INVESTIGATION OF THE INFLUENCES OF PUBERTY, GENETICS, AND ENVIRONMENTON THE COMPOSITION OF SUBGINGIVAL PERIODONTAL FLORAS

The classical twin model was utilized in this study in an attempt to d etermine the importance of host genetics to the composition of the sub gingival flora. Simultaneously, the effect of puberty on the flora com position was assessed. The compositions of the floras were significant ly different at ages 11 and 14 in the same people, indicating that tra nsition to an adult flora composition may be initiated during puberty. However, the numbers of subjects who had prepubertal and postpubertal testosterone levels in this study were too small to demonstrate signi ficant differences based solely on testosterone level (P = 0.053 and 0 .11 for tests of unrelated members, i.e., all twins ''a,'' the first t win of each pair, and all twins ''b,'' the second twin of each pair). Sixteen unrelated 11-year-old subjects had prepubertal levels of less than 30 ng of testosterone per dl of serum, and only six of these unre lated subjects had levels above 300 ng/dl by age 14. Of their twin sib lings, who formed the second group of unrelated individuals, 15 had pr epubertal levels and only 5 reached postpubertal levels. Unpaired t te sts indicated that Veillonella atypica, Prevotella denticola, and Prev otella melaninogenica were among the species that contributed most to changes in flora composition during puberty. The compositions of subgi ngival floras of 11-year-old monozygous and dizygous male twins were s ignificantly more similar than those of unrelated subjects in the stud y (P = 0.004 and 0.009, respectively). At 12.5 years of age, the flora s of monozygous twins remained more similar than those of unrelated su bjects (P = 0.001), but the dizygous-twin floras were not significantl y more similar than those of unrelated people. This difference corresp onded with moderate and varied testosterone levels within dizygous-twi n pairs at age 12.5. By age 14 both monozygous and dizygous twins agai n had floras with compositions more similar than those of unrelated pe ople (P = 0.008 and 0.002, respectively). Estimates of the genetic con tributions to the increased similarity of the floras of twins as compa red with floras of unrelated people indicated that the concentrations of several species in the flora may be influenced by host genetic fact ors. The prevalence of certain other species appeared to be controlled primarily by environment.