Incorporating environmental stochasticity within a biological population model.

The birth and death transition rates for a population are modelled as functions of both the population size and the environmental condition. An assortment of important theoretical results and techniques that can be utilized to analyze such a population's behaviour is covered. Consequently, these results and techniques are used to study two examples. Firstly, we study a population with a stable equilibrium state, whose per capita birth and death rates are linearly related to the environmental condition. (The environmental condition in turn is modelled as an Ornstein-Uhlenbeck process.) Secondly, we study a population affected by two interdependent environmental factors.

Microbiological impressions of teeth, saliva and dietary fibre can predict caries activity.

OBJECTIVES: Mutans streptococci and Lactobacilli on impressions of teeth and caries tests were used to identify caries prone subjects. METHODS: Twenty-seven dental students were examined for caries initially and after 4 years. At the initial examination plaque index; saliva flow, buffering capacity and lysozyme; sucrose and fibre consumption; Lactobacilli and mutans streptococci in saliva and on alginate impressions were measured. Data was analysed using Kruskal-Wallis, Wilcoxon-Mann-Whitney and Spearman's Rank correlation tests and linear discriminant analysis. RESULTS: The best predictor of caries increment was decay. Nine subjects had no caries or restored teeth with caries (Group A); 9 had restored teeth with no caries but developed an average of 8 new decayed surfaces (Group B); 9 had an average of 4.4 decayed surfaces and developed a further 9.6 (Group C). Group A had fewer filled surfaces than Group B (p=0.02) and Group C (p=0.024) a higher flow rate of stimulated saliva than Group B (p=0.02) and Group C (p=0.012). Microorganisms were cultured from all decayed teeth, 98% that developed decay, 89% filled and 69% sound teeth. Fibre intake, saliva flow and the percentage of teeth or sound teeth with Lactobacilli and mutans streptococci gave a specificity of 89%, a sensitivity of 100% and predicted an increase in decay in all Group B subjects while one subject from Group A was misclassified. When teeth with microorganisms were excluded four subjects were misclassified. CONCLUSIONS: Growth of cariogenic microorganisms on alginate impressions, saliva flow and dietary fibre predicted caries activity in most subjects.

Dental caries at five and twelve years in a South African Indian community: a longitudinal study.

In 1979, 515 of 767 available Indian children born in Lenasia in 1974 were examined and their dental caries status was described. In 1986, 515 of the original 715 were re-examined in order to determine the pattern of dental caries in the primary and permanent dentitions of the same individuals. In contrast to studies in the literature in which treatment records have been used, both investigations were formal epidemiological field studies using calibrated examiners and WHO (1971) caries diagnostic criteria. A firm association was found between caries in the primary and permanent dentitions (r = 0.34).

Trends in arthropod defensive secretions, an aquatic predator assay.

Twenty-five arthropod defensive chemicals were tested on a potential fish predator to assay basic repellency, interniche effectiveness and mimetic interactions among repellents, and predator tolerance to repellents.The defensive secretions of aquatic arthropods are more effective repellents than those of terrestrial or cryptozoic arthropods. Phenolic compounds are more effective than carbonylic or acidic compounds. Repellency is most effective in compounds of reduced water solubility. Repeated exposure to gradually increasing molar concentrations of benzoic acid resulted in a greater acceptability of this compound to fish predators. It is suggested that Mullerian mimicry systems based on large numbers of species may be susceptible to dilution effects in terms of effectiveness.

The onset of eruption of the permanent dentition amongst South African black children.

One thousand and twenty-four children with a mean age of 6.41 yr were examined to determine the mean ages of eruption for the first permanent molars and the permanent central and lateral incisors. The youngest observed age for the eruption of any permanent tooth amongst girls was 4.50 yr and amongst boys, 4.31 yr. The eruption ages were on the whole later than those reported in most African studies, but were very similar to those found for Kenyan African and American blacks.

Predictive value of conditional centile charts for weight and fundal height in pregnancy in detecting light for gestational age births.

OBJECTIVE: To estimate the predictive value of weight and symphysis fundal height (SFH) in pregnancy to detect light for gestational age (LiGA) births. STUDY DESIGN: New conditional centile charts for longitudinal monitoring of maternal weight and fundal height in pregnancy were developed based on the records of 676 women with singleton pregnancies and no complications. The records of these women and of a further sample of 102 women who had LiGA deliveries were used to assess the sensitivity and specificity of the charts in detecting LiGA during pregnancy. RESULTS: Maternal weight is a poor predictor of LiGA births. Fundal height shows moderate predictive ability. The simple cross-sectional chart for fundal height at the 20th percentile cutoff has sensitivity and specificity of 66% in detecting LiGA births. CONCLUSIONS: Monitoring via a cross-sectional chart of fundal height offers a potentially useful screening method. The results of this study add support to arguments that routine weighing in pregnancy should be abandoned.

