A Bayesian analysis of multivariate doubly-interval-censored dental data

A Bayesian survival analysis is presented to examine the effect of fluoride-intake on the time to caries development of the permanent first molars in children between 7 and 12 years of age using a longitudinal study conducted in Flanders. Three problems needed to be addressed. Firstly, since the emergence time of a tooth and the time it experiences caries were recorded yearly, the time to caries is doubly interval censored. Secondly, due to the setup of the study, many emergence times were left-censored. Thirdly, events on teeth of the same child are dependent. Our Bayesian analysis is a modified version of the intensity model of Harkanen et al. (2000, Scandinavian Journal of Statistics 27, 577-588). To tackle the problem of the large number of left-censored observations a similar Finnish data set was introduced. Our analysis shows no convincing effect of fluoride-intake on caries development.     

An analysis of the age and size of 483 human embryos

The crown-rump length of 483 fixed human embryos of Carnegie stages 6-23 was analyzed and median and predicted mean lengths were calculated. The results were compared with those of other series and confirmed that early human growth rates are different from those of macaques with which human embryo growth has previously been compared. The study indicated that it is possible to predict: 1. the median size of an embryo of given Streeter horizon or Carnegie stage; 2. the age of a fresh embryo, or one of undisputed Streeter staging, by comparison with mean figures of other authorities; and 3. the corrected age of an embryo of known length or known Streeter staging or both in terms of postovulation age. Since teratogens may reduce the embryonic growth rate this information is relevant in the analysis of teratogenic factors in human development.     

Wall shear stress distribution in a model human aortic arch: assessment by an electrochemical technique

Wall shear stress (WSS) distribution in a human aortic arch model is studied using 130 cathode electrodes flush-mounted on the model walls. Flow visualizations are made in a transparent geometry model to identify the regions of fluid mechanical interests, e.g. regions of flow separation, eddy formation and flow stagnancy. The 130 electrodes are strategically positioned in the arch based on information obtained from the flow visualizations. The measured data indicate that the aortic arch may be categorized into eight regions: three along the inner wall of the arch (A,B,C); and five near the outer wall (D,E,F,G,H). (1) The regions of low WSS are distributed along the inner wall of the ascending aorta A; the inner wall of the descending aorta C; and the upstream inner wall of the innominate and the common carotid branchings F. (2) The high WSS regions are distributed along the outer wall of the arch E; and the inner wall in the arch opposite to the left subclavian branching B. (3) In certain regions, high and low WSS may be found next to each other (e.g. G and H) without a definable boundary in between; and (4) as the Reynolds number increases, the areas of low WSS decrease, while the high WSS areas increase with no obvious change in magnitude of the stress along the inner wall of the arch. At the branchings, the WSS distribution is not affected by the Reynolds number within the range of observations. The measured WSS distribution is compared with Rodkiewicz's map of early atherosclerotic lesions in the aortic arch of cholesterol fed rabbits.     

An interactive multivariate analysis of FCM data

The procedure and results of the interactive multivariate analysis of FCM data are described. Using principal-components analysis, cluster analysis, and interactive maneuvers, this procedure facilitates an effective data compression from a four-dimensional space into two-dimensional space, then allows cluster separation. The procedure is especially effective for separating clusters, which are degenerated in the usual scattergrams. Programs were mostly written in C language on MS-DOS and were tested on four-dimensional analysis of the blood cells, which resulted in a successful separation of the degenerated clusters.     

