Document Type


Date of Degree

Spring 2017

Degree Name

PhD (Doctor of Philosophy)

Degree In

Oral Science

First Advisor

Steven M. Levy


My PhD projects were secondary analyses of data from a prospective study conducted at the University of Alabama at Birmingham. Two cohorts of low socioeconomic status, African-American children from Perry County, Alabama, were invited to participate. Children in the 1st Cohort (Cohort 1, n=98) were approximately six years old at baseline and followed for 6 years, while children in the 2nd Cohort (Cohort 2, n=95) were approximately one-year-old at baseline and followed for five years.

For the first dissertation project, the prevalence and incidence of dental decay were assessed for children in Cohort 1. The findings of this report showed that 60-70% of the children had dental decay experience at each of the six annual exams. Approximately a third of the children had additional new tooth decay from age 6 to age 12.

For the second project, risk factors for time to dental decay occurrence were assessed using a relatively new analytic approach which allowed the use of time-dependent risk factors for children in Cohort 1. This was the first time for this analytic approach to be used in the dental literature, although it is widely used in medical research. The merit of using this technique was that, since dental decay risk factors can change with time, the value of the risk factor was allowed to change over time. The second project showed that about 29% of the children had their first permanent tooth decay event during the six-year follow-up. Final results showed that greater consumption of water, milk and 100% juice were associated with lower dental decay hazards, while greater consumption of added-sugar juice was associated with greater hazard of having an event.

The third PhD project was designed to assess the patterns of and the relationship between initial Mutans Streptococci detection and dental caries experience occurrence in African-American pre-school children with mean age of 1 year at baseline. The third project dealt with the MS variable as a “time-dependent variable”, using a statistical analysis called “Extended Cox hazards modeling”. To the knowledge of the author, this is the first published study which has used this relatively new analytic approach to assess the complex relationship between MS detection and dental caries experience.

In addition, in the third project, the behavioral risk factors for having a positive salivary MS test were assessed. This study found that median MS acquisition survival (when 50% of the children had positive salivary MS test) was 2 years and mean survival time was 2.09±0.09 among African-American children who had valid MS acquisition tests (n=99). Approximately 23% of the children did not have any positive salivary MS test by age 4 years. Multivariable analysis showed that not having a positive salivary MS test at any of the study exams was associated with having acute illness in the previous 6 months and being recruited into the study before 10 months of age. Results of extended Cox proportional hazards modeling showed a significant relationship between having a caries experience event at any given time during the follow-up period and having a positive salivary MS test at any point in time (HR=2.25, 95% CI 1.06-4.75).


African American Children, Biostatistics, Dental Caries, Public Health


xiv, 178 pages


Includes bibliographical references (pages 166-178).


Copyright © 2017 Tariq Ghazal