees

The intensity of silvicultural interventions and the neighborhood composition determine branching patterns, crown shape, and trunk attributes of beech ( Fagus sylvatica L.) trees. The intensity of silvicultural interventions and the composition of tree species are important forest management decisions. Both determine tree shape and thus influence the value of a tree, be it in terms of economy (trunk form, branchiness), or in terms of ecology (microhabitats). However, our knowledge on the distinct changes in tree architecture due to silvicultural management intensity or different neighborhood diversities is still limited, especially if the focus is on single tree attributes, e.g., branching patterns or crown shapes. We used terrestrial laser scanner data to calculate 25 structural measures for 55 European beech (Fagus sylvatica L.) trees that grew either in pure stands along a gradient of management intensity or in intra or interspecific neighborhoods in unmanaged stands. We found a lower height of maximal horizontal crown extension, a higher crown surface area, and straighter trunks with increasing management intensity. Moreover, our study revealed that beech trees surrounded by valuable hardwoods showed a lower height of maximal horizontal crown extension, a lower height–diameter ratio, and longer branches with flatter branch angles than beech trees surrounded by conspecific neighbors. Our findings provide evidence of phenotypic plasticity of European beech to diverse environmental conditions. The differences in tree structure indicate an increasing crown competition with decreasing management intensity and stronger competitive pressure for beech surrounded by conspecific neighbors in comparison to alien neighbors.

Wood harvest by pollarding exerts long-term effects on Populus euphratica stands in riparian forests at the Tarim River, NW China

Populus euphratica (Euphrates poplar) is the dominant tree species of the riparian (“tugai”) forests of Central Asia, which provide important ecosystem services to a rapidly growing population. However, overuse of the forests by wood harvest (pollarding) contributes markedly to their destabilisation. At the upper reaches of the Tarim River (Xinjiang, NW China), we investigated the effects of past pollarding (in the 1970s and 1980s) on the stand structure, tree morphology, stem diameter increment and intrinsic water use efficiency (iWUE) of poplars with different pollarding intensities in the past (‘No Use’, ‘Moderate’, ‘Intense’) growing on three adjacent plots with the same distance to the groundwater level. Compared to the non-used trees, the pollarded poplars (in particular, the intensely used trees) exhibited smaller figures of the following morphological variables: ratio of tree height to diameter at breast height, vertical crown extension, crown projection area, crown volume, and tree-ring width as well as basal area increment (BAI) during the past 24years; but a higher number of secondary shoots, a higher percentage of hollow stems and a higher degree of hollowness of the stems. The pollarded trees were capable of regenerating to a certain extent, which was obvious from the formation of secondary shoots and, in the intensely pollarded trees, from a lower iWUE (inferred by more negative δ13C isotopic ratios of the tree rings; most probably due to higher rates of gas exchange) as well as from their capability of re-establishing a crown efficiency similar to non-pollarded trees. However, the BAI of the main trunk and the secondary branches of the pollarded trees decreased continuously during the last 24years of investigation. Whilst moderate intensities of pollarding seem to be sustainable for the riparian P. euphratica forests, intense pollarding reduces the growth increment of the trees and, even more importantly, results in a distinct increase in the percentage of hollow stems, which can render the trees less stable and more susceptible to secondary damaging factors. The significant correlations between BAI and morphological variables of crown projection area and crown volume are promising for developing approaches to assess the productivity of P. euphratica stands on a landscape level using methods of remote sensing.

Crown size and growing space requirement of common tree species in urban centres, parks, and forests

Tree crown size determines among others tree's growth, carbon sequestration, shading, filtering of fine air particulates, and risk of wind-breaking. The dependence of crown size on species, resource supply, and tree age complicates an accurate evaluation of a tree's space requirement, and its size-dependent functions and services in urban as well as in forested areas.Based on a world-wide dataset of tree crown measurements of 22 common urban tree species we first derived species-specific crown radius–stem diameter relationships for open grown conditions. By cluster analysis we then assigned the 22 species to 5 crown extension types and developed mean relationships of tree height, crown radius, crown projection area, and crown volume depending on tree diameter for each type. This allometric analysis yielded auxiliary relationships which can be used for estimating the species-specific crown size and dynamics at a given tree dimension. We discuss how the results can support the choice and initial spacing of particular species and the assessment and prognosis of their functions and services.

Effects of irregular stand structure on tree growth, crown extension and branchiness of plantation-grown Pinus patula

The practice of combining row and selective thinning in commercial pine plantation silviculture carries the risk of unwanted irregularities in tree distribution, a situation that is aggravated when tree selection during marking is poor. The potential consequences of poor tree selection are accentuated by gaps along row removal. This leads to spatially asymmetric growing space to adjacent trees. The effect of irregular stand structures on tree morphology and growth are investigated in this study, and are based on two stands of Pinus patula (Schiede ex Schltdl. et Cham.) in Langeni Plantation, South Africa. A comparison between trees grown in an all-sided and one-sided spatial competition situation is presented to assess the degree of differences between the two situations. Results of this study show significantly larger crown diameters, crown lengths, longer and thicker branches, disproportionately one-sided crown growth and a reduction in space-use efficiency in stands with irregular competitive status. These factors potentially negatively affect saw timber quality and volume production from the stands at final felling.