An improved technique for dental alloy etching with a potentiostatic device

Since a good retention of direct bonded retainers onto abutment teeth is the primary requirement for the fabrication of etched fixed partial dentures, successful formation of a micromechanical retentive architecture on the bonding surface is one of the most important procedures. For creating such a retentive dendritic pattern on nonprecious metal, a 2-electrode electrolytic method has been used. This equipment consists of a low-voltage DC power supply and two electrodes, namely, a working and a counter one. However, the current and voltage should be monitored during the entire processing time and the etching area must be pre-estimated. A potentiostat has been used to automatically stabilize the voltage across the working electrode and reference electrode by adjusting the current, as commonly employed in electro-chemical technology. A 3-electrode corrosion device originally developed for laboratory research was adapted for dental retainer etching in this study. The results revealed that the etching of dental nonprecious metal (Ni-Cr-Be alloy) could successfully be performed by using the system with a potentiostat. Moreover, the working potential was found to be approximately 1.3 volts by taking the midpoint between the breakdown and the critical potentials for passivation on the potentiostatic anode polarization curves. The optimal exposure time has been found to be in a range of 3 to 5 minutes and 4 minutes to be ideal as determined by SEM microphotographic observation which showed a uniform dendritic pattern with regular lattice form of alternating ridges and valleys.(ABSTRACT TRUNCATED AT 250 WORDS)     

Structural components of the arch of the foot analyzed by radiogrammetric and multivariate statistical methods

The structural component of the arches of the human foot were analyzed by a radiogrammetric method and multivariate statistical procedures. The right feet of 101 male university students were radiographed in the standing position from a lateromedial direction. 6 joint heights were measured directly on the radiographs. Factor analysis with varimax rotation showed 3 basic underlying factors for arch heights: (1) calcaneonavicular joint, cuneonavicular joint and first tarsometatarsal joint; (2) calcaneocuboidal joint and 5th tarsometatarsal joint and (3) subtalar joint. The first factor represented the medial longitudinal arch height, the second was associated with the lateral longitudinal arch height. No transverse factor indicating tarsometatarsal or transverse tarsal joints was found. Cluster analysis showed a similar configuration to that in factor analysis. Analysis suggested a key role of the subtalar joint which integrated both the medial and lateral longitudinal arch heights.     

Allometric analysis of dental variation in a human population

There exists an extensive literature that deals with interspecific allometry, eg, brain size-body size relationships among species. Yet comparatively little attention has been paid to intraspecific or static adult allometry. An intraspecfic allometric analysis was conducted on the complete permanent dentition of a prehistoric American Indian population (N = 156). Mesiodistal and buccolingual measurements were logarithmically transformed and regressed on log transformations of femur length, an estimate of body size. When measurements of antimeric teeth were introduced together into common regressions on femur length, 20 of the 32 slopes were significantly different from zero. Thirty-one of the slopes ranged between zero and one and clustered between 0.2 and 0.4. Hence, negative allometry describes the tooth size-body size association, ie, taller individuals in general possess absolutely but not relatively larger teeth than shorter individuals. In addition, no significant sex differences for the regression slopes were observed. Though significantly correlated, tooth size and body size variables are too weakly associated to permit accurate predictons from regression equations. Evolutionary implications of intraspecfic dental allometry are discussed.     

A multivariate analysis of phytoplankton and food web changes in a shallow biomanipulated lake

1. Phytoplankton dynamics, food chain changes and resilience in Lake Zwemlust, a shallow lake in The Netherlands, are described for the period 1986–94.
2. After biomanipulation in 1987, the lake moved through two alternative states, while the external nutrient loadings were maintained. A clear-water phase, mostly dominated by macrophytes, persisted from 1987 to 1991, and a rather turbid state, dominated by algae, occurred in the summers of 1992–94, after several consecutive and sustained perturbations affecting different parts of the food web in the lake. These two periods were characterized by different community structures.
3. The phytoplankton assemblage gradually changed in a pattern that reverted in later years towards that of the pre-biomanipulation stage, although the same species composition was not regained. This agrees with some mathematical models. During the clear-water phase, nutrient shortage, light climate and zooplankton feeding selected in favour of small, high surface : volume ratio and rapidly reproducing algae. However, in mid-summer of 1992–94, nutrient availability and cladoceran grazing on edible algae favoured cyanophytes.
4. Nutrients were transferred to higher trophic levels or lost from the system at relatively high rates when the lake was in a piscivore–macrophyte-dominated state, while they tended to accumulate in the algae in a planktivore-dominated chain without macrophytes. The role of weed beds was central for nutrient competition (mostly nitrogen) with algae, as well as a refuge and a base for alternative food sources to grazers. Weed beds seemed to have a strong effect in increasing connectedness, resilience and stability of the lake community.
5. The complete return of Zwemlust to a turbid state dominated by phytoplankton seems to have depended upon turnover of the limiting nutrient, which was retarded by macrophytes and stimulated by planktivorous fish and waterfowl.     