Dental caries and social factors in 12-year-old South African children.

Dental caries prevalence (percentage caries-free) and experience (DMFS) were recorded, in 414 12-yr-old Indian and 401 white children living in adjacent urban communities with the same fluoride concentration in the drinking water (0.21-0.33 ppm) using WHO (11) criteria. Details of social factors: education level, family income, home space and occupants and parental occupation were obtained by questionnaire. Dental caries was significantly worse in the Indian children with regard to numbers caries-free (30%--white and 40%--Indian) and DMFS mean (sd) (3.65 (3.98) and 2.66 (3.49) working group, respectively). Social class, white or blue collar, family income and room to person ratio were significantly associated with dental caries in the white children but there were no significant associations in the Indian children. Multiple regression analysis showed race and sex to be significant factors.

Dental caries in South African white children aged 1-5 years.

The dentitions of 499 white preschoolchildren aged 1-5 years from a low fluoride area were examined with mirror and probe. The dmft values ranged from 1.0 +/- 2.0 at 1 year of age to 5.1 +/- 4.5 at 5 years of age while the overall mean for the group was 3.7 +/- 4.1. ""Rampant" caries prevalence varied according to the definition used. It is suggested that for epidemiologic studies rampant caries should be defined as a dmft value of 5 or more and that labial caries should be regarded as a specific entity.

Relationships between fluoride in enamel, DMFT index and fluorosis in high- and low-fluoride areas in South Africa.

The DMFT Index, degree of fluorosis (DEGF), and enamel fluoride concentration (F) were determined in 88 children living in a high- and 79 children living in a low-fluoride area in South Africa. The following interrelationships between these parameters were found: in both areas there was a significant negative correlation between log F and age; in the high-fluoride area there was a significant positive correlation between log F and DEGF; and in the combined data from the two areas there were significant correlations between log F and area, log F and age, and log F and DEGF, and a significant association between DEGF and area. There were no significant correlations between DMFT and log F and between DMFT and DEGF.

Patterns of breast and bottle feeding and their association with dental caries in 1- to 4-year-old South African children. 1. Dental caries prevalence and experience.

In order to study associations between breast and bottle feeding and dental caries a questionnaire on feeding habits was completed by trained interviewers for 1,263 children aged 1 to 4 years from five South African communities. Of these, 73 to 94 per cent had been breast fed for mean periods of 9 to 16 months. The types of infant feeding practised (breast, bottle or mixed) varied little within the groups although each group differed significantly from the others for the preferred feeding practice. Using responses to a dietary interview the children were subdivided into those breast fed for 12 months or longer (n = 546), those who had mixed breast and bottle feeding (n = 527) and those who were bottle fed only (n = 190). Caries prevalence increased with the age of the child, more in bottle fed than other groups. Within all feeding groups caries prevalence was lowest among white children and in social class I. The dmfs and dmft scores showed irregular patterns and were significantly influenced by feeding group and the interaction between race and social class.

PIP: The importance of breast feeding in industrialized societies is increasing. As such, it is important to establish whether or not breast feeding on demand for a prolonged period is associated with nursing caries so that the necessary prevention measures may be implemented in both developing and developed countries. The authors present findings from an investigation of breast and bottle-feeding practices and their relationships to dental caries in infants and pre-school children in the Transvaal. The relationship between feeding groups, age, race, social class, and dental decay was explored. Mothers or child carers of 1263 children aged 1-4 years from 5 South African communities were interviewed. 73-94% of the children had been breast fed for mean periods of 9-16 months. Although types of infant feeding varied little within groups, preferred feeding practice differed significantly between groups. 546 children were breast fed for 12 months or longer, 527 had mixed breast and bottle feeding, and 190 were bottle fed only. The prevalence of caries increased with the age of the child and more among the bottle fed than others. The prevalence of caries was lowest among white children and in social class I within all feeding groups.

Patterns of breast and bottle feeding and their association with dental caries in 1- to 4-year-old South African children. 2. A case control study of children with nursing caries.

In a case control study, 109 children with nursing caries (> or = 2 decayed, missing, or filled labial or palatal surfaces of primary incisor teeth) were matched for age, race, gender, and social class to 109 children without nursing caries from the same study areas. Mean dmfs and dmft scores were statistically higher in the nursing caries group but no statistically significant differences were found for feeding patterns between the groups in relation to the prevalence of nursing caries. In the present study nursing caries was found to be unrelated to the length of type of feeding (breast or bottle).

Vascularity of the dental pulp after segmental osteotomy in the chacma baboon (Papio ursinus).

