The heading reads ろくがつよっかはむしばのひ and it means “4 June is the day of carious teeth.” In fact, in Japan, the week starting from 4 June is a week to promote “Dental Health” every year.
As you know in Japanese when we state a date, we say the month first and then the day. 六 for 六月(June) can be pronounced as む (as in むっつ) and 四 for 四日 (4th day) can be read as し and the sound “む(6)-し(4)” corresponds to the first part of むしば (carious teeth). I don’t know for sure why carious teeth are called 虫歯（むしば, the literal meaning is “bug teeth”） in Japanese but ancient people may have thought bugs （虫） are eating the teeth away to decay them and if you think of bacteria as bugs, their idea was not too far off!
So, I will finish this post by saying: 今日は歯をみがくのをわすれないで！(Don’t forget to brush your teeth today!)