Sphingolipid distribution changes with age in the human lens

The formation of an internal barrier to the diffusion of small molecules in the lens during middle age is hypothesized to be a key event in the development of age-related nuclear (ARN) cataract. Changes in membrane lipids with age may be responsible. In this study, we investigated the effect of age on the distribution of sphingomyelins, the most abundant lens phospholipids. Human lens sections were initially analyzed by MALDI mass spectrometry imaging. A distinct annular distribution of the dihydrosphingomyelin, DHSM (d18:0/16:0), in the barrier region was observed in 64- and 70-year-old lenses but not in a 23-year-old lens. An increase in the dihydroceramide, DHCer (d18:0/16:0), in the lens nucleus was also observed in the older lenses. These findings were supported by ESI mass spectrometry analysis of lipid extracts from lenses dissected into outer, barrier, and nuclear regions. A subsequent analysis of 18 lenses ages 20–72 years revealed that sphingomyelin levels increased with age in the barrier region until reaching a plateau at approximately 40 years of age. Such changes in lipid composition will have a significant impact on the physical properties of the fiber cell membranes and may be associated with the formation of a barrier.     

Banding pattern analysis of human chromosomes by use of a urea treatment technique

A new technique to reveal the banding pattern of human chromosomes is described. Slides prepared by the routine air drying technique were treated with urea-Sörensen buffer solution for ten minutes at pH 6.8 at 37° C. Individual pairs of all human chromosomes exhibited a characteristic banding pattern by this technique, and by its use the karyotypes were analysed. With the exception of some minor differences the banding patterns obtained by the present technique appeared to be identical with those obtained by the Giemsa staining and quinacrine fluorescence methods carried out by previous workers.Contribution No. 877 from the National Institute of Genetics, Japan. Supported by grant-in-aid No. 92332 from the Ministry of Education of Japan.     

Interference microscopy of human dental enamel at various age periods

Investigation of the human tooth enamel by means of interference contrast makes it possible to reveal certain peculiarities of the prismatic structure in various age groups. For example, in children the enamel has specific porosity of the superficial layers, that is peculiar for teeth with a delayed eruption. With age the enamel becomes more "homogeneous", amount and size of the pores decrease, aprismatic areas in the superficial layer are found more often. Erased teeth are characterized with formation of microdefects, destruction of prisms on the enamel surface and at the same time with increased mineralization of the subsuperficial layer. Thus, age changes of the enamel are of adaptive character--consolidation of structural elements promotes increasing resistivity of the teeth to influence of pathological factors.     

Tomographic measurements of age changes in the human parotid gland

This study involved 48 subjects of both sexes with ages ranging from 22 years to 90 years. Computerised tomography was used to scan the right and left parotid gland. Gland mean density was calculated in Hounsfield units and regression graphs drawn. A significant fall in gland density was noted with subject age but no differences were noted between male and female subjects. A significant correlation was observed between the mean density of right and left glands in the same individuals. It is postulated that the fall in gland density is related an increase in fibro-fatty tissue within the gland. This study provides evidence that age related changes occur in the human parotid gland from youth to old age. This work supports the earlier findings of Scott's who studied the superficial lobe of the parotid gland histologically and found an increase in adipose tissue in this area of the gland with age.     

A computer program for the analysis of dental arch form using the cubic spline function.

