Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Forty institutionalized adults, considered to be at high risk of root caries, were followed for a two year period. They were grouped according to whether the microorganisms under study (Streptococcus mutans, Streptococcus sanguis, Actinomyces viscosus, Actinomyces naeslundii and Lactobacillus) were present at baseline on one or more noncarious root surfaces with gingival recession and the incidence of root caries was then recorded. The null hypothesis was that the presence of these microorganisms is not associated with the occurrence of root caries. The effect of other variables shown to be associated with root caries, such as age, sex, number of teeth, previous dental caries experience, gingival recession, gingival pocket depth and between-meal snacks were also measured.;Both subjects and tooth root surfaces were used as the units of observation in this study. However, since tooth root surfaces within the same mouth violate the assumption of independent response on which conventional statistical methods rely, an adjustment was used to compensate for the lack of independence of sites within the same mouth.;The incidence of root caries in the forty subjects followed for two years was 0.33 per subject. The presence of Streptococcus mutans was associated with the incidence of root caries in both a statistically (P = 0.008) and clinically (odds ratio = 10.7) significant way using the subject as the unit of observation. A clinically (odds ratio = 2.9) but not statistically (p = 0.20) significant association between the presence of Streptococcus mutans and the incidence of root caries was evident using the tooth root as the unit of observation and adjusting for the clustering of teeth within mouths. A positive and possibly linear relationship between the number of tooth roots colonized by Streptococcus mutans in a subject and the risk of root caries was also observed. On the other hand, Streptococcus sanguis was negatively associated with the incidence of root caries suggesting that this microorganism contributes to tooth root health. None of the demographic or periodontal measurements made a statistically significant contribution to the multivariate model.



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