This data set is on dental caries (tooth decay) caused by mutans streptococci
(MS). The data set has variables for id, treatment group, sex, race, dmft,
 dmfs, age, mutpre, mutpost, mut1mos, and mut3mos.

151 persons with gum disease (elevated oral MS levels) were recruited into a
study at a mid-western research university and randomly assigned to one of
three treatment groups. The treatment under study was a gum with an active drug 
(Xylitol). There were two control groups: one group received gum with Sorbitol 
but no Xylitol and one group received no gum.  Participants in the gum groups 
were asked to chew the gum three times daily for a minimum of 5 minutes each 
time and carry out their usual oral hygiene (tooth brushing, mouthwash, etc.).  
Participants in the group without gum were asked to carry out their usual
oral hygiene only. Treatment group is recorded as Drug, Placebo, and NoGum.  

Subjects rinsed their mouths twice daily for 14 days with a 0.12 % CHZ 
gluconate mouthrinse. They then were assigned to one of the three treatment
groups.  They were asked to follow their assigned treatment for three months.
The four mut* variables are the levels of oral mutans streptococci at the 
four time periods in units of log(cfu/ml) (where cfu = "colony forming
units", a count of blotches on a standard sized petri dish after 
standard preparation).

Participants had their oral levels of mutans streptococci measured four
times: at baseline after the 14 days of CHZ gluconate mouthrinse (after which
they were randomly allocated to one of the three treatment groups), one week 
later, 1 month later, and 3 months later.  The question of interest is whether 
the treatment caused a decline in the levels of oral mutans streptococci.

Possible covariates are age, race, gender, and general condition of the 
teeth. This latter is measured by the variables dmft and dmfs.
The variable dmft stands for diseased/missing/filled teeth and dmfs
stands for diseased/missing/filled surfaces. (There are 5 surfaces to a 
tooth, the four sides and the chewing surface.)