This paper presents the details and logic of a FORTRAN computer program which fits a cubic interpolatory spline to a set of data points digitized from an exact size photographic reproduction of a dental model. It also measures the length of the arc and computes a set of normals to the curve to be used in evaluating the error in the fit of the spline. The program is used in studies of dental arch form and is useful in evaluating changes in the form of the arches due to orthodontic treatment. The measurement of the arc length provides an adequate assessment of space available in the dental arch, which is of importance to the orthodontist.     

An innovative application of a small-scale motion analysis technique to quantify human skin deformation in vivo

This study highlights a new experimental method developed to measure full-field deformation of human skin in vivo. The technique uses a small-scale Qualisys (Sweden) 3D motion capture system and an array of reflective markers placed on the forearm of five healthy volunteers. A load of up to 1.5 N was applied to induce skin deformation by pulling a fine wire attached to the centre of the marker configuration. Loading and marker displacements were recorded simultaneously. 3D marker trajectory data was generated for three different load directions. Tests were repeated to investigate accuracy and repeatability. Calibration results indicate the accuracy of the motion capture system with an average residual of 0.05 mm. The procedure was found to be repeatable and accurate for five repeated tests of measured displacements with a maximum variance of 5%. Experimental data are presented to demonstrate robustness and the ability to produce significant outputs. For all five subjects, at 1 N load, the mean and standard deviations of skin axial and lateral displacements were found to be 11.7±1.6 mm and 12.3±3.3 mm, respectively. The axial displacements ratio (u₉₀/u₀) ranges from 0.63 to 1.45 with mean±standard deviation of 0.982±0.34 and 0.982±0.32 for left and right arms, respectively. The experiments generated useful and accurate data that can be used to study the viscoelastic, hyperelastic or anisotropic behaviour of human skin. The measured displacements will be analysed further to determine the mechanical properties of skin using inverse Finite Element Analysis and Ogden model.     

An analysis of birth weight by gestational age in Canada.

Birth-weight-gestational-age standards help to identify infants in need of special care and to determine causes and means for preventing retardation of intrauterine growth. Previously published standards either were based on small samples, data several decades old or characteristics of subpopulations in the United States or they were not specific for type of birth and sex. We compared the data for live births in 1972 with those in 1986 to develop current Canadian standards for type of birth (singleton or twin) and sex. We found that the 10th, 50th and 90th percentile figures for weight were slightly higher in 1986 than in 1972 for term deliveries (at 37 weeks'' gestation or later), but the figures were virtually unchanged for preterm deliveries. The availability of reliable population-based standards should enhance the clinician''s ability to identify true cases of retardation or acceleration of intrauterine growth.     

The cryomicrotomy of rat dental tissues: a technique for histological and immunohistochemical analysis

Summary We have applied a method developed for the cryomicrotomy of non-decalcified bone to the histological preparation of the tooth and related dental tissues. Cryosections of rat mandible have been cut on a heavy-duty freezing microtome. Both cellular and extracellular structure was well preserved and the sections of tooth and bone appeared to be suitable for optical and scanning electron microscopy and for immunohistochemical analysis. However, there was an overall strong non-specific binding of immunohistochemical reagents to enamel which was not evident in the other mineralized tissues of the mandible. This may relate to important differences in the nature of this tissue.     

Metabolic fingerprinting of wild type and transgenic tobacco plants by 1H NMR and multivariate analysis technique

The metabolomic analysis of wild type and constitutive salicylic acid producing tobacco plants (CSA tobacco, Nicotiana tabacum 'Samsun' NN) plants overexpressing salicylate biosynthetic genes was carried out by 1H NMR spectrometry and multivariate analysis techniques. The principle component analysis (PCA) of the 1H NMR spectra showed a clear discrimination between those samples by PC1 and PC2. The discrimination of non-inoculated, TMV-virus inoculated, and systemic leaves or veins could also be obtained by PCA analysis. Major peaks in 1H NMR spectra contributing to the discrimination were assigned as those of chlorogenic acid, malic acid, and sugars. This method allows an efficient differentiation between wild type and transgenic plants without any pre-purification steps.