Diversifying the composition and structure of managed, late-successional forests with harvest gaps: What is the optimal gap size?

Managing forests for resilience is crucial in the face of uncertain future environmental conditions. Because harvest gap size alters the species diversity and vertical and horizontal structural heterogeneity, there may be an optimum range of gap sizes for conferring resilience to environmental uncertainty. We examined the impacts of different harvest gap sizes on structure and composition in northern hardwood forests of the upper Great Lakes region, USA using a robustly-designed experiment consisting of six harvest gap sizes replicated 12 times with over a decade of repeated measurements. We found that germinant (trees<0.15m tall) densities were greatest in year 2 (71.6stemsm−2) but were present in all measurement years (0, 2, 6, and 12years post-harvest), suggesting a continuous influx of tree seedlings on site. Sapling (>0.6m tall) densities were greatest (3.9stemsm−2) at the end of the study period (year 12) and were composed primarily of three species (Acer saccharum, Fraxinus americana, Ostrya virginiana) already present on site. The 6 and 10m diameter (dia.) harvest gaps had, on average, the minimum number of saplings (∼2stemsm−2) needed to fill dominant positions in small canopy openings, but, by year 12, small gaps were closed by crown extension of mature edge trees. Medium (20m dia.) to large harvest gaps (30 and 46m dia.) had fewer saplings than small gaps. The understory layer of medium and large gaps were dominated by shrubs (Rubus sp.) that dampened growth of species such as F. americana. Consequently, gap-filling from the sapling layer would not occur in the near future, and, from a management perspective, would be considered a regeneration failure within larger gaps. Our study suggests that the optimum gap size does not exist and using harvest gaps to create resilient forests with structural and compositional diversity alone is challenging on productive habitats. In particular, medium to large gaps will likely require microsite specific placement of desired advance regeneration or additional treatments (e.g., vegetation control) to cultivate a dense sapling layer in an acceptable timeframe after harvest.

Morphological plasticity of European beech (Fagus sylvatica L.) in pure and mixed-species stands

The question how tree species allometry in mixed stands differs from pure stands is approached by analyzing how crown morphology of European beech (Fagus sylvatica L.) behaves in intra- versus interspecific neighborhoods. Based on long-term experimental plots with individual tree records on tree allometry and competition, our results revealed that (i) in pure stands crown allometry of beech is far from constant, but closely related to intraspecific competition, (ii) in mixed stands crown allometry of beech is considerably modified by competition reduction when growing in the vicinity of spruce, oak or pine, and (iii) crown extension due to competition reduction by interspecific neighbors increases with site fertility. Implications for the allometric theory, the stress-gradient hypothesis and a general understanding/conceptual model for mixing reactions are discussed.

Modeling of light transmission under heterogeneous forest canopy: an appraisal of the effect of the precision level of crown description

Context: Light availability in forest understory is essential for many processes; it is, therefore, a valuable information regarding forest management. However, its estimation is often difficult and direct measurements are tedious. Models can be used to compute understory light, but they often require a lot of field data to accurately predict light distribution, particularly in the case of heterogeneous canopies. Aims : The influence of the precision level of crown description was studied with a model (MμSLIM) that can be used with both detailed and coarse parameterization with the aim of reducing field data requirements to a minimum. Methods :We analyzed the deterioration of the prediction quality of light distribution to the reduction of inputs by comparing simulations to transmitted light measurements in forests of increasing complexity in three different locations. Results : With a full set of parameters to describe the tree crown (i.e., crown extension in at least eight directions, crown height and length), the model accurately simulated the light distribution. Simplifying crown description by a geometric shape with a mean radius of crown extension led to deteriorated but acceptable light distributions. Allometric relationships used to calculate crown extension from trunk diameter at breast height seriously reduced light distribution accuracy.

Enamel microstructure in the fossil bovid Myotragus balearicus (Majorca, Spain): Implications for life-history evolution of dwarf mammals in insular ecosystems

The causes underlying the evolution of insular dwarfs and giants are a matter of ongoing debate. Because body size is among the principle life history traits, recent works aim to understand the evolution of insular dwarfs in the framework of life history theory. However, the hypotheses put forward so far are conflicting. Early studies, suggested that dwarfing is a consequence of selection for an increased reproduction associated to an accelerated life history (formerly r-selection). Recent work, however, based on the analysis of bone histology of the fossil insular dwarf bovid Myotragus balearicus (Balearic Islands, Spain), concluded that dwarfing on islands results from a decrease in growth rate associated to a slow life history (formerly K-selection) in response to selective forces peculiar to insular conditions. In the present work, we reconstruct the schedule of certain life history traits by estimating the rate of dental development and eruption times in M. balearicus and, for comparisons, in an extant caprine (Ovis aries). We used histological techniques to calculate crown formation time, daily secretion rate and crown extension rate, in the lower molars. Eruption pattern in M. balearicus was analysed through the radiological images of an ontogenetic series of mandibles. Our results show that dental crowns grew at slower rates and the period of crown formation was more extended in the dwarfed fossil bovid than in other extant caprines, resulting in dental development and eruption time that doubles that of extant bovids of similar body size. This suggests an important delay in life history schedules. Concordant with the delayed dental development, the striking hypsodonty of Myotragus is indicative of an extended lifespan. These results, together with previous findings from long bone histology, provide empirical evidence for a shift towards a slow life history in this insular dwarfed mammal. Density-dependent resource limitation is hypothesized as the main trigger of the life history and body size evolution of Myotragus.

