むし歯の原因であるミュータンス連鎖球菌は、生まれたばかりの赤ちゃんの口の中にはいません。ミュータンス連鎖球菌が生えてきたばかりの乳歯に定着せないようにする必要があります。
生後19ヵ月（1歳7
ヶ月）から31ヵ月（2歳7ヶ月）までの時期に感染し、定着します。この時期を「感染の窓：window of infectivity」と呼ばれています。
ミュータンス連鎖球菌の感染媒体は唾液であり、感染経路の多くは養育者から幼児への垂直感染です。おもに父母の唾液の中のミュータンス菌が、箸やスプーンを一緒にすることで感染します。箸やスプーンを分けていたお子さんのお口の健診をさせていただくと、プラークの付着が非常に少ないです。
幼児期にミュータンス連鎖球菌の定着を阻止することが、その後のむし歯発症に大きな影響を与えることになります。
J Dent Res. 1993 Jan;72(1):37-45.
Initial acquisition of mutans streptococci by infants: evidence for a discrete window of infectivity.
Caufield PW1, Cutter GR, Dasanayake AP.
Abstract
Oral bacterial levels of 46 mother-child pairs were monitored from infant birth up to five years of age so that the acquisition of mutans streptococci (MS) by children could be studied. The initial acquisition of MS occurred in 38 children at the median age of 26 months during a discrete period we designated as the "window of infectivity". MS remained undetected in eight children (17%) until the end of the study period (median age of 56 mo). The levels of both MS and lactobacilli in saliva of mothers of children with and without MS were not significantly different. Comparisons between a caries-active cohort colonized by MS (nine of 38) and children without detectable MS revealed similar histories in terms of antibiotic usage, gestational age, and birth weight. Interestingly, half of the children between the ages of one and two years who were not colonized by MS were attended by caretakers other than the mother, while all of the caries-active children during this same time period were cared for by their mothers; the difference was statistically significant. Here we report for the first time that MS is acquired by infants during a defined period in the ontogeny of a child. Support for the notion of a discrete window of infectivity comes from other sources, including animal models.
ちなみに、鶴見大学の調査では、ミュータンス連鎖球菌フリーの高校生が増加しているという報告があります。若い人のむし歯の罹患率は非常に低下しています。
福岡県柳川市の石井歯科医院
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