OBJECTIVE: To assess the vascularity of the dental pulp after segmental operations with and without interpositional autogenous bone grafting. DESIGN: Experimental study. SETTING: University Department, South Africa. ANIMALS: 26 chacma baboons. INTERVENTIONS: Maxillary and mandibular posterior segmental osteotomies were perfused with barium sulphate 3, 6, 12 and 18 months postoperatively. The animals were killed at 3, 6, 12 and 18 months after surgery and perfused with barium sulphate. Barium-filled vessels were counted in histological sections from 189 control and experimental teeth. MAIN OUTCOME MEASURE: Number of blood vessels. RESULTS: Blood vessel counts in mandibular teeth in osteotomy segments ranged from 0 to 1.15 compared with 2.27 to 4.58 in control teeth, while in maxillary teeth counts ranged from 0.54 to 2.22 for experimental teeth and 3.3 to 4.65 for controls. For both jaws, the numbers of vessels in experimental teeth gradually increased between 3 and 18 months but remained less than those in control teeth. Numbers of blood vessels were similar in graft and no-graft groups but both were less than half the counts in control teeth. CONCLUSION: Blood flow is present in the teeth at all times after posterior segmental osteotomy but there is a risk of ischaemia.

Head holder for panoramic dental radiography.

A radiolucent head holder for the Pancentric Panorex dental x-ray machine is constructed and evaluated. Features include a wooden pointer to orient the head in the midsagittal plane, movable components adjustable into a number of fixed positions and a spirit level on an ear rod fitting.

Examiner performance with visual, probing and FOTI caries diagnosis in the primary dentition.

To compare clinical reproducibility of dental caries diagnosis in the primary dentition under field conditions, a convenience sample of 5-year-old children in a nursery school in Germiston, was examined for dental caries by four dentists using visual (mirror), visual plus tactile (mirror plus probe) and fibre-optic transillumination (FOTI) methods. Seventeen children were examined on day one and 11 re-examined on day two. Inter-examiner agreement was high, above 90%. Visual examination on its own is comparable with the traditional visual plus tactile method and to FOTI under field conditions. New caries data collected by visual diagnosis alone may, reasonably, be compared with historical data diagnosed with visual + tactile examination.

Accurate diagnosis of occlusal carious lesions--a stereo microscope evaluation of clinical diagnosis.

This study was undertaken to validate the caries status of 214 teeth by serial sectioning and microscopy after caries diagnosis using four methods. Two hundred and fourteen extracted human teeth with varying degrees of caries were mounted in the jaws of nine training manikins. All tooth surfaces were examined and recorded for caries by four dentists using bitewing radiographs, fibre-optic transillumination (FOTI), mirror alone and a mirror and sharp probe on two separate occasions. Thereafter the teeth were serially sectioned and assessed microscopically for depth of caries lesion on a graded score of 0-7. This report assessed the diagnostic outcome of 2,183 observations for occlusal surfaces. Sound diagnoses predominated over unsound until caries was present in the inner half of dentine. Specificity was between 90% and 95% and sensitivity 26% and 50% depending on which diagnostic method was used and where the sound/unsound threshold was set. Negative and positive predictive values were similarly influenced and varied between 53% and 80% and 73% and 90%, respectively. Probit analysis showed no significant differences (P < 0.05) between examiners and diagnostic methods. Diagnosis of occlusal caries undertaken in an in vitro simulated clinical situation is inaccurate until the caries lesion extends deep into the dentine no matter which of the four methods was used.

The use (and abuse) of reference centiles with an application to weight gain in pregnancy.

Centile charts are commonly used in many areas of health research and practice, e.g. growth charts for children, Doppler ultrasonography in pregnancy and assessment of cholesterol levels at different ages. Yet there are a number of aspects of both their construction and application that are problematic and it is some of these issues that will be raised in this paper. The objective of the paper is to outline, in a non-technical way, some of the issues that need to be considered by the practitioner in estimating and using reference centile charts, but which frequently are either not known or ignored. These include: (i) the choice of reference population; (ii) how to estimate centiles; (iii) formally incorporating previous measurements on an individual, e.g. the interpretation of a child's weight that is on the 50th percentile for its age will be different if it has been moving along the 90th percentile at previous ages than if it has consistently been on the 50th percentile; and (iv) evaluation of centile charts used as a screen for problems. The concepts are introduced using an aspect of a study conducted at Tygerberg Hospital where centile charts for maternal weight gain in pregnancy were developed and assessed for their usefulness in detecting light-for-gestational-age (LiGA) births. The reference centile charts for maternal weight show poor discriminating ability between LiGA and normal births. These results support arguments in favour of abandoning the routine weighing of pregnant women.