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Biomedical subjects

R Schoen

Publications and source records attributed to R Schoen.

At least 19 recordsLinked to original sources
PubMed2006

Inferior alveolar nerve transposition--an in vitro comparison between piezosurgery and conventional bur use.

An in vitro comparison between a new ultrasound-based piezoelectric device and a conventional bur was performed for lateralization or transposition of the inferior alveolar nerve to evaluate the effects on soft and hard tissue. Transposition of the inferior alveolar nerve was performed in the cadaver mandibles of 10 sheep: the left nerve was uncovered with a saline-cooled diamond-coated spherical bur (2000 rpm), and the right nerve was uncovered with the piezoelectric device mounted with a spherical diamond tip. The surface, the zone of bone defect, and the nerve were examined by light microscopy and laser microscopy. Bone treated with the rotary bur showed significantly smoother surfaces and shallower defect zones (50 microm) in comparison with the piezoelectric device (150 microm). Lesions of the epineurium and an increased amount of bone particles were found in the lesions prepared with the piezoelectric device. In vitro preparation with the piezoelectric device was more invasive to the bone than was a conventional diamond bur. Touching the inferior alveolar nerve resulted in roughening of the epineurium without affecting deeper structures. The degree of injury was lower than when using the conventional rotary bur.

Animals↗
PubMed2005

Pathological mandibular fractures following third molar removal.

Seventeen patients, who presented mandibular fractures following third molar removal, were treated in the Department of Oral and Maxillofacial Surgery at the University Hospital Freiburg between 2000 and 2004. Clinical and radiological data were analysed to evaluate the possible risk of fracture following third molar removal. Our data show an increased rate of pathological mandibular fractures in males over 40 years of age, following removal of a difficult lower wisdom tooth with a high retention grade that necessitated bone removal. Fourteen out of 17 fractures occurred postoperatively. In six cases, no fracture was visible in radiographs during the primary investigation. Pathological mandibular fractures were typically located anterior to the mandibular angle (n=15). We recommend informing patients about possible risks and, in selective cases, a soft diet for up to 4 weeks after the operation. A cracking noise reported by the patient is the most important indication of a fracture. If, initially, the fracture is radiologically undetectable, we recommend the use of radiological controls.

Adult↗
PubMed2000

Cognitive impairment and syndromal depression in estimates of active life expectancy: the 13-year follow-up of the Baltimore Epidemiologic Catchment Area sample.

OBJECTIVE: Our hypothesis was that including cognitive status and syndromal depression in specifying functional impairment would result in significant differences in estimates of active life expectancy from specifications that included only standard functional measures (such as activities of daily living). METHOD: The subjects were the 3481 continuing participants of the Baltimore Epidemiologic Catchment Area Program. Interviews included criterion-based diagnosis of depression, assessment of cognitive status and standard survey questions on function. RESULTS: Estimates of active life expectancy decreased from 9.8 years to 8.9 years at age 65 years for men, and from 10 years to 8.4 years at age 65 years for women, when the definition of active life expectancy included measures of cognitive impairment and syndromal depression. CONCLUSION: Measurements of active life expectancy tend to ignore dependencies related to psychological causes, and should move beyond mere enumeration of activities of daily living and instrumental activities of daily living.

Adolescent↗
PubMed1997

Population momentum expresses population aging.

Population momentum and population aging occur when an initially growing population experiences a reduction in fertility to replacement level. Conceptually and empirically, momentum and aging express the same change, albeit on different scales. Fundamentally, they are two manifestations of the underlying process of demographic transformation. We consider three measures of aging over the transition to stationarity: the increase in mean population age, the decrease in the proportion under age 30, and the increase in the proportion over age 65. The three measures of aging are highly correlated, though the relationship to momentum is weakest for the increase in the proportion over age 65. We find that momentum is linearly related to aging. In both model and actual populations, a one-year increase in mean age translates into about 4.5% more population growth. The population below age 30 does not grow over the transition to stationarity and the ratio of initial to ultimate proportions under age 30 is virtually identical to momentum.

Adolescent↗
PubMed1996

Populations with sinusoidal birth trajectories.

Starting with a sinusoidal birth function, we derive an explicit expression for the associated wave of net maternity (R(t)). The phase shift and relative amplification of R(t) depend heavily on the cycle length of oscillation (T) relative to the mean age of net maternity (mu) and on the amplitude of oscillation of the birth function. For short cycle lengths (up to about 12 years), the birth and R(t) functions are virtually identical. When the cycle length is long (over 120 years), R(t) is essentially equal to the ratio of the number of births at time t to that at time t-mu. The R(t) function oscillates with the same cycle length as the birth function, but it is not sinusoidal and its asymmetry increase as the amplitude of birth function increases. This paper breaks new ground by providing a complete description of the dynamics of the model, including an analysis of the sensitivity of R(t) to the amplitude of the birth function, which was not accessible to previous approaches.

Age Distribution↗
PubMed1996

Stabilization, birth waves, and the surge in the elderly.

This study examines the transition of a population to stability following a shift to a new fixed set of vital rates. Specifically, the authors develop a simple discrete population model and use it to derive an explicit solution for the birth trajectory. "The new vital rates interact with the population's initial age composition and generate birth waves whose amplitude and attenuation depend on the ratio of ultimate to initial growth and on the new pattern of stable net maternity. A greater change in growth and a later stable net maternity pattern produce larger fluctuations in the number of births. Stabilization begins at the youngest ages and proceeds upward. Sixty years after the shift, the birth waves have largely disappeared and the proportion under age 15 approximates the stable level implied by the new rates. Those patterns are manifest in the stabilization of both observed and Coale-Demeny model stable populations." (SUMMARY IN FRE)

Age Distribution↗
PubMed1993

Two-state spatial dynamics in the absence of age.

