 The test tablets contain Probiora3 which is a trade mark for three probiotic streptococci strains S. uberis KJ2, S. oralis KJ3 and S. rattus JH145 at a concentration of 3x108 CFU. The tablets are sweetened by erythritrol which is a tooth-friendly polyol for nutrition facts, see Appendix B. The chew tablets test and placebo, identical in taste and appearance, will be supplied by the manufacturer Oragenics, USA in packages separated by the letter A or B. The participating families will be provided with tablets for three months use at the time and the compliance will be checked and registered at each follow-up. Parents will be instructed to report any perceived side- or adverse-effects immediately to the dental staffs and stop the intake. 