The isotope record of short- and long-term dietary changes in sheep tooth enamel: Implications for quantitative reconstruction of paleodiets

Quantitative reconstruction of paleodiet by means of sequential sampling and carbon isotope analysis in hypsodont tooth enamel requires a precise knowledge of the isotopic enrichment between dietary carbon and carbon from enamel apatite ( ε D–E), as well as of the timing and duration of the enamel mineralization process (amelogenesis). To better constrain these parameters, we performed a series of controlled feeding experiments on sheep ranging in age from 6 to 24 months-old. Twenty-eight lambs and 14 ewes were fed isotopically distinct diets for different periods of time, and then slaughtered, allowing the timing and rate of molar growth to be determined. High resolution sampling and stable carbon isotope analysis of breath CO 2 performed on six individuals following a diet-switch showed that 70–90% of dietary carbon had turned over in less than 24 h. Sequential sampling and carbon isotopic analysis was performed on the first (M 1) and second (M 2) lower molars of four lambs as well as on the third lower molar (M 3) of 11 ewes. The changes in diet were recorded in all molars. We found that the length of enamel matrix apposition is approximately one-quarter of the final tooth length during crown extension, and that enamel maturation spans slightly less than 3 months in M 1, and 4 months in M 2 and M 3. Portions of enamel in equilibrium with dietary carbon were used to calculate ε D–E values. Animals on grass silage diets had values similar to previous observations, whereas animal switched to pelleted corn diets had values ca. 4‰ lower, a pattern consistent with lower methane production observed for animals fed concentrate diets. The tooth enamel forward model of Passey and Cerling (2002) closely predicted the amplitude of isotope changes recorded in tooth enamel, but slightly underestimated the rate of isotope change, suggesting that the rate of accumulation of carbonate during maturation may not be constant over time. Although stable isotope profiles in tooth enamel represent underdetermined systems, our results demonstrate that they can provide useful information about dietary variability if the mineralization process is taken into account.

Brief communication: dental development and enamel thickness in the Lakonis Neanderthal molar.

Developmental and structural affinities between modern human and Neanderthal dental remains continue to be a subject of debate as well as their utility for informing assessments of life history and taxonomy. Excavation of the Middle Paleolithic cave site Lakonis in southern Greece has yielded a lower third molar (LKH 1). Here, we detail the crown development and enamel thickness of the distal cusps of the LKH 1 specimen, which has been classified as a Neanderthal based on the presence of an anterior fovea and mid-trigonid crest. Crown formation was determined using standard histological techniques, and enamel thickness was measured from a virtual plane of section. Developmental differences include thinner cuspal enamel and a lower periodicity than modern humans. Crown formation in the LKH 1 hypoconid is estimated to be 2.6-2.7 years, which is shorter than modern human times. The LKH 1 hypoconid also shows a more rapid overall crown extension rate than modern humans. Relative enamel thickness was approximately half that of a modern human sample mean; enamel on the distal cusps of modern human third molars is extremely thick in absolute and relative terms. These findings are consistent with recent studies that demonstrate differences in crown development, tissue proportions, and enamel thickness between Neanderthals and modern humans. Although overlap in some developmental variables may be found, the results of this and other studies suggest that Neanderthal molars formed in shorter periods of time than modern humans, due in part to thinner enamel and faster crown extension rates.

Variation in allometry and tree architecture among Symplocos species in a Japanese warm-temperate forest

We compared tree architecture and allometry among five Symplocos species (Symplocos myrtacea, Symplocos lancifolia, Symplocos lucida, Symplocos glauca, and Symplocos theophrastiifolia) in a Japanese warm-temperate forest to understand the causes of interspecific variations in these characteristics. S. lancifolia, S. glauca, and S. theophrastiifolia grew at elevations below 500 m, whereas S. lucida grew on ridges irrespective of elevations, and S. myrtacea grew at elevations above 590 m. The species that shared a habitat exhibited trade-offs between height growth and crown area extension that might reflect differentiation in their regeneration niches. S. lancifolia showed the lowest height growth and widest crown extension, whereas S. theophrastiifolia showed the greatest height growth and lowest crown extension. S. glauca was intermediate between these species. S. lucida grows on ridges characterized by strong winds and the absence of other Symplocos species; it had the thickest stem and second-narrowest crown of the five species, possibly due to mechanical stability constraints. S. myrtacea was smallest at the onset of reproduction, and its fruits developed under closed canopies. Its architecture and allometry may increase seed production. Variation in tree architecture and allometry among the five species appear to be related to differentiation among regeneration niches, mechanical stability, and reproduction constraints.