This paper investigates the simplest multistate population model, a one-age-group, two-living-state model with constant rates of birth, death, and interstate movement. A general solution for the model is presented, and special attention is given to the process of convergence to stability and its relationship to spatial population momentum. The constant ultimate level of the speed of convergence, or the intrinsic force of convergence, is found to be twice the difference between the two eigenvalues of the model's transition matrix. Spatial population momentum is shown to be directly proportional to the initial growth rate of the population under the stationary rates and inversely proportional to the intrinsic force of convergence. A population increases in size during the transition to zero growth only when the faster growing state is a larger fraction of the initial population than of the stationary population. Hypothetical calculations with an urban/rural population model illustrate the importance of the speed of convergence, and show the great growth potential inherent in spatial momentum.

Age Factors↗
PubMed1993

Crossovers that link populations with the same vital rates.

"In this paper, we consider crossovers of demographic density distributions from...populations that have the same fertility and mortality rates. We focus on observed populations and their associated stationary and stable models, and on proportional distributions of persons, births, deaths and reproductive values.... Three different populations were selected to represent a range of demographic behavior. Those populations are Japan 1963, a low mortality, low fertility population; Togo 1961, a high mortality, high fertility population; and the United States 1919-1921, a population whose fertility and mortality are intermediate."

Africa↗
PubMed1993

On the intrinsic force of convergence to stability.

"Observed populations differ greatly in the speed with which they approach the stable form, but what determines rates of convergence is not fully understood.... Here we examine the trajectory to stability, derive a mathematical expression for the force of convergence, and provide an approximate relationship in terms of the mean and variance of the stable net maternity function." Trajectories for Japan, Togo, and the United States are used as illustrations. (SUMMARY IN FRE)

Africa↗
PubMed1993

The slowing metabolism of marriage: figures from 1988 U.S. marital status life tables.

Marital status life tables for the United States, 1988, show a continuing retreat from marriage. For both sexes, the proportion ever marrying declined and the average age at first marriage rose. The 1988 rates imply that 43% of marriages end in divorce. That represents a slight decline from the 1983 figure, and suggests that divorce has peaked at a level below that estimated in earlier analyses.

Adult↗
PubMed1991

Movement toward stability as a fundamental principle of population dynamics.

Although convergence to stability is typically a complex and irregular process, the Kullback distance provides a measure that moves consistently to 0 as a population becomes stable. The roots of the Kullback distance are in information theory, but it is a meaningful demographic quantity. It reflects a population's log momentum, or the amount of growth built into a population's nonstable age distribution. The rate at which the Kullback distance moves toward 0 is neither constant nor monotonic. At any point in time, however, it decreases by the covariance between a population's age-specific growth rates and its log momentum. Although the present findings are couched in terms of movement toward stability, they are generally applicable because they relate to the behavior of any population at any instant. It is a fundamental principle of population dynamics that a population is always moving toward the stable population implied by its prevailing fertility and mortality rates, and that the extent of its movement is determined by the covariance between its age-specific growth and its log momentum.

Adult↗
PubMed1991

Momentum and the growth-free segment of a population.

In the scenario of a sudden drop in fertility to replacement level. Preston (1986) argued that the population segment under age T, the length of generation, remained growth-free. Here we first present a new relationship for the momentum of any observed population as the ratio of 1) the proportion of the observed population under the mean age at childbearing to 2) the proportion of its life table population under that mean age. We then use that relationship to demonstrate Preston's approximation. Growth factors for other population segments are also presented. When the initial population is stable, momentum can be approximated as a function of the net reproduction rate alone.

Age Factors↗
PubMed1990

Religious intermarriage in Switzerland, 1969-72 and 1979-82.

"Patterns of marriage between Protestants and Roman Catholics in Switzerland during 1969-72 and 1979-82 are investigated using magnitudes of marriage attraction, measures that reflect the propensity to marry independent of population composition. The results show high levels of intermarriage, with religious differences becoming less salient in marriage choice. There is no evidence that the propensity to intermarry is influenced by 'minority group' effects." (SUMMARY IN FRE)

Developed Countries↗
PubMed1988

Practical uses of multistate population models.

"The article provides a nontechnical description of multistate population models, useful analytical tools that can reflect changes over time in the characteristics of a closed group of persons. The multistate life table literature is reviewed, emphasizing applications of the models to studies of marital status, family and household status, interregional migration, and labor force participation and concluding with a discussion of the relationship between multistate and event history models."

Demography↗
PubMed1986

The two-sex multiethnic stable population model.

A two-sex multiethnic stable population is a model with fixed mortality and fertility parameters that explicitly recognizes the behavior of males and females in at least two distinct ethnic groups. The presence of intergroup fertility may allow the different ethnic groups to grow at a constant rate in a population with a fixed sex-ethnic composition. The present paper considers a variety of rules for determining the ethnicity of intergroup births based on the ethnicities of the mother and father, and examines the mathematical models implied by those rules. Numerical examples are presented for a two-ethnic-group population in cases where intergroup births are shared equally by the two groups, are all considered members of one particular group, and are all members of the father's group. A special case of a more general model, where sons become members of the father's group and daughters become members of the mother's group, is also considered. The results suggest that when intergroup fertility is not uncommon, how ethnicity is determined can substantially influence the ethnic composition of the population.

Ethnicity↗